Gugrajah_Yuvaan_ Ramesh_2003.pdf
Gugrajah_Yuvaan_ Ramesh_2003.pdf Gugrajah_Yuvaan_ Ramesh_2003.pdf
Conclusion Chapter 6 Results for packet delivery ratio and average end-to-end delay are obtained and show the new protocol performs better than the other protocols compared in all scenarios where there is high mobility and high offered load. This shows that load balancing in ad hoc networks is beneficial under certain circumstances. However, once again the computational cost of implementing more complex routing protocols need to be weighed against the benefits. Under low offered loads, the less complex AODV routing protocol performed almost as well as the DLAR protocols. This dissertation also proposes an analytical model for the evaluation of the blocking probability of a call offered to an ad hoc network that results from a particular routing protocol being implemented. All of the comparisons of the routing protocols are performed using simulators, which are not only time consuming but also do not allow as rapid optimisation of routing protocols by a network designer as would analytical models. Techniques for modelling fixed networks as loss networks are combined with those for the evaluation of cellular CDMA networks. CDMA was chosen because CDMA systems offer high spectrum efficiency and the potential use of advanced antenna and receiver structures. No previous work has been published on the type of full-scale analytical evaluation of ad hoc networks that is consider in this dissertation. Numerical results obtained provide a 3.9 % error as compared to simulation results of a similar network, with the analytical model providing a more conservative estimate. While the results of the analytical model compare favourably to simulation results, a major shortcoming of the analytical model proposed is the inability to account for mobility. Due to the potential number of topological configurations possible, all routes cannot be accounted for. The analytical model therefore is only capable of evaluating fixed wireless multihop ad hoc networks. Networks of this sort include wireless local loop extensions to the fixed wired telephone network in rural areas. Methods for evaluating and optimising routing protocols using the analytical model are demonstrated. 6-3
Conclusion 6.2. Future Work 6.2.1. Load Balancing and Cross-Layer Adaptations Chapter 6 The simulations results in Chapter 3 show that load balancing and signal monitoring are advantageous to the performance of the routing protocol. Other methods of monitoring the environment by allowing the interaction of various layers of the protocol stack can be investigated. For example, the medium access control protocol has already been used in some simulations discussed in the literature to provide the routing protocol with connectivity information. Route selection can benefit from information gained due to these interactions. 6.2.2. Simulator Mobility Models Software simulators are used in an attempt to simulate real life statistics. However, the assumptions that are made, such as arrival statistics, service statistics, propagation models and mobility models, are questionable. A potential area of investigation is in the determination of realistic mobility models that would apply to particular application scenarios. While the random movement models do provide certain insights in the behaviour of the protocols, the next step is to obtain actual user mobility traces so that the routing protocols can be evaluated in a more realistic scenario. Experiments could also provide the required physical layer propagation models that would allow the simulator to consider more realistic wireless environments. While too much detail results in slow and cumbersome simulators, simulations that lack necessary detail can result in misleading or incorrect results. 6.2.3. Analytical Model Assumptions The Poisson arrival is the fundamental assumption underlying the Erlang Formula. The reduced load approximation and many other strategies for evaluating networks rely on this assumption. The importance of this assumption is that the distribution of the call duration only shows through its mean value in the blocking probability. It is foreseeable that with long holding times in data networks (which implies infinite 6-4
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Conclusion<br />
Chapter 6<br />
Results for packet delivery ratio and average end-to-end delay are obtained and show<br />
the new protocol performs better than the other protocols compared in all scenarios<br />
where there is high mobility and high offered load. This shows that load balancing in<br />
ad hoc networks is beneficial under certain circumstances. However, once again the<br />
computational cost of implementing more complex routing protocols need to be<br />
weighed against the benefits. Under low offered loads, the less complex AODV<br />
routing protocol performed almost as well as the DLAR protocols.<br />
This dissertation also proposes an analytical model for the evaluation of the blocking<br />
probability of a call offered to an ad hoc network that results from a particular<br />
routing protocol being implemented. All of the comparisons of the routing protocols<br />
are performed using simulators, which are not only time consuming but also do not<br />
allow as rapid optimisation of routing protocols by a network designer as would<br />
analytical models. Techniques for modelling fixed networks as loss networks are<br />
combined with those for the evaluation of cellular CDMA networks. CDMA was<br />
chosen because CDMA systems offer high spectrum efficiency and the potential use<br />
of advanced antenna and receiver structures. No previous work has been published<br />
on the type of full-scale analytical evaluation of ad hoc networks that is consider in<br />
this dissertation. Numerical results obtained provide a 3.9 % error as compared to<br />
simulation results of a similar network, with the analytical model providing a more<br />
conservative estimate.<br />
While the results of the analytical model compare favourably to simulation results, a<br />
major shortcoming of the analytical model proposed is the inability to account for<br />
mobility. Due to the potential number of topological configurations possible, all<br />
routes cannot be accounted for. The analytical model therefore is only capable of<br />
evaluating fixed wireless multihop ad hoc networks. Networks of this sort include<br />
wireless local loop extensions to the fixed wired telephone network in rural areas.<br />
Methods for evaluating and optimising routing protocols using the analytical model<br />
are demonstrated.<br />
6-3
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