Channel state feedback schemes for the MIMO broadcast downlink have been
widely studied in the frequency-flat case. This work focuses on the more
relevant frequency selective case, where some important new aspects emerge. We
consider a MIMO-OFDM broadcast channel and compare achievable ergodic rates
under three channel state feedback schemes: analog feedback, direction
quantized feedback and "time-domain" channel quantized feedback. The first two
schemes are direct extensions of previously proposed schemes. The third scheme
is novel, and it is directly inspired by rate-distortion theory of Gaussian
correlated sources. For each scheme we derive the conditions under which the
system achieves full multiplexing gain. The key difference with respect to the
widely treated frequency-flat case is that in MIMO-OFDM the frequency-domain
channel transfer function is a Gaussian correlated source. The new time-domain
quantization scheme takes advantage of the channel frequency correlation
structure and outperforms the other schemes. Furthermore, it is by far simpler
to implement than complicated spherical vector quantization. In particular, we
observe that no structured codebook design and vector quantization is actually
needed for efficient channel state information feedback.

本文研究 MIMO-OFDM 广播信道下的三种信道状态反馈方案，包括模拟反馈、方向量化反馈和新的时域信道量化反馈，并推导出每种方案实现全复用增益的条件。其中，新的时域量化方案利用了信道频率相关性结构并优于其他方案。同时，本方案的实现比被动矢量量化更为简单。