Giao diện không khí ± tầng vật lý Các lớp vật lý GSM, mà cư trú trên RST ® trong bảy lớp của OSI Reference Model [55], có chức năng rất phức tạp. Các kênh vật lý được de ® Ned ở đây bởi một chương trình truy cập TDMA nhiều. Ngày đầu các kênh vật lý, một loạt các kênh logic được de ® Ned, được truyền trong các khe thời gian của các kênh vật lý. Hợp lý các kênh khác nhau như thực hiện một chức năng, chẳng hạn như vận tải trọng tải, tín hiệu, phát sóng. | GSM Switching Services and Protocols . Second Edition. Jörg Eberspächer Hans-Jörg Vögel and Christian Bettstetter Copyright 2001 John Wiley Sons Ltd Print ISBN 0-471-49903-X Online ISBN 0-470-84174-5 5 Air Interface - Physical Layer The GSM physical layer which resides on the first of the seven layers of the OSI Reference Model 55 contains very complex functions. The physical channels are defined here by a TDMA multiple access scheme. On top of the physical channels a series of logical channels are defined which are transmitted in the time slots of the physical channels. Logical channels perform a multiplicity of functions such as payload transport signaling broadcast of general system information synchronization and channel assignment. The structure of this chapter is as follows In Section we describe the logical channels. This serves as a foundation for understanding the signaling procedures at the air interface. The realization of the physical channels including GSM modulation multiple access duplexing and frequency hopping follows in Section . Next Section covers synchronization. The mapping of logical onto physical channels follows in Section where the higher-level multiplexing of logical channels into multiframes is also covered. Section contains a discussion of the most important control mechanisms for the air interface channel measurement power control disconnection and cell selection . The conclusion of the chapter is a power-up scenario with the sequence of events occurring from when a mobile station is turned on to when it is in a synchronized state ready to transmit Section . Logical Channels On Layer 1 of the OSI Reference Model GSM defines a series of logical channels which are made available either in an unassigned random access mode or in a dedicated mode assigned to a specific user. Logical channels are divided into two categories Table Traffic channels and signaling control channels. Traffic Channels The .
