some point on MIMO.

1. Multiple Input Multiple
Output (MIMO)
Multiple Input Multiple Output technology that uses multiple antennas to
make use of reflected signals to provide gains in channel robustness and
throughput.
By: Acharya Shree Krishna

2. Old age of MIMO..
 Up until 1990:
 system are switched between two antennas or combined the signal for
obtaining best signal.
 Also with various forms of beam switching.
 Spatial diversity was often limited.
 After 1990:
 Available of additional levels of processing power, it was possible to
utilize both spatial diversity and full spatial multiplexing.
 1993 : Two researcher Arogyaswami Paulraj and Thomos Kailath were first
to purpose the use of spatial multiplexing.
 1998 : Prototype of spatial Multiplexing fells on bell Lab.

3. MIMO basics….
 Spatial Diversity: used in narrow sense often refers to
transmit and receive diversity.
 Diversity : To provide the receiver with multiple versions of the
same signals. Different diversity modes are
Time/Frequency/Space.
 Spatial :
 space-time signal processing in which time is complement with
the spatial dimension inherent in the uses of multiple
antennas located in different points.
 Spatial Multiplexing:
 It provide additional data capacity by utilizing the different paths to
carry additional traffic.
 Multiplexing means combing many path of data to the single path
data.
General Outline of MIMO system

4. Different MIMO configuration….
 Single Input Single Output (SISO)
 Simplest form, no diversity and no additional processing
required.
 Limited in its performance , more impact by Interference and
fading then other.
 Bandwidth is limited by Shannon’s law and Throughput being
dependent upon channel bandwidth and SNR.
 Single Input Multiple Output (SIMO)
 Also known as receive diversity, it has number of independent source
to combat the effect of fading.
 Relatively easy to implement but processing is required in the
receiver.
 Applications- Where the label of processing may be limited by size,
cost and battery drain, such as cellphone handset.
 Two forms of SIMO 1) Switched diversity SIMO
2) Maximum ratio combining SIMO
 Multiple Input Single Output (MIMO)
 Also termed as transmit diversity, here same data is transmitted
redundantly from two transmitter antennas and receiver receive the
optimum one.
 Multiple antennas and redundancy coding/processing transfer to the
transmitter and also advantages in terms of space for antennas and
reducing the level of processing.
 Multiple Input Multiple Output (MIMO)
 More than one antenna at either end of radio link, improvements in
both channel robustness as well as channel throughput.
 Coding is necessary to separate the data from different paths.
 Key advantage: additional channel capacity due to MIMO spatial
Multiplexing.
SISO - Single Input Single Output
SIMO - Single Input Multiple Output
MISO - Multiple Input Single Output
MIMO - Multiple Input Multiple Output

5. Wireless Communications
8/1/2006
MIMO Design……
 MIMO Systems can provide two
types of gain
MIMO-5
Spatial Multiplexing Gain Diversity Gain
• Maximize transmission rate
(optimistic approach)
• Use rich scattering/fading to
advantage
• Minimize Pe (conservative
approach)
• Go for Reliability / QoS etc
• Counter fading
 As expected, there is a tradeoff
 System designs are carried out to achieve a little bit of both.

6. Shannon’s Law…..
 Shannon's law :“ The maximum rate at which error free data can be transmitted over a
given bandwidth in the presence of noise.”
Mathematically C = W log2(1 + S/N )
Where C=channel capacity
W= bandwidth in hertz
S/N = signal to noise ratio.
 Spectral Efficiency is defined as the number of bits transmitted per second per Hz
R x RS bits/s/Hz
W
As a result of filtering/signal reconstruction requirements, RS ≤ W. Hence Spectral
Efficiency = R if RS = W
 If I transmit data at a rate of R ≤ C, I can achieve an arbitrarily low Pe
 All above system’s capacity of maximum amount of data carried is limited by physical boundaries
under Shannon's law.
 Channel capacity can be increased by higher order of modulation schemes but needs better SNR,
due to this phenomena a balance exists between the data rate and the allowable error rate, SNR
and power.
 Some improvements are made they are not always easy or cheap, invariably compromise with
balancing various factors.
 MIMO is one way which wireless communication can be improved.

