EE392W Project Presentation Cooperative MIMO Techniques in Sensor Networks 03/08/2005 Wireless Systems Lab Stanford University Yifan Liang

EE392W - Stanford University 2 Target Problem Receiver node Transmitter node Assisting node THE BEST TRANSMISSION STRATEGY? OBJECTIVE: ENERGY EFFICIENCY

EE392W - Stanford University 3 Outline Non-cooperative Transmission Cooperative Transmission Diversity Gain Spatial Multiplexing Conclusion Cooperative scheme more energy efficient in the long- range transmission

EE392W - Stanford University 4 Outline Non-cooperative Transmission Cooperative Transmission Diversity Gain Spatial Multiplexing Conclusion Cooperative scheme more energy efficient in the long- range transmission

EE392W - Stanford University 5 Non-Cooperative Transmission

EE392W - Stanford University 6 Non-Cooperative Transmission No use of assisting nodes

EE392W - Stanford University 7 Non-Cooperative Transmission No use of assisting nodes Transmitter nodes: TDMA Node in active transmission Node in the waiting list

EE392W - Stanford University 8 Non-Cooperative Transmission No use of assisting nodes Transmitter nodes: TDMA Node in active transmission Node in the waiting list Transmission Completed

EE392W - Stanford University 9 Non-Cooperative Transmission No use of assisting nodes Transmitter nodes: TDMA Node in active transmission Node in the waiting list Transmission Completed

EE392W - Stanford University 10 Non-Cooperative Transmission No use of assisting nodes Transmitter nodes: TDMA Node in active transmission Node in the waiting list Transmission Completed

EE392W - Stanford University 11 Non-Cooperative Transmission No use of assisting nodes Transmitter nodes: TDMA Node in active transmission Node in the waiting list Transmission Completed

EE392W - Stanford University 12 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

EE392W - Stanford University 13 System Blocks DACLPFMixer SYN BPF PA ADCBPFMixer SYN LNA BPF AAFIFA Wireless Link TX RX

EE392W - Stanford University 14 System Blocks Ect = Pct * Ton PA Ecr = Pcr * Ton Wireless Link TX Circuitry RX Circuitry Transmission Energy Ec = (Mt * Pct + Mr * Pcr) * Ton

EE392W - Stanford University 15 Transmission Energy Tx Rx Square-Law Path loss Block Rayleigh Fading + EtEs ~ Et/d 2 Transmit energy Average receive energy; Only considers path loss With fading & noise BER Average over distribution of SNR

EE392W - Stanford University 16 Outline Non-cooperative Transmission Cooperative Transmission Diversity Gain Spatial Multiplexing Conclusion Cooperative scheme more energy efficient in the long- range transmission

EE392W - Stanford University 17 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) x1 x2 y2 y1 h11 h12 h21 h22

EE392W - Stanford University 18 Compare MIMO with SISO Pros Reduced transmission energy due to higher SNR Cons Increased circuit energy consumption Local data exchange: overhead

EE392W - Stanford University 19 Outline Non-cooperative Transmission Cooperative Transmission Diversity Gain Spatial Multiplexing Conclusion Cooperative scheme more energy efficient in the long- range transmission

EE392W - Stanford University 20 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

EE392W - Stanford University 21 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)

EE392W - Stanford University 22 Cooperation for Diversity Gain Transmission Timeline Transmission Sequence N1 data N2 data y1 data y1/y2 joint DEC Tx Local Data Exchange Long Haul Transmission Rx Local Data Exchange

EE392W - Stanford University 23 Compare MIMO with SISO Increased circuit energy consumption Local data exchange: overhead Reduced long-haul transmission energy Higher SNR

EE392W - Stanford University 24 Transmission Energy Tx Rx Square-Law Path loss Block Rayleigh Fading + EtEs ~ Et/d 2 Transmit energy Average receive energy; Only considers path loss With fading & noise BER Average over distribution of SNR

EE392W - Stanford University 25 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

EE392W - Stanford University 26 Compare SISO with MIMO Long haul Transmission Energy BER = 1e-3 Long haul Circuit Energy

EE392W - Stanford University 27 Compare SISO with MIMO Long-haul total energy BER = 1e-3 Total energy include local overhead BER = 1e-3

EE392W - Stanford University 28 Outline Non-cooperative Transmission Cooperative Transmission Diversity Gain Spatial Multiplexing Conclusion Cooperative scheme more energy efficient in the long- range transmission

EE392W - Stanford University 29 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)

EE392W - Stanford University 30 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)

EE392W - Stanford University 31 Cooperation for Spatial Multiplexing Transmission Timeline Transmission Sequence y1 data y1/y2 joint DEC NO Tx Local Data Exchange Long Haul Transmission Rx Local Data Exchange

EE392W - Stanford University 32 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

EE392W - Stanford University 33 Compare SISO with MIMO Total energy consumption Mt = Mr = 2 Total energy consumption Mt = 2 Mr = 3

EE392W - Stanford University 34 Compare SISO with MIMO

EE392W - Stanford University 35 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

A big THANK YOU to Prof. Aghajan, Sumanth Jagannathan and all fellow 392W students!