Quasi-Orthogonal FHMA System under Large Access Delay: Code Design and Performance Analysis

The performance of frequency-hopping multiple-access (FHMA) systems is mainly determined by the FH sequence set (FHS). Constructing the FHS with optimal Hamming cross- and auto-correlations under the varying access-delay is a major challenge for FHMA systems to achieve the superior performance. In this paper, we propose a novel kind of no-hit zone FH sequence (NHZ-FHS), which has the orthogonality for small access-delay and the near-orthogonality for large access-delay. A design algorithm of the new NHZ-FHS is presented based on the traditional FH sequences. Then, as a case study of FHMA system with $M$-ary frequency-shift-keying (MFSK/FHMA), the multiple-access interference (MAI) rejection benefited from the proposed FHS are analyzed, and the decision variable is derived as a function of the Hamming correlation, which is utilized for Monte Carlo simulation. The simulation and numerical results show that the proposed NHZ-FHS can completely avoid MAI for quasi-synchronous FHMA system; meanwhile it can provide the lower MAI and better performance for synchronous system, compared with the exiting pseudo-random FHSs. The proposed NHZ-FHS relaxes the requirement of strict synchronization mechanism, which is more suitable for the FHMA network deploying under the poor communication conditions.