On Optimal Code Hopping Pattern Design for Complementary Coded CHMA Systems

Code hopping multiple access (CHMA) is an emerging technology to implement code domain non-orthogonal multiple access (NOMA). In CHMA, multiple access interference and multipath interference can be mitigated with the help of complementary codes, namely complementary coded CHMA (CC-CHMA). However, traditional CC-CHMA works on random code hopping (CH) patterns, which leads to an irreducibly high bit error floor. To address this issue, this work proposes an optimal CH pattern design to minimize the bit error floor. In addition, code collision probability and bit error rate (BER) with binary phase shift keying modulation are derived explicitly. The results verify that CC-CHMA with the proposed optimal CH pattern exhibits a much better BER performance than traditional CC-CHMA, which at the same time also offers a higher overload rate than traditional NOMA in uplink multipath channels, paving a way for its possible applications in beyond 5G mobile communications.