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Summary: The heterogeneous ultra‐dense network (UDN) is a complex network environment where the small cells (SCs) are densely populated to acquire data transmission. The UDN is mainly adopted to deal with the explosive growth of mobile data and its consequential energy consumption issues. The UDN consists of mobile users, restricting the SCs from offering seamless services as the movement may disrupt the transmissions. To provide an effective solution, this paper introduces an energy‐efficient framework that enables effective data transmissions irrespective of the users' mobility. The proposed model considers the clustered SC deployment where the four‐tiered architecture is adopted. The architecture includes a macro base station (BS), microcells, picocells, and femtocells. The SCs are responsible for transferring the data received from the mobile users to the macro BS. The proposed model introduces the hybrid algorithm called the firefly oriented multiverse optimization (FF‐MVO) algorithm to identify the most optimal path for data transmission. This algorithm works iteratively to identify the optimal path to reach the macro BS for each transmission from the user. The proposed model is simulated in the network simulator 3 (NS3) platform, and the results are evaluated with the existing models. The outcomes proved that the proposed algorithm is more optimal than the other models in finding the optimal path to result in energy‐efficient transmissions. The proposed method achieved an average energy consumption of 0.24 J, an average energy efficiency of 10.965 bits/s/J and an average network throughput of 33.907 Gbps. [ABSTRACT FROM AUTHOR]

Summary: The use of small base stations (SBSs) to improve the throughput of cellular networks gave rise to the advent of heterogeneous cellular networks (HCNs). Still, the interleave division multiple access (IDMA) performance in sleep mode active HCNs has not been studied in the existing literature. This research examines the 24‐h throughput, spectral efficiency (SE), and energy efficiency (EE) of an IDMA‐based HCN and compares the result with orthogonal frequency division multiple access (OFDMA). An energy‐spectral‐efficiency (ESE) model of a two‐tier HCN was developed. A weighted sum modified particle swarm optimization (PSO) algorithm simultaneously maximized the SE and EE of the IDMA‐based HCN. The result obtained showed that the IDMA performs at least 68% better than the OFDMA on the throughput metric. The result also showed that the particle swarm optimization algorithm produced the Pareto optimal front at moderate traffic levels for all varied network parameters of SINR threshold, SBS density, and sleep mode technique. The IDMA‐based HCN can improve the throughput, SE, and EE via sleep mode techniques. Still, the combination of network parameters that simultaneously maximize the SE and EE is interference limited. In sleep mode, the performance of the HCN is better if the SBSs can adapt to spatial and temporal variations in network traffic. [ABSTRACT FROM AUTHOR]

Summary: The manifold increase in the number of cellular wireless network consumers has presented a monumental challenge to upgrade the current infrastructure for imparting superior throughput and good quality of service. End‐users of the network will want super high‐speed data with very low latency, as well as secure and with a lower packet data drop rate. Joint coordination between various network resources such as that of a dense heterogeneous network is crucial for achieving the above demands. It is also inevitable that such a dense arrangement of small cells or macro cells or other network equipment will be challenged by different forms of interference apart from being costly and less mobile. Beamforming is among the most advanced technology that is available up to date which has shown good results at handling interference and at guiding transmitted data to the desired end‐user. It is quite useful but also struggles from certain factors when deployed in a dense network. A thorough review of recent works of literature is detailed in the current paper with a focus placed on two major fields, which are interference mitigation techniques and gainful interference exploitation techniques. Some highly advanced interference mitigation techniques which are either developed or under development with their merits have been proposed. Most of these techniques use machine learning and artificial intelligence‐based methods to ensure the best quality of service (QoS) to every individual connected to the network. However some research works focused on negating away any kind of interference present in a signal, some focused on harnessing interference for optimizing the power of transmitted signals. [ABSTRACT FROM AUTHOR]

