WO1999011082A1

WO1999011082A1 - Method and apparatus for reconfiguring control channel provision within a cellular telephone system

Info

Publication number: WO1999011082A1
Application number: PCT/SE1998/001485
Authority: WO
Inventors: Nina Kopp; Lars Johansson; Simon Eneland
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 1997-08-22
Filing date: 1998-08-18
Publication date: 1999-03-04
Also published as: BR9811324A; AU8893498A; JP2001514474A; CA2299304A1

Abstract

In response to the blocking (100) of a base station (18) control channel, an attempt is first made to recover (102) the channel (perhaps using a deblock). If the recovery should fail, a reconfiguration of the control channel from a control channel transceiver to a selected traffic channel transceiver is effectuated. The traffic channel transceiver that is selected preferably is of the same type as the control channel transceiver and has as many idle channels as possible (108). Alternatively, the selected traffic channel transceiver may have a different type with as many idle channels as possible (112). The configuration and frequency of the selected traffic channel transceiver are then replaced (116) with the configuration and frequency of the control channel transceiver to complete the reconfiguration. The control channel is then deblocked (118) and the traffic channel(s) previously supported by the found transceiver are blocked.

Description

METHOD AND APPARATUS FOR RECONFIGURING

CONTROL CHANNEL PROVISION WITHIN

A CELLULAR TELEPHONE SYSTEM

BACKGROUND OF THE INVENTION

Technical Field of the Invention

The present invention relates to cellular telephone systems and, in particular, to a method and apparatus for reconfiguring a control channel of a cellular telephone system. Description of Related Art

Cellular telephone systems divide a large service area into a number of smaller discrete geographical areas called "cells" each typically ranging in size from about one-half to about twenty kilometers in diameter. Each cell is at least contiguous and/or overlapping with multiple adjacent cells to provide substantially continuous coverage throughout the service area. A base station is provided for each of the cells.

Each base station includes a plurality of transceivers, with each transceiver capable of operating independently on a different assigned radio frequency selected from the cellular frequency band. Via the transceivers, the base stations engage in simultaneous radio frequency communications on these channels with plural mobile stations operating within the area of the associated cell. The base stations further communicate via data links and voice trunks with a central control station, commonly referred to as a mobile switching center, which functions to selectively connect telephone calls to the mobile stations through the base stations and, in general, control operation of the system. The frequencies assigned to a cell support at least one control channel (CCH) and a plurality of voice/data (traffic) channels (TCHs). In an analog cellular telephone system, like the known advanced mobile phone service (AMPS) communications system, there is one frequency division multiple access (FDMA) analog communications channel (either control or traffic) per frequency. In a digital cellular telephone system, like the known D-AMPS or Global System for Mobile (GSM) communications systems, however, there are a plurality of time division multiple access (TDMA) digital communications channels per frequency.

The control channel serves as the service access point for mobile stations to the cellular telephone system. In order then to provide continuous telephone service to subscribers, it is imperative that failure of the control channel be avoided. Such a failure may, for example, occur when the control channel becomes automatically blocked due to a detected hardware (i.e., transceiver) fault. Many cells support the use of a backup control channel which is then utilized in the event of a such failure.

The backup control channel may be provided through an alternate transceiver which is activated when the transceiver supporting the control channel fails. This solution is not preferred, however, because it requires the inclusion of expensive additional hardware into each base station. If, instead, the alternate transceiver comprises one of the other transceivers in the base station which supports one or more traffic channels, the reconfiguration may result in the loss of calls currently being handled by that alternate transceiver. There is a need then for a reconfiguration procedure which takes into account lost call concerns when the backup control channel is activated. Furthermore, in some instances the reconfiguration is unnecessarily performed. Accordingly, there is a need for a procedure for handling control channel blocking which evaluates other options (such as a deblock or a recovery) before engaging in a reconfiguration.

