Lei Weijia

Performance analysis of complexity reduction BP decoding of rateless codes by deleting low reliable symbols

Abstract This paper investigates the performance of the method used to reduce the decoding complexity of rateless codes through the deletion of the received symbols with low reliability. In the decoder, the received symbols whose absolute value of logarithm likelihood ratio (LLR) is lower than the threshold are removed, together with their corresponding edges, and thus not involved in the decoding process. The relationship between the deletion probability and the likelihood ratio deletion threshold is derived. The average mutual information per received symbol is analyzed in the case of deletion. The required number of symbols for the decoder to keep the same performance as regular decoding decreases since the average mutual information per symbol increases with the deletion, thus reducing the decoding complexity. This paper analyzes the reduction of decoding computations and the consequent transmission efficiency loss from the perspective of mutual information. The simulation results of decoding performance are consistent with those of the theoretical analysis, which show that the method can effectively reduce the decoding complexity at the cost of a slight loss of transmission efficiency.

Two security transmission realization schemes for MIMO Gaussian wiretap channel with one helper

Abstract This paper presents noncooperative and cooperative security transmission schemes for multiple-input multiple-output (MIMO) Gaussian wiretap channel with one helper for antenna configuration with arbitrary number. In these two schemes, the transmitter performs beamforming based on generalized singular value decomposition (GSVD), where an appropriate power allocation algorithm is utilized. Meanwhile, the helper sends artificial noise for higher secrecy rate. However, the transmission strategies for the artificial noise are different in the two schemes. In the first scheme, the helper adopts GSVD-based beamforming. Nevertheless, in this scheme, the impact of the artificial noise on the information signal at the receiver is not considered. To solve the problem, the helper performs space projection (SP)-based beamforming in the second scheme. In this scheme, suboptimal weighting factors are introduced to reduce the computational complexity, which can be adapted to the change of the channel quality. Theoretical analysis for the performance of the two proposed schemes is then given. Furthermore, simulation results indicate that the two presented schemes perform better than the existed schemes without helper. They also show that in the second scheme the suboptimal parameter setting is better than equal parameter setting and quite close to optimal parameter setting.

Interference alignment and relay processing algorithm via sum rate maximization for asymmetric two-way relay X networks

Two-way relay X networks offer a higher degrees of freedom, in contrast to traditional wireless communication networks. The relay processing based on zero forcing only considers the interference, ignoring the desired signal, so that the sum rate of the network to be improved. Specifically, the lower user transmission power, the greater disadvantages. The interference alignment scheme was researched for asymmetric two-way relaying X networks, moreover the relay beamforming technique based on the desired signal and interference signal was also presented. Firstly, a mathematical model was obtained for the network sum rate by the spatial relationship between user signal vectors. Then, the relay beamforming scheme based on sum rate maximization was transformed into a linear search for the optimal value through the matrix analysis and numerical analysis theory, and the objective function of the network was approximated by the limitation. Furthermore, the objective function was approximated by the linear combinations of parameters of one-way network. Finally, the relay precoder matrix to maximize the sum rate was obtained. Simulation results show that the proposed scheme significantly improved the network rate compared with existing relay processing scheme, while simplifying the complexity of the algorithm.