Summary: The most challenging issue in long‐term evolution (LTE) mobile networks is the design of an optimal scheduler. The main target of the LTE scheduling strategy is to guarantee a certain level of quality of service (QoS) in order to satisfy users' needs. In this work, a novel queue‐optimized two‐level scheduling strategy is introduced. The queue‐optimized scheduler has the ability to support both real‐time (RT) and non‐RT (NRT) services in the LTE downlink framework. The first level of the proposed scheduler depends on an optimized queue length threshold that is dynamically adapted to adjust the assigned resources for the video traffic to maintain the throughput around its average value. The proposed scheduling strategy is utilized to efficiently enhance the radio resource allocation process for video traffic by minimizing the allocation of any excess unwanted resources, which consequently facilitates the support of more video connections and enhances the overall network spectral efficiency. The distribution of the resources among users for RT and NRT applications is actually performed at the second level of the scheduling process. The physical resource blocks (PRBs) are assigned according to the enhanced earliest due date first (EEDDF) mechanism. The proposed scheduling strategy prioritizes users according to their service requirements, to improve the QoS provision. The proposed scheduler maximizes the video applications throughput, and generally, minimizes the packet delay and the packet loss rate (PLR) for RT applications. [ABSTRACT FROM AUTHOR]

Summary: The cellular mobile communication network has been widely deployed in large regions to provide connectivity between billions of people. The population of cellular mobile users has been growing since the past decade. Therefore, we need a high capacity cellular system with extraordinary performance to meet the demand of the cellular users. To minimize the traffic load from the evolved Node Base (eNB) station, device‐to‐device (D2D) network must be deployed along with the commercial cellular network. D2D provides the direct connectivity between the proximal users without associating with eNB. This reduces the traffic load from the eNB. In other words, it enhances the capacity of the system. But D2D communication suffers a severe interference by the cellular user. In this paper, we have proposed a solution for the cross‐tier interference faced by the D2D users and eNB under uplink reuse transmission. We have proposed a semi‐distributed resource allocation and power quantization control (SRA–PQC) scheme. The simulation result shows that a better sum rate can be achieved using the proposed scheme. [ABSTRACT FROM AUTHOR]

Summary: Exhaustive research is being done to establish the technologies and standards of the fifth generation (5G) of wireless communication systems. Some of the most challenging requirements of 5G systems are to increase the spectral efficiency and the capacity by a factor of 10 and 1,000, respectively. New technologies must offer an adequate framework for the 5G uses cases, which will enable higher capacities and the flexibility to adapt to dynamic scenarios. To cope with these challenging demands, a compelling approach is to exploit the current radio service bands by means of spectrum sharing and cooperation techniques, which alleviate the bandwidth requirements. In addition, advanced modulation schemes have a fundamental role in ensuring the best usage of the spectrum available in band‐limited systems. In this manuscript, we present the ultra‐wideband (UWB) technology as a prospective solution for 5G picocells and femtocells. Its main feature is its capability to operate simultaneously, without introducing interference, with current radio services on an unlicensed basis. We report experimental results reaching data rates up to 35 Gbit/s using the multiband approach of carrierless amplitude phase (MB‐CAP) modulation. To validate the versatility of the proposed system, our experimental tests were performed under the UWB regulations defined by the United States' Federal Communications Commission (FCC), the European Electronic Communications Committee (ECC), and the Russian State Committee for Radio Frequencies (SCRF). The regulations chosen provide diversity enough to demonstrate the capacity of MB‐CAP modulation to comply with worldwide regulations. [ABSTRACT FROM AUTHOR]

Summary: Power lines present a more challenging communication environment compared to other media. Impedance mismatches and network branches render the channel frequency‐selective, leading to strong inter‐symbol interference (ISI). Moreover, devices connected to the power grid introduce impulsive noise on the network. Such factors may degrade the system performance drastically. Therefore, robust coding and modulation schemes are required to increase the communication reliability. Furthermore, multiple access communication allows many users to share a common medium to enhance the systems' throughput. This paper examines the behaviour of two schemes, turbo codes and multi‐fold turbo codes, against a two‐user adder channel under power‐line conditions operating below 500 kHz. Both schemes employ distinct codes for each user and make use of orthogonal frequency‐division multiplexing (OFDM) to cope with the ISI. Three configurations of a low‐voltage (LV) power‐line outdoor network are considered. Results obtained through simulations show that a gain, up to 3 dB, can be obtained for both users using the multi‐fold turbo coding over the conventional turbo coding. The effect of iterative decoding on the performance of both schemes is also reported. [ABSTRACT FROM AUTHOR]

