| 摘要 |
Closed loop MIMO FDD schemes can offer significant performance gains for OFDM based wireless communication systems over open loop MIMO schemes. However, the pre-coding weights (eigenvectors) on each of the frequency bands need to be updated and this adds extra overhead. The number of adjacent frequency fingers which can use the same pre-coding weights is governed by the coherence bandwidth of the eigen spatial modes. The receiver uses the average r.m.s. delay spread of the SISO channels as an indicator to the eigen coherence bandwidth, rather than explicitly calculating the eigen coherence bandwidth itself. This technique can be applied to TDD schemes as well, where the channel estimation is done with the reverse link, eliminating the need for feedback. The TDD transmitter can estimate the eigen coherence bandwidth on the basis of average r.m.s. delay spread, which saves computational effort. |
