Deployment Of Small Cells Research Articles

UNII-MAC protocol: Design and evaluation for 5G ultra-dense small cell networks operating in 5 GHz unlicensed spectrum

Ultra-densification and efficient spectrum utilization are key features for the next 5G wireless networks to address the well-known challenges of high capacity demands and mobile data traffic explosion. In this article, a physical layer and a medium access control (MAC) sublayer are presented for small cells to operate in the 5 GHz unlicensed national information infrastructure (UNII) band. The physical layer is based on filter bank multi-carrier modulation able to achieve better spectral efficiency and access flexibility. The MAC protocol is based on beacon-enabled superframe consisting of scheduled and contention access schemes. The proposed UNII-MAC design relies on a listen-before-talk procedure in order to comply with ETSI regulations and to fairly coexist with neighboring systems sharing the same band. The performance of the UNII-MAC is then evaluated in dense indoor/outdoor deployment scenarios under various parameters and traffic patterns. Moreover, the coexistence between UNII-MAC and WiFi systems is reported. Based on the obtained results, we provide recommendations for 5G small cell deployment in dense environments.

Optimal design of energy efficient two-tier HetNets with massive MIMO by coordinated multipoint beamforming

This paper presents an energy-efficient (EE) coordinated multipoint beamforming (CMBF) approach that minimizes the total power consumption based on both the dynamic emitted power and static hardware power while maintaining necessary quality of service (QoS) constraints and different coordinated schemes. We deduce expressions the optimal value of each parameter in a two-tier heterogeneous networks (HetNets) from the perspective of energy efficiency (EE), considering a massive multiple-input multiple output (MIMO) system in conjunction with CMBF and small cell deployment. We find that the EE of HetNets is sensitive to the coordinated scheme design, the number of macro-cell and small-cell base station antennas, and QoS constraints. As such, all these factors should be taken into account in system design. Furthermore, we provide promising analytical and simulation results demonstrating that the proposed HetNets generally provides a solution for achieving maximal EE performance with relatively low-complexity CMBF.

Towards 5G: Scenario-based assessment of the future supply and demand for mobile telecommunications infrastructure

Moving from 4G LTE to 5G is an archetypal example of technological change. Mobile Network Operators (MNOs) who fail to adapt will likely lose market share. Hitherto, qualitative frameworks have been put forward to aid with business model adaptation for MNOs facing on the one hand increasing traffic growth, while on the other declining revenues. In this analysis, we provide a complementary scenario-based assessment of 5G infrastructure strategies in relation to mobile traffic growth. Developing and applying an open-source modelling framework, we quantify the uncertainty associated with future demand and supply for a hypothetical MNO, using Britain as a case study example. We find that over 90% of baseline data growth between 2016 and 2030 is driven by technological change, rather than demographics. To meet this demand, spectrum strategies require the least amount of capital expenditure and can meet baseline growth until approximately 2025, after which new spectrum bands will be required. Alternatively, small cell deployments provide significant capacity but at considerable cost, and hence are likely only in the densest locations, unless MNOs can boost revenues by capturing value from the Internet of Things (IoT), Smart Cities or other technological developments dependent on digital connectivity.

Impact of Interference Between Neighbouring 5G Micro Operators

Local small cell deployments will become an important part of the future 5G networks, in particular in the higher frequency bands. In order to speed up the wide-spread deployment of such ultra-dense networks, new business and spectrum authorization models are needed. The recently proposed concept of micro operators with local spectrum micro licensing has gained significant interest in research, industry and regulation to complement the traditional models based on networks deployed and operated by the mobile network operators. While assessing the applicability of the proposed micro operator concept, one important aspect is to evaluate the impact of the inter-operator interference on the performance of the victim network when deployed in the same or adjacent channel. To support such interference evaluations between micro operators, this paper proposes a deployment scenario including two neighbouring buildings, propagation models for connections both within a building and between the buildings, and a criteria for the required minimum separation distance based on the observed throughput loss. Finally, system simulations are performed to evaluate the impact of the key deployment aspects on the required minimum separation distance between the micro operators in the 3.5 GHz band. The obtained results indicate that the required minimum separation distances are highly scenario-specific, which needs to be considered in the overall local spectrum micro licensing model development and the setup of appropriate rules to coordinate the interference.