Summary: The optimization of indoor femtocell base stations (FBS) placement is a highly complex problem in which multiple performance figures can be considered. In this paper, we propose a biobjective optimization approach based on non‐dominated sorting genetic algorithm II (NSGA‐II) to solve the indoor FBS deployment problem in residential scenarios where a single cell is deployed within the coverage of a single dominant interfering external macro base station (MBS). The optimization problem is formulated with the objective of jointly minimizing outage probability and maximizing normalized downlink average throughput. Several conditions are simultaneously considered under the framework of Monte Carlo simulations, such as the effect of co‐channel interference in uplink and downlink, buildings with arbitrary layouts, realistic transmission schemes and antenna radiation patterns, random user distributions, and a well‐established empirical path loss model. The proposed algorithm, which determines the location and orientation of the FBS's antenna that provides a suitable compromise between the two objective functions, is evaluated in this paper. First, two different experiments are proposed to investigate the algorithm convergence; then, statistical analyses are formulated to characterize the relation between the values achieved for both objective functions; finally, the computational load is evaluated. Results indicate the convergence of the proposed method towards the real Pareto front and a significant reduction of the computational time with respect to a reference method based on exhaustive search, while pointing at new criteria for the selection of the objective functions. [ABSTRACT FROM AUTHOR]

To guard the communication quality of cell edge users (CEUs) and simultaneously improve the energy-spectrum efficiency, a novel 3-tier heterogeneous network (HetNet) model is proposed, which consists of macro cells, femtocells, and device-to-device (D2D) networks. Specially, with a predefined cell split factor R, the macro cell users are split into as cell center users (CCUs) and CEUs, respectively. Correspondingly, the total available spectrum band consisting of N channels is divided into CCU band and CEU band with a given coefficient pm. The CCU band containing pmN subchannels is shared by CCUs and femtocell users (FUs), and the CEU band containing (1 - pm) N subchannels is shared by D2D users and CEUs. The perfect network synchronization is assumed, and a communication round consists of downlink transmission and uplink transmission phases. The battery-free D2D terminals harvest energy from the ambient radio frequency interference in the downlink transmission phase based on inverse power control scheme and communicate in the uplink transmission phase only when they harvest enough energy to perform channel inversion toward the receiver. For such 3-tier HetNets, by modeling the network elements as independent Poisson point processes (PPPs) and using stochastic geometry method, we first investigate the sufficiency probability that a D2D transmitter harvests enough energy to establish a communication link. Then, by combining sufficiency probability and channel access probability, the thinned independent PPPs for the locations of CCUs, CEUs, FUs, and D2D users are modeled. Based on these thinned PPP models, we perform a comprehensive investigation on the coverage probabilities of CCU, CEU, and FU uplinks as well as the D2D transmission. The simulated and numerical results show that using the presented cell split strategy enhances the performance of CCUs and CEUs because of the decrease of interference. The presented comparison analysis displays that the effect of D2D networks on the macro cell or the whole HetNets is limited and can be omitted. Therefore, the energy and spectrum efficiencies of networks are enhanced, simultaneously. At the same time, our results indicate that by using our derivations, we can perform the optimal design of the HetNets. [ABSTRACT FROM AUTHOR]

Multicast-Broadcast over Single Frequency Network (MBSFN) technology, as introduced by the Long Term Evolution Advanced group, is expected to be part of the upcoming cellular systems offering resource efficiency to broadcast services. MBSFN transmission is suitable to serve multicast groups searching the same content. In addition, the fast emerging technology of femtocells networks and their hybrid nature can lead to efficient resource sharing between non-subscribed users when located inside their coverage. The focus of this manuscript is 2-fold; firstly, we have contacted simulation experiments to compare the MBSFN transmission with the traditional Point-To-Point transmission for various femtocell distributions and network topology changes; secondly, a novel multicast transmissions mechanism is proposed from non-subscribed users who exploit femtocells resources for broadcast services, without limiting user's data requirements. The simulation results lead to a significant system's performance in terms of average throughput, total capacity, and energy consumption. [ABSTRACT FROM AUTHOR]

