Indoor Users Research Articles

Indoor cognitive radio operation within the broadcast TV protection contour

Although the broadcast television (TV) spectrum is currently open for unlicensed operation in the USA, a considerably large geographic area still remains excluded from the unlicensed operation due to potential interference to the licensed users. However, it might be possible to reuse primary spectrum within the protection contour if the frequency reuse occurs inside a building that shields radio signals and reduces interference to the primary system. Interference to outdoor licensed users from the indoor operations can be minimized if the unlicensed users adjust their transmit power according to their locations in the building. This paper presents an analysis and effectiveness evaluation of a novel cognitive radio (CR) system which enables CRs to access the licensed spectrum inside a building in the area within the protection contour. The system utilizes an indoor sensor network for (i) interference sensing, (ii) CR transmit power control, to limit the interference to the outdoor primary receiving antennas. Power control model of the indoor system has been developed to estimate safe transmit power for the indoor users. Two cases have been considered; single-user single-sensor (single indoor user and single sensor), and multi-user multi-sensor. Based on the power control model, a power control algorithm has been developed and its effectiveness is assessed through simulations. The algorithm is effective in realistic propagation scenarios, e.g. when internal partition walls and multipath fading are present. The outage probabilities in these propagation scenarios are found and the procedure of determining the transmit powers for CRs is presented.

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 performance guaranteed indoor positioning system using conformal prediction and the WiFi signal strength

ABSTRACTIndoor navigation provides the positioning service to the indoor users, where the GPS coverage is not available. The challenges for most signal-based indoor positioning systems are the unpredictable signal propagation caused by the complex building interiors, and the dynamic of the environment caused by the peoples' movements. However, most existing systems made no assumption about the quality of their predictions, which is crucial in such noisy indoor environment. To address this challenge, this article proposes a confidence measure to reflect the uncertainty of the positioning prediction. More importantly, the users may control the size of the prediction set by setting the confidence level tailoring to their personal requirement. The proposed approach in this article has been validated in three real office buildings with challenging indoor environments, which indicated that it performed up to 20% more accurate than traditional Naïve Bayes and Weighted K-nearest neighbours (W-KNN) algorithms.

Mobility and load aware radio resource management in OFDMA femtocell networks

Recent evolutions in mobile networks have led to increased resource demands, especially from indoor users. Although recent technologies such as LTE have an important role in providing higher capacity, indoor users are not satisfied adequately. Femtocell networks are one of the proposed solutions that support high data rates as well as better indoor coverage without imposing heavy costs to network providers. However, interference management is a challenging issue in femtocell networks, mainly due to dense and random deployment of femto access points (FAPs). Therefore, distinct radio resource management (RRM) methods are employed to ensure acceptable levels of call dropping/blocking probability and spectral efficiency. However, the mobility of mobile users is an important issue in resource management of femtocell networks that has not been considered adequately. In this paper, we propose an algorithm that predicts the resource requirements of FAPs regarding mobility of their users and allocates the resources to the FAPs based on an extended load-based RRM algorithm that prioritizes handoff calls to incoming calls. Simulation results illustrate that the proposed method has shown lower call dropping probability and higher spectral efficiency compared to the benchmark algorithms.

Stochastic Geometry Based Framework for Coverage and Rate in Heterogeneous Networks with Sectored Fractional Frequency Reuse

Modern day cellular networks are driven by the need to provide ubiquitous connectivity with very high spectral efficiency to both indoor and outdoor users, hence the need to deploy small cells over conventional macrocells in a Heterogeneous Network (Hetnet) deployment. To alleviate the resulting inter-cell and cross-tier interference, effective inter-cell interference coordination (ICIC) schemes such as Fractional Frequency Reuse (FFR) are employed, and have been widely studied in perfect geometry network scenarios which are too idealistic and not easily adaptable to the complexity of Hetnets. This work provides an analytical framework for the performance of such FFR schemes in Hetnets with antenna sectorization employed at the macro tier, by leveraging stochastic geometry tools to model base station locations of both macro and femto tiers using the Poisson Point Process (PPP). We study the effects of varying system parameters and consider cross-tier femto interference commonly ignored in many analytical works in literature. Furthermore, the femtocells employ a sensing algorithm to minimize spectrum sharing with macro users in close proximity, especially at the transition areas of center and edge region where cross-tier interference could be monumental. Numerical simulations are used to evaluate performance of the proposed framework in terms of coverage probability and average user rate, and results are compared with traditional FFR schemes and the No-FFR deployment. To the best of the author’s knowledge, this is the first analytical framework characterizing sectored-FFR schemes using stochastic geometry tools in Hetnets.

