Rethinking Grant-Free Protocol in mMTC
<|reference_start|>Rethinking Grant-Free Protocol in mMTC: This paper revisits the identity detection problem under the current grant-free protocol in massive machine-type communications (mMTC) by asking the following question: for stable identity detection performance, is it enough to permit active devices to transmit preambles without any handshaking with the base station (BS)? Specifically, in the current grant-free protocol, the BS blindly allocates a fixed length of preamble to devices for identity detection as it lacks the prior information on the number of active devices $K$. However, in practice, $K$ varies dynamically over time, resulting in degraded identity detection performance especially when $K$ is large. Consequently, the current grant-free protocol fails to ensure stable identity detection performance. To address this issue, we propose a two-stage communication protocol which consists of estimation of $K$ in Phase I and detection of identities of active devices in Phase II. The preamble length for identity detection in Phase II is dynamically allocated based on the estimated $K$ in Phase I through a table lookup manner such that the identity detection performance could always be better than a predefined threshold. In addition, we design an algorithm for estimating $K$ in Phase I, and exploit the estimated $K$ to reduce the computational complexity of the identity detector in Phase II. Numerical results demonstrate the effectiveness of the proposed two-stage communication protocol and algorithms.<|reference_end|>
@article{zhu2024rethinking,
    title={Rethinking Grant-Free Protocol in mMTC},
    author={Minhao Zhu, Yifei Sun, Lizhao You, Zhaorui Wang, Ya-Feng Liu, Shuguang
  Cui},
    journal={arXiv preprint arXiv:2404.16152},
    year={2024},
    archivePrefix={arXiv},
    eprint={2404.16152},
    primaryClass={cs.IT eess.SP math.IT}
}