Two Resource Optimization Applications in Wireless Networks
Sammanfattning: The demand for wireless applications is increasing every year. In a couple of years, much of the traffic in the networks is packet switched data. The radio resources are not increasing at the same rate as the demand for wireless communication. It is very important that the radio resources are used in an efficient manner allowing the networks to support as many users as possible. Resource allocation in wireless networks is about using the radio resources in an efficient way. The two types of networks studied in this thesis are frequency hopping GSM networks and ad hoc multi-hop networks.The rapid growth of the number of subscribers in cellular networks requires efficient cell planning methods. The trend of smaller cell sizes in urban areas for higher capacity raise the need for more efficient spectrum usage. Since the infrastructure of a second generation cellular system, such as GSM, already exists, and the available bandwidth of an operator is limited, frequency planning methods are of utmost importance. Because of the limited bandwidth in a GSM network, the frequencies must be reused. When planning a GSM network the frequencies can not be reused too tightly due to interferences between co-channel and adjacent-channel frequencies. The frequency planning problem in a GSM network is a very complex task. In this thesis an optimization model for frequency assignment in a frequency hopping GSM network is developed. The problem is to assign frequencies to the cells in the network, while keeping the interference to a minimum. Different meta heuristic methods such as tabu search and simulated annealing are used to solve the problem. Another type of network with a promising future are ad hoc multi-hop networks. The users in this kind of networks communicate with each other without base stations. Instead the signal can be sent directly between two users, or relayed over one or several other users before the final destination is reached. Resources are shared by letting the users transmit in time slots. The problem studied is to minimize the number of time slots used, when the users broadcast. Two different optimization models are developed for assigning time slots to the users. The models are solved by different techniques. In the two different types of networks investigated, frequency hopping GSM networks and ad hoc multi-hop networks, resource allocation achieves better performance. In the former network, the interference levels can be reduced to allow a capacity increase. In the latter the number of time slots can be reduced to decrease the delay for a user.
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