Heterogeneous Cellular Networks Research Articles

Analysis of Downlink Uplink Decoupled Dense Heterogeneous Cellular Network based on User Association using Multi-Slope Path Loss Model

Keeping in consideration the expected need of node densification of heterogeneous cellular networks in near future, it is imperative that more accurate path loss models be used when an ...

Green Base Station Assignment for NOMA-Enabled HCNs

In this paper, for the heterogeneous cellular networks (HCNs) with non-orthogonal multiple access (NOMA), we mainly concentrate on the design of green base station (BS) assignment integrating with power allocation. Note that the power allocation is mainly used for mitigating network interference and reducing energy consumption. To attain the goal of green communications, we take account of an optimization problem with maximizing the whole energy efficiency under users' signal-to-interference-plus-noise ratio (SINR) constraints, where such efficiency represents the ratio of the total throughput of users to the total power consumption of BSs selected by them. To solve the finally formulated problem in a nonconvex and nonlinear form, we first introduce an auxiliary parameter to convert it into a tractable one whose optimal solution can be found by employing an effective iterative algorithm. After that, the whole problem, being in a coupling form, can be broken into the BS assignment and power allocation subproblems that can be optimized alternately. To solve the former, a type of highly effective algorithm is designed according to a coalitional game. In addition, an approach based on a two-sided scalable (2.s.s.) function is developed for the latter. Then, we reveal the properties of these proposed algorithms, including computation complexity and convergence. In the simulation, we mainly investigate the impacts of densities of small BSs and users on the different performance indices of the designed and existing algorithms.

An ASAPPP Approach to the Spectrum Allocation in General Heterogeneous Cellular Networks

The increasing heterogeneity of cellular networks makes the signal-to-interference-ratio (SIR) distribution challenging to derive, which restricts the further analysis of metrics that depend on it. In this paper, we establish a general heterogeneous cellular network (HCN) model to investigate the problem of spectrum allocation to the different tiers and propose an equivalent orthogonal network (EON) model to formulate the optimization problems. Specifically, we first employ the ASAPPP method which refers to “an approximate SIR analysis based on the Poisson point process” to provide accurate approximations to the spectral and energy efficiency in the EON. The approximations are then applied to spectrum allocation optimization problems, where the optimal SIR thresholds are derived, and, in turn, the optimal solutions are obtained that maximize the area spectral efficiency (ASE) and network energy efficiency (NEE), respectively. Interestingly, the optimal SIR threshold can be well approximated by an extremely simple expression that merely depends on the path loss exponent alone. The results indicate that neither full spectrum sharing nor full spectrum partitioning is optimal for all network parameters, such as density, transmit power, and so on, in terms of both the ASE and NEE. Instead, a hybrid scheme may perform the best. Moreover, different constraints on the spectrum efficiency can have a drastic impact on the performance of spectrum allocation schemes.

Offloading Design for Energy and Spectral Efficiencies Tradeoff in Massive MIMO Enabled Heterogeneous Cellular Networks

To fully utilize the system resources and enhance the user experience, two types of offloading mechanisms are designed for massive MIMO (multiple-input-multiple-out) enabled heterogeneous cellular networks (HCNs). Such mechanisms can achieve a tradeoff between energy efficiency (EE) and spectral efficiency (SE) experiences, but also have a difference on whether or not a power coordination measure is mentioned. At last, they are mathematically written as the network-wide utility maximization problems that are closely related to the SEs and EEs of associated users. In them, we introduce a crucial parameter α to adjust the EE-SE preference. It is noteworthy that the finally formulated problems are in some relatively complicated forms. To solve them, some necessary changes should be made at first, and then we can design some feasible algorithms. Specifically, we try to design a distributed algorithm for a mere offloading problem using dual decomposition (DD), and develop a two-layer iterative algorithm for the joint power coordination and offloading problem using DD and two-sided scalable (2.s.s.) function update. Regarding such these algorithms, we show the corresponding computation complexity and convergence analyses. In the simulation, we mainly investigate different network parameters on an EE-SE tradeoff for our advocated mechanisms and another existing mechanism.

