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Energy and Spectrum Efficient User Association in 5G Heterogeneous Networks
Abstract and Figures
Due to the dense small cell deployment to cope with the increased data traffic of fifth generation (5G) networks, the direct backhaul (BH) connection of all small cells to the core network becomes challenging. To that end, millimeter wave (mmWave) is a promising solution for cost-efficient high capacity small cell BH links. However, due to the severe signal attenuation at high frequencies, mmWave can provide good coverage only for short distances, thus favoring a multi-hop 5G BH architecture. In this context, user association that impacts both the network and user performance calls for BH-aware strategies. Hence, in this paper, we study the user association problem aiming at the joint energy and spectrum efficiency maximization of the network, without compromising the user quality of service. The problem is formulated as a generalized assignment problem, which considers the capacity and energy consumption both in the access network and BH links. Provided that the considered problem is shown to be NP-hard, we employ optimization techniques to obtain an upper bound on system performance. We also propose a low complexity algorithm, which is shown to outperform the stateof- the-art while achieving near-optimal performance.
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... We may observe that D2D communications can be optimized in multiple aspects, of which QoS is extremely important from the perspective of users. Researchers have proposed energy and spectrum efficient algorithms for multihop 5G backhaul links, based on user association criteria, and optimal solutions have been derived for the given conditions [23]. Other multi-hop schemes for 5G networks have relied on offloading data to one user through another user requesting the same data at the same time [24]. ...
... SINR is also calculated using standard expressions for input power, path losses, thermal noise, noise figures, gains of the transmitter and receiver as well as fading losses [23] and interference [5,25,26]. ...
... MATLAB has been used for purposes of simulation since programming in MATLAB has allowed us the ease to process data in matrix form, allow the simulation of addition of nodes with randomized parameters, as well as obtain graphical outputs in a simple manner. We simulate the Evolutionary Game described in the previous section using known mathematical models for path loss [5] and interference [5,25,26], SINR (and experimental SINR datasets obtained by researchers) [1,5,23] and randomize the battery charge currently remaining, for all players to calculate the number of players forming D2D links by the three strategies (S,S), (B, B) and (P,P) where the (P,P) strategy involves link formation on the basis of path loss parameter. Then we introduce new players into the population and again calculate the number of players forming D2D linkages by the opposing strategies. ...
5G communication networks will dominate the global communications market in the next few years. Researchers working in the domain of 5G communication technologies are currently in the process of determining how device-to-device (D2D) communication networks may offer great benefits in urban metropolitan environments, due to their features. D2D networks can therefore offer an effective means to supplement the standard cellular communication networks, thereby reducing the load on the standard cellular networks while maintaining or enhancing the quality of service. In this work, we have discussed a user association scheme to determine optimal associations in D2D wireless networks based on game theory by deriving the Nash Equilibrium for games involving each pair of devices, using parameters such as SINR (signal to interference and noise ratio), path loss and battery charge remaining for each device acting as a node in the network. Further, we have developed an evolutionary game theoretic model for D2D link formation in the network when nodes are dynamically added, which, when simulated, can help identify an evolutionarily stable strategy or ESS.
... 4) While certain research efforts discuss the computational complexity of the non-linear optimization framework for the user association problem, e.g. [22], [24], [33], [34], none of these works provision a detailed analysis with regards to the computation time, solvability, as well as other network parameters such as achieved latency and backhaul utilization. ...
... Lastly, multiple studies such as [22], [24], [33], [34] propose a joint optimization approach towards user association. In these studies the objective function is maximized/minimized, depending on the utility, and an optimal association strategy that provisions the same is determined. ...
... However, a relaxation of these decision variables or a decomposition into simpler sub problems is in general possible. And so, in [22], [24], [33], [34] such techniques have been utilized and a discussion on the optimal solution obtained has been presented. ...
