Telecommunications – Transmitter and receiver at separate stations – Single message via plural carrier wave transmission
Patent
1994-06-20
1996-05-14
Eisenzopf, Reinhard J.
Telecommunications
Transmitter and receiver at separate stations
Single message via plural carrier wave transmission
455 331, 455 341, 455 342, 455 561, 370 951, 370 953, H04B 100, H04J 316
Patent
active
055176810
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a random access method in a radio system comprising a plurality of radio stations and at least one base station serving said radio stations, in which method the base station transmits an invoking message to the radio stations in a first time slot to grant the radio stations the right to send a random access message to the base station, one of the radio stations transmits a random access message containing a random identifier to the base station in a second time slot subsequent to the first time slot, the base station transmits a response message containing the random identifier to said radio station in a third time slot subsequent to the second time slot.
It is generally known to use a random access method in the implementation of control channel operation, in connection with the registration of a radio telephone in a network, and in call establishment. By means of the random access method a radio telephone, typically a mobile radio, connected via a radio path to a base station and thus to a radio telephone network, informs the base station that it wishes to use the signalling capacity of the system. A radio telephone needs signalling capacity in order to be able to use a speech channel or to send for instance messages, such as short messages.
A typical random access method currently used is the so-called slotted Aloha method, which is described in Computer Networks by A. S. Tanenbaum, 1981, Prentice Hall, Englewood Cliffs, pp. 249-323, particularly pp. 253-257. The use of the slotted Aloha method in connection with modern radio systems is described more closely in the standard MPT 1327, 1991, "A Signalling Standard for Trunked Land Mobile Radio Systems", Radiocommunications Agency, London, Chapter 1.3.3 and particularly Chapter 7. The slotted Aloha method is a random access method in which a radio telephone can attempt access to the control channel only within accurately defined time slots. The control channel is a radio channel or a time divided part of a radio channel used by a base station for call establishment in radio communication between it and mobile stations, i.e. radio telephones and other radio equipment. Typically, a base station transmits repeatedly--although at intervals it has defined, and irregularly if necessary--call attempt invocations, i.e. invoking messages, to radio telephones within the coverage area of its own transmitter. By means of the invoking message it has sent, the base station defines one or typically several time slots for all or a given part of the radios for random access, i.e. for the transmission of the first communication message. The radio which attempts access, i.e. which tries to establish a radio connection with the base station, selects at least one time slot for its random access message according to a rule, and transmits a random access message in that time slot, i.e. random access time slot. The random access message contains at least data for the identification of the radio which attempts access or its user. This identification data may be an address which uniquely identifies either the radio equipment or its user.
Modern radio systems must, however, be prepared for a large number of radio telephones within the area of one base station, and thereby for an extremely high load in the system. The aim is therefore to increase the random access signalling capacity between the base station and the radio equipment. The latest advance in this respect is to shorten the random access message by deleting the address which uniquely identifies the user. Even in this case, however, it is advantageous to distinguish the radio telephones attempting access in some way from each other. The address uniquely identifying the user has therefore been replaced by a random number, a random audio frequency AF, or by sending a random access message on a discrete frequency other than the nominal radio frequency. In cases like this, the (real) address data uniquely identifying the radio telephone is not sent to the base station until
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Tanenbaum, A. S., Computer Networks, 1981, pp. 249-323.
Eisenzopf Reinhard J.
Nguyen Lee
Nokia Telecommunications Oy
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