Part 5-2 and 25G systems - University of Hong Kongsdma/elec6040_2008/Part_5... · – data are broken up every 13th frame by SACCH or idle frames – the 26th frame contains idle

ELEC6040 Mobile Radio Communications, Dept. of E.E.E., HKUp. 1

Part 5. 2G and 2.5G Mobile Communication Systems


GSM (Global System for Mobile Communications)


Global GSM Subscribers

20072006200520042001199819961994

500

1000

1500

2000

2500

1 50 100Num

ber o

f GSM

Sub

scrib

ers

(Mill

ion)

0Year

3000

2008


GroupeSpecial Mobile

established by CEPT

Several proposals for GSM multiple access:

wideband TDMA, narrowband TDMA, DS-CDMA, hybrid

CDMA/FDMA, narrowband FDMA

Eight prototype systems tested in

CNET laboratories in France;

Permanent nucleus set up

Basic transmission principles selected: 8-slot TDMA, 200-kHz

carrier spacing, frequency hopping;

MoU signed

GSM phase 1 specifications frozen (drafted 1987-1990)

GSM1800 standardization began

GSM 1800 specifications frozen; commercial

operation delayed due to the lack of terminals; GSM: God

Send Mobiles

1982 1984 1986 1987

1990 1991

History (1)

GSM (Global System for Mobile communications) became an ETSI

technical committee

1988


1996

History (2)

Enhanced full rate (EFR) speech codec standard ready;

14.4-Kbps standard ready; GSM1900 commercial

operation started

GSM submitted as a PCS technology candidate to the

United States; PCS1900 standard adopted in the

United States

1995

GSM900 commercial operation started;GSM phase 2+

development started

1992

HSCSD standard ready; GSM cordless system (home base station) standardization

started; EDGE standardization started

GPRS standard ready; WCDMAselected as the

third generation air interface

EDGE standard

ready

GSM standardization moved to 3GPP

and TSG GERAN established

1997 1998 1999 2000


Some Facts

For providing telephone and ISDN services.

Initially designed to unite mobile communication standards that were previously used over European countries. Huge success achieved afterwards. Became deployed globally.

Advantages over 1G analog systems from users’ viewpoint:– Higher digital voice quality and low cost alternatives to making calls

such as text messaging– Introduction of Subscriber Identity Module (SIM): a memory device

that stores information such as subscriber’s identification number, networks that can be used, and other user-specific information; offering convenience to users.

– Improved on-the-air privacy due to data encryption.


GSM System Architecture

All copied from Rappaport’sWireless Communications

Mobile Station

Base Transceiver

Station

Base Station

Controller

Mobile Switching

Center

Home Location Register

Visitor Location Register

Authentication Center

Operation and Maintenance

Center


Terminologies (1)BSS– Consists of many BSCs

which connect to a single MSC

– Provides and manages radio transmission paths between MSs and MSCs.

– Also manages the radio interface between MSsand other GSM subsystems.

BSC– May co-locate with a BTS– Connects to remote BTSs by microwave links, leased lines or optical fibers.– Controls up to several hundred BTSs.– Controls handovers when BTSs involved are under the control of the same BSC,

thereby alleviating the burden of the MSC in handling handovers.


Terminologies (2)

NSS– Manages the

switching functions of the system.

– Allows MSCs to communicate with other networks such as PSTN and ISDN.

MSC–Is the central unit in NSS.–Controls the traffic among all BSCs


1

2

3

4

5

6When the car moves from the cell covered by BTS1 to the cell covered by BTS2, a so-called handoff operation is needed to transfer the communication with the MS from BTS1 to BTS2. Which function blocks are involved in this operation? What about when the car moved from BTS3 to BTS4?

Example


Terminologies (3)

HLR– Is a database that

contains subscriber information and location information for each user who resides in the same city as the MSC.

– Contains the International Mobile Subscriber Identity(IMSI) for each user, used to identify each home user.


Terminologies (4)

VLR– Is a database which

temporarily stores the IMSI and customer information for each roaming subscriber who visits the coverage area of a particular MSC.

– Is linked between severaladjoining MSCs in a particular market or geographic region.

– [When a roaming mobile is logged onto a particular VLR, the MSC sends the necessary information to the visiting subscriber’s HLR so that calls to the roaming mobile can be appropriately routed over the PSTN by the roaming user’s HLR.]


