Overview about MIMO Contents: Diversity Definition Why Diversity Types of Diversity Types of combining MIMO Definition Why MIMO ? MIMO Advantages and disadvantages Applications of MIMO

1. Multi Input Multi Output
(MIMO)
 Contents
- Diversity Definition
- Why Diversity
- Types of Diversity
- Types of combining
- MIMO Definition
- Why MIMO ?
- MIMO Advantages and disadvantages
- Applications of MIMO

2. Diversity Definition
 Diversity is a technique by which we
transmit many copies of the signal or
versions of the signal but effected with
different fading over time, frequency or
space.

3. Diversity Definition
Diversity means send the same message
signal or replica of message signal by
using two or more communication
channels with different characteristics.

4. Why Diversity
 To overcome fading and
 To combat cochannel interference
(CCI) and
 To avoid error bursts .

5. Types of Diversity
Diversity
Time Diversity Frequency Diversity Space Diversity

6. Types of Diversity

7. Space diversity
1. Many copies of the transmitted signal
effects with different fading over the space .
2. we use multi-antenna systems:
 At the transmitter ( transmit diversity) or
 At the receiver ( reception diversity) or
 At both of them( MIMO).

8. Frequency diversityFrequency diversity
This type of diversity used for the frequency
selective channels as we will averaging or
avoiding fading over the frequency by
using:
 Multi-carrier technique like OFDM.
 FHSS (frequency hope spread spectrum).
 DSSS (direct sequence spread spectrum).

9. Frequency Diversity
 The signal is transmitted using several
frequency channels or spread over a wide
spectrum that is affected by frequency
selective fading.

10. Time Diversity
Multiple versions of the same signal are
transmitted at different time instants.
We averaging the fading of the
channel over time by using :-
 The channel coding and interleaving or
 Sending the data at different times

11. Space Diversity

12. Types of space diversity

13. SISO( single input single output)

14. SISO
SISO stands for single input and signal output. It
uses one antenna at the transmitter and one
antenna at the receiver . SISO channel is more
susceptible to problem caused by multipath effect
however it is cheap to implement.
For SISO system the capacity is given by Shannon
formula : C = B log2(1 + SNR).

15. SIMO( single input multi output)
reception diversity

16. SIMO
 SIMO stands for single input and multiple
outputs. It uses single antennas at
transmitter and multiple antennas at the
receiver. SIMO system is preferably used in
uplink.

17. MISO( multi input single output)
transmit diversity

18. Alamouti space time block code
(STBC) scheme

19. 2 Transmit, 1 Receive Alamouti STBC coding

20. MIMO( multi input multi output)
transmit and reception diversity

21. MIMO

22. Combining techniques
 The presence of reception diversity poses an
interesting problem : how do we use effectively the
information from all the antennas to demodulate the
data.

23. Combining techniques
 Combines the independent fading paths
signals to obtain a signal that passed through
demodulator.
 The combining techniques can be applied to
any type of diversity.
 The combining techniques are linear as the
output of is a weighted sum of the different
fading signals of branches.
 The combining techniques needs cophasing.

24. Types of combining techniques

25. Selection combining (SC)

26. Selection combining (SC)
Selection combining used in spatial diversity
systems involves the sampling of several
antenna signals, and sending the largest
one to the demodulator. Selection
combining ( SC) is relatively easy to
implement but not optimal because it does
not make use of all the received signals
simultaneously .

27. Selection combining (SC)
 This is the simplest combining method. Consider a
MR receiver system. In (SC), we select the signal
coming into each of the MR antennas that has the
highest instantaneous SNR at every symbol interval.
The output of the combiner equal to that of the best
incoming signal.

28. Selection combining (SC)
 The advantage of SC is that it does not require any
additional RF receiver chain.
 All receive antennas share a single RF receiver
chain. This keeps the cost down.
 In practice the strongest signals are selected because
it is difficult to measure SNR alone.

29. Maximal ratio combining (MRC)

30. In maximal ratio combining (MRC), the signals from
all of the several branches are weighted according to
their individual SNRs and then summed. The
individual signals are cophased before being summed.
Maximal ratio combining (MRC)

31. Maximal ratio combining (MRC)

32. Maximal ratio combining (MRC)
 In maximal ratio combining (MRC) the
output is a weighted sum of all branches
due to its SNR.

33. Maximal ratio combining (MRC)

34. Maximal ratio combining (MRC)
 Maximal-ratio combining produces an average
SNR γM−− equal to the sum of the individual
average SNRs where we assume that each branch
has the same average SNR.
 Maximal-ratio combining can produce an
acceptable average SNR, even when none of the
individual i γ is acceptable. It uses each of
the M branches in a cophased and weighted
manner such that the largest possible SNR is
available at the receiver.

35. Equal gain combining (EGC)

36. Equal gain combining (EGC)
Equal gain combining (EGC) is similar to
maximal ratio combining (MRC) except that
the weights are all set to unity. The
possibility of achieving an acceptable output
SNR from a number of unacceptable inputs
is still retained. The performance is
marginally inferior to maximal ratio
combining.

