A Weighted Least Squares Approach to Precoding With Pilots for MIMO-OFDM

Next-generation wireless systems are expected to leverage multiple-antenna, commonly called multiple-input multiple-output (MIMO), technology transmitting over broadband channels via orthogonal frequency-division multiplexing (OFDM). It is now well known that MIMO systems can obtain error rate and capacity improvements by adapting the transmitter to the current channel conditions. Linear spatial precoding is a popular technique for channel adaptation where the transmitted space-time signal for each subcarrier is multiplied by a precoding matrix before transmission. Spatial precoding is complicated, however, in OFDM because channel information is often only known for a small number of pilot tones. In this correspondence, we present a subspace interpolation method for designing spatial precoders for all subcarriers by using the precoders known on pilot tones. The nonpilot precoders are solutions to a weighted least-squares design on the Grassmann manifold. Simulation results show performance benefits over existing MIMO-OFDM techniques