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.

Promoting femtocell cooperation through incentive for improving data rate of indoor users in underlay heterogeneous network

This study proposes an incentive-based femtocell cooperation scheme for indoor macrocell users (MUs) in an underlay two-tier heterogeneous network which helps the indoor MUs to achieve higher data rate through time sharing access from the femtocell. Due to underlay spectrum sharing nature of the femtocell, the network suffers from severe cross-tier interference. To manage this cross-tier interference, a price-based power control scheme is also proposed for the femtocell access point (FAP) whereby the macrocell base station (MBS) controls the transmit power of the FAP by pricing their resulted cross-tier interference power level subject to a maximum tolerable interference limit. A Stackelberg game has been formulated and analysed for joint pricing-based power control and incentive-based cooperation game. Numerical results show the performance of the proposed scheme in terms of achievable rate of indoor users and utilities of both the MBS and the FAP for different locations of the femtocells.

Macro cellular network transition from traditional frequency range to 28 GHz millimeter wave frequency band

The target of this article is to analyze the impact of transition from cellular frequency band i.e. 2.1 GHz to Millimeter Wave (mmWave) frequency band i.e. 28 GHz. A three dimensional ray tracing tool “sAGA” was used to evaluate the performance of the macro cellular network in urban/dense-urban area of the Helsinki city. A detailed analysis of user experience in terms of signal strength and signal quality for outdoor and indoor users is presented. Indoor users at different floors are separately studied in this paper. It is found that in spite of considering high system gain at 28 GHz the mean received signal power is reduced by almost 16.5 dB compared with transmission at 2.1 GHz. However, the SINR is marginally changed at higher frequency. Even with 200 MHz system bandwidth at 28 GHz, no substantial change is witnessed in signal quality for the outdoor and upper floor indoor users. However, the users at lower floors show some sign of degradation in received signal quality with 200 MHz bandwidth. Moreover, it is also emphasized that mobile operators should take benefit of un-utilized spectrum in the mmWave bands. In short, this paper highlights the potential and the gain of mmWave communications.

Analysis of Urban Two-Tier Heterogeneous Mobile Networks With Small Cell Partitioning

In this paper, we investigate the performance of typical indoor users in urban two-tier heterogeneous mobile networks with indoor-deployed small cell base stations (BSs) and outdoor BSs. The urban topology is modeled by a Boolean scheme of blockages, which is tied together with the deployment of outdoor and indoor BSs as well as the signal propagation characteristics. Each building is assumed to be served by an indoor small cell BS with a certain probability, which is denoted as occupation probability. Indoor and outdoor environments are partitioned by walls with a certain penetration loss. We separately account for outdoor BSs in line of sight (LOS) and non-line of sight (NLOS), as well as small cell BSs in neighboring and non-neighboring buildings. We derive expressions for the signal to interference ratio (SIR)-coverage probability and the average spectral efficiency of a typical indoor user. Numerical evaluations are performed with 3GPP compliant macro- and pico-BS scenarios. Our results exhibit that the indoor area coverage, which is a function of the building density and size, significantly affects the impact of the target building’s wall penetration loss. The analysis is simplified by various assumptions, which are verified by extensive Monte Carlo simulations.

An energy efficient framework for user association and power allocation in HetNets with interference and rate-loss constraints

Dense deployment of femtocells has proved to be an effective solution to handle increasing demands of indoor mobile data. A femtocell not only helps reducing operational and capital expenditure but also improves the energy efficiency of the network. Femtocells are able to increase spectrum efficiency by manyfold by reusing the available spectrum for indoor users. However, it has been seen that traditional cell selection schemes limit the user count under femtocell. Additionally, dense deployment of femtocells comes with the cost of increased interference to the neighbouring femtocell and macrocell users. In this paper, we first analyse various cell selection schemes to improve user association and resource utilization in femtocells. Then, we focus on improving energy efficiency and throughput of femtocell based cellular networks. For this, we formulate an optimization problem that efficiently reuses macrocell spectrum in femtocells with power control while satisfying macrocell users’ interference and rate-loss constraints.

