chapter  17
Broadcast Applications of WiMAX Networks
Pages 30

WiMAX networks have been designed to provide broadband wireless access with QoS parameters, and provide assured service flows for each connection. WiMAX also has a service class, “real-time polling service” (rtPS), which is designed to cater to variable rate data packets such as those generated in MPEG with low latencies in order to meet video transmission requirements. Transmission of video over wireless networks, prior to deployment of WiMAX systems, had always been a challenge because of the high sustained bit rates, which need to be maintained for every user on the network. WiMAX networks, by providing a very efficient multi-carrier OFDM-based physical layer which overcomes intersymbol interference, modulation adapted to transmission conditions, frequency selective assignment to subcarriers to overcome interference, HARQ, beamforming, and efficient error correction mechanisms, present a combination of technologies, which deliver sustained high bit rates. This combined with the characteristics of the MAC layer to establish service classes and ensure service flows with each class, complete the environment needed for delivery of high bit rate low-latency services such as audio and video, which overcome the vagaries of the wireless medium associated with nonline of sight transmission, sharp changes in signal levels and interference. Finally, in addition to guaranteed service flows, mobile WiMAX also brings in the multicast and broadcast services (MBS) wherein video can be efficiently multicast over a wireless medium, thus using

only a fraction of the capacity available in a cell for delivering video services.