Bit-allocation strategies for MIMO fading channels with channel knowledge at transmitter

The singular-value decomposition can be used to transform a MIMO fading channel into an equivalent bank of scalar subchannels, a strategy known as eigenbeamforming or closed-loop MIMO, provided that the transmitter knows the channel. We consider the problem of allocating bits to subchannels after such processing, and propose simple strategies, which achieve near-optimal performance, by exploiting statistical properties of singular values. For large antenna arrays, a fixed bit-allocation becomes an attractive choice without any significant performance loss. For example, on the 6-input 6-output Rayleigh-fading channel, the fixed allocation strategy performs only 0.25 dB worse than the optimal bit-allocation.