Signal Superposition in NOMA With Proper and Improper Gaussian Signaling

• Published in: IEEE transactions on communications 2020-10, Vol.68 (10), p.6537-6551
• Main Authors: Nasir, Ali Arshad, Tuan, Hoang Duong, Nguyen, Ha H., Duong, Trung Q., Poor, H. Vincent
• Format: Article
• Language: English
• Subjects: Cellular radio; Conveying; Decoding; Gaussian channels; improper Gaussian signaling (IGS); max-min throughput optimization; Multiaccess communication; NOMA; non-orthogonal multiple access (NOMA); Nonorthogonal multiple access; Optimization; orthogonal multiple access (OMA); Signal superposition; Signaling
• ISSN: 0090-6778; 1558-0857
• DOI: 10.1109/TCOMM.2020.3008233

Recent studies of single-cell two-user networks have shown that a higher network throughput is achieved by using a common message to be decoded by both users and conveying partial information for both users, rather than using the common message to convey the entire information for one of the two users. The latter is essentially the conventional non-orthogonal multiple access (NOMA), which performs better than orthogonal multiple access (OMA) only under users' dissimilar channel conditions. Unlike NOMA, the former performs consistently better than OMA. This paper generalizes such a signaling strategy to a general multi-cell multiuser network, which leads to a new NOMA approach (called n-NOMA) in which each pair of users decodes a message that conveys partial information for one of them only. Unlike the conventional NOMA, whose performance is dependent on the users' pairing strategy, the proposed n-NOMA consistently outperforms both NOMA and OMA schemes. Both proper and improper Gaussian signaling is considered for all the concerned schemes and it is shown that the latter is clearly more advantageous than the former.