Variable-Length Two-Stage Preamble for mMTC

To enhance the access success performance and energy efficiency (EE) of preamble transmission for IoT devices in massive machine-type communications (mMTC), this paper introduces variable-length two-stage preamble (V-TSPA) to the random access (RA) policy. The proposed V-TSPA can not only resolve detection ambiguity issues in multi-stage preamble but also increase the number of available preambles, thereby improving the access success probability. Additionally, to meet the EE requirements of IoT systems, a feedback mechanism is incorporated into the proposed V-TSPA-based RA scheme. Simulation results show that, compared to traditional single-stage preamble (S-PA)-based RA schemes, the proposed scheme can effectively improve the access performance and energy efficiency of IoT devices.