Advanced Transmission Techniques in WiMAX

Abstract

Electronic devices such as mobile phones and laptop computers are parts of modern life. Users of portable wireless devices always desire such devices to be of small volume, light weight, and low cost. Thanks to the rapid advances in very large scale integration (VLSI) technology, this dream has become a reality in the past two decades. As technology grows rapidly, a mobile is not just a phone recently. The highly integration of circuits makes the mobile phone and the PDA (personal digital assistant) been combined into a single handset, which is called a smart phone. Also, the Internet carries various information resources and services, such as electronic mail, online chat, file transfer and file sharing, these attractive proprieties make wireless internet service becomes an important function that should be integrated into mobile devices. There are many ways for the user to connect to the internet. The traditional wireless local area network (WLAN) is a popular communication system for accessing the Internet. However, the reach of WiFi is very limited. WLAN connectivity is primarily constrained to hotspots, users need to find the access points and can only use it in certain rooms or areas. As the user get out of range of the hotspot, the signal will become very weak and the user may lose the connection. This disadvantage limits the mobility of wireless communication. Except for the widely used wireless local area network, third generation (3G) mobile telephony based on the High Speed Downlink Packet Access (HSDPA), which is part of the UMTS standards in 3G communications protocol, is another high speed wireless internet access service. It has become popular nowadays that people can get to the internet via cellular communication system. This technology gives the users the ability to access to the Internet wherever the signal is available from the cellular base station. However, the quality sometimes depends on the number of users simultaneously connected per cellular site. In addition to utilizing WLAN/3G dual-mode terminals to enhance efficiency of mobile number portability service, WiMAX (the Worldwide Interoperability for Microwave Access) is an emerging telecommunications technology that provides wireless data transmission in a variety of ways, ranging from point-to-point links to full mobile cellular-type access. WiMAX is similar to Wi-Fi but it can also permit usage at much greater distances. The bandwidth and range of WiMAX make it suitable for the applications like VoIP (Voice over Internet Protocol) or IPTV (Internet Protocol Television). Many people expect WiMAX to emerge as another technology that may be adopted for handset devices in the near future.