Mobile Communications(KECE425)

Lecture Note 103-03-2014

Prof. Young-Chai Ko

114년 3월 3일 월요일

Prof. Y. -C. Ko

Course Information

Instructor

Prof. Young-Chai Ko (koyc@korea.ac.kr, Tel: x3254, Room#416)

Textbook

Principles of mobile communications (by G. Stuber)

Wireless communications (by A. Goldsmith)

Grading

Midterm (40%), Final (45%), Homework (10%), Attendance (5%)

Office Hour: (1:00-2:00 PM on Mon. and Wed.)

TA

Young-Jun Kim and Sungkyung Jo (x3778)

214년 3월 3일 월요일

Prof. Y. -C. Ko

Summary

Introduction

Downlink and uplink channels

Half duplex division (HDD) and full duplex division (FDD)

TDD and FDD

Cellular concept

314년 3월 3일 월요일

Prof. Y. -C. Ko

Basic Mobile Communications

downlin

k (forw

ard) c

hanne

ldownlink (forward) channelup

link (r

everse

) chan

nel

uplink (reverse) channel

Base station (BS)Mobile station (MS) Mobile station (MS)

A direct link is not allowed yet between two communication parties !

414년 3월 3일 월요일

Prof. Y. -C. Ko

Half Duplex and Full Duplex

Half-duplex

Walkie-Talkie (push and talk)

X

Xor

Full-duplex

Full-duplex emulation

Time division duplex (TDD) or frequency division duplex (FDD)

514년 3월 3일 월요일

Prof. Y. -C. Ko

Frequency Band Allocation for Mobile Service Companies

Company Frequency band (MHz) Bandwidth Systems

SKT

824~834 (10) / 869~879 (10) 20 MHz 2G (CDMA)

SKT

834~839(5) / 879~884(5) 10 MHz 3G or LTE

SKT

1755~1765(10) / 1850~1860(10) 20 MHz 3G or LTE

SKT 1930~1940(10) / 2120~2130(10) 20 MHz 3G or LTESKT

1940~1960(20) / 2130~2150(20) 40 MHz 3G or LTE

SKT

2300~2327(27) 27 MHz WiBro

SKT

Total 137 MHz

KT

819~824(5) / 864~869(5) 10 MHz 3G or LTE

KT

905~915(10) / 950~960(10) 20 MHz 3G or LTE

KT1745~1755(10) / 1840~1850(10) 20 MHz 2G, 3G or LTE

KT1960~1980(20) / 2150~2170(20) 40 MHz 3G or LTE

KT

2331.5~2358.5(27) 27 MHz WiBro

KT

Total 117 MHz

LGU+

839~849(10) / 884~894(10) 20 MHz 3G or LTE

LGU+1779~1780(10) / 1860~1870(10) 20 MHz 2G, 3G or LTE

LGU+1920~1930(10) / 2110~2120(10) 20 MHz 3G or LTE

LGU+

Total 60 MHz

614년 3월 3일 월요일

Prof. Y. -C. Ko

FDD vs. TDD

DL (BS Tx, MS Rx)

UL (BS Rx, MS Tx)

time (ms) 5

Freq

uenc

y (M

Hz)

0

1940

1945

2130

21355 MHz

5 MHz

• FDD transmits and receives on two

frequency bands simultaneously.

‣ 2X5MHz so total bandwidth is

10MHz.

‣ For binary modulation, total data

transmitted is 5MbpsX5ms

‣Total data received is 5MbpsX5ms

• TDD transmits and receives on two

time slots simultaneously.

‣ Total bandwidth is 10MHz.

‣ Total data transmitted is

10MbpsX2.5ms

‣Total data received is 10MbpsX2.5ms

[FDD]

time (ms) 5

Freq

uenc

y (M

Hz)

0

2360

2370

DL(BS Tx, MS Rx)

UL (BS Rx, MS Tx) 10 MHz

[TDD]

714년 3월 3일 월요일

Prof. Y. -C. Ko

FDD vs. TDD

• In terms of data throughput, FDD and TDD are identical.

