Macrocell Deployment Research Articles

X2-Based Signalling Mechanisms for Downlink Uplink Decoupling in Next Generation Communication Systems

Cell selection in cellular networks is an important aspect that impacts the quality of service. The traditional cell selection mechanism is based on downlink received power. Despite the dense deployment of macrocells, mobile network operators are still confronting the daunting challenge of providing capacity and coverage. Deployment of a large number of small cells has emerged as a promising solution towards addressing this problem. However, this success expands the heterogeneous cellular networks where there is a significant disparity in the transmit power of the different base station types. Downlink and Uplink Decoupling (DUDe) can improve efficiency by associating the downlink cell based on the downlink received power and the uplink based on the pathloss. While the higher layer signalling has not been proposed in detail for the DUDe mechanism yet, we aim to propose a solution for the problem. This work addresses four different signalling mechanisms to realise decoupled up/downlinks connections in the radio access network for the next-generation communication systems with handling mobility. Our proposed signalling mechanisms cover uplink decoupling, downlink coupling, downlink decoupling, and uplink coupling scenarios. We analyse the proposed signalling mechanisms using ns3 simulation and present the impact of applying the DUDe mechanism, which mainly shows improvements for the uplink. For the selected mobility scenario, delay and lost packets are reduced by 30% and 26%, respectively. Delay and lost packets are reduced by 36% and 27% for the fix location scenario, respectively. The improvements imply that it reaches particular demand considering next-generation communication systems, with a massive number of smart devices demanding high quality of service requirements.

Automated Self-Optimization in Heterogeneous Wireless Communications Networks

Traditional single-tiered wireless communications networks cannot scale to satisfy exponentially rising demand. Operators are increasing capacity by densifying their existing macro cell deployments with co-channel small cells. However, cross-tier interference and load balancing issues present new optimization challenges in channel sharing heterogeneous networks (HetNets). One-size-fits-all heuristics for allocating resources are highly suboptimal, but designing ad hoc controllers requires significant human expertise and manual fine-tuning. In this paper, a unified, flexible, and fully automated approach for end-to-end optimization in multi-layer HetNets is presented. A hill climbing algorithm is developed for reconfiguring cells in real time in order to track dynamic traffic patterns. Schedulers for allocating spectrum to user equipment are automatically synthesized using grammar-based genetic programming. The proposed methods for configuring the HetNet and scheduling in the time–frequency domain can address ad hoc objective functions. Thus, the operator can flexibly tune the tradeoff between peak rates and fairness. Far cell edge downlink rates are increased by up to 250% compared with non-adaptive baselines. Alternatively, peak rates are increased by up to 340%. The experiments illustrate the utility and future potential of natural computing techniques in software-defined wireless communications networks.

A simple approach for the suppression of Rician interference in a relay backhaul using limited feedback

The benefits of Decode and Forward (DF) relaying span from deployment flexibility to coverage extension and improved capacity distribution in the network. Accordingly, relaying has become an integral part of the modern radio access network standards. Besides the evident benefits of DF relaying, the fact is that it uses part of the valuable radio access resources for the communication between network elements. Thus, the amount of radio resources allocated to the Relay Link (RL) between serving Donor Base Station (DBS) and the Relay Node (RN) should be minimised. This easily makes the RL a bottleneck in conventional two-hop infrastructure relaying. Furthermore, current mobile systems apply universal frequency reuse in macrocell deployments where macrocell BS’s serve RN’s as well. As a result, RL’s may suffer from severe interference.We propose a practical limited feedback approach that can be used to simultaneously improve the signal strength and to suppress the interference in the RL. To that end, we deduce analytical formulae for the distribution of the Signal to Interference and Noise Ratio (SINR) in the RL by assuming Rice and Rayleigh fading combinations in desired and interfering links. Furthermore, we compute two-hop end-to-end (e2e) outage probabilities for different interference and limited feedback scenarios. Results show that especially in Rice fading environment, large performance gains can be obtained with only few bits feedback in case where RL has scarce radio resources and suffers from dominant interferer. This makes the proposed method very feasible for the infrastructure relaying where RN’s can be placed either in the rooftop level or other locations that provide a line of sight towards macro BS’s.

