Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Patent
1996-01-25
1998-10-20
Vu, Huy D.
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
370436, 370524, 455 63, 455522, H04J 400, H04B 726
Patent
active
058257586
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/FI95/00285 filed May 24, 1995 published as WO95/33313 Dec. 7, 1995.
FIELD OF THE INVENTION
This invention relates to a method for improving the detectability of a broadcast control channel of a base station in a radio system in which the transmitting and receiving frequency resources of the transceiver units a plurality of have been divided on the TDMA/FDMA principle into channels, the base stations comprising means for establishing a radio connection to radio units in their radio coverage area, and means for transmitting a broadcast control channel, whereby the system includes at least two base stations that have been arranged to transmit the broadcast control channel by utilizing the same predetermined frequency channel. The invention further relates to a cellular radio system comprising base stations, the transceiver units of which have their transmitting and resources divided on the TDMA/FDMA principle into channels, the base stations comprising means for establishing a radio connection to radio units in their radio coverage area, and means for transmitting a broadcast control channel, whereby the system includes at least two base stations that have been arranged to transmit the broadcast control channel by utilizing the same predetermined frequency channel.
BACKGROUND OF THE INVENTION
The invention is related to mobile communication systems divided into traffic channels on the TDMA/FDMA principle (Time Division Multiple Access/Frequency Division Multiple Access), and especially to the GSM (Groupe Special Mobile) system and DCS (Digital Cellular System). The invention is particularly related to a problem that arises when the same frequency channels have to be used in several radio cells situated near each other so that signals of different radio cells will intermingle and disturb one another.
The BCCH channel (Broadcast Control Channel) of the GSM and DCS systems is one example of a channel that is transmitted on the same frequency channel by a base station of several radio cells situated near each other. Base stations also use the frequency channel now being discussed for other purposes, for example, as a normal traffic channel, since the BCCH channel needs only one available time slot. The base station transmits information on the broadcast control channel concerning the respective radio cell, such as information on the frequencies of traffic channels to be used, for example.
In addition to the broadcast control channel of its own radio cell, a radio unit in a certain radio cell also listens to the broadcast control channel of the surrounding cells, decodes the received radio signals and performs measurements concerning the power levels of the received signals, that is, RSSI measurements (Received Signal Strength Indication). For instance, handovers, i.e. transitions from one radio cell to another are performed on the basis of such measurements. In the GSM/DCS system, base stations transmit information only in the first time slot of the BCCH broadcast control channel, i.e. in time slot 0, whereby transceivers decode signals received only in that time slot. Other time slots are either used as traffic channels or fill frames are transmitted in them. Bursts transmitted in each time slot of the BCCH channel, i.e. even fill frames, are taken into account in the RSSI measurements of the transceiver.
SUMMARY OF THE INVENTION
Since the base stations of radio cells situated near each other transmit the BCCH channel by utilizing the same frequency channel, interference occurs between signals transmitted by different base stations, which will particularly disturb the radio units situated farther away. In practice, it has been shown that because of the interference, radio units situated farther have had problems with decoding faultlessly signals on the BCCH channel transmitted in time slot 0.
The object of the present invention is to solve the above-mentioned problem. This object is achieved with the method of the invention that is charact
REFERENCES:
patent: 5487185 (1996-01-01), Halonen
patent: 5570352 (1996-10-01), Poyhonen
Heikkinen Eero
Uola Risto
Nokia Telecommunications Oy
Vu Huy D.
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