On downlink beamforming methods: capacity and error probability performance

In space-division multiple access (SDMA) different beamforming or space-domain precoding techniques can be applied. We investigate two different space-domain precoding methods the maximum capacity (MC) and the minimum mean square error (MMSE) precoders for the downlink channel. It is shown that the MMSE precoding which is practically implementable can provide a reasonable performance in terms of the capacity and error probability while the MC precoding is not practical (although it is optimum in terms of the capacity). Space-domain precoding methods are also applied to code-division multiple access (CDMA) systems.