Femtocells Research Articles

Resource Allocation in Macrocell–Femtocells via Combined Rain and Whale Optimization Algorithm

Femtocell (FC) dense exploitation imposes a novel challenge for the resource allotment in a 2-tier network, like: (1) dynamic resources allotment among the 2 tiers by considering the off-load traffic from macrocell (MC), (2) permitting access to users when ensuring QoS for FC subscribers, and (3) suitable power setting, which discovers cooperation among the overall bandwidth allotted to FCs and system performances. This research work examines the problems existing on cross-tier interfering as well as resource allocation alleviation in “full-duplex (FD) Orthogonal Frequency Division Multiple Access (OFDMA) oriented Heterogeneous Networks (HetNets), which involves macrocell with underlying femtocells”. Here, three primary contributions are concerned: a single objective issue together with power allocation, price allocation & subcarrier allocation of MC-FC networks. In addition, this research establishes a new hybrid algorithm termed Hybrid Whale and Rain Optimization (HW-RO) for solving the optimization problem in MC-FC Networks. Finally, the superiority of the suggested technique is evaluated in comparison to various existing approaches.

Semi‐distributed dynamic inter‐cell interference coordination scheme for interference avoidance in heterogeneous networks

Inter‐cell interference (ICI) is a major problem in heterogeneous networks, such as two‐tier femtocell (FC) networks, because it...

Application of Adaptive Neuro-Fuzzy Inference System for Interference Management in Heterogeneous Network

Femtocell (FC) technology envisaged as a cost-effective approach to attain better indoor coverage of mobile voice and data service. Deployment of FCs...

Femtocell‐enhanced multi‐target spectrum allocation strategy in LTE‐A HetNets

Due to prominent advantages in local coverage enhancement and indoor cellular capacity improvement, femtocell (FC) is considered as a vital component in long-term evolution advanced (LTE-A) heterogeneous networks (HetNets). A two-tier LTE-A HetNet with conventional macro base stations in the first tier and femto base stations in the second tier is considered. Under this architecture, a new downlink interference evaluation scheme is proposed, based on which a FC enhanced multi-target resource allocation algorithm is developed to maximise user equipment (UE) throughput in a dense FC deployment scenario meanwhile providing every UE a minimum signal to interference plus noise rate (SINR) guarantee. The optimal resource allocation problem is formulated as a MAX-K cut problem based on the graph theory approach. System-level simulations reveal that intra-cell interference is greatly reduced and the spectral efficiency is significantly improved by using the proposed resource allocation scheme. Femtocell throughput is elevated significantly without causing much degradation on the macrocell throughput.

Distributed Power Allocation for Femtocell Networks Subject to Macrocell SINR Balancing

We consider the power allocation for the two-tier heterogeneous network where a macrocell (MC) coexists with multiple femtocells (FCs). Each FC aims to maximize the weighted sum-rate of its users subject to MC signal-to-inter-ference-plus-noise ratio (SINR) balancing, which means that a prescribed SINR is guaranteed to MC users. We formulate a noncooperative game which captures bidirectional cross-tier interference. We develop a fully decentralized algorithm, and derive a sufficient condition for its convergence to a unique equilibrium.

An improved cooperative spectrum sensing of femtocells with hybrid TDD access scheme in massive MIMO system

SummaryTo improve the sensing performance and achieve higher throughput of the femtocells (FCs) while alleviating the influence to the macrocell in the cognitive massive multiple‐input and multiple‐output system (MIMO), we propose in this paper a hybrid time‐division duplex (TDD) access scheme of the FCs with confidence factor–based weighted cooperative spectrum sensing (CSS). A first, we present an efficient hybrid TDD access scheme for better spectrum reuse of the FCs based on the typical TDD and reversed TDD schemes. Furthermore, confidence factor–based weighted CSS has been used for better spectrum sensing and interference alleviation. In the cognitive massive MIMO system, FC base stations will form dynamical clustering based on the channel conditions, sense the spectrum through cooperative scheme, and decide whether to access the spectrum or not. After information exchange within each FC cluster, the FC base stations can obtain and update their confidence factors and weight factors based on the sensing results and reliability. Numerical results and theoretical analysis show that the proposed scheme can get more accurate sensing results, increase the throughput and the spectrum access opportunity of the FCs, and efficiently alleviate the interference to the macrocell tier.

QoS provisioning for multiple Femtocells via game theory

We consider a system with multiple Femtocells (FCs) operating in a Macrocell. The transmissions in one Femtocell interfere with its neighboring Femtocells. Each Femtocell has multiple users, each requiring a minimum transmission rate. There is also peak transmit power constraint in each channel to control interference to the BS and the users in the Macrocell. We formulate the problem of channel allocation and power control in each Femtocell as a noncooperative Game. We develop efficient decentralized algorithms to obtain a Nash equilibrium (NE) that satisfies the Quality of Service (QoS) of each user, in an efficient way. We also obtain efficient decentralized algorithms to obtain fair NE when it may not be feasible to satisfy the QoS of all the users in FCs. Finally, we extend our algorithms to the case where there may be voice and data users in the system.

