In the last decade, the popularity of UAVs has increased tremendously. Nowadays, many researchers are interested in UAV swarms. Coordinating a swarm of UAVs is a complicated task and many problems should be addressed before wide-spread adoption. In this work, we focus on the take-off for large-scale UAV swarms, with an extra focus on the assignment phase. The assignment phase is the first take-off stage whereby we decide which UAV on the ground goes to which place in the air. A good assignment algorithm, is quick, and at the same time reduce the total distance travelled as much as possible. We assess the performance of three different assignment algorithms: a heuristic, the original Kuhn-Munkres algorithm (KMA), and the KMA adapted for GPU use. Each algorithm was tested while varying the number of UAVs, as well as the type of flight formation. During the experiments, we measured the calculation time, total distance travelled, and number of flight paths crossing. In terms of total distance travelled, the KMA always outperforms the heuristic. However, the KMA takes longer (orders of magnitude) to calculate the assignment. Realistically, the KMA algorithm can only be used as long as the swarm does not contain more than 500 UAVs. From that point the GPU version of the KMA is faster. We can conclude that, in most cases, it is recommendable to use the KMA for the assignment as it will reduce the distance travelled to a minimum and, consequently, also reduce the number of flight paths crossing.

Abstract Wireless communication technologies have now greatly impact our daily lives. From indoor wireless LANs to outdoor cellular mobile networks, wireless technologies have benefited billions of users around the globe. The era of vehicular ad hoc networks (VANETs) is now evolving, gaining attention and momentum. Researchers and developers have built VANET simulation software to allow the study and evaluation of various media access, routing, and emergency warning protocols. VANET simulation is fundamentally different from MANETs (mobile ad hoc networks) simulation because in VANETs, vehicular environment imposes new issues and requirements, such as constrained road topology, multi‐path fading and roadside obstacles, traffic flow models, trip models, varying vehicular speed and mobility, traffic lights, traffic congestion, drivers' behavior, etc. Currently, there are VANET mobility generators, network simulators, and VANET simulators. This paper presents a comprehensive study and comparisons of the various publicly available VANET simulation software and their components. In particular, we contrast their software characteristics, graphical user interface (GUI), popularity, ease of use, input requirements, output visualization capability, accuracy of simulation, etc. Finally, while each of the studied simulators provides a good simulation environment for VANETs, refinements and further contributions are needed before they can be widely used by the research community. Copyright © 2009 John Wiley & Sons, Ltd.

Deploying and testing vehicular ad hoc networks (VANETs) involves high cost and intensive labor. Hence simulation is a useful alternative prior to actual implementation. Most works found in the literature employ very simplistic radio propagation models (RPMs), ignoring the dramatic effects presented by buildings on radio signals. In this paper, we present three different RPMs that increase the level of realism, thereby allowing us to obtain more accurate and meaningful results. These models are: (a) the distance attenuation model (DAM), (b) the building model (BM), and (c) the building and distance attenuation model (BDAM). We evaluated these different models and compared them with the two-ray ground model implemented in ns-2. We then carried out further study to evaluate the impact of varying some important parameters such as vehicle density and building size on VANET warning message dissemination. Simulation results confirmed that our proposed BDAM significantly affects the percentage of blind vehicles present and the number of received warning messages, and that our models can better reflect realistic scenarios.

In MANETs, ACK loss can affect TCP communication performance, since end-to-end reliable delivery of data packets is guaranteed by using ACK packets sent from a TCP receiver. This ACK loss may force a TCP sender to produce unnecessary retransmissions (called spurious retransmissions). These spurious retransmissions can also degrade the performance of TCP flows in the network because they will create more channel contention and interferences. These issues have been overlooked and hence require attention. We, therefore, propose new solutions to reduce such spurious retransmissions. Our scheme allows a TCP sender to be correctly informed of the sequence number that the TCP receiver expects to receive (i.e., ACK sequence). This ACK sequence is piggybacked onto routing control packets during a new route discovery process invoked by the TCP receiver. Using the ACK sequence tossed by the routing layer, the TCP sender can reduce spurious retransmissions. We evaluated and compared our scheme with TCP-Reno via simulation on ns-2. Simulation results showed that our proposed solutions outperformed general TCP (for both static and dynamic networks cases under multiple cross TCP traffic) in terms of aggregate throughput and number of spurious retransmissions.

