Heterogeneous Cellular Networks Research Articles

Opportunistic Use of Successive Interference Cancellation in Reverse TDD HetNets

Cross-tier interference management is one of the major challenges in heterogeneous cellular networks (HetNets). Though the network throughput increases due to a better area spectral efficiency of a HetNet, there is possibility that high interference will make few link capacities close to zero when users regard interference as noise (IAN). In this letter, successive interference cancellation (SIC) is used to cancel the cross-tier interference in a reverse time division duplexing (RTDD) scheme. We demonstrate that by opportunistic use of SIC, a minimum guarantee on the sum link capacity can be ensured for an RTDD HetNet. This minimum sum link capacity is later on proved to be the maximum that can be achieved by orthogonal resource allocation schemes. Through system-level simulations for random allocation, it is shown that the proposed scheme is better than using SIC and IAN alone. To further improve the overall system capacity, an optimization problem for selecting co-channel users is formulated, and the Hungarian algorithm is employed to solve it.

Optimal Picocell Base Station Density for Energy-efficient Heterogeneous Cellular Network Under Received Power Constraint

Heterogeneous cellular networks (HCNs) have emerged as the primary solution for overwhelming traffic demands. However, the dense deployment of small cell base stations (BSs) inevitably triggers a tremendous escalation of energy consumption. In this paper, we apply tools from stochastic geometry to investigate and optimise the energy efficiency (EE) for a two-tier HCN. The average successful transmission rate per unit area of a two-tier HCN is derived, and then the total power consumption of all the BSs in per unit area of a two-tier HCN is derived. Based on that, the EE expression of the whole HCN is formulated. We analysis the received signal power constraint for a typical user and convert the power constraint to density constraint. Finally, we use a one-dimensional optimisation algorithm to maximise the EE by optimising picocell BS density. Simulation results validate the accuracy of the theoretical analysis and demonstrate the proposed optimal picocell BS density can obviously improve EE.

Optimal picocell base station density for energy-efficient heterogeneous cellular network under received power constraint

Heterogeneous cellular networks (HCNs) have emerged as the primary solution for overwhelming traffic demands. However, the dense deployment of small cell base stations (BSs) inevitably triggers a tremendous escalation of energy consumption. In this paper, we apply tools from stochastic geometry to investigate and optimise the energy efficiency (EE) for a two-tier HCN. The average successful transmission rate per unit area of a two-tier HCN is derived, and then the total power consumption of all the BSs in per unit area of a two-tier HCN is derived. Based on that, the EE expression of the whole HCN is formulated. We analysis the received signal power constraint for a typical user and convert the power constraint to density constraint. Finally, we use a one-dimensional optimisation algorithm to maximise the EE by optimising picocell BS density. Simulation results validate the accuracy of the theoretical analysis and demonstrate the proposed optimal picocell BS density can obviously improve EE.

A New Framework for Mobile Edge Caching by Proposing Flexible User in Heterogeneous Cellular Networks

The bursting increase in requesting wireless data has caused several issues in network peak-traffic duration. This negatively results in significant data delivery delay imposed on users that can eventually impact the network's quality of service and users' quality of experience. In this research, regarding mobile edge caching as a potential solution to decrease such delay, we propose a new framework in which we introduce the concept of the flexible user where he requests for a set of multiple files from the library with a unique feature, e.g., 5 movies within comedy genre from the library in the peak-traffic duration. The satisfactory criterion for the flexible user is to receive any of the files within the requested set. This definition of the flexible user indicates a new concept which captures interesting scenarios. In order to model this concept, we generalize the conventional Zipf distribution to a multivariate one as the modeling method for popular data. We formulate the problem of finding the optimal cache data placement, which minimizes the average total delivery delay in the network while satisfying the helpers' cache size constraints. To this end, we derive the average delivery delay per user as well as the average total delivery delay in the network, according to the new generalized Zipf distribution. Finding the optimal solution is proved to be NP-Hard. We leverage on the problem property to propose an efficient approximation method, called greedy algorithm, which performs within a constant factor as good as the optimal solution. Afterwards, we propose an algorithm called speedy-greedy to significantly reduce the computational complexity of the greedy algorithm while achieving the same performance. Simulation results indicate that our proposed framework significantly decreases the average total delivery delay of the system model that can help the network maintain its quality of service in network peak-traffic duration.

