ee392w project presentation cooperative mimo techniques in sensor networks 03/08/2005 wireless...

EE392WProject Presentation

Cooperative MIMO Techniques

in Sensor Networks

03/08/2005Wireless Systems Lab Stanford University

Yifan [email protected]

2EE392W - Stanford University

Target Problem

Receiver nodeTransmitter nodeAssisting node

THE BEST TRANSMISSION STRATEGY?

OBJECTIVE: ENERGY EFFICIENCY


Outline

Non-cooperative Transmission Cooperative Transmission

Diversity Gain Spatial Multiplexing

Conclusion Cooperative scheme more energy efficient in the

long-range transmission


Outline






Non-Cooperative Transmission



No use of assisting nodes




Transmitter nodes: TDMANode in active transmission

Node in the waiting list






Transmission Completed



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


System Blocks

DAC LPF Mixer

SYN

BPF PA

ADC BPF Mixer

SYN

LNA BPFAAFIFA

Wireless Link

TX

RX


System Blocks

Ect = Pct * Ton PA

Ecr = Pcr * Ton

Wireless Link

TX Circuitry

RX Circuitry

TransmissionEnergy

Ec = (Mt * Pct + Mr * Pcr) * Ton


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


Outline






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


Compare MIMO with SISO

Pros Reduced transmission energy due to higher SNR

Cons Increased circuit energy consumption Local data exchange: overhead


Outline






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



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)



Transmission Timeline


N1 data

N2 data

y1 data

y1/y2

joint DEC

Tx Local Data Exchange

Long HaulTransmission

Rx Local Data Exchange


Compare MIMO with SISO

Increased circuit energy consumption Local data exchange: overhead Reduced long-haul transmission energy

Higher SNR


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


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


Compare SISO with MIMO

Long haul Transmission EnergyBER = 1e-3

Long haul Circuit Energy



Long-haul total energyBER = 1e-3

Total energy include local overheadBER = 1e-3


Outline







Alamouti Scheme

Local data exchange necessary at Tx Data rate R = 1


x1 (1)

x1* (1)

…………x2 (1)

-x2* (1) x1 (2)

x1* (2)x2 (2)

-x2* (2)


Cooperation for Spatial Multiplexing

No local data exchange at Tx Increased data rate R = 2 Reduced transmission time


x1 (1) …………x2 (1)

x1 (2)

x2 (2)

x1 (3)

x2 (3)

x1 (4)

x2 (4)


Cooperation for Spatial Multiplexing

Transmission Timeline


y1 data

y1/y2

joint DEC

NO Tx Local Data Exchange

Long HaulTransmission

Rx Local Data Exchange


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



Total energy consumptionMt = Mr = 2

Total energy consumptionMt = 2 Mr = 3


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!

ee392w project presentation cooperative mimo techniques in sensor networks 03/08/2005 wireless...

Documents

active transmission

ee392w stanford university

waiting list transmission

long range transmission

best transmission strategy

tdma node

ton slide

energy efficiency slide