Heterogeneous FD-mm-Wave Cellular Networks With Cell Center/Edge Users

In this paper, we assess the effect of full-duplex (FD) radio in the context of millimeter-wave (mm-Wave) communications. Particularly, we propose an analytical framework, based on stochastic geometry, to evaluate the performance of heterogeneous FD-mm-Wave cellular networks for two user location-based classifications, namely cell-center users (CCUs) and cell-edge users (CEUs). Moreover, we evaluate the performance of the considered networks with successive interference cancellation (SIC) capabilities. Based on the proposed framework, analytical expressions for the coverage and sum-rate performance are derived. We investigate the impact of FD-mm-Wave communications on the network performance of CCUs/CEUs and quantify the associated performance gains under different network parameter settings. Our results demonstrate the beneficial combination of FD radio with heterogeneous mm-Wave cellular networks, since it increases the spectral efficiency but also alleviates the effects of the multi-user interference. Furthermore, we present the tradeoff between the coverage and sum-rate performance of heterogeneous FD-mm-Wave cellular networks for the considered user classifications. The results show that half-duplex mode is beneficial for the CEUs to achieve better network performance, as opposed to the CCUs for which FD mode is more efficient. Finally, we show the effectiveness of SIC on the network performance, with significant performance gains for the CEUs.

$P$ -Persistent Energy-Aware Handover Decisions Employing RF Fingerprint for Adaptive-Sized Heterogeneous Cellular Networks

The diverse architectural evolution and intensive data explosion in the forthcoming 5G will have severe impacts on providing seamless and robust mobility management. In this paper, P-persistent energy-aware handover (HO) decision strategies with mobility robustness are proposed both for intra-handover cases while a femto user equipment (FUE) roams into another femto access point (FAP) and for cross-tier handover cases while a macro user equipment (MUE)/FUE roams into/out of the FAP in a dynamic cell sizing involving macro-femto two-tier networks. To approximate the densely deployed small-cells, a unique RF fingerprint (RFF)-based localization is employed to enable efficient small-cell detection by an RFF matching mechanism. The prediction of the HO trigger is jointly determined by a P-persistent decision mechanism that formulates the specific HO behaviors when an MUE/FUE roams into (HO-in) and out of (HO-out) a femtocell in terms of the correlated coverage variance and UE trajectory features, whereas the target selection follows a utility function in consideration of the UE traveling time and the achievable throughput. The closed-form stationary probabilities of the proposed VHO/HHO decisions are analyzed by a Semi-Markov-based framework. In addition, an adjustable sensing mechanism with dynamic intervals is proposed when UE is located far from the RFF matching region, which can have a positive influence on reducing unnecessary UE energy consumption. Numerical results are presented for the decision accuracy analyses (too early, too late, and ping-pong HOs), energy-efficiency, and resource utilization of the two-tier system. The comprehensive evaluations indicate that the proposed scheme can enhance the mobility robustness and enable an optimal trade-off between the energy efficiency (EE) and system capacity while eliminating the architectural impacts caused by the dynamic topology and the dense deployment for the next-generation macro-femto two-tier networks.

Physical Layer Security in <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math> </inline-formula>-Tier Heterogeneous Cellular Networks Over Nakagami-<inline-formula> <tex-math notation="LaTeX">$m$ </tex-math> </inline-formula> Channel During Uplink and Downlink Phases

In this paper, we study the physical layer security performance under K-tier heterogeneous cellular network during both downlink and uplink phases. Especially, Nakagami-m fading is used to capture the characteristics of line-of-sight (LoS) propagation. Using stochastic geometry tool, tractable expressions of connection probability are derived accordingly. Upper-bound expression of secrecy probability is derived through only considering the closest eavesdropper, whose rationality is validated theoretically. While lowerbound expression of secrecy probability is derived through using Jensen's inequality. Moreover, we demonstrate the effects of parameter setting upon network connection and secrecy performances through numerical simulation. For example, Rayleigh fading and LoS scenario (an extreme Rician case) can be regarded as special cases of this paper through properly setting m 0 value. Connection probability is insensitive to BS density during downlink phases, while it is an increasing function of BS density during the uplink phase. We also find that connection probability is an increasing function of m 0 value. Secrecy probability is insensitive to m 0 value, while it is an increasing function of BS density during both downlink and uplink phases.

Enhanced interference cancellation techniques for downlink of LTE-A heterogeneous networks

The formation of Heterogeneous Network (HetNet) into the cellular system improves the overall spectral efficiency and network capacity of the system. Although the forming of the heterogeneous cellular network increases the complexity and overall interference of the system, the interference between the macro cell and smaller cells like femto/pico reduces the overall performance of the system in the downlink. In downlink, the Common Reference Signal (CRS) is used at the User Element (UE) to estimate the channel characteristics and is available throughout the entire frequency band. The presence of CRS of the neighbouring cells creates interference to the users. Linear Minimum Mean Square Error (LMMSE) based equaliser is proposed to reduce the effect of the non-colliding CRS at the UE. Enhanced space alternating generalised expectation maximisation-maximum a posteriori probability (ESAGE-MAP) estimator is used at the UE to mitigate colliding CRS interference. The simulation results have proved that the proposed LMMSE and ESAGE-MAP interference cancellation techniques perform better than the existing methods.

