Femtocell Base Stations Research Articles

Power allocation and relay selection for network-coded D2D communication underlay heterogeneous cellular networks

Underlay device-to-device (D2D) communication is an attractive technology enabling nearby cellular users to communicate with each other directly in order to increase data rate and spectral efficiency. The current cellular heterogeneous networks consist of macrocell base stations and small cell base stations with different transmit powers and coverage areas. Femtocell is the most popular small cell which is expected to be utilized in dense and ultra-dense scenarios in the future. Network coding in relay-assisted multi-hop communications improves achievable transmission rate and coverage of D2D communications. In this paper, two-hop random linear network coding network in cooperative D2D communication (RLNC-CDC) is considered. We propose to use femtocell base station (FBS) as a relay. We assume that the D2D pair and relay operate in the frequency band which is allocated to femtocell network. Therefore, there would be interference from the relay node and the D2D communication on the femtocell network users. To reduce the interference, the sum of transmit powers of the D2D pair and selected relay FBS should be minimized in a way that the highest transmission rate for the D2D pair is achieved. The constraints on the bounds of transmit powers of the D2D and relay node as well as the minimum required transmission rate for D2D communication are considered and the optimum solution is obtained. Simulation results indicate that the proposed RLNC-CDC achieves higher data rate and smaller outage probability than the direct D2D transmission.

An adaptive step-size spectrum auction mechanism for two-tier heterogeneous networks

Recently, with the rapid growth of demands for wireless communications, dynamic spectrum allocation is one of the key technologies in cognitive radio networks to resolve the realistic problem of low utilization efficiency of spectrum. It mainly focuses on how the spectrum owner dynamically allocates idle spectrum to secondary users who have no licensed spectrum for communications. In this paper, a dynamic spectrum allocation model based on auction theory in a two-tier heterogeneous network is proposed, in which the primary users (PUs) are the sellers, the central processor (CP) auctioneer is the coordinator, and femtocell base station (FBS) as the buyer bids for the idle spectrum and act as a wireless access point that provides communication services for secondary users (SUs). Its basic process is as follows: the auctioneer gradually raises the spectrum price from the reserved price; each bidder decides whether participates in the purchase or not. It is characterized by distributed execution and low complexity which can reduce unnecessary information exchange between primary users or secondary users. Meanwhile it can enhance the utilization of spectrum and improve the efficiency of the auction by generate the incentive mechanism.

Research on Resource Allocation based on Clustering in Femtocell Networks

<p>Aiming at the problem that existing femtocell base station searching the optimal clustering scheme based on the clustering resource allocation algorithm is complex. we propose that building an conflict graph and adjacency matrix before clustering to calculate the number of clusters needed for FBS group by using the adaptive clustering heuristic algorithm. We follow maximization the sum of the FBS distances in the cluster and group the femtocell base stations to narrow the search range to reduce the computational complexity. In order to achieve different business types service, based on the above clustering algorithm, this paper proposes a new method that using the weighted energy efficiency, which including the user interruption and the network spectral efficiency as a fitness function of the power control scheme to solve the problem. The simulation results show that the same rate requirement reduces the complexity, while the same complexity increases the user's average rate.</p>

Deployment of Resource Allocation and Power Control Schemes in Long Term Evolution Advanced (LTE-A) Hybrid Network

Long Term Evolution Advanced (LTE-A) Hybrid network integrates Femtocell and Macrocell networks to obtain better coverage and improved capacity. One of the limiting factors faced by Hybrid network is Inter-Cell Interference (ICI). One way to get rid of the ICI is through Inter-Cell Interference coordination technique. In the last few years, interference coordination such as Fractional Frequency Reuse (FFR) technique is considered as the utmost important research topic in LTE cellular technology. This paper revisited FFR method and deployed Dynamic Femtocell Resource Allocation (DFRA) scheme to ensure the resources assigned to Femtocells are mutually exclusive with adjacent Macrousers or adjacent Femtocells. Furthermore, in the scenario of high density Femtocells (when orthogonal resource exhausted), the power control schemes such as Power based Femtocell Base Station Power Control (PPC), SINR based Femtocell Base Station Power Control (SPC) and SINR based Neighboring Femtocell Power Control (SNPC) are integrated into the system. The deployment of the schemes has augmented the performance of the network and shows increment of 11.43% supported active users with an average data rate inclined by 22.19 Mbps.

