基于APG合并及拓扑势优化的启发式用户关联策略

doi:10.11959/j.issn.1000-436x.2022121

通信学报 ›› 2022, Vol. 43 ›› Issue (6): 98-107.doi: 10.11959/j.issn.1000-436x.2022121

基于APG合并及拓扑势优化的启发式用户关联策略

胡志蕊, 毕美华, 许方敏, 何美霖, 郑长亮

杭州电子科技大学通信工程学院，浙江杭州 310018

修回日期:2022-04-18 出版日期:2022-06-01 发布日期:2022-06-01
作者简介:胡志蕊（1987- ），女，山东德州人，博士，杭州电子科技大学讲师，主要研究方向为协作通信、资源分配、信能同传技术
毕美华（1981- ），女，山东济宁人，博士，杭州电子科技大学副教授，主要研究方向为光与无线融合接入、新型光接入网系统的物理层安全、可重构的智能数据中心网络系统、IMDD/相干光传输系统中的新型均衡算法等
许方敏（1980- ），女，浙江瑞安人，博士，杭州电子科技大学讲师，主要研究方向为小区间干扰抑制、无线资源管理、MIMO建模及干扰删除等
何美霖（1986- ），女，湖南衡阳人，博士，杭州电子科技大学讲师，主要研究方向为 NOMA、多速率编码、多用户信息论和无线通信等
郑长亮（1980- ），男，河北唐山人，博士，杭州电子科技大学讲师，主要研究方向为无线通信、移动通信等
基金资助:
浙江省自然科学基金资助项目(LY22F010012);浙江省自然科学基金资助项目(LY20F050004);浙江省自然科学基金资助项目(LQ20F010007);国家自然科学基金资助项目(62101169);江苏省新型光纤技术与通信网络工程研究中心开放研究课题基金资助项目(SDGC2120);毫米波国家重点实验室开放课题基金资助项目(K202111)

APG mergence and topological potential optimization based heuristic user association strategy

Zhirui HU, Meihua BI, Fangmin XU, Meilin HE, Changliang ZHENG

School of Communication Engineering, Hangzhou Dianzi University, Hangzhou 310018, China

Revised:2022-04-18 Online:2022-06-01 Published:2022-06-01
Supported by:
Zhejiang Provincial Natural Science Foundation of China(LY22F010012);Zhejiang Provincial Natural Science Foundation of China(LY20F050004);Zhejiang Provincial Natural Science Foundation of China(LQ20F010007);The National Natural Science Foundation of China(62101169);The Project of Jiangsu Engineering Research Center of Novel Optical Fiber Technology and Communication Network, Soochow University(SDGC2120);The Open Grant of State Key Laboratory of Millimeter Waves(K202111)

摘要/Abstract

摘要：

目的：去蜂窝网络通过接入点（AP）间协同服务网络内的用户，可突破传统蜂窝网络因密集小区间干扰造成的性能瓶颈，但需要大量的信息交互及信号处理，导致网络的可扩展性较差。为此，本文研究可提升去蜂窝网络可扩展性的用户关联策略。

方法：设计网络可扩展度作为可扩展性的衡量指标，以此为基础，利用优化理论研究提高网络可扩展度的用户关联策略。1）优化问题建模方面，首先，以节点间关联度是影响网络可扩展度的关键因素为突破点，构造表征节点间关联度的网络耦合度指标，以此建立起网络可扩展度与接入点簇（APG）间的数学关系，从而将提高网络可扩展度问题建模为最小化网络耦合度问题。然后，建立网络耦合度最小和用户速率最大的多目标优化问题，以此寻求网络可扩展度与网络服务质量的均衡。2）优化问题求解方面，为避免求解多目标优化问题的高计算复杂度，提出基于APG合并及拓扑势优化的启发式算法。所提算法通过APG合并的方式降低APG数目，并通过AP退出APG的方式降低AP所属APG的数目，从而降低网络耦合度，提高网络可扩展度。在APG合并方面，定义 $β {I, J} = 2 | I \cap J | / (| I | + | J |)$ 表示集合 $I, J$ 间的重叠率，并将重叠率超过一定门限值的APG进行合并；在AP退出APG方面，利用拓扑势函数建立网络耦合度和用户速率的关系，以此作为AP选择退出APG的性能指标。

