Upload
mai-tieu-phong
View
221
Download
0
Embed Size (px)
Citation preview
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 1/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 1
Chapter 7. CDMA Technologiesfor Cellular Phone System
Công nghệ CDMA cho hệ thống điện thoại tổong.
Sources:1) July 7th, 2004 - Takashi INOUE –KDDI R&D Laboratories Inc.
2) IS-95 - ECE 371VV - Erik Stauffer Yu Li Yan Sun
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 2/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 2
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 3/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 3
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 4/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 4
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 5/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 5
Contents
• Introduction (giới thiệu) • Spread Spectrum Technology(công nghệ trải phổ) • DS-CDMA
• Spreading Codes(mã trải phổ) • Features of CDMA
Đặc tính của cdma – RAKE Receiver (bộ thu rake)
– Power Control (điều khiển công suất) – Frequency Allocation (cấp phép tần số) – Soft Handoff (chuyển giao mềm)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 6/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 6
Contents
• CDMA Links – Forward Link (cdma đường xuống) – Reverse Link (cdma đường lên)
• Special Features of IS-95 CDMA
(đặc tính đặc biệt của cdma is-95)
• Brief Comparison to other second-generation standards
• Possible Improvements
• Conclusion
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 7/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 7
7.1. Introduction (giới thiệu)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 8/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 8
Modern Wireless Systems(hệ thống ko dây hiệnđại)
• Outdoor voice/data communication (thoại ngoài trời, giao tiếp dữliệu) – Cellular phone, PCS (điện thoại tổ ong, PCS) – Paging, Satellite (tìm gọi, vệ tinh)
• Indoor data communication (giao tiếp dữ liệu trong nhà)
– Cordless phone – WLAN
– Low cost low power: Bluetooth, Zigbee, UWB
• Outdoor data broadcast (quảng bá dữ liệu ngoài trời) – Wide area wireless data service (dịch vụ dữ liệu ko day băng
rộng) – Broadband wireless access: WLL, LMPD (truy nhập không
dây băng hẹp)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 9/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 9
7.1. IntroductionEvolution of Cellular Systems (phát triển của hệthống điện thoại tổ ong)
1st.Generation
(1980s)(thế hệ thứ nhất) Analog
NMT CT0
TACS CT1AMPS
3rd. Generation
(2000s)
2nd. Generation
(1990s)
Digital
GSM DECT
DCS1800 CT2
PDC PHS
IS-54
IS-95
IS-136UP-PCS
IMT-2000
CDMA2000
W-CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 10/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 10
Cellular System
• Two-way voice/data communication with large
coverage (hai đường thoại/dữ liệu với vùng phủsóng rộng)
• Spectrum efficiency: frequency reuse (since powerfalls off with distance) (hiệu quả phổ, tần số tái sửdụng) (công suất tỉ lệ nghịch với khoảng cách) – Macrocells and microcells: trade-off among
capacity, interference, cost (tính thương mại giữadung lượng, nhiễu, giá cả)
– System is interference limited (hệ thống giới hạn
nhiễu) • advaced techniques for interference reduction can
enhance performance: cell sectoring, directional/smartantennas, multi-user detection, dynamic resourceallocation (công nghệ tiên tiến giảm nhiễu có thể thựchiện bằng cách sector hóa, hướng/anten thông minh,hướng đa thuê bao, cấp phép tài nguyên động)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 11/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 11
• 1G Cellular network (mạng tổ ong thế hệ thứ nhất)
– AMPS: FDMA/FDD• 2G Cellular network (mạng tổ ong thế hệ thứ 2)
– TDMA/FDD, or CDMA/FDD
• GSM, 8 users/200KHz channel, TDMA
• IS-136, 3 users/30kHz channel, TDMA• IS-95 (CDMA One): 64 users/1.25MHz channel, CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 12/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 12
• 2.5G Cellular Network (thế hệ 2,5G)
– General objective: support packet data servicewith higher data rate (tính năng chung: hỗ trỡ dịchvụ dữ liệu gói với tốc độ cao hơn)
– GPRS: 170 kbps (max), TDMA (enhanced GSM
by channel aggregating) – EDGE: >384 kbps, TDMA (enhanced GSM by
high-level modulation)(nâng cấp GSM bởi điềuchế mức cao hơn)
– IS-95B: 115 kbps, CDMA (enhance IS-95 byaggregating spreading codes) (nâng cấp IS-95 bởimã trải phổ)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 13/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 13
• 3G Cellular Network (thế hệ thứ 3) – Objective: support higher data rate: from 384kbps
(pedestrian) or 144 kbps (vehicular) to 2 Mbps(indoor)( hỗ trợ tốc độ dữ liệu cao)
– General: work in 2GHz band, ~2Mbps, FDD/TDD
– WCDMA (UTRA), evolved from GSM (phát triển từ
GSM)• Always on (packet radio), 2Mbps, ~8Mbps future, 5MHz
bandwidth(băng thông 5M)
– CDMA 2000, evolved from IS-95 CDMA• Use the same 1.25MHz bandwidth as IS-95(sử dụng
cùng băng thông 1.25 như IS-95)• Multi-carrier mode 3xTT (đa sóng mang) • 5 MHz bandwidth (băng thông 5M) • 2 Mbps and higher (tốc độ 2M và cao hơn)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 14/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 14
– 3G incompatible with 2G, need much investment
for deployment, such as the cost for buyingspectrum( thế hệ thứ 3 tương thích với thế hệ thứ2 phải đầu tư phát triển giống như chi phí muaphổ tần số)
– 3G first deployed in Japan (thế hệ 3G đầu tiênđược triển khai ở Nhật)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 15/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 15
Introduction
• Spread Spectrum Communications(giao tiếp trải phổ)
• Multiple Access Technique(công nghệ đa truy nhập)
– Direct Sequence DS-CDMA (trực tiếp tuần tự)
• CDMA standards(chẩn cdma)
– CDMAOne (2G) – IS 95A, (2.5G) IS-95B
– CDMA 2000 and WCDMA (3G) – IMT2000
• 4G in the future (tương lai thế hệ thứ 4
• Conclusions (kết luận)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 16/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 16
Requirements for 3G mobile systems
• High Capacity (dung lượng cao) • Tolerance for interference (loại bỏ
nhiễu)
• Privacy( bảo mật)
• Tolerance for fading(giảm pha đing)
• Ability to various data ratetransmission(có khả năng truyền với tốc
độ dữ liệu thay đổi) • Flexible QoS (đảm bảo hệ số dịch vụ)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 17/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 17
IMT-2000 systems approved by ITU-R
Popularname
Accessmethod
Body ofTechnical
Specproduction
IMT-DS IMT-MC IMT-TC IMT-SC IMT-FT
(Direct Sequence) (Multi Carrier) (Time Code) (Single Carrier) (Frequency Time)
W-CDMA CDMA2000
UTRA-TDD
UWC-136 DECT
CDMA-FDD CDMA-TDDCDMA-FDD TDMA-TDDTDMA-FDD
3GPP(FDD) 3GPP2 3GPP(TDD)
CWTS
IS-136 DECT
ESTIESTI TIA
TTA
T1
CWTS
ARIB/TTC ARIB/TTC
CWTS
TTA
ESTI
TTA
T1
CWTS
TIA
Approved in 2000 as ITU-R M.1457
TD-CDMA
TD-SCDMA
OrganizationPartners
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 18/225CDMA Technologies for Cellular Phone System , Sept. 11, 2003 18
What is CDMA ?
