2014 Volume 5 Issue 2 Pages 140-156
Ensuring security at the physical layer in wireless communications is important and effective because it can omit upper-layer secure protocols in ad hoc or multi-hop relay transmissions, or it can enhance security together with upper-layer protocols. To realize this system, we have proposed a chaos-based multiple-input multiple-output (MIMO) transmission scheme that enables both physical-layer security and a channel coding effect in a MIMO multiplexing transmission. However, the transmission rate is equivalent to binary phase shift keying (BPSK), that is, one bit/symbol, and multilevel modulations are needed to achieve higher-capacity communication. Moreover, the channel coding gain is limited, which needs to be improved. Therefore, in this paper, we propose a two- and four-bit/symbol chaos-MIMO scheme, equivalent to quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (16QAM) rate-efficiency, with an adaptive chaos processing scheme enhancing the channel coding gain. The improved performances of the proposed scheme are shown in the numerical results. In addition, we describe the concept of identification modulation using this chaos transmission.