Three-tier Heterogeneous Network Research Articles

A congestion-aware user–cell association scheme to assist with traffic offloading in a three-tier heterogeneous network

In this work, we aim to expand the cell range in congestion areas. To achieve this goal, we integrate UAV network into macro–micro cellular network to enhance coverage. However, the gain of deploying heterogeneous nodes is limit if there are no CRE (cell range expanding)-based method to steer users towards low-power nodes. Therefore, in order to further improve system access capacity, we propose a congestion-aware UA (user–cell association) scheme to offload queued traffic of cellular network into UAV network. To verify the superiority of proposed scheme, we utilize the low-complexity SG (stochastic-geometry) methods. Then in simulation analysis phase, we obtain five primary results: (a). The SG-based methods have lower computation complexity, and the convergence of derived expressions are verified. (b). The SG-based methods do not need the exact users’ location but the users’ density, which have improved the operability and robustness in infrastructure construction of wireless network. (c). The congestion-aware UA scheme can prompt network to adjust association tier flexibly, which is very suitable for traffic unevenly-distributed regions. (d). The optimal offsets of virtual power are estimated as B2 = −4 dB for small-cell and B3 = 3 dB for drone-cell, the resulting improvement in communication capacity is 8%. (e). We suggest the deployment density of UAV sites will no need to exceed λ3 = 41 (pks/km2).

ADV-LEACH2 Energy-Efficient Clustering Protocols for Three-Tier Heterogeneous Wireless Sensor Networks

This paper presents energy-efficient clustering protocols for three-tier heterogeneous wireless sensor networks (WSNs) along with their applications to the systems. The performance of a new dynamic, modified, probability-based approach to finding the most energy-efficient cluster head nodes is intended to extend network lifetime. Mathematical modeling and simulation results from using MATLAB-2017b provide a comparative analysis of several heterogeneous and homogeneous WSN variants in terms of energy consumption, active versus dead nodes, and network lifetime based on first node dead (FND) and last node dead (LND). ADV-LEACH2 in a three-tier heterogeneous network performs better than homogeneous and two-tier heterogeneous networks owing to super nodes with higher energy levels.

An Interference-Managed Hybrid Clustering Algorithm to Improve System Throughput.

In the current smart era of 5G, cellular devices and mobile data have increased exponentially. The conventional network deployment and protocols do not fulfill the ever-increasing demand for mobile data traffic. Therefore, ultra-dense networks have widely been suggested in the recent literature. However, deploying an ultra-dense network (UDN) under macro cells leads to severe interference management challenges. Although various centralized and distributed clustering methods have been used in most research work, the issue of increased interference persists. This paper proposes a joint small cell power control algorithm (SPC) and interference-managed hybrid clustering (IMHC) scheme, to resolve the issue of co-tier and cross-tier interference in the small cell base station cluster tiers. The small cell base stations (SBSs) are categorized based on their respective transmitting power, as high-power SBSs (HSBSs) and low-power SBSs (LSBSs). The simulation results show that by implementing the IMHC algorithm for SBSs in a three-tier heterogeneous network, the system throughput is improved with reduced interference.

Energy Efficiency and Hover Time Optimization in UAV-Based HetNets

In this article, we investigate the downlink performance of a three-tier heterogeneous network (HetNet). The objective is to enhance the edge capacity of a macro cell by deploying unmanned aerial vehicles (UAVs) as flying base stations and small cells (SCs) for improving the capacity of indoor users in scenarios such as temporary hotspot regions or during disaster situations where the terrestrial network is either insufficient or out of service. UAVs are energy-constrained devices with a limited flight time, therefore, we formulate a two layer optimization scheme, where we first optimize the power consumption of each tier for enhancing the system energy efficiency (EE) under a minimum quality-of-service (QoS) requirement, which is followed by optimizing the average hover time of UAVs. We obtain the solution to these nonlinear constrained optimization problems by first utilizing the Lagrange multipliers method and then implementing a sub-gradient approach for obtaining convergence. The results show that through optimal power allocation, the system EE improves significantly in comparison to when maximum power is allocated to users (ground cellular users or connected vehicles). The hover time optimization results in increased flight time of UAVs thus providing service for longer durations.