In this paper, we provide a novel application aware user association and resource allocation framework, i.e., AURA-5G, which utilizes a joint optimization strategy to accomplish the same. Concretely, our methodology considers all the real network constraints that will be prevalent in the 5G networks as well as practical deployment scenarios. Furthermore, AURA-5G, being an application aware framework, considers the resource requirements of both eMBB and mMTC services whilst performing the optimization task. We have demonstrated that our strategy performs significantly better than the baseline algorithm, given any of the multiple combinations of network constraints explored in this paper. In addition, we have also presented a novel computational complexity analysis for the AURA-5G framework as well as a solvability and convergence time analysis. Such an analysis will be beneficial for both industry and academia in determining the applicability and performance of the AURA-5G framework, given the scenario and constraints. Lastly, we have also provisioned a short study on the aspect of network re-dimensioning, wherein we demonstrate the efficacy of the AURA-5G framework in providing insights to the operators with regards to their deployment and how they can utilize it to optimize the performance of their networks.
... The work of [15] introduced a heuristic method to jointly maximize the spectral and energy efficiency of HetNet by formulating the problem as a generalized assignment problem. In [16], Niu et al. considered a multi-objective optimization problem by modeling the traffic delay and the power consumption as the performance objectives. ...
Heterogeneous networks (HetNets) are a promising communication paradigm to satisfy the diverse requirements of Long Term Evolution-Advanced (LTE-A). Associating users with different base station tiers using the conventional technique based on the highest received SINR is not viable in HetNets due to its rigid association, which only aims at throughput maximization. Many e orts have been made to tackle the optimization problem of user association with a single objective such as throughput, fairness or energy efficiency. In this paper, we propose a novel multi-objective user association technique using particle swarm optimization (PSO) with the aim of jointly maximizing the throughput and the network balance index (NBI). By incorporating weight factors into the proposed scheme, the system operator has the flexibility to configure the priority levels of throughput and NBI. Numerical results demonstrate that our proposed multi-objective user association technique achieves better performance in terms of fitness values compared to the single-objective user association schemes.
... The authors in [7] considered a resource allocation framework to maximize the sum-rate on a per resource block (RB) basis while the authors in [8], [9] explored the joint RB assignment and power allocation to maximize the sum throughput. Similarly, the authors in [10] focused on the EE through joint mobility (handover) and power allocation optimization while SE-EE trade-off was considered via user association optimization in [11] and interference management for UDNs via coalition game formation approach in [12]. ...
Scheduling algorithms allocate radio resources to optimize network efficiency with respect to some competing performance metrics. Common schedulers include the Round Robin (RR), Proportional Fair (PF) and the Best Channel Quality Indicator (Best CQI) schedulers, as well as their different variants, modified or hybrid versions. RR promotes fairness, Best CQI targets increased throughput while PF guarantees a balance in the fairness and throughput objectives of the network. In this paper, we propose a multi-objective hybrid scheduler (MOHS), a hybrid of RR and Best CQI schedulers, that adapts the scheduling policy by toggling between RR and Best CQI schedulers to optimize system performance. The results show that the proposed scheduler provides higher spectral efficiency, energy efficiency and area network capacity than RR and PF, as well as significantly higher fairness than the Best CQI scheduler. By improving multiple system objectives, MOHS enables efficient radio resource allocation that optimizes the network efficiency for ultra-dense 5G networks and beyond.
Macro base stations are overlaid by small cells to satisfy the demands of user equipment in heterogeneous networks. To provide wide coverage, some small cells are not directly connected to macro base stations and thus backhaul connections are required to connect small cells to macro base stations. Millimeter wave backhauls which have high bandwidths are preferred for small cell backhaul communication, since they can increase the capacity of network considerably. In this context, association of user equipment to base stations becomes challenging due to the backhaul architecture. Considering environmental concerns, energy efficiency is a vital criterion in designing user association algorithms. In this paper, we study the user association problem aiming at the maximization of energy efficiency given a specific spectral efficiency target. We develop centralized and distributed user association algorithms based on sequentially minimizing the power consumption. Finally, we evaluate the performance of the proposed algorithms under two scenarios and show that they achieve higher energy efficiency compared to the existing algorithms in the literature, while maintaining high spectral efficiency and backhaul load balancing.