SUMMARY OF THE INVENTION

To address the foregoing and other concerns, the present invention responds to the blocking of a base station control channel by first attempting to recover the channel. Such a recovery may be accomplished through a deblock. If the recovery fails, the control channel is reconfigured from the non-operational control channel transceiver to another transceiver in the base station which supports traffic channels. The transceiver selected for reconfiguration is preferably that traffic channel supporting transceiver having the same type as the control channel transceiver with as many idle channels as possible. Alternatively, the selected transceiver has a different type with as many idle channels as possible. Once the selected transceiver has been found, its configuration and frequency are replaced with the configuration and frequency of the control channel transceiver. The control channel is then deblocked on this selected transceiver, and the previously supported traffic channels are blocked. In the meantime, the control channel transceiver maintains its configuration and frequency until such time as the equipment again becomes operational. At that point, it returns to supporting the control channel, and the selected transceiver is returned to its original configuration and frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the method and apparatus of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying Drawings wherein:

FIGURE 1 is a schematic diagram of a cellular telephone system; FIGURE 2 is an exemplary transceiver configuration for a base station; and FIGURE 3 is a flow diagram illustrating a control channel reconfiguration operation in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is now made to FIGURE 1 wherein there is shown a schematic diagram of a cellular telephone system. An arbitrary geographic region (hereinafter "the service area") is divided into a plurality of contiguous cells 10 schematically represented by hexagons. A cellular service area can cover a large geographic region, and in many instances there will be a need for a large number of cells. Often times, the number of cells needed exceeds the number of cells provided by dividing the available frequencies in the allocated cellular frequency band amongst the cells in such a manner as to handle expected subscriber usage per cell. In such a case there are simply not enough frequencies for unique assignment to the included cells. In order then to provide sufficient call handling capacity throughout the service area, the cells are grouped into clusters of cells and the frequencies are divided amongst and reused in each of the clusters in accordance with a certain frequency assignment plan. Each of the cells 10 in a cellular telephone system such as that illustrated in FIGURE 1 includes at least one base station (BS) 18 configured to facilitate radio frequency communications with mobile stations 20 moving throughout the service area. The base stations 18 are illustrated as being positionally located at or near the center of each of the cells 10. However, depending on geography and other known factors, the base stations 18 may instead be located at or near the periphery of, or otherwise away from the centers of, each of the cells 10. In such instances, the base stations 18 may broadcast and communicate with mobile stations 20 located within the cells 10 using directional rather than omni-directional antennas. The base stations 18 are connected by communications links 16 (and perhaps through a base station controller — not shown) to at least one mobile switching center (MSC) 22 which functions to control the operation of the system for providing cellular communications with the mobile stations 20. Each base station 18 includes a plurality of transceivers (not shown, see FIGURE 2) capable of operating independently on different radio frequencies from the allocated cellular frequency band assigned to the cell. Operation of the mobile switching center 22 and base station 18 to provide cellular telephone service is well known to those skilled in the art, and will not be described.

Reference is now made to FIGURE 2 wherein there is shown an exemplary transceiver configuration for a base station 18. The base station 18 includes a plurality of transceivers (Tx) 26. Each transceiver 26 is tuned to operate on a selected frequency (or more particularly a pair of associated frequencies assigned for uplink and downlink communications, respectively). The base station 18 further includes a control module 28 which controls transceiver 26 operation and configuration. Among performing other well known transceiver control operations related to assisting in the provision of cellular telephone service, the control module 28 further instructs each transceiver 26 as to which frequency (i.e., pair of frequencies) it should use for operation. In this regard, the transceivers 26 of each base station 18 are selectively tunable in response to a control module 28 command.

At least one of the transceivers 26(1) in the base station 18 is assigned to support a control channel for the cell. Depending on the type of cellular telephone system implemented, this particular transceiver 26(1) may also support one or more voice (traffic) channels for the cell. In an analog cellular telephone system, like the known advanced mobile phone service (AMPS) communications system, where there is one frequency division multiple access (FDMA) analog communications channel per frequency, the transceiver 26(1) assigned to support the control channel supports only that control channel. The remaining transceivers 26(2) each then support an analog voice (traffic) channel for the cell. In a digital cellular telephone system, like the known D-AMPS or Global System for Mobile (GSM) communications systems, where there are a plurality of time division multiple access (TDMA) digital communications channels per frequency, the transceiver 26(1) assigned to support the control channel supports that control channel as well as plural digital voice (traffic) channels. The remaining transceivers 26(2) each also support plural digital voice (traffic) channels. In a dual mode analog/digital cellular telephone system, one transceiver 26(1) assigned to support an analog control channel supports only that control channel, and another transceiver 26(1) assigned to support a digital control channel supports that control channel as well as plural digital voice (traffic) channels.

The remaining transceivers 26(2) each support either a single voice (traffic) channel for analog mode or plural voice (traffic) channels for digital mode.

The control module 28 monitors transceiver 26 operation and detects instances of hardware fault. Responsive thereto, the control module implements an automatic blocking function to disable use of the channels (control and/or traffic) supported by the faulty transceiver 26. An indication of the blocking event may further be provided to the mobile switching center.