Handover Authentication Scheme for Device-to-Device Outband Communication in 5G-WLAN Next Generation Heterogeneous Networks

The idea of future generation 5G-WLAN heterogeneous network communication lies in increasing multiple fold increase in base station capability, higher data rate up to order of Gbps, vital enhancement in clients’ observed quality of experience, and ultra low latency as compared to the modern day 4G LTE-WLAN heterogeneous networks. Heterogeneous deployment of small and macrocells is considered as a primary network configuration in 5G-WLAN networks. It is vital to accomplish consistent handovers between a small cell base station and a mobile device under the device-to-device (D2D) outband relaying communication with cellular operator-controlled link establishment scenario. A handover from a small cell base station to a new mobile device under D2D communication demands complex methodology for a cellular operator-controlled link establishment scenario, which increases the system complexity. The mobile devices with two unique interfaces (5G network and Wi-Fi) can simultaneously access the 5G network and provide the Internet services to a client. Here, we present a quick and safe handover authentication scheme to suit in D2D outband-controlled communication mobility situations in the 5G-WLAN heterogeneous networks. Compared to other handover schemes, our scheme not only accomplishes a re-authentication procedure with attractive proficiency, but also provides numerous security features, user anonymity, mutual authentication, and perfect backward/forward secrecy. The security and performance analysis demonstrate that the presented scheme is proficient and secured against many kinds of attacks.

Towards Studying the Two-Tier Intra-Frequency X2 Handover Based on Software-Defined Open LTE Platform

The next generation cellular systems are rapidly evolving from a homogeneous macrocell deployment to a heterogeneous deployment of macrocells overlaid with femtocells, which is referred to as heterogeneous networks (HetNets). In macro-femto HetNets, the handover issue is more important than that in macrocell networks. On one hand, more frequent handovers are triggered because the coverage range of the femtocell is small, and the multiple femtocells are overlaid with macrocells. On the other hand, some schemes, such as load balancing, aimed at improving network performance, will also cause frequent handover in macro-femto HetNets. Therefore, the study on handover is of great importance, especially in macro-femto HetNets. In this paper, based on the software-defined open long-term evolution (LTE) platform, we propose an analytical model to study the two-tier intra-frequency X2 handover in realistic macrocell-femtocell HetNets scenario. Specifically, we first construct the software-defined open LTE platform. Based on the open LTE platform, we then characterize the relation between the handover failure and the ping-pong rates in a macro-femto HetNets scenario as a function of the relevant system parameters such as the time-to-trigger, user equipment velocity, etc. Finally, we derive the handover failure and ping-pong rates in closed-form expressions. The handover experiment results have verified the accuracy of our analytical derivations, which shed new light on key aspects of the handover process in macro-femto HetNets.

Competitive Resource Allocation in HetNets: The Impact of Small-Cell Spectrum Constraints and Investment Costs

Heterogeneous wireless networks with small-cell deployments in licensed and unlicensed spectrum bands are a promising approach for expanding wireless connectivity and service. As a result, wireless service providers (SPs) are adding small-cells to augment their existing macro-cell deployments. This added flexibility complicates network management, in particular, service pricing and spectrum allocations across macro- and small-cells. Further, these decisions depend on the degree of competition among SPs. Restrictions on shared spectrum access imposed by regulators, such as low power constraints that lead to small-cell deployments, along with the investment cost needed to add small cells to an existing network, also impact strategic decisions and market efficiency. If the revenue generated by small-cells does not cover the investment cost, then there will be no deployment even if it increases social welfare. We study the implications of such spectrum constraints and investment costs on resource allocation and pricing decisions by competitive SPs, along with the associated social welfare. Our results show that while the optimal resource allocation taking constraints and investment into account can be uniquely determined, adding those features with strategic SPs can have a substantial effect on the equilibrium market structure.

Interference Alignment and Cancelation for the Uplink of Heterogeneous Networks

In this paper, we propose an interference alignment and cancelation (IAC) scheme for the uplink of heterogeneous networks (HetNets). Due to the random deployment of small cells and the heterogeneous deployment of macrocells and small cells, complex interference occurs in HetNets. This makes the optimal interference cancelation order and the corresponding interference alignment (IA) scheme of IAC hard to determine. To address this problem, we first develop a set of constraints that should be satisfied by users, base stations, and interference cancelation when IAC is carried out in the HetNets. Meanwhile, by giving the design method of the precoding and decoding vectors, we prove that IAC is feasible if the developed constraints are satisfied. Then, to determine the optimal IAC scheme, based on the developed constraints, we construct an optimization problem with the aim of maximizing the number of data streams that can be transmitted in the network. By solving the optimization problem, the optimal interference cancelation order and the corresponding IA scheme can be obtained. The simulation results show that the proposed IAC scheme can significantly increase the number of data streams transmitted in the whole network.

