EE392WProject Presentation
Cooperative MIMO Techniques
in Sensor Networks
03/08/2005Wireless Systems Lab Stanford University
Yifan [email protected]
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Target Problem
Receiver nodeTransmitter nodeAssisting node
THE BEST TRANSMISSION STRATEGY?
OBJECTIVE: ENERGY EFFICIENCY
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Outline
Non-cooperative Transmission Cooperative Transmission
Diversity Gain Spatial Multiplexing
Conclusion Cooperative scheme more energy efficient in the
long-range transmission
4EE392W - Stanford University
Outline
Non-cooperative Transmission Cooperative Transmission
Diversity Gain Spatial Multiplexing
Conclusion Cooperative scheme more energy efficient in the
long-range transmission
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Non-Cooperative Transmission
No use of assisting nodes
Transmitter nodes: TDMANode in active transmission
Node in the waiting list
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Non-Cooperative Transmission
No use of assisting nodes
Transmitter nodes: TDMANode in active transmission
Node in the waiting list
Transmission Completed
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Non-Cooperative Transmission
No use of assisting nodes
Transmitter nodes: TDMANode in active transmission
Node in the waiting list
Transmission Completed
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Non-Cooperative Transmission
No use of assisting nodes
Transmitter nodes: TDMANode in active transmission
Node in the waiting list
Transmission Completed
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Non-Cooperative Transmission
No use of assisting nodes
Transmitter nodes: TDMANode in active transmission
Node in the waiting list
Transmission Completed
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Non-Cooperative Transmission
No use of assisting nodes Transmitter nodes work in a TDMA
manner Only one node in active transmission at any time Call it a Single-Input-Single-Output (SISO) scheme
Energy consumption analysis Transmission energy Circuit Energy
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System Blocks
DAC LPF Mixer
SYN
BPF PA
ADC BPF Mixer
SYN
LNA BPFAAFIFA
Wireless Link
TX
RX
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System Blocks
Ect = Pct * Ton PA
Ecr = Pcr * Ton
Wireless Link
TX Circuitry
RX Circuitry
TransmissionEnergy
Ec = (Mt * Pct + Mr * Pcr) * Ton
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Transmission Energy
TxRxSquare-Law Path loss
Block Rayleigh Fading
+
Et Es ~ Et/d2
Transmit energy
Average receive energy;
Only considers path loss
22
02SNR
N
ES
With fading & noise
BER
Average over distribution of SNR
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Outline
Non-cooperative Transmission Cooperative Transmission
Diversity Gain Spatial Multiplexing
Conclusion Cooperative scheme more energy efficient in the
long-range transmission
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Cooperative Transmission
Channel Model Similar to SISO
Vector input/output Channel gain matrix
Assume a simple case Two transmit nodes One receive node One assisting node Multiple-Input-Multiple-Output (MIMO)
2
1
2
1
2221
1211
2
1
n
n
x
x
hh
hh
y
y
x1
x2 y2
y1h11
h12
h21
h22
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Compare MIMO with SISO
Pros Reduced transmission energy due to higher SNR
Cons Increased circuit energy consumption Local data exchange: overhead
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Outline
Non-cooperative Transmission Cooperative Transmission
Diversity Gain Spatial Multiplexing
Conclusion Cooperative scheme more energy efficient in the
long-range transmission
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Cooperation for Diversity Gain
Basic idea Tx side: The same symbol is sent through each
node Rx side: Combine multiple copies of the same
symbol
Motivation for diversity It is unlikely all links experience deep fading at the
same time
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Cooperation for Diversity Gain
Alamouti Scheme
Local data exchange necessary at Tx Data rate R = 1
Transmission Sequence
x1 (1)
x1* (1)
…………x2 (1)
-x2* (1) x1 (2)
x1* (2)x2 (2)
-x2* (2)
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Cooperation for Diversity Gain
Transmission Timeline
Transmission Sequence
N1 data
N2 data
y1 data
y1/y2
joint DEC
Tx Local Data Exchange
Long HaulTransmission
Rx Local Data Exchange
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Compare MIMO with SISO
Increased circuit energy consumption Local data exchange: overhead Reduced long-haul transmission energy
Higher SNR
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Transmission Energy
TxRxSquare-Law Path loss
Block Rayleigh Fading
+
Et Es ~ Et/d2
Transmit energy
Average receive energy;
Only considers path loss
22
02SNR
N
ES
With fading & noise
BER
Average over distribution of SNR
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Long-haul Received SNR
Received SNR Es: signal
power No: noise power Mt: number of
Tx nodes
Chi-squared r.v,
degrees of freedom 2MtMr
22
02SNR
rtMMt
S
NM
E
22 rtMM
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Compare SISO with MIMO
Long haul Transmission EnergyBER = 1e-3
Long haul Circuit Energy
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Compare SISO with MIMO
Long-haul total energyBER = 1e-3
Total energy include local overheadBER = 1e-3
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Outline
Non-cooperative Transmission Cooperative Transmission
Diversity Gain Spatial Multiplexing
Conclusion Cooperative scheme more energy efficient in the
long-range transmission
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Cooperation for Diversity Gain
Alamouti Scheme
Local data exchange necessary at Tx Data rate R = 1
Transmission Sequence
x1 (1)
x1* (1)
…………x2 (1)
-x2* (1) x1 (2)
x1* (2)x2 (2)
-x2* (2)
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Cooperation for Spatial Multiplexing
No local data exchange at Tx Increased data rate R = 2 Reduced transmission time
Transmission Sequence
x1 (1) …………x2 (1)
x1 (2)
x2 (2)
x1 (3)
x2 (3)
x1 (4)
x2 (4)
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Cooperation for Spatial Multiplexing
Transmission Timeline
Transmission Sequence
y1 data
y1/y2
joint DEC
NO Tx Local Data Exchange
Long HaulTransmission
Rx Local Data Exchange
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Long-haul Received SNR
ZF receiver Requires Mr >= Mt
Received SNR Es: signal power No: noise power Mt: number of Tx nodes Mr: number of Rx nodes
2)1(2
02SNR MtMr
t
S
NM
E
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Compare SISO with MIMO
Total energy consumptionMt = Mr = 2
Total energy consumptionMt = 2 Mr = 3
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Conclusions
Cooperative vs. non-cooperative scheme Saves transmission energy Consumes more circuit energy Local data exchange an overhead Preferable in the long-range transmission
Spatial Diversity vs. Multiplexing Multiplexing scheme only beats SISO when Mr>Mt For fixed (Mt, Mr), diversity scheme edges out More energy saving not guaranteed with more
collaborative nodes
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