Unsourced Random Access Using Multiple Stages of Orthogonal Pilots: MIMO and Single-Antenna Structures

• Published in: IEEE transactions on wireless communications Vol. 23; no. 2; pp. 1343 - 1355
• Main Authors: Ahmadi, Mohammad Javad, Kazemi, Mohammad, Duman, Tolga M.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-02-2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antennas; Channel estimation; Codes; Decoding; Encoding; Fading channels; Iterative decoding; Iterative methods; massive MIMO; Messages; MIMO communication; orthogonal pilots; pilot detection; Pilots; power diversity; Random access; Receiving antennas; the Internet of Things (IoT); Unsourced random access (URA); Wireless communication
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/TWC.2023.3288376

We study the problem of unsourced random access (URA) over Rayleigh block-fading channels with a receiver equipped with multiple antennas. We propose a slotted structure with multiple stages of orthogonal pilots, each of which is randomly picked from a codebook. In the proposed signaling structure, each user encodes its message using a polar code and appends it to the selected pilot sequences to construct its transmitted signal. Accordingly, the transmitted signal is composed of multiple orthogonal pilot parts and a polar-coded part, which is sent through a randomly selected slot. The performance of the proposed scheme is further improved by randomly dividing users into different groups each having a unique interleaver-power pair. We also apply the idea of multiple stages of orthogonal pilots to the case of a single receive antenna. In all the set-ups, we use an iterative approach for decoding the transmitted messages along with a suitable successive interference cancellation technique. The use of orthogonal pilots and the slotted structure lead to improved accuracy and reduced computational complexity in the proposed set-ups, and make the implementation with short blocklengths more viable. Performance of the proposed set-ups is illustrated via extensive simulation results which show that the proposed set-ups with multiple antennas perform better than the existing MIMO URA solutions for both short and large blocklengths, and that the proposed single-antenna set-ups are superior to the existing single-antenna URA schemes.