The MIMO antenna technologies used are key to the overall MIMO performance. Additionally MIMO beamforming is an option that is coming to the fore.
As various forms of technology improve the MIMO antenna technology can be pushed further allowing techniques like MIMO beamforming to be considered.
MIMO antenna & MIMO beamforming development
For many years antenna technology has been used to improve the performance of systems. Directive antennas have been used for very many years to improve signal levels and reduce interference.
Directive antenna systems have, for example, been used to improve the capacity of cellular telecommunications systems. By splitting a cell site into sector where each antenna illuminates 60° or 120° the capacity can be greatly increased - tripled when using 120° antennas.
With the development of more adaptive systems and greater levels of processing power, it is possible to utilise antenna beamforming techniques with systems such as MIMO.
MIMO beamforming smart antennas
Beamforming techniques can be used with any antenna system - not just on MIMO systems. They are used to create a certain required antenna directive pattern to give the required performance under the given conditions.
Smart antennas are normally used - these are antennas that can be controlled automatically according the required performance and the prevailing conditions.
Smart antennas can be divided into two groups:
- Phased array systems: Phased array systems are switched and have a number of pre-defined patterns - the required one being switched according to the direction required.
- Adaptive array systems (AAS): This type of antenna uses what is termed adaptive beamforming and it has an infinite number of patterns and can be adjusted to the requirements in real time.
MIMO beamforming using phased array systems requires the overall system to determine the direction of arrival of the incoming signal and then switch in the most appropriate beam. This is something of a compromise because the fixed beam is unlikely to exactly match the required direction.
Adaptive array systems are able to direct the beam in the exact direction needed, and also move the beam in real time - this is a particular advantage for moving systems - a factor that often happens with mobile telecommunications. However the cost is the considerable extra complexity required.
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