Differential Space Time Shift Keying for Dispersive Multi-user Scenarios using OFDM

Spatial modulation (SM) is a recently developed transmission technique that uses multiple antennas. The concept of SM is extended to both the space and time dimensions to provide a general shift-keying framework. A new modulation scheme called Differential STSK (DSTSK) scheme, assisted by the Cayley unitary transform is proposed to OFDM aided Multiple Input Multiple Output (MIMO) Communication Systems. The main advantage of this modulation technique is that it does not require any Channel State Information (CSI) at the receiver. More specifically, by employing the Cayley transform in the proposed DSTSK scheme we arrive at a linearized equivalent system model. Cayley codes encode the transmitted data differentially using unitary matrices at the transmitter, and hence the transmitted data can be decoded differentially at the receiver without knowing the channel coefficients. Since channel knowledge is not required at the receiver, differential schemes are ideal for use on wireless links where channel tracking is undesirable or infeasible, due to rapid changes in the channel characteristics or limited system resources. Further the proposed scheme enables us to achieve a flexible diversity and multiplexing gain tradeoff.