Abstract
A massive multiple-input multiple-output (MIMO) system uses a large number of antennas in the base station (BS) to serve multiple users, which significantly improves the capacity of the system. However, in time division duplex (TDD) mode, the pilot contamination (PC) is inevitable due to the multiplexing of pilots. This paper proposed a pilot assignment based on graph coloring and location information (GC-LI) to improve the performance of users. Specifically, based on graph coloring, the proposed GC-LI algorithm combines location information like the angle of arrival (AoA), distance, and correlation to construct an interference graph. Then, we calculate the interference between any two users and use the postprocessing discrete Fourier transform (DFT) filtering process to effectively distinguish the users with nonoverlapping AoAs. Finally, according to the interference graph, the GC-LI algorithm is proposed to mitigate the intercell interference (ICI) between users with the same pilot by assigning different pilots to connected users with high ICI metrics based on some regulation. Simulation results show that the GC-LI algorithm is suitable for various types of cells. In addition, compared with the existing pilot assignment algorithms based on graph coloring, users’ average signal-to-interference-plus-noise ratio (SINR) and uplink achievable sum rate (ASR) are significantly improved.
Highlights
The 5G network is regarded as the foundation of the Internet of Things (IoT), Internet of Vehicles (IoV), and other things in the future [1, 2]
We can see that the method based on pilot assignment is the premise of the other two methods, so this paper focuses on the pilot assignment strategy to suppress the pilot contamination (PC) problem
The location information is further combined in the construction of the interference graph, which considers the influence of the large-scale fading coefficient caused by the distance and the angle of arrival (AoA) of users
Summary
The 5G network is regarded as the foundation of the Internet of Things (IoT), Internet of Vehicles (IoV), and other things in the future [1, 2]. In [23, 24], the pilot assignment methods based on graph coloring are proposed Both take the large-scale fading coefficient as a metric to establish an interference graph for all users in multicell. The location information is further combined in the construction of the interference graph, which considers the influence of the large-scale fading coefficient caused by the distance and the angle of arrival (AoA) of users (2) The postprocessing discrete Fourier transform (DFT) filtering process is used to filter out the pilot interference of users with nonoverlapping AoAs. The potential intercell interference (ICI) strength between any two users in different cells is measured, and an interference graph including all cell users is constructed (3) For the multicell multiuser massive MIMO system, a pilot assignment algorithm GC-LI is proposed to reduce the ICI in the system.
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