Handover and SINR Optimized Deployment of LTE Femto Base Stations in Enterprise Environments

The data rates for indoor users can be boosted using low power consuming nodes like Femtos base stations (FBSs) in long term evolution networks. The manner in which Femtos are deployed inside a building environment, with large number of users, can significantly affect the throughput and number of handovers among Femtos. In our system model, we take into account the following parameters: co-channel interference between FBS and macro BSs, wall attenuation factor and user density in the enterprise building environment. In this work, we formulate two mixed integer linear programming (MILP) optimization models: optimal constant threshold signal to interference plus noise ratio (OptCTSINR) which guarantees a certain minimum SINR and also minimizes the number of Femtos needed for the coverage of enterprise buildings and optimal handover (OptHO) which reduces the number of handovers when the user passes through a certain portion (i.e., within a room or corridor) of the building. We solve these MILP models by utilizing branch and cut framework of CPLEX solver using General Algebraic Modeling System (GAMS) tool. When compared to K-means clustering based placement scheme, for a given number of Femtos, proposed OptCTSINR scheme results in an average SINR improvement of 28 %. Similarly, our proposed OptHO scheme reduces 30 % of the unnecessary handovers when compared to OptCTSINR scheme.

User localisation using wireless signal strength - an application for pattern classification using fuzzy decision tree

Due to prevalent availability of wireless networks, there is enormous usage of mobile devices among the public in all sectors. Locating the mobile devices using the wireless signal strength received enables transparent and immediate services for both indoor and outdoor users. For indoor users, a smart environment could be provided by giving smart facilities like automating switching on/off of room lights, air conditioning, etc., by finding the user's exact location using their mobile device. Similarly, outdoor users can get services from the mobile service providers based on their current location. In this paper, we consider indoor user localisation as a pattern classification problem and propose to apply fuzzy decision tree FDT for locating users. As far as our knowledge is concerned, this is the first attempt to apply FDT for locating users in indoor environment using wireless signal strength received by user's handheld devices.

A Distributed Coverage Organization Algorithm for Femtocell Networks

Coverage area adjustment is one of the crucial problems to be solved to utilize the full potential of heterogeneous systems. The power levels should be adjusted such that the leakage to outdoor users is limited while providing high signal quality for indoor users. In this paper, we propose a coverage adjustment algorithm for two-tier femtocell networks with possible extensions to multi-tier networks. The proposed algorithm aims to achieve fairness among users in a distributed manner, without relying on channel state information or predefined target parameters. Convergence analysis under both fixed and time-varying communication infrastructure setups are investigated. The performance of the proposed algorithm is further verified by comparisons and simulations which are in agreement with the theoretical analysis.

Improving indoor positioning precision by using received signal strength fingerprint and footprint based on weighted ambient Wi-Fi signals

Positioning is the foremost process in the location based service (LBS). With the GPS signal strength obstructed by the wall, indoor users cannot obtain their positions with the assistance from the global positioning satellites. Most of the indoor positioning systems have relied on received signal strengths (RSSs) from indoor wireless emitting devices, such as Wi-Fi access points (APs). Integrating indoor position information into the application on the modern handheld devices can increase the application diversity and quality in an indoor environment. In this paper, we propose a novel indoor positioning scheme assisted by the RSS fingerprint and footprint. Smartphone users can get their indoor position based on RSSs from the surrounding Wi-Fi APs. With the assistance of collecting ambient Wi-Fi RSSs from not only the intrinsic APs but also the extrinsic APs, filtering RSSs by directions/orientations, and mitigating signal fluctuation, our proposed scheme can overcome the severe signal instability problem in the indoor environment and raise the positioning accuracy. In order to reduce the time complexity of the indoor positioning procedure, we design a close designated location set (CDLS) algorithm that only uses the designated locations with the similar footprints of current user's position to determine the user's location. The proposed RSS fingerprint and footprint matching mechanism can speed up the positioning process. Meanwhile, to lessen the possible negative effect of extrinsic APs, the weighted voting positioning (WVP) algorithm would assign higher reference weights to the signals from the intrinsic APs, and adjust the weights to the signals from the extrinsic APs by their failure probability. The evaluation results show that our proposed scheme can achieve a certain level of accuracy in the indoor environments and outperform other solutions.