A study on cell association in heterogeneous networks with joint load balancing and interference management

Exponential growth in the demand for network capacity has led to extensive research on advanced cellular network technology. A heterogeneous network in which traditional well-planned macro cell deployment is overlaid by small-scale unplanned base stations is one effective solution for next-generation networks. However, the cell association techniques currently used in macro-only cellular networks are not suitable for next-generation heterogeneous networks. Finding effective methods to handle the cell association problem in this new type of network is a hot topic of research in this field. This paper provides an overview of the cell association problem in heterogeneous networks and discusses the main issues that need to be addressed by an efficient cell association technique in order to maximize the network throughput. It has been shown that an efficient cell association scheme in heterogeneous networks must balance the load among different cells while minimizing the inter-cell interference at the same time. Jointly considering these two objectives is a challenge currently being investigated by researchers. An overview on load balancing and interference management in heterogeneous networks is provided in this paper. A review of the existing literature shows that there is a need for an efficient distributed solution in which load balancing approaches are observed and at the same time users prone to harmful interference are protected. A framework for modeling the heterogeneity of this type of network is presented, a simulation is performed in order to verify the effects of different parameters, and, finally, the problem is formulated. Future research directions are also provided in the paper.

Technical Economic Analysis of Photovoltaic Systems in Heterogeneous Mobile Networks

Abstract: Mobile telecommunications operators are having to deal with an unprecedented increase in energy consumption due to the installa- tion of heterogeneous mobile networks (HetNets), which are based on the deployment of macrocells and simultaneous use of large numbers of small cells. Although it has an efficient energy strategy, HetNets leads to a considerable increase in the consumption of energy, owing to its densification, because the importance of Backhaul is often overlooked. The use of renewable sources of energy is suggested as a means of overcoming this problem, since it entails diversifying the energy matrix and reducing the volume of CO 2 emissions in the environment, as well as being economically viable. Thus, the aim of this study is to make a techno-economic assessment of the acquisition and installation of photovoltaic systems within HetNets, while taking account of the combined energy consumption of radio networks, fronthaul and backhaul. On the basis of the results, there was clear evidence of its financial viabil- ity with regard to the adoption of the photovoltaic framework, as well as the environmental sustainability ensured by a considerable reduction in CO 2 emissions.

Design, Modeling, and Performance Analysis of Multi-Antenna Heterogeneous Cellular Networks

This paper presents a stochastic geometry-based framework for the design and analysis of downlink multi-user multiple-input multiple-output (MIMO) heterogeneous cellular networks with linear zero-forcing transmit precoding and receive combining, assuming Rayleigh fading channels and perfect channel state information. The generalized tiers of base stations may differ in terms of their Poisson point process spatial density, number of transmit antennas, transmit power, artificial-biasing weight, and number of user equipments served per resource block. The spectral efficiency of a typical user equipped with multiple receive antennas is characterized using a non-direct moment-generating-function-based methodology with closed-form expressions of the useful received signal and aggregate network interference statistics systematically derived. In addition, the area spectral efficiency is formulated under different space-division multiple-access and single-user beamforming transmission schemes. We examine the impact of different cellular network deployments, propagation conditions, antenna configurations, and MIMO setups on the achievable performance through theoretical and simulation studies. Based on the state-of-the-art system parameters, the results highlight the inherent limitations of baseline single-input single-output transmission and conventional sparse macro-cell deployment, as well as the promising potential of multi-antenna communications and small-cell solution in interference-limited cellular environments.

Local Anchor Schemes for Seamless and Low-Cost Handover in Coordinated Small Cells

Cellular systems are rapidly evolving from a homogeneous macrocell deployment to a heterogeneous deployment of macrocells overlaid with many small cells. The striking features of small cells include small coverage area, ad-hoc deployment, and flexible backhaul connectivity. These features call for a profound rethinking of traditional cellular concepts including mobility management and interference management among others. Owing to the unique features, coordinated small cells or commonly referred to as network of small cells promises several benefits including efficient mobility management in a rapid and scalable fashion. The problem of handover in a high-density small cell deployment is studied in this work. A novel local anchor-based architecture for a static cluster of small cells is proposed using which new handover schemes are presented. Such clusters are prevalent in the evolving cellular systems involving high-density small cell deployments in urban, residential, and enterprise environments. A mathematical framework is developed using discrete-time-Markov-models to evaluate the proposed schemes. Using this, closed-form expressions for key handover metrics including handover cost and interruption time are derived. Extensive numerical and simulation studies indicate significant savings of over 50 percent in the handover costs and, more importantly, up to 80 percent in the handover interruption time compared to the existing 3GPP scheme for coordinated small cells.