The three articles in this special section are devoted to on-the-road mobile network communication services, including: design and evaluation techniques; push-to-talk services; and local density estimation and transmission-range assignment.

Abstract A great deal of research has been directed toward reducing energy consumption at the 802.11‐based MAC layer for mobile ad hoc networks (MANETs). There exists an approach that uses maximum power during the RTS‐CTS exchange and computes the required amount of power in order for DATA and ACK messages to reach the receiver and sender. It, however, does not consider the existence of an interference range (IR), or often called a carrier sensing zone. In order to address the problem, an existing approach forces nodes, located within a sender's carrier sensing zone, to defer their transmission trials in order to avoid collisions at the sender. It, however, does not consider possible collisions at the receiver, which can result in frequent retransmissions and hence greater energy consumption. Therefore, we propose an efficient protocol called Fragmentation‐based Power Control MAC (F‐PCM), which utilizes the fragmentation mechanism of the IEEE 802.11 MAC protocol so as to avoid collisions at senders as well as those at receivers. Through extensive simulations, our F‐PCM has performed better in terms of providing a higher throughput and incurring lower energy consumption. This is particularly advantageous in a dense mobile network environment where collisions are more severe. Copyright © 2006 John Wiley & Sons, Ltd.

Clustering is an effective topology maintenance technology to provide better scalability for WSN. When loop structures are deployed to clustering, it can provide better robustness and convenient routing, because the topology information can be disseminated within a loop instead of a single clusterhead and the nature of the loop that there are two paths between each pair of nodes within a loop provides backup routes. In this paper, we propose a loop-based approach to combine clustering and routing for cost saving, which consists of setup procedure, regular procedure and recovery procedure. For the setup procedure, we propose a loop discovery algorithm, which is a fully distributed, on-demand and configurable algorithm achieving route discovery and clustering at the same time. The algorithm prefers a low-mobility network which is typically suitable for wireless sensor networks.

We present an experimental context-aware application that provides context depended information to the visitors of a museum. The application combines the productivity of the Java platform with the universal connectivity of Bluetooth wireless technology. We present our first experiences using BIuetooth and Java technology in ubiquitous . We describe the overall architecture and detail the implementation steps taken to create our BIuetooth and Java based context-aware application. Finally we run some initial experiments in a small test-bed to evaluate the proposal performance and behaviour.

Mobile Ad Hoc Networks (MANET) consists of mobile nodes interconnected by multihop communication paths can experience higher packets loss rate and lower bandwidth compare with wired network because of node mobility and characteristic of wireless channel. Multicast could prove to be an efficient way of providing necessary services for many kinds of applications. In this paper, we consider the performances of different scheduling algorithms in MANET which have both multicast and unicast applications. Here we discuss four scheduling models; that are one-queue model, priority-queue model, dynamic priority-queue model and adaptive queue-model. In these algorithms, we compare the difference between multicast and unicast application performance. In addition we analyze the impact of quality of service (QoS) parameters on hop-by-hop and end-to-end performance. These show that the scheduling algorithms, which we analyzed, have much better hop-by-hop and end-to-end traffic performance than simple scheduling.

To join an IP network and communicate with others, a node needs to be configured either manually by an administrator or automatically through a DHCP server. However, the former method is impractical for large networks, while the latter is infeasible in the case of a mobile ad hoc network due to the mobility of the nodes. This paper introduces two distributed IP address auto-configuration mechanisms for mobile ad hoc networks, namely (a) RADA (random address allocation) and (b) LiA (linear allocation). RADA is based on random IP address selection, while LiA linearly assigns new addresses by utilizing the current maximum IP address value. We have also introduced an improved version of LiA, known as LiACR (linear allocation with collision resolution), which reduces control overhead. Then, we discuss extensions of these mechanisms capable of handling network partitioning and merging. Performance evaluations of RADA, LiA and LiACR were conducted through simulation. The results related to address allocation time and control overhead are presented and compared.

