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DAV Nguyên tắc và các ứng dụng P7

Tham khảo tài liệu 'dav nguyên tắc và các ứng dụng p7', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Digital Audio Broadcasting Principles and Applications. Edited by Wolfgang Hoeg Thomas Lauterbach Copyright 2001 John Wiley Sons Ltd ISBNs 0-471-85894-3 Hardback 0-470-84170-2 Electronic 7 The Broadcast Side WOLFRAM TITZE and STEPHEN BAILY 7.1 General This chapter explains the broadcast side of DAB namely the transmitters and the corresponding transmission networks. Planning and evaluation aspects for single frequency networks are also covered. Signal delivery to transmitter sites is covered in detail in Chapter 6. 7.1.1 Difference between FM and DAB Networks Planning of transmission networks for FM broadcasting is traditionally based on the concept of multiple frequency networks MFNs . In an MFN adjacent transmitters radiate the same programme but operate on different frequencies to avoid interference of the signals where the coverage areas of different transmitters overlap. Basic FM receivers cannot cope with interfering signals from other transmitters of the same network. Coverage planning for an FM network requires frequency planning for the different transmitter sites to optimise use of the scarce resource frequency 1. DAB in contrast allows single frequency networks SFNs where all transmitters of the network transmit exactly the same information on the same frequency. The main condition for a working SFN is that all transmitters are synchronised to each other in frequency and fulfil certain time delay requirements which will be explained later in this chapter. Coverage planning for a DAB network requires time delay planning between the different transmitters instead of frequency planning as in the case of FM. The SFN capability of DAB allows complete coverage of very large regions without the receiver having to tune to a different frequency while moving around in the area. Digital Audio Broadcasting Principles and Applications edited by W. Hoeg and T. Lauterbach 2001 John Wiley Sons Ltd. 182 Digital Audio Broadcasting Principles and Applications In contrast .