• FDD uses half the bandwidth for twice the time compared to TDD, so overall data transmitted

is the same whether TDD or FDD is used.

Tx/Rx switch

PA

LNA

Tx

Rx

Filter(Tx)

Filter(Rx)

PA

LNA

Tx

Rx

[TDD RF front end] [FDD RF front end]

PA: Power amplifier

LNA: Low noise amplifier

814년 3월 3일 월요일

Prof. Y. -C. Ko

“Real” Full-Duplex

time (ms) 5

Freq

uenc

y (M

Hz)

0

2360

2370

DL(BS Tx, MS Rx)

UL (BS Rx, MS Tx)

Co-time and co-frequency transmission/reception will be

“real” implementation of full-duplex!

914년 3월 3일 월요일

Prof. Y. -C. Ko

Frequency Allocation per Frequency Band

[Ref: 한국전파진흥협회, http://www.rapa.or.kr]

1014년 3월 3일 월요일

Prof. Y. -C. Ko

[Ref: 한국전파진흥협회, http://www.rapa.or.kr]

1114년 3월 3일 월요일

Prof. Y. -C. Ko

Omni-Directional and Directional Antennas

rPomni Pdire

Pdire

=2⇡

✓dPomni

r

✓d rad/s

[Omni-directional antennas] [Directional antennas]

1214년 3월 3일 월요일

Prof. Y. -C. Ko

Path loss

Pt

Pr

rPr ⇠ Pt

r2

Pr = kPt

r2

or

where k is a constant.

1314년 3월 3일 월요일

Prof. Y. -C. Ko

Signal-to-Noise Ratio

In digital communications, we study that the bit-error-rate (BER) or

symbol-error-rate (SER) is a function of only the signal-to-noise ratio.

For example, BER of BPSK is

Pb = Q⇣p

2�⌘

where � is the received signal-to-noise ratio (SNR) defined as

� =Pr

N0W• Pr: received signal power

• N0: one-sided noise power spectral density

• W : signal’s bandwidth

1414년 3월 3일 월요일

Prof. Y. -C. Ko

BER of BPSK versus Distance

• Then we can easily show that �(d)dB = 10 log10

⇣0.52

d2

⌘+ 16

• Let �(0.5km)dB = 10 log10

⇣Pr(0.5)N0W

⌘= 16 [dB] at 500 m distance long.

- where Pr(d) is the received power at the distance d.

or �(d) = 10

�(d)dB/10in linear scale.

1514년 3월 3일 월요일

Prof. Y. -C. Ko

0.5 1 1.5 210−8

10−7

10−6

10−5

10−4

10−3

10−2

10−1

d [km]

BER

BER of BPSK versus the distance [km]

Quality of service requirement for voice communications

1614년 3월 3일 월요일

Prof. Y. -C. Ko

SER of M-QAM

Pe = 4

✓1� 1p

M

◆Q

r3

M � 1

EavN0

!

�4

✓1� 1p

M

◆2

Q2

r3

M � 1

EavN0

!

• For a given time T , as M increases, the spectral e�ciency gets higher.

- which means we can transmit more data (bits) given a certain time

duration.

• M -QAM transmits log2 M bits for the time symbol interval T .

• Symbol error rate

1714년 3월 3일 월요일

Prof. Y. -C. Ko

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 210−8

10−7

10−6

10−5

10−4

10−3

10−2

10−1

100

d [km]

SER

BER of M-QAM versus the distance [km]

M = 4M = 16

M = 64

1814년 3월 3일 월요일

Prof. Y. -C. Ko

Cellular Systems

�f1 +�f2 +�f3 = �fTotal bandwidth

�f1�f2

�f3

1914년 3월 3일 월요일

Prof. Y. -C. Ko

Cellular Concept

Key idea of cellular system: frequency reuse

�f1

�f1

�f2

�f2

�f3

�f3

�f3

�f1

�f2

. . .. . .

�f1 +�f2 +�f3 = �fTotal bandwidth

. . .

. . .

2014년 3월 3일 월요일