As interests in MANET (mobile ad hoc networks) have increased, routing protocols suitable for MANET have been standardized specially in IETF (Internet Engineering Task Force). In addition to routing protocols, efforts to adopt the TCP stack as a reliable end-to-end transport protocol with some modifications appropriate for MANETs have been made for the smooth integration with the fixed Internet. Unlike previous approaches to improve TCP performance in MANETs, we modified the fast retransmission technique on the standard TCP. Basically, the fast retransmission technique utilizes the third duplicate ACK to trigger retransmission. However, if TCP is served by on-demand reactive ad-hoc routing protocols like DSR (dynamic source routing), AODV (ad hoc on-demand distance vector) and ABR (associativity-based routing) which can be considered as kinds of connection-oriented routing protocols until a route breakage occurs after a route acquisition, we can improve TCP performance by advancing the retransmission time using the first duplicate ACK triggered retransmission technique, without waiting for the third duplicate ACK packet. We show the performance improvement with this approach by using GIoMoSim simulator with AODV used as its underlying routing protocol, one of standardized on-demand reactive routing protocols in IETF.

Current efforts on ad hoc wireless network research are focused more on routing and multicasting protocols. However, there is an increasing need to understand what sort of media could be transported over wireless ad hoc networks other than data. Existing research on multimedia wireless communications often addresses broadband wireless networks with a connection-oriented backbone. In this paper, we address the possibility of transporting audio traffic over wireless ad hoc networks. We examine the impact of wireless multi-hop links on audio data relay and how the audio quality at the receiver is affected. In particular, we examine communication parameters such as latency, jitter, packet loss, and their impact on perceived audio quality.

Many protocols used in mobile ad hoc networks rely on the broadcasting capability, especially when performing a route discovery process. However, an efficient broadcasting protocol should be devised to reduce the unnecessary redundant rebroadcasting at some nodes (redundancy) as well as to increase the coverage area as much as possible (reachability). A few approaches have been developed in the literature. We propose a bounding algorithm, which is known to be an efficient candidate to accommodate the two goals, that is to increase reachability while limiting redundancy.

This paper proposes an integrated solution to handoffs in wireless ATM networks. The proposed method has the following features: 1) combining soft handoff and hard handoff into one, 2) solving the crossed path problem due to both ends of a connection making handoffs at the same time, 3) minimizing overheads due to move back, and 4) minimizing QoS adaptation by load balancing. Previous studies cover at most one aspect of the proposed protocol. The crossed path problem arises when the crossover switch found by one end does not lie on the new path determined by the other end of the same connection. The proposed protocol minimizes handoff delay and cell delay. Simulation results show excellent scalability, adaptability, stability, and flexibility of the protocol. Performance analysis of the protocol is also provided.

This paper proposes a solution to the problem of crossed path, which may occur when both ends of the connection are mobile hosts (MHs) for wireless ATM networks. Previous studies cover the case when only one MH makes a handoff. To minimize circuit setup cost, most of these studies propose the crossover switch (CX) solution so that parts of the original path can be retained in the new path. This study deals with the case when both MHs make handoffs. In such a case, CX found by one end may not lie on the new path determined by the other end, and a crossed path situation occurs. This paper proposes a protocol to resolve the crossed path problem so that a new path can satisfy the QoS requirement of the virtual connection (VC) when a QoS guaranteed path exists. In addition, this paper solves the "moveback" problem that also exists in a single handoff. The proposed protocol has the best performance with CDMA because of its soft handoff feature. Simulation results reveal the scalability, flexibility and robustness of the protocol. Performance analysis of the protocol is also provided.

