Spectral efficiency and transmission security are both essential metrics for wireless communication. Rate compatible modulation (RCM) is an adaptive transmission scheme to improve the spectral efficiency. However, the mapping matrix of RCM is fixed. Once the mapping matrix is known to eavesdroppers, information will be leaked. Physical layer encryption (PLE) is a secure approach to enhance the security using encryption at physical layer. In this paper, we propose a secure transmission scheme

more »

... RCM, namely, secure RCM (S-RCM). The construction method of RCM mapping matrix is of great random. Combined with PLE, S-RCM mainly uses the secret key extracted from the channel information to generate mapping matrix. Due to the randomness of channel, the mapping matrix will also be random. Security analysis shows that the demapping of S-RCM must be based on the right mapping matrix. It also shows that S-RCM owns extremely large cipher mapping matrix space, which makes it impossible for eavesdropper to guess the mapping matrix. Furthermore, known-plaintext attack (KPA) is hardly impossible to get the mapping matrix due to the high calculations and multiple possibilities. Simulation result shows that the S-RCM have the same throughput performance and bit error rate (BER) performance as RCM. In addition, the simulation results also show that eavesdropper faces extremely high complexity, which is thought safe. INDEX TERMS Rate compatible modulation, physical layer encryption, security, eavesdropper, throughput, BER. 2100 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see http://creativecommons.org/licenses/by/4.0/ VOLUME 8, 2020