Different queuing policies for handover requests in low Earth orbitmobile satellite systems

In this paper, a mobility model suitable for low Earth orbit mobile satellite systems (LEO-MSS's) has been presented, and its statistical parameters have been derived in order to evaluate the impact of the mobility on the performance of the fixed channel allocation (FCA) strategy. Moreover, we have foreseen that interbeam handover requests, which do not immediately find service, can be queued to reduce the handover failure rate. Two different queuing disciplines have been assumed: (1) the first-input-first-output (FIFO) scheme and (2) an idealized strategy that requires knowledge of the last useful instant (LUI) within which the handover procedure must be completed in order to rank the queued handover requests. An analytical approach has been developed to compare these queuing techniques, and its results have been validated through simulations     

On the performance analysis of dynamic channel allocation with FIFO handover queuing in LEO-MSS

The exact analysis of dynamic channel allocation (DCA) with first-in/first-out (FIFO) queuing of handover (QH) requests is highly complex, due to the dynamic nature of channel allocation to different cells. This letter presents an approximate but accurate analytical method to evaluate the performance of DCA in conjunction with FIFO-QH in low earth orbit mobile satellite systems. The accuracy of the proposed analysis has been verified by means of computer simulation.     

Efficient dynamic channel allocation techniques with handoverqueuing for mobile satellite networks

Efficient dynamic channel allocation techniques with handover queuing suitable for applications in mobile satellite cellular networks, are discussed. The channel assignment on demand is performed on the basis of the evaluation of a suitable cost function. Geostationary and low Earth orbit (LEO) satellites have been considered. In order to highlight the better performance of the dynamic techniques proposed, a performance comparison with a classical fixed channel allocation (FCA) has been carried out, as regards the probability that a newly arriving call is not completely served. It has also been shown that a higher traffic density, with respect to GEO systems, is manageable by means of LEO satellites     

Handover and dynamic channel allocation techniques in mobilecellular networks

This paper deals with an efficient dynamic channel allocation (DCA) technique applicable to terrestrial mobile cellular networks. A channel (or resource) is a fixed frequency bandwidth (FDMA), a specific time-slot within a frame (TDMA), or a particular code (CDMA), depending on the multiple access technique used. A cost function has been defined by which the optimum channel to be assigned on demand can be selected. In addition, a suitable mobility model has been derived to determine the effects of handovers on network performance. The performance of the proposed DCA technique has been derived by computer simulations in terms of call blocking and handover failure probabilities. Comparisons with the classical fixed channel allocation (FCA) technique and other dynamic allocation algorithms recently proposed in the literature have been carried out to validate the proposed technique     

Handover prioritizing scheme for reducing call failure probability in cellular wireless network

This paper proposes a scheme suitable for managing handover in wireless cellular network. The main objective of the proposed scheme is to reduce the probability of forced termination of ongoing call due to handover failure. The scheme employs a queuing discipline, and the priority of queued is based on the residual time of the mobile user in the overlap region between two adjacent cells, assuming that the user's location and speed can be determined, then we applied the ascending priority; it means that the users having a shorter residual time join the head of the queue (i.e., high priority) while those having longer residual time at the end of the queue (i.e., low priority). Fixed channel allocation strategy (FCA) is employed and simulation results obtained concern: call blocking probability (CBP), handover failure probability, and average waiting time in the queue. Also simulation results are compared to those obtained by: non‐prioritized scheme (FCA), and FCA queuing with FIFO discipline. Results show that our proposed method decreases significantly handover failure probability compared with other two schemes. Copyright © 2009 John Wiley & Sons, Ltd.     

Satellite-UMTS traffic dimensioning and resource managementtechnique analysis

The universal mobile telecommunications system (UMTS) will consist of space UMTS (S-UMTS) and terrestrial UMTS (T-UMTS) components. An algorithm for predicting the traffic capacity in terms of the number of subscribers for the satellite component of UMTS is presented. The algorithm takes into account the takeup characteristics of new products, the growth of gross domestic product (GDP), the projection of population, the tariff of the service, and price fall over the forecast period. The predicted traffic is used to generate a traffic grid in terms of Erlang of dimension 36×72 in steps of 5° in both the latitude and longitude directions. The traffic grid is used to evaluate the performance of a dynamic channel allocation (DCA) technique as, well as a fixed channel allocation (FCA) technique. Both channel allocation techniques have been considered with the queuing of handover (QH) requests. In order to compare the respective techniques' performance, a low-earth orbit mobile satellite system (LEO-MSS) mobility model is developed to take into account the effect of satellites' motion during interbeam handovers. A theoretical model for obtaining the values of blocking probabilities for low-traffic loads is presented. Finally, the performance of the DCA-QH technique is compared with the FCA-QH technique under suitably defined traffic and mobility conditions     