结果：1）问题建模的合理性方面，如图2和图5所示，网络可扩展度η与网络耦合度κ的大小成反比，因此将提高网络可扩展度问题建模为最小化网络耦合度问题是合理的，通过降低网络耦合度来提高网络可扩展度是可行的；2）启发式算法的计算复杂度方面，所提算法的计算复杂度上限为 $O (K N \log_{2} N + k^{2} + N N {\bar{N}}_{p})$ ，而直接求解优化问题的计算复杂度为 $O (N^{{\bar{N}}_{u} K})$ ;3）网络可扩展度的理论分析方面，以图3为例，假设AP2发生变动，图3(a)中受影响的AP有12个，网络可扩展度为η₂=0.51，而图3(c)中受影响的AP有4个，网络可扩展度为η₂=0.79;4）网络可扩展度的仿真验证方面，如图5所示，与传统策略相比，用户速率损失4.43%时，可扩展度可提高9.59%；与文献[10]的策略相比，用户速率损失4.99%时，可扩展度可提高22.15%;5）所提算法中重叠率门限β₀和AP所关联AP数上限N₀的影响方面，如图6所示，随着β₀或N₀的减小，h提高，用户总速率降低。随着 ${\bar{N}}_{p}$ 的增大，β₀的影响度增加，N₀的影响度降低。以 ${\bar{N}}_{p} = 40, 60$ 为例，β₀=0.5和β₀=0.9间h的差距由5.97%增大到14.17%，用户速率差距由47 bit/(s·Hz)增大到155 bit/(s·Hz)；而N₀=20和N₀=60间η的差距由1.4%减小到0.4%，用户速率差距由76 bit/(s·Hz)减小到29 bit/(s·Hz)。

结论：所提用户关联策略以较小的用户速率损失为代价，提高了去蜂窝网络的可扩展度。所提策略中重叠率门限或AP所关联AP数上限越小，则网络可扩展度提升越多，速率损失越大。

关键词: 去蜂窝网络, 用户中心网络, 可扩展性, 用户关联策略

Abstract:

Objective: In cell-free networks, access points (AP) collaborate to serve users. This coordination can break the performance bottleneck of traditional cellular network caused by inter-cell interference. However, it needs significant amounts information interaction and signal processing, which results in poor scalability. This paper studied the user association strategy that could improve the scalability of cell-free networks.

Methods:The network scalable degree was designed as a measure of scalability,and then a user association strategy to improve network scalable degree was studied by using optimization theory. 1) For modelling the optimization problem, firstly, the network coupling degree, representing the degree of association among nodes, was constructed to establish the mathematical relationship between the network scalable degree and AP group (APG).Thus,the problem of improving the network scalable degree was modeled as the problem of minimizing the network coupling degree.Then,a multi-objective optimization problem of minimum network coupling degree and maximum user rate was established to find the balance between network scalable degree and network service quality. 2) For solving the optimization problem,to avoid the high computational complexity,a heuristic user association strategy based on APG mergence and topological potential optimization was proposed.With the proposed algorithm,the number of APG could be reduced by APG mergence,and the number of APG that AP belongs to could be reduced by AP exiting APG. Thus,it can reduce the network coupling degree and improve the network scalable degree. For APG mergence, $O (K N \log_{2} N + k^{2} + N N {\bar{N}}_{p})$ was defined as the overlap rate between set $I, J$ , and the APG whose overlap rate exceeds a certain threshold value would be merged. In terms of AP exiting APG, the relationship between network coupling degree and user rate was established by topological potential function,which was used as the performance index of AP exiting APG.

