Sparse vector coding (SVC) is emerging as a key enabler for short-packet ultrareliable and low-latency communications (URLLCs), since it displays good block error rate (BLER) performance and can achieve low transmission latency. In this article, we propose an SVC-based sparse superimposed transmission (SVC-ST) coding scheme to further enhance the BLER performance of the SVC scheme. At the encoding side, a portion of transmission bits is represented by nonzero position indices of the sparse vector. The remaining bits are equally split into multiple streams and then mapped into the nonzero positions of sparse vector via quadrature amplitude modulation (QAM) with constellation rotation (CR). We afterward adopt the multipath matching pursuit-based soft decoding (MMP-SD) to recover the transmission packet. The BLER and bit error rate (BER) analyses of the SVC-ST scheme demonstrate the validity and rationality of our study. Moreover, we find from the simulation results that the proposed SVC-ST scheme outperforms SVC and its enhanced version (ESVC) schemes in terms of BLER and latency performance.

Sparse code multiple access (SCMA), which helps improve spectrum efficiency (SE) and enhance connectivity, has been proposed as a non-orthogonal multiple access (NOMA) scheme for 5G systems. In SCMA, codebook design determines system overload ratio and detection performance at a receiver. In this paper, an SCMA codebook design approach is proposed based on uniquely decomposable constellation group (UDCG). We show that there are N+1 ( N ≥ 1) constellations in the proposed UDCG, each of which has M (M ≥ 2) constellation points. These constellations are allocated to users sharing the same resource. Combining the constellations allocated on multiple resources of each user, we can obtain UDCG-based codebook sets. Bit error ratio (BER) performance will be discussed in terms of coding gain maximization with superimposed constellations and UDCG-based codebooks. Simulation results demonstrate that the superimposed constellation of each resource has large minimum Euclidean distance (MED) and meets uniquely decodable constraint. Thus, BER performance of the proposed codebook design approach outperforms that of the existing codebook design schemes in both uncoded and coded SCMA systems, especially for large-size codebooks.

The Industrial Internet of Things (IIoT) greatly facilitates industrial production and economic development. However, it has more vulnerabilities facing the security issues introduced by the openness of wireless communications. Hence, a lightweight combined physical layer encryption and authentication (PLEA) scheme is proposed in this paper to protect resource-constrained IIoT devices. In the proposed PLEA scheme, quadrature phase shift keying (QPSK) modulation is adopted and the quadrant feature is extracted along with the shared key to generate a dynamic encrypting sequence and a tag. Then, physical layer encryption (PLE) and tag-embedding are carried out by phase reverse and power assignment according to the encrypting sequence and the tag, correspondingly. At the receiver, the same quadrant feature is extracted from the received signals and then is used to regenerate the tag and the decrypting sequence in order to execute physical layer authentication (PLA) and decryption. The error rates of the signal detection and tag detection are given, then the probability of detection and false alarm probability of the proposed PLA scheme are also obtained. In addition, the unified average changing intensity is defined and derived to analyze the performance of the PLE. Finally, computer simulation results show that the proposed scheme could provide effective security protection for IIoT.

In this paper, we consider an ultra-reliable low-latency communication (URLLC) scheme for one uplink massive single-input multiple-output (SIMO) system with three users. In our design, to enable all the users to update status information to the base station (BS) concurrently with an extremely low latency, we specifically decompose a cross 8-QAM constellation into one additive uniquely decomposable constellation group (AUDCG), and then devise a new multiuser space-time modulation scheme at the transmitters accordingly. For the receiver side, to assure that the BS can detect all the transmitted signals of different users simultaneously with a high reliability and a low latency, we investigate a noncoherent maximum likelihood (ML) receiver in comparison to a minimum Riemannian distance (MRD) estimator and a minimum Euclidean distance (MED) detector when the antenna array size is scaled up. Finally, extensive computer simulations are carried out to validate the effectiveness of our proposed design when the antenna array size is large.