Sender bộ gửi Receiver bộ thu
Code A
A
Code B
B
A B
A B
C B
C
A
Code A
A B
C
Time
BC
B
A
Base-band Spectrum
băng cơ bản)
Radio Spectrum phổ
vô tuy ến
spread spectrum
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 19/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 19
Summary of Multiple Access
FDMA
TDMA
CDMA
p o w e r
p o w e r
p o w
e r
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 20/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 20
7.2. Features of CDMA Systems đặc
tính của hệ thống cdma
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 21/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 21
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 22/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 22
IS-95 CDMA - Radio Aspects
• Spread spectrum techniques adapted from military (used since 1950)
—Narrowband signal is multiplied by very large bandwidth signal(spreading signal)(tín hiệu băng hẹp được ghép bởi tín hiệu băng rộng) —All users, each with own pseudorandom codeword approximatelyorthogonal to all other codewords, can transmit simultaneously withsame carrier frequency(tất cả thuê bao, mỗi người có một mã giả ngẫunhiên và trực giao với nhau có thể truyền đồng thời trên cùng một tầnsố sóng mang) —Receiver performs a time correlation operation to detect only desiredcodeword (bộ nhận thực hiện một lần tương quan để chỉ xác định mãmong muốn)—All other codewords appear as noise due to decorrelation(tất cả cácmã khác xuất hện như là nhiễu do bộ giải mã tương quan) —Receiver needs to know only codeword used by transmitter
(bộ nhận chỉ cần biết mã hóa sử dụng ở bộ phát) —In other words, users are separated by theircodes rather than frequency and time slot (Nói một cách khác, mỗingười dùng được phân biệt bởi mã hơn là tần só và thời gian)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 23/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 23
IS-95 CDMA Interesting Features
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 24/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 24
IS-95 CDMA Interesting Features
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 25/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 25
IS-95 CDMA Interesting Features
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 26/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 26
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 27/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 27
Drawbacks of CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 28/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 28
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 29/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 29
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 30/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 30
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 31/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 31
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 32/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 32
Drawbacks of CDMA
So far, CDMA looks like a step backwards:Tight synchronization is required to use orthogonalcodes, which then break in a multipath channel anyway
Quasi-orthogonal codes cause self-interference, whichdominates the performance in most CDMA systems
Near-far problem is a serious hindrance, requiring fastand accurate power control (that uses up bits we couldotherwise send information with)
And for all this, the required bandwidth is now J times
larger than it was before, so there doesn‘t appear to bea capacity gain
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 33/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 33
PHYSICAL PROPERTIES
OF WIRELESSCHANNELS thuộc tính vật
lý của kênh vô tuyến
COS598u: Pervasive Information Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 34/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 34
<------
----------->
<---------------
|
|
|
|
|
|
|
Recall the Model
Now we’ll focus attention on the channel.
COS598u: Pervasive Information Systems
G l C t ( á
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 35/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 35
General Comments (cácchú thích)
COS598u: Pervasive Information Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 36/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 36
Noise nhiễu
COS598u: Pervasive Information Systems
Whit N i hiễ
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 37/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 37
f 0
White Noise nhiễutrắng
• The spectrum of a random process specifies how the process’ energyis distributed as a function of frequency.Phổ của ngẫu nhiên cho thấyxử lý phân bố năng lượng như một chức năng của tần số. • The integral under the spectrum over any given band of frequencies
equals the amount of energy in that band.Toàn bộ vùng dưới phổ đượctạo ra bở băng tần số bằng tổng năng lượng trong băng đó. COS598u: Pervasive Information Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 38/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 38
• A key parameter of the noise is the spectral height or noise level,
often designated as No /2.
Tham số chính của nhiễu là độ cao của phổ hoặc mức nhiễu
thường định nghĩa là No/2
• A key parameter of the signal is the received energy per bit,
usually designated by Eb.
Tham số chính của tín hiệu là năng lương thu được trên bit thường
định nghĩa là Eb
• The ratio Eb /No (“ebno”) is a measure of signal-to-noise ratio
(SNR), and is a key parameter in determining the quality of acommunications link.
Tỉ lệ Eb/No là SNR đây là tham số chính để xác định chất lượng
tuyến giao tiếp.
Signal-to-Noise Ratio (SNR) tỉ số tínhiệu trên nhiễu
COS598u: Pervasive Information Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 39/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 39
• The performance of a digital link can be measured in partby the bit-rate; but performance depends also on the qualityof transmission, as measured by the bit-error rate (BER).
Thực hiện tuyến số có thể đo bởi tốc độ bit nhưng phụ thuộc vào chất lượng truyền dẫ đo bở tốc độ bit lỗi BER
• The BER (also known as the “probability of bit error”) is,as its name implies, the rate at which errors are introducedinto the transmitted data stream by the channel.
BER còn được biết như là xác suất bit lỗi.• E
b
/No
determines the rate of bit errors caused by whitenoise.
Tỉ lệ này xác định tốc độ lỗi nguyên nhân do nhiễu trắng • This varies with modulation type.Điều này thay đổi tùy thuộc vào loại điều chế.
Bit Error Rate (BER)bit lỗi
COS598u: Pervasive Information Systems
BER f Bi M d l ti BER h
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 40/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 40
BERs for Binary Modulation BER chođiều chế nhị phân
COS598u: Pervasive Information Systems
BER f Hi h O d M d l ti BER ới
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 41/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 41
BERs of Higher-Order Modulation BER vớiđiều chế mức cao hơn
COS598u: Pervasive Information Systems
Error Rates of M ary Modulation tốc độ lỗi
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 42/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 42
Error Rates of M-ary Modulation tốc độ lỗicủa điều chế mảng M
COS598u: Pervasive Information Systems
Propagation Effects hiệu
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 43/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 43
Propagation Effects hiệutứng xác suất
COS598u: Pervasive Information Systems
L S l P ti Eff t hiệ
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 44/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 44
Large Scale Propagation Effects hiệuứng xác suất tỉ lệ lớn
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 45/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 45
Multipath
Multipath Fading(đa
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 46/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 46
• Multiple copies of the transmitted signal arrive at the receiver due to
reflections (off buildings, walls, etc.).nhiều tín hiệu của bộ phát đến bộ thu
bằng các đường khác nhau nhờ phản xạ
• The destructive and constructive interference of the different paths causes
fading; i.e., fluctuations in Eb: Phá hủy và khôi phục nhiễu của các đường khác
nhau là nguyên nhân fading.
– Superposition of widely separated paths causes frequency-selective
fading; modeled via a channel impulse response.
Sự chồng của các đường với kc rộng nguyên nhân bởi fading lựa chọn
tần số
– Superposition of many closely separated paths causes flat fading;
modeled as independent Gaussian random variables in I and Q
channels (so-called Rayleigh fading).
Sự chồng của nhiều đường với kc gần nhau bởi fading mỏng.
• Mobility adds dynamism to the fading:
– slow fading is steady over many symbol intervals
– fast fading changes very rapidly (bad!)
Multipath Fading(đađường)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 47/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 47
• The use of wideband signals (e.g., spread spectrum),
allows different paths to be resolved and added
constructively. (The technique for this is called aRAKE receiver.)