Fuzzy-logic based Q-Learning interference management algorithms in two-tier networks

Unloading from macrocell network and enhancing coverage can be realized by deploying femtocells in the indoor scenario. However, the system performance of the two-tier network could be impaired by the co-tier and cross-tier interference. In this paper, a distributed resource allocation scheme is studied when each femtocell base station is self-governed and the resource cannot be assigned centrally through the gateway. A novel Q-Learning interference management scheme is proposed, that is divided into cooperative and independent part. In the cooperative algorithm, the interference information is exchanged between the cell-edge users which are classified by the fuzzy logic in the same cell. Meanwhile, we allocate the orthogonal subchannels to the high-rate cell-edge users to disperse the interference power when the data rate requirement is satisfied. The resource is assigned directly according to the minimum power principle in the independent algorithm. Simulation results are provided to demonstrate the significant performance improvements in terms of the average data rate, interference power and energy efficiency over the cutting-edge resource allocation algorithms.

Scheduling and Power Allocation for Hybrid Access Cognitive Femtocells

This paper addresses the problem of resource and power allocation for hybrid access femtocells. We introduce a refund mechanism to incentivize femtocell basestations (FBSs) to serve macrocell users (MUEs) suffering from low signal to interference and noise ratio (SINR) to enhance overall performance. Our goal is to guarantee quality of service for users, while allowing spectrum sharing between macrocell basestation (MBS) and the underlying FBSs. We exploit overheard user channel quality indicator (CQI) reports using different channel models in order to assess the interfered channel state and channel parameter distribution. We analyze the distribution of the SINR for both femtocell users and MUEs. Based on the analytical results, our solution decomposes the scheduling and power allocation problem into two sub-problems and tackles them sequentially. Using problem reduction/transformation, we convert the decomposed problems into well known reduced forms and provide solutions in accordance. Finally, we verify the presented results through simulations.

Prediction-based association control scheme in dense femtocell networks.

The deployment of large number of femtocell base stations allows us to extend the coverage and efficiently utilize resources in a low cost manner. However, the small cell size of femtocell networks can result in frequent handovers to the mobile user, and consequently throughput degradation. Thus, in this paper, we propose predictive association control schemes to improve the system’s effective throughput. Our design focuses on reducing handover frequency without impacting on throughput. The proposed schemes determine handover decisions that contribute most to the network throughput and are proper for distributed implementations. The simulation results show significant gains compared with existing methods in terms of handover frequency and network throughput perspective.

Novel sensing and joint beam and null steering based resource allocation for cross-tier interference mitigation in cognitive femtocell networks

Cognitive radios and femtocell networks are gaining much popularity due to the formers ability to carry out unlicensed transmission in licensed bands and the latter’s ability to increase the indoor capacity by bringing the transmitter and receiver closer to each other. The combination of the two provides us with a joint benefit of unlicensed transmission and increased system capacity. However, deployments of such cognitive radio based femtocell networks (CRFN) can pose some severe cross-tier interference towards the primary system. In this paper, we propose a novel spectrum sensing technique based on Uniform Linear array (ULA) combined with Genetic Algorithm to detect not only the presence of a Primary user but also estimate its parameters such as range, frequency, angle of arrival and amplitude. Furthermore, a joint beamforming and null steering technique is proposed to maximize the signal to interference plus noise ratio (SINR) towards the secondary user equipment (SUE) while minimizing the interference towards the primary Base Station (PBS). We are reutilizing the sensed uplink (UL) frequency of the Primary users for the downlink (DL) transmission; the cognitive femtocell base station (CFBS) calculates such weight vector that aims at sending the maximum signal power towards the femto user and null in the direction of PBS.

Study of Indoor Path Loss Computational Models for Femtocell Based Mobile Network

Path loss minimization in next generation mobile network is a challenging research area. The signal transmitted by a base station degrades due to various obstacles in the environment. The received signal level at the mobile station is less than the transmitted signal level of the base station. This loss in the signal level is referred as path loss in mobile network. In this paper different path loss models are discussed for indoor environment covered by femtocell. It is assumed that the mobile users in that region exclusively access the services of femtocell. As only indoor area is considered, non-line of sight propagation is examined. Signal-to-interference-plus-noise-ratio for a femtocell base station is calculated. The performance of the path loss models are analyzed using vector signal generator and vector signal analyzer. A comparative analysis is carried out between the models. Based on the comparative analysis, a case study is performed to demonstrate how an appropriate path loss model will be selected depending on the frequency range, building type, walls and floors.

