Predictive transmit beamforming for MIMO-OFDM in time-varying channels with limited feedback
IWCMC '07 Proceedings of the 2007 international conference on Wireless communications and mobile computing
Feedback quantization for linear precoded spatial multiplexing
EURASIP Journal on Advances in Signal Processing
Time-domain transmit beamforming for MIMO-OFDM systems with finite rate feedback
IEEE Transactions on Communications
feedback reduction based on clustering in MIMO-OFDM beamforming systems
WiCOM'09 Proceedings of the 5th International Conference on Wireless communications, networking and mobile computing
| Hi-index | 0.01 |
We investigate an adaptive MIMO-OFDM system with a feedback link that can only convey a finite number of bits. We consider three different transmitter configurations: i) beamforming applied per OFDM subcarrier, ii) precoded spatial multiplexing applied per subcarrier, and iii) precoded orthogonal space time block coding applied per subcarrier. Depending on the channel realization, the receiver selects the optimal beamforming vector or precoding matrix from a finite-size codebook on each subcarrier, and informs the transmitter through finite-rate feedback. Exploiting the fact that the channel responses across OFDM subcarriers are correlated, we propose two methods to reduce the amount of feedback. One is recursive feedback encoding that selects the optimal beamforming/precoding choices sequentially across the subcarriers, and adopts a smaller-size time-varying codebook per subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal decisions for all subcarriers at once along a trellis structure via the Viterbi algorithm. Our methods are applicable to different transmitter configurations in a unified fashion. Simulation results demonstrate that the trellis-based approach outperforms the recursive method as well as an existing interpolation-based alternative at high signal-to-noise-ratio, as the latter suffers from "diversity loss"