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Researches on 5th generation mobile communication networks (5G) are emerging to meet the demands of rapidly developing communications applications. The reliability and security of data have become key factors of its development, and thus 5G has put forward higher requirements for new coding and encryption technologies. In this paper, a physical layer encryption algorithm based on polarization codes and chaotic sequences is proposed to improve the reliability and confidentiality of transmission. In our scheme, chaotic sequences are allocated in the frozen bits of polar codes. Therefore, error correction and encryption can be performed simultaneously. Since the frozen bits are unknown to the eavesdroppers, it is difficult for them to decode the transmitted bits without the knowledge of the chaotic sequences. To further improve the security, we propose to generate the chaotic sequences by using the channel state information. Besides, the chain effects of delayed feedback are applied to increase the decrypted complexity of the eavesdroppers in this paper. Theoretic analysis and simulation results both show that the proposed algorithms can achieve high security without any error rate performance loss. INDEX TERMS Physical layer encryption, polar codes, chaotic sequences, frozen bits.

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In recent years, OFDM with index modulation (OFDM-IM) has become a potential technique due to its improvement of diversity gain. In typical OFDM-IM schemes, incoming information bits are divided into two parts, symbols bits, and index bits. However, the symbol bits conveyed by each OFDM symbol suffer from low diversity order, which has a negative impact on diversity gain. In this paper, we propose the scheme called OFDM with all index modulation (OFDM-AIM), which replaces the PSK/QAM constellation modulator with subblock modulator and simplifies the structure. With such an arrangement, the subblocks of OFDM-AIM become flexible, which contributes to achieving the higher diversity order of the system. Moreover, we study the effects of Euclidean distance and diversity order based on the unconditional pair error probability, which gives the guideline to design a legitimate subblocks set. Then the algorithm to build the subblocks set with higher diversity order is proposed, which can achieve better diversity gain. Theoretical and simulated results show that the OFDM-AIM scheme is capable of achieving better BER performance than other index modulated OFDM schemes.INDEX TERMS OFDM-IM, diversity order, diversity gain, all index modulation, Euclidean distance, subblocks set design, pairwise error probability.

Channel coding and security are important in a communication system. The 5th generation (5G) mobile communication networks call for higher requirements of new coding technologies and encryption technologies. As an efficient coding method, polar codes have attracted more attention in recent years. Besides, the peak-to-average-power ratio (PAPR) is a major problem of the orthogonal frequency-division multiplexing (OFDM) system, which will significantly affect the performance of the OFDM system. In this paper, joint physical-layer encryption and PAPR reduction scheme is proposed, aiming to solve the PAPR problem and achieve high security of the transmission system. In this scheme, we utilize the key generation technology of wireless channels to get the initial value of chaotic sequences. Then, the chaotic sequences can be used to encrypt the information and reduce PAPR simultaneously. Moreover, we use the best information bits of polar codes to store the serial number index of chaotic sequences. The theoretic analysis and simulation results show that the proposed scheme can not only achieve high security in the physical layer but also reduce PAPR in the OFDM system without increasing system complexity and latency.