Research On Adaptive Power Allocation Scheme And Physical Layer Security Of Cooperative Spatial Modulation

Spatial modulation(SM)is a low-complexity multi-antenna transmission technique that employs antenna indices to convey information.SM can eliminate inter-channel interference(ICI)and requires no inter-antenna synchronization with relatively high spectral efficiency.Cooperative communication,which uses nodes in the same network as relays to help the transmission of information,increases coverage range and improves transmission reliability.In this thesis,SM is introduced into a cooperative amplify-and-forward(AF)relaying system to obtain the performance gains of these two techniques simultaneously.Based on the AF-SM system,the performance analysis and the design of optimization schemes under nonideal channels are developed.The main contributions of this paper are shown as follows:1.Considering imperfect channel state information(CSI),the performance of AF-SM is investigated,and a power allocation scheme is proposed.Combining SM and cooperative relaying,the cooperative SM system is presented.Based on the system,assuming that channel estimation error exists at the receiver,the theoretical expression of average bit error rate(BER)is derived,also the asymptotically approximated BER expression is given.Minimizing the approximated BER,the sub-optimal power allocation coefficients are obtained by the gradient descent method and Cardano's formula.Simulations show that the theoretical results of average BER are consistent with the simulated ones,and the proposed power allocation scheme can improve the BER performance effectively.2.The performance of AF-SM over correlated Rayleigh channel is investigated,and the corresponding power allocation scheme is given.Considering the antenna correlation at the source and destination,the moment generation functions of effective signal-to-noise ratios(SNRs)are derived,thereby the approximately closed-form expression of average BER is attained.Based on the BER and the asymptotically approximated expression under high SNR region,a sub-optimal power allocation scheme is given.When the destination is equipped with multiple antennas,the scheme provides the closed forms of power allocation coefficients,and when the destination is equipped with a single antenna,the scheme provides an iteration algorithm to obtain the coefficients.Simulations illustrate that the derived expressions and the given power allocation scheme are effective.3.The secrecy performance of AF-SM system with cooperative jamming under imperfect CSI is analyzed.While the source transmits signals,the destination transmits jamming simultaneously for against eavesdropping.Based on this system,the closed-form expressions of approximated ergodic rates of legitimate receiver and eavesdropper with estimation error are deduced,thus the theoretical expression of secrecy rate is obtained,which is close to the simulation.Moreover,the ergodic rate and BER performance of eavesdropper are obviously lower than those of legitimate receiver for the existence of jamming.Simulations show that the adopted physical layer security scheme based on cooperative jamming can improve the secrecy performance effectively.