Results:1)For the rationality of problem modeling,Fig.2 and Fig.5 show that the network scalable degree is inversely proportional to the network coupling degree. Therefore, it is reasonable to model the problem of improving network scalable degree as minimizing network coupling degree,and it is feasible to improve network scalable degree by reducing network coupling degree.2)The upper limit of computational complexity of the proposed algorithm is $O (K N \log_{2} N + k^{2} + N N {\bar{N}}_{p})$ ,while that of directly solving the optimization problem is $O (N^{{\bar{N}}_{u} K})$ .3)For theoretical analysis of the network scalable degree,take Fig.3 as an example.If AP2 changes,12 APs in Fig. 3(a)are affected and the network scalable degree is η₂=0.51,while 4 APs in Fig.3(c)are affected and the network scalable degree is η₂=0.79.4)Fig.5 shows the simulation results of network scalable degree.Compared with the traditional strategy,the network scalable degree is improved by 9.59% with 4.43% user rate loss.Compared with the strategy in[10],the network scalable degree is improved by 22.15% with 4.99% user rate loss. 5) The algorithm parameters, the threshold β₀of overlap rate and the upper limit number N₀of AP associated, effect the performance.As shown in Fig.6,with β₀or N₀decreases,η increases and the total user rate decreases. With ${\bar{N}}_{p}$ increases,the effect of β₀increases and that of N₀decreases.Take ${\bar{N}}_{p} = 40, 60$ as an example.The η gap between β₀=0.5 and β₀=0.9 increases from 5.97% to 14.17%, and the user rate gap increases from 47 bit/(s·Hz) to 155 bit/(s·Hz). The η gap between N₀ =20 and N₀ =60 decreases from 1.4% to 0.4%, and the user rate gap decreases from 76 bit/(s·Hz)to 29 bit/(s·Hz).

Conclusions: The proposed user association strategy can improve the network scalable degree of cell-free networks at the cost of less rate loss. The smaller the overlap rate threshold or the upper limit of APs associated with an AP,the more the network scalable degree increases and the greater the rate loss.

Key words: cell-free network, user-centric network, scalability, user association strategy

中图分类号:

TN929.5

胡志蕊, 毕美华, 许方敏, 何美霖, 郑长亮. 基于APG合并及拓扑势优化的启发式用户关联策略[J]. 通信学报, 2022, 43(6): 98-107.

Zhirui HU, Meihua BI, Fangmin XU, Meilin HE, Changliang ZHENG. APG mergence and topological potential optimization based heuristic user association strategy[J]. Journal on Communications, 2022, 43(6): 98-107.

图/表 7

表1

参数的含义"

参数	含义
N、K、N_t	AP数、用户数、AP的天线数
$N, K$	AP集合、用户集合
$X = {x_{i, k}}$	用户与AP间的关联矩阵
${\bar{N}}_{u}, {\bar{N}}_{p}$	AP可服务的用户数上限，用户关联的AP数上限
$g_{k}$	用户k的主AP
${\bar{G}}_{k}, G_{k}$	用户k的CAPG及APG
$C_{l}$	不完全重叠的APG
$U_{i}, V_{l}$	AP i服务的用户集合，APG $C_{l}$ 服务的用户集合
$T_{i}$	AP i所属的APG $G_{k}$ 集合
$η_{i}, η$	节点i变动下的网络可扩展度，网络可扩展度
$κ$	网络耦合度
$r_{i, k}, r_{k}$	用户k接收的来自AP i的速率，用户k的速率

表1

图1

图2

图3

图4

图5

图6

参考文献 12

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[8]	BJ?RNSON E , SANGUINETTI L . Scalable cell-free massive MIMO systems[J]. IEEE Transactions on Communications, 2020,68(7): 4247-4261.
[9]	CHEN S F , ZHANG J Y , BJ?RNSON E , ,et al. Structured massive access for scalable cell-free massive MIMO systems[J]. IEEE Journal on Selected Areas in Communications, 2021,39(4): 1086-1100.
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基于APG合并及拓扑势优化的启发式用户关联策略

APG mergence and topological potential optimization based heuristic user association strategy

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