A dynamic channel allocation technique based on Hopfield neuralnetworks

The interest in global spectrum allocation techniques is growing with the always increasing spectrum demand for (cellular) mobile communications. However, the best algorithms suffer from high computational times that reduce the possibility of a practical implementation. This paper deals with a dynamic channel allocation (DCA) technique based on an energy function whose minimization gives the optimal allocation. Due to the particular formulation of such an energy function, the minimization can be performed by a Hopfield neural network for which a fast hardware implementation has been recently proposed in the literature. The performance of the proposed DCA technique is derived by computer simulations. Comparisons with a classical fixed allocation technique (FCA) and a different DCA technique are shown to highlight the better performance of the proposed DCA technique     

Performance Evaluation of a Virtual Queuing – Channel Allocation Scheme for Microcellular Networks

This paper deals with the performance evaluation of a novel distributed channel allocation scheme that attains a high resource reuse in cellular networks. A suitable interference model has been envisaged. Resources are nominally assigned to cells with Fixed Channel Allocation (FCA), according to a given reuse distance. Whenever a channel demand from a mobile user does not find a free nominal resource in a cell, a channel is temporarily borrowed violating the reuse distance constraint, provided that the co-channel interference level is acceptable. As soon as a nominal channel becomes available in this cell, the borrowed resource is released (virtual queuing). The performance of the proposed channel allocation scheme has been evaluated considering both uniform and non-uniform traffic patterns. A performance analysis approach has been also developed and validated by simulations. Comparisons with the classical FCA scheme and other dynamic and borrowing channel allocation strategies have permitted to highlight the good performance of the proposed technique.     

Supporting Asymmetric Traffic in a TDD/CDMA Cellular Network via Interference-Aware Dynamic Channel Allocation and Space–Time LMMSE Joint Detection

In a time-division duplexing (TDD)/code-division multiple-access (CDMA) cellular network with asymmetric data traffic, dynamic channel allocation (DCA) enhances resource utilization compared with fixed channel allocation (FCA). However, it also induces base-to-base and mobile-to-mobile crossed-slot intercell interference, which can severely degrade system performance. To deal with this problem, a decentralized scheme is proposed, which combines an interference-aware DCA algorithm with space–time linear minimum-mean-square-error (LMMSE) joint detection at the base and mobile stations. The former assigns active links to timeslots in a way that crossed-slot interference is mitigated, while the latter suppresses the remaining intercell interference (along with intersymbol and intracell interference), exploiting its spatio-temporal autocorrelation statistics. The performance of this scheme is evaluated in terms of downlink and uplink signal-to-interference-plus-noise ratio (SINR) outage and average throughput via analytical approximations and Monte Carlo simulations, and it is compared with that of benchmark random DCA (RDCA) and FCA schemes. The cases of single- and dual-antenna reception with perfect and imperfect channel state information are examined. It is shown that the proposed scheme achieves higher average throughput than FCA (particularly for dual-antenna reception) as well as RDCA (for heavy traffic loads). These throughput gains are more significant in uplink than in downlink.      

A New Connection Admission Control for Spotbeam Handover in LEO Satellite Networks

Frequent spotbeam handovers in low earth orbit (LEO) satellite networks require a technique to decrease the handover blocking probabilities. A large variety of schemes have been proposed to achieve this goal in terrestrial mobile cellular networks. Most of them focus on the notion of prioritized channel allocation algorithms. However, these schemes cannot provide the connection-level quality of service (QoS) guarantees. Due to the scarcity of resources in LEO satellite networks, a connection admission control (CAC) technique becomes important to achieve this connection-level QoS for the spotbeam handovers. In this paper, a geographical connection admission control (GCAC) algorithm is introduced, which estimates the future handover blocking performance of a new call attempt based on the user location database, in order to decrease the handover blocking. Also, for its channel allocation scheme, an adaptive dynamic channel allocation (ADCA) scheme is introduced. By simulation, it is shown that the proposed GCAC with ADCA scheme guarantees the handover blocking probability to a predefined target level of QoS. Since GCAC algorithm utilizes the user location information, performance evaluation indicates that the quality of service (QoS) is also guaranteed in the non-uniform traffic pattern.     

