Doctoral Theses (Mathematical & Computer Sciences)

Permanent URI for this collectionhttps://dspace-upgrade.is.ed.ac.uk/handle/10399/37

Browse

Now showing 1 - 2 of 2

Enhanced multichannel routing protocols in MANET
(Heriot-Watt University, 2019-09) Mirza, Nawaf Saleh; King, Doctor Peter; Taylor, Doctor Hamish; Abdelshafy, Doctor Mohamed
Utilising multiple non-overlapping channels in MANET networking can improve performance and capacity. Most multichannel MAC and routing protocols rely on an extra radio interface, a common control channel or time synchronisation to support channel selection and routing, but only at the expense of hardware and power consumption costs. This thesis considers an alternative type of multichannel wireless network where each node has a single half-duplex radio interface and does not rely on a common control channel or time synchronisation. Multichannel MAC and routing protocols that adopt the Receiver Directed Transmission (RDT) communication scheme are investigated to assess their ability to implement a multichannel MANET. A novel multipath multichannel routing protocol called RMMMC is proposed to enhance reliability and fault-tolerance in the MANET. RMMMC introduces new route discovery and recovery processes. The former establishes multiple node and channel disjointed paths in different channels and accumulates them to acquire a full multi-hop path to each destination. The latter detects broken links and repairs them using pre-discovered backup routes. To enhance communication reliability, a novel cross-layer multichannel MAC mechanism called RIVC is proposed. It mitigates transmitting/rerouting data packets to a node that does not have an updated route information towards a destination and only allows data packets with valid routes to occupy the medium. The optional access mode in the MAC protocol is modified to early detect invalid routes at intermediate nodes and switchover to an alternative path. A new cross-layer multichannel MAC mechanism called MB is proposed to reduce contention in a busy channel and enhance load balancing. MB modifies the MAC back-off algorithm to let a transmitter node invoke an alternative path in the alternative channel when the retry count threshold is reached. The proposed multichannel protocols are implemented and evaluated by extensive NS2 simulation studies.
Route discovery schemes in Mobile Ad hoc Networks with variable-range transmission power
(Heriot-Watt University, 2019-02) Alghamdi, Atif A.; King, Doctor Peter; Taylor, Doctor Hamish; Abdelshafy, Doctor Mohamed
Broadcasting in MANETs is important for route discovery but consumes significant amounts of power that is difficult to renew for devices that rely heavily on batteries. Most existing routing protocols make use of a broadcast scheme known as simple flooding. In such an on-demand routing protocol (e.g. AODV) the source node originates a Route Request (RREQ) packet that is blindly rebroadcast via neighbouring nodes to all nodes in the network. Simple flooding leads to serious redundancy, together with contention, and collisions, which is often called the broadcast storm problem. This thesis proposes two improvement strategies: topology control (adjusting transmission power) and reduced retransmissions (reducing redundant rebroadcasts) to reduce energy consumption. For energy efficient route discovery the main idea is to reduce the energy consumed per broadcast during route discovery. An Energy Efficient Adaptive Forwarding Algorithm (called EEAFA) is proposed to reduce the impact of RREQ packet flooding in on-demand routing protocols. The algorithm operates in two phases: 1) Topology construction phase, which establishes a more scalable and energy efficient network structure where nodes can adjust their transmission power range dynamically, based on their local density. 2) A Forwarding Node Determination phase, that utilises network information provided by the constructed topology, where nodes independently decide to forward a RREQ packet or not without relying on GPS or any distance calculations. A further Enhanced EEAFA (called E-EEAFA) algorithm is also proposed, which combines two techniques: graph colouring and sectoring techniques. Graph colouring increases awareness at network nodes to improve the determination of a forwarding node, while the sectoring technique divides neighbours into different forwarding sectors. This helps to reduce overlap between forwarding nodes and select suitable nodes in each sector to forward RREQ packets. These techniques are employed in a distributed manner and collaborate to reduce the number of forwarding nodes, which thus reduces the volume of RREQ packets populating the network. These algorithms have been validated as effective by NS2 simulation studies that are detailed in the thesis.