Sử dụng tín hiệu băng rộng cho phép các đường khác
nhau được quyết định và thêm vào để khôi phục tín
hiệu (cộng nghệ này được gọi là bộ thu RAKE)
• With narrowband signals, frequency-selective fading is
an impairment; i.e., it negatively effects
performance.với tín hiệu băng hệ fading lựa chọn tần só
là một sự suy yếu.
Frequency-Selective Fading fadinglựa chọn tần số
Multipath: Dispersion đa
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 48/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 48
Multipath: Dispersion đađường: phân tán
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 49/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 49
Interference nhiễu
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 50/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 50
Multiple Access Capabilities
• Multiple wireless terminals
(WT) receive and send to thebase station (BS)
- WT near to the base station
receive with higher quality than
WT that a far away
- Different quality in terms of bit
error probability
- To overcome unfairness and
achieve a higher system
capacity power control is
applied
Interference Averaging dung lượng đa
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 51/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 51
Interference Averaging dung lượng đatruy nhập
Interference from neighboring cells (CCI and ICI)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 52/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 52
Interference from neighboring cells (CCI and ICI)nhiễu từ các cell lân cận
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 53/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 53
Dynamism
Further Issues các lỗi
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 54/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 54
Further Issues các lỗikhác
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 55/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 55
Mobile Propagation EnvironmentMulti-path Fading
The peaks and bottoms of received power appear,in proportion to Doppler frequency.
Base Station (BS)Mobile Station (MS)
multi-path propagation
Path Delay
P o w e
r
path-2
path-2path-3
path-3
path-1
path-1
Time
P o w e
r
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 56/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 56
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 57/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 57
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 58/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 58
Fading in non-CDMA System
Path Delay
P o w e r path-1
path-2
path-3
With low time-resolution,
different signal paths cannot be discriminated.
••• These signals sometimes strengthen,
and sometimes cancel out each other,
depending on their phase relation.
••• This is ―fading‖. ••• In this case, signal quality is damaged
when signals cancel out each other.
In other words, signal quality is dominated
by the probability for detected power
to be weaker than minimum required level.
This probability exists with less than two paths.
Time
P o w e r
Detected Power
In non-CDMA system, ―fading‖ damages signal quality.
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 59/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 59
Fading in CDMA System ...
Because CDMA has high time-resolution,
different path delay of CDMA signalscan be discriminated.
••• Therefore, energy from all paths can be summed
by adjusting their phases and path delays.
••• This is a principle of RAKE receiver. Path Delay
P o w
e r path-1
path-2
path-3
CDMAReceiver
CDMAReceiver
• • •
S y n c h r oni z a t i on
A d d
er
Path Delay
P o w e r
CODE Awith timing of path-1
path-1
P
o w e r
path-1
path-2
path-3
Path Delay
P o w e r
CODE Awith timing of path-2
path-2
interference from path-2 and path-3
• • •
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 60/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 60
Fading in CDMA System (continued)
In CDMA system, multi-path propagation improves
the signal quality by use of RAKE receiver.
Time
P o w e r
Detected Power
RAKEreceiver
Less fluctuation of detected power,because of adding all energy .
P o w e r
path-1
path-2
path-3
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 61/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 61
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 62/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 62
Demodulation (Correlator)
.
.
.
.
.
.
.
.
.
.
Pick thelargestCross
CorrelationMetrics
receivedsignal
r(t)
c1
(t)
c2(t)
ck(t)
.
.
.
.
.
.
.
.
.
.
r1
r2
rk
outputbitsb(n)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 63/225
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 64/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 64
Principles of operation-transmitter
• The narrowband message signalmi(t) is multiplied by a pseudo noisecode sequence that has a chip rate >>data rate of message.
• All users use the same carrier frequencyand may transmit simultaneously. The k-th transmitted signal is given by:
k s s k k c kS (t) (2E / T )1/ 2m (t)p (t)cos(2 f t )
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 65/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 65
CDMA Receiver
c k
cos(2 f t )
r(t) km (t)(.)dt
k
iZ ( t )
K
PN (t)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 66/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 66
Principles of operation-receiver
At the receiver, the received signal iscorrelated with the appropriate signaturesequence to produce desired variable.
1
1
iT
1
i 1 1 c 1 1
(i 1)T
Z (t) r(t)p (t )cos[2 f (t ) ]dt
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 67/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 67
Message Signal
• m(t) is a time sequence of non-overlappingpulses of duration T, each of which has anamplitude (+/-) 1.
• The PN waveform consists of N pulses or
chips for message symbol period T.
NTC = T
where TC is the chip period.
Example:
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 68/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 68
Example:
Assume N=4
PN Wave for N =4
1
-1
-1
1
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 69/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 69
Correlator output for first user
•The multiplied signal will be p2(t) = 1 for thecorrect signal and will yield the dispersedsignal and can be demodulated to yield themessage signal m
i(t).
1
1
iT
1
i 1 1 c 1 1
(i 1)T
Z (t) r(t)p (t )cos[2 f (t ) ]dt
1/ 2
1 s s 1 1 c 1S (t) (2E / T ) m (t)p (t) cos(2 f t )
ấ ỗ
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 70/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 70
Probability of bit error xác suất của bít lỗi
• Probability of bit errorPe = Q {1/ [(K –1)/3N + (N0 /2Eb)]
1/2}
K = Number of users số người sử dụng
N = Number of chips/ symbol số chip/ký tự
• When Eb /No
Pe = Q{[3N/(K-1)]
1/2
}
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 71/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 71
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 72/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 72
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 73/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 73
Concept of CDMA Systems Diversity
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 74/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 74
Concept of CDMA Systems Diversity
• IS-95 Air Interface Standards
• Space diversity
• Frequency diversity
• Path diversity
• Time diversity
• Macro-diversity
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 75/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 75
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 76/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 76
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 77/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 77
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 78/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 78
N F P bl
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 79/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 79
Near-Far Problem
CODE B
CDMATransmitter
DATA B
CODE A
CDMAReceiverCODE A
CDMATransmitter
DATA A
P
• Desired Signal Power = P/ Lp-a
• Interfered Signal Power =
P/ Lp-b /(processing gain )
Demodulated DATA
P
Lp-a
Lp-b
When user B is close to the receiver anduser A is far from the receiver,
Lp-a could be much bigger than Lp-b.In this case, desired signal power is
smaller than the interfered power.
The Near-Far Problem
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 80/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 80
The Near Far Problem
• Users may be received with
very different powers:- Users near the base stationare received with high power
- Users far from the basestation are received with low
power- For a path loss exponent of 4and a cell size of 1 km,example:
• Nearby users will completelyswamp far away users
• Solution: Power Control
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 81/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 81
Power Control
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 82/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 82
Power Control
Power Control …
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 83/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 83
Power Control …
• Power control adjust power level while conveying data to thebase station in that way that all received signals at the basestation have the same signal strength (not trivial)
• This process needs time to adjust in case of changing in the cellin terms of power/interference
Power Control …
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 84/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 84
Power Control …
• In case of misadjusted power control entities some WTS might havebetter/worse quality conditions
• The highest cell capacity can be achieved all WTs have exactly the samepower level• For support of heterogeneous QoS support the power control is a viable
option• All signals (even the undesired ones) from the base station will receive the
WT with the same strength (some path)
Power Control …
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 85/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 85
Power Control …
• IS-95 Air Interface Standards
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 86/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 86
Power Control
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 87/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 87
Power Control...
