1. MIMO(A SHORT DISSCUSSION)
PRESENTED BY-PRITAM MOHANTY
REGD.NO-0901304189
GUIDED BY-Mr. Shakti Narayana Mishra(lect. In ECE dept.)
DEPT.-ELECTRONICS AND COMMUNICATION ENGINEERING
GANDHI INSTITUTE OF TECHNOLOGY AND MANAGEMENT
BHUBANESWAR
2. CONTENTS
Motivations for the development of MIMO
systems
MIMO Antenna Configuration
Design Criterion for MIMO Systems (Diversity )
MIMO-OFDM
Conclusions
3. Aspirations of a
System Designer Achieve
High data rate “Channel Capacity (C)”
Quality
Minimize Probability of Error
(Pe)
Minimize complexity/cost of
System
Real-life Issues Minimize transmission power
Minimize Bandwidth
4. Antenna Configurations
Single-Input-Single-Output (SISO) antenna system
User data stream
channel
User data stream
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
5. MIMO Antenna Configuration
Use multiple transmit and multiple receive antennas for a
1 1
single user
2 2
User data stream User data stream
. channel .
. .
. .
. .
. .
MT MR
Now this system promises enormous data rates!
6. MIMO System Model
h11
s1 y1
h12
s2 . y2 User data stream
User data stream
. .
. .
. Channel
. .
sM Matrix H yM
s y
TRANSMITTED RECEIVED
VECTOR y = Hs + n VECTOR
MT
h11 h21 …….. hM1
h12 h22 …….. hM2
Where H = MR
. . …….. .
h1M h2M …….. hMM
7. 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]
8. 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?
9. 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
10. Alamouti’s Scheme - Diversity
Transmission/reception scheme easy to implement
Space diversity because of antenna transmission. Time
diversity because of transmission over 2 symbol periods
Consider (2, MR) system
1. Receiver uses combining and ML detection
2. rs = 1
+
• If you are working with a (2,2)
system, stick with Alamouti!
𝑥1 −𝑥2
+
• Widely used scheme: CDMA 𝑥2 −𝑥1
2000, WCDMA and IEEE 802.16-
2004 OFDM-256
11. Orthogonal Frequency Division
Multiplexing(OFDM)
It is a special kind of FDM
The spacing between carriers are such that they are
orthogonal to one another
Therefore no need of guard band between carriers.
11
12. MIMO-OFDM
OFDM 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
13. Conclusions
MIMO Systems are getting us closer to the 1Gbps
landmark
At the same time, they provide reliable
communications
Different architectures available for use
Developing efficient network protocols for a
MIMO PHY layer is an area of open research
14. 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