Robust Physical Layer Security for Power Domain Non-Orthogonal Multiple Access-Based HetNets and HUDNs: SIC Avoidance at Eavesdroppers

In this paper, we investigate the physical layer security in downlink of Power Domain Non-Orthogonal Multiple Access (PD-NOMA)-based heterogeneous cellular network (HetNet). In this paper, we assume two categories of users are available: 1) Trusted users and 2) untrusted users (eavesdroppers) at which transparency of users is not clear for the BSs, i.e., they are potential eavesdroppers. Our aim is to maximize the sum secrecy rate of the network. To this end, we formulate joint subcarrier and power allocation optimization problems to increase sum secrecy rate. Moreover, we propose a novel scheme at which the eavesdroppers are prevented from doing Successive Interference Cancellation (SIC), while legitimate users are able to do it. In practical systems, perfectly availability of all eavesdroppers' Channel State Information (CSI) at legitimate transmitters are impractical. Also CSIs of legitimate users may be also imperfect due to the error of channel estimation. Hence, we study two cases of CSI availability: 1) Perfect CSI of nodes (legitimate users and eavesdroppers) are available at the BSs and 2) imperfect CSI of nodes are available at the BSs. Since the proposed optimization problems are non-convex, we adopt the well-known iterative algorithm called Alternative Search Method (ASM). In this algorithm, the optimization problems are converted to two subproblems, power allocation and subcarrier allocation. We solve the power allocation problem by the Successive Convex Approximation approach and solve the subcarrier allocation subproblem, by exploiting the Mesh Adaptive Direct Search algorithm (MADS). Moreover, in order to study the optimality gap of the proposed solution method, we apply the monotonic optimization method. Moreover, we evaluate the proposed scheme for secure massive connectivity in Heterogeneous Ultra Dense Networks (HUDNs). Furthermore, we investigate multiple antennas base stations scenario in this literature. Finally, we numerically compare the proposed scheme with the conventional case at which the eavesdroppers are able to apply SIC. Numerical results highlight that the proposed scheme significantly improves the sum secrecy rate compared with the conventional case.

Impact of Frequency Reuse and Flexible Cell Association on the Performance of Dense Heterogeneous Cellular Networks Using Dual-Slope Path Loss Model

Impact of Frequency Reuse and Flexible Cell Association on the Performance of Dense Heterogeneous Cellular Networks Using Dual-Slope Path Loss Model

Offloading With Hybrid Cell Association in Non-Uniform Heterogeneous Cellular Networks: Modeling and Performance Analysis

Offloading With Hybrid Cell Association in Non-Uniform Heterogeneous Cellular Networks: Modeling and Performance Analysis

Enhanced interference cancellation techniques for downlink of LTE-A heterogeneous networks

The formation of Heterogeneous Network (HetNet) into the cellular system improves the overall spectral efficiency and network capacity of the system. Although the forming of the heterogeneous cellular network increases the complexity and overall interference of the system, the interference between the macro cell and smaller cells like femto/pico reduces the overall performance of the system in the downlink. In downlink, the Common Reference Signal (CRS) is used at the User Element (UE) to estimate the channel characteristics and is available throughout the entire frequency band. The presence of CRS of the neighbouring cells creates interference to the users. Linear Minimum Mean Square Error (LMMSE) based equaliser is proposed to reduce the effect of the non-colliding CRS at the UE. Enhanced space alternating generalised expectation maximisation-maximum a posteriori probability (ESAGE-MAP) estimator is used at the UE to mitigate colliding CRS interference. The simulation results have proved that the proposed LMMSE and ESAGE-MAP interference cancellation techniques perform better than the existing methods.

