Heterogeneous Wireless Systems Research Articles

Proportionally fair scheduler for heterogeneous wireless systems

ABSTRACTThe proportional fair allocation depends firstly upon the priority weights given to users and secondly upon the proportional distribution of resources according to these weights. This distribution is trivial in single‐technology systems but remains unresolved for heterogeneous wireless systems. This letter addresses this allocation problem not paying attention to the weights calculation, because this issue has been widely studied in the past. The novel proportionally fair scheduler for heterogeneous wireless systems (PFS‐H) is based on linear programming and allocates any arbitrary resource quantity to users that are simultaneously served by several technologies. Given a priority list, the solution of the optimisation problem divides users and technologies into clusters to perform the fairest allocation of resources among users while maximising its usage. Results show that the PFS‐H improves fairness up to 60% as compared with a single‐technology policy. Copyright © 2011 John Wiley & Sons, Ltd.

Context-based user grouping for multi-casting in heterogeneous radio networks

Abstract. Along with the rise of sophisticated smartphones and smart spaces, the availability of both static and dynamic context information has steadily been increasing in recent years. Due to the popularity of social networks, these data are complemented by profile information about individual users. Making use of this information by classifying users in wireless networks enables targeted content and advertisement delivery as well as optimizing network resources, in particular bandwidth utilization, by facilitating group-based multi-casting. In this paper, we present the design and implementation of a web service for advanced user classification based on user, network, and environmental context information. The service employs simple and advanced clustering algorithms for forming classes of users. Available service functionalities include group formation, context-aware adaptation, and deletion as well as the exposure of group characteristics. Moreover, the results of a performance evaluation, where the service has been integrated in a simulator modeling user behavior in heterogeneous wireless systems, are presented.

Vertical Handoff Decision System based on Support Vector Machine

It is expected that many heterogeneous wireless systems, such as 3GPP LTE systems, WiMAX systems and WLAN systems, will coexist in the next generation wireless communication environments. Integrated radio resource management and seamless vertical handoff (VHO) should be supported to provide integrated communication services over multi-radio access networks. A new class of adaptive VHO system that views the handoff problem as a pattern recognition problem is proposed. In this paper, we propose a unified radio resource management (URRM) architecture and Support Vector Machine (SVM) based vertical handoff decision system. Extensive simulation studies show the proposed VHO algorithm outperforms RSS based VHO algorithms in terms of throughput and service cost.

Physical Layer Cryptography and Cognitive Networks

Recently the huge development of different and heterogeneous wireless communication systems raises the problem of growing spectrum scarcity. Cognitive radio tends to solve this problem by dynamically utilizing the spectrum. Security in cognitive radio network becomes a challenging issue, since more chances are given to attackers by cognitive radio technology compared to conventional wireless network. These weaknesses are introduced by the nature itself of cognitive radio, and they may cause serious impact to the network quality of service. However, to the authors' knowledge, there are no specific secure protocols for cognitive radio networks. This paper will discuss the vulnerabilities inherent to cognitive radio systems, identify novel types of abuse, classify attacks, and analyze their impact. Security solutions to mitigate such threats will be proposed and discussed. In particular, physical payer security will be taken into account. A new modulation technique, able to encrypt the radio signal without any a priori common secret between the two nodes, was previously proposed by the authors (Mucchi et al. 2009, WPC 51, 67---80; Mucchi et al. 2010, WPC 53, 329---347). The information is modulated, at physical layer, by the thermal noise experienced by the link between two terminals. A loop scheme is designed for unique recovering of mutual information. This contribution improves the previous works by proposing the noise loop modulation as physical layer security technique for cognitive radio networks.