7. In practical MIMO…
Design parameter are…
Redundancy in time
Coding rate = rc
Space- time redundancy over
T symbol periods
Spatial multiplexing gain = rs
1
2
MT
Channel
coding
Symbol
mapping
Space-
Time
Coding
.
.
R bits/symbol
rs : number of
different symbols N
transmitted in T
symbol periods
rs = N/T
Spectral efficiency = (R*rc info bits/symbol)(rs)(Rs symbols/sec)
w
= Rrcrs bits/s/Hz assuming Rs = w
rs is the parameter that we are concerned about: 0 ≤ rs ≤ MT
** If rs = MT, we are in spatial multiplexing mode (max transmission rate)
**If rs ≤ 1, we are in diversity mode
Non-redundant
portion of
symbols

8. MIMO Spatial Multiplexing…..
 Utilizing several set of antenna gives additional throughput
capability, just two are used. Here
Mathematically , MIMO working as
Number of receiving antennas >= Number of transmitting
antennas.
 No reason why further antennas cannot be employed and this
increase the throughput, but matrix system design provide
advantage.
 In matrix format this can be represented as:
[R] = [H] x [T]
 Where [R] = receiver antennas matrix [H] = channel
properties matrix [T]= Data stream matrix.
 To recover the transmitted data-stream in receiver,
[T] = [H]-1 x [R]
 Before using this we need to add coding to the different
channel.
 MIMO uses a space time block codes usually represent by
matrix forms. The differential space time block code does not
need to know channel impairment in order for the signal to be
decoded. Basic diagram of transmitting and receiving data stream with coding

9. MIMO Beamforming smart antennas…..
 Beamforming: It is the technique that are used to
create a certain required antenna pattern to give the
required performance under the given conditions.
 Strategies are: 1) Maximum ratio Transmission(MRT)
2)Zero forcing (ZF)
 Smart antennas: Those antennas that can be controlled
automatically according the required performance and the
prevailing conditions.
 Types of smart antenna:
 1) Phased Array system (PAS)
 2) Adaptive array system (AAS)
 Beamforming has fixed beam system this is some how
unlikely exactly match the required direction.
 Adaptive array system solve this problem but cost is high
and complexity required.

10. Multi-user MIMO or (MU-MIMO)….
 MU-MIMO is an enhanced form of MIMO where multiple
independent radio terminals are enabled for enhancing the
communication capabilities with scheduling multiple users.
 Spatial sharing of the channels, it can be achieved by
addition of the hardware –filters and antennas but does not
expense of additional bandwidth.
 Advantages
 Directive gain α base station antenna employed
 Channel correlation might not a major issues for multi user diversity.
 With-out multiple antenna system spatial multiplexing gain achieved.
 Addition of hardware and channel state information.

11. Massive MIMO…
 Large MIMO system often uses tens or
hundreds of antennas in communication
terminals.
 Pre-coder and De-coder are used for counter
effect of the interference.
 Space division Multiple Access (SDMA) i.e. non-
orthogonal approaches such as superposition
coding.
 Advantages
 Increasing data rate
 Increasing basic link SNR
 channel hardening i.e. less sensitive.
 Antenna placements:
 Correlation between antennas must be small and spacing
of λ/2 (where λ is the wavelength of the signal)
 Application: used on recent 3GPP, Wi-max,
technology.

12. Micro-diversity MIMO…
 Coherent communication with multiple
transmit or receive base antennas.
 Long distance transmitter due to this
causes of different long term-channel
impairments-path loss, shadow fading.
 Unprecedented theoretical and practical
challenges.
 how the different average link SNRs affect the overall
system.
 individual user performance in fading environment.

13. MIMO with OFDM/OFDMA…
 Spatial multiplexing techniques makes the receiver
very complex.
 To remove problem of multipath channel spatial
multiplexing are combined with OFDM/OFDMA.
 Orthogonal Frequency Division Multiplexing o with
Orthogonal Frequency Division Multiple
Access(OFDMA) has major parameter that remove
multipath error are:
 Cyclic Prefix(CP).
 Cyclic Suffix(CS).
 Zero Padding (ZP).
 OFDM Guard band
 Those time limited complex signals are orthogonal
if the integral of their common period is Zero.

14. Some MIMO standards…

15. Research area of MIMO…
 This is planed to be use on 3GPP family like 3GPP, 3GPP2.
 Other areas are High speed Packet Access Plus(HSPA+), Long
Term Evolution(LTE).
 MIMO research consortia (IST-MASCOT) purpose to develop
advanced MIMO technique.
 In advanced MIMO has following parameter:
1) controller: controller are designed by polynomial design and
smartphones.
2) Wi-Fi can be secured than wired connection(Ethernet).
3) signals with high peak-to-average ratio(PAR).
4) To overcome distance record 382km (237mil) in June 2007
and the Swedish Space agency transferred 420 km (260Mil).
5) Data transfer rate greater than 3 mbps on moving
automobile vehicle.

16. Thank you