Ad-hoc networks are infrastructureless networks formed on-the-fly by devices with wireless communication capabilities. They have bandwidth and device power limitations, as well as the need to deal with mobility. If client server interactions are to be present in such networks, a method for performing service location is needed. When two nodes that are several hops apart communicate, resources on all the intermediate nodes are wasted, so it is better to find services that are "closer" to the clients. This paper evaluates distributed and centralized architectures for service location. In particular it examines service availability and message overhead performance using simulations. The findings reveal the best approach that can be used as an underlying structure for higher layer service location protocols.

Existing routing protocols for mobile ad hoc networks assume that all nodes have the same radio transmission range. In other words, the mobile ad hoc network has symmetric links, which means that two neighboring nodes A and B are within the transmission range of one another. However, since nodes consume battery power independently according to their computing and communication load, there exist asymmetric links, which means that node A is within node B's transmission range, but not vice versa. In this paper, two approaches are presented to support routing in the existence of asymmetric links: GAHA (GPS-based Hop-by-hop Acknowledgment) and GAPA (GPS-based Passive Acknowledgment) schemes. Both GAHA and GAPA can be applied to any routing protocols by utilizing GPS (Global Positioning System) location information. Simulation results reveal that both GAHA and GAPA protocols cope well in the presence of asymmetric wireless links and nodes' mobility.

This paper proposes a QoS adaptation scheme for both wireline and wireless networks. Multiplexed adaptive queuing (MAQ) requires only three queues per output port in any switch router; thus minimizing the complexity associated with queue management. MAQ provides a multitude of features that enable networks to adapt QoS mechanisms. The scheme is a scalable closed-loop control protocol based on dynamic priority labeling of packets at edge nodes and bandwidth assignment at both edge and core nodes using the rate-based feedback from the network. The connections with a wide spectrum of end-to-end QoS requirements are statistically multiplexed to the extent that their requirements can be satisfied while still maintaining simplicity and scalability of scheduling and buffer management inside the network. Therefore, individual flows are mapped to fine-grain QoS classes at the edge nodes, while at the core nodes, coarse-grain QoS is provided by aggregating flows into limited number of priority queues. Analysis and simulation studies demonstrate the effectiveness of the proposed scheme.

Adaptive and self-organizing wireless networks are gaining in popularity. Several media access and routing protocols were proposed for such networks and the performance of such protocols were evaluated based on simulations. In this paper, we evaluate the practicality of realizing an ad hoc wireless network and investigate on performance issues. Several mobile computers were enhanced with ad hoc routing capability and were deployed in an outdoor environment and communication performance associated with ad hoc communications were evaluated. These computers periodically send beacons to their neighbors to declare their presence. We examined the impact of varying packet size, beaconing interval, and route hop count on route discovery time, communication throughput, end-to-end delay, and packet loss. We had also performed mobility experiments and evaluated the route reconstruction time incurred. File transfer times associated with sending information reliably (via TCP) over multihop wireless links are also presented. The experimental results obtained revealed that it is feasible to augment existing wireless computers with ad hoc networking capability. End-to-end performance in ad hoc routes are less affected by beaconing intervals than packet size or route length. Similarly, communication throughput is more dependent on packet size and route length with the exception at very high beaconing frequencies. Packet loss, on the other hand, is not significantly affected by packet size, route length or beaconing frequency. Finally, route discovery time in ad hoc wireless networks are more dependent on channel conditions and route length than variations in beaconing intervals.

The existing routing protocols in mobile ad hoc networks assume that all nodes have the same transmission range. In other words, the mobile ad hoc network has only symmetric links. However, since nodes consume battery power independently according to their computing and communication load, there exist asymmetric links, which means that node A is within node B's transmission range, but not vice versa. This paper present two protocols that accommodate asymmetric links: link-level and end-to-end Approaches. The link-level approach can be applied to any routing protocols by utilizing GPS(Global Positioning System) location information of nodes at link level. On the other hand, the end-to-end approach does not need GPS devices and employs dual paths between source and destination. Simulation results reveal that these protocols cope well with ad hoc network having asymmetric wireless links under the presence of mobility.