AUC– Is a strongly protected

database that handles the authentication and encryption keys for every single subscriber in the HLR and VLR.

– Contains a register called the Equipment Identity Register (EIR) which identifies stolen or fraudulently altered phones that transmit identity data that do not match with information contained in either the HLR or VLR.

Terminologies (5)


Example

Suppose that you are a local customer of GSM services provided by Hutchison in Hong Kong. In which function block of Hutchison’s local GSM network will your subscriber information and location information be stored? If you travel to Paris and enjoy the international roaming mobile service, in which function block of the network in Paris will your information be stored? If your phone is lost and Hutchison disables your phone number as you requested, where will this number be stored in the network?


Terminologies (6)

OSS– Supports the

operation and maintenance of GSM.

– Allows engineers to monitor, diagnose and troubleshoot the system.

Main functions:– to maintain all

telecom hardware and network operations with a particular market– to manage all charging and billing procedures– to manage all mobile equipment in the system


All copied from Rappaport’s Wireless Communications

Radio Air InterfaceAbis Interface– carries traffic and

maintenance dataA Interface– uses an SS7 protocol

called the signaling correction control part (SCCP)

– supports communication between the MSC and the BSS, and network messages between the individual subscribers and the MSC

SS7 (Signaling System 7)– is a set of telephony signaling protocols which are used to set up the vast

majority of the world's public switched telephone network telephone calls.

GSM System Interfaces


Radio Interface (1)Frequency domain– Two bands of 25MHz– Divides into 200kHz wide channels called ARFCNs (Absolute Radio

Frequency Channel Numbers)– Each channel is time shared between 8 subscribers using TDMA

Multiple Access Method– Combination of TDMA and FDMA

f (MHz)890 915 935 960

25MHz 25MHz

for reverse link (Uplink) for forward link (Downlink)

200kHz

45MHz


Radio Interface (2)Time domain– 8 time slots (TSs) per frame; each frame occupies 4.615ms; each time

slot has 576.92µs.

modulation data rate:156.25bits 270.83kbps576.92 sµ

=


Radio Interface (3)Collision of received signals– MSs at different distances from the BS: different round trip delay– Collision of the signals from mobiles assigned to adjacent time slots


Radio Interface (4)Solution: Time Advance– Transmit and receive time spacing: 3 time slots – Time Advance: BS commands MSs to advance their transmission

by the round trip delay


Radio Interface Summary

FDD (frequency division duplex)

ARFCN (Absolute Radio Frequency Channel Number)– Specifies the

carrier frequency that is used.

Each radio channel occupies 200kHz.

Copied from Rappaport’s Wireless Communications


Channel Types

Physical channel:– Is the combination of a TS number and an ARFCN.– Is the channel that is used by a user.– E.g., user 3 is assigned a pair of physical channels TS2-ARFCN3 and

TS7-ARFCN1000

Logical channel:– Each specific time slot of frame may be dedicated to either handling

traffic data, signaling data, or control channel data.– link the physical layer with the data link layer– Traffic channel (TCH): is used to carry digitized speech or data for a

user.– Control channel (CCH): Carries signaling or synchronizing

commands between the BS and MS.


Traffic Channels (1)Multiframe structure for TCH– 26 frames per multiframe; each multiframe occupies 120ms– data are broken up every 13th frame by SACCH or idle frames– the 26th frame contains idle bits when full-rate TCHs are used and

contains SACCH data when half-rate TCHs are used


Traffic Channels (2)

Half-rate is an optional feature of GSM– Used when the cell is nearly congested or when MS has low battery since

it saves 30% more energy– Could double the network capacity for voice traffic, at the expense of

quality

carrying speech:

carrying data:

Full-Rate TCH: channel data rate: 22.8kbps; Full-Rate Speech Channel (TCH/FS): carries user speech digitized at a raw data rate of 13kbps

Half-Rate TCH: channel data rate: 11.4kbps; Half-Rate Speech Channel (TCH/HS): carries digitized speech sampled at a rate half that of a full-rate channel, 6.5kbps

Data Channel for 9600bps (TCH/F9.6) Data Channel for 4800bps (TCH/F4.8)Data Channel for 2400bps (TCH/F2.4)


Traffic Channels (3)

