TAILIEUCHUNG - WiMAX Technology for Broadband Wireless Access 2007 phần 4

Khu vực này là một trong những được bao phủ bởi một BS. Bất cứ khi nào người dùng di chuyển ra khỏi khu vực, thông tin liên lạc (hoặc phiên) bị gián đoạn. Một ví dụ điển hìnhĐường trục: đài phát thanh liên kết Internet Backbone: có dây liên kết (sợi quang học cũ) | 6 The Physical Layer of WiMAX The Physical Transmission Chains The modulation and OFDM transmission aspects described in the previous chapter are the major building blocks of the WiMAX PHYsical Layer. In this chapter some elements of the transmission chains of WiMAX are described for both OFDM and OFDMA PHYs. The Global Chains The PHY transmission chains of OFDM and OFDMA are illustrated in Figures and . The blocks are the same with the small difference that OFDMA PHY includes a repetition block. The modulation is one of the four digital modulations described in the previous chapter BPSK QPSK 16-QAM or 64-QAM. The modulated symbols are then transmitted on the OFDM orthogonal subcarriers. In the following WiMAX channel coding building blocks are described. The building blocks of channel coding are described in Section . A possible FEC code is the Turbo Code. Turbo Code theory and the basic elements of its use in WiMAX can be found in Section . The Transmission Convergence Sublayer TCS which can be applied in OFDM PHY is described in Section . Finally the burst profiles of OFDM and OFDMA PHY an important building block of IEEE MAC layer are described in Section . Channel Coding The radio link is a quickly varying link often suffering from great interference. Channel coding whose main tasks are to prevent and to correct the transmission errors of wireless systems must have a very good performance in order to maintain high data rates. The channel coding chain is composed of three steps randomiser Forward Error Correction FEC and interleaving. They are applied in this order at transmission. The corresponding operations at the receiver are applied in reverse order. Error detection is realised with HCS and CRC see Chapter 8 . WiMAX Technology for Broadband Wireless Access Loutfi Nuaymi 2007 John Wiley Sons Ltd. ISBN 0-470-02808-4 70 WiMAX Technology for Broadband Wireless Access To OFDM Part IFFT CP etc. see Chapter 5

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