Joint channel estimation for downlink base station cooperative transmission exploiting channel asymmetry

In this paper, we study uplink joint channel estimation for downlink base station cooperative transmission orthogonal frequency division multiplexing systems. We present three linear estimators which jointly estimates the channel coefficients from users in different cells with minimum mean square error (MSE), robust design and least square criterion, then we analyze their performance. We find that due to the asymmetric feature of the multi-cell channels in cooperative transmission systems, the MSE for different links with three joint estimators differ. When the channel energy information is exploited for channel estimation, the cross channels that experience large attenuation have smaller estimation MSEs than the local channels, and using non-orthogonal training sequences among users in different cells leads to minor performance loss. This is in contrast to the traditional understanding. To reduce the complexity of the estimators when non-orthogonal training sequences are used, we also present an interference cancelation based estimator. Both the channel estimation errors and the throughput of the cooperative transmission system are simulated to verify our analysis.