A B
Time
D e t e c t e d P o w e r
from A
from B
When all mobile stations transmit the signals at the same power (MS),
the received levels at the base station are different from each other,
which depend on the distances between BS and MSs.
Moreover, the received level fluctuates quickly due to fading.
In order to maintain the received level at BS, power control technique must be
employed in CDMA systems.
Power Control (continued)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 88/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 88
Power Control (continued)
②
①
Open Loop Power Control Closed Loop Power Control
estimating pathloss
calculatingtransmission
power
transmitmeasuringreceived power
transmit receive
decidetransmission
power
transmit measuringreceived power
power controlcommand
about 1000 timesper second
①
②
Effect of Power Control
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 89/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 89
Effect of Power Control
A B
Time
D
e t e c t e d P o w e r
from MS Bfrom MS A
Effect of Power Control
• Power control is capable of compensating the fading fluctuation.
• Received power from all MS are controlled to be equal.
... Near-Far problem is mitigated by the power control.
Frequency Allocation (1/2)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 90/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 90
Frequency Allocation (1/2)
In FDMA or TDMA,
radio resource is allocated not to interfere among neighbor cells.
f1f2
f3f4
f5f6
f7
cell :
a ―cell‖ means covered area by one base station.
• Neighbor cells cannot use thesame (identical) frequencyband (or time slot).
• The left figure shows the
simple cell allocation withseven bands of frequency.
• In actual situation, because ofcomplicated radiopropagation and irregular cellallocation, it is not easy to
allocate frequency (or timeslot) appropriately.
Frequency Allocation (2/2)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 91/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 91
Frequency Allocation (2/2)
In CDMA,identical radio resource can be used among all cells,
because CDMA channels use same frequency simultaneously.
• Frequency allocation in CDMAis not necessary.
• In this sense, CDMA cellularsystem is easy to be designed.
Handoff in CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 92/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 92
Handoff in CDMA
• Two types of handoffs—hard handoff
—Soft handoff
•Hard handoff is needed when the call ismoved from one frequency to another and
when the mobile moves the coverage area
of another MSC
Soft handoff
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 93/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 93
• Two base stations receive signals from the mobile.
The signals are sent to the MSC that decides whichone has lowest bit error rate.
Vocoder in CDMA is in the switch.
• Mobile receives signals from two base stations and
combine them before decoding. Uses rake receiver.Each tunes to one base station.
• This requires synchronization of the base stations.All base stations are equipped with GPS and receive
information from it, including lat.., long and time.• It also requires that the mobile dedicates one
correlator for searching other pilot channels.
Soft Handoff (1/2)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 94/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 94
Handoff :
•Cellular system tracks mobile stations in order to maintain their
communication links.•When mobile station goes to neighbor cell, communication link switches fromcurrent cell to the neighbor cell.
Hard Handoff :
• In FDMA or TDMA cellular system, new communication establishes afterbreaking current communication at the moment doing handoff.
Communication between MS and BS breaks at the moment switchingfrequency or time slot.
Hard handoff : connect (new cell B) after break (old cell A)
switching
Cell BCell A
Soft Handoff (2/2)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 95/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 95
Σ
CellB
Cell A
Soft handoff : break (old cell A) after connect (new cell B)
transmitting same signal from both BS A and
BS B simultaneously to the MS
Soft Handoff :
•In CDMA cellular system, communication does not break even at
the moment doing handoff, because switching frequency or timeslot is not required.
Soft Handoff
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 96/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 96
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 97/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 97
CDMA and Soft Handover
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 98/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 98
CDMA and Soft Handover
• A unique advantage of CDMA issoft handover more reliable
– All cells use same carrier
– Mobile contact with 6~7nearby cells simultaneously
– No need to stop contact withcell 1 before switching to cell2
Soft-Handover
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 99/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 99
• IS-95 Air Interface Standards
Mobility Management in CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 100/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 100
Mobility Management in CDMA
• Five type of registration—Periodic
—Power up
—Power down
—Zone change
—Distance. When the distance between the
current base station and the previously
registered base station exceeds a certain
limit.
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 101/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 101
Capacity of CDMA Systems
Voice Activity
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 102/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 102
Voice Activity
• In TDMA and FDMA systems: - If a user doesn‘t have anything to send, the time/frequency
slot allocated to them is wasted
- It is typically very difficult to dynamically allocate time and
frequency slots
• In CDMA systems:
- If a user doesn‘t have anything to send, it causes less
interference to other users of the system
- Typically, each user needs to transmit less than half the time
- Since interference-limited, this doubles the capacity
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 103/225
Uplink Single-cell System Model
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 104/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 104
BTS
...
.
.
.
...
.
.
.
User 1
User 2
User k
User Ku
User n
Assumptions
• Total active users Ku
• The intra-cell MAI can be
modeled as AWGN
• Perfect power control is
assumed
• Random sequences
• Coarse estimate of the reverse link (uplink) capacity
–Assumptions:
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 105/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 105
Assumptions:
1. Single Cell.
2. The interference caused by other users in the cell can be
modeled as AWGN.3. Perfect power control is used, i.e. the received power of
each user at the base station is the same.
If the received power of each user is Ps watts, and the
background noise can be ignored (ex: microcells), then the
total interference power (MAI) at the output of the desired
user’s detector is
where Ku is the total number of equal energy users in the cell.
Suppose each user can operate against Gaussian noise at abit-energy-to-noise density level of Eb /Io. Let W be the entire
spread bandwidth, then the interference spectral density can
be expressed as:
su PK I 1
)( / 0
sided one HzWattsW
I I
Interference Also, the bit energy Eb iss
b
R
P E
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 106/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 106
Interference
limited
, gy b
Thus,
b
b
R
0
01 I E
RW
R E
W I
P
I K
b
b
bbsu
Now, if we consider the factors of voice activity (Gv),
sectorized antenna gain (GA), and other-cell interface factor (f),
where
– Gv 1/v = 2.67
– GA (three sectors) 2.4
– f = (Interference form other cells)/(Interference from
given cell) 0.6
In this case, Ku can be approximated by
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 107/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 107
Ex: If Gv 2.67, GA 2.4, f 0.6
If (Eb /Io) required is 6 dB (i.e. Eb /Io = 4)
which will be larger than the TDMA or FDMA systems inthe cellular environment.
f
GG
I E
RW K Av
b
bu
10
ob
b
u I E
RW K
4
b
u R
W K
Capacity Comparison
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 108/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 108
• Comparing the capacity of TDMA/FDMA/CDMA is
very controversial• In 1991, a famous (notorious?) Qualcomm paper
claimed that due to voice activity, frequency reuse,
and sectorization, CDMA increased capacity by:
- Factor of 18 relative to AMPS
- Factor of 6 relative to US TDMA (and similar forGSM)
• This turned out to be optimistic, about 1/3 of this
gain actually happened (still depends who you ask)
• Still, twice as many users is nothing to snear at!