Efficient RF Circuit Simulation Using an Innovative Mixed Time-Frequency Method

This paper suggests an answer to the problem of simulating heterogeneous wireless systems composed of baseband and RF blocks, as the former demand for SPICE-like engines, while the latter are more efficiently solved with frequency-domain tools as harmonic balance. The proposed time-frequency hybrid technique splits the circuit's node voltages or mesh currents into fast and slowly varying state variables treating the former with the popular envelope transient harmonic balance technique and the latter with a pure time-marching engine. This way, the circuit's hardest nonlinearities - and their rich harmonic content responses - are appropriately computed in the natural time domain, while the more moderate ones - and their corresponding smooth narrowband RF modulated signals - are efficiently processed in the frequency domain. Simulation tests performed in two illustrative application examples, revealed evident gains in computation speed over state-of-the-art RF simulation tools without any noticeable loss in accuracy.

Game-theoretic approach for pricing strategy and network selection in heterogeneous wireless networks

User selection for access network is considered to be one of the distinct features of heterogeneous wireless systems, in which users with multi-network interface terminals can freely select access network for better quality of service with lower expense. On the other hand, service providers (SPs) will have to face more intense competition for attracting more subscribers and increasing their profits, which can be achieved through either non-cooperative or cooperative strategies. In this study, the authors propose a unified quantification model for evaluating the access service of heterogeneous systems. The relation between competitive SPs and users is described by different game models, based on general assumptions and practical application scenarios. A novel network selection scheme for maximising user performance–cost ratio (PCR) is proposed. Numerical results demonstrate that all SPs can achieve Nash equilibrium price under non-cooperative game framework and coalition price for cooperative game case to maximise their absolute profits, and the maximal PCR criterion for user network selection scheme is analysed under different scenarios.

An autonomic-oriented framework based IEEE 802.21 for mobility management in 4G networks

The main challenge in the development of future wireless communication systems is to provide users with a wide range of services across different radio access technologies through a single mobile terminal, while maintaining the quality of service requirements. Thus, the need for seamless interworking between heterogeneous wireless communication systems consisting of multiple radio access technologies and overlapping networks emerges. In this article, we address the main issues that arise while implementing the interworking mechanisms between different radio access networks. An interworking mechanism based on IEEE 802.21 framework is proposed and described in detail. We combine concepts of autonomic networking in the design of the framework in order to use intelligence to provide flexibility, accessibility and transparency to the mobile users.

A decision theoretic approach for channel ranking in crowded unlicensed bands

Interference is disruptive to the operation of wireless sensor networks (WSNs) in unlicensed bands as wireless systems proliferate on the spectrum. The design of a spectrum sharing scheme for WSNs to enable coexistence with geographically collocated heterogeneous wireless systems having multiple parallel interfering channels is a persistent challenge. In this context, interference identification and channel ranking in terms of spectrum access opportunities are addressed in this paper. The goal is to develop a low complexity channel ranking algorithm from channel energy measurements at sensors when a packet-reception-ratio to signal-to-interference-and-noise-ratio (PRR-SINR) interference model is unavailable at network initialization phase. The interference characterizing estimators, temporal occupancy and strength level of a channel, are proposed for interference identification. The effectiveness of the estimators is tested on a sensor platform at 2.4 GHz ISM band under interference from WLAN. Subsequently, the impact of the interference estimators on a channel quality from a receiver perspective is determined with a decision theoretic approach. The estimators are weighted according to their influence on the fitness of a channel and channel ranking is established. The proposed channel ranking achieves a significant gain over heuristic channel ranking (HCR) and gives an accurate interference profile of the channels.

A practical heterogeneous network optimisation algorithm based on reinforcement learning

Owing to the increasing and diversifying service requirements of wireless communications, wireless networks must coexist with heterogeneous radio systems. To realise the interconnection between different networks, it is important for the radio access network elements, such as the cellular network base stations (BSs) and the wireless local area network (WLAN) access points (APs) to be reconfigurable based on the real-time network environment. In this paper, we propose an efficient distributed reconfiguration algorithm for heterogeneous networks: the dynamic network self-optimisation algorithm (DNSA). This algorithm is based on the Q-learning algorithm and the self-optimisation of each network entity acting as independent agents. In the proposed algorithm, multiple agents perform the optimisation cooperatively to reduce the system blocking rate and improve network revenue. The dynamic network self-optimisation problem is transformed into a multiple-agent reinforcement learning problem which has much lower complexity and better performance.