5G wireless networks will be extremely dense, given the projected increase in the number of users and access points (APs), as well as heterogeneous, given the different types of APs and the applications being accessed by the users. In such challenging environments, efficient mobility management (MM), and specifically user association, will be critical to assist the 5G networks in provisioning the Quality of Service (QoS) of diverse applications 5G targets to serve. Whilst determining the most suitable AP for the users, multiple constraints such as available backhaul capacity, link latency, etc., will need to be accommodated for. Hence, to provide an optimal user association solution, in this paper we present a joint optimization framework, namely AURA-5G. Under this framework we formulate our user association strategy as a Mixed Integer Linear Program (MILP) that aims to maximize the total sum rate of the network whilst optimizing the bandwidth assignment and access point selection. We analyze multiple active application profiles simultaneously, i.e. enhanced Mobile Broadband (eMBB) and massive Machine Type Communication (mMTC), in the network and study the performance of AURA-5G. Additionally, we provision a novel study on the multiple dual connectivity modes, wherein the user can be connected to either one macro cell and a possible small cell, or with any two favorable candidate access points. Utilizing the AURA-5G framework, we perform a novel comparative study of all the considered scenarios on the basis of total network throughput, performance against baseline scenario and system fairness. We show that the AURA-5G optimal solutions improve the performance of different network scenarios in terms of total network throughput (by 38×–690×) and system fairness as compared to the baseline scenario, which is a conventional user association solution. Further, we also present a fidelity analysis of the AURA-5G framework based on the backhaul utilization, latency compliance, convergence time distribution and solvability. And since, a given network cannot always guarantee to satisfy the future network loads and application constraints, we show that AURA-5G can be utilized by the operators/vendors to evaluate the myriad network re-dimensioning approaches for attaining a feasible and optimal solution. Henceforth, we then explore the possibility of network re-dimensioning and study its impact on system performance for scenarios where the performance of AURA-5G is severely impacted due to the extremely strict nature of the constraints imposed in the MILP.
<<Accepted for publication in IEEE WCNC 2021>>
The Third Generation Partnership Project (3GPP) Fifth Generation (5G) network employs Software Defined Networking (SDN) paradigm allowing for a clear separation of control and data plane functionalities in the 5G network. However, the control plane in a 5G network not only performs network control tasks involving control and management of data plane functions but is also responsible for executing UE-specific control tasks. We think these two tasks are independent of each other and 5G and beyond mobile networks. The paper presents preliminary analysis and evaluation of the proposed architecture through flow diagrams. As demonstrated, 5G-Serv simplifies the information flow in the 5G network and enhances its modularity and flexibility. The architecture may also be better aligned with the standard SDN paradigm vis-a-vis the 3GPP architecture.
A user-centered network model can significantly optimize connectivity issues between a user and the corresponding base station (BS). This article shall evaluate the user-centric (UC) model targeted for Fifth Generation telecommunication systems and will attempt to optimize communication between users and BSs. The authors suggest a resource-aware mechanism that targets improving coverage through the network decoupling into two separate and independent uplink and downlink networks. The mechanism shall fully respect each user's initially requested throughput demands and aims to solve the network user BS association problem with efficient resource management techniques. Simulations revealed that the mechanism perfectly preserves quality of service (QoS) and offers increased data rates in favor of ultimate user coverage, in both scenarios. Additionally, Frequency Range 2 offers an increased amount of resources, both increased data rates and higher amounts of devices that are covered by the overall network.
