Multiple Preambles for High Success Rate of Grant-Free Random Access With Massive MIMO

Abstract

Grant-free random access (RA) with massive MIMO is a promising RA technique with low signaling overhead that provides significant benefits in increasing the channel reuse efficiency. Since user equipment (UE) detection and channel estimation in grant-free RA rely solely on the received preambles, preamble designs that enable high success rate of UE detection and channel estimation are very much in need to ensure the performance gain of grant-free RA with massive MIMO. In this paper, a super preamble consisting of multiple consecutive preambles is proposed for high success rate of grant-free RA with massive MIMO. With the proposed approach, the success of UE detection and channel estimation for a RA UE depends on two conditions: 1) it is a solvable UE; 2) its super preamble is detected. Accordingly, we theoretically analyze the solvable rate of RA UEs with multiple preambles and propose a reliable UE detection algorithm to obtain the super preambles of RA UEs by exploiting the quasi-orthogonality characteristic of massive MIMO. Theoretical analysis and simulation results show that turning a preamble into a super preamble consisting of two or three shorter preambles, the success rate of UE detection and channel estimation could be significantly increased using the proposed approach.

A Grant-Free Random Access Scheme for M2M Communication in Massive MIMO Systems

“…Similar to step 2, based on the received pilot signal, the BS generates and broadcasts the precoded random access responses again, and each UE reselecting its pilot during step 3 employs the rule in Eq. (14) to judge whether it is detected. If UE p is a detected UE, it compensates its timing error for uplink message transmission.…”

“…Let λ l denote the probability of an edge connecting to a variable node with degree l, and ρ l denote the probability of an edge connecting to a factor node with degree l. Then, we transfer the node-perspective presentations in (19) and (20) into the edge perspective presentations, respectively…”

“…Then, the BS utilizes a proposed CICA algorithm to decode uplink message and estimate CSIs of UEs whose CSIs cannot be estimated by the SIC algorithm. Simulation results show that, compared to the detection method proposed in [20], the number of successful UEs can be improved even multiple UEs having the same super pilot sequence. • For the SIC algorithm, we propose to employ the estimated CSIs without other overhead to find edges connecting to a recovered variable node, by utilizing the asymptotic favorable propagation of massive MIMO systems.…”

“…We analyze the successful access probability, missed detection probability, and uplink throughput of the GCICA-RA scheme. Numerical results show that, compared to the random access scheme proposed in [20], the GCICA-RA scheme significantly improves the successful access probability and uplink throughput, decreases missed detection probability, and provides low CSI estimation error at the same time.…”

“…The above-mentioned grant-free random access schemes consider the single pilot structure. Jiang et al proposed to concatenate multiple orthogonal sub-pilots into a super pilot sequence, and the super pilot sequence is utilized for activity detection and CSI estimation [20]. Simulation results show that, compared to the single pilot structure, this super pilot structure can improve the number of successful UEs by utilizing their proposed detection approach.…”