Summary: With increase in the number of smart wireless devices, the demand for higher data rates also grows which puts immense pressure to the network. A vast majority of this demand comes from video files, and it is observed that only a few popular video files are requested more frequently during any specified time interval. Recent studies have shown that caching provides a better performance as it minimizes the network load by avoiding the fetching of same files multiple times from the server. In this paper, we propose to combine two ideas; proactive caching of files and content‐based pricing in macro‐femto heterogeneous networks. The femtocell access point (FAP) is allowed to manipulate its users' demand through content‐based pricing and serve the users' requests by proactively downloading suitable content into its cache memory which reduces the load of the femtocell. In addition, an incentive mechanism is also proposed which encourages the FAP to help macrocell users under its coverage zone by allowing access to its cached content and thereby reduces the macrocell load. The proposed content‐based pricing and proactive caching scheme for femtocells is modeled as a Stackelberg game among the macrocell base station and the FAP to jointly maximize both of their utilities. Performance analysis of the scheme is presented for a single femtocell scenario and compared with the conventional flat pricing‐based scheme via numerical examples. The results demonstrate significant reduction in network load using our proposed scheme. [ABSTRACT FROM AUTHOR]

Summary: In fact, the demand for mobile data has turned out to be one of the most pressing needs of the human race. In more details, the researcher deals with the voice calling performance and good network signal, which are needed to achieve the above. The femtocells are mostly designed for indoor environments. It enables voice calling and traffic loading, where it improves network coverage. Thus, a femtocell is deployed for signal improvement in the indoor setting. Interference occurs among femtocells. The optimisation of femtocells depends on system factors that require performance and capacity of the network for indoor users. In the above circumstance, the authors considered using the cost function to optimise the mobile coverage, whereby reducing the interference within the users. Adequate MATLAB simulation was utilised for this study. The simulated results were satisfactory since they illustrate the benefits of the methods for the service performance. [ABSTRACT FROM AUTHOR]

Future heterogeneous networks with dense cell deployment may cause high intercell interference. A number of interference coordination (IC) approaches have been proposed to reduce intercell interference. For dense small-cell deployment with high intercell interference between cells, traditional forward link IC approaches intended to improve edge user throughput for best effort traffic (ie, file transfer protocol download), may not necessarily improve quality of service performance for delay-sensitive traffic such as voice over long-term evolution traffic. This study proposes a dynamic, centralized joint IC approach to improve forward link performance for delay-sensitive traffic on densely deployed enterprise-wide long-term evolution femtocell networks. This approach uses a 2-level scheme: central and femtocell. At the central level, the algorithm aims to maximize network utility (the utility-based approach) and minimize network outage (the graphic-based approach) by partitioning the network into clusters and conducting an exhaustive search for optimized resource allocation solutions among femtocells (femto access points) within each cluster. At the femtocell level, in contrast, the algorithm uses existing static approaches, such as conventional frequency reuse (ReUse3) or soft frequency reuse (SFR) to further improve user equipment quality of service performance. This combined approach uses utility- and graphic-based SFR and ReUse3 (USFR/GSFR and UReUse3/GReUse3, respectively). The cell and edge user throughput of best effort traffic and the packet loss rate of voice over long-term evolution traffic have been characterized and compared using both the proposed and traditional IC approaches. [ABSTRACT FROM AUTHOR]

In 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. [ABSTRACT FROM AUTHOR]

