Dynamic Channel Allocation

The peer-to-peer technology offers many advantages, but at the same time, it poses many novel challenges for the research community. Modern peer-to-peer systems are characterized by large scale, poor reliability, and extreme dynamism of the participating nodes, with a continuous flow of nodes joining and leaving the systems. Selection of an optimal network requires estimation of its rank using attributes such as storage, average load, cost, reliability etc. There are multiple networks, each vying for users business by providing them novel services. The user in turn has to decide which network best meets its service requirements and accordingly join a network.

In this paper, we investigate the impact of retrial phenomenon on loss probabilities and compare loss probabilities of several channel allocation schemes giving higher priority to hand-off calls in the cellular mobile wireless network. In general, two channel allocation schemes giving higher priority to hand-off calls are known; one is the scheme with the guard channels for hand-off calls and the other is the scheme with the priority queue for hand-off calls. For mathematical unified model for both schemes, we consider theMAP 1,MAP 2/M/c/b, ∞ retrial queue with infinite retrial group, geometric loss, guard channels and finite priority queue for hand-off class. We approximate the joint distribution of two queue lengths by Neuts' method and also obtain waiting time distribution for hand-off calls. From these results, we obtain the loss probabilities, the mean waiting time and the mean queue lengths. We give numerical examples to show the impact of the repeated attempt and to compare loss probabilities of channel allocation schemes.

Dynamic allocation has received considerable attention since it was first proposed in the 1970s as an alternative means of allocating treatments in clinical trials which helps to secure the balance of prognostic factors across treatment groups. The purpose of this paper is to present a generalized multidimensional dynamic allocation method that simultaneously balances treatment assignments at three key levels: within the overall study, within each level of each prognostic factor, and within each stratum, that is, combination of levels of different factors Further it offers capabilities for unbalanced and adaptive designs for trials. The treatment balancing performance of the proposed method is investigated through simulations which compare multidimensional dynamic allocation with traditional stratified block randomization and the Pocock-Simon method. On the basis of these results, we conclude that this generalized multidimensional dynamic allocation method is an improvement over conventional dynamic allocation methods and is flexible enough to be applied for most trial settings including Phases I, II and III trials.

The artificial neural net development has had something of a renaissance in the last decade with an impressive range of application areas. From the viewpoint of telecommunication networks and systems, an increasing number of studies can be observed in recent literature dealing with proposed applications of neural nets in telecommunication environments, such as connection admission control in broadband networks, the control of high-speed interconnection networks, channel allocation in cellular mobile systems, adaptive routing, etc. These proposed applications largely use three main neural net classes: feed-forward nets with backpropagation learning, Hopfield feedback nets, and selforganising neural nets. In this paper, we first give an overview of neural net classes and their main properties, and then present a review of applications in telecommunication systems, where attention is devoted to numerical aspects such as the convergence property and learning speed of the proposed neural nets.

The standard end-to-end flow control implemented by the TCP protocol is ill-suited when it comes to achieving fair bandwidth allocation among competing TCP flows. Indeed, the lack of feedback from intermediate nodes does not allow a TCP source to regulate its throughput so that it is not sending more than its fair share, thus penalizing other, less aggressive flows. In this paper, we propose a novel scheme that, building on existing work on network-layer stateless fair queueing, extends the approach to the TCP layer. Also, we discuss a possible implementation of both the network-layer and the transport-layer architecture. We test our solution under different traffic scenarios and show that not only is a fair bandwidth allocation achieved, but the overall network utilization for TCP flows is also increased.

Enhancing system capacity is an important issue in wireless cellular networks. In this paper, we present a new channel sharing scheme to address this problem. Our basic idea is to allow channels to be shared b etween adjacent cells. We propose a xed channel assignment scheme to maximize channel reuse e ciency while allowing channel sharing. An important feature o f o u r sharing scheme is that channel management is localized b etween adjacent cells, and no global coordination or optimization is required, thus simplifying implementation. We provide simulation results comparing our scheme with the xed channel assignment scheme.

