Cooperative spectrum sharing protocol using spatial modulation

In this study, a new cooperative spectrum sharing protocol based on overlay system paradigm is proposed for different relaying strategies. In the considered model, a single-antenna primary transmitter (PT) communicates with a primary receiver (PR) by the assistance of a secondary transmitter (ST) which seeks an opportunity to realise spectrum sharing by adopting spatial modulation (SM). The proposed protocol consists of two time slots. In the first time slot, primary M-ary modulated signal is transmitted from PT to ST and PR. ST processes the received signal according to the relaying strategy it adopts and transmits the processed signal by SM to PR and secondary receiver (SR) in the second time slot. Thanks to SM at ST, primary information is carried by conventional M-ary modulation whereas secondary information is conveyed by antenna indices. Therefore, the need for superposition of different users' information and power allocation at ST are avoided. Upper bounds on bit error probability according to three different relaying strategies: fixed and incremental amplify-and-forward, and selective decode-and-forward, are derived for both users. The theoretical results are supported via computer simulations and error performance comparisons with two existing reference systems are performed to show the superiority of the proposed protocol.