Decoupled Downlink and Uplink Access for Aerial Terrestrial Heterogeneous Cellular Networks

To enable reliable connectivity in highly dynamic and dense communication environments, aerial-terrestrial heterogeneous cellular networks (AT-HCNs) have been proposed as a plausible enhancement to the conventional terrestrial HCNs (T-HCNs). In dense urban scenarios, users are often located in clusters and demand high bandwidth in both downlink (DL) and uplink (UL). We investigate this scenario and model the spatial distribution of clustered users using a Matern cluster process (MCP). Based on our analysis we then argue that decoupling of DL and UL in such a setting can significantly improve coverage performance and spectral efficiency. We further obtain closed-form expressions for the system coverage probability, spectral efficiency, and energy efficiency by using the Fox H-function. The obtained results confirm the validity of the proposed analytical model. Our simulations further indicate a significant performance improvement using decoupled access and provide quantitative insights on AT-HCN system design.

Energy Efficiency Techniques in Heterogeneous Networks

According to the present data 0.5% of global energy is consumed by wireless networks. Energy efficiency is required for the environment and to lower the network operational cost. In this paper, we are about to discuss various methods of energy conservation in the heterogeneous cellular network. Energy consumption is reduced by self-organization algorithm and message passing algorithm by switching off-peak Base station controllers (BSC). Along with the increasing demands for cellular networks, the various problems for energy conservation in cellular networking have also increased. There are various models present which help in increasing the energy efficiency of cellular networking such as the Novel power consumption model and refined power consumption model. Also, an increase in the higher performance of cellular networks leads to an increase in energy consumption. In this paper, we are about to discuss various challenges which are faces for increasing energy efficiency and their solution.

Stochastic Downlink Power Control for Various User Requirements

Power Control (PC) can coordinate mutual interference between cells in heterogeneous cellular networks (HCNs). Most of the existing works focus on real-time PC problems based on instantaneous channel state information (CSI) for all users. However, such scheme may result in low feasible probability and high energy consumption. If the PC problem is frequently infeasible, the users that require low latency communications will fail to get services in time. In this paper, we classify the users into two categories according to their sensitivity to latency: delay-sensitive-users (DSUs) and non-delay-sensitive-users (NDSUs). We use instantaneous signal-to-interference-plus-noise-ratio (SINR) constraints to ensure the success of data transmission per time slot to meet DSUs’ low latency requirements, and the long-term mean data rate constraints to ensure NDSUs’ average data rate requirements. On the one hand, the long-term constraints allow the system to sacrifice NDSUs’ short-term performance to guarantee DSUs’ instantaneous performance when the channel condition is poor. On the other hand, the system will appropriately improve NDSUs’ performance to ensure their target mean data rate when the channel condition is good. Under this scheme, we formulate the PC problems under perfect CSI, bounded CSI error and stochastic CSI error scenarios as a uniform problem, which is a non-convex stochastic constrained problem. The recently proposed constrained stochastic successive convex approximation (CSSCA) technique is utilized to handle this problem. Simulation results show that the proposed scheme can significantly improve the feasible probability of DSUs’ instantaneous constraints and reduce the network’s energy consumption.

Cluster-Based Load Balancing Algorithm for Ultra-Dense Heterogeneous Networks

In a highly dense heterogeneous cellular network, the loads across cells are uneven due to random deployment of cells and the mobility of user equipments (UEs). Such unbalanced loads result in performance degradation such as throughput and handover success. In order to solve the uneven load problem for better network performance, we propose a cluster-based mobility load-balancing algorithm for heterogeneous cellular networks. Traditional mobility load balancing (MLB) schemes that consider only the adjacent neighbors cannot provide enough improvement in network performance. On the other hand, the previous MLB schemes consider neighbors in the entire network suffer from unnecessary MLB actions. However, in the load balancing process, the proposed algorithm considers overloaded cells and their neighbors within then-tiers. First, the algorithm models the network as a directed multi-graph and constructs clusters taking the overloaded cells and their n-tier neighbors. Therefore, by adjusting cell individual offset parameters of the cells in the clusters the algorithm achieves load balancing locally. Since load balancing is performed inside the clusters, the network can be optimized more efficiently by avoiding unnecessary MLB actions. Simulations show that the proposed algorithm distributes the load across the network more evenly than other MLB algorithms, and in a low UE velocity scenario, it increases the overall network throughput by 6.42% compared to a non-optimized network without an MLB algorithm.