The implementation of automatic blocking with respect to a transceiver 26(2) supporting one or more voice (traffic) channels affects base station 18 capacity to handle mobile station communications. Otherwise normal operation of the base station 18 continues. The implementation of automatic blocking with respect to a transceiver 26(1) supporting a control channel, however, may render the base station 18 completely inoperable since the control channel is used as the access point to the cellular telephone system for served mobile stations. Accordingly, special care must be taken in responding to a channel blocking event with respect to a transceiver 26(1 ) supporting a control channel. Reference is now additionally made to FIGURE 3 wherein there is shown a flow diagram illustrating a control channel reconfiguration operation in accordance with the present invention. Upon the implementation in step 100 by the control module 28 of automatic channel blocking with respect to a transceiver 26(1) supporting a control channel (either digital or analog), the control module first attempts in step 102 to recover the blocked channel (perhaps through a deblock). Other recovery operations and procedures are well known in the art, and thus will not be further described here. If the recovery fails, as determined in decision step 104, reconfiguration 106 of the control channel is effectuated. The action of reconfiguration 106 involves the finding in step 108 of another transceiver 26(2) in the base station 18 of the same type as the transceiver supporting the blocked channels, which supports only traffic channels, and has as many idle traffic channels as possible. By "same type" it is meant that transceiver 26(2) having the same number of logical channels as the blocked channel transceiver 26(1) supporting the control channel. Same type transceivers 26 are preferred for reconfiguration because the number of logical channels does not change as a result of the reconfiguration. Traffic channel only transceivers 26(2) are preferred in order to ensure that the reconfiguration does not take away any other control channels supported by the base station 18. Transceivers 26 with idle traffic channels are preferred as this minimizes disturbances to subscriber communications (calls) resulting from the reconfiguration. The service provider may selectively set a threshold value for the number of idle traffic channels which must be present in order for the transceiver 26(2) to be considered. If such a transceiver 26(2) cannot be found, as determined in decision step 110, the action of reconfiguration in step 106 further involves the finding in step 112 of another transceiver 26(2) in the base station 18 not of the same type as the transceiver supporting the blocked channels, which supports only traffic channels, and has as many idle traffic channels (limited again by the threshold) as possible. Once a suitable transceiver 26(2) has been found through either step 108 or step 112, as determined in decision steps 110 or 114, the configuration and frequency of the found suitable reconfiguration transceiver 26(2) is replaced in step 116 with the configuration and frequency of the blocked channel transceiver 26(1). This replacement operation requires the control module 28 to command the found transceiver 26(2) at issue to effectuate a frequency retime. Once the replacement is complete, the previously blocked control channel is deblocked (along with any similarly supported traffic channels that were also blocked), and the traffic channel(s) supported by the reconfiguration transceiver are blocked (step 118). If no suitable reconfiguration transceiver 26(2) is found (see, decision steps 110 and 114) no reconfiguration is implemented (step 120). In the meantime, the transceiver 26(1) maintains its control channel configuration and frequency assignment awaiting the time when the equipment again becomes operational (path 122). At that point, a replacement (step 116) back to the original configurations and frequencies for the transceivers 26(1) and

26(2) is performed. The previously blocked traffic channels are then deblocked (step 118).

A more complete understanding of the present invention may be obtained by examination of two examples in connection with the execution of the process of FIGURE 3.

In a first example, assume that the present invention is implemented with respect to a base station providing analog cellular telephone service like the known advanced mobile phone service (AMPS) communications system, where there is one frequency division multiple access (FDMA) analog communications channel per frequency. The base station accordingly includes one transceiver 26(1) assigned to support the control channel, along with a plurality of remaining transceivers 26(2) each supporting an analog voice (traffic) channel.