Distributed Resource Allocation With Local CSI Overhearing and Scheduling Prediction for OFDMA Heterogeneous Networks

We propose a resource allocation method for the downlink of an orthogonal-frequency-division-multiple-access (OFDMA)-based macrocell/femtocell overlaid heterogeneous network. To mitigate the interference caused by femtocell base stations (FBSs) on nearby macrocell users (MUs), conventional methods rely on the information of the interference channel states, as well as MU allocation mapping provided by a control channel, causing a substantial overhead increase. Instead, the proposed methods enable the FBS to predict the subchannels that are likely to be used by its neighbor MUs, based on their locally overheard channel state information, and to set appropriate constraints on those subchannels. Moreover, by letting the FBS fully reuse the subchannels estimated to be free from nearby MUs, the femtocell throughput is increased while scarcely degrading the macrocell throughput. The simulation results demonstrate the validity of our analysis for MUs' allocation estimation error probability and threshold optimization. Moreover, the proposed methods efficiently mitigate the interference from FBSs to nearby MUs, providing an excellent macrocell/femtocell throughput tradeoff, while drastically decreasing signaling overhead, compared with conventional methods.

Handling cross-tier interference in underlay macrocell system for future small cell networks

Spectrum sharing technology optimizes the usage of li- censed spectrum. Macrocell underlaid with femtocells constitutes a typical two-tier network for improving spectral efficiency and indoor coverage. Considering the end-user access control over a femtocell base station (FBS), with shared usage of the macrocell's spectrum, we propose a cross-tier interference management be- tween the FBS and the macrocell base station (MBS).Our proposal uses the network infrastructure for interference cancellation at the FBS. Besides, we profit from terminal discovery to derive the inter- ference level from the femtocell to the macrocell. Thus, addition- ally we propose a power control method without cooperation from the MBS. Through simulation results and analysis, our proposal improves the underlay network performance for future advanced small cell networks.

A Distributed Coverage Adjustment Algorithm for Femtocell Networks

In two-tier femtocell networks, adjusting the transmission power values of femtocell base stations (BSs) such that indoor users receive high signal quality while limiting leakage to outdoor users is an important problem. This paper proposes a novel distributed and self-optimized power adjustment algorithm for two-tier femtocell networks, in which a BS adjusts the transmission power based on the signal quality of neighboring BSs. Achieving fairness among users with minimal information exchange is desired. There are no predefined target parameters used to adjust transmission power, contrary to existing approaches in the literature. The convergence properties of the algorithm under fixed and time-varying communication infrastructures are investigated. The performance is further verified by simulations and comparisons with other algorithms for the coverage problem.

A tractable analytical model for interference characterization and minimum distance enforcement to reuse resources in three‐dimensional in‐building dense small cell networks

SummaryIn this paper, we address mainly 2 important issues, namely, characterizing co‐channel interference and enforcing a minimum distance between femtocell base stations (FCBSs) for reusing resources in FCBSs deployed in a 3‐dimentional multi‐floor building. Each floor is modeled as a group of square‐grid apartments, with one FCBS per apartment. We propose a simple yet reasonable analytical model by using planar‐Wyner model for intra‐floor interference and linear‐Wyner model for inter‐floor interference modeling in a 3‐dimensional multi‐floor building to derive a minimum distance between co‐channel FCBSs for optimization constraints, namely, link level interference, spectral efficiency, and capacity. As opposed to orthogonal resource reuse and allocation (ORRA) where resources are reused once, using the proposed model, we develop 2 strategies for reusing resources more than once, that is, non‐ORRA, within a multi‐floor building. An algorithm of the proposed model is developed by including an application of the model to an ultra‐dense deployment of multi‐floor buildings. With an extensive numerical analysis and system level simulation, we demonstrate the capacity outperformance of non‐ORRA over ORRA by manifold. Further, with a fairly accurate yet realistic estimation, we show that the expected spectral efficiency of fifth‐generation networks can be achieved by applying the proposed model to an ultra‐dense deployment of FCBSs.

Outage Constrained Robust Hybrid Coordinated Beamforming for Massive MIMO Enabled Heterogeneous Cellular Networks

