tailieunhanh - Điện thoại di động mạng lưới Radio P6

Trunked Mobile Radio and Packet Data Radio In addition to the public radio telephone service and the paging service, there are other radio services that are not accessible by the public. These radio systems, called the non-public land mobile radio network , have access to frequencies that cannot be used by the public but only by specific users or groups of users. Probably the best known non-public mobile radio service is analogue Private Trunked Mobile Radio (PTMR), which has been used for many years by large firms such as airlines, taxi and transport companies, the railways, and ports, as well. | Mobile Radio Networks Networking and Protocols. Bernhard H. Walke Copyright 1999 John Wiley Sons Ltd ISBNs 0-471-97595-8 Hardback 0-470-84193-1 Electronic 6 Trunked Mobile Radio and Packet Data Radio In addition to the public radio telephone service and the paging service there are other radio services that are not accessible by the public. These radio systems called the non-public land mobile radio network have access to frequencies that cannot be used by the public but only by specific users or groups of users. Probably the best known non-public mobile radio service is analogue Private Trunked Mobile Radio PTMR which has been used for many years by large firms such as airlines taxi and transport companies the railways and ports as well as by government departments and organizations responsible for security. What is characteristic of previous PTMR systems is that they have one radio channel that is used exclusively by all the mobile terminals of a specific user group. An analysis of conventional commercial radio systems reveals a number of weaknesses that affect both the customer and the operator Because of too many PTMR users the fixed allocation of radio channels in congested areas leads to a frequency overload. Radio supply areas are too small. There is the possibility of eavesdropping by unauthorized persons. There is no link to the public telephone networks. There is limited support of voice and data transmission. Frequency overload was the main reason for considering new radio systems and infrastructures. This led to the introduction of trunked mobile radio systems as the successors to analogue PTMR. Although it is not possible for trunked mobile radio systems to expand the frequency spectrum available they are able to improve the quality of service both for the end user and for the network operator through the optimization of frequency utilization and increased channel use. Advances in trunked mobile radio technology have resulted not only in providing user