A Pilot Allocation Scheme Based on Joint User Classification and Coalition Game for Massive MIMO Three-Tier HetNets

Many researches demonstrate that pilot contamination is a major factor that affects the overall performance of massive MIMO systems. Based on this, this paper proposes a dynamic pilot allocation scheme based on joint user classification and coalition game (JUC-CG) to mitigate pilot contamination for Massive MIMO Three-tier heterogeneous networks (HetNets). It contains two steps: (1) According to the constraint in definition 2, the users are divided into two classes, namely A1 and A2. Users in pico-cell and sufferred from strong interference are classified into class A1, and remaining users of HetNets are classified into class A2. (2) The users of class A1 use a set of orthogonal pilots, and the users of class A2 reuse another set of orthogonal pilots by means of coalition game. In the coalition game for the users of class A2, users are divided into several disjoint user sub-coalitions, users belonging to different sub-coalitions are allocated different orthogonal pilot sequences, and users in the same sub-coalition reuse the same pilot sequence. The corresponding pilot allocation algorithm of JUC-CG is given. From the algorithm, we can see that JUC-CG scheme is flexible and can be used for scenarios that all users and base stations (BSs) are randomly distributed (such as multi-tier HetNets, ultra-dense HetNets and so on). In addition, the pilot allocation algorithm can obtain the overall optimal solution through cyclic searching. The simulation results demonstrate that the JUC-CG scheme can effectively reduce the average mean square error (MSE) of user signal detection and improve spectral efficiency (SE) in the uplink.

Performance Analysis of Weighted Rank Constrained Rank Minimization Interference Alignment for Three-Tier Downlink Heterogeneous Networks

Performance Analysis of Weighted Rank Constrained Rank Minimization Interference Alignment for Three-Tier Downlink Heterogeneous Networks

Conditional dual‐connectivity decoupling design framework for OMA and NOMA heterogeneous networks and performance comparison

In order to enhance simultaneously the association robustness of mobile users and spectrum efficiency (SE) of systems, by integrating the decoupled uplink (UL)/downlink (DL) association (DUDA) and cross-tier dual connectivity (DC), the orthogonal multiple access (OMA)-mode and non-OMA (NOMA)-mode design schemes are investigated over a three-tier heterogeneous network (HetNet) accompanying with the proposition of a conditional association analysis method. The scheme exploits effectively the DC requirement of NOMA. Additionally, in the proposed conditional association design and analysis method, the decoupling UL association designs are conducted only under a given DL association condition. Owing to low complexity, this method shows that it is very easy to achieve the possible decoupling UL DC designs and the corresponding condition association probabilities. Then, the conditional coverage probabilities and SEs of the OMA-mode and NOMA-mode HetNets are derived by specially considering DUDA and coupled UL/DL association strategies. The proposed conditional design framework can be easily extended to multi-tier HetNets and is helpful to select feasible DL candidate from all possible DL associations so that the resulting UL associations are optimal. Besides this, the cross-tier DC design ensures the effective exploitation of the whole network resources because different tiers have different serving levels.

Joint UAV Hovering Altitude and Power Control for Space-Air-Ground IoT Networks

Unmanned aerial vehicles (UAVs) have been widely used in both military and civilian applications. Equipped with diverse communication payloads, UAVs cooperating with satellites and base stations constitute a space-air-ground three-tier heterogeneous network, which are beneficial in terms of both providing the seamless coverage as well as of improving the capacity for increasingly prosperous Internet of Things networks. However, cross-tier interference may be inevitable among these tightly embraced heterogeneous networks when sharing the same spectrum. The power association problem in satellite, UAV and macrocell three-tier networks becomes a critical issue. In this paper, we propose a two-stage joint hovering altitude and power control solution for the resource allocation problem in UAV networks considering the inevitable cross-tier interference from space-air-ground heterogeneous networks. Furthermore, Lagrange dual decomposition and concave-convex procedure method are used to solve this problem, followed by a low-complexity greedy search algorithm. Finally, simulation results show the effectiveness of our proposed two-stage joint optimization algorithm in terms of UAV network’s total throughput.

