A Novel Codebook Construction and Blind Detection Method for Grant-Free mMTCs

The grant-free transmission supports user devices to activate and transmit at any time without requiring a connection establishment beforehand, therefore it is well-suited for massive machine type communications. The existing grant-free schemes suffer from a small codebook size and consequently a high collision probability of spreading sequences among users. To address this issue, this paper proposes a novel method for constructing the codebook by concatenating sequences for a potentially large number of users. The codebook size is significantly increased while the low-correlation property is maintained. To guarantee a low complexity at the receiver, two types of blind phased detection schemes are proposed as well, which deal with the blind user recognition in a successive or parallel manner. The phased detection greatly reduces the complexity compared with the traditional multiuser detection through sequence traversal. Simulation results are provided, which verify the advantages of the proposed scheme in collision probability, user recognition and block error rate.