Performance Analysis of a Wireless Backhaul in a Three-Tier Hybrid Network With Directional Antennas

In this paper, a three-tier hybrid cellular heterogeneous network is considered using the microwave ( $\mu $ Wave) links for the first two tiers and millimeter (mmWave) links for the last tier. The two-tiers with $\mu $ Wave links form a wireless backhaul to the last tier with mmWave links. The main challenge in having a wireless backhaul is to suppress interference. Thus, we propose a novel and practical model where we can reuse the $\mu $ Wave infrastructure, but equip the BSs with directional antennas to have a robust wireless backhaul network. To solve the bottleneck rate problem, we assume that the rate required by the mmWave users is comparable to that offered by the $\mu $ Wave links. Different configurations based on the placement of the directional antennas at each tier are explored. The analysis of the key performance indicators, namely, the coverage probability, area spectral efficiency, and energy efficiency using the conventional minimum rate model, and the simulation results associated with these parameters are presented. In order to analyze this hybrid network with a wireless backhaul, an optimization problem for the overall area spectral efficiency and energy efficiency with respect to the optimal signal-to-interference ratio (SIR) threshold required for $\mu $ Wave and mmWave links is investigated. Results indicate that the optimal SIR threshold required for the $\mu $ Wave tiers (wireless backhaul) depends only on the path-loss exponent and that for the mmWave tier depends on the area of the line-of-sight region. Finally, instead of the conventional minimum rate model, we consider the average rate under coverage and show that the area spectral efficiency and energy efficiency are strictly decreasing functions with respect to the threshold, thereby concluding that they can be maximized by choosing the lowest possible SIR threshold available in the system.

Spectral Efficiency of Full-Duplex Wireless Backhaul with Hardware Impaired Massive MIMO for Heterogeneous Cellular Networks

The paper analyzes the sum spectral efficiency (SE) for a heterogeneous cellular network (HetNet) which has the backhaul, provided with wireless full-duplex massive multiple-input multiple-out (MIMO) with hardware distortions. We derive approximate expressions to obtain the uplink/downlink sum SE of the backhaul. The analytic results have been shown to be exact when compared to Monte Carlo simulations. From the analysis, it is shown that the desired signal and the hardware distortion noise have the same order. The sum SE generally improves when the number of receive antennas increases but degrades when the hardware quality reduces. A sum SE performance ceiling is introduced by the hardware quality level.

Distributed resource allocation in caching-enabled heterogeneous cellular networks based on matching theory

Caching mechanism has been identified as an effective solution in reducing mobile users’ (MUs’) transmission delay. In order to allocate proper files into small-cell base stations (SBSs) which are close to a certain group of MUs, distributed algorithms are proposed based on matching theory in minimizing MUs’ transmission latency and maximizing their satisfactions. Specifically, we first investigate the file allocation and MUs association problems in minimizing MUs’ transmission latency, and then we study the SBSs association problem to maximize MUs’ satisfactions. Moreover, the performance of the proposed algorithms is analyzed from the perspectives of stability, overhead, and complexity. Simulation results demonstrate that our proposed algorithms have a better performance compared to the benchmarks.

Secure Transmission for Heterogeneous Cellular Networks With Wireless Information and Power Transfer

In this paper, we investigate an artificial-noise-aided secure beamforming design for simultaneous wireless information and power transfer in a two-tier downlink heterogeneous cellular network, in which each energy receiver in a femtocell is seen as a potential eavesdropper to wiretap the confidential message intended for the information receiver. Our design objective is to maximize the secrecy rate at the information receiver, while satisfying the signal-to-interference-plus-noise ratio requirement of each macrouser and the energy harvesting and transmit power constraints. Both the scenarios of perfect and imperfect channel state information (CSI) are considered. With perfect CSI, the formulated optimization problem constitutes a difference of a convex function programming problem, which is hard to directly solve. To tackle this challenge, we transform it into a series of semidefinite programs by using successive convex approximation, and an iterative algorithm is proposed to arrive at a provably convergent solution. With imperfect CSI, we address robust secure beamforming relying on the worst-case design philosophy. To circumvent this predicament, we resort to the S-procedure to reformulate the robust quadratic matrix inequality (QMI) constraints and then obtain the linear matrix inequality representations for these QMIs. Numerical results are finally presented to demonstrate the performance of our proposed schemes in improving the secrecy rate of heterogeneous cellular networks.