Cross-Tier Dual-Connectivity Designs of Three-Tier Hetnets With Decoupled Uplink/Downlink and Global Coverage Performance Evaluation

In the conventionally coupled uplink (UL) and downlink (DL) association (CUDA) scheme, the UL performance is limited greatly by the DL parameters such as the density and power of base stations (BSs). To overcome this issue, this paper focuses on a novel three-tier heterogeneous network (HetNet) as well as global performance evaluation, where the cross-tier dual-connectivity (DC) and decoupled UL and DL association (DUDA) are integrated. On one hand, with the cross-tier DC, in DL or UL, typical user equipment is associated simultaneously with the primary and secondary BSs that are located at different tiers. On the other hand, with DUDA the primary and secondary access points of UL and DL are not necessarily the same. The proposed cross-tier DC scheme meets the need of the next generation networks where control channel comes from Macro BS and data channels from small cell BSs. For such HetNets, the work first presents a comprehensive investigation of the cross-tier DC design of all possible DUDA modes and the corresponding association conditions. Second, by simplifying the association conditions the work gives the comprehensive derivations in terms of the association probabilities and the statistical descriptions of the primary and secondary UL access distances. Third, by using the method from stochastic geometry this paper derives the general form of UL coverage probabilities by creating a common model of DUDA designs so that the global UL average coverage probability (ACP) of the whole network is achieved. The presented numerical and simulated analysis first validates the derivations. Then, the analysis focuses on the global UL ACP comparison of the whole HetNet between the DUDA and CUDA designs. The comparison of global ACP shows that the ACP of DUDA design is higher than the one of the CUDA design. Although the powers and densities of BSs impose the outstanding impact on the ACP of the CUDA designs, they have a very limited effect on one of the DUDA designs due to the utilization of decoupling association.

PCF-Based LTE Wi-Fi Aggregation for Coordinating and Offloading the Cellular Traffic to D2D Network

Device-to-device (D2D) communication is a promising technology towards 5G networks. D2D communication can offload traffic using licensed/unlicensed band by establishing a direct communication between two users without traversing the base station or core network. However, one of the major challenges of D2D communication is resource allocation and guaranteeing quality-of-service (QoS). In this paper, we establish an optimal queuing scheduling and resource allocation problem for three-tier heterogeneous network based on LTE Wi-Fi aggregation, to offload voice/multimedia traffic from licensed band to unlicensed band using scalable MAC protocol (SC-MP) under various static delay constraints. The access mechanism used for Wi-Fi in SC-MP is point coordination function, which further offloads the multimedia traffic using D2D communication in unlicensed band. Resource allocation and optimal joint queuing scheduling problems are formulated with diverse QoS guarantee between licensed and unlicensed band to minimize the bandwidth of licensed band. Furthermore, an iterative algorithm is proposed to express the nonconvex problem as a series of subproblems based on block coordinate descent and difference of two convex functions (D.C) program. We have simulated the proposed scheme using two scenarios: voice traffic using licensed band and voice traffic using both licensed and unlicensed band, whereas multimedia traffic uses unlicensed band for both the scenarios. The simulation results show that both the schemes perform better than the existing scheme and scenario 2 outperforms scenario 1.