Possible Security Attack Modeling in Ultradense Networks Using High-Speed Handover Management

The next generation of mobile communication has progressed toward the deployment of small cells to meet the growing demands of increased capacity and QoS as compared to the conventional method, where all the computations were performed by the base station (BS)'s only. To reduce burden at the BS side, small cells deployment has been stressed upon, thus resulting in the formation of ultradense networks (UDN) having high concentration of small cells (e.g., picocell, femtocell, hotspots) and as a counter effect of which distance between two small cells is reduced to a greater extent. With such a close association of cells in UDN, the probability of frequent handovers also increases abruptly. As a result, the chances for attacker to spoof the bandwidth also increases many folds. In this paper, we have analyzed SNR, signal-to-interference-plus-noise ratio, and channel quality information channel parameters, such that the position of moving users at which handover is initiated in picocell deployment of UDN can be traced out successfully or region where the probability of attackers presence is high. Through this paper, we have tried to introduce the attacking scenario for the high mobility conditions in UDN.

Interference Coordination in Heterogeneous Small-Cell Networks: A Coalition Formation Game Approach

Heterogeneous small-cell networks have been identified as key technological components in accomplishing objectives of the fifth generation wireless communication system, in which the key point is the hyper dense deployment of small-cells. However, the interference among dense small-cells exacerbates in hyper dense deployment coupled with incessant use of multimedia services. In this paper, a network-side self-organized coalition formation approach for intra-tier interference mitigation primarily through neighborhood cooperation is proposed. By forming disjoint coalitions, small-cell access points (SAPs) are able to mitigate the interference within a coalition and thus improve their achievable data rates. The cooperative behavior among the neighborhood SAPs is formulated as a coalition formation game in partition form with non-transferable utility. Instead of fully reversible and irreversible methods used in prior studies, a merge and split based algorithm with partial reversibility rule which can obtain a final stable partition in the recursive core is proposed. The proposed algorithm converges to a final stable partition in a finite number of steps and works efficiently for both co-channel and orthogonal radio resource allocation modes. Simulation results have verified that the proposed algorithm can significantly improve the individual SAP throughput for both modes when compared with the conventional and the non-cooperative schemes.

Semi-cooperative game theoretic framework for resource allocation in cognitive cellular networks

Deployment of small cells beside macro cells has become the promising solution to meet the increasing service demand with limited bandwidth. However, the inter- and intra-tier interference limit the network capacity. Here, we present a semi-cooperative based resource allocation (SCRA) framework for cognitive small cells. The proposed framework allocates the underutilized spectrum of primary network for the downlink transmission of cognitive small cells such that the interference to primary users is below the threshold and the QoS (Quality of Service) of the associated user is satisfied. The game theoretic approach is adapted for distributed resource allocation where players (i.e. cognitive small cells) access primary channels in a non-cooperative manner. The utility of players is modeled as a negative weighted sum of the transmission power in the primary channels. We assume that the macro cell, after a specific interval of time, uses the primary users’ cooperation to obtain the channel weights for the players. We show that there exists the Nash Equilibrium (NE) in the proposed game of resource allocation. Finally, the performance of proposed SCRA enabled two-tier networks is demonstrated through extensive simulations.

Efficient Use of the Spectrum in Small Cell Deployments for 5G Wireless Communications Networks

Efficient Use of the Spectrum in Small Cell Deployments for 5G Wireless Communications Networks

Uplink Area Spectral Efficiency Analysis for Multichannel Heterogeneous Cellular Networks With Interference Coordination