Advances in battery technology have fallen behind that of CPU technology. Since each node in an ad hoc wireless network operates on batteries, power consumption becomes an important factor. To maximize the lifetime of ad hoc wireless networks, the power consumption rate of each mobile host must be evenly distributed. Also, the overall transmission power for each connection request must be minimized. These two objectives, however, cannot be satisfied concurrently with existing ad hoc routing algorithms. Hence, we present a new power-aware routing scheme to satisfy these two constraints simultaneously. Simulation results reveal that our proposed scheme outperforms others.

Abstract Mobile ad hoc networks are recognized by their abilities to form, sustain, and deform networks on‐the‐fly without the need for any pre‐established and fixed infrastructures. This wireless multi‐hop technology requires adaptive networking protocols with low control overhead and low power consumption to operate efficiently. Existing research so far are mainly concerned with unicast routing for ad hoc mobile networks. There is a growing interest in supporting multicast communication in an ad hoc mobile environment. In this paper, the associativity‐based ad hoc multicast (ABAM) routing protocol is proposed. The concept of association stability is utilized during multicast tree discovery, selection, and reconfiguration. This allows routes that are long‐lived to be selected, thereby reducing the frequency of route reconstructions. ABAM employs a localized route reconstruction strategy in response to migrations by source, receiver, and tree nodes. It can repair an affected subtree via a single route reconstruction operation. ABAM is robust since the repair can be triggered by a node in the tree or by the migrated node itself. ABAM is also capable of handling multicast group dynamics when mobile hosts decide to join and leave an existing multicast group. Our simulation results reveal that under different mobility scenarios and multicast group size, ABAM has low communication overhead and yields better throughput performance. Copyright © 2001 John Wiley & Sons, Ltd.

Reliable data transmission over a wireless multi-hop network, called the ad hoc network, has proven to be non-trivial. The TCP (transmission control protocol), a widely used end-to-end reliable transport protocol in a wired network, is not entirely suitable when applied to a wireless ad hoc network due to TCP's congestion control schemes. In particular, the TCP at the source considers the network as congested when detecting packet losses or timeouts. However, in a wireless ad hoc network when a route disconnection occurs because of node movement, the network mistakes this as a congestion. Therefore, the conventional TCP congestion control mechanism cannot be applied, because a route disconnection must be handled differently from a network congestion. We propose a new mechanism that improves the TCP performance in a wireless ad hoc network where each node can buffer packets during a route disconnection and reestablishment. Additionally, we incorporate new measures to deal with the reliable transmission of important control messages. Our simulation results further confirmed these advantages.

The existing routing protocols in mobile ad hoc networks assume that all the nodes have the same transmission range. In other words, the mobile ad hoc network has only symmetric links, which means that two neighboring nodes A and B are within the transmission range of one another. However, since nodes consume battery power independently according to their computing and communication load, there exist asymmetric links, which means that node A is within node B's transmission range, but not vice versa. In this paper, to cope with asymmetric links, a new routing protocol based on source-initiated on-demand routing (called RODA-routing protocol with dual paths to support asymmetric links) is presented. In order to perform route maintenance in an efficient manner, dual paths-forward (source to receiver) and backward (receiver to source) paths-are used to send and receive data packets. In addition, a timer mechanism is introduced to deal with simultaneous and consecutive broken links on both forward and backward paths. Simulation results reveal that RODA copes well with an ad hoc network having asymmetric wireless links under the presence of mobility.

Infrastructureless mobile networking relies on an ad hoc wireless network capable of forming and deforming communication routes on-the-fly. This paper describes the experience of implementing a distributed, adaptive and long-lived routing protocol called ABR (associativity-based routing) (C-K Toh, International Phoenix Conference on Computers & Communications (IPCCC'96), pp.480-486, 1996; C-K Toh, Journal on Wireless Personal Communications, vol.4, no.2, March 1997), which is based on the concept of associativity. Our implementation revealed that the modifications required to an existing TCP/UDP/IP/Ethernet protocol stack to support infrastructureless networking were minimal. We have also revealed that the experimental results (delay, throughput, and packet loss) obtained are satisfactory and the protocol can support many existing applications transparently.