Example of system state at arbitrary time


Three main control channelsBroadcast Channel (BCH)

– operates on the forward link of a specific ARFCN within each cell, and transmits data only in TS0

– other seven timeslots for the same ARFCN are available for TCH data or DCCH data

– provides synchronization for all mobiles within the cellCommon Control Channel (CCCH)

– occupies TS0 that is not otherwise used by the BCH or the Idle frame– most commonly used control channels– used to page specific subscribers, assign signaling channels to specific

users, and receive mobile requests for serviceDedicated Control Channel (DCCH)

– may exist in any time slot and on any ARFCN except TS0 of the BCH ARFCN

– bidirectional, forward and reverse link

Control Channels


Broadcast Control Channel (BCCH)– occupies frame 2 to frame 5 of a control channel multiframe (illustrated

later)– broadcast information: cell and network identity, operating characteristics

of the cell (current control channel structure, channel availability and congestion)

– broadcast a list of channels that are currently in use within the cellFrequency Correction Channel (FCCH)

– occupies TS0 for the very first frame (frame 0) and is repeated every ten frames within a control channel multiframe

– allows each MS to synchronize its local oscillator to the exact frequency of BS

Synchronization Channel (SCH)– occupies TS0 of the frame immediately following the FCCH frame– allows each MS to frame synchronize with the BS– broadcast frame number (FN), base station identity code (BSIC), time

advancement commands

BCH


Paging Channel (PCH) (forward)– provides paging signals from the base station to all mobiles in the cell– notifies a specific mobile of an incoming call which originates from the

PSTN– provides cell broadcast text message to all subscribers, SMS feature

Random Access Channel (RACH) (reverse)– used by a MS to acknowledge a page from the PCH– used by a MS to originate a call– uses a slotted ALOHA access scheme

Access Grant Channel (AGCH) (forward)– used by the BS to respond to a RACH sent by a MS – carries data which instructs the MS to operate in a particular physical

channel (time slot and ARFCN)– the final CCCH message sent by the BS before the MS is moved off the

control channel

CCCH


Standalone Dedicated Control Channel (SDCCH)– bidirectional, ensures that the MS and the BS remain connected while the BS

and MSC verify the MS and allocate resources for the MS– an intermediate and temporary channel – used to send authentication and alert messages

Slow Associated Control Channel (SACCH)– associated with a TCH or a SDCCH– forward link: send slow but regularly changing control information, like

transmit power level instructions and specific timing advance instructions– reverse link: carries information about the received signal strength and the

quality of the TCHFast Associated Control Channel (FACCH)

– carries urgent messages, same type of information as the SDCCH – replaces all or part of a TCH when there is a need for some heavy-duty

signaling (e.g., a handoff request)

DCCH


Example of Control Channel Multiframe

channel combination: FCCH+SCH+CCCH+BCCH


Examples of How a MS Behaves ― Synchronization with the Network

When MS is turned onSearch for the BCH: BCH operates at a specific ARFCN, just search for the freq. channel with the highest power levelSearch for the FCCH: BS transmits, during certain known intervals, a pure sine wave for the period of exactly one time slot; the received signal exhibits a tone at 1/4th of the GSM symbol rate, i.e., 67kHz Search for the SCH: SCH is in the time slot following FCCHRead broadcast info. in BCCH: location of the cell, how to access BS, etc..

1.

2. FCCH


Registration

A procedure that the MS informs its presence to the network when the MS is switched on.

Copied from An Introducation to GSM

RACH

AGCHSDCCHSDCCHSDCCH

SDCCH

SDCCH

SDCCH


Call Establishment (MOC)

Mobile-originated call

(MOC)

Mobile-terminated call

(MTC)

– Procedure almost identical


RACHAGCHSDCCHSDCCHSDCCHSDCCHSDCCHSDCCHSDCCHSDCCH

FACCH

FACCHFACCHFACCH

TCH


Call Establishment (MTC)

Mobile-originated call

(MOC)

Mobile-terminated call

(MTC)

– Procedure almost identical



Speech Transmission



Speech coding– Based on Residually Excited Linear Predictive Coding (RELP)– Yields 260 bits per 20ms block of speech ⇒ Gives a bit rate of 13kbps.