Comparison of Vertical Handover Mechanisms Using Generic QOS Trigger for Next Generation Network

Next Generation Network (NGN) is envisage to integrate heterogeneous wireless systems. NGN is expected to have Quality as the major challenging issue. More specifically, NGN aims at providing guaranteed Quality of Service (QoS) and Quality of Experience (QoE) i.e. what quality a network provider can offer (or claims) & what quality user experiences. NGN user may be interested in changing its network operator or is forced to change the serving access point (AP) or base station (BS) in order to achieve a given level of QoE. Seamless transfer of user’s service from existing operator to a new operator bearing dissimilar radio access technology is called Vertical Handover (VHO). VHO decision may depend on the popular signal to noise ratio (SNR) criteria or other performance metrics like bit error rate, delay, jitter etc or combination of these metrics. Performance of candidate target network depends on the type of traffic i.e. whether conversational, streaming, interactive or background is implemented. Therefore to optimise VHO mechanism, all these metrics & traffic types should be evaluated. Paper elucidates contemporary VHO approaches i.e. hybrid ANP/ RTOPSIS & Oliver blume method. Different Interworking scenarios & NGN testbeds are prepared considering Wi-Fi, WiMAX, UMTS etc. as the candidate networks. Neuro-fuzzy based MCDM weight assignment technique is applied & overall network cost function is computed based on Qualnet simulation. At the end of the paper investigation suggests that Blume algorithm is better than the hybrid ANP mechanism because it is simple to implement, more efficient (40% more accurate), quickly computed (20 times less) and more dynamic (application oriented).

Scheduling Heterogeneous Wireless Systems for Efficient Spectrum Access

The spectrum scarcity problem emerged in recent years, due to unbalanced utilization of RF (radio frequency) bands in the current state of wireless spectrum allocations. Spectrum access scheduling addresses challenges arising from spectrum sharing by interleaving the channel access among multiple wireless systems in a TDMA fashion. Different from cognitive radio approaches which are opportunistic and noncollaborative in general, spectrum access scheduling proactively structures and interleaves the channel access pattern of heterogeneous wireless systems, using collaborative designs by implementing a crucial architectural component--the base stations on software defined radios (SDRs). We discuss our system design choices for spectrum sharing from multiple perspectives and then present the mechanisms for spectrum sharing and coexistence of GPRS+WiMAX and GPRS+WiFi as use cases, respectively. Simulations were carried out to prove that spectrum access scheduling is an alternative, feasible, and promising approach to the spectrum scarcity problem.

Towards cross layer mobility support in metropolitan networks

The next generation mobile networks (4G) is expected to integrate a large number of heterogeneous wireless systems. Practically, metropolitan networks will play an important role in such integration since they include a great variety of mobile systems. Mobility management as well as the integration of existing/future wireless technologies remain an important task to be investigated. A number of interworking proposals are available in the literature, yet none can claim to be the ultimate and unique integrated solution. Moreover, these proposals fail to guarantee seamless mobility and service continuity. This paper proposes a one suite integration solution that includes a Hybrid Interworking Architecture (HIA) for metropolitan networks coupled with a cross layer mobility scheme that aims to guarantee seamless roaming through homogeneous and heterogeneous mobile systems within a city coverage. Performance analyses show that our proposals exhibit net improvements of QoS guarantee compared to existing solutions.

