OBILE IRELESS COMMUNICATIONS NTRODUCTION · CDMA)/UMTS (Universal Mobile Telecommunication Telephony, video System) streaming 3G CDMA 2000 384 Kbps Video Telephony, video streaming

MOBILE WIRELESSCOMMUNICATIONS INTRODUCTIONCOMMUNICATIONS ‐ INTRODUCTION

Aditya K. JagannathamIndian Institute of Technology KanpurIndian Institute of Technology KanpurCommonwealth of Learning Vancouver

MOOC on M4D 2013

2G Wireless Systems2G Wireless Systems

Generation

Standard Rate Services

2G GSM (Global System for Mobile Communications)

10 Kbps Voice calls

2G CDMA (Code Division for Multiple Access)

10 Kbps Voice calls

2.5G GPRS (General Packet Radio Service)

50 Kbps Internet/ e‐mail access

2.5G EDGE (Enhanced Data Rates for GSM Evolution)

200 Kbps Internet/e‐mail access

MOOC on M4D 2013

3G Wireless Systems3G Wireless SystemsGener Standard Rate ServicesGeneration

Standard Rate Services

3G WCDMA (Wideband 384 Kbps Video3G WCDMA (Wideband CDMA)/UMTS (Universal Mobile Telecommunication

384 Kbps VideoTelephony, video 

System) streaming3G CDMA 2000 384 Kbps Video

Telephony, video streamingstreaming

3 5G HSDPA (High Speed Downlink 5 30 Mbps Online

MOOC on M4D 2013

3.5G HSDPA (High Speed Downlink Packet Access)/HSUPA (High Speed Uplink Packet Access)

5‐30 Mbps Online Gaming, HD Streaming

4G Wireless Systems4G Wireless Systems

Geneti

Standard Rate Servicesration

( )4G LTE (Long Term Evolution) 100‐200 Mbps Mobile TV, Multiplayer GamingGaming

4G WiMAX (WorldwideInteroperability for

100 Mbps Mobile TV, MultiplayerInteroperability for 

Microwave Access)Multiplayer Gaming

MOOC on M4D 2013

Wireless Signal PropagationWireless Signal Propagation

MOOC on M4D 2013

Wireless Channel FadingWireless Channel Fading

• The wireless signal can reach the receiver via direct and multiple scattered paths.– Multipath Propagation

– As a result, the receiver sees the superposition of multiple copies of the transmitted signal.

• These signal copies experience differentg p p– AttenuationsDelays– Delays 

MOOC on M4D 2013

Wireless Channel FadingWireless Channel Fading

• Results in interference, amplifying or attenuating the signal power seen at the Rx. – This phenomenon is termed as fading.

• Strong destructive interference is referred to as a St o g dest uct e te e e ce s e e ed to as adeep fade.

MOOC on M4D 2013

Wireless Channel FadingWireless Channel Fading0

Fading Channel Magnitude vs Time

4

-2

-6

-4

nitu

de

10

-8

anne

l mag

n

-12

-10

cha

Deep fade

16

-14Deep fade

MOOC on M4D 2013

0 20 40 60 80 100 120 140 160 180 200-16

t (ms)

Multipath Delay CharacterizationMultipath Delay Characterization

• Each replica of the wireless signal s(t) is delayed,Each replica of the wireless signal s(t) is delayed, attenuated, phase shifted.

T

Td

MOOC on M4D 2013

Multipath Delay CharacterizationMultipath Delay Characterization

• T is the symbol duration. 

• Td is the delay spread.Td is the delay spread.

MOOC on M4D 2013

Multipath Delay CharacterizationMultipath Delay CharacterizationT

Td

• If Td > T, i.e. delay spread is larger than symbol time, there is ISI (Intersymbol Interference).

d

MOOC on M4D 2013

there is ISI (Intersymbol Interference).

WSSUS Channel Variables Delay• Typical wireless channel delay spreads are of the

WSSUS Channel Variables ‐ DelayTypical wireless channel delay spreads are of the order of  1km/3 x 105kms‐1 ~ 3 μs.

~ Km~ Km~ Km

MOOC on M4D 2013

WSSUS Channel Variables DelayWSSUS Channel Variables ‐ Delay

• Therefore, to avoid ISI, T > Td = 3 μs.• It is immediately clear the maximum symbol rate in outdoor channels is,

Kbps3331031

6max R p103 6max

MOOC on M4D 201315

Frequency Domain InterpretationH(f)h(t)

BBc f

0TTd

• Let H(f) denote the FT of the wireless channel (f)impulse response h(t)

• The bandwidth of the channel response isThe bandwidth of the channel response is termed the coherence bandwidth Bc.

MOOC on M4D 2013

Frequency Domain Interpretation

Bcf

0TdTd

Bcf

Td0

• As the delay spread Td increases coherenceMOOC on M4D 2013

As the delay spread Td increases, coherence bandwidth Bc decreases. Bc ~ 1/Td

Implication of Coherence BandwidthImplication of Coherence Bandwidth• If Bc is greater than the wireless signal bandwidth Bs, c g g s

there is NO distortion.

Bcf

Bsf

00

• Such a wireless channel is also known as a Flat Fading channel.

MOOC on M4D 2013

Implication of Coherence BandwidthImplication of Coherence Bandwidth• If Bc is smaller than the wireless signal bandwidth Bs, c g s,

there is distortion.

Bsf

Bcff

0

f

0

• Such a wireless channel is also known as a Frequency Selective channel.

MOOC on M4D 2013

Coherence bandwidthCoherence bandwidth

• Coherence bandwidth of the channel is defined in terms of delay spread as, 

c TB 1

d

c T

• For outdoor channels, Td ~ 3 s as seen earlier.– Hence, the coherence bandwidth Bc is given as,, c g ,

KHz3331B

MOOC on M4D 2013

KHz333103 6

cB

Back to Time Domain• If the coherence bandwidth is lesser than the 

wireless signal bandwidthwireless signal bandwidth

sc BB sc

11

d TT

d

d

TT • Hence, ISI in time domain is equivalent to Frequency 

d

MOOC on M4D 2013Selective distortion in frequency domain.

Doppler Effect in Wireless ChannelsDoppler Effect in Wireless Channels

• Relative motion between transmitter (Base station) and receiver (mobile) causes a shift in the frequency f h i d i lof the received signal.– This change in frequency is known as the Doppler shift fd.

MOOC on M4D 2013

Doppler Effect in Wireless ChannelsDoppler Effect in Wireless Channels

• The bandwidth corresponding to the maximum Doppler shift is known as the Doppler spread Bd.

MOOC on M4D 2013

Doppler Effect in Wireless ChannelsDoppler Effect in Wireless Channels• The Doppler shift fd for a path is given by theThe Doppler shift fd for a path is given by the expression below.

v

cd fc

f

cosv

MOOC on M4D 2013

Doppler Effect in Wireless ChannelsDoppler Effect in Wireless Channels• f is the carrier frequency.fc is the carrier frequency.• v is the relative velocity of motion between transmitter and mobile receivertransmitter and mobile receiver.

• is the angle between the incident wave and the direction of observer motiondirection of observer motion.

• At  60 Km/Hr, 2 GHz and  = 0,  fd ~ 55 Hz.

Hz551021560 9

f Hz55102

1031860 8

df

MOOC on M4D 2013