High-Quality and Low-Complexity Polar-Coded Radio-Wave Encrypted Modulation Utilizing Multipurpose Frozen Bits

Abstract

In recent years, physical layer security (PLS), which utilizes the inherent randomness of wireless signals to perform encryption at the physical layer, has attracted attention. We propose chaos modulation as a PLS technique. In addition, a method for encryption using a special encoder of polar codes has been proposed (PLS-polar), in which PLS can be easily achieved by encrypting the frozen bits of a polar code. Previously, we proposed a chaos-modulated polar code transmission method that can achieve high-quality and improved-security transmission using frozen bit encryption in polar codes. However, in principle, chaos modulation requires maximum likelihood sequence estimation (MLSE) for demodulation, and a large number of candidates for MLSE causes characteristic degradation in the low signal-to-noise ratio region in chaos polar transmission. To address this problem, in this study, we propose a versatile frozen bit method for polar codes, in which the frozen bits are also used to reduce the number of MLSE candidates for chaos demodulation. The numerical results show that the proposed method shows a performance improvement by 1.7 dB at a block error rate of 10 -3 with a code length of 512 and a code rate of 0.25 compared with that of conventional methods. We also show that the complexity of demodulation can be reduced to 1/16 of that of the conventional method without degrading computational security. Furthermore, we clarified the effective region of the proposed method when the code length and code rate were varied.

Error-Control Information Reconciliation Scheme for Continuous-Variable Quantum Key Distribution Using Fixed-Bit Polar Codes

“…In fixed-bit polar codes, the input bits that induce fixed bits are selected from frozen bits for efficient sharing. However, these bits are located at the tail of the input bits, regardless of the channel capacity, which degrades the errorcorrection performance of polar codes in exchange for the useful properties provided by the fixed bits [10,11].…”

“…Although fixed bits degrade the error-correction performance of polar codes, they can be employed for additional functions. We proposed the application of fixedbit polar codes for channel estimation in free-space optical communications [10] and decoding complexity reduction in chaos modulation [11].…”