Outage analysis of spatial modulation in cognitive radio networks

Cognitive radio (CR) intelligently adapts particular transmission or reception parameter by sensing the environment. It has received great attention recently for its ability to improve spectrum efficiency by enabling secondary users to access spectrum resource, when it is being unoccupied by primary users. In this paper, spatial modulation technique is employed in overlay cognitive radio networks, in which the primary and secondary networks share the same spectrum band. In CR system model, the direct link between the primary transmitter and receiver is not available along with the Cognitive Radio transmitter assists the primary network as a relay to Decode-and-forward (DF) the transmitted symbols of the primary. Spatial modulation is used in the secondary transmitter to split the transmission space into two data in spatial domains. The secondary transmitter retransmits the primary symbols, while its own information is transmitted by the index of transmitting antenna, similar to space shift keying, without causing any interference to the primary receiver. Outage probability of the spatial modulation in cognitive radio networks is improved by using Transmit Antenna Selection (TAS) at the cognitive transmitter and Maximal Ratio Combiner (MRC) at the primary destination and cognitive destination. A closed form of outage probability expression is derived for primary and secondary destinations. Analytical simulations are also carried out in MATLAB software.