Discontinuous Transmission Mode (DTX)– Exploits the fact that a normal person speaks for only 40% of time.– No transmission during silent period => a longer subscriber battery life

and less instantaneous radio interferenceRelative importance of speech-coder outputs– Ia bits: the most important 50 bits out of 260 bits of speech– Ib bits: the 132 bits that are less important than Ia bits– Type II bits: the rest of 78 bits out of 260 bits

Physical Layer (1)


Channel coding for the speech signal:– 50 Ia bits appended with 3

parity check bits– 50 Ia bits & 3 parity bits &

132 Ib bits are altogether coded by a convolutional code with rate 1/2 and constraint length 5.

– The 78 Type-II bits are unprotected.

– The resultant gross data rate of the GSM speech with channel coding is 22.8kbps.

Physical Layer (2)



Channel coding for data channel: half rate punctured convolutional codeChannel coding for control channel: a shortened binary cyclic fire code followed by a half rate convolutional codeInterleaving– To mitigate the effect of sudden fade.– 456 encoded bits for each 20ms speech frame are broken into eight 57-bit sub-

blocks. The 8 sub-blocks are transmitted over eight consecutive traffic-channel (TCH) time slots.

– Each TCH time slot carries two 57-bit blocks for two segments of 20ms speech.


Physical Layer (3)


Burst formatting– Adds binary data to the cipher text to help synchronization and

equalization.Ciphering– Security achieved by encryption– Encryption algorithm changed from call to call.

Modulation– 0.3 GMSK (Gaussian minimum shift keying) [0.3 means the 3dB

bandwidth of the Gaussian pulse shaping filter with relation to the bit rate is BT = 0.3.]

– Binary ones and zeros are represented by shifting the RF carrier by ±67.708kHz, one fourth of the channel data rate of GSM (270.833333kbps).

Physical Layer (4)

Refer to Proakis’sDigital Communications


Frequency hopping– To avoid persistent staying at a bad channel.– Maximum hopping rate is 217.6 hops per second– Maximum number of hopping frequencies = 64

Physical Layer (5)


Channel equalization– To combat against the adverse effects due to multipath propagation and

fading– With the help of training sequences in the midamble of every time slot.

Physical Layer (6)

D D D

h(t,τ0) h(t,τ1) h(t,τ2) h(t,τL-1)

Transmitted Signal

Received Signal

Multipath Channel: H(t,τ)

Received Signal

Channel Equalization

Recovered Signal

inverse the channel effect: H-1(t,τ)


Handover (1)

The MS continuously monitors the neighboring cells’ perceived power levels.The home BS gives the MS a list of channels of other BSs for measurement.The measurement report is periodically sent from the MS back to the home BS.Different types of handover situations:– Handover between BTSs under the control of the same BCS. [The

MSC is not troubled to handle handover, so that MSC is relieved in the handover burden. But the MSC has to be notified about the switching of BTSs.]

– Handover between BTSs under the control of different BSCs but the same MSC. [The MSC has to control the handover procedure.]

– Handover between BTSs under the control of different MSCs (and, implicitly, different BSCs). [Communications between different MSCsrequired.]


Handover (2)



Handover (3)



Summary

GSM system architecture is important. It is the base of other mobile ratio communication systems. BSC, MSC, HLR, VLR, AUC: full names and main functions.Main system parameters of GSM: in frequency domain, each channeloccupies 200kHz bandwidth. And each frequency channel is further divided into 8 time slots, shared by 8 subscribers using TDMA.Collision of received signal in GSM: reason and solution.Half rate codec: advantages and disadvantages.Logical channels: BCCH, FCCH, SCH, PCH, RACH: full name, main function. How are these channels used when the MS synchronizes with network, register, and establish a call?Discontinuous transmission: reason and benefitsInterleaving: combat sudden fadeFrequency hopping: combat frequency selective fading


IS-95 (cdmaOne)


Frequency SpectrumIS-95: cdmaOneKey player: QualcommUse direct-sequence spread-spectrum techniqueFrequency reuse factor = 1 so that– No frequency planning is required.– System capacity is increased.

Each CDMA channel occupies 1.25MHz.Chip rate = 1.2288 M chips per second.


IS-95 System Architecture

InternetInternet

BTS

BTS

BTS

BSC

BSC

MS

MSC

MSC

EIR

VLRVLR

HLR/AC

PSTN

IWF

Interworking Function (IWF): a technique for interfacing data between a wireless system and the telephone network; involves the use of modems or data terminal adapters to convert the data transmitted over the air interface and mobile network to a format that can be recognized and carried by the public telecommunications network.

