International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / An Ad hoc network with unicasting is considered, in which each node has an M element antenna array. Transmission from node l(i) to i is quasi-synchronous, so that code acquisition is not required. Space-Time (S-T) waveforms are transmitted with temporal dimension Ns Nyquist samples. An adaptive, distributed S-T waveform design algorithm is developed, which maintains QoS while attempting to minimize transmit power. The resulting Iterative Minimum Mean-Square Error{Time Reversal algorithm (IMMSE-TR) sets the transmit S-T vector at node i to the conjugate time-reverse of the linear MMSE S-T detector. It is shown that IMMSE-TR corresponds to a noncooperative game which attempts to minimize transmit power while paying an interference tax. Simulation results are presented demonstrating high power efficiencies for heavily-loaded systems.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / The Broadcast Scheduling Problem (BSP) is a well known NP-complete problem that arises in the study of wireless networks. In the BSP, a finite set of stations are to be scheduled in a time division multiple access (TDMA) frame. The objective is a collision free transmission schedule with the minimum number of TDMA slots and maximal slot utilization. Such a schedule will minimize the total system delay. We present variations of a Greedy Randomized Adaptive Search Procedure (GRASP) for the BSP. Path-relinking, a post-optimization strategy is applied. Also, a reactivity method is used to balance GRASP parameters. Numerical results of our research are reported and compared with other heuristics from the literature.

Mobile Ad hoc Network of Networks (MANoN) are a group of large autonomous wireless nodes communicating on a peer-to-peer basis in a heterogeneous environment with no pre-defined infrastructure. In fact, each node by itself is an ad hoc network with its own management. MANoNs are evolvable systems, which mean each ad hoc network has the ability to perform separately under its own policies and management without affecting the main system; therefore, new ad hoc networks can emerge and disconnect from the MANoN without conflicting with the policies of other networks. The unique characteristics of MANoN makes such networks highly vulnerable to security attacks compared with wired networks or even normal mobile ad hoc networks. This thesis presents a novel security-management system based upon the Recommendation ITU-T M.3400, which is used to evaluate, report on the behaviour of our MANoN and then support complex services our system might need to accomplish. Our security management will concentrate on three essential components: Security Administration, Prevention and Detection and Containment and Recovery. In any system, providing one of those components is a problem; consequently, dealing with an infrastructure-less MANoN will be a dilemma, yet we approached each set group of these essentials independently, providing unusual solutions for each one of them but concentrating mainly on the prevention and detection category. The contributions of this research are threefold. First, we defined MANoN Security Architecture based upon the ITU-T Recommendations: X.800 and X.805. This security architecture provides a comprehensive, end-to-end security solution for MANoN that could be applied to every wireless network that satisfies a similar scenario, using such networks in order to predict, detect and correct security vulnerabilities. The security architecture identifies the security requirements needed, their objectives and the means by which they could be applied to every part of the MANoN, taking into consideration the different security attacks it could face. Second, realising the prevention component by implementing some of the security requirements identified in the Security Architecture, such as authentication, authorisation, availability, data confidentiality, data integrity and non-repudiation has been proposed by means of defining a novel Security Access Control Mechanism based on Threshold Cryptography Digital Certificates in MANoN. Network Simulator (NS-2) is a real network environment simulator, which is used to test the performance of the proposed security mechanism and demonstrate its effectiveness. Our ACM-MANoN results provide a fully distributed security protocol that provides a high level of secure, available, scalable, flexible and efficient management services for MANoN. The third contribution is realising the detection component, which is represented by providing a Behavioural Detection Mechanism based on nodes behavioural observation engaged with policies. This behaviour mechanism will be used to detect malicious nodes acting to bring the system down. This approach has been validated using an attacks case study in an unknown military environment to cope with misbehaving nodes.

