In frequency-hopping systems, the multiple-access interference (MAI) occurs when more than one user appear on the same frequency at the same time. In this paper, we address the multi-user detection (MUD) problem for slow frequencyhopping (SFH) system with binary phase shift keying (BPSK). We first built a MAI model taking the hopping patterns and the phase offset into account, whereby the MAI is considered as independent yet unnecessarily identically distributed random variable. Under the proposed model, we further simplify the MAI by exploiting the Lyapunov central limit theorem and propose an iterative per-chip multiuser detection (PC-MUD) algorithm. By simulations, it's verified that the performance of proposed algorithm is near to the performance of single user bound in additive white Gaussian noise environment.

In this paper, we propose an iterative detection algorithm that reconstructs and cancels the multiple-access interference jointly without the knowledge of hopping patterns of the interfering users for SFH/BPSK systems in an ad hoc scenario. Since users are asynchronous in this scenario, signal in one hop of the desired users is affected by partial signals in unaligned hops, called the interference fragments, of the interfering users. We address the interference model by defining a virtual user, which has the same hopping pattern as that of the desired user and contains the feature of the interfering fragments. Then, we derive the joint interference reconstruction and multiple-user detection (MUD) algorithm using the factor graph framework. Simulation results show that the performance of the proposed algorithm can be improved by up to 2 dB than that of the traditional single user detection (SUD) in AWGN at the packet error rate of 10 −2 for a total of 8 users over 20 hopping frequencies, and an outstanding performance may also be achieved in the channel with Doppler.