An efficient way to bound the size of clusters in large-scale self-organizing wireless networks is to rely on a budget-based strategy. The side effect of conventional budget- based clustering approaches is that they generate a potentially large number of small, even single-node, clusters. The consequence is that while clusters are bounded, their average size may be far from the expected value (the budget), which negatively impacts the performance of the communication systems running on top of it. In contrast, we propose Fair and Flexible Budget- Based Clustering (FFBC) to form size-controlled clusters in large-scale self-organizing networks. For a given target cluster size, our approach outperforms previous budget-based algorithms by creating clusters of average size closer to the requested value and avoiding isolated nodes.

The IEEE 802.15.4 standard defines a set of procedures to set-up a Low-Rate Wireless Personal Area Network where nodes self-organize into a logical communication structure through which data can be routed, hop by hop, from sources to destinations. The network formation of the IEEE 802.15.4 does not impose constraints on the topology. The ZigBee Alliance uses the IEEE 802.15.4 layers to build a complete protocol stack for the implementation of wireless sensor networks. ZigBee specifies the network layer for star, tree and peer-to-peer topologies. Starting from these, more complex cluster-tree topologies can be formed. To control the network topology ZigBee fixes the maximum number of routers and end-devices that each router may have as children and also fixes the maximum depth of the tree. To better understand the importance of these constraints we simulate and analyze the IEEE 802.15.4 formation procedure in different network settings (single-sink and multi-sink scenarios). The goal is to provide guidelines for the practical implementation of ZigBee network formation with the aforementioned constraints.

This paper presents a performance study of two new proposed strategies for the reorganization of a cluster-tree and its address space: proactive and reactive algorithms. The goal of the proactive reconfiguration is to minimize the average number of hops between the possible source and destination pairs. It is achieved by attempting to reconnect nodes to a parent node with the highest possible level. The goal of the reactive reconfiguration is to reorganize the cluster on- demand when a node wishing to join the cluster cannot do it, because the possible parents exhausted their free address space. Our simulation results show that with an optimized reconfiguration a higher performance in terms of connection time and connectivity of the cluster-tree can be achieved.

In this paper we propose a handover method for multiservice non-geo satellite systems. The proposed algorithm can be used for satellite handover as well as for cell handover when a fixed amount of resources is allocated to each cell. Specifically, we consider the case in which the satellite system provides services to users of different QoS requirements. The first type of users require the minimization and, if possible, the elimination of the probability of forcing a connection in progress to termination during a handover. On the other hand, the users of the second category do not have any specific handover requirements. The new method is evaluated through extensive simulations and is proved to meet the requirements of the first type of users while at the same time maximizes the system utilization for both types of users.

No abstract available.

Wireless networks are expected to support real-time interactive multimedia traffic and must be able, therefore, to provide their users with quality-of-service (QoS) guarantees. Although the QoS provisioning problem arises in wireline networks as well, mobility of hosts and scarcity of bandwidth makes QoS provisioning a challenging task in wireless networks. It has been noticed that multimedia applications can tolerate and gracefully adapt to transient fluctuations in the QoS that they receive from the network. The additional flexibility afforded by the ability of multimedia applications to tolerate and adapt to transient changes in QoS can be exploited by protocol designers to significantly improve the overall performance of wireless systems. This paper presents a fair resource allocation protocol for multimedia wireless networks that uses a combination of bandwidth reservation and bandwidth borrowing to provide network users with QoS in terms of guaranteed bandwidth, call blocking, and call dropping probabilities. Our view of fairness was inspired by the well-known max-min fairness allocation protocol for wireline networks. Simulation results are presented that compare our protocol to similar schemes.

Abstract The paper describes a media access system for satellite network uplinks. The media access protocol is designed to support a range of low‐level protocols using a dual‐framing system, that is, there is a synchronous traffic subframe in which registered station requests are assigned fixed blocks or slots and an asynchronous traffic subframe for unregistered station random access on a contention basis. Slots for the registered stations are assigned through request to the satellite; the remaining frame time is assigned to unregistered stations. Capacity waste through contention resulting in collisions is minimized. The system uses dynamic bandwidth (bit rate) allocation for each channel, that is, the base frequency and bandwidth are changed for each channel at frame boundaries. The total bandwidth for the sum of all uplink channels is fixed. Channels that have low load based upon their request in a prior uplink frame are assigned lower bandwidth, while those with higher loading are provided larger bandwidth. By sharing bandwidth over channels at frame boundaries, overall network efficiency and fairness are significantly enhanced. Bandwidth allocation is decided in the satellite. It allocates sufficient bandwidth for all synchronous traffic and then commits the remaining bandwidth to asynchronous traffic. Here, the allocation for asynchronous traffic provides each channel with sufficient slots so that equal probability of success for stations sharing the channel can be expected. The combination of traffic assignment and bandwidth allocation provides significant improvement in overall network efficiency and fairness for all traffic types. The hardware implementation of media access for variable bandwidth sharing between channels use the concepts of Digital Software Radio. Copyright © 2003 John Wiley & Sons, Ltd.

Multimedia LEO satellite networks will play an important role in providing truly global coverage required by mobile personal communication services. Due to the high mobility inherent to LEO systems, a number of challenging technical problems arise. The first contribution of this work is to propose a realistic mobility model, taking into account the rotation of the Earth, which was systematically ignored in the literature. Our second contribution is a novel resource reservation strategy, termed sequential probabilistic resource reservation (SPR), specifically designed to minimize connection interruption due to handoffs. Finally, we propose a novel connection admission control (CAC) algorithm, differentiating real-time and non-real-time services. Performance results obtained by simulation show that the novel mobility model is essential for a realistic network performance evaluation and that the novel SPR strategy offers low handoff blocking probability for both service classes and low new call blocking probability for non-real-time connections.

Unlike terrestrial networks, LEO satellite networks are expected to provide a truly global coverage and to support sophisticated PCS services including multimedia communications. However, LEO satellite networks are known to have a serious mobility management problem. The main contribution of this work Is to propose a predictive handoff management and admission control strategy for multimedia LEO satellite networks. Simulation results have shown that our scheme offers very low call dropping probability for multimedia connections while, at the same time, keeping resource utilization high.

In the paper, we address low Earth orbit (LEO) satellite ATM networks with ATM on-board switching, focusing on an on-board ATM switch buffer architecture and onboard resource management while taking into account the handoff traffic. We introduce and examine four buffer architectures capable of handling both delay and loss sensitive traffic, where we propose to use an additional buffer space for the handoff traffic. A comparison of their performances in terms of delay, delay jitter and buffer space requirements is obtained by means of simulation.

Wireless networks are expected to support real-time interactive multimedia traffic and must be able, therefore, to provide their users with Quality-of-Service (QoS) guarantees. Although the QoS provisioning problem arises in wireline networks as well, mobility of hosts and scarcity of bandwidth makes QoS provisioning a challenging task in wireless networks. It has been noticed that multimedia applications can tolerate and gracefully adapt to transient fluctuations in the QoS that they receive from the network. The additional flexibility afforded by the ability of multimedia applications to tolerate and adapt to transient changes in QoS can be exploited by protocol designers to significantly improve the overall performance of wireless systems. This paper presents a fair resource allocation protocol for multimedia wireless networks that uses a combination of bandwidth reservation and bandwidth borrowing to provide network users with QoS in terms of guaranteed bandwidth, call blocking and call dropping probabilities. Our view of fairness was inspired by the well-known maxmin fairness allocation protocol for wireline networks. Simulation results are presented that compare our protocol to similar schemes.