Performance Evaluation of eICIC Scheme for Small Cell Data Offloading in Heterogeneous Cellular Network

Performance Evaluation of eICIC Scheme for Small Cell Data Offloading in Heterogeneous Cellular Network

Proactive Uplink Interference Management for Nonuniform Heterogeneous Cellular Networks

In homogeneous cellular networks, fractional power control (FPC) is employed to partially compensate the path-loss and, hence, improve uplink ( $U_{L} $ ) signal-to-interference ratio (SIR). However, this scheme is less effective in heterogeneous cellular networks (HetNets) because: (i) except the typical user, all other users with variable $U_{L} $ transmit power (UTP) act as interferers, (ii) FPC leads to high UTP by edge users and, hence, more interference, and (iii) small base stations (SBSs)’ densification further increases network interferences. Leveraging FPC in HetNets, we propose nonuniform SBS deployment ( $\text {NU-SBS}_{\mathcal {D}} $ ) to reduce interference and, thus, increase network performance. According to our $\text {NU-SBS}_{\mathcal {D}} $ model, SBS deployment ( $\text {SBS}_{\mathcal {D}} $ ) near macro base station (MBS) is avoided, whereas MBS coverage edge area is enriched with ultra-dense $\text {SBS}_{\mathcal {D}} $ . $\text {NU-SBS}_{\mathcal {D}} $ model leads to: (i) better SIR reception of MBS coverage edge users, (ii) fewer $\text {SBS}_{\mathcal {D}} $ requirement, and (iii) better SBS coverage in the MBS coverage edge area. Moreover, to make a model more proactive, we also consider reverse frequency allocation (RFA) to further abate both $U_{L} $ and downlink $(D_{L}) $ interferences. The coverage probability expressions are derived for both uniform SBS deployment ( $\text {U-SBS}_{\mathcal {D}} $ ) and $\text {NU-SBS}_{\mathcal {D}} $ while using RFA and FPC. Through simulation and numerical results, we characterize coverage probability for different values of SIR threshold, path loss compensation factor, SBS density, users density, and the distance between the typical user and the associated base station. The proposed $\text {NU-SBS}_{\mathcal {D}} $ model along with RFA leads to reduced network interference as compared with $\text {U-SBS}_{\mathcal {D}} $ and, thus, leverages FPC in HetNets.

Joint Device Association and Power Coordination for H2H and IoT Communications in Massive MIMO Enabled HCNs

The integration of massive multiple-input and multiple-output (MIMO) enabled heterogeneous cellular networks (HCNs) and Internet of Things (IoT) is a promising treatment for future networking paradigms. In such networks, the human-to-human (H2H) devices and IoT devices have some distinct service requirements. Specifically, the former mainly concentrates on downlink throughput, but the latter pays more attention to uplink power consumption. Based on this, we design a device association mechanism (scheme) to achieve a tradeoff between these two performance metrics under devices' association requirements. Through some appropriate adjustments of weighting parameters, different types of devices can improve their performance metrics of interest. At last, such a scheme is formulated as a network-wide logarithmic utility maximization problem in a nonlinear and combinatorial form. To solve it, we develop two types of association algorithms, whose primary difference lies in the treatment of weighting parameters. Then, we show the corresponding convergence and computation complexity analyses for them. Finally, we investigate the impacts of weighting parameters, the BS power and the number of antennas on some certain performance metrics of designed algorithms and other existing one. The simulation results show that the designed algorithms can meet different devices' association requirements by properly adjusting weighting parameters.

Energy Efficiency Analysis in Cache-Enabled D2D-Aided Heterogeneous Cellular Networks

Small cells (SCs) offer a promising approach to meeting the exponentially growing data rate demands. However, dense deployment of SCs can degrade the energy-efficiency (EE) of the network due to the additional deployed base stations (BSs). Under heterogeneous network (HetNet) deployments, SCs can be dynamically switched off for energy saving when traffic load decreases. We do this by defining a load-dependent transmission power coefficient (TPC) for SC BSs. In addition, with Device-to-Device (D2D) communication, mobile users in proximity can establish a direct link and bypass the BSs, thereby offloading the network infrastructure and providing further improvement of EE. In this paper, the objective is to rely on both D2D communications and sleeping SC BSs to offload traffic from the mains powered macrocell BSs leading to energy saving in the network. Furthermore, in order to consider D2D requirements under the practical application scenarios, we assume a framework for wireless video sharing, where users can store popular video files and share files via D2D communication. To begin with, we derive the EE expression of the cache-enabled D2D-aided HetNet. Then, to maximize the EE of the cache-enabled D2D-aided HetNet, the optimal load-dependent TPC for SC BSs is obtained under constraints on both network's coverage and rate. Using simulations, we will investigate the potential effects of the TPC defined for SC BSs as well as the introduced D2D layer on the network EE.