37. Equal gain combining (EGC)
 EGC is the same as MRC but with equal
weighting for all branches.
 The performance is marginally inferior to
MRC, but the complexities of EGC
implementation are much less than MRC.

38. MIMO Definition
The use multiple transmitters and receivers to transfer more data at the
same time.
MIMO technology takes advantage of a radio wave phenomenon called
multipath where transmitted information bounces off walls and other
objects, reaching the receiving antenna multiple times via different angles
and at slightly different times.

39. Configurations overview
 SISO : Stands for Single Input
Single Output
 SIMO : Stands for Single Input
Multi Output (reception
diversity)
 MISO : Stands for Multi Input
Single Output ( transmit
diversity)
 MIMO : Stands for Multi Input
Multi Output ( transmit and
reception diversity)

40. MIMO Configurations
MIMO configuration
can described by :-
 N (Transmitter) *N
(Receiver)
 Most common MIMO
configuration is: 2*2,
2*3, 2*4, and 4*4

41. Why MIMO?
 MIMO can exploit multiple transceivers at
both the enhanced node B (base station BS)
and the user equipment (UE)
So we can increase the data rates of the
mobile system.

42. Why MIMO?
 MIMO increase data rate via Spatial ( space) Multiplexing
by allowing to transmit different streams of data
simultaneously on the same resource block(s) by exploiting
the spatial dimension of the radio channel.

43. Why MIMO?
MIMO increase the robustness
of data transmission via
Transmit Diversity
 Each transmit antenna
transmits the same stream of
data. This increases the signal
to noise ratio at the receiver
side and thus the robustness of
data transmission especially in
fading scenarios

44. Why MIMO?
 MIMO enhance link reliability in
challenging propagation conditions when
the signal strength is low and multipath
conditions are challenging. Thus, MIMO
lower bit error rate

45. MIMO Advantages
Major advantages of MIMO
 Higher capacity.
 Increase data rate.
 Lower bit error rate.
 Increased coverage.
 Improved position estimation.

46. MIMO disadvantages
 Computational complexity
 Channel modeling complexing

47. MIMO Applications
 MIMO provides high speed wireless
communication link to support wide
range of applications without the
expansion of the available
bandwidth or increase of
transmitted power.

48. MIMO Applications
 Communication network applications such as
broadcasting network, cellular network, satellite
communication.
 Narrowband Applications where limited
bandwidth and lower data rate, higher
performance required ( since space-time block
coding (STBC) is attractive).
 Pager, text messaging applications such as
blackberry.

49. BER for BPSK modulation with Selection combining (SC) inBER for BPSK modulation with Selection combining (SC) in
Rayleigh channelRayleigh channel
0 5 10 15 20 25 30 35
10
-5
10
-4
10
-3
10
-2
10
-1
Eb/No, dB
BitErrorRate BERfor BPSKmodulationwithSelectiondiveristy inRayleighchannel
nRx=1(sim)
nRx=2(sim)

50. BER for BPSK modulation with Equal Gain Combining (EGC) in Rayleigh
channel
0 5 10 15 20 25 30 35
10
-5
10
-4
10
-3
10
-2
10
-1
Eb/No, dB
BitErrorRate BERfor BPSK modulationwithEqual GainCombining inRayleighchannel
nRx=1(sim)
nRx=2(sim)

51. BER for BPSK modulation with Maximal Ratio Combining (MRC) in RayleighBER for BPSK modulation with Maximal Ratio Combining (MRC) in Rayleigh
channelchannel
0 5 10 15 20 25 30 35
10
-5
10
-4
10
-3
10
-2
10
-1
Eb/No, dB
BitErrorRate BERfor BPSKmodulationwithMaximal RatioCombininginRayleighchannel
nRx=1(sim)
nRx=2(sim)

52. Comparison among no diversity, Alamouti and max ratio combiningComparison among no diversity, Alamouti and max ratio combining
(MRC)(MRC)
0 2 4 6 8 10 12 14 16 18 20
10
-4
10
-3
10
-2
10
-1
10
0
Eb/No(dB)
BER
Transmit vs. ReceiveDiversity
NoDiversity (1Tx, 1Rx)
Alamouti (2Tx, 1Rx)
Maximal-RatioCombining(1Tx, 2Rx)

53. 0 2 4 6 8 10 12
10
-4
10
-3
10
-2
10
-1
10
0
Eb/No (dB)
BER
G2-coded 2x2 System
No Diversity (1Tx, 1Rx)
Alamouti (2Tx, 1Rx)
Maximal-Ratio Combining (1Tx, 2Rx)
Alamouti (2Tx, 2Rx)
Comparison among no diversity, Alamouti transmit diversityComparison among no diversity, Alamouti transmit diversity
and max ratio combining (MRC) reception diversity and MIMOand max ratio combining (MRC) reception diversity and MIMO