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Message-Passing Receiver Design for Joint Channel Estimation and Data Decoding in Uplink Grant-Free SCMA Systems | IEEE Journals & Magazine | IEEE Xplore

Message-Passing Receiver Design for Joint Channel Estimation and Data Decoding in Uplink Grant-Free SCMA Systems


Abstract:

The conventional grant-based network relies on the handshaking between the base station and active devices to achieve dynamic multi-user scheduling, which may result in l...Show More

Abstract:

The conventional grant-based network relies on the handshaking between the base station and active devices to achieve dynamic multi-user scheduling, which may result in large signaling overheads as well as system latency. To address those problems, a grant-free receiver design is considered in this paper based on sparse code multiple access (SCMA), one of the promising air interface technologies for 5G wireless networks. With the presence of unknown multipath fading, the proposed receiver performs joint channel estimation and data decoding without knowing the user activity in the network. Formulating a factor graph representation for the problem, we devise a message-passing receiver for the uplink SCMA that performs joint estimation iteratively. Motivated by the idea of approximate inference, we use expectation propagation to project the intractable distributions into Gaussian families such that a linear complexity decoder is obtained. The simulation results show that the proposed receiver can detect active devices in the network with a high accuracy and can achieve an improved bit-error-rate performance compared with existing methods.
Published in: IEEE Transactions on Wireless Communications ( Volume: 18, Issue: 1, January 2019)
Page(s): 167 - 181
Date of Publication: 06 November 2018

ISSN Information:

Funding Agency:


I. Introduction

With the explosive growing demand on network capacity, throughput and connected wireless devices, the mobile broadband network is evolved into fifth generation, in which the enhanced mobile broadband (eMBB), ultra-reliable low latency communication (URLLC), and massive machine type of communication (mMTC) are three typical application scenarios. Current air interface technologies, such as orthogonal frequency-division multiple access (OFDMA) cannot fulfill the requirements in the above scenarios as orthogonal multiple access (OMA) assigns the time-frequency resources to each user exclusively. Therefore, OMA is spectrum inefficient and cannot support large throughput as well as the massive connected users in the network. In contrast, non-orthogonal multiple access (NOMA) where each resource unit shared by multiple users is supposed to be more spectrum efficient. Sparse code multiple access (SCMA) [1] is a code domain NOMA and is designed based on the multi-dimensional sparse signal constellation. Due to the shaping gain of multi-dimensional constellation, SCMA has a better bit-error-rate (BER) performance compared with other NOMA schemes, such as low density signature (LDS) [2].

References

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