Equipment Identity Register


Forward Channel (1)

Forward channel:– BS simultaneously transmits the user data for all mobiles in the cell by using

different spreading sequences for mobiles.– A pilot signal, spread by a specific code, is transmitted from the BS for

channel estimation and enabling coherent detection at the receivers.– Coherent detection at the MS

forward link: BS MS

time

One pilot signal for all MSs in the cell; simple and efficient


Forward Channel (2)

Forward channel:– Spread by one of 64 orthogonal spreading sequences (Walsh codes)– Orthogonality among all users’ signals is maintained as the signals are

synchronously transmitted.– Scrambled by a cell-specific long pseudorandom sequence (215) to reduce the

interference between mobile using the same spreading sequence in different cells

– Frame length: 20ms


Forward Channel (3)

Forward Link Channel Structure


Reverse Channel (1)Reverse channel:– Mobiles’ signals are asynchronously transmitted. – Orthogonality among all users’ signals is destroyed as a result of

asynchronous transmission.– no pilot signals, non-coherent detection at BS

reverse link: MS BS

time

Coherent: each MS needs a pilot signal; inefficient and complicated


Reverse Channel (2)Reverse channel:– Power control enables all mobiles to transmit with power levels such that

received power levels of all signals are nearly the same.– Orthogonal modulation: Each block of six encoded symbols of a user’s data

stream is mapped to one of the 64 orthogonal Walsh functions, resulting in 64-ary orthogonal signaling.

– Frame length: 20ms

encoded user data stream:10110101001001011100...

1011010100...

4 orthogonal Walsh functions

+1 +1 +1 +1+1 -1 +1 -1+1 +1 -1 -1+1 -1 -1 +1

+1 +1 -1 -1 +1 -1 -1 +1


Reverse Channel (3)

Reverse Link Channel Structure


All copied from Rappaport’s Wireless Communications

Forward Link


Reverse Link


Illustration of Main Functions (1)

Rate Sets– Rate Set 1: 9600, 4800, 2400, 1200bps– Rate Set 2: 14400, 7200, 3600, 1800bps

Speech coding:– Original: Qualcomm 9600 bps Code Excited Linear Predictive (QCELP)

coding; coding rate: 9600 bps (for Rate Set 1)– Detects voice activity; Reduces to 1200 bps during silence periods.– Enhanced: QCELP13; introduced in 1995; coding rate: 14.4 kbps (for Rate

Set 2)Channel coding:– Forward link: convolutional code with rate 1/2 and constraint length 9 (for

Rate Set 1), punctured convolutional code with 3/4 (for Rate Set 2)– Reverse link: convolutional code with rate 1/3 and constraint length 9 (for

Rate Set 1), convolutional code with rate 1/2 (for Rate Set 2)


Repetition of symbols:– Repetition of coded symbols is required in order that a constant coded rate

of 19200 symbols per second is obtained for all possible information data rates.

– Required because IS-95 supports variable-rate transmission: 1200bps, 2400bps, 4800bps, 9600bps.

Block interleaver:– 20ms block interleaver

a 24 by 16 array for forward link, a 32 by 18 array for reverse link– To randomize the data errors in a fading channel, so that channel coding

can perform betterRAKE receiver at both the MS and BS

– To exploit multipath diversity by means of spread-spectrum transmission.

Illustration of Main Functions (2)


Power Control (1)

Tight power control:– CDMA: interference limited system– BS: noncoherent detection, interference on reverse link is more critical

than it would be on the forward link– Performance criterion

target SIR is not sufficient, certain FER (0.2%~3%) should be maintained– Near-far problem solved by a combination of open-loop and fast, closed-

loop power control.– Fast power control’s update rate is 800 updates per second. A simple up

or down request is sent for each update.


BS MSforward link

Measure received power.Decide to reduce orincrease the transmit power

MS:

MS:BSreverse link

1.

2.

