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MIMO Formats - SISO, SIMO, MISO, MU-MIMO- overview and definitions about MIMO formats or configurations: SISO, SIMO, MISOand MIMO for receiver diversity and transmitter diversity, etc..

IN THIS SECTION

There is a number of different MIMO configurations or formats that can be used. These are termed SISO, SIMO,MISO and MIMO. These different MIMO formats offer different advantages and disadvantages - these can bebalanced to provide the optimum solution for any given application.

The different MIMO formats - SISO, SIMO, MISO and MIMO require different numbers of antennas as well ashaving different levels of complexity. Also dependent upon the format, processing may be needed at one end ofthe link or the other - this can have an impact on any decisions made.

SISO, SIMO, MISO, MIMO terminology

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SISO, SIMO, MISO, MIMO terminologyThe different forms of antenna technology refer to single or multiple inputs and outputs. These are related to theradio link. In this way the input is the transmitter as it transmits into the link or signal path, and the output is thereceiver. It is at the output of the wireless link.

therefore the different forms of single / multiple antenna links are defined as below:

SISO - Single Input Single Output

SIMO - Single Input Multiple output

MISO - Multiple Input Single Output

MIMO - Multiple Input multiple Output

The term MU-MIMO is also used for a multiple user version of MIMO as described below.

MIMO - SISOThe simplest form of radio link can be defined in MIMO terms as SISO - Single Input Single Output. This iseffectively a standard radio channel - this transmitter operates with one antenna as does the receiver. There is nodiversity and no additional processing required.

SISO - Single Input Single Output

The advantage of a SIS system is its simplicity. SISO requires no processing in terms of the various forms ofdiversity that may be used. However the SISO channel is limited in its performance. Interference and fading willimpact the system more than a MIMO system using some form of diversity, and the channel bandwidth is limitedby Shannon's law - the throughput being dependent upon the channel bandwidth and the signal to noise ratio.

MIMO - SIMOThe SIMO or Single Input Multiple Output version of MIMO occurs where the transmitter has a single antennaand the receiver has multiple antennas. This is also known as receive diversity. It is often used to enable areceiver system that receives signals from a number of independent sources to combat the effects of fading. Ithas been used for many years with short wave listening / receiving stations to combat the effects of ionosphericfading and interference.

SIMO - Single Input Multiple Output

SIMO has the advantage that it is relatively easy to implement although it does have some disadvantages in thatthe processing is required in the receiver. The use of SIMO may be quite acceptable in many applications, butwhere the receiver is located in a mobile device such as a cellphone handset, the levels of processing may be

7/9/2015 MIMO Formats | SISO, SIMO, MISO, MIMO | Tutorial - Radio-Electronics.Com

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limited by size, cost and battery drain.

There are two forms of SIMO that can be used:

Switched diversity SIMO:   This form of SIMO looks for the strongest signal and switches to that antenna.

Maximum ratio combining SIMO:   This form of SIMO takes both signals and sums them to give the acombination. In this way, the signals from both antennas contribute to the overall signal.

MIMO - MISOMISO is also termed transmit diversity. In this case, the same data is transmitted redundantly from the twotransmitter antennas. The receiver is then able to receive the optimum signal which it can then use to receiveextract the required data.

MISO - Multiple Input Single Output

The advantage of using MISO is that the multiple antennas and the redundancy coding / processing is movedfrom the receiver to the transmitter. In instances such as cellphone UEs, this can be a significant advantage interms of space for the antennas and reducing the level of processing required in the receiver for the redundancycoding. This has a positive impact on size, cost and battery life as the lower level of processing requires lessbattery consumption.

MIMOWhere there are more than one antenna at either end of the radio link, this is termed MIMO - Multiple InputMultiple Output. MIMO can be used to provide improvements in both channel robustness as well as channelthroughput.

MIMO - Multiple Input Multiple Output

In order to be able to benefit from MIMO fully it is necessary to be able to utilise coding on the channels toseparate the data from the different paths. This requires processing, but provides additional channel robustness/ data throughput capacity.

There are many formats of MIMO that can be used from SISO, through SIMO and MISO to the full MIMOsystems. These are all able to provide significant improvements of performance, but generally at the cost ofadditional processing and the number of antennas used. Balances of performance against costs, size, processingavailable and the resulting battery life need to be made when choosing the correct option.

By Ian Poole (https://plus.google.com/104687638164370436625?rel=author)

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