Heterogeneous network (HetNet), employing massive multiple-input multiple-output (MIMO), has been recognized as a promising technique to enhance network capacity, and to improve energy efficiency for the fifth generation of wireless communications. However, most existing schemes for coordinated beamforming (CoBF) for a massive MIMO HetNet unrealistically assume the availability of perfect channel state information (CSI) on one hand, and cascade of each antenna with a distinct radio-frequency chain in massive MIMO is neither power nor cost-efficient on the other hand. In this paper, we consider a massive MIMO-enabled HetNet framework, consisting of one macrocell base station (MBS) equipped with an analog beamformer, followed by a digital beamformer, and one femtocell base station (FBS) equipped with a digital beamformer. In the presence of Gaussian CSI errors, we propose a robust hybrid CoBF (HyCoBF) design, including an analog beamforming design for MBS, and a digital CoBF design for both MBS and FBS. To this end, an outage probability-constrained robust HyCoBF problem is formulated by minimizing the total transmit power. The analog beamforming mechanism at MBS is a newly devised low-complexity beam selection scheme by selecting analog beams from a discrete Fourier transform matrix codebook. Then, a conservative approximate CoBF solution is obtained via semidefinite relaxation and an extended Bernstein-type inequality. Furthermore, a distributed implementation for the obtained CoBF solution using alternating direction method of multipliers is proposed. Finally, numerical simulations are provided to demonstrate the efficacy of the proposed robust HyCoBF algorithm.

Secure Wireless Information and Power Transfer in Heterogeneous Networks

In this paper, we investigate secure simultaneous wireless information and power transfer (SWIPT) in a two-tier downlink heterogeneous network (HetNet), wherein the ambient interference signals are exploited for both secure communications and wireless energy harvesting. We assume one macrocell base station (MBS) and several femtocell base stations (FBSs) simultaneously send information to their macrocell users (MUs) and femtocell users, respectively. Meanwhile, the FBSs also transfer energy to some energy receivers, who act as the potential eavesdroppers and are able to wiretap the confidential messages to one MU via the cross-tier interference links. Exploiting interference in the considered HetNet, we jointly optimize the beamforming vectors and artificial noise of the MBS and the FBSs to maximize the secrecy rate of the eavesdropped MU under the quality-of-service, energy harvesting, and transmit power constraints at relevant receivers/transmitters. In particular, we first investigate the ideal case with perfect eavesdropper’s channel state information (ECSI) and the optimization problem turns out to be nonconvex. By using the tools of semidefinite relaxation (SDR) and one-dimensional line search, we successfully transfer the original problem into a more tractable two-stage problem to obtain the optimal solution. Furthermore, we extend our study to the imperfect ECSI case, where the worst-case based solution is obtained with the aid of SDR and successive convex approximation. Simulation results demonstrate the effectiveness of the proposed algorithms and also bring useful insights into the design of secure SWIPT in the presence of interference.

Downlink Power Optimization for Heterogeneous Networks With Time Reversal-Based Transmission Under Backhaul Limitation

In this paper, we investigate an application of two different beamforming techniques and propose a novel downlink power minimization scheme for a two-tier heterogeneous network (HetNet) model. In this context, we employ the time reversal (TR) technique to a femtocell base station, whereby we assume that a macrocell base station uses a zero-forcing-based algorithm, and the communication channels are subject to frequency selective fading. Additionally, the HetNet backhaul connection is unable to support a sufficient throughput for signaling an information exchange between two tiers. Given the considered HetNet model, a downlink power minimization scheme is proposed, and closed-form expressions concerning the optimal solution are provided by taking this constraint into account. Furthermore, considering imperfect channel estimation at TR-employed femtocell, a worst-case robust power minimization problem is formulated. By devising TR worst-case analysis, this robust problem is transformed into an equivalent formulation that is tractable to solve. The results presented in our paper, show that the TR technique outperforms the zero-forcing one from the perspective of beamforming methods for femtocell working environments. Finally, we validate the proposed power loading strategy for both cases of perfect and imperfect channel estimations.

Energy Efficiency Perspectives of Femtocells in Internet of Things: Recent Advances and Challenges

Energy efficiency is a growing concern in every aspect of the technology. Apart from maintaining profitability, energy efficiency means a decrease in the overall environmental effects, which is a serious concern in today’s world. Using a femtocell in Internet of Things (IoT) can boost energy efficiency. To illustrate, femtocells can be used in smart homes, which is a subpart of the smart grid, as a communication mechanism in order to manage energy efficiency. Moreover, femtocells can be used in many IoT applications in order to provide communication. However, it is important to evaluate the energy efficiency of femtocells. This paper investigates recent advances and challenges in the energy efficiency of the femtocell in IoT. First, we introduce the idea of femtocells in the context of IoT and their role in IoT applications. Next, we describe prominent performance metrics in order to understand how the energy efficiency is evaluated. Then, we elucidate how energy can be modeled in terms of femtocell and provide some models from the literature. Since femtocells are used in heterogeneous networks to manage energy efficiency, we also express some energy efficiency schemes for deployment. The factors that affect the energy usage of a femtocell base station are discussed and then the power consumption of user equipment under femtocell coverage is mentioned. Finally, we highlight prominent open research issues and challenges.