3. Transmit signal withadjusted power

Reverse link open loop power control– Aims to compensate the long-term channel variations caused by distance

and shadowing– Principle: the MS closer to the BS needs to transmit less power as

compared to a MS that is farther away from the BS– The MS adjusts its transmit power based on total power received in the

forward link. If the received power is high (low), the MS reduces (increases) its transmit power

– BS is not involved

Power Control (2)


Reverse link open loop power control– Simple but significant error due to

Assumption of reciprocity on the forward and reverse linksUse of total received power including power from other BSsToo slow response time ~30ms to counter fast fading

Reverse link closed loop power control– Aims to compensate the short-term channel variations caused by fast

fading– Provides correction to the open loop power control– Quick response time 1.25ms– Consists of two parts

inner-loop: keep the MS as close to its target SIR as possibleouter-loop: adjust the BS target SIR for a given MS

Power Control (3)


Reverse link closed loop power control

Power Control (4)


Forward link power control– aim at reducing interference on the forward link– limit the in-cell interference, reduce other cell/sector interference– set each traffic channel transmit power to the minimum required to

maintain the desired FER at the mobile– The MS continuously measures forward traffic channel FER, and

reports this measurement to the BS periodically. After receiving the measurement report, the BS takes the appropriate action to increase or decrease power on the measured logical channel.

Power Control (5)

BS MS:forward link Measure FER on

the forward link

MS:

MS:BSforward link

1.

2.

3.Adjust the transmittingpower according to the

measurement report

Report themeasured FERto BS

BSreverse link


Soft Handoff (1)

Hard handofff– A definite decision is made on whether to handoff or not– Is initiated and executed without the user attempting to have simultaneous

traffic channel communications with the two base stations– Break before make strategy. The connection with the old traffic channel is

broken before the connection with the new traffic channel is establishedSoft handoff

– A conditional decision is made on whether to handoff or not– The user has simultaneous traffic communication with all candidate BSs.

Depending on the changing pilot signal strength for the BSs involved, when it is evident that the signal from one BS is considerably stronger than those from the others, a hard decision will be made to communicate with only one.

– Make before break, universal frequency reuse of CDMA– Diversity gain


Soft Handoff (2)

Old BS

New BS

• Hard Handoff

Old BS

New BS

• Soft Handoff

New BS

Soft handoff– Forward link: multiple BSs transmit signal for one MS, MS uses Rake to

achieve diversity gain, extra interference– Reverse link: multiple BSs receive signal from one MS, selection combining

is used to provide diversity gain, no additional interference


Soft Handoff (Illustration)

Copied from CDMA Systems Engineering Handbook.


Summary-Soft Handoff

Procedure:– Make before break during switching.

Advantages– Contacting the new base station before switching avoids mobile

stations from losing contact with the system and hence avoids calls dropped.

– Diversity combining of multiple signals is possible; performanceenhanced.

– Ping-pong effect in base station switching is avoided.– The system is relieved from the burden of determining signal

strengths, as it is done at mobile stations.

Note:– Carrier frequency is not required to be changed during soft handoff.


2.5G Data Services


2.5G

Operators have invested a lot of money on the existing infrastructure. Before 3G can be deployed, a rapid way to upgrade the existing 2G infrastructure to support high-data-rate transmission and packet switching is essential because of the explosive demand on the Internet access.

Evolved standards:GPRS (General Packet Radio Services)EDGE (Enhanced Data Rates for GSM and TDMA/136 Evolution)IS-95B


GSM Migration Paths

Copied from http://www.netlab.tkk.fi/opetus/s38118/s98/htyo/54/index.shtml

HSCSD: high-speed circuit-switched data service, combines two to four of the time slots (out of a total of 8 in each frame) to provide service from 28.8 Kbps to 56 Kbps, attractive to carriers because it requires minimal new infrastructure


As a service providing optimized access to the Internet, while reusing to a large degree existing GSM infrastructure.Introduce packet-switched services into GSM: Many new protocols and nodes are added to the GSM networkPrimary features:– Circuit- and packet-switched services in one mobile radio network

circuit-switched: a data connection establishes a circuit, and reserves the full bandwidth of that circuit during the lifetime of the connection

GPRS - Introduction (1)

A

B

Data C

D

Data

Data

Data

waiting

waitingtime


Primary features (Cont')– packet switched: multiple users share the same transmission channel,

only transmitting when they have data to send; the total available bandwidth can be immediately dedicated to those users who are actually sending at any given moment, providing higher utilisationwhere users only send or receive data intermittently; the data is transmitted in small parts called packages, ideal for bursty traffic, cost efficient and optimize the use of radio and network resources


