MIMO Systems

1. MIMO SYSTEMS
PRESENTED BY YAWER ABBAS
REG.NO. SP17-REE-
DEPT.-ELECTRICAL ENGINEERING
COMSATS INSTITUTE OF ENGINEERING AND
TECHNOLOGY, LAHORE

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
High 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

4. Antenna Configurations
 Single-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

5. MIMO Antenna Configuration
 Use multiple transmit and multiple receive antennas for a
single user
User data stream
User data stream
.
.
1
2
MT
.
.
.
1
2
MR
.
.
.
.
.
channel
 Now this system promises enormous data rates!

6. 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

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!
• Widely used scheme: CDMA
2000, WCDMA and IEEE 802.16-
2004 OFDM-256
𝑥1 −𝑥2
+
𝑥2 −𝑥1
+

11. 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.

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

15. THANK YOU