The deployment of small cells (SCs) in heterogeneous cellular networks (HCNs) has been shown to be a promising approach to increase the system capacities of wireless communications. However, the bandwidth sharing and densification of the SCs cause co-tier and cross-tier interferences that limit the system spectral efficiency. In this paper, a framework of an uplink area spectral efficiency (ASE) analysis for multichannel HCNs using a proposed biased cell association scheme with coordinated subchannel allocation and channel inversion power control for mitigating the interferences is developed. The coordinated subchannel allocation is proposed to alleviate the severe cross-tier interference caused by macrocell users around the edges of the SCs. By incorporating the coordinated subchannel allocation into the biased cell association scheme with a bias factor, the proposed scheme is able to design the bias factor to reshape the coverage areas of the SCs providing an effective tradeoff between user offloading and cross-tier interference avoidance. By applying the tools of stochastic geometry, the uplink ASE is analytically derived as a function of the bias factor for the multichannel HCNs. The optimal bias factor can be obtained numerically by maximizing the system ASE. It is shown that the ASE performance analysis agrees with computer simulation very well. The results demonstrate that the proposed scheme can substantially improve the ASE performance of the multichannel HCNs for different small cell densities and outperform upon an existing biased cell association scheme.

Game-Based Approach for QoS Provisioning and Interference Management in Heterogeneous Networks

For the current 5G era, the deployment of small cells in residential and commercial areas plays an imperious preamble in improving network coverage and the quality of service (QoS). Major technical problems associated with the mass deployment of small cells, such as femtocells are interference management and QoS provisioning. These are important for service-providing operators because the system capacity and achievable data rates mainly depend on interference. Future generation wireless networks will use autonomous and distributed architecture for ameliorating the efficacy and flexibility of communication systems. In this paper, we propose a game theory-based model along with dynamic channel allocation and self-optimizing power control scheme for resolving priority-based access exposure by applying the concept of primary and secondary users. It is expected that the consumers will experience better QoS with reduced interference levels, and the service-providing operators will be able to increase their revenue, while ensuring optimal price for the consumers. We assimilated extensive numerical results to demonstrate the efficacy of our proposed model.

Memory-Full Context-Aware Predictive Mobility Management in Dual Connectivity 5G Networks

Network densification with small cell deployment is being considered as one of the dominant themes in the fifth generation (5G) cellular system. Despite the capacity gains, such deployment scenarios raise several challenges from mobility management perspective. The small cell size, which implies a small cell residence time, will increase the handover (HO) rate dramatically. Consequently, the HO latency will become a critical consideration in the 5G era. The latter requires an intelligent, fast, and light-weight HO procedure with minimal signaling overhead. In this direction, we propose a memory-full context-aware HO scheme with mobility prediction to achieve the aforementioned objectives. We consider a dual connectivity radio access network architecture with logical separation between control and data planes because it offers relaxed constraints in implementing the predictive approaches. The proposed scheme predicts future HO events along with the expected HO time by combining radio frequency performance to physical proximity along with the user context in terms of speed, direction, and HO history. To minimize the processing and the storage requirements whilst improving the prediction performance, a user-specific prediction triggering threshold is proposed. The prediction outcome is utilized to perform advance HO signaling whilst suspending the periodic transmission of measurement reports. Analytical and simulation results show that the proposed scheme provides promising gains over the conventional approach.

Data-Driven Deployment and Cooperative Self-Organization in Ultra-Dense Small Cell Networks

Ultra-dense small-cell network is widely acknowledged as a key enabler for high capacity wireless networks. Some of the key challenges that ultra-dense networks face are profitable deployment distribution under complex traffic loads and efficient radio resource management (RRM) in excessive interference environments. Poor small-cell deployment locations can lead to excessive interference without clear profit margins and inefficient resource utilization. As such, data-driven small-cell deployment and self-organizing RRM of small-cell clusters are regarded as the two main technologies that can improve ultra-dense small-cell services. This paper first reviews the latest research in data-driven small-cell deployment using structured and unstructured social media data. A combination of irregular clustering techniques is used to identify hotspots, and natural language processing algorithms are used to identify blackspots. This paper then reviews recent advances in self-organization of small-cell RRM and analyzes how data can improve self-organization performance. Moreover, the idea of cooperative self-organization is introduced to further promote the self-organization capability. Finally, two ultra-dense small-cell RRM case studies are presented to demonstrate the performance which improves of cooperative self-organization.

