obile ireless communications ntroduction · cdma)/umts (universal mobile telecommunication...
Post on 15-May-2020
3 Views
Preview:
TRANSCRIPT
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
top related