Current cellular spectrum at below 3 GHz bands is experiencing severe shortage and cannot keep up with the dramatic proliferation of mobile traffic in the near future, requiring the search for innovative solutions to enable the 5G era. mmWave communications, with a possible gigabit-per-second data rate, have attracted great attention as a candidate for 5G broadband cellular communication networks. However, a complete characterization of mmWave links for 5G wireless networks still remains elusive and there are many challenges and research areas that need to be addressed. In this work we discuss several key elements to enable mmWave communications in 5G: · Channel characteristics regarding mmWave signal attenuation due to free space propagation, atmospheric gaseous and rain are explained. · The hybrid (digital plus analog) beamforming architecture in mmWave system is discussed. · The blockage effect in mmWave communications due to penetration loss and possible approaches are presented. · The application of mmWave transmission with narrow beams in non-orthogonal device-todevice communication is proposed. · mmWave transmission in the booster cell of heterogeneous anchor-booster networks. · mmWave transmission for small cell backhaul is further discussed.
Due to the ever increasing data traffic demands, which are directly connected to increased energy consumption, it becomes challenging for operators to achieve capacity enhancement while limiting their electric bill. To that end, exploiting the context awareness of future cognitive networks is expected to play a key role. Next generation cellular networks are about to include a plethora of small cells, with users being able to communicate via multiple bands. Given that small cells are expected to be eventually as close as 50 m apart, not all of them will have a direct connection to the core network; thus, multihop communication through neighboring small cells may be required. In such architectures, the user association problem becomes challenging, with backhaul energy consumption being a definitive parameter. Thus, in this article, we study the user association problem in cognitive heterogeneous networks. We evaluate the existing approaches in terms of energy efficiency and show the potential of exploiting the available context-aware information (i.e., users’ measurements and requirements, knowledge of the network architecture, and the available spectrum resources of each base station) to associate the users in an energy-efficient way, while maintaining high spectrum efficiency. Our study considers both the access network and backhaul energy consumption, while the performance of the association algorithms is evaluated under two different case study scenarios.
Cellular networks are in a major transition from a carefully planned set of large tower-mounted base-stations (BSs) to an irregular deployment of heterogeneous infrastructure elements that often additionally includes micro, pico, and femtocells, as well as distributed antennas. In this paper, we develop a tractable, flexible, and accurate model for a downlink heterogeneous cellular network (HCN) consisting of K tiers of randomly located BSs, where each tier may differ in terms of average transmit power, supported data rate and BS density. Assuming a mobile user connects to the strongest candidate BS, the resulting Signal-to-Interference-plus-Noise-Ratio (SINR) is greater than 1 when in coverage, Rayleigh fading, we derive an expression for the probability of coverage (equivalently outage) over the entire network under both open and closed access, which assumes a strikingly simple closed-form in the high SINR regime and is accurate down to -4 dB even under weaker assumptions. For external validation, we compare against an actual LTE network (for tier 1) with the other K-1 tiers being modeled as independent Poisson Point Processes. In this case as well, our model is accurate to within 1-2 dB. We also derive the average rate achieved by a randomly located mobile and the average load on each tier of BSs. One interesting observation for interference-limited open access networks is that at a given sinr, adding more tiers and/or BSs neither increases nor decreases the probability of coverage or outage when all the tiers have the same target-SINR.
To meet the ever-increasing traffic demands, future cellular networks are about to include a plethora of small cells (SCs), with user equipments (UEs) being able of communicating via multiple bands. Given that SCs are expected to be eventually as close as 50 m apart, some of them will not have a direct connection to the core network, and thus will forward their traffic to the neighboring SCs until they reach it. In such architectures, the user association problem becomes challenging with backhaul (BH) energy consumption playing a key role. Thus, in this paper, we study the user association problem aiming at maximizing the network energy efficiency. The problem is formulated as an optimization problem, which is NP-hard. Therefore, we propose a cognitive heuristic algorithm that exploits context-aware information (i.e., UE measurements and requirements, the HetNet architecture knowledge and the available spectrum resources of each base station (BS)) to associate the UEs in an energy-efficient way, while considering both the access and the BH energy consumption. We evaluate the performance of the proposed algorithm under two study-case scenarios and we prove that it achieves significantly higher energy efficiency than the reference algorithms, while maintaining high spectral efficiency.