FHC-PCIA: A Physical Cell Identification Allocation Method Based on Fuzzy Hierarchical Clustering for Heterogeneous Cellular Network

When users seek for Network in a heterogeneous cellular network, physical cell identification (PCI) is used to distinguish different cellular cells. However, the number of PCIs is extremely limited. Moreover, they are unable to satisfy large-scale random deployment of small cellular cells as well as difficult to guarantee users’ quality of service. Therefore, this paper presents a fuzzy hierarchical clustering-physical cell identification allocation scheme. The proposal is based on the “activity” of cellular base station (CBS) and uses the Euclidean distance method to obtain the degree of similarities between the CBSs. After dynamic fuzzy clustering, the optimal clustering results are obtained by using the analysis of variance. In this paper, high priority of allocating and reusing the PCIs are given to those CBSs with higher activity. Simulation results show a clear increase in PCI allocation efficiency and reduction in PCI-conflict and PCI-confusion possibilities when compared with the existing schemes.

On Downlink NOMA in Heterogeneous Networks With Non-Uniform Small Cell Deployment

Compared to orthogonal multiple access (OMA), non-orthogonal multiple access (NOMA) can achieve higher spectral efficiency by exploiting the power domain multiplexing. In this paper, we investigate the performance of NOMA in a two-tier heterogeneous network (HetNet) with non-uniform small cell deployment, where critical performance metrics like coverage probability and achievable rate are analyzed. First, a NOMA-based HetNet model is established, where users are paired based on the proposed user pairing scheme. Then the distribution of the order statistics for the distances between different NOMA users and the serving base station (BS) is presented considering the channel qualities from the NOMA users to the BSs. On this basis, we analytically demonstrate the impact of various network parameters on the coverage probability and achievable rate of NOMA users, such as signal-to-interference-plus-noise ratio threshold and BS density. Furthermore, an analysis is presented to provide insight into the energy efficiency of the considered system. Finally, extensive simulation and comparisons are conducted, which validate the advantages of NOMA over OMA in the considered HetNet environment.

Adaptive Hysteresis Margin Based on Fuzzy Logic for Handover in Mobile Networks With Dense Small Cells

To satisfy requirements on future mobile network, a large number of small cells should be deployed. In such scenario, mobility management becomes a critical issue in order to ensure seamless connectivity with a reasonable overhead. In this paper, we propose a fuzzy logic-based scheme exploiting a user velocity and a radio channel quality to adapt a hysteresis margin for handover decision in a self-optimizing manner. The objective of the proposed algorithm is to reduce a number of redundant handovers and a handover failure ratio while allowing the users to exploit benefits of the dense small cell deployment. Simulation results show that our proposed algorithm efficiently suppresses ping pong effect and keeps it at a negligible level (below 1%) in all investigated scenarios. Moreover, the handover failure ratio and the total number of handovers are notably reduced with respect to existing algorithms, especially in scenario with high number of small cells. In addition, the proposed scheme keeps the time spent by the users connected to the small cells at a similar level as the competitive algorithms. Thus, the benefits of the dense small cell deployment for the users are preserved.

Multi-Criteria Handover Using Modified Weighted TOPSIS Methods for Heterogeneous Networks

Ultra-dense small cell deployment in future 5G networks is a promising solution to the ever increasing demand of capacity and coverage. However, this deployment can lead to severe interference and high number of handovers, which in turn cause increased signaling overhead. In order to ensure service continuity for mobile users, minimize the number of unnecessary handovers and reduce the signaling overhead in heterogeneous networks, it is important to model adequately the handover decision problem. In this paper, we model the handover decision based on the multiple attribute decision making method, namely Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). The base stations are considered as alternatives, and the handover metrics are considered as attributes to selecting the proper base station for handover. In this paper, we propose two modified TOPSIS methods for the purpose of handover management in the heterogeneous network. The first method incorporates the entropy weighting technique for handover metrics weighting. The second proposed method uses a standard deviation weighting technique to score the importance of each handover metric. Simulation results reveal that the proposed methods outperformed the existing methods by reducing the number of frequent handovers and radio link failures, in addition to enhancing the achieved mean user throughput.

