4.1 Introduction

OFDM-based access techniques are the most appropriate candidate for 4G, as it has been discussed in Chapter 3. In order to provide the required quality of services to users of 4G, several key technologies will be used with OFDM. Therefore, the next task is to present and update information on key technologies, namely MIMO technology, radio resource management, software defined radio (SDR) communication system, mobile IP, and relaying techniques [1 175]. This chapter starts with the multiantenna technologies in Section 4.2. Multiantenna is one of the key technologies for mitigating the negative effects of the wireless channel, providing better link quality and/or higher data rate without consuming extra bandwidth or transmitting power. The use of multiple antennas at either receiver, transmitter, or both ends provides several benefits: array gain, interference reduction, diversity gain, and/or multiplexing gain. Section 4.3 focuses on the main radio resource management functions. They constitute a fundamental aspect for the provision of a variability degree of the quality of service and the effective explanation of the limited radio resource, thus representing a hot research area. The concept of SDR is one of the bridges between software programming and real hardware implementation. Section 4.4 defines radio communication systems and summarizes the advantages of SDR. In addition, this section discusses the problems that must be overcome to realize the SDR communication system and explains the remarkable technologies developed to realize such a system. Section 4.5 deals with IP network issues: Mobile IP architecture, proposed for supporting mobility in...