Fast game-based handoff mechanism with load balancing for LTE/LTE-A heterogeneous networks

Due to the development of femtocell technologies, indoor LTE/LTE-A signal quality can be significantly improved. However, since femtocells and macrocell are deployed into a coexisted heterogeneous network, handoff from macrocell to femtocell turns out to be one of the major design issues to achieve better user experience provided by femtocells. In general, the macrocell user equipment (MUE) selects a handoff target femtocell base station (FBS) in the handoff procedure solely based on the received signal strength indicator (RSSI), signal to interference plus noise ratio (SINR), or signal to noise ratio (SNR). Although this approach is very simple and easy to implement, it can result in load imbalance among FBSs. Hence, this paper proposes a novel game-based handoff mechanism that combines the modified Dutch Auction (MDA) and stochastic election process (SEP) to jointly take the uplink and downlink signal qualities and load balance of the handoff candidate FBSs into consideration when selecting handoff target FBS. Besides, in order to speed up the execution of the handoff mechanism and reduce the percentage of handoff failures, the Fast SEP and Go Back B are further developed, respectively. Simulation results confirm that the proposed MDA+Fast SEP+Go Back B handoff mechanism provides better load balance, faster handoff and higher percentage of successful handoffs.

Load Balancing in Two-Tier Cellular Networks With Open and Hybrid Access Femtocells

Femtocell base station (BS) is a low-power, low-price BS based on cellular communication technology. It is expected to become a cost-effective solution for improving the communication performance of indoor users, whose traffic demands are large in general. There are mainly three access strategies for femtocell, i.e., closed access, open access and hybrid access strategies. While it has been generally known that open/hybrid access femtocells contribute more to enhancing the system-wide performance than closed access femtocells, the operating parameters of both macro and femtocells should be carefully chosen according to the mobile operator's policy, consumer's requirements, and so on. We propose long-term parameter optimization schemes, which maximize the average throughput of macrocell users while guaranteeing some degree of benefits to femtocell owners. To achieve this goal, we jointly optimize the ratio of dedicated resources for femtocells as well as the femtocell service area in open access femtocell networks through the numerical analysis. It is proved that the optimal parameter selection of open access femtocell is a convex optimization problem in typical environments. Then, we extend our algorithm to hybrid access femtocells where some intra-femtocell resources are dedicated only for femtocell owners while remaining resources are shared with foreign macrocell users. Our evaluation results show that the proposed parameter optimization schemes significantly enhance the performance of macrocell users thanks to the large offloading gain. The benefits provided to femtocell users are also adaptively maintained according to the femtocell users' requirements. The results in this paper provide insights about the situations where femtocell deployment on dedicated channels is preferred to the co-channel deployment.

Incentive and Architecture of Multi-Band Enabled Small Cell and UE for Up-/Down-Link and Control-/User-Plane Splitting for 5G Mobile Networks

Abstract In this paper, a multi-band enabled femtocell base station (FCBS) and user equipment (UE) architecture is proposed in a multi-tier network that consists of small cells, including femtocells and picocells deployed over the coverage of a macrocell for splitting uplink and downlink (UL/DL) as well as control-plane and user-plane (C-/U-plane) for 5G mobile networks. Since splitting is performed at the same FCBS, we define this architecture as the same base station based split architecture (SBSA). For multiple bands, we consider co-channel (CC) microwave and different frequency (DF) 60 GHz millimeter wave (mmWave) bands for FCBSs and UEs with respect to the microwave band used by their over-laid macrocell base station. All femtocells are assumed to be deployed in a 3-dimensional multi-storage building. For CC microwave band, cross-tier CC interference of femtocells with macrocell is avoided using almost blank subframe based enhanced inter-cell interference coordination techniques. The co-existence of CC microwave and DF mmWave bands for SBSA on the same FCBS and UE is first studied to show their performance disparities in terms of system capacity and spectral efficiency in order to provide incentives for employing multiple bands at the same FCBS and UE and identify a suitable band for routing decoupled UL/DL or C-/U-plane traffic. We then present a number of disruptive architectural design alternatives of multi-band enabled SBSA for 5G mobile networks for UL/DL and C-/U-plane splitting, including a disruptive and complete splitting of UL/DL and C-/U-plane as well as a combined UL/DL and C-/U-plane splitting, by exploiting dual connectivity on CC microwave and DF mmWave bands. The outperformances of SBSA in terms of system level capacity, average spectral efficiency, energy efficiency, and control-plane overhead traffic capacity in comparison with different base stations based split architecture (DBSA) are shown. Finally, a number of technical and business perspectives as well as key research issues of SBSA are discussed.