Mobile Ad-hoc Networks (MANETs) have received considerable research interest in recent years. Because of dynamic topology and limited resources, it is challenging to design routing protocols for MANETs. In this dissertation, we focus on the scalability and efficiency problems in designing routing protocols for MANETs. We design the Way Point Routing (WPR) model for medium to large networks. WPR selects a number of nodes on a route as waypoints and divides the route into segments at the waypoints. Waypoint nodes run a high-level inter-segment routing protocol, and nodes on each segment run a low-level intra-segment routing protocol. We use DSR and AODV as the inter-segment and the intra-segment routing protocols, respectively. We term this instantiation the DSR Over AODV (DOA) routing protocol. We develop Salvaging Route Reply (SRR) to salvage undeliverable route reply (RREP) messages. We propose two SRR schemes: SRR1 and SRR2. In SRR1, a salvor actively broadcasts a one-hop salvage request to find an alternative path to the source. In SRR2, nodes passively learn an alternative path from duplicate route request (RREQ) packets. A salvor uses the alternative path to forward a RREP when the original path is broken. We propose Multiple-Target Route Discovery (MTRD) to aggregate multiple route requests into one RREQ message and to discover multiple targets simultaneously. When a source initiates a route discovery, it first tries to attach its request to existing RREQ packets that it relays. MTRD improves routing performance by reducing the number of regular route discoveries. We develop a new scheme called Bilateral Route Discovery (BRD), in which both source and destination actively participate in a route discovery process. BRD consists of two halves: a source route discovery and a destination route discovery, each searching for the other. BRD has the potential to reduce control overhead by one half. We propose an efficient and generalized approach called Accumulated Path Metric (APM) to support High-Throughput Metrics (HTMs). APM finds the shortest path without collecting topology information and without running a shortest-path algorithm. Moreover, we develop the Broadcast Ordering (BO) technique to suppress unnecessary RREQ transmissions.

Routing is the fundamental problem for Wireless Ad hoc networks, including Wireless Mobile Ad hoc networks (MANETs) and Wireless Sensor networks (WSNs). Although the problem has been extensively studied in the past decade, the existing solutions have deficiencies in one or more aspects including efficiency, scalability, robustness, complexity, etc.This dissertation proposes several new solutions for routing in WSNs and MANETs. Spiral is a data-centric routing algorithm for short-term communication in unstructured static WSNs. Spiral is a biased walk that visits nodes near the source before more distant nodes. This results in a spiral-like search path that is not only more likely to find a closer copy of the desired data than random walk, but is also able to compute a shorter route because the network around the source is more thoroughly explored. Compared with existing flooding and random walk approaches, Spiral has a lower search cost than flooding and returns better routes than random walk.Closest Neighbor First Search (CNFS) is a query processing algorithm for mobile wireless sensor networks. It is also walk-based and biased to visit nodes close to the source first. Different from Spiral, CNFS collects topology information as the search progresses. The topology information is used to compute the shortest return path for the query result and to tolerate the network topology changes caused by node mobility, which could otherwise cause the query to fail. CNFS requires fewer messages to process a query than flooding-based algorithms, while tolerating node mobility better than random walk-based algorithms.Address Aggregation-based Routing (AAR) is a novel routing protocol designed for MANETs. It reactively performs route discovery, but proactively maintains an index hierarchy called a Route Discovery DAG (RDD) to make route discovery efficient. The RDD contains aggregated node address information, requiring fewer packets for route discovery than the flooding used in existing protocols, while handling mobility better than pre-computing routes to all nodes. Compared with some existing popular protocols, AAR shows better performance in delivery rate, message overhead, latency and scalability.

