Secure Transmission With Randomized Constellation Rotation for Downlink Sparse Code Multiple Access System

Ke Lai,Gaojie Chen,Wei Li,Jing Lei,Lei Wen,Pei Xiao

doi:10.1109/access.2017.2772259

Abstract

Sparse code multiple access (SCMA) is a promising candidate air interface of next-generation mobile networks. In this paper, we focus on a downlink SCMA system where a transmitter sends confidential messages to multiple users in the presence of external eavesdroppers. Consequently, we develop a novel secure transmission approach over physical layer based on a highly structured SCMA codebook design. In our proposed scheme, we rotate the base constellations (BCs) with random angles by extracting channel phases from the channel state information. By employing randomized constellation rotation, the security of downlink SCMA can be ensured. In addition, a tight SCMA upper bound is introduced to guide the design of the encrypted codebook. As a result, we propose an approach to avoid the significant error rate performance loss caused by using codebooks that are designed using our method. The proposed upper-bound-aided codebook design scheme can select relatively good codebooks with low complexity. By combining SCMA codebook design and secure communication, our scheme ensures security for massive quantities of users with low encrypted and decrypted complexity at the cost of transmission rate and possible error rate performance loss. Moreover, the proposed scheme can achieve robustness against channel estimation errors. Analyses and Monte Carlo simulations confirm the effectiveness of our scheme.

Highlights

Since the commercialization of 4th generation (4G) mobile networks, researchers have focused on the new air-interface technology, which is more efficient and reliable, to meet the demands of the 5th generation (5G) mobile networks [1]
It can be inferred that the eavesdropper can recover partial information with deviated rotated angles rather than the completely accurate angles in a conventional Sparse code multiple access (SCMA) system, even though the codebook is unknown to the eavesdropper
RCR-SCMA employs the technique of channel key extraction to scramble the codebook at the transmitter to make it unknown to the eavesdropper

Summary

Introduction

Since the commercialization of 4th generation (4G) mobile networks, researchers have focused on the new air-interface technology, which is more efficient and reliable, to meet the demands of the 5th generation (5G) mobile networks [1]. Sparse code multiple access (SCMA) [2] is a code domain NOMA that is considered to be a promising 5G candidate due to its excellent ability to support massive quantities of users under heavily loaded conditions.. In the possible application scenarios for NOMA, such as massive machine type of communication (mMTC), millions of nodes must be accessed. New secure transmission approaches that are adapted to NOMA should be considered. We focus on designing a secure transmission scheme for a downlink SCMA system

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Conclusion