Delay Analysis of an Improved Wimax Macro-Femto Handover Technique and Cell Selection Algorithm

Femtocells (FC) have been introduced in WiMAX networks due to the high data rate broadband access provided by Wimax networks. The key features like increased cell coverage, high throughput indoors and system capacity of FC are widely being accepted. However, issues regarding macro/femto handover decision are still being considered. This paper evaluates a technique for a macro/femto handover. The analyzed procedure offers communication with the mobile station having reduced delay. Moreover, it minimizes the number of FC(s) to be scanned during cell selection on the basis of cell ratio thus saving handover decision time.

Dynamic Heterogeneous Learning Games for Opportunistic Access in LTE-Based Macro/Femtocell Deployments

Interference is one of the most limiting factors when trying to achieve high spectral efficiency in the deployment of heterogeneous networks (HNs). In this paper, the HN is modeled as a layer of closed-access LTE femtocells (FCs) overlaid upon an LTE radio access network. Within the context of dynamic learning games, this work proposes a novel heterogeneous multiobjective fully distributed strategy based on a reinforcement learning (RL) model (CODIPAS-HRL) for FC self-configuration/optimization. The self-organization capability enables the FCs to autonomously and opportunistically sense the radio environment using different learning strategies and tune their parameters accordingly, in order to operate under restrictions of avoiding interference to both network tiers and satisfy certain quality-of-service requirements. The proposed model reduces the learning cost associated with each learning strategy. We also study the convergence behavior under different learning rates and derive a new accuracy metric in order to provide comparisons between the different learning strategies. The simulation results show the convergence of the learning model to a solution concept based on satisfaction equilibrium, under the uncertainty of the HN environment. We show that intra/inter-tier interference can be significantly reduced, thus resulting in higher cell throughputs.

Modeling and Performance of a Mesh Network with Dynamically Appearing and Disappearing Femtocells as Additional Internet Gateways

The number of hops from Mesh Routers (MRs) to an Internet gateway (IGW) plays an important role in determining the performance of a wireless mesh network (WMN). A recent patent has introduced a mechanism of using an existing femtocell (FC) as an additional potential IGW so that the performance of a WMN could be enhanced. Such an integration of WMN with FCs enables an increase in WMN's overall capacity. But, due to FCs' unpredictable operating times and uninformed disconnections, MRs require reliable and efficient schedule for switching between available FCs which has not been analyzed in the patent. The switching can be done in a push based preemptive or a pull based non-preemptive manner. In this paper, we formulate both these switching schemes for a WMN-FC integrated network as approximate statistical models based on a Markovian process. We also determine a switching schedule of FCs for each of MR based on reliable uncapacitated facility location (RUFL) problem. We extend an existing RUFL problem to incorporate dynamic operating nature of multiple FCs which display dynamic available/unavailable patterns for additional potential IGWs. Extensive simulations are carried out to validate our proposed statistical models and establish the performance of these switching schemes.

Femtocell Interference, SINR and the Probability of Connection at Downlink

A Femtocell (FMC) is a low power cellular home base station, which is low in cost and operating in licensed spectrum. Nowadays, because of the requirement for high data rate and large area coverage indoors, FMC provides the solution to these requirements. FMC is deployed mainly indoors and sometimes outdoors at the cell edge to increase the area of coverage, capacity and in order to enhance the received signal in the user's premises. In this paper, a novel technique and a Monte Carlo simulation is implemented to calculate the interference, the SINR and the probability of connection at the downlink for a varied number of FMCs based on LTE and WiMAX OFDMA range. Moreover, a novel Monte Carlo simulation is used to carry out the comparison of interference, SINR and probability of connection for three different numbers of FMCs. Furthermore, a novel comparison of FMCs at various SINR threshold values is presented. The downlink interference occurs from neighbouring FMCs to the target user equipment (UE) when the signal transmits from the serving FMC to the target UE and the signals which are transmitted from the neighbouring FMCs would have the same subchannels during the downlink transmission. This paper will explore the appropriate number of FMCs that could serve a specific indoor area and the proper number of UEs in the specified area.

Analysis and Design of Distributed Antenna-Aided Twin-Layer Femto- and Macrocell Networks Relying on Fractional Frequency Reuse

Distributed antenna systems (DASs) and FemtoCells (FCs) are capable of improving the attainable performance in the cell-edge area and in indoor residential areas, respectively. To achieve high spectral efficiency (SE), both the distributed antenna elements (DAEs) and FC base stations (FBSs) may have to reuse the spectrum of the macrocellular network. As a result, the performance of both outdoor MacroCell (MC) users (OMU) and indoor FC users (IFUs) suffers from CoChannel Interference (CCI). Hence, in this paper, heterogenous cellular networks are investigated, where the DAS-aided MCs and FCs coexist within the same area. Both the outage probability (OP) and the spatially averaged throughput are derived, and the network is optimized either to minimize the OP or to maximize the MC's throughput. Our analysis demonstrates that surprisingly, the unity frequency-reuse (UFR)-based macrocellular system can be optimized in isolation, without considering the impact of FCs. We found that the MCs relying on fractional frequency reuse (FFR) tend to be converted to several small cells, illuminated by the DAEs, when the density of FCs becomes high.