The geometric dynamic channel allocation as a practical strategy inmobile networks with bursty user mobility

We refer to a specific class of dynamic channel allocation (DCA) strategies, namely the interference-free, timid, not-conditioned class. The main concern of this work is to verify if and to what extent strategies belonging to this class can offer better performance than fixed channel allocation (FCA). The interest in this kind of strategies is motivated by their feasibility with current TDM technologies, the limited amount of information required to carry out channel assignments and their intrinsic stability. In this framework we present a simple, but very attractive DCA strategy, the so-called geometric DCA (GDCA). A performance evaluation is carried out to compare some representative DCA strategies of the considered class, by using a user mobility model that accounts for the large fluctuations of the number of users in a cell coverage area expected in a microcellular environment. The effect of the non-null propagation time required by the information exchange in the DCA strategies is also taken into account. It emerges that the proposed GDCA allows better performance than more sophisticated strategies already proposed, at the expense of a frequency planning carried out only at network configuration. This is due to the ability of GDCA to exploit the a priori information to maintain a tight geometric packing of used carriers. The reported results also show that DCA strategies in the considered class cope with large and sudden traffic fluctuations remarkably better than the FCA scheme does and that the advantage becomes more evident as the burstiness of the user mobility process (hence of the offered traffic) increases     

Dynamic channel allocation in interference-limited cellular systemswith uneven traffic distribution

Most recently proposed wireless dynamic channel allocation methods have used carrier-to-interference (C/I) information to increase the system performance. Power control is viewed as essential for interference-limited systems. However, the performance of such systems under an imbalance of load among cells, as may occur often in microcells, is largely unknown. Here, we study a typical interference-limited dynamic channel allocation policy. Calls are accepted if a channel can be assigned that will provide a minimum C/I, and power control and intracell handoffs are used to maintain this level. We focus on the relationship between system performance and the amount of imbalance in load among neighboring cells. Previous studies for systems that do not use C/I information have found that dynamic channel allocation (DCA) outperforms fixed channel allocation (FCA) in all but heavily loaded systems with little load imbalance. We present two principal new results. First, we find that with use of C/I information, the difference in performance between FCA and DCA (in terms of throughput or blocking probability) is increasing with load imbalance. DCA was found to be more effective in congestion control at the cost of a slightly lower call quality. Second, we find that use of power control to maintain a minimum C/I results in two equilibrium average power levels for both DCA and FCA, with DCA using a higher average power than FCA, and that while DCA's power is increasing with load imbalance, FCA's average power is decreasing with load imbalance     

Performance analysis of A dynamic channel allocation technique for satellite mobile cellular networks

This paper deals with an efficient dynamic channel allocation (DCA) technique suitable for applications in mobile satellite cellular networks. A cost function is defined to allow an optimum selection of channels to be allocated on demand. A mobility model suitable for low earth orbit (LEO) satellite systems is presented. The performance of the novel DCA technique in terms of call blocking probability has been derived by simulations. The obtained results are compared with those achieved by a fixed channel allocation (FCA) technique to show a better behaviour.     

Performance of a cellular network based on frequency hopping with dynamic channel allocation and power control

A frequency- and time-division multiple-access (F-TDMA)-based mobile radio system using both dynamic channel allocation (DCA) and frequency hopping (FH) is investigated. We propose a new interference adaptive DCA (IA-DCA) algorithm that is suitably designed for a network implementing FH. The role played by the power control algorithm in this DCA-FH context is also investigated. We compare the performance of our proposal to that of fixed channel allocation (FCA) with and without FH and the well-known IA-DCA schemes investigated in the literature in the absence of FH. The performance results show that interesting synergic effects can be obtained in terms of forced termination and user satisfaction probability by using both DCA and FH. The results we show in the paper have been achieved by means of a system-level simulation tool which takes propagation, user mobility, interference, traffic, and channel allocation into account. The advantages of using FH are accounted for by using a suitable analytical model that gives the frame error rate as a function of the carrier-to-interference ratio and the number of hopping frequencies, at link level; this model is taken from the literature where it was presented for FCA, and here it is modified in order to be applicable to the DCA case.     

一种基于GSM／GPRS的动态信道分配策略

针对GSM／GPRS网络中某些小区因频繁切换导致掉话率高的问题,提出了一种新的动态信道分配策略。该方案将信道划分为数据业务专用信道和语音／数据业务共享信道,并在共享信道中为切换型语音呼叫预留保护信道以降低其呼叫失败率。对于数据业务采用FIFO排队机制。最后利用一种近似计算方法求取该策略的呼叫阻塞率等指标。实验结果表明该方案能有效降低语音呼叫掉话率。     

Performance Evaluation and Resource Management of Hierarchical MACRO-/MICRO Cellular Networks using MOSEL-2

