MIMO(A SHORT DISSCUSSION)PRESENTED BY-PRITAM MOHANTY

REGD.NO-0901304189GUIDED BY-Mr. Shakti Narayana Mishra(lect. In ECE dept.)

DEPT.-ELECTRONICS AND COMMUNICATION ENGINEERING

GANDHI INSTITUTE OF TECHNOLOGY AND MANAGEMENT

BHUBANESWAR

CONTENTSMotivations for the development of MIMO

systemsMIMO Antenna ConfigurationDesign Criterion for MIMO Systems

(Diversity )MIMO-OFDMConclusions

Aspirations of a System DesignerHigh data rate

Quality

Achieve

“Channel Capacity (C)”

Minimize Probability of Error (Pe)

Real-life Issues

Minimize complexity/cost of

System

Minimize transmission power

Minimize Bandwidth

Antenna ConfigurationsSingle-Input-Single-Output (SISO) antenna

system

1Gbps barrier can be achieved using this configuration if you are allowed to use much power

and as much BW

A combination a smart modulation, coding and multiplexing techniques have yielded good

results but far from the 1Gbps barrier

channel

User data stream

User data stream

MIMO Antenna Configuration

Use multiple transmit and multiple receive antennas for a single user

User data streamUser data stream

.

.

1

2

MT

.

.

.

1

2

MR

.

.

.

.

.

channel

Now this system promises enormous data rates!

MIMO System Model

y = Hs + n

User data stream

.

.

User data stream

.

.

.

.

Channel

Matrix H

s1

s2

sM

s

y1

y2

yM

y

TRANSMITTED VECTOR RECEIVED VECTOR

.

.

h11

h12

Where H =

h11 h21 …….. hM1

h12 h22 …….. hM2

h1M h2M …….. hMM

. . …….. .

MT

MR

Capacity of MIMO Channels

We assume M RX and N TX antennas. The capacity in bits/sec/Hz of a MIMO channel under an average transmitter power constraint is given by

C = log 2 [det(IM + p/N H H*) b/s/Hz]

Capacity (contd)The capacity expression presented was over one

realization of the channel. Capacity is a random variable and has to be averaged over infinite realizations to obtain the true ergodic capacity. Outage capacity is another metric that is used to capture this

So MIMO promises enormous rates theoretically! Can we exploit this

practically?

DIVERSITY: Reliable reception is achieved when

multiple independently-faded replicas of the data symbol can be obtained at the receiver end.

The maximal diversity gain dmax is the total number of independent signal paths that exist between the transmitter and receiver

The higher my diversity gain, the lower my Pe

Alamouti’s Scheme - DiversityTransmission/reception scheme easy to

implementSpace diversity because of antenna transmission.

Time diversity because of transmission over 2 symbol periods

Consider (2, MR) system1. Receiver uses combining and ML detection

2. rs = 1

• If you are working with a (2,2) system, stick with

Alamouti!

• Widely used scheme: CDMA 2000, WCDMA and

IEEE 802.16-2004 OFDM-256

𝑥1 −𝑥2+𝑥2 −𝑥1+൨

11

Orthogonal Frequency Division Multiplexing(OFDM)

It is a special kind of FDMThe spacing between carriers are such that

they are orthogonal to one anotherTherefore no need of guard band between

carriers.

MIMO-OFDMOFDM extends directly to MIMO channels with the IFFT/FFT

and CP operations being performed at each of the transmit and receive antennas. MIMO-OFDM decouples the frequency-selective MIMO channel into a set of parallel MIMO channels with the input–output relation for the ith (i = 0, 2,…,L-1) tone,

yi = Hisi + ni i = 0, 2,…, L-1

ConclusionsMIMO Systems are getting us closer to

the 1Gbps landmark At the same time, they provide reliable

communicationsDifferent architectures available for useDeveloping efficient network protocols for

a MIMO PHY layer is an area of open research

References(1) “Layered Space-Time Architecture for

Wireless Communication in a Fading Environment When using Multi-Element Antennas”, G.J.Foschini, Bell Labs Tech Journal, 1996

(2)“An Overview of MIMO Communications – A Key to Gigabit Wireless”, A.J Paulraj, Gore, Nabar and Bolcskei, IEEE Trans Comm, 2003

(3)“Improving Fairness and Throughput of Ad Hoc Networks Using Multiple Antennas”, Park, Choi and Nettles, submitted Mobicom 2004

THANK YOU