Mimo dr. morsi

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

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.

Diversity Definition

Diversity means send the same message signal or replica of message signal by

using two or more communication channels with different characteristics.

Why Diversity

To overcome fading and To combat cochannel interference

(CCI) and To avoid error bursts .

Types of Diversity

Diversity

Time Diversity Frequency Diversity Space Diversity

Types of Diversity

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).

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).

Frequency Diversity

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

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

Space Diversity

Types of space diversity

SISO( single input single output)

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).

SIMO( single input multi output)reception diversity

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.

MISO( multi input single output)transmit diversity

Alamouti space time block code (STBC) scheme

2 Transmit, 1 Receive Alamouti STBC coding

MIMO( multi input multi output) transmit and reception diversity

MIMO

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.

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.

Types of combining techniques

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 .


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.


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.

Maximal ratio combining (MRC)

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.




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



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.

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.


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.

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.

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)

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

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.

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.

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

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

MIMO Advantages

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

MIMO disadvantages

Computational complexity Channel modeling complexing

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.

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.

BER for BPSK modulation with Selection combining (SC) in BER for BPSK modulation with Selection combining (SC) in Rayleigh channelRayleigh channel

0 5 10 15 20 25 30 3510

-5

10-4

10-3

10-2

10-1

Eb/No, dB

Bit E

rror Rate

BER for BPSK modulation with Selection diveristy in Rayleigh channel

nRx=1 (sim)

nRx=2 (sim)

BER for BPSK modulation with Equal Gain Combining (EGC) in Rayleigh channel

0 5 10 15 20 25 30 3510

-5

10-4

10-3

10-2

10-1

Eb/No, dB

Bit E

rror Rate

BER for BPSK modulation with Equal Gain Combining in Rayleigh channel

nRx=1 (sim)

nRx=2 (sim)

BER for BPSK modulation with Maximal Ratio Combining (MRC) in Rayleigh BER for BPSK modulation with Maximal Ratio Combining (MRC) in Rayleigh channelchannel

0 5 10 15 20 25 30 3510

-5

10-4

10-3

10-2

10-1

Eb/No, dB

Bit E

rror Rate

BER for BPSK modulation with Maximal Ratio Combining in Rayleigh channel

nRx=1 (sim)

nRx=2 (sim)

Comparison among no diversity, Alamouti and max ratio combining Comparison 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

100

Eb/No (dB)

BER

Transmit vs. Receive Diversity

No Diversity (1Tx, 1Rx)

Alamouti (2Tx, 1Rx)Maximal-Ratio Combining (1Tx, 2Rx)

0 2 4 6 8 10 12

10-4

10-3

10-2

10-1

100

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

Engineering

Mimo dr. morsi