The concept of dynamic spectrum access will allow the radio spectrum to be traded in a market like scenario allowing wireless service providers (WSPs) to lease chunks of spectrum on a short-term basis. Such market mechanisms will lead to competition among WSPs where they not only compete to acquire spectrum but also attract and retain users. Currently, there is little understanding on how such a dynamic trading system will operate so as to make the system feasible under economic terms.

M Ma as ss sa ac ch hu us se et tt ts s I In ns st ti it tu ut te e o of f T Te ec ch hn no ol lo og gy y E En ng gi in ne ee er ri in ng g S Sy ys st te em ms s D Di iv vi is si io on n Abstract-The open access, unlicensed or spectrum commons approach to managing shared access to RF spectrum offers many attractive benefits, especially when implemented in conjunction with and as a complement to a regime of marketbased, flexible use, tradable licensed spectrum ([Benkler02], [Lehr04], [Werbach03]). However, as a number of critics have pointed out, implementing the unlicensed model poses difficult challenges that have not been well-addressed yet by commons advocates ([Benjam03], [Faulhab05], [Goodman04], [Hazlett01])

A new dynamic channel allocation scheme (DCAS) has been proposed for mobile satellite systems with the aim of improving the utilization of the network resources by reducing the handoff call dropping probability (HODP) while guaranteeing a certain quality of service for the new call blocking probability (NCBP). The arriving calls are given channels based on their priority. The handoff calls

Cognitive Radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum aware communication paradigm in wireless communications. Such networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse Quality-of-Service (QoS) requirements. Specifically, in Cognitive Radio Ad Hoc Networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, current research challenges of the CRAHNs are presented. First, spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. Moreover, the influence of these functions on the performance of the upper layer protocols are investigated and open research issues in these areas are also outlined. Finally, the proposed tools, and best simulator to solve research challenges in spectrum management are explained. This gives an insight in choosing the suitable tool, and the suitable simulator that fit for solving different challenges.

In this paper, we propose a channel-assignment algorithm at the Access Points (APs) of a Wireless Local Area Network (WLAN) in order to maximize Signal-to-Interference Ratio (SIR) at the user level. We start with the channel assignment at the APs, which is based on minimizing the total interference between APs. Based on this initial assignment, we calculate the SIR for each user. The algorithm can be applied to any WLAN, irrespective of the user distribution and user load. Results show that the proposed algorithm is capable of significantly increasing the SIR over the WLAN, which in turn improves throughput.

This paper describes some of the outcome of the FP7 project PHYDYAS, whose main objective was to propose a new physical layer that will enable introduction of cognitive radios and dynamic access spectrum management. During the project both a software simulator and a demonstrator have been developed. A description of the demonstrator and some simulation results that show the differences in spectral efficiency and the sensititvity to synchronisation errors between OFDM and FBMC are given.

Multicast is a key technology that provides efficient data communication among a set of nodes for wireless multi-hop networks. In sensor networks and MANETs, multicast algorithms are designed to be energy efficient and to achieve optimal route discovery among mobile nodes, respectively. However, in wireless mesh networks, which are required to provide high quality service to end users as the "last-mile" of the Internet, throughput maximization conflicting with scarce bandwidth has the paramount priority. We propose a Level Channel Assignment (LCA) algorithm and a Multi-Channel Multicast (MCM) algorithm to optimize throughput for multi-channel and multiinterface mesh networks. The algorithms first build a multicast structure by minimizing the number of relay nodes and hop count distances between the source and destinations, and use dedicated channel assignment strategies to improve the network capacity by reducing interference. We also illustrate that the use of partially overlapping channels can further improve the throughput. Simulations show that our algorithms greatly outperform the single-channel multicast algorithm. We observe that MCM achieves better throughput and shorter delay while LCA can be realized in distributed manner.