Cross-Layer QoE Optimization for D2D Communication in CR-Enabled Heterogeneous Cellular Networks

Device-to-device (D2D) communication based on cognitive radio (CR) technology can significantly improve the coverage and spectral efficiency. Existing research on D2D communications mainly focus on optimizing the network quality of service in single-tier networks. However, the exponential growth in data traffic has inspired the move from traditional single-tier cellular networks toward heterogeneous cellular networks. Hence, in this paper, we consider a CR-based HetNet coexisting with cognitive D2D pairs and cellular users, where the cellular users are primary users and D2D pairs are secondary users. Considering quality of experience (QoE) is an important metric to quantify and measure quality of experience from the user perspective, we focus on the QoE optimization of the D2D pairs via the BS association, the discrete power control, and the resource block (RB) assignment. To do so, we first formulate the cross-layer optimization problem to maximize the average QoE of the D2D pairs while satisfying the QoE requirements of cellular users. We then propose the centralized resource allocation, namely the genetic algorithm (GA), and semi-distributed resource allocation method, namely Stackelberg game based algorithm, to solve the non-convex optimization problem. The GA is proposed to ensure the maximum achievable QoE with known channel state information (CSI), whereas the Stackelberg game based algorithm is proposed to cope with the strong needs for distributed D2D solutions with only local CSI of each D2D link. Our proposed algorithms can achieve substantial improvement of QoE performance for D2D pairs via increasing the number of RBs.

SVC Video Delivery in Cache-Enabled Wireless HetNet

In heterogeneous cellular network (HetNet), costly transmissions from the macro base stations can be reduced by caching popular videos at small base station and user equipment. In this paper, we consider the joint transmission scheduling and rate allocation problem of scalable video coding streaming over cache-enabled wireless HetNet. We formulate the joint optimization problem to maximum system capacity with an mixed-integer linear programming, and prove that finding the optimal solution is NP-hard. Heuristic solution was proposed based on an iterative algorithm focusing on transmission scheduling decision and rate allocation, where transmission capacity is allocated flexibly and the quality of service of users is satisfied. Simulation results have shown that the proposed scheme can significantly improve the video-delivery performance for all users, in comparison with existing schemes.

Security-Reliability Tradeoff for Distributed Antenna Systems in Heterogeneous Cellular Networks

In this paper, we investigate physical-layer security for a spectrum-sharing heterogeneous cellular network comprised of a macro cell and a small cell, where a passive eavesdropper is assumed to tap the transmissions of both the macro cell and small cell. In the macro cell, a macro base station (MBS) equipped with multiple distributed antennas sends its confidential information to a macro user (MU) through an opportunistic transmit antenna. Meanwhile, in the small cell, a small base station (SBS) transmits to a small user (SU) over the same spectrum used by MBS. We propose an interference-canceled opportunistic antenna selection (IC-OAS) scheme to enhance physical-layer security for the heterogeneous network. To be specific, when MBS sends its confidential message to MU through an opportunistic distributed antenna, a special signal is artificially designed and emitted at MBS to ensure that the received interference at MU from SBS is canceled out. For comparison, the conventional interference-limited opportunistic antenna selection (IL-OAS) is considered as a benchmark. We characterize the security-reliability tradeoff (SRT) for the proposed IC-OAS and conventional IL-OAS schemes in terms of deriving their closed-form expressions of intercept probability and outage probability. Numerical results show that compared with the conventional IL-OAS, the proposed IC-OAS scheme not only brings SRT benefits to the macro cell, but also has the potential of improving the SRT of small cell by increasing the number of distributed antennas. Additionally, by jointly taking into account the macro cell and small cell, an overall SRT of the proposed IC-OAS scheme is shown to be significantly better than that of the conventional IL-OAS approach in terms of a sum intercept probability versus sum outage probability.

Dual-Battery Enabled Profit Driven User Association in Green Heterogeneous Cellular Networks

With awareness of the potential harmful effects to the environment and climate change, on-grid brown energy consumption of information and communications technology (ICT) has drawn much attention. Cellular base stations (BSs) are among the major energy guzzlers in ICT, and their contributions to the global carbon emissions increase sustainedly. It is essential to leverage green energy to power BSs to reduce their on-grid brown energy consumption. However, in order to furthest save on-grid brown energy and decrease the on-grid brown energy electricity expenses, most existing green energy related works only pursue to maximize the green energy utilization, while compromising the services received by the mobile users. In reality, dissatisfaction of services may eventually lead to loss of market shares and profits of the network providers. In this paper, we propose a dual-battery enabled profit driven user association scheme by jointly considering the traffic delivery latency and green energy utilization to maximize the profits for the network providers in heterogeneous cellular networks. Since this profit driven user association optimization problem is NP-hard, we further propose some heuristics to solve the problem with low computational complexity. Finally, the performance of the proposed algorithm has been validated through extensive simulations.