The Design of Ad Hoc Networks with Minimum Power and Maximum Battery Life

Multi-hop wireless ad hoc networks consist of terminals that can communicate without the support of fixed infrastructure. Nodes may communicate directly from source to destination or can use other nodes in the network as relays to facilitate a path from source to destination. These networks can be rapidly deployed and are therefore well suited to emergency service applications where fixed infrastructure has become unavailable or in situations where a temporary network is required. The essence of this type of network is the agreed co-operation between users and the underlying principle that each user is willing to make itself available as a relay for the overall benefit of the network group. In most cases the terminals in these networks are battery powered and so, to maximise the lifetime of, the network, the power consumption of each node needs to be managed. This thesis studies the optimum design of a multi-hop ad hoc network. Each layer is analysed and cross layering is considered where it is able to improve the performance. Four routing strategies for managing node usage are investigated; a minimum power routing scheme, a minimum power routing with a battery charge threshold scheme, a residual battery charge scheme and a proposed minimum power routing/maximum battery lifetime scheme. A network model has been developed to evaluate these schemes and the results show that a network lifetime (defined as the time until the first node reaches zero battery charge) of 21 hours can be obtained using the proposed routing scheme which represents an improvement of 5% over the power aware routing scheme and the residual battery charge scheme, 31 % over the minimum power routing with a battery charge threshold scheme, and 133% over the minimum power routing scheme. Space, frequency and time division multiple access schemes are analysed for supporting multiple simultaneous transmissions in the network. Space division multiplexing allows multiple access without affecting the bandwidth or data rate, but five to nine simultaneous routes can be supported. A time division scheme is considered the best solution when guaranteed access is required by all nodes, but this reduces the maximum bit rate per user. The throughput per unit time in a multi-hop route using a single frequency channel varies inversely with the number of hops. A novel cross layer scheme is proposed that selects the modulation order to match the number of hops in a route to maximise the throughput per unit time. Simulation results for this scheme show that this can improve the throughput on 52% of the routes using a proposed routing scheme, but the extra power required for the higher order modulation reduces the network lifetime by 14%. A total network design solution is presented, including both the transmission and signalling subsystems that shows how the novel routing and cross layer features proposed in the thesis can be implemented