Toward Optimal Admission Control and Resource Allocation for LTE-A Femtocell Uplink

The Third-Generation Partnership Project (3GPP) has incorporated femtocell (FC) technology in the Long-Term Evolution Advanced (LTE-A) standard to enhance the quality of service of indoor mobile users and extend the coverage area of existing macrocells (MCs). In such two-tier LTE-A MC/FC systems, cotier and cross-tier interference exists in cochannel deployment, exerting adverse effects on system performance. In this paper, we study the single-carrier frequency-division multiple-access (SC-FDMA)-based LTE-A FC uplink. We propose the use of transport-layer data admission control (AC) in femto user equipment (FUE) and interference-aware resource allocation (RA) in each base station (BS) to manage the intercell interference (ICI). We first formulate the problem as a constrained Markov decision problem (CMDP) that aims at maximizing the time-average throughput of the entire FC tier subject to the queue stability constraint for each FUE. Then, we propose a joint AC and RA (JACRA) algorithm to obtain the optimal AC and RA policies. In light of the NP-hardness of the RA subproblem, we further propose an iterative heuristic with polynomial time complexity. Simulation studies show that the proposed JACRA algorithm is throughput optimal, outperforming alternative proportional fair (PF) and round robin (RR) scheduling schemes. Moreover, the proposed heuristic achieves near-optimal throughput with substantial improvement in computational complexity.

Energy-Efficient Resource-Allocation Model for OFDMA Macrocell/Femtocell Networks

Femtocells (FCs) are introduced to enhance the indoor coverage and system capacity of traditional cellular networks. However, the network performance could be significantly deteriorated due to the increase in cochannel interference in dense deployment. In the literature, three spectrum usage schemes that deal with the cross-tier interference have been proposed, i.e., orthogonal assignment, underlay, and controlled underlay using mainly closed-access FCs. This paper targets the optimization of resource allocation, together with the selection of base stations (BSs) in two-tier networks assuming hybrid access FCs, to reduce the cross-tier interference. Moreover, this model aims to achieve effective spatial reuse between the macrocell (MC) and FCs while guaranteeing quality-of-service (QoS) transmissions by means of joint power control in both tiers. Simulations are conducted to show a comparison with the other three approaches.

Uplink Performance Characterization and Analysis of Two-Tier Femtocell Networks

This paper provides a cross-layer analysis of uplink (UL) performance in femtocell (FC) networks. It characterizes the UL physical interference in FC networks and studies its impact on the delay and the data loss rate of constant-bit-rate (CBR) traffic and on the maximum achievable femto user (FU) throughput. This paper derives data-link layer quality-of-service (QoS) performances as a function of physical layer parameters, thereby establishing key cross-layer relationships that can be useful for designing efficient resource-allocation techniques for FC networks.

Dynamic Radio Resource Allocation for Macro-Femto Hybrid Cellular Network Maintaining Fairness

Macro-Femto Hybrid Cellular Network (MFHCN) has been considered as one of the most promising infrastructure for the upcoming next generation cellular network. Femto-Cell (FC) is very effective when it comes to reducing poor signal coverage. The range of the device might be low but it functions to reduce the traffic congestion of the larger Macro Network as well as provide enhanced data rate for both voice and data transmission. In short, it provides better Quality of Service (QoS), i.e., reduce congestion, increase capacity, reduce system outage, while using minimal power consumption. In this work we propose a suboptimal Resource Allocation algorithm for MFHCN. Multiuser and Multiservice are considered in this proposed model. A priority parameter is introduced to maintain fairness amongst all users. By doing so, we were successful in achieving improved outage probability without compromising the total system throughput.

Intercell Interference Management in OFDMA Networks: A Decentralized Approach Based onReinforcement Learning

This paper presents a decentralized framework for dynamic spectrum assignment in multicell orthogonal frequency division multiple access (OFDMA) networks. The proposed framework allows each cell to autonomously decide the frequency resources it should use through a procedure that incorporates concepts from self-organization and machine learning in multiagent systems (MASs). Simulation results have been obtained for several scenarios, including both macrocells (MCs) and femtocells (FCs), revealing important improvements in terms of spectral efficiency and intercell interference mitigation over reference approaches, and close performance with the one obtained by a centralized strategy. Results also suggest that the framework would be practical for future FC cellular deployments where a high degree of independence of the network nodes is expected to reduce operational costs.