Cognitive Radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum aware communication paradigm in wireless communications. Such networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse Quality-of-Service (QoS) requirements. Specifically, in Cognitive Radio Ad Hoc Networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, current research challenges of the CRAHNs are presented. First, spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. Moreover, the influence of these functions on the performance of the upper layer protocols are investigated and open research issues in these areas are also outlined. Finally, the proposed tools, and best simulator to solve research challenges in spectrum management are explained. This gives an insight in choosing the suitable tool, and the suitable simulator that fit for solving different challenges.

With the introduction of femtocells, cellular networks are moving from the conventional centralized network architecture to a distributed one, where each network cell should make its own radio resource allocation decisions, while providing inter-cell interference mitigation. However, realizing such distributed network architecture is not a trivial task. In this paper, we first introduce a simple self-organization rule, based on minimizing cell transmit power, following which a distributed cellular network is able to converge into an efficient resource reuse pattern. Based on such self-organization rule and taking realistic resource allocation constraints into account, we also propose two novel resource allocation algorithms, being autonomous and coordinated, respectively. Performance of the proposed self-organization rule and resource allocation algorithms are evaluated using system-level simulations, and show that power efficiency is not necessarily in conflict with capacity improvements at the network level. The proposed resource allocation algorithms provide significant performance improvements in terms of user outages and network capacity over cutting-edge resource allocation algorithms proposed in the literature.

A wireless sensor network (WSN) is a collection of tiny and limited-capability sensor nodes that report their sensed data to a data collector, referred to as a sink node. WSNs are used in many applications, but are challenged by memory and energy constraints. To address these issues, solutions have been proposed on different levels including the topological level where multiple sinks can be used in the network to reduce the number of hops between a sensor and its sink node. Topological level solutions are very crucial in time-sensitive applications where the maximum worst case delay incurred by a message to get from a sensor to the corresponding sink should be minimal or at least less than a certain value. In turn, the maximum worst case delay can be minimized by choosing near optimal locations of the sinks. Consequently the network lifetime will be extended since the energy consumed by the sensor nodes will be reduced. In this paper, we propose an efficient and robust approach based on Particle Swarm Optimization (PSO) heuristic to solve the multiple sink placement problem; more specifically we use Discrete PSO (DPSO) with local search (LS). We start by formulating the problem then discretizing it and finally applying PSO while introducing local search to the inner workings of the algorithm. When compared to Genetic Algorithm-based Sink Placement (GASP), which is considered the state-of-the-art in solving the multiple sink placement problem, our approach improved the results in most scenarios while requiring less runtime.

Mobile computing and vehicular communications are becoming a very important paradigm for wireless communications, mainly because of their ability to adapt to different mobile applications. In this paper, we propose a new scheme for reducing the interference level during mobile transmissions in the VehiculAr inter-NETworking (VANET) environment, taking the advantage of the multi-channel nature of IEEE802.11p standard. In order to relieve the effects of the cochannel interference perceived by mobile nodes, transmission channels are switched on a basis of a periodical Signal-to-Interference Ratio (SIR) evaluation. The attention is focused on the routing level of VANET and we propose an interference aware routing scheme for multi-radio vehicular networks, wherein each node is equipped with a multi-channel radio interface. A new metric is also proposed, based on the maximization of the average SIR level of the connection between source and destination. Our solution has been integrated with the AODV routing protocol to design an enhanced Signal-to-Interference-Ratio-AODV (SIR-AODV). NS-2 has been used for implementing and testing the proposed idea, and significant performance enhancements were obtained, in terms of throughput, packet delivery and, obviously, interference.

Ph: 9 1-80-309-2658, Fax: 9 1-80-360-099 1 anand@cellular.ece.iisc.ernet.in Abstruct-Dynamic Channel allocation in Cellular Networks have become very popular off late due to the flexibility obtained by using any of the available channels in any cell as long as the Interference level is below a given threshold.

Cognitive Radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum aware communication paradigm in wireless communications. Such networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse Quality-of-Service (QoS) requirements. Specifically, in Cognitive Radio Ad Hoc Networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, current research challenges of the CRAHNs are presented. First, spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. Moreover, the influence of these functions on the performance of the upper layer protocols are investigated and open research issues in these areas are also outlined. Finally, the proposed tools, and best simulator to solve research challenges in spectrum management are explained. This gives an insight in choosing the suitable tool, and the suitable simulator that fit for solving different challenges.