Improving Quality of Service of Femto Cell Using Optimum Location Identification

To enhance the throughput and Quality of Service (QoS) of indoor users, Femto cells became the best solution. The placement of a femtocell is always a challenging task due to its interference constraints with other cells. If the base stations has limited number of Femto-cells, then there is need to focus much on interference constraints. In the dense countries like India, there is a need to install more number of Femto-cells to get the proper throughput. But, the limiting factor here is frequency and interference management. This paper explained the interference management issues and hand over issues. This paper proposed method of optimal placement of Femto cell to increase the QoS in dense environment where macro-cell holds many number of Femto cells. This solution made an assumption that the interference effect was considerably strong when compared to Noise. Hence, we have not considered Noise parameter in the analysis. It was shown that the optimal placement has better throughput when compared to blind placement. Two cases were considered as blind placements and their throughput was analyzed with respect to optimal placement. The proposed method was tested in both single and multi-room buildings. Finally, it was observed that the gain of 50% was increased with respect to large buildings with many rooms. Index Terms—Femto cell, Quality of Service, throughput and interference.

Evaluation of SPMA and higher order sectorization for homogeneous SIR through macro sites

This paper highlights the performance of single path multiple access (SPMA) and discusses the performance comparison between higher order sectorization and SPMA in a macrocellular environment. The target of this paper is to emphasize the gains and significance of the novel concept of SPMA in achieving better and homogeneous SIR and enhanced system capacity in a macrocellular environment. This paper also explains the algorithm of SIR computation in SPMA. The results presented in this paper are based on sophisticated 3D ray tracing simulations performed with real world 3D building data and site locations from Seoul, South Korea. Macrocellular environment dominated with indoor users was considered for the research purpose of this paper. It is found that by increasing the order of sectorization, SIR along with spectral efficiency degrades due to the increase in inter-cell interference. However, as a result of better area spectral efficiency due to increased number of sectors (cells), the higher order sectorization offers more system capacity compared to the traditional 3-sector site. Furthermore, SPMA shows an outstanding performance and significantly improves the SIR for the individual user over the whole coverage area, and also remarkably increases the system capacity. In the environment under consideration, the simulation results reveal that SPMA can offer approximately 424 times more system capacity compared to the reference case of 3-sector site.

Efficiency Evaluation for Femtocell Spectrum Access in LTE-Advanced

Femtocells are considered one of the ultimate solutions for the ever increasing demand in LTE-Advance. Recently, wireless industries have resorted to femtocell networks in order to enhance indoor coverage and quality of service since macro-antennas fail to reach these objectives. In enabling indoor home or enterprise users with mobile broadband solutions, role of femtocells are crucially important. While considering low cost solutions for higher coverage and data rate, femtocells apparently have one of the best potentials for indoor users. Due to the dense self-deployment of femtocells in a limited area, serious inter-femtocell interference (IFI) may cause, which consequently results in severe performance degradation. To mitigate the IFI and utilize spectrum resource more efficiently, this paper proposes a cluster based femtocell deployments along with a capacity based cognitive resource allocation scheme .Three different channel configurations in a hybrid access femtocell network are considered for performance analysis. The results of a performance analysis of the cluster based femtocell configurations in a priority based users’ network are presented.

Distributed games for coordinated coalition formation in femtocell networks

For performance enhancement of indoor users, we consider a femtocell network consisting of densely deployed femto base stations (FBSs) which use a set of empty sub-channels to serve the end user. In this environment, users may still suffer from high inter-femtocell interference problem over downlink, which can be solved through cooperation among femto base stations. In this paper, we investigate a game-theoretic approach by which FBSs can form distributed and stable coalitions, which enhances the utility function that is defined as the ratio of obtained capacity to the cost of cooperation. Our proposed kernel-based algorithm for coalition formation is stable as well as Pareto-optimal in both closed and open access modes. In closed access mode, only registered users are able to access a FBS, whereas in open access mode, access is granted to any users. For both modes, we define two different kernel-stability criteria. Through simulation experiments, we confirm that our algorithm yields better utility for end users compared to non-cooperative transmission in both closed and open access modes. Our results further illustrate a tradeoff between the achieved utility and the overhead incurred by coalition members.