Adaptive Traffic Route Control in QoS Provisioning for Cognitive Radio Technology with Heterogeneous Wireless Systems

As one of the dynamic spectrum access technologies, “cognitive radio technology,” which aims to improve the spectrum efficiency, has been studied. In cognitive radio networks, each node recognizes radio conditions, and according to them, optimizes its wireless communication routes. Cognitive radio systems integrate the heterogeneous wireless systems not only by switching over them but also aggregating and utilizing them simultaneously. The adaptive control of switchover use and concurrent use of various wireless systems will offer a stable and flexible wireless communication. In this paper, we propose the adaptive traffic route control scheme that provides high quality of service (QoS) for cognitive radio technology, and examine the performance of the proposed scheme through the field trials and computer simulations. The results of field trials show that the adaptive route control according to the radio conditions improves the user IP throughput by more than 20% and reduce the one-way delay to less than 1/6 with the concurrent use of IEEE802.16 and IEEE802.11 wireless media. Moreover, the simulation results assuming hundreds of mobile terminals reveal that the number of users receiving the required QoS of voice over IP (VoIP) service and the total network throughput of FTP users increase by more than twice at the same time with the proposed algorithm. The proposed adaptive traffic route control scheme can enhance the performances of the cognitive radio technologies by providing the appropriate communication routes for various applications to satisfy their required QoS.

Architectural aspects of automated network selection in heterogeneous wireless systems

Next-generation heterogeneous wireless systems using an all-IP transport allow converged services such as those based on IP Multimedia Subsystem (IMS) to be delivered over a variety of access technologies. These services however require underlying access technologies to support certain capabilities like Quality of Service. For devices supporting multiple access technologies this results in a complex problem of selection of an optimal service delivery access network. This paper addresses the architectural aspects of the problem by enhancing the roles of policy related components defined in cellular standards and by combining them with novel network selection components to enable automated network selection.

A quality of service negotiation-based vertical handoff decision scheme in heterogeneous wireless systems

This paper introduces a novel vertical handoff decision scheme. The objective is to provide users with enhanced quality of service (QoS) and maximize the network revenue. This scheme balances both-side interests via a suitably defined network merit function and a user–operator negotiation model. The merit function evaluates network performance based on user preferences and decides the most appropriate network for users. The negotiation model is defined as a semi-Markov decision process (SMDP). An optimal policy that maximizes the network revenue without violating QoS constraints is found by resolving the SMDP problem using Q-learning. Furthermore, a time-adaptive QoS monitoring mechanism is combined with the merit function in order to decrease the power consumption on terminal interface activation. The simulation results demonstrate that the proposed vertical handoff decision scheme enhances the performance in terms of power consumption, handoff call-dropping probability (HCDP) and network revenue.

Mobility Modeling and Performance Evaluation of Heterogeneous Wireless Networks

The future-generation wireless systems will combine heterogeneous wireless access technologies to provide mobile users with seamless access to a diverse set of applications and services. The heterogeneity in this inter-technology roaming paradigm magnifies the mobility impact on system performance and user perceived service quality, necessitating novel mobility modeling and analysis approaches for performance evaluation. In this paper, we present and compare three mobility models in two-tier integrated heterogeneous wireless systems, the independence model as a naive extension of the traditional cell residence time modeling techniques for homogeneous cellular networks, the basic Coxian model which takes into consideration the correlation between the residence time within different access technologies, and the extended-Coxian model for further improved estimation accuracy. We propose a general stochastic performance analysis framework based on application session models derived from these mobility models, applying it to a 3G-WLAN integrated system as an example. Our numerical and simulation results demonstrate the general superiority of Coxian-based mobility modeling over the independence model. Furthermore, using the proposed modeling and analysis methods, we investigate the impact of different parameters on system performance metrics such as network utilization time, handoff rates, and forced termination probability, for a wide range of user applications.