• All 3G systems use CDMA for multiple access
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 109/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 109
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 110/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 110
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 111/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 111
7.3. Direct Spread Spectrum Technology
Spread Spectrum Technique
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 112/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 112
p p q
• Low power spectral density• Rejection to jamming signal and interference
• Pseudorandom sequence
– Randomness and noise properties – Walsh, M-sequence, Gold, Kasami, Z4
– Provide signal privacy
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 113/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 113
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 114/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 114
Direct Sequence Spread Spectrum
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 115/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 115
q p p
• Spreading
– Source signal is multiplied by a PN signal
• Processing Gain:
• Despreading
– Spread signal is multiplied by the spreading code
DataRate
ChipRate
T
T
T
T G
b
c
c
b
p
1
1
Spreading & Despreading
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 116/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 116
p g p g
• Polar {±1} signal representation
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 117/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 117
System Block Diagram
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 118/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 118
Jammer/Noise/Interference
j(t)
BPSKModulator
BPSK
Matched
Filter
Channel
PseudorandomSequence
Generator
PseudorandomSequence
Generator
Source
DataOutput
Data
(to detector)
b(t)
c(t)
s(t) x(t) u(t)
c(t)
y(t) rn
y(t) = j(t) + x(t)
u(t) = s(t) + j(t)c(t)
rn = bn + jammer projection
s(t) = b(t)cos(wot)
x(t) = s(t)c(t)
How to spread spectrum...
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 119/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 119
Direct Sequence (DS)
Modulation(primary modulation)
user data
S p r e a d i n g
( s e c o n
d a r y m o d u l a t i o n )
Tx
Base-bandFrequency
P o w e r
D e n s i t y
RadioFrequency
P o w e r
D e n s i t y
TIME
data rate
10110100
spreading sequence (spreading code)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 120/225
Demodulating DS Signals (2/2)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 121/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 121
If you don‘t know the correct spreading sequence (code) •••
Base-bandFrequency
received signal
spreading sequence (spreading code)
you cannot findthe spreadingtimingwithout correctspreading code,and
Accumulate forone bit duration
Demodulated data
Radio
Frequency
P o w e
r
D e n s i t y
01010101 01010101 01010101
10101010 10101010 10101010
TIME
0100101110110100 10110100
No data can be detected
- --
1011010010110100 10110100
Feature of SS
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 122/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 122
Privacy, Security
Radio
Frequency
P o w e r
D e n s i t y
Power density of SS-signals could be lower than the noise density.
transmitted SS-signal
• • • • • •
Noise
P o w e r
D e n s i t y
Radio
Frequency
Noise
• • • • • •
received signal de-modulator
Base-bandFrequency
P o w e r
D e n s i t
y
With incorrect code(or carrier frequency),SS-signal itselfcannot be detected.
They cannot perceive the existence of communication,because of signal behind the noise.
With correct code(and carrier frequency),data can be detected.
Base-band
Frequency
P o w e r
D e n s i t y
Feature of SS
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 123/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 123
Direct Sequence Spread Spectrum:Transmission Technique
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 124/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 124
Cross-Correlation
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 125/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 125
Cross-Correlationbetween Code A and Code B = 6/16
Self-Correlationfor each code is 1.
one data bit duration
Spreading Code A
1 0 1 0 1 1 0 0 1 0 1 0 1 0 0 1
one data bit duration
Spreading Code A
1 0 0 1 1 1 0 0 1 0 1 0 1 0 0 1
Spreading Code A
1 0 0 1 1 1 0 0 1 0 1 0 1 0 0 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Spreading Code B
1 0 0
1 1 0 0 1 1 1 0 0 1 0 1 1
0 0 0 0 0 1 0 1 0 1 1 0 0 0 1 0
Preferable Codes
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 126/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 126
In order to minimize mutual interference in DS-CDMA ,
the spreading codes
with less cross-correlation should be chosen.
Synchronous DS-CDMA :Orthogonal Codes are appropriate. (Walsh code etc.)
Asynchronous DS-CDMA :
• Pseudo-random Noise (PN) codes / Maximum sequence
• Gold codes
Multiplexing using Walsh Code
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 127/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 127
C o d e f o r 0 0
C o d e f o r 0 1
C o d e f o r 1 0
C o d e f o r 1 1
D a t a
M o d u l a t o r
C o d e f o r 0 1
C o d e f o r 1 0
C o d e f o r 1 1
0 d t T
S e l e c t
m a x i m u m v a l u e
C o d e f o r 0 0
0 d t T
0 d t T
0 d t T
D e m o d u l a t o r
Synchronous DS-CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 128/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 128
Forward Link(Down Link)
Synchronous Chip Timing
A
A
Signal for B Station(after re-spreading)
Less Interference for A station
Synchronous CDMA Systems realized in Point to Multi-point System.e.g., Forward Link (Base Station to Mobile Station) in Mobile Phone.
Asynchronous DS-CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 129/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 129
In asynchronous CDMA system, orthogonal codes have bad cross-correlation.
Reverse Link(Up Link)
BA
Signal for B Station(after re-spreading)
Big Interferencefrom A station
Asynchronous ChipTiming
Signals from A and B areinterfering each other.
A
B
CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 130/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 130
• Code Division Multiple Access
• Start with data signal rate D ( Called bit data rate)• Break each bit into k chips by multiplying by a k bit user
code (known as a Walsh code)
• Channel has chip data rate kD chips per second
• User code (Walsh code) is orthogonal to all otherpossible user codes
– User code 1 * User code 2 = 0
– User code 1 * User code 1 = signal for user 1
• Signals for several users can be added and sent as asingle signal within the same band (multiplexed)
CDMA user code and data
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 131/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 131
Stallings 2003: Figure 9.10
CDMA Explanation
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 132/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 132
• Consider a user communicating with a base station
• Base station knows user A‘s code
• Assume communication already synchronized
• Base station receives a message from A and wants todecode it. To extract the signal from A the basestation
multiplies the signal by A‘s code • Decoder ignores other sources by using A‘s code to
decode
– For all other stations code station I * code station A =
0 so only the signal for station A remains
CDMA for DSSS
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 133/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 133
• When the basestation sends messages to nusers each message multiplied by a differentorthogonal Walsh code sequence, thosesignals are added before transmission.
• At each receiving station, the signal for thatstation is extracted by multiplying by thatstations Walsh code.
CDMA: two-senders, eight bit Walsh codes
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 134/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 134
Walsh
Code 2
WalshCode 1
DataStation 1
DataStation 2
Data multiplied by Walsh Code
Data multiplied by Walsh Code
(Sum of all stations)Transmitted data
CDMA: eight bit Walsh codes
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 135/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 135
Walsh Code 1
Received Data multiplied
by Walsh Code
Decoded Received DataStation 1
-2 -2 -2
2
-2
2 2 2
Receive Data (Sum)
Summary of Channel Partitioning
CDMA (Code Division Multiple Access)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 136/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 136
CDMA (Code Division Multiple Access) • Used mostly in wireless broadcast channels such as cellular
phones• All users share same frequency band. Information from each useris spread throughout that frequency band
• Each user has their own orthogonal Walsh code ‗chipping‘sequence to encode data.
• encoded signal = (original data) X (Walsh code)
• Encoded signals from each channel are added, the summedsignal is transmitted
• The orthogonal property of Walsh codes guarantees that (ignoringtransmission errors) multiplying the received signal by a Walshcode will extract the data for the channel encoded using thatWalsh code from the received (summed) signal.
• Decoded signal = (received summed signal X Walsh code)
CDMA in a DSSS Environment
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 137/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 137
Stallings 2003: Figure 9.11
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 138/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 138
7.4. DS-CDMA Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 139/225
DS-CDMA System Overview(Reverse Link)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 140/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 140
Freq.Freq.
