Haowei Wang

Channel state information (CSI) is differently available at each terminal in state-dependent wiretap channels (SD-WTCs). Considering a random channel state non-causally available only at the encoder, this paper investigates an explicit polar coding scheme for the discrete and memoryless SD-WTC, where Alice aims to transmit a secret message (SM) and a secret key (SK) to Bob while concealing them from Eve. Based on a two-layer superposition coding, which includes an inner layer and an outer layer, the proposed polar coding scheme can achieve the inner bound of the current optimal SM-SK capacity region for the discrete and memoryless SD-WTC with CSI non-causally available only at the encoder. A cross-layer construction is proposed to address the issue where the regular chaining construction used in wiretap polar codes cannot be applied in the inner layer. Results show that the decoding error probability (DEP) of the legitimate decoder vanishes to zero as the block length increases. In addition, the proposed scheme is proven to satisfy strong secrecy.

The multiple access channel with confidential messages (MAC-CM) generalizes the traditional multiple access channel by allowing both users to receive channel outputs. Achievable secrecy rate region of this model has been established using random coding arguments, whereas practical codes design remains to be further discussed. In this paper, we develop an explicit polar coding scheme that achieves the secrecy rate region of the MAC-CM under strong secrecy. In particular, our scheme mainly relies on monotone chain rules and polar coding techniques for single-user channels. A proper chaining scheme is constructed to align polar indices and to provide strong secrecy. Finally, a rigorous analysis is provided to validate the performance of our scheme.

Superposition modulation(SM) separates the transmitters and the bits to be sent into two parts, respectively, and aims that the low-order symbols modulated by different bit sequences reach the legitimate receiver (Bob) synchronously. Then the receiver receives a high-order superposition symbol superimposed by the low-order symbols. Its diversity makes a great fluctuation of communicating channels, which is a great feature for the physical-layer security. So the potential security of SM is deserved to be discussed. This paper investigates the security performance of SM scheme in a wiretap system, and its symbol error rete (SER) at the eavesdropper (Eve) is much higher compared with the traditional QAM scheme. Furthermore, we discuss the effect of channel estimation errors. It shows that SM scheme is as sensitive to estimation error as traditional QAM scheme for Eve, such that SM is still have a better secrecy performance. The results show agreement with computer simulations.

The wiretap channel with shared key (WTC-K) refers to the classic wiretap channel with a secret key of arbitrary rate shared between the transmitter and the legitimate receiver. While the secrecy capacity of WTC-K has been obtained using random coding arguments, in this paper we propose a lowcomplexity polar coding scheme achieving the secrecy capacity under the strong secrecy condition. Our construction consists of choosing the sets of information indices and using the shared key properly. Specifically, we utilize the structure of superposition coding in the proposed scheme.