Abstract
In this paper, the scaling laws of scheduling gain and the feasibility of user scheduling for uplink massive multiple input–multiple output (MIMO) systems are investigated by analyzing the second moment of mutual information. We consider two well-known linear receivers of matched filter (MF) and zero-forcing (ZF). The exact distribution of the signal-to-interference-plus-noise ratio (SINR) and its moment-generating function are first obtained, and the approximated variance of the mutual information for a user is derived as a closed form with a function of the number of antennas. The achievable scheduling gain under the optimal user scheduler is then derived using the Gaussianity of the sum rate. From the analyses and simulation results, it is found that the scheduling gain for the MF receiver increases with the number of base station (BS) antennas, while that for the ZF receiver decreases as the number of BS antennas increases, for most cases (except some impractical scenarios). Therefore, it is verified that user scheduling is still beneficial for the MF receiver while random user selection is sufficient for the ZF receiver in massive MIMO systems.
Highlights
The fifth-generation (5G) wireless communication system, known as new radio (NR), has been successfully commercialized globally
It is verified that user scheduling is still beneficial for the matched filter (MF) receiver while random user selection is sufficient for the ZF receiver in massive multiple input–multiple output (MIMO) systems
From the analyses and simulation results, we verified that the scheduling gain for the MF receiver increases as the number of antennas increases, regardless of the user selection algorithm and channel state information (CSI) availability for user scheduling
Summary
The fifth-generation (5G) wireless communication system, known as new radio (NR), has been successfully commercialized globally. Many previous studies [7,18,19,20] have analyzed the performance of massive MIMO systems in terms of the ergodic sum rate. In this paper, we investigate the scaling laws of scheduling gain for uplink multiuser massive MIMO systems in order to verify the feasibility of user scheduling for massive MIMO, assuming MF and ZF receivers at the BS for data demodulation. The scheduling gain of the ZF receiver still decreases to zero with the increasing number of antennas when the user selection is performed based on the imperfect CSI.
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