Spectral efficiency analysis of millimeter-wave heterogeneous cellular networks based on PCP

To solve the interference problem in densely populated areas, this paper proposes a new scheme that taking user equipment (UE) as the center of millimeter-wave heterogeneous networks based on Poisson cluster process (PCP) model. Under the network model, the UE is divided into cluster-center UE or cluster-edge UE by using the ratio of the first and second closest distances of the UE from pico base stations. The random geometry and PCP methods are used to study the downlink spectral efficiency and the correct derivation results are verified. At last, the influence of relevant parameters about system performance is analyzed.

Energy Efficient Resource Allocation Approach for Renewable Energy Powered Heterogeneous Cellular Networks

In this paper, maximizing energy efficiency (EE) through radio resource allocation for renewable energy powered heterogeneous cellular networks (HetNet) with energy sharing, is investigated. Our goal is to maximize the ne... | Find, read and cite all the research you need on Tech Science Press

Uplink Performance Analysis of User- Centric Small Cell Aided Dense HCNets With Uplink-Downlink Decoupling

The deployment of low power small base stations (SBSs) in high density user areas enhances the performance of heterogeneous cellular networks (HCNets). Such user-centric SBS deployment (UCSD) is more appropriate as compared with the conventional uniformly deployed user equipment (UE) based HCNets, because it captures the correlation between UEs and SBSs. In the literature, the downlink (DL) performance of UCSD based HCNet (UC-HCNet) has been analyzed under maximum received signal power (MRSP) association strategy. In this paper, we develop and analyze the uplink (UL) performance of UC-HCNets with decoupled UL-DL association (DUDA) using stochastic geometery. We evaluate the total UL interference considering two special cases of Poisson cluster process (PCP), i.e., Matern cluster process (MCP) and Thomas cluster process (TCP), in UC-HCNet. The proposed DUDA scheme enhances the system performance gain by assuming dual connectivity of UE and BSs in the UL and DL directions. Furthermore, fractional power control (FPC) policy is considered to limit the UL power consumption. The system performance is evaluated in terms of outage probability and rate coverage. The numerical results are validated through simulations. Numerical results show that the performance improvement of DUDA in sparse scenario is higher as compared with dense scenario. Furthermore, it is investigated that the performance gain of DUDA is higher for larger UE variance and cluster radius in case of MCP and TCP, respectively.

Edge Caching in Multi-UAV-Enabled Radio Access Networks: 3D Modeling and Spectral Efficiency Optimization

Unmanned-aerial-vehicle (UAV) enabled radio access is an effective technology to improve the wireless coverage, in particular for remote and disaster-struck areas. It will become a key enabler in the forthcoming 5G heterogeneous cellular networks to provide improved and resilient coverage. In this article, we study edge caching for multiple UAV-enabled radio access networks (UAV-RANs) and investigate how the overall spectral efficiency (SE) can be improved by efficient edge caching. In this context, UAV base stations (UBSs) may not serve the immediate close-by users, but serve the users based on the requested contents, which brings the service contents closer to users. Based on analyses of the SE achieved by the content-centric UAV-RAN, a hybrid caching strategy is proposed to further improve the SE. In order to cache more files with limited cache resources while guaranteeing the quality-of-service, the contents are divided into two subsets, a popular set and a less popular set, based on their popularity profile that follows Zipf distribution. The popular files, according to the proposed hybrid caching strategy, are cached at all the UBSs, while each less popular file is cached at one UBS only. The overall SE is maximized by finding an optimal popularity threshold between the two subsets. By relaxing the formulated problem, analytical expression for the optimized threshold is derived. The effectiveness of the proposed method is verified by numerical examples where existing benchmark schemes are compared and outperformed.

