Technical Field

The invention relates to a method for securing the operation of a base station having a radio cover¬ age area divided into at least two sectors, the base station comprising antenna means and at least one channel unit for each sector, which allow the base station to establish a radio connection with active radio transceivers currently located in the sectors of the base station, wherein the base station is provided with an additional channel unit the traffic capacity of which is selectably switchable to one of the base station sectors. The invention also relates to a base station in a radio system, the radio coverage area of the base station being divided into at least two sectors and the base station comprising antenna means and at least one channel unit for each sector, which allow the base station to establish a radio connection with active radio transceivers currently located in the sectors of the base station, the base station further comprising an additional channel unit the traffic capacity of which is selectably switchable to one of the base station sectors.

As used herein, the term antenna means refers not only to the antenna required for transmission and reception but also to the means that connect the antenna attachments of a channel unit to the antenna of the base station. Such means include a combiner means, which combines signals transmitted by channel units intended to be used in the same sector before they are applied to the antenna, and a branching means, which filters and amplifies signals received by the antenna of a specific sector and branches them to

the receivers of different channel units.

Technical Background Art

Finnish Patent Application 911 199 discloses a solution where an additional channel unit is connected to a sectored base station in a cellular radio system. The additional channel unit can be connected to a sector that instantaneously needs additional capacity. In this solution, the additional channel unit is connected so that its transmitter can be switched by a relay switch to a combiner means belonging to the antenna means of the selected sector. On the contrary, the reception side of the additional channel unit is implemented such that signals received from different sectors are combined by a combiner means and applied to the receiver of the additional channel unit. Ac¬ cordingly, signals received from each sector of the base station are thus continually applied to the re- ceiver of the additional channel unit.

The solution according to Finnish Patent Appli¬ cation 911 199, where signals from each sector of the base station are applied continually to the additional channel unit, has several drawbacks, the most severe being:

- complicated cabling;

- susceptibility to interference when the fixed channel unit of one of the sectors fails in such a way that the antenna attachment of the receiver of the failed channel unit forwards signals interfering with the other channel units of the base station; this interference may render all of the receivers of the base station inoperative, as the receiver of the failed channel unit is still connected to the other receivers of the base station through the combiner

means of the reception side;

- susceptibility to interference during normal traffic operation due to the fact that the additional channel unit is permanently connected to all of the sectors of the base station so that it also gathers interferences and background noise from within all sectors. In the worst case, it may happen that a signal received by the receiver of the additional channel unit from a cell of another mobile radio network covers a desired signal or at least substan¬ tially deteriorates the quality of the connection (the solution does not follow the frequency re-use scheme that has been made specifically for each sector);

- greater attenuation due to the summing of signals on the reception side, which causes a greater attenuation on the signal path, so that the sensit¬ ivity of the receivers is impaired.

Disclosure of the Invention

The object of the present invention is to avoid the above problems and to provide a method by means of which a failed channel unit of a sectored base station in a cellular radio system can be replaced with an additional channel unit, and which ensures that the failed channel unit will not interfere with the oper¬ ation of the other channel units of the base station when the antenna attachment of the failed channel unit forwards signals at a frequency such that they would otherwise interfere with the operation of the base station. These objects are achieved by a method according to the invention, which is characterized by monitoring the operation of the channel units of the base station; and switching, when one of the channel units fails, the additional channel unit to the

antenna means of the sector of the failed channel unit by a switching means which connects the antenna attachments of the additional channel unit to the antenna means of one sector at a time. The invention also relates to a base station where the method according to the invention can be applied. The base station according to the invention is characterized in that the additional channel unit is switched to the antenna means of a selected sector by a switching means, which connects the antenna attachments of the additional channel unit to the antenna means of one sector at a time.