BPF
Despreader
Code B
Freq.Freq.
BPFDespreader
Code A
CDMA is a multiple spread spectrum.
Difference between each communication path is only the spreading code
Data B
Code B
BPF
Freq.Freq.
• • •
Data A
Code A
BPF
Freq.Freq.
• • • MS-B
MS-A
BS
Data A
Data B
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 141/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 141
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 142/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 142
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 143/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 143
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 144/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 144
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 145/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 145
7.5. IS-95 CDMA SYSTEMS
IS-95 CDMA SYSTEMS
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 146/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 146
Interim Standard 95 – CDMA
Viterbi, Qualcomm
Outline
Forward Link
Reverse Link
Special Features of IS-95 CDMA
Brief Comparison to other second-generation standards
Possible Improvements
2G: IS-95A (1995)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 147/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 147
• Known as CDMAOne• Chip rate at 1.25Mbps
• Convolutional codes, Viterbi Decoding
• Downlink (Base station to mobile): – Walsh code 64-bit for channel separation
– M-sequence 215 for cell separation
• Uplink (Mobile to base station):
– M-sequence 241 for channel and userseparation
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 148/225
2.5G: IS-95B (1998)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 149/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 149
• Increased data rate for internet applications
– Up to 115 kbps (8 times that of 2G)
• Support web browser format language
– Wireless Application Protocol (WAP)
MC-CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 150/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 150
Network Architecture of IS-95 CDMA Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 151/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 151
Mobile Station (MS)
-The Mobile Station (MS) is the subscriber‘sinterface with the CDMA network.
-Both hand-held MS units having a low-power radio transmitter and vehicle-
mounted MS units are permitted.-The manufacturer assignes a unique 32-bitElectronic Serial Number (ESN) to eachMS.
-ESN is a permanent and privateidentification code of the mobile terminal.
Network Architecture of IS-95 CDMA Systems
B St ti S b t (BSS)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 152/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 152
Base Station Subsystem (BSS) • Each Base Station has a unique pilot PN-offset, a delay applied
to a random number sequence (PN Short Code) at the basestation.
• This sequence is applied to forward direction transmissions thatenables the terminals in a cell to decode the desired signal andreject the signals from other base stations.
• Pilot PN offsets ensure that the received signal from one cell
does not correlate with the signal from a nearby cell.• It is possible for adjacent cells to use the same CDMA radio
channel frequency (f 1).• Reusing the same frequency in every cell eliminates the need
for frequency planning in a CDMA system.
• Pilot PN-offset planning must be done in stead.
• In an area where the ranges of two cells overlap, there is anincreased interference, but this only reduces the number ofusers that can share the radio channel.
Network Architecture of IS-95 CDMA Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 153/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 153
Base Transceiver Station (BTS)
• The BTS comprises several base radiotransceivers.
• Each transceiver consists of a transmitter and a
receiver which has a duplicated front end tomatch up with the two receiving antennas used inthe base antenna assembly.
Network Architecture of IS-95 CDMA Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 154/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 154
Base Station Controller (BSC)
• The BSC comprises control logic, datacommunication facilities and multiplexing anddemultiplexing equipment.
• The BSC can control the radio power levelsof the various transceivers in the BTS, andalso can autonomously control the mobilestations‘ radio transmitter power levels.
• A single BSC can control several BTS radioequipment transmitters.
Network Architecture of IS-95 CDMA Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 155/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 155
GPS Receiver
• CDMA ‗soft handover‘ (an MS establishescontact with a new base station before givingup its radio link to the original base station)
requires base stations to operate insynchronism with one another.
• Therefore each base station contains a GPSreceiver.
Network Architecture of IS-95 CDMA Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 156/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 156
Mobile Switching Centre (MSC)
• The MSC is a switching network thatinterconnects calls between Mobile Stationsand between Mobile Stations and the Public
Switched Telephone Network (PSTN).• The MSC is also needed for ‗automatic
roaming‘ capabilities.
2G Network Architecture
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 157/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 157
Internet
BTS
BTS
BTS
BSC
BSC
M S
MSC
MSC
T-1
T-1
T-1T-1
EIR
VLR VLR
HLR/AC
PSTN
IWF
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 158/225
869 to 894 MHz (each channel is 1.25 MHz wide)
7.5.1. Forward Link
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 159/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 159
Subdivided into 4 sub channels
1.Pilot:
a. Timing
b. Phase Reference for Coherent Demodulation
c. Means for Signal Strength Comparison
2.Sync
a. Broadcasts future state of the long code register
3.Paginga. Call Control Information
4.Traffic
Voice Data (includes power control sub channel)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 160/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 160
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 161/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 161
Forward Link Radio Transmission
• The forward link is by convention the transmission from
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 162/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 162
• The forward link is by convention the transmission fromBase Station to Mobile Station (MS).
Forward Link Radio Transmission
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 163/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 163
Traffic Channel
• The traffic channel can accept data rates of 9600 bps,4800 bps, 2400 bps and 1200 bps comming from avariable-bit-rate speech coder (QCELP = QualcommCode Excited Linear Prediction).
• Check digits and tail bits (convolutional encoder tailsequence to drive the convolutional encoder into a knownstate at the end of each frame) are included. The signalsare processed in frames of duration of 20 ms.
• A convolutional code , with constraint length K=9 and rate½ protects each signal.
Forward Link Radio Transmission
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 164/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 164
• When the rate is less than 19200 bps, the transmitter
repeats code bits (factor 1, 2, 4 or 8) to bring the rateup to 19200 bps, corresponding to 384 bits in aframe of 20 ms.
• An interleaver permutes the code bits in each frame.This will spread the influence of burst errors, typicalfor wireless communications.
• The baseband sequence is scrambled by the PNsequence derived from a Long Code Generator (aPN sequence with length 242 – 1 at a rate of 1.2288
Mbps) and Long Code Mask (a time-offsetdetermined by the ESN of the MS for trafficchannels).
Forward Link Radio Transmission
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 165/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 165
•The Long Code period is :
to match the rate of the Long Code sequence to the 19200bps baseband rate, a decimator extracts 1 bit out of 64 bitsof the Long Code sequence.
IS-95 CDMA Logic Channels
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 166/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 166
IS 95 CDMA Logic channels
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 167/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 167
Forward Link Radio Transmission
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 168/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 168
• The baseband symbol stream is spread by
multiplication with a Walsh sequence of length 64 ,thus creating a baseband chip rate of 1.2288 Mcps.
• There are 64 orthogonal Walsh sequences of length64, certain of which are assigned to different users of
the channel.• All user‘s transmissions occur synchronously from thebase station, so these transmissions are alsosynchronized at any individual subscriber‘s receiver (synchronous CDMA).
• The use of a set of orthogonal sequences thus allowsperfect rejection of other-user interference associatedwith any given transmission path within the cell.
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 169/225
Forward Link Radio Transmission
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 170/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 170
• Signals received from other base stations, with
different values of ‗PN-offset‘, appear as low-level noise in the receiver of the MS, due to thecorrelation properties of the sequences.
• There are 512 possible ‗PN-offsets‘, with offseti corresponding to a time delay of 64i chips ( adelay of 64 chips @ 52 ms @ 15km).
• Since the period of the sequence is 215 chips,
there are 215 /26 = 29 = 512 possible offsets.
