Mobile Communications: 4G

4G of mobile communications describes the main research and development directives and technologies beyond the 3G of mobile communications. The name is interpreted slightly differently in various publications but signifies similar ideas. Mobile communications have been one of the hottest areas of telecommunications, famous for fast development and growth. First steps of cellular telephony reach back to the year 1981 which is the year of introduction of Nordic mobile telephone (NMT), termed also the first generation (1G). In 2006 there are approximately 2.5 billion mobile phone users worldwide. 3G has been introduced to most of the developed countries around the world and has already reached the number of 100 million subscribers in 2006. It seems that the number of mobile devices connected to Internet will soon exceed the number of static desktop clients. Next generation has not been defined yet but various scenarios and ideas have been proposed. In this entry we summarize some most important published predictions of future mobile communications, and its main concepts and technology background. It seems that next generation is going to be ‘‘user-centric’’, which means that user needs and wishes will drive the research and development. Undoubtedly high data transfer rates, quality of service (QoS) and continuous coverage will be the most important features. We point out the key technologies which will form the basic platform for future mobile networks and list the most important forums and research groups in this area.