Secure Modulation Based on Constellation Mapping Obfuscation in OFDM Based TDD Systems

In this paper, we propose a secure modulation technique based on constellation mapping obfuscation to harden computational complexity for security at the physical-layer. To obfuscate mapping from bit stream to modulated symbols, our proposed scheme randomly changes a constellation mapping rule at each packet transmission opportunity, instead of employing a pre-determined mapping rule (e.g., Gray-coded mapping) at every packet transmission opportunity. Furthermore, to securely share the mapping rule between the transmitter and the desired receiver, the proposed scheme uses wireless channel based encryption and the fuzzy commitment with an error correction coding. We derive asymptotic bit error rate of the proposed scheme and validate our analysis through extensive simulations. We verify that our proposed scheme can further improve wireless security at the physical-layer irrespective of the upper layers' cryptographic schemes, which can be achieved by computational hardness - M! computations are required for the eavesdropper to crack the mapping rule when M -quadrature amplitude modulation (QAM) is considered (e.g., 64! \approx 1.27\times 10^{89} combinations for 64-QAM).