Distribution of Cell in Mobile Network

Femtocell concept has emerged as a cost-effective solution to manage indoor environment coverage and increasing capacity requirements. Compare to the conventional control macrocell deployment, femtocells are spread in the uncontrolled manner as they are deployed in network by customers themselves. This paper discusses multi-distance spatial analysis, Ripley's K function, to describe distribution of femtocells in a macrocell. In our study, we investigate various femtocell distributions and various numbers of femtocells in the macrocell.

Potential of dynamic spectrum allocation in LTE macro networks

Abstract. In recent years Mobile Network Operators (MNOs) worldwide are extensively deploying LTE networks in different spectrum bands and utilising different bandwidth configurations. Initially, the deployment is coverage oriented with macro cells using the lower LTE spectrum bands. As the offered traffic (i.e. the requested traffic from the users) increases the LTE deployment evolves with macro cells expanded with additional capacity boosting LTE carriers in higher frequency bands complemented with micro or small cells in traffic hotspot areas. For MNOs it is crucial to use the LTE spectrum assets, as well as the installed network infrastructure, in the most cost efficient way. The dynamic spectrum allocation (DSA) aims at (de)activating the available LTE frequency carriers according to the temporal and spatial traffic variations in order to increase the overall LTE system performance in terms of total network capacity by reducing the interference. This paper evaluates the DSA potential of achieving the envisaged performance improvement and identifying in which system and traffic conditions the DSA should be deployed. A self-optimised network (SON) DSA algorithm is also proposed and evaluated. The evaluations have been carried out in a hexagonal and a realistic site-specific urban macro layout assuming a central traffic hotspot area surrounded with an area of lower traffic with a total size of approximately 8 × 8 km2. The results show that up to 47 % and up to 40 % possible DSA gains are achievable with regards to the carried system load (i.e. used resources) for homogenous traffic distribution with hexagonal layout and for realistic site-specific urban macro layout, respectively. The SON DSA algorithm evaluation in a realistic site-specific urban macro cell deployment scenario including realistic non-uniform spatial traffic distribution shows insignificant cell throughput (i.e. served traffic) performance gains. Nevertheless, in the SON DSA investigations, a gain of up to 25 % has been observed when analysing the resource utilisation in the non-hotspot cells.

The sector offset configuration concept and its applicability to heterogeneous cellular networks

Wireless data traffic is increasing in an exponential manner, and thus vendors and operators are looking for cost-effective solutions to meet user equipment demands. In this article a joint optimization of the deployment and operation of small cells and macrocells is presented through the novel concept of sector offset configuration, which helps to significantly improve user equipment performance. The proposed sector offset configuration complements Release 10 enhanced intercell interference coordination, and further increases its interference mitigation capabilities. Simulation results for a Long Term Evolution network show that compared to a network that uses standardized Release 10 almost blank subframes, the proposed configuration can improve cell-edge user equipment performance by 50 percent. The proposed configuration can mitigate handover failures by 46 percent, since hand overs start at a higher signal quality due to alleviated interference conditions. These benefits come at the cost of an increased number of antennas at the macrocell site to achieve the sector offset configuration.

Load balancing mechanisms for indoor temporarily overloaded heterogeneous femtocell networks

Macrocell and small cell deployments and self-organizing network (SON) techniques work together to increase indoor cellular network capacity and ensure better quality of service (QoS). As a consequence of uneven local user densities and temporal or spatial fluctuations of traffic, the network may suffer overload situations, which partially degrades network performance. Load balancing self-optimization introduces automatic and intelligent mechanisms to tune network parameters in order to improve the overall cellular network performance. This paper proposes novel load balancing methods based on fuzzy logic controllers (FLC) that evaluate temporarily overloaded situations and resize cell coverage areas by an adaptive process of adjusting cell transmission power. To accomplish this goal, classical network indicators are analyzed (e.g., call blocking ratio, available radio resources) while a novel and simple, although powerful, indicator (not mentioned in the literature yet) is additionally proposed as the system input. This indicator is related to the maximum allowed number of users in a femtocell. The proposed methods have been evaluated and compared with the literature in a realistic scenario.

Coordinated TDD-Underlay for Self-organizing Femtocells in Two-Tier Coexistence Scenarios

In this contribution, we investigate the concept of time division duplexing (TDD) mode as an alternative to underlay short-range femtocells on the uplink of legacy macrocell deployments. To mitigate the resulting co-channel interference, the underlaid femtocell tier uses a distributed mechanism which is based on regular busy tones and relies on minimal signaling exchange. Stochastic geometry is used to model practical scenarios by capturing network dynamics and channel variations. The impact of the fading correlation on the performance of the coordination mechanism is examined as well. Higher-order statistics through the cumulants concept are used to recover the distribution of the co-channel interference and evaluate the system performance in terms of the outage probability and average channel capacity. We observe that our analytical framework matches well with numerical results obtained using Monte Carlo simulations. In contrast to the uncoordinated frequency division duplexing mode, the coordinated TDD-underlay solution shows a reduction in the outage probability of nearly 80%, while the average spectral efficiency increases by approximately 90% in high loads.