The aim of this work is to design and implement an FPGA-based Multi-Standard Software Radio Receiver. WLAN and UMTS are taken as the case study. Xilinx FPGA Virtex-IV is the target platform. Bandpass sampling technique at 840MHz is used to alias the combined band of WLAN and UMTS. In the channelization process, in contrast to conventional channelizer, polyphase channelizer is employed. The designed prototype filter for WLAN has 50 taps, partitioned into 5 polyphase sub-filters whereas for the UMTS the prototype filter has 2520 taps, partitioned into 210 polyphase sub-filters. In the implementation, serial polyphase structure with parallel MAC is selected. An implementation analysis based on the area requirements for multipliers, adders and registers for different structures is performed. For 16-tap filter, the structures for Parallel-Multiply and Accumulate, DA, Fast FIR, and Frequency domain filtering require 2896 (without adders), 3072, 4064, and 5572 slices, respectively. The DA is found to be suitable for the implementation due to being resource efficient. Polyphase subfilter is implemented with Distributed Arithmetic structure and also with Xilinx-DSP48 slices for improved performance.

In this contribution we demonstrate that the peak-to-average power ratio (PAPR) of a Multi-Carrier Code Division Multiple Access (MC-CDMA) signal can be suitably minimized by resorting to a judicious strategy for the allocation of the spreading signature codes. A low-complexity implementation of the proposed strategy is presented and its performance gain over conventional random allocation strategy is numerically assessed.

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multi-channel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that compared to typical multi-channel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.

Providing approximate max-min fair bandwidth allocation among flows within a network or at a single router has been an important research problem. In this paper, we study the space complexity of fairness algorithms, and the communication complexity of distributed global fairness algorithms. We show that in order to enforce max-min fairness with bounded errors, a router must maintain per-flow state. Then we present a practical edge-marking based architecture to demonstrate the enforcement of approximate global max- ...

General Packet Radio Service (GPRS)-a bearer service to GSM-has been deployed worldwide, and is widely considered a technology precursor to the evolving third generation (3G) wireless networks. The general conception has been that while users will be exposed to faster wide-area wireless data access, experience gained from GPRS could well prove useful for 3G, and also for systems beyond 3G deployment. In this paper, we present a comprehensive simulation study for different traffic scheduling algorithms for Quality of Service in General Packet Radio Service (GPRS) at the IP level. We first study the correlation between GSM and GPRS users, and show how a dynamic channel allocation scheme between GSM-GPRS can give substantially better performance than the static ones. We then extend our study by taking into account users' requirements for different QoS profiles, based on seven different scheduling algorithms in GPRS. By simulating traffic related to an ATIS (Advanced Travelers Information System) at the IP level, we show how traffic scheduling algorithms perform by taking into account different performance parameters such as the average traffic, average waiting time in the scheduler, packet loss probabilities in the scheduler based on static and dynamic channel allocation schemes, packet priorities as well as average throughput per-GPRS user. The study gives a comparative analysis for various scheduling algorithms OE network designers can benefit from this study, and by extending this to several other scenarios.

A data network may not be stable at the connection level under some unfair bandwidth allocation policies, even when the normal offered load condition is satisfied i.e. average traffic load at each link is less than its capacity. In this paper, we present that a data network is stable when the bandwidth of the network is allocated so as to provide a minimum bandwidth using max min fairness algorithm. Thus each user will be guaranteed for a minimum bandwidth he will be getting.