The paper presents a performance evaluation and resource management of hierarchical MACRO-/MICRO cellular networks using the new Modeling and Evaluation Language (MOSEL-2). MOSEL-2 with new constructs has the ability to find the performance and reliability modeling and evaluation of systems with exponential and non-exponential distributions. A MACRO/MICRO cell structure is solved numerically and mathematically in this paper to handle the handoff calls. Additionally, a simulation program is written to validate these results. In order to reduce the loss probability, a guard channels are introduced at the MICRO cell and channel reservation at the MACRO cell. Additionally, the concept of queuing is introduced where there is a possibility for the handoff calls from both MACRO and MICRO layers to be queued when all the resources are occupied. MOSEL-2 is used to find the numerical solution for this problem with both exponential and general exponential (GE) distribution. The performance analysis show the efficiency of the proposed scheme to manage the handoff calls and the ability of the suggested scheme to reduce the blocking probability of handover calls and the loss probability as the main objective is to block the new connection rather than terminating the ongoing connection as well as balancing the load all over the whole network. It is shown in this paper that there are a set of important factors that affect the performance, such as: reservation policy, channel allocation, handover ratio, capacity of the queue and the variation of the inter-arrival times. These factors are discussed via some important performance measures, such as: new call blocking probability, blocking probability of handover calls, loss probability, utilization and the average delay of the queue.     

Dynamic channel allocation techniques using adaptive modulation andadaptive antennas

This article studies the impact of adaptive quadrature amplitude modulation (AQAM) on network performance when applied to a cellular network, using adaptive antennas in conjunction with both fixed channel allocation (FCA) and locally distributed dynamic channel allocation (DCA) schemes. The performance advantages of using adaptive modulation are investigated in terms of the overall network performance, mean transmitted power, and the average network throughput. Adaptive modulation allowed an extra 51% of users to be supported by an FCA 4-QAM network, while in conjunction with DCA, an additional 54% user capacity was attained     

Performance analysis of multihop cellular network with fixed channel assignment

Multihop cellular network (MCN) has been proposed to incorporate the flexibility of ad hoc networks into traditional single-hop cellular networks (SCNs). The performance analysis of MCN through analytical models is not trivial because the classic Erlang B formula no longer applies to MCN where multihop transmission is allowed. In this paper, we first propose a clustered MCN (cMCN) architecture with the use of dedicated information ports (DIPs), which are deployed wireless ports functioning as central controllers for multihop users. The proposed cMCN can be considered as a complement of the existing cellular network. Then, we study the feasibility of modeling time division multiple access (TDMA)-based cMCN with fixed channel assignment (FCA) scheme for uplink transmission. An exact multi-dimensional Markov chain model to analyze the performance of cMCN with FCA is developed. Furthermore, an approximated model which results in reduced complexity is also presented. The analytical results from both models are matched with the simulation results closely. The results show that cMCN with the proposed FCA scheme can reduce the call blocking probability significantly as compared to SCNs with either the conventional FCA or a dynamic channel assignment (DCA) scheme.     

Application of dynamic channel allocation strategies to the GSMcellular network

We refer to the implementation and the performance of a specific class of dynamic carrier allocation (DCA) strategies which is suitable for being introduced in the pan-European Global System for Mobile communications (GSM) cellular network. One of the main concerns of this work is to verify if and to what extent strategies belonging to this class can offer better performance than fixed channel allocation (FCA) in realistic traffic and propagation conditions. The impact of the introduction in a real network of two of the more promising DCA strategies in the considered class is assessed. In particular, solutions are presented concerning the signaling exchanges entailed by the implementation of each of the considered DCA strategies. A performance evaluation of a realistic cellular network exploiting the above-mentioned DCA strategies is carried out, taking into account all of the main GSM transmission and network aspects. The simulations have been performed by considering a realistic cell layout corresponding to the urban area of Rome, its realistic propagation environment, and a user mobility model based on the building percentages in such an area. The results of the performance evaluation show that, by carefully choosing the values of the parameters characterizing each of the considered DCA strategies, a conspicuous increase in the number of users supported by the cellular network can be achieved     

Handoff ordering using signal prediction priority queuing inpersonal communication systems

Handoffs in a mobile cellular communications environment will become an increasingly important issue as cell sizes shrink to accommodate an increasingly large demand for services. A new handoff ordering method is proposed which can be used to provide rapid handovers with a smaller percentage of dropped calls than other methods. Signal prediction priority queuing (SPPQ) is a generic queuing method which can be adapted to almost any handover technique for the benefit of decreased dropped calls. In typical personal communication systems (PCSs) environment, it is shown that for realistic call-blocking probabilities (2%-6%), SPPQ leads to about 15% fewer dropped calls compared to first-in-first-out (FIFO) queuing. This benefit comes at the expense of a slight increase (<1%) in blocked call percentage. The proposed SPPQ scheme is also compared to a previously developed method called measurement-based priority scheme (MBPS), and, based on worst case scenarios, it is shown to outperform MBPS as well