Receiver rate adaptation for MIMO system

This paper presents a novel design of linear random space time coding (LRSTC) scheme. This scheme is able to achieve the dual benefits for MIMO receiver rate adaptation: (1) rateless coding and modulation and (2) approximately universal tradeoff between diversity gain and multiplexing gain. In this scheme, an LRSTC symbol is the superposition of a block of randomly rotated QPSK symbols. Such superposition generates a dense constellation that ensures a high saturation rate. The random rotation guarantees the pseudo-orthogonality between QPSK symbols. Through utilizing the orthogonality of symbols, a power gain can be generated at receiver end. The power gain can be increased by transmitting more LRSTC symbols to the receiver in order to resist stronger noise of the MIMO system. Therefore, the rate can be seamlessly adapted through varying the number of transmitted symbols rather than the adopting conventional strategies in terms of modulation, coding and antenna selection. Moreover, the transmission of LRSTC symbols will span over all of the transmit antennas which allows the spatial diversity to be fully exploited. When the rank of MIMO matrix is greater than 1, more linear independent symbols can be received in each time slot. Hence, multiplexing gain can also be achieved. We have carried out both analysis and simulations to verify this LRSTC design. The simulation results show that LRSTC not only achieves the throughput comparable with the ideal conventional rate adaptation, but also accomplishes a seamless switching between diversity and multiplexing gain.