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 171/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 171
Forward Link Radio Transmission
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 172/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 172
Forward Link Radio Transmission
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 173/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 173
• The bandwidth of a CDMA signal is 1.23
MHz.
• The bandwidth of an AMPS channel (usingthe same frequency band) is 30 kHz.
• Therefore the bandwidth of a CDMA signalcorresponds to an aggregate bandwidth of41 AMPS channels.
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 174/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 174
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 175/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 175
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 176/225
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 177/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
177
The sync channel
S
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 178/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
178
• The sync channel uses WALSH 32, a
sequence of 32 0s, followed by 32 1s.
• It provides the MS with critical timesynchronization data: system time (obtained
from GPS), the PN-offset of the pilotsequence and the rate of the base stationpaging channels (4.8 kbps or 9.6 kbps).
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 179/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
179
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 180/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
180
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 181/225
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 182/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
182
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 183/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
183
Traffic channel
Traffic channel on the forward direction has
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 184/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
184
• Traffic channel on the forward direction has
three components
—user data
—power control (puncturing convolutional code)
—signaling message
• Traffic channel on the reverse direction has
two components
—user data
—signaling message
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 185/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
185
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 186/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003
186
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 187/225
W l h C d G
PN Generator
IS-95 Forward Link
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 188/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 188
Output
data
Rate:
9600 bps
4800 bps
2400 bps
1200 bps
Audio
Compressor
R=1/2
K=9
24x16
array =
384 bits
19.2kbps
Data
Scrambling
2^14-1 Permutations
(14 bit maximum
length shift register)
1.2288 Mcbs
L=64
(takesevery 64th
bit)
19.2kbps L=6(takes every 6th
bit)
4bits @
800Hz =
3200bps
Power Control
Bit
Specifies Forward
Channel Id (0-63)
One of 64 possible
19.2kbps
1.2288Mcps
I-Channel
Pilot PN
Sequence
2^15-1
Q-ChannelPilot PN
Sequence
2^15-1
1.2288Mcps
1.2288Mcps
Data to I
channel of
QPSK RF
modulator
Data to Q
channel of
QPSK RF
modulator
19.2kbps
Convolutional
Encoder
Block
Interleaver.MUX
Long Code Generator DecimatorDecimator
Walsh Code Generator
PN Generator
1.2288Mbps
Adds redundancy to data transmitionsfor error robustness.
Rate, r=1/2, where r = input bits / output bits,
Convolutional Encoder and Repetition
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 189/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 189
Maintains an output data rate of 19.2kbps regardless of input rate.
D0 D1 D2 D3 D4 D5 D6 D7 D8
9 Element Shift
Register
From Audio
Compressor
Possible
rates:
9600bps4800bps
2400bps
1200bps
752 octal =
111101011
XOR
G0
561 octal =
101110001
G1
Incoming Data
XOR
Note, while this is
easy to implement
at the transmitter,
it is nontrivial to
undue at thereceiver
Separates when consecutive data bits are sent, therefore adding to transmission
robustness.
Block Interleaver
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 190/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 190
Provides Time Diversity
2 pages, one is being filled as one is emptied
Each page contains all the data for one 20ms frame
24x16 bits = 384 bits
19.2kps * 20ms per frame = 384 bits!
Data is read in as rows and out as columns.
This sequence will be used to scramble the data and to code when to send a
power control bit.
Long PN Sequence
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 191/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 191
42 bit maximum length shift register, corresponds to 2^42-1 possiblepermutations
Contents of shift register are XOR’d with a public or a private key (depending onthe stage of the call) to generate one output bit at a rate of 1.2288Mcps
Takes a very long time to repeat.
Used for Data Encryption. Make call more secure.
Randomizes data. Prevents the transition of a long series of 1’s or 0’s
Scrambler
Dynamic, Decentralized, closed-loop power control scheme
Power Control Bit
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 192/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 192
Control Scheme: BS decides what to do based on the measured Frame ErrorRate
FER < threshold decrease mobile power by 1dB
FER > threshold increase mobile power by 1dB
One bit sent every 1.25ms = 800Hz or 16 power control bits per frame.
The power control bit is sent in one of 16 possible locations coded by the 4 bit
output of the second decimator.
(decimator #2 output = 4bits * 800Hz = 3.2kbps. This was reduced by a
factor of 6 from the 19.2kbps at the scrambler)
64 Orthogonal Channels for all users, assuming negligible multi-path delays
Provides some spreading
Orthogonal Covering Via Walsh Codes
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 193/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 193
Provides some spreading
64 X 64 Walsh Matrix. 1 Row = 1 Walsh Code
Each row of the matrix is exported at 19.2kHz (one row for each bit that is sent
from the scrambler)
64 bits per row * 19.2kHz per row = 1.2288Mbps (the output of the Walsh
generator)
Channel 0 is assigned to the pilot and is given more power then the rest of the
channels
Channel 32 is assigned to synchronization.
Mobile Paging Channels are usually on the lower Walsh ID’s
Provides more spreading, as not all Walsh codes have sufficient spreading.
Based on a 15 bits maximum length shift register (2^15 1 possible permutations)
Quadrature Modulation (Short Code)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 194/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 194
Based on a 15 bits maximum length shift register (2^15-1 possible permutations)
-This is the pilot sequence if it’s modulated by Walsh code 0.
PN generator outputs data at 1.2288Mbps. (The same rate as the Walsh code
generator)
Different cells use different time offsets of the short code as to identify themselvesso that Walsh codes can be reused.
The PN sequence for the I channel is based on a different polynomial then the Q
channel and they therefore evolve differently.
The output I and Q channels are converted to analog and are modulated by an RF
carrier -> QPSK
• 824 to 849 MHz (each channel is 45 MHz away
7.5.2. Reverse Link
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 195/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 195
from the forward counterpart)• Access channel
– 4800 bps
– Initiate communication
– Respond to paging channel message
• Reverse voice traffic channel
– 9600, 4800, 2400, 1200 bps
• Very similar to forward link, but there are importantdifferences.
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 196/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 196
The IS-95 Reverse Link
• The reverse link is quite different
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 197/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 197
q
- Instead of Walsh Codes, ―psuedorandom noise‖ (PN)codes- PN codes are deterministic Bernoulli sequences of {-1,+1}- While not orthogonal, they have low cross-correlation,
e.g.<Ci , Ck > ≈ 1, unless i = k <Ci , Ck > = J , if i = k
- These codes have good properties even when notsynchronized
- Very strong error correcting codes make up thedifference
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 198/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 198
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 199/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 199
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 200/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 200
I-Channel
Pilot PN
Sequence
2^15-1
PN Generator
IS-95 Reverse Link
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 201/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 201
PN Generator
Output data
Rate:
9600 bps
4800 bps
2400 bps
1200 bps
Audio
Compressor
R=1/
3
K=9
32 x 18
= 576
bits
28.8kbps
Q-Channel
Pilot PN
Sequence
2^15-1
1.2288Mcps
1.2288Mcp
s
Data to I
channel of
OQPSK RF
modulator
Data to Q
channel of OQPSK RF
modulator
Convolutional
Encoder
Block
Interleaver.
