Differential spatial multiplexing techniques for high spectrum efficiency on very fast fading MIMO links

Spatial multiplexing (sometimes referred to as 'BLAST') is a way to increase the throughput of a wireless system by exploiting multiple antennas at both transmitter and receiver (MIMO) - potentially it can increase capacity by a factor equal to the minimum of the number or transmit and receive antennas. However it requires the receiver to estimate the exact characteristics of the channel, which is difficult when the channel varies (fades) very rapidly, as in mobile communcation at high speeds. Differential techniques have been developed for single antenna systems and for space-time coded MIMO systems (which do not increase capacity), which avoid the need to estimate the channel by sending information as the difference between one transmitted symbol and the next. However this has not previously been possible for spatial multiplexing. The proposers have developed a technique which allows this, but the current scheme suffers from poor diversity, resulting in less robust communication, and requires high complexity at the receiver. The proposed research is intended as a feasibility study to determine whether these problems can be mitigated, using appropriate mapping schemes at the transmitter and techniques such as sphere decoding or SGA at the receiver, or using FEC coding with iterative decoding. It will also examine potential applications, including techniques like CDMA and OFDM to enable its use on a multi-user wideband channel.