Adaptive modulation scheme for spatially correlated OFDM with Time Shifted Sampling

In this report, an adaptive modulated orthogonal frequency division multiplexing (OFDM) scheme that provides efficient data transmission for correlated receiver antenna arrays is proposed. Previously reported adaptive modulation schemes generally select the modulation scheme based on the estimated carrier-to-noise ratio (CNR) on each subcarrier. However, in antenna array communication in addition to the CNR, the spatial fading correlation should also be considered to evaluate the system performance. Especially, when the Time Shifted Sampling (TSS) technique is applied which overcomes the spatial correlation for some subchannels of an OFDM symbol, the spatial correlation varies dramatically through subcarriers. In this work, modulation scheme is selected based on the CNR and the spatial correlation coefficient for each subcarrier when the TSS technique is employed at the receiver. Numerical results through computer simulation show that the proposed scheme outperforms the conventional systems in achieving a target BER and establishing reliable communication while having almost the same transmission rate.