Grant-Free Rateless SCMA for Cellular Internet of Things Networks

Abstract

For supporting the massive connectivities and better adapting the high dynamical channel states of the cellular Internet of things networks, in this paper we proposed a new grant-free rateless sparse code multiple access (RSCMA) protocol. In the proposed grant-free RSCMA, users switch from the inactive mode to the active mode as soon as they receive data packages, and start to transmit the data without the request-grant process between the base station (BS) and users. In each transmission, the active users firstly choose a certain number of the modulated SCMA symbols according to the pre-assigned access control function (ACF), and then transmit the linearly superimposed SCMA symbols to the BS over the available resource elements. At the BS, owing to the sparsity of RSCMA, message passing algorithm which allows multi-user detection with near-optimal performance can be utilized to decode the messages. The transmission will continue until the user successfully receives an ACK signal sent back from the BS. Theoretical analysis in terms of achievable constellation constrained throughput is provided to show the maximal sum rate of RSCMA and to optimize the ACF design under the trade-off between the complexity and throughput performance. Both theoretical and simulation results show that the RSCMA can achieve higher throughput than the existing rateless multiple access schemes, such as hybrid automatic repeat request SCMA, LT code coded SCMA, and rateless multiple access.

On the robustness of three classes of rateless codes against pollution attacks in P2P networks

“…Thanks to their flexibility and simplicity rateless codes have found their way in numerous fields such as distributed storage [2,31], Wireless Ad Hoc Networks [16], peer-topeer based applications [43], communications in 5G [37], vehicular networks and Internet of Things applications [13,34]. In the broad area of peer-to-peer rateless codes have been exploited in application ranging from multimedia delivery to distributed storage systems [1,5,35,42,46,47].…”

Channel Estimation and User Activity Identification in Massive Grant-Free Multiple-Access

“…In the NOMA family, sparse-code multiple-access (SCMA) is an attractive scheme, which allows to support the multiple-access of significant overloading but still achieve near optimum performance by exploiting the message-passing algorithm (MPA)-assisted detection [31]. Hence, SCMA has been introduced to GFMA, e.g., in [2,12,[32][33][34]. Specifically in [35], the joint UE activity detection and data detection were considered, when assuming that all UEs (both active and inactive) transmit the headers for activity detection, while the channels of all UEs are known to BS.…”

“…In [32], a faster-than-Nyquist (FTN) singling SCMA was proposed to support uplink GFMA, where only very small systems (6 UEs supported by 4 resource units) were investigated. In [33], the authors considered the MPA-assisted information detection in a rate-less SCMAbased GFMA systems, when assuming a constant number of active UEs, and that receiver has ideal knowledge about the active users and their channels. While one UE employs only one codebook in the above-mentioned references, the authors in [34] proposed to map a UE's consecutive data symbols to the codewords chosen from different codebooks, which achieves code diversity.…”