The aim of this book is to present the modern design and analysis principles of millimeter-wave communication system for wireless devices and to give postgraduates and system professionals the design insights and challenges when integrating millimeter wave personal communication system. Millimeter wave communication system are going to play key roles in modern gigabit wireless communication area as millimeter-wave industrial standards from IEEE, European Computer Manufacturing Association (ECMA) and Wireless High Definition (Wireless HD) Group, are on their way to the market. The book will review up-to-date research results and utilize numerous design and analysis for the whole system covering from Millimeter wave frontend to digital signal processing in order to address major topics in a high speed wireless system. This book emphasizes the importance and the requirements of high-gain antennas, low power transceiver, adaptive equalizer/modulation, channeling coding and adaptive multi-user detection for gigabit wireless communications. In addition, the book will include the updated research literature and patents in the topics of transceivers, antennas, MIMO, channel capacity, coding, equalizer, Modem and multi-user detection. Finally the application of these antennas will be discussed in light of different forthcoming wireless standards at V-band and E-band.
The problem of joint downlink cell association (CA) and wireless backhaul
bandwidth allocation (WBBA) in two-tier cellular heterogeneous networks
(HetNets) is considered. Large-scale antenna array is implemented at the macro
base station (BS), while the small cells within the macro cell range are
single-antenna BSs and they rely on over-the-air links to the macro BS for
backhauling. A sum logarithmic user rate maximization problem is investigated
considering wireless backhauling constraints. A duplex and spectrum sharing
scheme based on co-channel reverse time-division duplex (TDD) and dynamic soft
frequency reuse (SFR) is proposed for interference management in two-tier
HetNets with large-scale antenna arrays at the macro BS and wireless
backhauling for small cells. Two in-band WBBA scenarios, namely, unified
bandwidth allocation and per-small-cell bandwidth allocation scenarios, are
investigated for joint CA-WBBA in the HetNet. A two-level hierarchical
decomposition method for relaxed optimization is employed to solve the
mixed-integer nonlinear program (MINLP). Solutions based on the General
Algorithm Modeling System (GAMS) optimization solver and fast heuristics are
also proposed for cell association in the per-small-cell WBBA scenario. It is
shown that when all small cells have to use in-band wireless backhaul, the
system load has more impact on both the sum log-rate and per-user rate
performance than the number of small cells deployed within the macro cell
range. The proposed joint CA-WBBA algorithms have an optimal load approximately
equal to the size of the large-scale antenna array at the macro BS. The cell
range expansion (CRE) strategy, which is an efficient cell association scheme
for HetNets with perfect backhauling, is shown to be inefficient when in-band
wireless backhauling for small cells comes into play.
In order to expand the downlink (DL) coverage areas of picocells in the presence of an umbrella macrocell, the concept of range expansion has been recently proposed, in which a positive range expansion bias (REB) is added to the DL received signal strengths (RSSs) of picocell pilot signals at user equipments (UEs). Although range expansion may increase DL footprints of picocells, it also results in severe DL inter-cell interference in picocell expanded regions (ERs), because ER picocell user equipments (PUEs) are not connected to the cells that provide the strongest DL RSSs. In this paper, we derive closed-form formulas to calculate appropriate REBs for two different range expansion strategies, investigate both DL and uplink (UL) inter-cell interference coordination (ICIC) to enhance picocell performance, and propose a new macrocell–picocell cooperative scheduling scheme to mitigate both DL and UL interference caused by macrocells to ER PUEs. Simulation results provide insights on REB selection approaches at picocells, and demonstrate the benefits of the proposed macrocell–picocell cooperative scheduling scheme over alternative approaches.
