Abstract
We address the problem of access point (AP) placement in small-cell networks with partial infrastructure flexibility, i.e., a novel class of problem in Beyond 5G, resultant from the utilization of unmanned aerial vehicles (UAVs) with AP functionalities (UAV-APs), to aid fixed wireless networks in coping with momentary peak-capacity requirements. We use the signal-to-generated-interference-plus-noise ratio (SGINR) metric as an alternative to the traditional signal-to-interference-plus-noise ratio (SINR) to quantify the effects of inter-cell interference (ICI) on the per-user capacity. From average SGINR, we derive the ICI-aware distortion measure leading to the Inter-AP Lloyd algorithm to obtain throughput-optimal AP placement for a fully flexible infrastructure. We then impose a hybridity constraint to the AP placement problem which turns a fraction of the network into a fixed infrastructure composed of terrestrial APs (T-APs) while the remainder is constituted by UAV-APs with flexibility in position. This newly formulated AP placement problem is solved by the proposed Lloyd-type algorithm called Hybrid AP Placement Algorithm (HAPPA). Furthermore, we present an initialization method for the Lloyd and Lloyd-type algorithms for Gaussian mixture models (GMMs) that offers an AP allocation leading to a higher rate compared to the k-means++ initialization. Finally, computer simulations show that the Inter-AP Lloyd algorithm can improve the performance of the worst users by up to 42.75% in achievable rate, assuming a fully flexible network. By using HAPPA on hybrid networks, we achieve improvements of up to 71.92% in sum rate over the fixed network and close the performance gap with fully flexible networks down to 2.02%, when an equal number of UAV-APs and T-APs is used. Further, our proposed initialization scheme always results in a balanced AP allocation, which means a more even distribution of users per AP, whereas the k-means++ scheme results in unbalanced allocations at least 30% of the time, resulting in a worse minimum rate.
Highlights
M ASSIVE multiple-input-multiple-output (MIMO) systems have emerged as a prevalent technology for the fifth generation (5G) of wireless communication systems [1]– [5]
For the proposed Hybrid AP Placement Algorithm (HAPPA), we evaluate the effects of access point (AP) placement on the throughput performance of the hybrid network as we add additional unmanned aerial vehicles (UAVs)-APs under the Gaussian mixture models (GMMs)-2 configuration
We have addressed the AP placement problem in the small-cell uplink paradigm for hybrid network composed of terrestrial APs (T-APs) and AP-enabled UAVs (UAV-APs) in the presence of inter-cell interference (ICI)
Summary
M ASSIVE multiple-input-multiple-output (MIMO) systems have emerged as a prevalent technology for the fifth generation (5G) of wireless communication systems [1]– [5]. We investigate the AP placement problem, with the objective of maximizing throughput in a small-cell system, with prevalent ICI and varying user distributions. Based on the Inter-AP Lloyd algorithm, we formulate and develop an algorithm for hybrid networks that places UAV-APs in an area occupied by T-APs currently providing sub-optimal throughput performances due to a change in user configuration. This is the Hybrid AP Placement Algorithm (HAPPA) that outperforms the T-APs (fixed network) alone.
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