Cognitive radio (CR) technology is an innovative radio design philosophy in order to increase the spectrum utilization by exploiting the unused spectrum in dynamically changing environments. Specifically, the CR technology will allow a group of potential users (referred to as secondary users) to access available spectrum resources unused by primary users (PUs) for whom the band has been licensed. The spectrum available for secondary users (SUs) depends on PUs' activity in the licensed spectrum. In this paper, we develop a queuing analytic framework to study important performance measures experienced by SUs in a CR network. We study queuing delay and buffer statistics of SUs' packets by modeling PUs' activity as a two state Markov chain and SUs' channel quality variation as a finite state Markov chain (FSMC). In order to allocate available channels among the SUs, an opportunistic channel allocation scheme is considered. The proposed framework facilitates to design an admission controller for SUs' network in order to maintain a given quality service (QoS) requirement which is specified in the form of statistical delay guarantee.

This paper introduces T-Lohi, a new class of distributed and energy-efficient media-access protocols (MAC) for underwater acoustic sensor networks (UWSN). MAC design for UWSN faces significant challenges. For example, acoustic communication suffers from latencies five orders-ofmagnitude larger than radio communication, so a naive CSMA MAC would require very long listen time resulting in low throughput and poor energy efficiency. In this paper, we first identify unique characteristics in underwater networking that may affect all MACs, such as space-time uncertainty and deafness conditions. We then develop T-Lohi employing a novel tone-based reservation mechanism that exploits space-time uncertainty and high latency to detect collisions and count contenders, achieving good throughput across all offered loads. It employs our low-power wake-up receiver to significantly reduce energy consumption. Finally, we evaluate design choices and protocol performance through extensive simulation. The results show that the energy cost of packet transmission is within 3-9% of optimal, that our protocols achieve good channel utilization, within 30% of the theoretical maximum. We also show that our protocols are stable and fair under both low and very high offered loads.

We discuss a wavelength-division-multiplexed-based passive-optical-network (PON) architecture that allows for incremental upgrade from single-channel time-division multipleaccess PONs in order to provide higher bandwidth in the access network. Various dynamic-wavelength and bandwidth-allocation algorithms (DWBAs) for wave-division multiplexed PON are presented; they exploit both interchannel and intrachannel statistical multiplexing in order to achieve better performance, especially when the load on various channels is not symmetric. Three variants of the DWBA are presented, and their performance is compared. While the first variant incurs larger idle times (and, hence, poor performance), the other two algorithms achieve better but different performance with critical dissimilarities. Our analysis also focuses on the fair assignment of excessive bandwidth in the upstream direction to highly loaded optical network units. We compare the performance of DWBA to another algorithm that relies on static-channel allocation. Furthermore, a study is presented wherein the number of wavelengths increases, and a comparison with interleaved polling with adaptive cycle time is shown. We use extensive simulations throughout this paper.

An important problem that arises in the design of cellular radio networks is the channel assignment problem that addresses the key issue of the scheduling of the transmissions of all stations in the network while avoiding interference. The problem consists of identifying a frame of minimum length that avoids interference while satisfying channel demands of the stations and maximizing channel utilization. The problem is known to be NP-hard and is formulated as a nonlinear integer program in prior research. This paper develops, for the first time, an integer programming formulation for the problem and presents a Probabilistic Greedy Algorithm that avoids the basic shortcoming of the classical greedy approach which is getting trapped in local optima. The algorithm incorporates simultaneously two diversification techniques, namely randomization and perturbation. Computational experiments are conducted on benchmark data sets and randomly generated problem instances with up to 500 stations. The results show the proposed algorithm is very effective in generating good solutions in short computing time. While a general-purpose branch-and-bound algorithm fails to find feasible solutions even for small instances, the proposed algorithm produces solutions that are far better than those obtained using a classical greedy approach in acceptable time.