Energy‐spectrum‐efficient three‐tier heterogeneous networks with D2D harvesting energy and uplink coverage analysis

SummaryTo guard the communication quality of cell edge users (CEUs) and simultaneously improve the energy‐spectrum efficiency, a novel 3‐tier heterogeneous network (HetNet) model is proposed, which consists of macro cells, femtocells, and device‐to‐device (D2D) networks. Specially, with a predefined cell split factor R, the macro cell users are split into as cell center users (CCUs) and CEUs, respectively. Correspondingly, the total available spectrum band consisting of N channels is divided into CCU band and CEU band with a given coefficient pm. The CCU band containing pmN subchannels is shared by CCUs and femtocell users (FUs), and the CEU band containing (1 − pm) N subchannels is shared by D2D users and CEUs. The perfect network synchronization is assumed, and a communication round consists of downlink transmission and uplink transmission phases. The battery‐free D2D terminals harvest energy from the ambient radio frequency interference in the downlink transmission phase based on inverse power control scheme and communicate in the uplink transmission phase only when they harvest enough energy to perform channel inversion toward the receiver. For such 3‐tier HetNets, by modeling the network elements as independent Poisson point processes (PPPs) and using stochastic geometry method, we first investigate the sufficiency probability that a D2D transmitter harvests enough energy to establish a communication link. Then, by combining sufficiency probability and channel access probability, the thinned independent PPPs for the locations of CCUs, CEUs, FUs, and D2D users are modeled. Based on these thinned PPP models, we perform a comprehensive investigation on the coverage probabilities of CCU, CEU, and FU uplinks as well as the D2D transmission. The simulated and numerical results show that using the presented cell split strategy enhances the performance of CCUs and CEUs because of the decrease of interference. The presented comparison analysis displays that the effect of D2D networks on the macro cell or the whole HetNets is limited and can be omitted. Therefore, the energy and spectrum efficiencies of networks are enhanced, simultaneously. At the same time, our results indicate that by using our derivations, we can perform the optimal design of the HetNets.

Multiobjective Optimization in 5G Hybrid Networks

The increasing adoption of the Internet of Things has led to the need for systems with higher spectral and energy efficiency (EE) in order to enable communication. Larger data rate demands had led researchers to look at millimeter wave (mmWave) bands to boost network rates. This paper investigates the downlink performance of a three-tier heterogeneous network that consists of sub-6 GHz macrocells overlaid with small cells operating on both the mmWave and sub-6 GHz bands. A model is developed using tools from stochastic geometry to analyze the coverage, rate, area spectral efficiency, and EE of such a network. Various deployment strategies and their impacts on the considered metrics are studied. Simulation results are used to verify the validity of the proposed model.

Saving Energy on the Edge: In-Memory Caching for Multi-Tier Heterogeneous Networks

Recent years have witnessed billions of new manufactured sensors, equipments, and machines being connected to our almost omnipotent Internet. While enjoying the comfort and convenience brought by IoT, we also have to face tremendous energy consumption and carbon emissions that even cause climate deterioration. Extended from cloud computing, edge/fog computing and caching provide new thoughts on processing big data generated from distributed IoT devices. With the purpose of helping deal with the data explosion problem by edge caching, in this article we apply in-memory storage and processing to reduce energy consumption. We design two kinds of TTL in four cache replacement policies to cache data at the edge. We carry out a simulation experiment in a three-tier heterogeneous network structure using the RWP model and test the performance of in-memory caching and the traditional method. The analysis results manifest that our in-memory method is able to obtain better energy efficiency in edge caching, and has stable and low backhaul rate.

