MIMO Wireless Channel and How to Determine Its Capacity Under Different Conditions

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‘‘If I have seen farther, it is by standing on the shoulders of giants.’’ is very truly coated by Sir Isaac Newton. Ideas gave way to idea. When Marconi invented wireless communication 100 years ago, we had no idea that one day life will seem to be impossible without it. It has penetrated each and every aspect of human life and has resulted into endless demands on bandwidth and spectrum. And by standing on the shoulders of giants, Teletarand Foschinigave the technique of MIMO system which would increase the spectral efficiency of the wireless system to its maximum compared to all the current technologies. Multiple antennas are used for transmission and reception to increases the capacity of the wireless channel.Capacity is expressed as the…show more content…

Fig1: Different antenna configurations in space-time systems.

Now we know that MIMO is an array, so we need to be some terms related to antenna array, which is Array gain, the average increase in the signal-to-noise ratio (SNR) at the receiverthat arises from the coherent combining effect of multiple antennas at the receiveror transmitter or both.If the channel is known to the multiple antenna transmitter,
The transmitter will weigh the transmission with weights, depending on the channelcoefficients, so that there is coherent combining at the single antenna receiver.The array gain in this case is called transmitter array gain. And vice versa for SIMO case, which will be known as receiver Array Gain. Basically, multiple antenna systems require perfectchannel knowledge either at the transmitter or receiver or both to achieve thisarray gain. Next important term is Diversity Gain. Multipath fading is a significant problem in communications. In a fading channel,signals experience fades.When the signalpower drops significantly, the channel is said to be in a fade. This gives rise tohigh bit error rates (BER).This involvesproviding replicas of the transmitted signal over time, frequency, or space. Thereare three types of diversity schemes in wireless communications:

I .Temporal diversity: In this case replicas of the transmitted signal are provided across time by a combination of channel coding and time interleaving strategies.
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