A self‐organized resource allocation scheme for heterogeneous macro‐femto networks

AbstractThis paper investigates the radio resource management (RRM) issues in a heterogeneous macro‐femto network. The objective of femto deployment is to improve coverage, capacity, and experienced quality of service of indoor users. The location and density of user‐deployed femtos is not known a‐priori. This makes interference management crucial. In particular, with co‐channel allocation (to improve resource utilization efficiency), RRM becomes involved because of both cross‐layer and co‐layer interference. In this paper, we review the resource allocation strategies available in the literature for heterogeneous macro‐femto network. Then, we propose a self‐organized resource allocation (SO‐RA) scheme for an orthogonal frequency division multiple access based macro‐femto network to mitigate co‐layer interference in the downlink transmission. We compare its performance with the existing schemes like Reuse‐1, adaptive frequency reuse (AFR), and AFR with power control (one of our proposed modification to AFR approach) in terms of 10 percentile user throughput and fairness to femto users. The performance of AFR with power control scheme matches closely with Reuse‐1, while the SO‐RA scheme achieves improved throughput and fairness performance. SO‐RA scheme ensures minimum throughput guarantee to all femto users and exhibits better performance than the existing state‐of‐the‐art resource allocation schemes.Copyright © 2014 John Wiley & Sons, Ltd.

A Survey on Cell Selection Schemes for Femtocell Networks

With ever increasing number of mobile devices, operators have to search for new alternative to handle user demands. Deployment of additional base stations is always an option to improve coverage of capacity. However, it comes with the cost of incresed operational and capital expenditure. Interestingly, it has been seen that nearly 80% of mobile data demands are originating from indoor home and office users. To handle these indoor demands, deployment of small, low power femtocell access points have been suggested. However, in current deployment scenario, most femtocell are underutilised. To improve user association and resource utilization in femtocell, various cell selection schemes have been suggested. In this paper, we analyse various cell selction schemes available in the literature. Additionally, we look at energy efficiency aspect of these cell selection schemes. Keywords—Femtocell, cell selection schemes, energy efficiency, performance evaluation I. Introduct ion With availability of smart phones and tablets, users now expect 24X7 connectivity to the Internet. As these Internet devices are getting cheaper and cheaper, the demands for wireless data is increasing. Study shows that cellular data demands are expected to increase 18 fold by the end of year 2020 [1]. To handle these demands, cellular operators are deploying additional base stations, using better modulation and coding techniques. However, they are still unable to satisfy this increasing data demands. Interestingly, nearly 80% of mobile data demands are originating from indoors [2]. Also, these indoor users experience the worst signal quality due to high wall penetration loss. To overcome this indoor data demand problem, cellular operators are deploying small, low cost, low power femtocell base stations. Femtocell are miniature cellular base stations deployed inside users homes and offices to provide improved coverage and bitrate.Femtocell have proved to improve network capacity and coverage by eliminating wall loss and spatial reuse of available spectrum [3]. Inherent low transmission capabilities of femtocell when combined with high path loss limit the users association in femtocell. To reap the gains of femtocell deployment, more users should be offloaded to femtocells. Regarding this, various cell selection schemes have been suggested in the literature. Most basic techniques based on Reference Signal Received Power (RSRP) based association where users get associated with base stationshaving highest received signal power [4]. However, such techniques may not be optimal in terms of users' Quality of Service (QoS). Considering users' perspective, expected bitrate based association is suggested in [5][6]. These techniques try to associated users to base stations based on the expected bitrate they might receive. Expected bitrate based association performs better then RSRP based techniques because it incorporates schedulingopportunities at base stations. To best of our knowledge, a comprehensive analysis of energy efficiency aspect of cell selection schemes is not done in the literature. In this paper, we analyse various cell selection techniques available for femtocell networks. We explain each of them in details with corresponding advantage and limitations. Additionally, we also look at energy efficiency aspect of these cell selection techniques which was ignored in all previous works. Rest of the papers is organises as follows. In section II, we get an overview of femtocell architecture. Section III discusses various cell selection schemes for femtocell based cellular network, along with their advantages and limitations. Section IV discusses performance of various cell selection schemes in terms of network capacity and energy efficiency. Finally, we conclude our work in section V with direction for future research. I