Improving the performance of the UCA when using LTE codebook feedback

In Release 8 (R8) LTE a 4 antenna codebook was designed primarily with a uniform linear array (ULA) in mind. The consequence is that when using an array at the base other than a ULA (for example a uniform circular array (UCA)) the performance with codebook feedback will be degraded relative to a codebook optimized for that array structure. In this paper methods for improving the performance of LTE codebook feedback for non-ULAs (and in particular the UCA) are presented. All of methods have no impact on how the user equipment (UE) operates (i.e., the methods are transparent to the UE) and hence have no impact on the standard. Using these methods improvements of up to 1.2 dB are obtained when using a UCA with the 4 antenna LTE codebook.