The invention is based on the idea that the operation of a sectored base station can be secured more efficiently and reliably than previously when one of the channel units fitted in the base station fails by providing an additional channel unit in the base station. The antenna attachments of the additional channel unit can be switched to one of the antennas of the base station by a relay-type switch. This switch¬ ing ensures that the failed channel unit will not interfere with the other receivers at the base station due to signals possibly propagating through its antenna attachments. The most important advantage of the method and the base station according to the in¬ vention is thus that they minimize the disadvantage caused by the failure of a channel unit. At best, the failed channel unit can be replaced with the addi¬ tional channel unit, whereby normal traffic operation can be continued immediately even in the sector of the failed channel unit. Not even in the worst case is the failure able to interfere with traffic taking place in the other sectors.

Another major advantage of the method and the base station according to the invention is that a

single switching means, i.e. a relay-type switch, is needed for the switching which replaces the failed channel unit with the additional channel unit. The solution according to the invention is thus simpler and cheaper than the prior art solutions.

Other advantages of the method and the base station according to the invention over the prior art include simple cabling, lower level of background noise in reception, excellent sensitivity of recep- tion, and the possibility to utilize the additional channel unit while following the sector-specific frequency re-use scheme.

Preferred embodiments of the method and the base station according to the invention appear from the attached dependent claims 2 to 4 and 6 to 9.

Description of a Preferred Embodiment

In the following the invention will be described more fully by means of a preferred embodiment with reference to the attached figure, which shows a pre¬ ferred embodiment of a base station according to the invention.

The figure shows a sectored GSM base station the coverage area of which is divided into three sectors. The structure and operation of the GSM system are described e.g. in The GSM System for Mobile Communi¬ cations , M. Mouly & M-B Pautet, Palaiseau, France, 1992, ISBN: 2-9507190-0-7, wherefore they will not be described more closely herein.

The base station 13 shown in the figure com¬ prises a fixed channel unit (TRX) 1, 2 and 3, and an antenna 4, 5 and 6 for each sector of the base station, respectively, whereby the base station is able to establish a radio connection with active radio

transceivers located in the sectors. The transceivers 1, 2 and 3 are connected to the antennas 4, 5 and 6 by combiner means 7 and branching means 8. If required, more than one channel units can be connected to each antenna, while the combiner means 7 combine signals from the different transmitters before they are applied to the antenna, and the branching means 8 apply the signals received by the antenna to the re¬ ceivers of the different channel units. The antenna, combiner means and branching means will be referred to as antenna means below.

The base station 13 shown in the figure further comprises, in addition to the fixed channel units 1, 2 and 3, an additional channel unit 9, the antenna attachments of which can be connected by a switching means 10 to the antenna means of sector 1, sector 2 or sector 3 so that the traffic capacity of the addi¬ tional channel unit is available to the concerned sector. The switching means 10 is a relay-type switch, the operation of which is controlled by a control unit 11.

The control unit 11 monitors the operation of the fixed channel units 1, 2 and 3 during the normal operation of the base station. The control unit is connected to a base station controller (BSC) 12. If one of the channel units fails, the control unit 11 connects the antenna attachments of the additional channel unit 9 by the switch 10 to the sector of the failed channel unit. This measure thus requires a single component, i.e. the relay-type (or semi¬ conductor-type) switch 10.

As appears from the figure, there is no con¬ nection between the antenna attachments of the channel units 1, 2 and 3, which ensures that if there should occur such a failure in one of the channel units that

the antenna attachment of the channel unit would for¬ ward signals of a frequency which could interfere with the operation of the other channel units of the base station, these signals would not be able to propagate to the other channel units of the base station.

It is to be understood that the above descrip¬ tion and the figure related to it are only intended to illustrate a preferred embodiment of the base station according to the invention without limiting the in- vention as such. Accordingly, it is obvious that the number of base station sectors, fixed channel units and additional channel units may differ from the above example, and that the method and the base station according to the invention can also be utilized in other systems than the GSM system, even though the invention has been described above by way of example with reference to the GSM system. The preferred embodiments of the method and the base station accord¬ ing to the invention may vary within the scope of the attached claims.