Efficient heuristic solutions for wireless communication systems

Recent years have witnessed tremendous developments regarding wireless network access. In this paper emphasis is given to methods for the design of in-door Coded Division Multiple Access (CDMA) based wireless networks and Fixed Wireless (e.g. Wireless Local Loop WLL) networks, which are referred to as wireless access networks. In these networks, two main types of network components are considered: the access point/base station and the fixed wireless user/terminal. The fixed wireless terminals (test points) claim for access to the network and the access points/base stations connect the terminals to the network. With the set T of fixed wireless terminals and the set S of possible (predefined) locations for the placement of access points/base stations. Each terminal i ∈ T should be connected to only one access point/base station j ∈ S and each access point/base station together with its associated terminals, constitute an access subnetwork. Moreover, the access points/base stations can be connected to one or more other subnetworks (e.g. the backbone subnetwork). A typical network that includes wireless access subnetworks is illustrated in Figure 1. The process of wireless network planning basically consists of two phases: 1. Base station placement. A number of base stations must be placed in a number of (predefined) candidate sites, essentially one base station in each selected site. 2. Wireless terminal (test point) allocation to the selected base station(s) in phase 1. Practically, both phases can be considered as one. However, the design cost that here refers to base station placement (installation) and operation, should be minimum. Unfortunately, today there are no systematic methods to address the problem of wireless network planning, especially for CDMA based networks, fixed wireless and UMTS access networks. In fact, the planning process is mainly based on empirical approaches [1]. Nevertheless, recent design approaches [2, 3], based on Integer Linear Programming (ILP) and Mixed Integer Programming (MIP) techniques, deal with the above problem in a rather interesting way that it may be very advantageous in practice. A wireless system planning procedure for in-door CDMA networks based on a complex ILP model is presented in [2]. However, no simulation results regarding topologies with more than 27 wireless users are provided. In [3] a series of complex MIP optimization models specially suited for UMTS base station planning are presented. Figure 1. Typical network example