Shu (Marloon) Wang

[How Much Feedback Is Enough for MIMO? I Introduction] [How Much Feedback Is Enough for MIMO? II Channel Estimation] [How Much Feedback Is Enough for MIMO? III Codebook Design] [How Much Feedback Is Enough for MIMO? V Feedback Reliabilities] [How Much Feedback Is Enough for MIMO? VI Rank Deficiency] Generally, MIMO channel quantizer or CQI generation, maps the input channel estimation vector to the index of a codeword in the codebook. The decode will do the reverse. It is similar to the vector coding in EVRC, AMR, MPEG-4, etc. The designing a best codebook as well as finding the general boundary of Voronoi cell is NP-hard. Figure 1. MIMO Precoding Mismatching With Figure 1, it is shown that there are multiple issues involving MIMO precoding mismatching. In most existing MIMO beamforming systems, the receiver tracks the channel norm information for link adaptation purpose and the phase information for beamforming precoding. In this case, D h can be rewritten by D h = 2M σ

[How Much Feedback Is Enough for MIMO? I Introduction] [How Much Feedback Is Enough for MIMO? II Channel Estimation] [How Much Feedback Is Enough for MIMO? IV Channel Quantization] [How Much Feedback Is Enough for MIMO? V Feedback Reliabilities] [How Much Feedback Is Enough for MIMO? VI Rank Deficiency] Figure 2. Voronoi cell and various bounds MIMO beamforming mismatch upper bound depends on the codebook design. The maximum MIMO beamforming mismatch can be determined by the largest radius of the codebook’s Voronoi cell {  V i  : 1   ≤ i ≤ 2 R }, which in general is the solution to the disk-covering problem that still is open. Instead of finding the exact boundary for the Voronoi cell V i , a heuristic approach using sphere-packing bound and sphere cap to approximate the actual polytope boundary can be used. The result is an approximate of the sphere packing solution, in which all spheres are supposed to be non-overlappedly placed. With this approach, sphere caps are over