A

B

C

D

Data

Data

Data Data

time


Primary features (Cont')– Seamless connection to other external packet data networks, based on

IP or X.25– Fast setup/access times: typically from 0.5~1s– Support of QoS.– Volume-based charging, GSM: time-based charging– new GRPS radio channels: flexible allocation of timeslots per TDMA

frameGSM: one timeslot for one user, 9.6 and 14.4kbpsGPRS: one to eight timeslot for one user, increase data rate, 9-150kbps



GPRS Network Structure (1)GPRS network structure

Copied from http://www.item.ntnu.no/fag/tm8100/Pensumstoff2004/GPRS_Tutorial.pdf


GPRS Network Structure (2)Upgraded BSC– adding a Packet Control Unit (PCU) – PCU: differentiates data destined for the standard GSM network (or

circuit switched data) and for the GPRS network (or packet switched data)

Two new functional elements– Serving GPRS supporting node (SGSN)

routing, handover and IP address assignment– Gateway GPRS supporting node (GGSN)

basically a gateway, router and firewall rolled into one– GPRS tunneling protocol (GTP)

the connection between SGSN and GGSN, sits on top of TCP/IP, responsible for the collection of mediation and billing information


GPRS Handset ClassesHandset Classes– Class A: have two transceivers, allow to send / receive data and voice

at the same time, example: Nokia N93 may be required to transmit on two different frequencies at the same time, and thus will need two radios. To get around this expensive requirement, a GPRS mobile may implement the dual transfer mode (DTM) feature.

– Class B: can send / receive data or voice but not both at the same time, During GSM service (voice call or SMS), GPRS service is suspended, and then resumed automatically after the GSM service (voice call or SMS) has concluded. Most GPRS mobile devices are Class B.

– Class C: connected to either GPRS service or GSM service. Must be switched manually between one or the other service, such as a GPRS PCMCIA card in a laptop


GPRS Coding Schemes Coding Schemes– GPRS provides a number of coding schemes with different levels of

error detection and correction. Different coding schemes are used according to channel conditions and service requirement.

20.0kbps1 (no coding)CS-4

14.4kbps3/4CS-3

12.0kbps2/3CS-2

8.0kbps1/2CS-1

Data Rate (using one timeslot)

Coding RateCoding Schemes


An Example of GPRS QoSThe QoS profile

Copied from R. Kalden, I. Meirickand M. Meyer, “Wireless Internet access based on GPRS,” IEEE Personal Communications, pp. 8-18, Apr. 2000.

CS-4CS-3CS-2CS-1Coding schemes

Best effort

<50<5<0.5Mean (s)

<1.5 Best effort

<25 <250

160kbpsGPRS limit (in 2000)

0.22bps~111kbpsMean bit rate

8kbps~2MbpsMaximum bit rate

95% (s)

Delay for packets of 128 octets

Packet loss probability: e.g., 10-9, 10-4, 10-2

Reliability

High, normal, lowPrecedence

ValuesParameters


Enhanced Data rates for GSM Evolution (EDGE) or Enhanced GPRS (EGPRS): a new TDMA-based radio access technology for both TDMA/136 (or D-AMPS) and GSM systems for providing good Internet access to mobile users.Objective– increase data transmission rates and spectrum efficiency– facilitate new applications and increased capacity for mobile use

A method to increase the data rates on the radio link for GSM– support circuit- and packet-switched services– add new modulation and channel coding to GPRS– make adjustments to the radio link protocols– offer significantly higher throughput and capacity.

EDGE - Introduction


EDGE - Network Structure

Copied from Ericsson, "EDGE Introduction of high-speed data in GSM/GPRS networks", white paper.

EDGE is an add-on of GPRS and cannot work alone. A new physical layer with new modulation and channel coding techniques. Data rate: up to 384kbps


EDGE - Basic Radio Parameters

Copied from T. Ojanpera and R. Prasad, WCDMA: Towards IP Mobility ...


