dcast and multicast services are expected to be an important part of an operator's service offering in the future. Presence to allow a set of users to be informed about the availability, willingness, and means of communication of the other users in a group. Usability and interactiveness of applications to allow easy and convenient use of services. The usability may include voice recognition and user-friendliness of human-to-machine interfaces. Good user experience plays a crucial role in the acceptance and proliferation of services. In defining the framework for development of IMT-Advanced, and systems beyond IMT-Advanced, it is important to understand the user demands and technology trends that will affect the development of such systems. In particular, the framework should be based on increasing user expectations and the growing demand for mobile services, as well as the evolving nature of the services and applications that may become available. Figure 1-1 shows four service classes (conversational, interactive, streaming, and background services) and their characteristics in terms of reliability, bit rate, and latency [12]. We will further discuss these requirements and characteristics in the next sections. In this figure, BER denotes bit error rate which is a measure of reliability of communication link, and is the ratio of the number of incorrectly- received information bits to the total number of information bits sent within a certain time interval. CHAPTER 1 Introduction to Mobile Broadband Wireless Access Background Services BER 10-6 Streaming Services 10-9 < BER < 10-6 Interactive Services 10-9 BER < 10-6 Conversational Services 10-6 < BER < 10-3 Delay (ms) FIGURE 1-1 Service classes and their characteristics Prominent standards developing organizations such as the 3rd Generation Partnership Project (3GPP), i the 3rd Generation Partnership Project 2 (3GPP2), ii and the Institute of Electrical and Electronics Engineers Standards Association (IEEE-SA) iii have actively contributed to the design, developmen