Secure multiple access based on multicarrier CDMA with induced random flipping

In this paper, we study secure multiple access based on multicarrier (MC) code division multiple access (CDMA) systems with induced random (chip) flipping of spreading sequence, which is suitable for machine-Type communications (MTC). In MTC, devices may use low-cost hardware-based random number generators for pseudo-random noise (PN) sequences in secure communications. Since PN sequences can be estimated by correlation attacks at an eavesdropper, induced random (chip) flipping of spreading sequences is proposed to make correlation attacks infeasible. However, induced random flipping can also degrade the performance of detection and decoding at a legitimate receiver that only knows original spreading sequences. To avoid the performance degradation, we derive low-complexity iterative receiver algorithms for multiuser signal detection and decoding based on the expectation-maximization (EM) algorithm.