Cognitive radios (CRs) have a great potential to improve spectrum utilization by enabling users to access the spectrum dynamically without disturbing licensed primary radios (PRs). A key challenge in operating these radios as a network is how to implement an efficient medium access control (MAC) mechanism that can adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most existing works address this issue via suboptimal heuristic approaches or centralized solutions. In this paper, we propose a novel joint power/channel allocation scheme that improves the performance through a distributed pricing approach. In this scheme, the spectrum allocation problem is modeled as a noncooperative game, with each CR pair acting as a player. A price-based iterative water-filling (PIWF) algorithm is proposed, which enables CR users to reach a good Nash equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved through pricing. Depending on the different orders according to which CRs take actions, we study sequential and parallel versions of the PIWF algorithm. We show that the parallel version converges faster than the sequential version. We then propose a corresponding MAC protocol to implement our resource management schemes. The proposed MAC allows multiple CR pairs to be first involved in an admission phase, then iteratively negotiate their transmission powers and spectrum via control-packet exchanges. Following the negotiation phase, CRs proceed concurrently with their data transmissions. Simulations are used to study the performance of our protocol and demonstrate its effectiveness in terms of improving the overall network throughput and reducing the average power consumption.

General Packet Radio Service (GPRS) -a bearer service to GSM -has been deployed worldwide, and is widely considered a technology precursor to the evolving third generation (3G) wireless networks. The general conception has been that while users will be exposed to faster wide-area wireless data access, experience gained from GPRS could well prove useful for 3G, and also for systems beyond 3G deployment. In this paper, we present a comprehensive simulation study for different traffic scheduling algorithms for Quality of Service in General Packet Radio Service (GPRS) at the IP level. We first study the correlation between GSM and GPRS users, and show how a dynamic channel allocation scheme between GSM-GPRS can give substantially better performance than the static ones. We then extend our study by taking into account users' requirements for different QoS profiles, based on seven different scheduling algorithms in GPRS. By simulating traffic related to an ATIS (Advanced Travelers Information System) at the IP level, we show how traffic scheduling algorithms perform by taking into account different performance parameters such as the average traffic, average waiting time in the scheduler, packet loss probabilities in the scheduler based on static and dynamic channel allocation schemes, packet priorities as well as average throughput per-GPRS user. The study gives a comparative analysis for various scheduling algorithms OE network designers can benefit from this study, and by extending this to several other scenarios.

AbstTact-A coherent receiver with a decision-feedback equalizer (DFE) operating on a Rayleigh fading channel under a suitable adaptive algorithm is considered. In the analysis of a DFE, a common assumption is that the receiver has perfect knowledge of the channel impulse response. However, this is not the case in practice, and for a rapidly fading channel, errors in channel tracking can become significant. We analyze theoretically the impact of these errors on the performance of a multichannel DFE. T h e expressions obtained for the achievable average MPSK bit error probabilities depend on the estimation error covariance. In order to specify this matrix, we focus on a special case when a Kalman filter is used as an optimal channel estimator. In this case, the probability of bit error can b e assessed directly in terms of channel fading model parameters, the most interesting of which is the fading rate. Our results show the penalty imposed by imperfect channel estimation, as well as the fading-induced irreducible error rates.

Context-awareness is a vital requirement of heterogeneous devices which allows them to predict future network conditions with sufficient accuracy. In this paper we present a proactive modelling-based approach for policy management which allows the mobile node to calculate Time Before Vertical Handover for open and closed environments. The paper explains how the knowledge of this component can improve the manner in which multi-class traffic streams are allocated to available network channels. Simulation results confirm the feasibility of the concept.

Channelization in multi-standard Software-Defined Radio base stations presents a significant challenge. In this paper, two different channelization structures designed for a multi-standard SDR base station are studied. As a basis for comparing their computational efficiency and reconfigurability, both are applied to a specific case study of a TETRA and TEDS standards base station. Uniform narrow band spectrum division followed by channel recombination demonstrates greater flexibility than a non-uniform parallel spectrum division alternative. However, computational advantages between both structures depend on the channel allocation patterns considered.

In this work, we have proposed two algorithms for the Fixed and the Dynamic Channel Allocation Schemes in GPRS. We started with a simple channel allocation problem in GPRS and showed that it is closely related to the One dimensional Standard Bin Packing Problem. We used two online bin packing algorithms, namely tne First Fit (FF) and the Best Fit (BF) Algorithms, for channel allocation and obtained their performance for Single slot %operation, Multislot operation and also for a realistic case wiih Multislot Class 21 MS. We have also analysed the Fixed Channel Allocation, Single slot operation case and analytical' results are found to compare favourably with the results from simulations.

