Using multiple antennas for reception and transmission at the base station (BS) and the user equipment (UE) in order to improve system and link performance is a key enabler for the high performance offered by the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) standard; both in terms of peak throughput and system capacity [1]. In LTE, the data streams are mapped to transmission layers. The number of layers transmitted is denoted the rank. In 3GPP rel. 8 [2], up to four layers are supported for downlink. The layers are mapped to antenna ports in a precoding step. In closed-loop spatial multiplexing, one or several layers are transmitted using one or several precoding matrices, selected from a predefined codebook.