Short range, low power, plug-and-play femtocell has carved a niche for itself because of its potential for higher rate indoor voice and data service, coverage enhancement over cell edges, high network capacity, and negligible greenhouse gas emission. The frequency reuse phenomenon in two-tier cellular network subjects the cell-edge macrouser to severe downlink interference from co-channel deployed femtocells in the same province. Downlink power control approach is a recommended remedy to overcome such type of interferences. This paper proposes release-11-based maximum downlink power control (R-11-based MDPC) approach to protect macrouser's service from co-channel interference. The feedback strategy incorporated in this paper is formulated by R-11 of 3rd Generation Partnership Program for Long Term Evolution standard. Implementation of new R-11-based feedback strategy between femto-base station and macro-base station with MDPC approach ensures instantaneous power control with minimal feedback delay, higher signal-to-interference-plus-noise ratio (SINR), simple receiver module design, and better service availability. Simulation results of R-11-based MDPC approach clearly indicate reduced feedback delay, better power control with minimal interference, improved SINR, and negligible outage probability. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The deployment of femtocells can effectively improve the capacity of cellular networks without significant increase in the network management costs. Femtocell base stations are usually installed by users, which poses unique challenges for future mobile communication standards. The randomness of the locations of femtocells brings us many difficulties to analyze and compare. In this paper, we explore the performance on two different access methods under Rayleigh fading channel: accessing to the nearest and accessing to the strongest femtocell base station. Two performance indexes are of most interest in this paper: how the different path loss exponents and femtocell densities affect the difference of performance between the two different access methods. In the first part of this paper, the distributions of received strength for both access methods are achieved, in which we elaborate the characteristics of received signal strength including the cumulative distribution and the median signal strength. In the second part, we explore the characteristic of SINR distribution, which can be interpreted as the probability of coverage. This paper provides detailed illustrations about how performance changes for these two different access methods under Rayleigh fading channel. All results are mathematically tractable. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

With the adoption of long-term evolution standard for 4G mobile communications, the deployment of femtocell base stations (FBSs) to cope with the surging traffic in mobile wireless communication is becoming increasingly popular. However, with the random installation of FBSs, the problem of interference among FBSs is still a challenge. In this paper, assuming the presence of a femtocell management system that can control and coordinate the densely deployed FBSs, a novel power backoff scheme is proposed that determines the appropriate transmit power of each FBS so that the interference is reduced. Simulation results for randomly deployed FBSs in an environment with shadowing using MATLAB are provided, showing that our proposed methods can effectively mitigate the co-tier downlink interference while improving the system capacity in a densely deployed femtocell network with shared spectrum use. Quantitatively, the average interference is reduced by roughly 90% to 100% of dBm, and the average capacity is increased by more than 80%. These results attest to the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

