Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Patent
1996-09-18
1998-07-07
Mullen, Thomas
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
370341, 455511, H04Q 700
Patent
active
057783187
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/F195/00009, filed Jan. 13, 1995.
BACKGROUND OF THE DISCLOSURE
The invention relates to a method for allocating channels in a radio system comprising base stations and subscriber stations communicating with the base stations over control and traffic channels.
A typical feature of trunking radio telephone systems is that the number of radio channels allocated to such radio systems has very often been too small in relation to the need. One base station typically has only 1 to 4 radio channels available, one of them is typically allocated for control channel use, and the others are traffic channels. If the traffic density is high within the area of the base station, it is easy to notice that the capacity of the control channels of the base station is too low at congestion hours. This becomes apparent in that there are not enough control and traffic channels for subscribers requesting them, that is, traffic congestion occurs. Traffic congestion appears particularly on the uplink channel of the control channel of the base station, i.e. on the channel over which subscriber stations try to establish a connection to the base station. On this control channel the radio telephones select the time of transmission on some kind of random access principle. In the random access method known from the prior art, only a predetermined proportion of the total capacity, possibly only 30%, can be used successfully in the uplink direction due to collisions between signalling messages. This indicates that the uplink direction of the control channel often forms a bottle-neck on the control channel.
It is also widely known that interferences occur in radio systems. Interferences occur, e.g. when radio transmitters operating on the same frequency or on frequencies too close to each other interfere with each other. In cellular radio networks, for instance, several base stations may use the same radio channel; normally, such base stations are so remote from each other that an individual radio station is able to communicate on the same frequency with one base station only. Under exceptional radio wave propagation conditions, however, a signal from an individual radio station may reach the receiver of the wrong base station, thus interfering with the normal radio traffic of the base station. This is particularly disastrous for the control channel operation, as the operation of normal traffic channels of the radio system is based on the control channel operation. Correspondingly, an individual radio telephone, i.e. subscriber station, may receive a signal from a base station which is normally out of range. Interfering with the desired traffic by a radio signal transmitted on the wrong frequency cannot be prevented by using identities, which only prevent responding to wrong impulses.
As used in this dowment, a channel refers to a single individual frequency or to a single time slot of a single individual frequency, that is, a single direction of transmission.
Furthermore, faults occur in radio systems as radio devices may operate contrary to the protocol used in the network, e.g. in the case of a failure when a radio keeps transmitting on a control channel or in a control channel time slot more or less continuously. A similar interference situation may also result from crosstalk between completely different radio systems. In some situations, the operation of a radio system may be interfered with intentionally by sending out interfering radio signalling particularly on the control channel.
The control channel operation of a mobile or fixed radio system can be interfered with intentionally at least in the following ways:
Over a wide band of the entire available frequency band in such a way that the interference affects the receiver of the control channel of the base station, i.e. the receiving frequency range of the base station is interfered with partially or entirely.
Over a wide band of the entire available frequency band in such a way that the interference affects the rec
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patent: 5235598 (1993-08-01), Sasuta
patent: 5239678 (1993-08-01), Grube et al.
patent: 5377193 (1994-12-01), Grube et al.
patent: 5442809 (1995-08-01), Diaz et al.
patent: 5483667 (1996-01-01), Faruque
patent: 5504803 (1996-04-01), Yamada et al.
Patent Abstracts of Japan, vol. 6, No. 81, E-107, Abstract of JP 57-17246 (A), Jan. 1982.
Lehmusto Mika
Talarmo Reino
Mullen Thomas
Nokia Telecommunications Oy
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