Secrecy Rate of Time Switched Transmit Diversity System

Time switched transmit diversity (TSTD) system uses only one out of several transmit antennas at a time in order to exploit the benefit of transmit diversity while keeping the system simple by having only one RF chain. We show that while average rate of such a system remains similar to the capacity of the single transmit antenna, outage secrecy capacity is greatly improved. In particular, as the number of transmit antenna is increased or outage probability decreased, the gains over single antenna system improve significantly - gains of over 20 dB with respect to the single antenna system are achieved for 1% outage rate. Furthermore, the probability of existence of secrecy capacity is improved as well for cases when the main channel has higher SNR than the eavesdropper channel.