Various wireless network technologies have been developed to offer Internet access to end users. The technologies have been developed for different purposes and thus provide different services, coverage areas, network bandwidths, and so on. For example, the second-generation (2G) and third-generation (3G) cellular networks have been developed to cover large areas, whereas wireless LANs (WLANs) [1] offer smaller areas. Furthermore, 2G/3G cellular networks provide relatively low data rates up to 14.4 Mbps while WLANs offer higher data rates up to 54 Mbps. According to these heterogeneous and complementary characteristics, various wireless networks will coexist and interwork together to support the different requirements of end users such as high usability, seamless connectivity, delay-sensitive applications, etc., in next-generation (4G) wireless networks.