A utility‐based capacity optimization framework for achieving cooperative diversity in the hierarchical converged heterogeneous wireless networks

AbstractA hierarchical convergence mechanism for the heterogeneous wireless communication system via the heterogeneous cooperative relay node is presented in this paper, in which the techniques of cooperative communication and wireless relay are utilized to improve performances of the individual user and the overall converged networks. In order to evaluate the benefits of the proposal, a utility‐based capacity optimization framework for achieving the heterogeneous cooperative diversity gain is proposed. The heterogeneous cooperative capacity, relay selection and power allocation theoretical models are derived individually. The joint optimization model for relay selection and power allocation is presented as well. Owing to the computation complexity, the sub‐optimal cooperative relay selection algorithm, the sub‐optimal power allocation algorithm and the sub‐optimal joint algorithm are determined to approach the maximum overall networks' spectrum efficiency. These proposed algorithms are designed in conformance to guarantee the equivalent transmission rates of the different wireless access networks. The simulation results demonstrate that the utility‐based capacity model is available for the heterogeneous cooperative wireless communication system, and the proposed algorithms can improve performances by achieving the cooperative gain and taking full advantage of the cross‐layer design. Copyright © 2008 John Wiley & Sons, Ltd.

Managing Resources and Quality of Service in Heterogeneous Wireless Systems Exploiting Opportunism

We propose a novel class of opportunistic scheduling disciplines to handle mixes of real-time and best-effort traffic at a wireless access point. The objective is to support probabilistic service rate guarantees to real-time sessions while still achieving opportunistic throughput gains across users and traffic types. We are able to show a ldquotightrdquo stochastic lower bound on the service a real-time session would receive assuming that the users possibly heterogeneous capacity variations are known or estimated, and are fast fading across slots. Such bounds are critical to enabling predictable quality of service and thus the development of complementary resource management and admission control strategies. Idealized simulation results show that the scheme can achieve 80%-90% of the maximum system throughput capacity while satisfying the quality of service (QoS) requirements for real-time traffic, and that the degradation in system throughput is slow in the number of real-time users, i.e., inter- and intra-class opportunism are being properly exploited. We note however, that there is a tradeoff between strictness of QoS requirements and the overall system throughput one can achieve. Thus if QoS requirements on real-time traffic are very tight, one would need to simply give priority to real-time traffic, and in the process lose the throughput gains of opportunism.

Advanced reconfiguration framework based on game theoretical techniques in autonomic communication systems

The Autonomic Communications concept forms one promising solution to accommodate the increased complexity of legacy and emerging systems, fostering the automation and minimizing the need for human intervention. This notion implies the introduction of advanced mechanisms for autonomic decision making and self-configuration. The focus of this work is on the introduction of an advanced reconfiguration framework for the support of the following functionalities: i) efficient strategies of terminal attachment to heterogeneous wireless systems are proposed dependent on the evaluation of input stimuli from the surrounding telecom environment. ii) it is shown how to enable optimized selection and attribution of resources, iii) the application of new device configuration is examined, proposing a framework for dynamic protocol stack adaptation. It is indeed necessary to introduce a framework that will enable, policy based reconfiguration decisions supporting dynamic and optimal discovery, download and replacement of necessary protocol functionality. In this context, legacy management and control mechanisms should be enriched with such features operating in either terminal or network equipment. Namely, this contribution discusses cognitive reconfiguration management issues by introducing two basic reconfiguration units encapsulated in a unified management and control architecture: i) the component based protocol stack reconfiguration framework and ii) the resource usage optimization unit. Simulation and performance results presented in the paper prove the technical feasibility of the proposed mechanisms as well as the optimization of reconfiguration actions.

Performance of multiuser network-aware prefetching in heterogeneous wireless systems

We study the performance of multiuser document prefetching in a two-tier heterogeneous wireless system. Mobility-aware prefetching was previously introduced to enhance the experience of a mobile user roaming between heterogeneous wireless access networks. However, an undesirable effect of multiple prefetching users is the potential for system instability due to the racing behavior between the document access delay and the user prefetching quantity. This phenomenon is particularly acute in the heterogeneous environment. We investigate into alleviating the system traffic load through prefetch thresholding, accounting for server queuing prioritization. We propose a novel analysis framework to evaluate the performance of the thresholding approach. Numerical and simulation results show that the proposed analysis is accurate for a wide variety of access, service, and mobility patterns. We further demonstrate that stability can be maintained even under heavy usage, providing both the same scalability as a non-prefetching system and the performance gain associated with prefetching.