Device-to-Device Communications Enabled Energy Efficient Multicast Scheduling in mmWave Small Cells

To keep pace with the rapid growth of mobile traffic demands, dense deployment of small cells in millimeter wave (mmWave) bands has become a promising candidate for next generation wireless communication systems. With a greatly increased data rate from huge bandwidth of mmWave communications, energy consumption should be mitigated for higher energy efficiency. Due to content popularity, many content-based mobile applications can be supported by the multicast service. mmWave communications exploit directional antennas to overcome high path loss, and concurrent transmissions can be enabled for better multicast service. On the other hand, device-to-device (D2D) communications in physical proximity should be exploited to improve multicast performance. In this paper, we propose an energy efficient multicast scheduling scheme, referred to as EMS, which utilizes both D2D communications and concurrent transmissions to achieve high energy efficiency. In EMS, a D2D path planning algorithm establishes multi-hop D2D transmission paths, and a concurrent scheduling algorithm allocates the links on the D2D paths into different pairings. Then the transmission power of links is adjusted by the power control algorithm. Furthermore, we theoretically analyze the roles of D2D communications and concurrent transmissions in reducing energy consumption. Extensive simulations under various system parameters demonstrate the superior performance of EMS in terms of energy consumption compared with the state-of-the-art schemes. Furthermore, we also investigate the choice of the interference threshold to optimize network performance.

Heterogeneous Cellular Networks With LoS and NLoS Transmissions—The Role of Massive MIMO and Small Cells

We develop a framework for downlink heterogeneous cellular networks with line-of-sight (LoS) and non-LoS transmissions. Using stochastic geometry, we derive tight approximation of average downlink rate that enables us to compare the performance between densifying small cells and expanding base station (BS) antenna arrays. Interestingly, we find that adding small cells into the network improves the downlink rate much faster than expanding antenna arrays at the macro BS. However, when the small cell density exceeds a critical threshold, the spatial densification will lose its benefits and further impair the network capacity. To this end, we provide the optimal small cell density that maximizes the rate via numerical results for practical deployment guidance. In contrast, expanding macro BS antenna array can always benefit the capacity until an upper bound caused by pilot contamination, and this bound also surpasses the peak rate obtained from the deployment of small cells. Furthermore, we find that allocating part of antennas to distributed small cell BSs works better than centralizing all antennas at the macro BS, and the optimal allocation proportion is also given numerically for practical configuration reference. In summary, this paper provides a further understanding on how to leverage small cells and massive MIMO in future heterogeneous cellular networks deployment.

An SDN-Based Video Multicast Orchestration Scheme for 5G Ultra-Dense Networks

Predictions indicate that mobile video streams will dominate mobile traffic in the near future. Heterogeneous UDN is a promising technique for 5G mobile networks. This technique offers high access speeds for video watchers through the dense deployment of small cells. However, the backhaul of a UDN will become a bottleneck with the rapid increase in mobile video traffic. Additionally, the considerable video traffic generated from and to UDNs induces significant stress on the core network of a 5G network. Therefore, it is necessary to optimize the distribution of video content for 5G UDNs. Multicasting is considered to be a good communication method for distributing video content. This article examines a video multicast orchestration scheme based on SDN, named HCM, for 5G UDNs. To adapt well to a heterogeneous UDN environment in 5G networks and effectively save spectrum resources, HCM implements wireless multicast functionality based on a common unicast channel. HCM performs concurrent multicasting to clearly reduce the bandwidth consumption of a 5G network, particularly the backhaul, and further controls video traffic passed through the backhaul using a traffic-aware method. During the packet loss recovery of HCM, SDN-based elastic area multicast is used to more effectively retransmit recovered packets. The experimental results indicate that our proposed scheme can distribute video content with high effectiveness.

Hypergraph Theory: Applications in 5G Heterogeneous Ultra-Dense Networks

Heterogeneous ultra-dense networks (HUDNs) can significantly increase the spectral efficiency of cellular networks and cater for the explosive growth of data traffic in 5G communications. Due to the dense deployment of small cells, interference among neighboring cells becomes severe. As a result, effective resource allocation and user association algorithms are essential to minimize inter-cell interference and optimize network performance. However, optimizing network resources in an HUDN is extremely complicated as resource allocation and user association are coupled. Therefore, an HUDN requires low-complexity but effective resource allocation schemes to address these issues. Hypergraph theory has been recognized as a useful mathematical tool to model the complex relations among multiple entities. In this article, we show how the hypergraph models can be used to effectively tackle resource allocation problems in an HUDN. We also discuss several potential research issues in this field.