Performance Evaluation of Interference Rejection Combining Receiver in Heterogeneous Networks for LTE-Advanced Downlink

The interference rejection combining (IRC) receiver effectively improves the cell-edge user throughput by suppressing interference from the surrounding cells. The work item (WI) for the specification of the IRC receiver is now ongoing for Release 11 Long-Term Evolution (LTE)-Advanced. Furthermore, heterogeneous networks where low power nodes such as picocells are overlaid onto macrocells are important to further improve the system throughput per unit area. In heterogeneous networks, to achieve an offloading gain from macrocells to picocells, cell range expansion (CRE) is applied. Additionally, inter-cell interference coordination (ICIC) is applied to reduce the severe inter-cell interference imposed from the macrocells onto the sets of user equipment (UEs) connected to picocells. In such cases, the interference statistics are completely different from traditional well-planned macrocell deployments, which have been investigated for the IRC receiver. This paper clarifies the effect of the IRC receiver in a heterogeneous network employing CRE and ICIC. Simulation results show that when both CRE and ICIC are applied, the effect of the IRC receiver becomes small due to a reduction in the severe inter-cell interference from ICIC. However, we clarify that the user throughput gain at the cumulative distribution function of 5% from the IRC receiver exceeding 10% is achieved compared to the conventional minimum mean square error (MMSE) receiver in a heterogeneous network regardless of the usage of ICIC. Furthermore, in heterogeneous networks employing CRE and ICIC, we clarify that an average user throughput gain exceeding 5% is achieved from the IRC receiver and the improvement in the average user throughput is high especially for the UEs connected to picocells compared to UEs connected to macrocells.

Energy-Efficient Base Station Operation in Heterogeneous Cellular Networks

In this paper, we study the ON/OFF control policy of base stations in two-tier heterogeneous cellular networks to minimize the total power consumption of the system. Using heterogeneous cellular networks is a potential approach of providing higher throughput and coverage compared to conventional networks with only macrocell deployment, but in fact heterogeneous cellular networks often operates regardless of total power consumption, which is a very important issue of modern cellular networks. We propose a policy that controls the activation/deactivation of base stations in heterogeneous cellular networks to minimize total power consumption. Under this policy, the total power consumed can be significantly reduced when the traffic is low while the QoS requirement is satisfied.

Techno-economic analysis of femtocell deployment in long-term evolution networks

In this article, we evaluate the economic gains of a joint deployment of femtocells and macrocells for the provision of long-term evolution mobile broadband services in urban environments. Frequency bands of 2.6 GHz and 900 MHz are analyzed and different parameters related to the business model are considered for a 30% market share operator. Results show important benefits for the case where the service is based on a closed subscriber group access to the femtocells, which the operator does not subsidy: up to 74% for small bandwidth (5 MHz). A business model approach based on open subscriber group access to the femtocell can also be interesting for the operator, although in this case, wholesale subscriber loop costs and femtocells cost are taken into account; thus, savings slightly decrease compared to the previous case. In addition, initial savings are reduced in 8–20% if the operator’s existing sites are reused.

Resource allocation with interference mitigation in OFDMA femtocells for co-channel deploymenta

Femtocells have been considered as a promising technology to provide better indoor coverage and spatial reuse gains. However, the co-channel deployment of macrocells and femtocells is still facing challenges arising from potentially severe inter-cell interference. In this article, we investigate the uplink resource allocation problem of femtocells in co-channel deployment with macrocells. We first model the uplink power and subchannel allocation in femtocells as a non-cooperative game, where inter-cell interference is taken into account in maximizing the femtocell capacity and uplink femto-to-macro interference is alleviated by charging each femto user a price proportional to the interference that it causes to the macrocell. Based on the non-cooperative game, we then devise a semi-distributed algorithm for each femtocell to first assign subchannels to femto users and then allocate power to subchannels. Simulation results show that the proposed interference-aware femtocell uplink resource allocation algorithm is able to provide improved capacities for not only femtocells, but also the macrocell, as well as comparable or even better tiered fairness in the two-tier network, as compared with existing unpriced subchannel assignment algorithm and modified iterative water filling-based power allocation algorithm.