This thesis presents the Forecasting Routing Technique (FORTEL), a routing protocol for Mobile Ad-Hoc Networks (MANETs) based on the nodes' Location Information. FORTEL stores the nodes' location information in the Location Table (LT) in order to construct routes between the source and the destination nodes. FORTEL follows the source routing strategy, which has rarely been applied in position-based routing. According to the source routing strategy, the end-to-end route is attached to the packet, therefore, the processing cost, in regards to the intermediate nodes that simply relay the packet according to route, is minimized. FORTEL's key mechanisms include: first, the location update scheme, employed to keep the LT entries up-to-date with the network topology. Besides the mobility variation and the constant rate location update schemes applied, a window location update scheme is presented to increase the LT's information accuracy. Second, the switching mechanism, between "Hello" message and location update employed, to reduce the protocol's routing overhead. Third and most important is the route computation mechanism, which is integrated with a topology forecasting technique to construct up-to-date routes between the communication peers, aiming to achieve high delivery rate and increase the protocol robustness against the nodes' movement. FORTEL demonstrates higher performance as compared to other MANET's routing protocols, and it delivers up to 20% more packets than AODV and up to 60 % more than DSR and OLSR, while maintaining low levels of routing overhead and network delay at the same time. The effectiveness of the window update scheme is also discussed, and it proves to increase FORTEL's delivery rate by up to 30% as compared to the other update schemes. A common and frequently occurring phenomenon, in wireless networks, is the Hidden Terminal problem that significantly impacts the communication performance and the efficiency of the routing and MAC protocols. Beaconless routing approach in MANETs, which delivers data packets without prior knowledge of any sort `of information, suffers from packet duplication caused by the hidden nodes during the contention process. Moreover, the throughput of the IEEE MAC protocol decreases dramatically when the hidden terminal problem occurs. RTS/CTS mechanism fails to eliminate the problem and can further degrade the network's performance by introducing additional overhead. To tackle these challenges, this thesis presents two techniques, the Sender Suppression Algorithm and the Location-Aided MAC, where both rely on the nodes' position to eliminate packet duplication in the beaconless routing and improve the performance of the 802.11 MAC respectively. Both schemes are based on the concept of grouping the nodes into zones and assign different time delay to each one. According to the Sender Suppression Algorithm, the sender's forwarding area is divided into three zones, therefore, the local timer, set to define the time that the receiver has to wait before responding to the sender's transmission, is added to the assigned zone delay. Following the first response, the sender interferes and suppresses the receivers with active timer of. On the other hand, the Location-Aided MAC, essentially a hybrid MAC, combines the concepts of time division and carrier sensing. The radio range of the wireless receiver is partitioned into four zones with different zone delays assigned to each zone. Channel access within the zone is purely controlled by CSMA/CA protocol, while it is time-based amongst zones. The effectiveness of the proposed techniques is demonstrated through simulation tests. Location-Aided MAC considerably improves the network's throughput compared to CSMA/CA and RTS/CTS. However, remarkable results come when the proposed technique and the RTS/CTS are combined, which achieves up to 20% more throughput as compared to the standalone RTS/CTS. Finally, the thesis presents a novel link lifetime estimation method for greedy forwarding to compute the link duration between two nodes. Based on a newly introduced Stability-Aware Greedy (SAG) scheme, the proposed method incorporates the destination node in the computation process and thus has a significant advantage over the conventional method, which only considers the information of the nodes composing the link.

Student Number : 0006936H - MSc research report - School of Electrical and Information Engineering - Faculty of Engineering and the Built Environment / Code division duplexing (CDD) has steadily garnered attention in the telecommunication community. In this project report we propose a physical layer implementation of CDD that utilizes orthogonal Gold codes as the means of differentiating transmission directions, in order to implement an ad-hoc networking infrastructure that is overlaid on a standard mobile networking topology, and hence creating a hybrid networking topology. The performance of the CDD based system is then comparatively assessed in two ways: from the perspective of the physical layer using point-to-point simulations and from the perspective of the network layer using an iterative snapshot based simulation where node elements are able to setup connections based on predefined rules.

Energy efficiency is crucial for ad hoc networks because of limited energy stored in the battery. Recharging the nodes frequently is sometimes not possible. Therefore, proper energy utilization is paramount. One possible solution of increasing energy efficiency is to optimize the transmitted packet size. But, we claim that only optimal packet size can not boost the energy efficiency in the noisy channel due to high packet loss rate and overhead. Hence, to reduce the overhead size and packet loss, compression and Forward Error Correction (FEC) code are used as remedy. However, every method has its own cost. For compression and FEC, the costs are computation energy cost and extra processing time. Therefore, to estimate the energy-optimize packet size with FEC or compression, processing energy cost and delay need to be considered for precise estimation. Otherwise, for delay sensitive real time applications (such as: VoIP, multimedia) over ad hoc network, energy efficient optimal packet size can be overestimated. We will investigate without degrading the Quality of Service (QoS) with these two different techniques FEC and compression, how much energy efficiency can be achieved by using the energy efficient optimal packet size for different scenarios such as: single hop, multi-hop, multiple source congested network etc. This thesis also shows the impact of time variable channel, packet fragmentation, packet collision on the optimal packet size and energy efficiency. Our results show that, for larger packets, error correction improves the energy efficiency in multi-hop networks only for delay tolerant applications. Whereas for smaller packets, compression is more energy efficient most of the cases. For real-time application like VoIP the scope of increasing the energy efficiency by optimizing packet after maintaining all the constraints is very limited. However, it is shown that, in many cases, optimal packet size improves energy efficiency significantly and also reduces the overall packet loss.