Multicasting exhibits a very attractive characteristic by efficiently distributing a single stream of data to a large number of recipients. Several multicast routing protocols have been proposed for mobile ad hoc networks. Issues associated with such a network include dynamics in network topology, limited link bandwidth and limited power life. We present the performance evaluation of two categories of multicast routing algorithms for mobile ad hoc networks, namely: (a) flooding-based, and (b) associativity-based multicast routing. Two multicast routing protocols based on these two classes are simulated in a common network environment. Simulation results obtained reveal the superior characteristics of our proposed associativity-based multicast routing scheme under the scenario of low to moderate mobility. The flooding-based scheme, however, results in very high communication overhead even though it is able to maintain good throughput in a scenario with very high mobility.

We introduce an end-to-end QoS adaptation framework to resolve QoS inconsistencies as a result of mobile handoffs in wireless ATM (WATM) networks. We define mobile QoS (M-QoS) to comprise of wired, wireless and handoff QoS parameters. We introduce two forms of adaptation, namely: (a) application and (b) network QoS adaptation. The former is concerned with bandwidth, delay variation and packet loss adaptation by the mobile application while the latter refers to M-QoS fulfilment, upgrade and downgrade. New procedures are defined for M-QoS upgrade and downgrade, so that QoS 'refresh' traffic is controlled and the overall time required to perform a handoff remains largely unaffected. Results obtained from a call-level mobile network simulator further confirms the advantages of the proposed QoS adaptation scheme.

This paper examines the current status of research work on mobile ATM and presents the authors' view on pending technical challenges that require attention and investigation. Mobile ATM is not restricted to the local area and it need not be ground based. This paper examines: (a) location management, (b) connection management, (c) handoff management, (d) routing, and (e) media access for two evolving architectures, namely: (a) wireless ad-hoc ATM networks, and (b) LEO-based satellite ATM networks.

In a connection-oriented wireless LAN, the mobility of mobile hosts results in the establishment and disconnection of new and old virtual circuits. The resulting increase in signalling traffic along with the need to support multimedia stream handovers demand a fast, continuous and bandwidth-efficient handover protocol. We adopt a handover scheme based on partial re-establishments, where a new partial path converges to an existing path. Connection rerouting (CR) operations are then performed at the convergence/crossover switch (CX). To achieve localised handovers, a wireless cell clustering scheme is proposed. The clustering of base stations to cluster switches (CLSs) provides fast intra-cluster handovers since the CR operations are performed at the CLS. To support fast inter-cluster handovers, four CX discovery schemes (loose select, prior path, distributed hunt and backward tracking) are introduced. Simulation results obtained from a trace-driven mobile network simulator on four different network topologies (random, star, tree and hierarchical redundancy) reveal that both prior path and distributed hunt discoveries outperform the others by providing the fastest convergence with shorter resulting paths and higher circuit reuse efficiency.

Handovers for multi-media Wireless LAN3 (WLANs) have special requirements, unlike those in the public wireless networks.In this paper, the problems and challenges faced in a multi-media WLAN environment are presented and a multi-tier wireless cell clustering architecture is introduced.New design issues for multi-media handovers are specified and a fast, wn2inuous and eficient hybrid handover protocol is proposed.A prototype of the proposed handover protocol is implemented into a Cambridge Fairisle ATM switch and the results are evaluated.We found that implementing transport mobility for a Wireless ATM environment is not practical as the cell E-routing function is not scalable lo increasing cell rate and to the number of mobile connections.It also changes the characteristics of the traffic.Instead, the data link layer mobility implementation is found to work well.The protocol provides symmetric data disruption to trafic jlows in both directions and up lo seventy five intm-cluster handovers can be supported in a second.Throughout the ezperimenl, cells arrive in sequence with no cell loss observed during the handover, up lo the capacity limit of the ATM switch.