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We investigate the multi-faceted access point (AP) placement problems in uplink small-cell and cell-free networks in the context of throughput-optimality and to what extent the popular Lloyd algorithm from vector quantization (VQ) is suited to solve them. We develop single user throughput optimization formulations and solutions related to VQ considering the small cell scenario, after which we expand the formulations to multiple users. For the cell-free scenario, we consider the mean throughput of all users and a max-min technique. We compare the rate performances of the AP placement solutions from both scenarios with the Lloyd algorithm. While the Lloyd algorithm is found not to strictly solve for small cell AP locations and its approach is divergent from the cell-free perspective, we conclude from numerical experiments that it is good enough for both scenarios.
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Vector Quantization Methods for Access Point Placement in Cell-Free Massive MIMO Systems
We examine the problem of uplink cell-free access point (AP) placement in the context of optimal throughput. In this regard, we formulate two main placement problems, namely the sum rate and minimum rate maximization problems, and discuss the challenges associated with solving the underlying optimization problems with the help of some simple scenarios. As a practical solution to the AP placement problem, we suggest a vector quantization (VQ) approach. The suitability of the VQ approach to cell-free AP placement is investigated by examining three VQ-based solutions. First, the standard VQ approach, that is the Lloyd algorithm (using the squared error distortion function) is described. Second, the tree-structured VQ (TSVQ), which performs successive partitioning of the distribution space is applied. Third, a probability density function optimized VQ (PDFVQ) procedure is outlined, enabling efficient, low complexity, and scalable placement, and is aimed at a massive distributed multiple-input-multiple-output scenario. While the VQ-based solutions do not explicitly solve the cell-free AP placement problems, numerical experiments show that their sum and minimum rate performances are good enough, and offer a good starting point for gradient-based optimization methods. Among the VQ solutions, PDFVQ, with its distinct advantages, offers a good trade-off between sum and minimum rates.
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- PAR ID:
- 10524104
- Publisher / Repository:
- IEEE
- Date Published:
- Journal Name:
- IEEE Transactions on Wireless Communications
- Volume:
- 23
- Issue:
- 6
- ISSN:
- 1536-1276
- Page Range / eLocation ID:
- 5425 to 5440
- Subject(s) / Keyword(s):
- Throughput, Interference, Wireless communication, Optimization, Signal to noise ratio, Massive MIMO, Standards
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1109/TWC.2023.3326453
