On Unsourced Random Access for the MIMO Channel

Abstract

In this paper, we consider massive machine-type communications (mMTC), a crucial communication scenario for future 5G/6G wireless networks. Indeed, the number of devices connected to the network grows exponentially. At the same time, the traffic of the devices is significantly different from the traffic generated by human users and consists of short and sporadically sent packets. The main goal is not to increase spectral efficiency but to provide connectivity and energy efficiency. Current transmission schemes are highly inefficient in this regime. The most promising way to deal with the problem is to use the random-access schemes or, equivalently, a grant-free transmission, i.e., the device transmits the packet without any prior communication to the base station. As the number of devices is extreme, creating different encoders for the users is impossible, and the promising strategy is to employ the same encoder for all the users. In this case, the receiver can not identify the source of the message, and, thus, such schemes are called unsourced random access (URA) schemes. To increase the battery life, the transmitters in the mMTC scenario must be as simple as possible. At the same time, the restrictions for the receiver (base station) are not so strict, and one can equip the receiver with multiple antennas. In this talk, we focus on this scenario. The existing papers on this topic consider either a single receive antenna case or a massive (with 100-800 antennas) MIMO receivers. In this talk, we focus on moderate (8) antenna count. That is more realistic for long-range narrowband transmissions. We evaluate different methods for the Rayleigh fading channel and the MIMO-enabled base station. We start our analysis with a coded compressed-sensing-based approach for different types of outer code. Next, we investigate a covariance-based method, which performs well in a massive MIMO scenario. Finally, we evaluate the TIN-SIC approach, which shows good performance for a single-antenna case. We present our results as minimal energy per bit (E <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</inf> /N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> ) required to achieve the target per-user probability of error (PUPE). The TIN-SIC scheme with blind detection shows a substantial increase in energy efficiency and active users number (14 dB and ×3 respectively for 8 antennas at the BS).