Spectrum sensing and non-orthogonal multiple access based massive grant-free random access scheme

A massive grant-free random access scheme based on spectrum sensing provided by cognitive radio (CR) and non-orthogonal multiple access (NOMA) was proposed for massive machine type communication scenarios. Firstly, a three-step grant-free random access protocol based on CR-NOMA was put up, which could support end users to obtain uplink channel state information through spectrum sensing so as to reduce random access conflicts in a targeted manner. Then, an access channel and power level optimization strategy according to spectrum sensing results was designed, and the uplink transmission signal model of users and reception signal model of base station were established. Finally, the multi-user signal detection algorithm with channel filtering, power level detection, preamble and data detection, as well as collision detection jointly was proposed. The performance of random access was theoretically analyzed and simulated, too. The simulation results show that, compared with existing solutions, the proposed CR-NOMA scheme has stronger overload capacity since it has nearly doubled the user access probability and overload rate under high system load. It also has better robustness.