In the upcoming generation of mobile networks, femtocells will play a major role because they provide cost-efficient improvement in data rates and coverage. High penetration is expected in the upcoming ultra-dense 5G networks, increasing the probability of femtocells' clusters. This, in turn, will require interference mitigation techniques to protect nearby non-subscribed users, especially in weak macrocell signal areas. In this paper, we present a mechanism where multiple femtocells coordinate their transmission to serve multiple non-subscribed users through hybrid access. First, we introduce an algorithm that determines the spectrum allocation of femtocells' hybrid access. The algorithm aims to compensate for the performance reduction of subscribed users, due to reduced spectrum. For the second step of the mechanism, we introduce a power control algorithm that balances the impact of hybrid access among all the members of the femtocell cluster. First, we investigate the case where only one femtocell operates in hybrid access, and then we refine the power control algorithm by allowing multiple femtocells in the same cluster to operate in hybrid mode and by taking into account the effect that any change in power transmission will have on neighbouring femtocells. Simulations for the evaluation of the hybrid access algorithm compared with closed and other hybrid access schemes show improvement in the throughput of the non-subscribed users connected to femtocell and the most impacted subscribed users at weak macrocell signal areas and in the fairness of the hybrid access application scheme. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Femtocell is regarded as a promising technology to enhance indoor coverage and improve network capacity. However, highly dense and self-organized femtocells in urban environment will result in serious inter-femtocell interference. To solve this problem, this paper proposes a distributed power self-optimization scheme for the downlink operation of dense femtocell networks. First, a novel convex pricing mechanism is presented to price the transmit power of femtocells and construct the utility function of femtocells. Then, a noncooperative game framework for power self-optimization of femtocells in dense femtocell networks is established on the basis of the exact potential game theory, which is demonstrated to converge to a pure and unique Nash equilibrium. Finally, combined with firefly algorithm, an effective power self-optimization algorithm with guaranteed convergence is proposed to achieve the Nash equilibrium of the proposed game. With practical LTE parameters and a 3GPP dual-strip femtocell model, simulation results show that the proposed game with convex pricing mechanism increases the femtocell network throughput by 7% and reduces the average transmit power of femtocells by 50% in dense femtocell networks, with respect to the compared schemes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The coexistence of a macrocell and a number of femtocells often leads to a two-tier heterogeneous network, where the co-tier interference (CotIN) and cross-tier interference (CrotIN) both degrade users' quality of service. In order to suppress these interferences, we propose a precoding scheme in a heterogeneous network with cooperative femtocells, called CotIN elimination and CrotIN suppression with precoding criterion selection (ESPS) scheme. In this scheme, we first eliminate the CotINs of each user by applying the QR decomposition to channel matrix. Then the CrotINs of macrocell users and femtocell users are suppressed via the macrocell base station (MBS) and femtocell access points (FAPs) with precoding criterion selection, respectively. By using the ESPS scheme, spatial resources can be efficiently exploited. In addition, our ESPS scheme requires little information exchange between MBS and FAPs without iteration and thus significantly reduces the implementation complexity. Furthermore, the robustness is increased through introducing the information of channel uncertainty into the ESPS when channel estimation or quantization error exists. The performance analysis for the ESPS demonstrates that the ESPS is practical in the heterogeneous networks. Finally, simulation results show that the ESPS can decrease users' bit error rates and increase their transmission rates. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Two-tier heterogeneous networks, where the current cellular networks, that is, macrocells, are overlapped with a large number of randomly distributed femtocells, can potentially bring significant benefits to spectral utilization and system capacity. In a two-tier network, the cross-tier interference needs to be handled properly. Unlike the downlink interference, the uplink (UL) interference at femtocell caused by macrocell user equipment (MUE) has not been addressed sufficiently. When an MUE is located near the coverage of femtocell, its transmit power may cause UL interference to the femtocell receiver, especially for the closed subscriber group femtocells that share the entire frequency spectrum with macrocell. We propose a novel quasi-access strategy, which allows the interfering MUE to connect with the interfered femtocell access point (FAP) while only via UL. It can significantly alleviate the UL interference at the FAP as well as its neighbors, in the meantime, benefit the macro-tier. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Cognitive femtocell has been considered as a promising technique that can improve the capacity and the utilization of spectrum efficiency in wireless networks because of the short transmission distance and low transmit power. In this paper, we study the win-win solution of energy-efficient radio resource management in cognitive femtocell networks, where the macrocell tries to maximize its revenue by adjusting spectrum utilization price while the femtocells try to maximize their revenues by dynamically adjusting the transmit power. When the spectrum utilization price is given by macrocell, we formulate the power control problem of standalone femtocells as an optimization problem and introduce a low-complexity iteration algorithm based on gradient-assisted binary search algorithm to solve it. Besides, non-cooperative game is used to formulate the power control problem between collocated femtocells in a collocated femtocell set, and then low complexity and widely used gradient-based iteration algorithm is applied to obtain the Nash-equilibrium solution. Specially, asymptotic analysis is applied to find the approximate spectrum utilization price in macrocell, which can greatly reduce the computational complexity of the proposed energy-efficient radio resource management scheme. Finally, extensive simulation results are presented to verify our theoretical analysis and demonstrate the performance of the proposed scheme. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY Femtocell technology has been drawing considerable attention as a cost-effective means of improving cellular coverage and capacity. However, under co-channel deployment, femtocell system in dense environment may incur high uplink interference to existing macrocells and experiences strong inter-cell interference at the same time. To manage the uplink interference to macrocell, as well as the inter-cell interference, this paper proposes a price-based uplink interference management scheme for dense femtocell systems. Specifically, on the one hand, to guarantee the macrocell users' quality of service, the macrocell base station prices the interference from femtocell users (FUEs) subject to a maximum tolerable interference power constraint. On the other hand, the inter-cell interference is also taken into consideration. Moreover, a Stackelberg game model is adopted to jointly study the utility maximization of the macrocell base station and FUEs. Then, in order to reduce the amount of information exchange, we design a distributed power allocation algorithm for FUEs. In addition, admission control is adopted to protect the active FUEs' performance. Numerical results show that the price-based interference management scheme is effective. Meanwhile, it is shown that the distributed power allocation combined with admission control is capable of robustly protecting the performance of all the active FUEs. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Small cell traffic is expected to experience a continuous increase during the upcoming years, and thus, backhauling challenges should be timely addressed. Regardless the fact that radio resource management continues to be a major research problem in coexisting heterogeneous wireless networks, a mentality shift is observed in the research community towards dealing with wired backhaul bottleneck situations, too. Hence, specific small cell network deployments such as the one considered in this paper have to adopt an integrated quality of service provisioning approach. A femtocell utilizing an existing internet protocol (IP) infrastructure has usually to share the backhaul capacity with several IP networks. As these networks do not provide an efficient admission control process, the capacity allocated to the femtocell can fluctuate unpredictably over time. As a remedy, we propose a scheme for small cells' efficient integration (SCEI) in the IP infrastructure. SCEI is able to manage the total incoming traffic load and continuously adjust the distribution of the backhaul capacity among the existing networks. Simulation results show that SCEI provides significantly higher utilization of the backhaul capacity and more resilience regarding quality-of-service-related metrics in overload state situations compared with state-of-the-art hybrid partitioning techniques. Finally, this work also provides hints on ways that SCEI concepts can be applicable in more future Internet and small cell network deployment variants. [ABSTRACT FROM AUTHOR]

