Active Users Detection Based on Deterministic Sequences for Massive Connectivity To support massive Machine Type Communications (mMTC) applications, especially for overcoming the high overhead problem, compressive sensing algorithm for grantfree multiple access is advocated. For an mMTC system with a large number of users, in most existing research, each user is allocated a complex Gaussian random sequence, and approximated message passing (AMP) algorithm is normally employed at the receiver to detect the active users. In this paper, binary deterministic sequences are considered, resulting much simpler implementation. It is shown that, due to the smaller coherence value, significant performance gain can be obtained by employing the binary deterministic sequences into AMP process. In particular, binary quasiorthogonal sequences (QOS) exhibit excellent performance in the shortpacket transmission. Moreover, an improved AMP algorithm is presented by designing a new stopping criterion to reduce the number of iterations without loss of accuracy.

Performance Evaluation of IDMABased Random Access Considering User Detection and Channel Estimation This paper evaluates the performance of interleave division multiple access (IDMA)based random access in order to support massive machinetype communications (mMTC) in the fifth generation mobile communication system taking into account actual user detection and channel estimation using a preamble attached to the packet. To suppress the packet loss due to contention and achieve multipacket reception, accurate user detection and channel estimation, which are used in the successive interference canceller (SIC)process in IDMA, are essential. Multiple preamble sequences, each of which has a onetoone relationship with the interleaver pattern prepared in the system, are generated by applying a cyclic time shift and orthogonal masking operations to ZadoffChu (ZC) sequences. Based on the threshold decision on the correlation between the received signal and each preamble sequence, user detection and channel estimation are performed. Computer simulation results show the impact of the preamble overhead, miss detection and false alarm in the user detection, channel estimation error, and the case when multiple users simultaneously select the same interleaver on the achievable performance of IDMAbased random access.