Multi-hop wireless networks have been widely considered as promising approaches to provide more convenient Internet access for their easy deployment, extended coverage, and low deployment cost. However, providing high-speed and reliable services in these networks is challenging due to the unreliable wireless links, broadcast nature of wireless transmissions, and frequent topology changes. On the other hand, network coding (NC) is a technique that could significantly improve the network throughput and the transmission reliability by allowing intermediate nodes to combine received packets. More recently proposed symbol level network coding (SLNC), which combines packets at smaller symbol scale, is a more powerful technique to mitigate the impact of lossy links and packet collisions in wireless networks. NC, especially SLNC, is thus a particular effective approach to providing higher data rate and better transmission reliability for applications such as mobile content distribution in multihop wireless networks. This dissertation focuses on exploiting NC in multihop wireless networks. We studied the unique features of NC and designed a suite of distributed and localized algorithms and protocols for content distribution networks using NC and SLNC. We also carried out a theoretical study on the network capacity and performance bounds achievable by SLNC in mobile wireless networks. We proposed CodeOn and CodePlay for popular content distribution and live multimedia streaming (LMS) in vehicular ad hoc networks (VANETs), respectively, where many important practical factors are taken into consideration, including vehicle distribution, mobility pattern, channel fading and packet collision. Specifically, CodeOn is a novel push based popular content distribution scheme based on SLNC, where contents are actively broadcast to vehicles from road side access points and further distributed among vehicles using a cooperative VANET. In order to fully enjoy the benefits of SLNC, we proposed a suite of techniques to maximize the downloading rate, including a prioritized and localized relay selection mechanism where the selection criteria is based on the usefulness of contents possessed by vehicles, and a lightweight medium access protocol that naturally exploits the abundant concurrent transmission opportunities. CodePlay is designed for LMS applicaitions in VANETs, which could fully take advantage of SLNC through a coordinated local push mechanism. Streaming contents are actively disseminated from dedicated sources to interested vehicles via local coordination of distributively selected relays, each of which will ensure smooth playback for vehicles nearby. CodeOn pursues a single objective of maximizing downloading rate, while CodePlay improves the performance of LMS service in terms of streaming rate, service delivery delay, and bandwidth efficiency simultaneously. CodeOn and CodePlay are among the first works that exploit the features of SLNC to simplify the protocol design whilst achieving better performance. We also developed an analytical framework to compute the expected achievable throughput of mobile content distribution in VANETs using SLNC. We presented a general analytical model for the expected achievable throughput of SLNC in a static wireless network based on flow network theory and queuing theory. Then we further developed the model to derive the expected achievable accumulated throughput of a vehicle driving through the area of interest under a mobility pattern. Our proposed framework captures the effects of multiple practical factors, including vehicle distribution and mobility pattern, channel fading and packet collision, and we characterized the impacts of those factors on the expected achievable throughput. The results from this research are not only of interest from theoretical perspective but also provide insights and guidelines on protocol design in SLNC-based networks.

Mobile Ad hoc networks (MANETs) are flexible networks that transmit packets node-by-node along a route connecting a given source and destination. Frequent link breaks (due to node mobility) and quick exhaustion of energy (due to limited battery capacity) are two major problems impacting on the flexibility of MANETs. Cooperative communication is a key concept for improving the system lifetime and robustness and has attracted considerable attention. As a result, there is much published research concerning how to utilize cooperative communication in a MANET context. In the past few years, most cooperative technologies have focused on lower layer enhancements, such as with the Physical Layer and MAC Layer, and have become very mature. At the Network Layer, although some research has been proposed, issues still remain such as the lack of a systematically designed cooperative routing scheme (including route discovery, route reply, route enhancement and cooperative data forwarding), the use of cooperative communication for mobility resilience, and route selection (jointly considering the energy consumption, energy harvesting potential and link break probability). Driven by the above concerns, a novel Constructive Relay based CooPerative Routing (CRCPR) protocol based on a cross-layer design is proposed in this thesis. In CRCPR, we fi rst modify the traditional hello message format to carry some additional neighbour information. Based on this information, a key aspect of this protocol is to construct one or more small rhombus topologies within the MANET structure, which are stored and maintained in a COoPerative (COP) Table and Relay Table. Next, the route request procedure is re-designed to improve resilience to node mobility with a scheme called Last hop Replacement. Finally, assuming nodes are mostly battery-powered, destination node based route-decision criteria are explored that can consider energy consumption, energy harvesting and link break probability to determine an appropriate route across the MANET. As the hello message format is modi ed to carry additional information, the control overhead is increased. However, in order to improve the control message eficiency, a new generalised hello message broadcasting scheme entitled Adjust Classi ed Hello Scheme is developed, which can be deployed onto every routing protocol employing a hello mechanism. As well as designing a new routing protocol for MANETs, including route discovery, route selection, route reply, route maintenance, route enhancement and cooperative data forwarding, the proposed scheme is implemented within an Opnetbased simulation environment and evaluated under a variety of realistic conditions. The results con rm that CRCPR improves mobility resilience, saves energy via cooperative communication and reduces the control overhead associated with the hello message mechanism.