EDGE - MCS

8-PSK8-PSK8-PSK8-PSK8-PSKGMSKGMSKGMSKGMSK

Modulation Technique

59.21.0MCS-954.40.92MCS-844.80.76MCS-729.60.49MCS-622.40.37MCS-517.61.0 (no coding)MCS-414.80.80MCS-311.20.66MCS-28.4kbps0.53MCS-1

Data Rate (using one timeslot)

Coding RateModulation Coding Schemes

MCS: Modulation Coding Schemes


Comparison

Copied from Ericsson, "EDGE Introduction of high-speed data in GSM/GPRS networks", white paper.

GPRS and EDGE: a comparison of technical data


CDMAIS-95A

IS-95B

1xRTT 1xEV-DV CDMA20003xRTT

2G 2.5G 3G

CDMA Migration Path

1995 1998 1999 2002 2005

1xEV-DO

2003

CDMA2000 family

Data OnlyData and

Voice


IS-95B (1)

Is an enhancement to IS-95A standard

Offers the highest possible performance using the same air interface design as IS-95A

IS-95A supports– 9.6 kb/s using RS1 (Rate Set 1)– 14.4 kb/s using RS2 (Rate Set 2)

IS-95B uses, instead of one code channel, up to 8 code channels forhigh-rate data transmission, so that it supports– 9.6-76.8 kb/s at RS1– 14.4-115.2 kb/s at RS2


IS-95B (2)

Enhancement over IS-95A– Forward code channels: Up to eight walsh codes (1 walsh code per

code channel) are assigned for the data burst to the high rate user– Reverse code channels: Each reverse supplemental channel is

assigned a different PN sequence mask derived from its fundamental PN sequence mask. Each mask corresponds to a different PN sequence shift.

– Power control: Power control for the supplemental code channels is derived from the fundamental code channel. That is, there is no independent power control loop for the supplemental code channels.

– Permitted code rates: During a data burst, all the code channels are transmitted at full rate; partial rates are not permitted.

Due to "time-to-market" reasons, IS-95B is not popular. Most operators skip IS-95B and go directly to CDMA20001xRTT

Source: D.N. Knisely, etc., "Evolution of wireless data services: IS-95 to cdma2000". IEEE Comm. Mag..


CDMA2000 1xRTT (1)CDMA2000 1XRTT– 1X: the number of 1.25 MHz wide radio carrier channels used– RTT: radio-transmission technology– a convenient stepping stone for CDMA carriers moving to 3G, can

also be thought of as a 2.5G technology since it uses the same 1.25 MHz bandwidth as IS-95

– can be deployed in existing spectrum to double voice capacity with only a modest investment in infrastructure (fast forward power control, lower code rates, a coherent reverse link)

– Improvements over IS-95A: more sophisticated power control, new modulation on the reverse channels, improved data encoding methods => significantly higher capacity, provide IP-based packet-data rates of up to 144 Kbps

– Offers 50% longer stand by times: supported by Quick Paging Channel

– Backward and forward compatible with IS-95A/BSource: D.N. Knisely, etc., "Evolution of wireless data services: IS-95 to cdma2000". IEEE Comm. Mag..


CDMA2000 1xRTT (2)

Main differences between IS-95 and CDMA2000 1xRTT– 64 more traffic channels on the forward link that are orthogonal to the

original set– Some changes were also made to the data link layer to accommodate

the greater use of data services—CDMA-2000 has media and link access control protocols and QoS control. In IS-95, none of these were present, and the data link layer basically consisted of a "best effort delivery" RLP—this arrangement is still used for voice.

Source: D.N. Knisely, etc., "Evolution of wireless data services: IS-95 to cdma2000". IEEE Comm. Mag..


Summary

Main system parameters of IS-95: in frequency domain, each CDMA channel occupies 1.25M bandwidth. The chip rate is 1.2288Mbps. Frequency reuse factor is one.Power control: reverse link, forward linkHard handoff and soft handoffGPRS introduces packet switched services to GSM. System architecture is modified: PCU, SGSN and GGSN are added.Measures employed by GPRS to provide higher data rates than GSM:various coding rate, multi-time slot transmissionMeasures employed by EDGE to provide higher data rates than GSM: new modulation (8PSK) schemes, various coding rate, multi-time slot transmissionMeasures employed by IS-95B to provide higher data rates than IS-95A: multi-code transmission

Documents

Part 5-2 and 25G systems - University of Hong Kongsdma/elec6040_2008/Part_5... · – data are broken up every 13th frame by SACCH or idle frames – the 26th frame contains idle