Analysis and Scheduling in a 5G Heterogeneous Content Delivery Network

Caching popular multimedia content constitutes a promising solution to mitigate the congestion in the ultimate potential for 5G networks. Moreover, a three-tier heterogeneous network, where device-to-device pairs, small cells, and macro base stations (BSs) are included, is suggested in 5G wireless networks. In addition, local caching of popular multimedia content for small-cell base stations (SBSs) and user equipment has been considered to decrease the BS transmission cost without requiring high capacity backhaul or access to the core network. Thus, in this paper, we first analyze the numerous relevant performances in this three-tier content delivery network. For the independent Poisson point process and uniform distribution, where there are two regular different SBS assumption modes, we first provide theoretical analysis of the hitting probability in this heterogeneous network in different user request transmission modes based on a stochastic geometry theory. Then, we further propose a novel resource selection and scheduling algorithm satisfying the signal-to-interference-plus-noise ratio and signal-to-interference ratio criteria and the optimal transmission link selections and scheduling strategy for the three-tier heterogeneous network in order to reasonably allocate restricted resources. Finally, the numerical results reveal that the theoretical results are in agreement with the simulation results of the Zipf-distribution caching scheme. Meanwhile, the proposed algorithm performs well compared with the theoretical limit and an increase in the state of the art.

Two-stage resource allocation scheme for three-tier ultra-dense network

In 5G Ultra-dense Network (UDN), resource allocation is an efficient method to manage inter-small-cell interference. In this paper, a two-stage resource allocation scheme is proposed to supervise interference and resource allocation while establishing a realistic scenario of three-tier heterogeneous network architecture. The scheme consists of two stages: in stage I, a two-level sub-channel allocation algorithm and a power control method based on the logarithmic function are applied to allocate resource for Macrocell and Picocells, guaranteeing the minimum system capacity by considering the power limitation and interference coordination; in stage II, an interference management approach based on K-means clustering is introduced to divide Femtocells into different clusters. Then, a prior sub-channel allocation algorithm is employed for Femtocells in diverse clusters to mitigate the interference and promote system performance. Simulation results show that the proposed scheme contributes to the enhancement of system throughput and spectrum efficiency while ensuring the system energy efficiency.

Femtocaching assisted multi-source D2D content delivery in cellular networks

The influxes of diversified services and mass data lead to exponential growth of traffic load in mobile cellular networks. Cache-enabled device-to-device (D2D) communication provides a general framework to alleviate this situation. In contrast to previous single-source D2D models, this paper investigates a comprehensive content delivery framework based on a three-tier heterogeneous network (HetNet), where base station (BS), femtocaching auxiliary equipments (FAEs), and user terminals(UTs) are included. The cooperative D2D communication can be implemented from both FAEs and UTs to handle the ongoing explosive increase in ultra-dense scenario. Moreover, duplicate storage for requesting data in multiple neighbor nodes makes many-to-one D2D communication possible at the user layer. Considering the case that cellular users and D2D links reuse the same resources in the uplink period, the non-outage probability of the cellular communication is defined to guarantee the main communication quality. Under the constraints subject to cumulative interference, an optimization objective function based on multi-source D2D communication is deduced to achieve unprecedented average data rate. Numerical simulations show that our system yields network throughput exponentially while transferring traffic load of the BS reasonably.

Analysis on Cache-Enabled Wireless Heterogeneous Networks

Caching popular multimedia content is a promising way to unleash the ultimate potential of wireless networks. In this paper, we propose and analyze cache-based content delivery in a three-tier heterogeneous network (HetNet), where base stations (BSs), relays, and device-to-device (D2D) pairs are included. We advocate proactively caching popular content in the relays and parts of the users with caching ability when the network is off-peak. The cached content can be reused for frequent access to offload the cellular network traffic. The node locations are first modeled as mutually independent Poisson point processes (PPPs) and the corresponding content access protocol is developed. The average ergodic rate and outage probability in the downlink are then analyzed theoretically. We further derive the throughput and the delay based on the multiclass processor-sharing queue model and the continuous-time Markov process. According to the critical condition of the steady state in the HetNet, the maximum traffic load and the global throughput gain are investigated. Moreover, impacts of some key network characteristics, e.g., the heterogeneity of multimedia contents, node densities, and the limited caching capacities, on the system performance are elaborated on to provide valuable insight.