SUMMARY Femto cell technology is a promising solution for indoor coverage of cellular systems. The interference between macro and femto cells can be mitigated via cooperation between the macro base station (BS) and the inside femto sites (FSs). In this paper, the idea of multi-cell multi-input and multi-output is introduced, whereby the macro BS shares the same frequency band with the inside FSs in support of the femto users. Both single-user and multi-user precoding at the macro BS are proposed to support the cooperative transmission between the macro BSs and FSs. In single-user precoding and multi-user precoding without power allocation, only the angle information of the FS-user channels is required to be sent from the users to the macro BS. If the magnitude information is also sent by each user, multi-user precoding with power allocation can be employed to support cooperation between macro BSs and FSs, which is an extension of the classical water-filling optimization problem. Theoretical derivations and an iterative algorithm are both presented to solve this optimization problem. Analytical and simulation results with respect to the signal received with interferences validate the effectiveness of cooperation between the macros BSs and FSs.Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Loss performance modeling is important for the purpose of developing efficient dimensioning tools for large complicated networks. The performance modeling involves two challenging problems:(i) it is difficult to achieve in heterogeneous wireless networks, where different networks have different statistical characteristics in service and traffic models and (ii) capacity-constrained femto-macro overlay networks pose significant challenges due to the wide variety of bandwidth requirement of Internet services, the large number of femtocells overlaid by a macrocell, and the need for fast computations imposed by practical requirements of dynamic real-time resource allocation. This paper proposes a new computationally efficient numerical method for the loss probability approximation in hierarchical heterogeneous wireless networks. Verified by simulations, the performance and accuracy of the proposed numerical method is evaluated in a two-tier hierarchical cellular network and compared with an existing approximation method based on multidimensional Markov-modulated Poisson process. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To 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. [ABSTRACT FROM AUTHOR]

In this paper, we study the resource allocation problem of the uplink transmission with delay quality-of-service constraints in two-tier femtocell networks. Particularly, to provide statistical delay guarantees, the effective capacity is employed as the network performance measure instead of the conventional Shannon capacity. To make the problem computationally efficient and numerically tractable, we decompose the problem into three subproblems, namely, cluster configuration subproblem, intra-cluster subchannel allocation subproblem and inter-cluster power control subproblem. Firstly, we develop a low-complexity heuristic semi-dynamic clustering scheme, where the delay of the channel state information feedback via backhaul is considered. We model such system in the framework of networked partial observation Markov decision process and derive a strategy to reduce the search range for the best cluster configuration. Then, for a given cluster configuration, the cluster heads deal with subchannel allocation and power control within each cluster. We propose a subchannel allocation scheme with proportional fairness. Thereafter, the inter-cluster power control subproblem is modeled as a set of exact potential games, and a channel quality related pricing mechanism is presented to mitigate inter-cluster interference. The existence and uniqueness of Nash equilibriums for the proposed game are investigated, and an effective decentralized algorithm with guaranteed convergence is designed. Simulation results demonstrate that the proposed algorithms not only have much lower computational complexity but also perform close to the exhaustive search solutions and other existing schemes. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]