Enabling Full-Duplex and Energy Harvesting in Uplink and Downlink of Small-Cell Network Relying on Power Domain Based Multiple Access

In this article, we introduce a small-cell network operating in the context of heterogeneous cellular networks for both downlink (DL) and uplink (UL) by deploying three techniques of full-duplex transmission mode, energy harvesting, and power domain-based non-orthogonal multiple access (NOMA) schemes. Compared to the conventional half-duplex orthogonal multiple access (OMA) scheme that has been widely implemented in current wireless communication systems, the full-duplex (FD) NOMA relying on energy harvesting scheme has a great potential to further enhance the system performance in terms of connectivity capability, spectral efficiency and outage performance. In the proposed two-user small-cell relying on NOMA scheme, the small-cell base station first transfers an energy-bearing signal to serve the two users in the DL phase. Later, an energy harvesting technique is proceeded to encourage the strong user and the weak user to transmit their messages in the UL phase in a FD manner. However, one major challenge related to the FD strategy is the self-interference signal due to a signal leakage from the terminal’s output to the input. Besides that, the interference from macro-cell users is also main reason of degradation of the system performance. In this article, we derive analytical expressions to describe the system’s performance in terms of the outage probability and throughput. Moreover, extensive numerical simulations are performed to compare and highlight the performance of the proposed small-cell network with several practical scenarios.

Green Deployment Method of Micro Base Station for Ultra-Dense Heterogeneous Cellular Networks Based on Constrained Dolphin Swarm Algorithm

This paper proposes a green deployment method for micro base stations for ultra-dense heterogeneous cellular networks to balance network energy efficiency and electromagnetic radiation and meet certain user service quality. Firstly, a constrained multi-objective mathematical model for the green deployment of the micro base station is established for the two-dimensional communication scenario, with the user rate as the constraint, aiming at maximizing the network energy efficiency and minimizing the average electromagnetic radiation. Then, a multi-objective dolphin swarm algorithm which considering the evolutionary advantages of excellent infeasible solutions and feasible solutions, improving the individual search mechanism in the dolphin group algorithm, combined with the improved two-population strategy is proposed and tested on the CTP test set. It shows that compared with the other three methods, the method has certain advantages in convergence and distribution. Finally, a green deployment method for micro base stations based on constrained multi-objective dolphin swarm algorithm is established. Experiments on nine communication scenarios show that the proposed method can balance network energy efficiency and electromagnetic radiation.

Spatial Modeling of Interference in Inter-Vehicular Communications for 3-D Volumetric Wireless Networks

Unmanned aerial vehicle (UAV) assisted cell-free communications hold promise for enhancing the coverage and capacity of heterogeneous cellular networks. However, the network interference in such scenarios must be accurately modeled for efficient system design. The spatial characteristics of the desired and interfering signals can be jointly modeled by considering the characteristics of the signal-to-interference ratio (SIR). This work proposes a generalized framework for modeling the spatial statistics of the SIR encountered in 3-D volumetric inter-vehicular communication channels. Though the novel paradigm of UAV-assisted cell-free vehicular communications is analyzed in particular, the proposed framework is more general in that it incorporates 3-D mobility at both link ends. Also, this framework is shown to include as its special cases, several notable 2-D propagation models of network interference including those for terrestrial vehicle-to-vehicle and fixed-to-vehicle scenarios. Analytical expressions are derived for the SIR level-crossing-rate (LCR), average-fade-duration (AFD), spatial auto-covariance (SAC), and coherence distance (CD). Both single- and multi-cluster scattering environments are analyzed and the impact of channel parameters such as the direction and velocity of mobile nodes as well as the altitudes of the UAV and scattering cluster(s) on the SIR fading statistics is investigated. Finally, some future extensions of this work are also discussed such as the integration of intelligent reflective surfaces in the propagation scenario to generate favorable channel conditions.

Energy-Efficient Resource Allocation in Single-RF Load-Modulated Massive MIMO HetNets

Due to the dramatic increase in wireless data traffic and the associated increase in energy consumption, designing energy-efficient wireless networks with improved spectral efficiency is a pressing concern. The focus of this article is the design of a green, highly energy-efficient cellular heterogeneous network (HetNet) by taking advantage of multiple-input-multiple-output (MIMO) structure and deployment of small cells. We consider the downlink of a two-tier HetNet, in which multiple-antenna small cells are coordinated to serve users. Even though the deployment of MIMO together with small cells improves the communication system's performance in terms of data rate and reliability, circuit energy consumption in such a network is a critical issue. To address this, an energy-efficient antenna selection and radio resource block assignment algorithm is proposed for the small cells, and a single radio-frequency (RF) chain structure is considered for the massive MIMO macro base station. Then, while coordinating transmissions between cells subject to user-centric clustering, an energy-efficient beamforming design and power allocation optimization problem with respect to the quality of service requirement of users, transmit power budget of base stations, and fronthaul capacity is formulated; the problem is solved using the Dinkelbach method. Simulation results demonstrate the performance potential of our proposed algorithm in terms of energy efficiency and spectral efficiency.