Walsh Code
Generator
1.2288Mbps
1.2288Mbps
1.2288Mbps
64-ary
Orthogonal
Modulator
Codes 6 bits
Long Code PN
Generator1.2288Mcps
Data Burst
Randomizer
D
307.2kbps
½ PN chip
= 409.6ns
Total spreading gain J = 128
Orthogonal Modulation
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 202/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 202
– 64-ary orthogonal modulation using the same Walshfunction in the forward link
– Contrary to the forward link, used for orthogonal datamodulation
– One Walsh function is transmitted for six coded bits – Modulated symbol rate
• 28.8 kbps*64 chips /6 coded bits = 307.2 kcps
– Increase interference tolerance (refer to ECE459)
Data burst randomizer
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 203/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 203
– Turns off the Transmitter when the data rate fallsbelow 9.6kbps so that each redundant bit is sentonly once.
– Used to reduce interference to other users
– Each 20ms frame is divided into 16 1.25ms slotswhich are selected as a function of the long PN
code
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 204/225
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 205/225
• BS: base station
– Low-power, multi-channel, two-
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 206/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 206
way radios in a fixed location – Handling traffic between MS
and MSC
– Many BSs connected to one
central MSC• MS: mobile station
– All user equipment andsoftware needed for wireless
networks, such as cell phone
• Channel types in cellular system
– Control channel: transmit control information about
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 207/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 207
a call• Usually has only a few for each cell site
– Forward channel: used for transmission from BSto MS
– Reverse channel: used for transmission from MSto BS
– Paging channel: used to broadcast brief messageover entire service area
• Usually one channel for the entire network
• Main channels in a cell
– Four channel types
FVC for ard oice channel
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 208/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 208
• FVC: forward voice channel
• FCC: forward control channel
• RVC: reverse voice channel
• RCC: reverse control channel
– Voice channel: high rate, multiple
– Control channel: low rate, fewer
• Special working mode
– Handoff: transfer a call or data session
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 209/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 209
– Handoff: transfer a call or data sessionfrom one channel to another, or from oneBS to another, or from one MSC toanother.
• Handover: the process of transferring a call• Hard handover: the process needs to drop the
call for a short time, e.g., GSM handover
• Soft handover: MS simultaneously use multiple
BS, no need to drop the call when adding newBS, e.g., CDMA system
– Roaming:
• Extend connectivity service to locations otherthan home location
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 210/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 210
than home location
• Regional roaming, national roaming,international roaming
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 211/225
• MS receiving calls from PSTN
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 212/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 212
PSTN MSC
BSMS
1 (MIN)
2
3
4
5 6
7
8
9
10
3: FCC (page)4: ACK5: relay ACK6: Verify channel7: FCC (channel info)8,9,10: Voice
• MS initializing calls (to PSTN, or to another MS)
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 213/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 213
PSTN MSC
BSMS
MS
1
23
4
455
1. RCC: req. (MIN)2. Relay3. Verify (channel)4. FCC (assign channel)
5. voice
Bandwidth Recycling
Enhancing the system capacity due to the increase of reuse
7.5.3. Special Features of IS-95 CDMA System
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 214/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 214
efficiency.Achieving higher bandwidth efficiency (interference
limited) and simplifying the system planning.
Achieving flexibility due to the bandwidth on demand.
Power Control
Reducing the interference and increasing the talk time of
mobile station by using the efficient power control scheme.
Soft handoffsContributing to the achievement of the diversity and
reduce the chance of loss of link midway through the
conversation.
Diversity
Taking advantage of multiple levels of diversity: frequency
Special Features of IS-95 CDMA System
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 215/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 215
Taking advantage of multiple levels of diversity: frequency
diversity (spreading), spatial diversity (multiple antennas), pathdiversity (rake receiver) and time diversity (block interleaver), all of
which reduce the interference and improve speech quality.
Variable Rate Vocoder
Offering high speed coding and reducing background noise and
system interference based on the detection of the voice activity.
Coding Technique
Enhancing the privacy and security.
7.5.4. A Comparison between IS-95 and other 2nd
Generation Cellular Phone Systems
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 216/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 216
Generation Cellular Phone Systems
IS-54/136 GSM IS-95
TDMA/FDMA CDMA
Hard Handoff Soft Handoff
Open-loop and Slow Power
Control
Close-loop and Faster Power
Control
Fixed Rate Vocoder Variable Rate Vocoder
Increasing the channel bandwidth beyond 1.25MHz.
7.5.5. Possible Improvements on IS-95
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 217/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 217
Increasing the channel bandwidth beyond 1.25MHz.
Directional antennas on mobile stations.
Better power control algorithms.
Using MANET technology.
Adaptive filtering.
2G: IS-95A (1995)
• Known as CDMAOne
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 218/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 218
Known as CDMAOne
• Chip rate at 1.25Mbps
• Convolutional codes, Viterbi Decoding
• Downlink (Base station to mobile):
– Walsh code 64-bit for channel separation
– M-sequence 215 for cell separation
• Uplink (Mobile to base station):
– M-sequence 241 for channel and userseparation
2G: IS-95A (1995)
Standard IS-95, ANSI J-STD-008
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 219/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 219
Multiple Access CDMA
Uplink Frequency 869-894 MHz
Downlink Frequency 824-849 MHz
Channel Separation 1.25 MHz
Modulation Scheme BPSK/QPSK
Number of Channel 64
Channel Bit Rate 1.25 Mbps (chip rate)
Speech Rate 8~13 kbpsData Rate Up to 14.4 kbps
Maximum Tx Power 600 mW
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 220/225
MC-CDMA
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 221/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 221
Conclusions
• CDMA can increase the capacity of mobile
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 222/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 222
p y
system
• Goals of next generation cellular
– Further increase data rate
– Reduce interference among users• Future research:
– Search for good non-binary sequences
• Ideal 2-level autocorrelation• Low cross correlations
7.6. Conclusion
• CDMA is based on the spread spectrum
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 223/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 223
technique which has been used at military field.• CDMA cellular system is deemed superior to the
FDMA and TDMA cellular systems for the timebeing.
• Therefore, CDMA technique becomes moreimportant in radio communication systems.
Conclusions
• CDMA can increase the capacity of mobile
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 224/225
CDMA Technologies for Cellular Phone System , Sept. 11, 2003 224
system
• Goals of next generation cellular
– Further increase data rate
– Reduce interference among users• Future research:
– Search for good non-binary sequences
• Ideal 2-level autocorrelation• Low cross correlations
Reference:
1.T. S. Rappaport, “Wireless communications principles&practice”, Prentice Hall, 1996
8/3/2019 Bai Giang Chuong 7 He Thong Cdma is 95 Stt 20-19-18 9828
http://slidepdf.com/reader/full/bai-giang-chuong-7-he-thong-cdma-is-95-stt-20-19-18-9828 225/225
2.C. Y. Lin and J. Shieh, “IS-95 North American strandard-a CDMA based digital cellularsystem”, IEEE Website. 3.A. J. Viterbi, “CDMA principles of spread spectrum communication”, Addison-Wesley
Publishing Company, 1995.
4.R. Paul and K. V. Shah, “An objective comprison of second generation cellular systems -
GSM, IS-136 and IS-95”, IEEE, 1997.
5.Motorola, Inc. “CDMA Technology & Benefits: An introduction to the benefits of CDMA for wireless technology”, 1996. 6.S. G. Glisic and P. A. Leppanen, “Code division multiple access communications”,
Kluwer Academic Publishers, 1995.
7.C. Tsui, S. Cheng and C. Ling, “Using transformation to reduce power consumption of IS 95 CDMA i ” I t ti l S i L P El t i d