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Base station (BS) cooperative transmission can improve the spectrumefficiency of cellular systems, whereas using which the channels will becomeasymmetry. In this paper, we study the impact of the asymmetry on theperformance of channel estimation and precoding in downlink BS cooperativemultiple-antenna multiple-carrier systems. We first present three linearestimators which jointly estimate the channel coefficients from users indifferent cells with minimum mean square error, robust design and least squarecriterion, and then study the impact of uplink channel asymmetry on theirperformance. It is shown that when the large scale channel information isexploited for channel estimation, using non-orthogonal training sequences amongusers in different cells leads to minor performance loss. Next, we analyze theimpact of downlink channel asymmetry on the performance of precoding withchannel estimation errors. Our analysis shows that although the estimationerrors of weak cross links are large, the resulting rate loss is minor becausetheir contributions are weighted by the receive signal to noise ratio. Thesimulation results verify our analysis and show that the rate loss per user isalmost constant no matter where the user is located, when the channelestimators exploiting the large scale fading gains.

Impact of Channel Asymmetry on Performance of Channel Estimation and Precoding for Downlink Base Station Cooperative Transmission