The transmission opportunity (TXOP) mechanism defined in the IEEE 802.11e Hybrid Coordination Function (HCF) is not optimized to meet the QoS requirements of heterogeneous applications, since it is usually allocated by default according to the different Access Categories (AC).

The WiMAX (IEEE 802.16) technology offers a mechanism to create a multi-hop mesh network and provides a low cost alternative to the cabled access networks. This paper proposes a fuzzy rule based channel allocation technique for efficient spectrum management in multi-channel IEEE 802.16 network (WiMAX). The Subscriber Stations are categorized on the basis of their average traffic pattern. The frequency use by the network is optimized through re-allocation of sub-carrier frequency without degrading the QoS. Simulation using Matlab have been used to demonstrate the effectiveness of the proposed method in terms of Channel Utilization Ratio and Channel Acquisition Delay.

Hierarchical Genetic Algorithms (HGA) as a tool for search and optimizing methodology have now reached a mature stage. The minimum resource facility to carry user traffic, termed a channel unit (CU), is composed of a one time-slot and one code in the TD-CDMA/TDD system. The control of the number of CUs depends on the traffic load solves varied and asymmetrical traffic problems in the 3G system. In a cellular network, the call arrival rate, call duration and the communication overhead between the base stations and the control center are vague and uncertain, regardless of whether the criteria of concern are nonlinear, constrained, discrete or NP hard. In this paper, the HGA is used to tackle the neural network (NN) topology as well as the fuzzy logic controller for the dynamic CU allocation scheme in wireless cellular networks. Therefore, we propose a new efficient HGA CUs Allocation (HGACA) in cellular networks. It aims to efficiently satisfy the diverse quality-of-service (QoS) requirements of multimedia traffic. The results show our algorithm has a lower blocking rate, lower dropping rate, less update overhead, and shorter channel-acquisition delay than previous methods.

Özetçe Bu makalede öncelikle çizge kuramÕ hakkÕnda ön bir bilgi vermekteyiz. Çizge kuramÕnÕn çeúitli uygulamalarÕnÕ incelemekteyiz ve sonrasÕnda OSI (AçÕk Sistemler Araba÷laúÕmÕ)' nin 7 katmanÕna dayanarak bunlarÕ sÕnÕflandÕrmaktayÕz. UygulamalarÕn ço÷u renklendirme problemi ve MAC katmanÕ uygulamasÕ olan düzgün kanal tayini yapmak ile ilgilidir. Di÷er uygulamalar ise veri yönlendirme, topoloji kontrolü, giriúim azaltma, algÕlama iúlev atama, kafes ve durum diyagramlarÕ olarak özetlenebilir.

Dynamic routing of point-to-point connections in a waveband selective linear lightwave network is addressed. Linear lightwave networks are all optical networks in which only linear operations are performed on signals in a waveband selective manner. Special constraints arise because of the linearity in the linear lightwave network. The overall problem of finding a path satisfying all the routing constraints for point-to-point connections is shown to be very complex. Owing to the complexity, the overall routing problem is decomposed into several subproblems. In particular, given a request for a point-to-point connection a waveband is first chosen for the call. Two heuristics, MAXBAND which allocates the most used band to a call and another MINBAND (least used band) are studied. Then, the problem of routing in a given waveband is further divided into smaller subproblems of finding a path in the waveband, checking for feasibility of the path in the chosen waveband and channel allocation (within the waveband). For finding paths in a waveband, K-SP, BLOW-UP and MIN-INT algorithms are proposed. A recursive algorithm checks for feasibility of the path on the waveband. Two channel allocation schemes (within a single waveband) MIN and MAX are presented. Simulations show that using MAXBAND (waveband), MIN-INT (path on waveband) and MIN (channel within waveband) policies resulted in the best performance (least blocking)