2G Wireless Systems 2G Wireless Systems Gener Standard Rate - - PowerPoint PPT Presentation

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2G Wireless Systems 2G Wireless Systems Gener Standard Rate - - PowerPoint PPT Presentation

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M OBILE W IRELESS C OMMUNICATIONS I NTRODUCTION C OMMUNICATIONS I NTRODUCTION Aditya K. Jagannatham Indian Institute of Technology Kanpur Indian Institute of Technology Kanpur Commonwealth of Learning Vancouver MOOC on M4D 2013 2G Wireless

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SLIDE 1

MOBILE WIRELESS COMMUNICATIONS INTRODUCTION COMMUNICATIONS ‐ INTRODUCTION

Aditya K. Jagannatham Indian Institute of Technology Kanpur Indian Institute of Technology Kanpur Commonwealth of Learning Vancouver

MOOC on M4D 2013

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SLIDE 2

2G Wireless Systems 2G Wireless Systems

Gener ation 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

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SLIDE 3

3G Wireless Systems 3G Wireless Systems

Gener Standard Rate Services Gener ation Standard Rate Services

3G WCDMA (Wideband 384 Kbps Video 3G WCDMA (Wideband CDMA)/UMTS (Universal Mobile Telecommunication 384 Kbps Video Telephony, video System) streaming 3G CDMA 2000 384 Kbps Video Telephony, video streaming streaming 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

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SLIDE 4

4G Wireless Systems 4G Wireless Systems

Gene ti Standard Rate Services ratio n

( ) 4G LTE (Long Term Evolution) 100‐200 Mbps Mobile TV, Multiplayer Gaming Gaming 4G WiMAX (Worldwide Interoperability for 100 Mbps Mobile TV, Multiplayer Interoperability for Microwave Access) Multiplayer Gaming

MOOC on M4D 2013

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SLIDE 5
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SLIDE 6

Wireless Signal Propagation Wireless Signal Propagation

MOOC on M4D 2013

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SLIDE 7

Wireless Channel Fading Wireless 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 different

g p p

– Attenuations Delays – Delays

MOOC on M4D 2013

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SLIDE 8

Wireless Channel Fading Wireless 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 a deep fade.

MOOC on M4D 2013

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SLIDE 9

Wireless Channel Fading Wireless Channel Fading

Fading Channel Magnitude vs Time 4

  • 2
  • 6
  • 4

nitude 10

  • 8

annel magn

  • 12
  • 10

cha

Deep fade

16

  • 14

Deep fade

MOOC on M4D 2013

20 40 60 80 100 120 140 160 180 200

  • 16

t (ms)

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SLIDE 10
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SLIDE 11

Multipath Delay Characterization Multipath 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

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SLIDE 12

Multipath Delay Characterization Multipath Delay Characterization

  • T is the symbol duration.
  • Td is the delay spread.

Td is the delay spread.

MOOC on M4D 2013

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SLIDE 13

Multipath Delay Characterization Multipath Delay Characterization

T 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).

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SLIDE 14

WSSUS Channel Variables Delay

  • Typical wireless channel delay spreads are of the

WSSUS Channel Variables ‐ Delay

Typical wireless channel delay spreads are of the

  • rder of 1km/3 x 105kms‐1 ~ 3 μs.

~ Km ~ Km ~ Km

MOOC on M4D 2013

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SLIDE 15

WSSUS Channel Variables Delay WSSUS Channel Variables ‐ Delay

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

Kbps 333 10 3 1

6 max

  R p 10 3

6 max

MOOC on M4D 2013 15

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SLIDE 16

Frequency Domain Interpretation

H(f) h(t) Bc

f

Td

  • Let H(f) denote the FT of the wireless channel

(f)

impulse response h(t)

  • The bandwidth of the channel response is

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

MOOC on M4D 2013

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SLIDE 17

Frequency Domain Interpretation

Bc

f

Td Td

Bc

f

Td

  • As the delay spread Td increases coherence

MOOC on M4D 2013

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

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SLIDE 18

Implication of Coherence Bandwidth Implication of Coherence Bandwidth

  • If Bc is greater than the wireless signal bandwidth Bs,

c

g g

s

there is NO distortion.

Bc

f

Bs

f

  • Such a wireless channel is also known as a Flat

Fading channel.

MOOC on M4D 2013

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SLIDE 19

Implication of Coherence Bandwidth Implication of Coherence Bandwidth

  • If Bc is smaller than the wireless signal bandwidth Bs,

c

g

s,

there is distortion.

Bs

f

Bc

f f f

  • Such a wireless channel is also known as a Frequency

Selective channel.

MOOC on M4D 2013

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SLIDE 20

Coherence bandwidth Coherence bandwidth

  • Coherence bandwidth of the channel is defined in

terms of delay spread as,

c

T B 1 

d c

T

  • For outdoor channels, Td ~ 3 s as seen earlier.

– Hence, the coherence bandwidth Bc is given as, ,

c

g ,

KHz 333 1   B

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KHz 333 10 3

6 

 

 c

B

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SLIDE 21

Back to Time Domain

  • If the coherence bandwidth is lesser than the

wireless signal bandwidth wireless signal bandwidth

s c

B B 

s c

 1 1

d

T T  

d d

T T  

  • Hence, ISI in time domain is equivalent to Frequency

d

MOOC on M4D 2013

Selective distortion in frequency domain.

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SLIDE 22

Doppler Effect in Wireless Channels Doppler Effect in Wireless Channels

  • Relative motion between transmitter (Base station)

and receiver (mobile) causes a shift in the frequency f h i d i l

  • f the received signal.

– This change in frequency is known as the Doppler shift fd.

MOOC on M4D 2013

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SLIDE 23

Doppler Effect in Wireless Channels Doppler Effect in Wireless Channels

  • The bandwidth corresponding to the maximum

Doppler shift is known as the Doppler spread Bd.

MOOC on M4D 2013

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SLIDE 24

Doppler Effect in Wireless Channels Doppler Effect in Wireless Channels

  • The Doppler shift fd for a path is given by the

The Doppler shift fd for a path is given by the expression below.

    v

c d

f c f         cos v

MOOC on M4D 2013

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SLIDE 25

Doppler Effect in Wireless Channels Doppler 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 receiver transmitter and mobile receiver.

  •  is the angle between the incident wave and the

direction of observer motion direction of observer motion.

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

Hz 55 10 2 1 5 60

9

        f Hz 55 10 2 10 3 18 60

8

          

d

f

MOOC on M4D 2013