A fault of the transceiver 26(1) assigned to support the control channel is detected and automatic blocking of the control channel is implemented in step 100. An attempt is then made in step 102 to recover the blocked channel. Assuming this fails (step 104) a reconfiguration 106 of the control channel is effectuated. First, another transceiver 26(2) of the same type as the transceiver 26(1) assigned to support the control channel, which supports only traffic channels, and is idle, is found in step 108. If no such transceiver 26(2) is found in step 108, another transceiver 26(2) of a different type as the transceiver 26(1) assigned to support the control channel, which supports only traffic channels, and is idle, is found in step 112. Assuming now that such a transceiver 26(2) is found (preferably from step 108), the configuration and frequency of the transceiver 26(1) assigned to support the blocked control channel replaces (step 116) the configuration and frequency of the found transceiver 26(2). This replacement operation requires that the transceiver 26(2) at issue effectuate a frequency retune to the assigned control channel frequency. Once the replacement is complete, the previously blocked control channel is deblocked, and the traffic channel previously supported by the found transceiver 26(2) is blocked (step 118). Eventually, when the transceiver 26(1) again becomes operational, its support of control channel operation is returned (path 122). A replacement (step 116) is made back to the prior configurations and frequencies, and the traffic channel supported by transceiver 26(2) is deblocked (step 118).

In a second example, assume that the present invention is implemented with respect to a base station providing digital cellular telephone service like the known D- AMPS or Global System for Mobile (GSM) communications systems, where there are a plurality of time division multiple access (TDMA) digital communications channels per frequency. The base station accordingly includes one transceiver 26(1) assigned to support the control channel and a plurality of digital voice (fraffic) channels, along with a plurality of remaining transceivers 26(2) each supporting a plurality of digital voice (traffic) channels. A fault of the transceiver 26(1) assigned to support the control channel and plural traffic channels is detected and automatic blocking of the control/traffic channels is implemented in step 100. An attempt is then made in step 102 to recover the blocked channels. Assuming this fails (step 104) a reconfiguration 106 of the control channel is effectuated. First, another transceiver 26(2) of the same type as the transceiver 26(1) assigned to support the control/traffic channels, which supports only traffic channels, and has more than a threshold number of idle traffic channels, is found in step 108. If no such transceiver 26(2) is found in step 108, another transceiver 26(2) of a different type as the transceiver 26(1) assigned to support the control channel, which supports only fraffic channels, and has more than a threshold number of idle traffic channels, is found in step 112. Assuming now that such a transceiver 26(2) is found (preferably from step 108), the configuration and frequency of the transceiver 26(1) assigned to support the blocked control/traffic channels replaces (step 116) the configuration and frequency of the found transceiver 26(2). This replacement operation requires that the transceiver 26(2) at issue effectuate a frequency retune to the assigned control channel frequency. Once the replacement is complete, the previously blocked control/traffic channels are deblocked, and the traffic channels previously supported by the found transceiver 26(2) are blocked (step 118). Eventually, when the transceiver 26(1) again becomes operational, its support of control channel operation is returned (path 122). A replacement (step 116) is made back to the prior configurations and frequencies, and the traffic channels supported by transceiver 26(2) are deblocked (step 118).

Although the method and apparatus of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiment(s) disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method for control channel reconfiguration, comprising the steps of: responding to a blocking of a control channel supported by a first transceiver in a base station by finding a second transceiver in the base station supporting as many idle traffic channels as possible; replacing a configuration and frequency of the second transceiver with a configuration and frequency of the first transceiver; and deblocking the control channel which is now supported by the second fransceiver.

2. The method as in claim 1 further including the step of blocking the one or more traffic channels previously supported by the second transceiver and now supported by the first transceiver.

3. The method as in claim 1 further including the step of first attempting a recovery of the blocked confrol channel before finding the second transceiver.

4. The method as in claim 1 wherein the step of finding the second transceiver comprises the step of finding a second transceiver having a same type as the first fransceiver with as many idle fraffic channels as possible.

5. The method as in claim 4 wherein the same type comprises a second transceiver having the same number of logical channels as the first fransceiver.

6. The method as in claim 4 wherein the step of finding further comprises the step of finding a second transceiver having a different type as the first transceiver with as many idle fraffic channels as possible.

7. The method as in claim 1 wherein the step of finding the second transceiver comprises the step of finding a second transceiver having more than a threshold number of idle traffic channels.

8. The method as in claim 1 further including the step of restoring the configuration and frequency of the second transceiver following termination of the first fransceiver related blocking.

9. A base station for a cell, comprising: a selectively tunable first fransceiver supporting a control channel of the cell; a plurality of selectively tunable second transceivers each supporting at least one fraffic channel of the cell; and a control module operating in response to a blocking of the control channel to select a certain one of the plurality of selectively tunable second transceivers having as many idle traffic channels as possible and reconfigure support of the control channel to the certain second fransceiver by having the certain second fransceiver adopt a configuration and frequency of the first fransceiver.

10. The base station as in claim 9 wherein the control module is further operating to select that certain second transceiver of the plurality of second transceivers having more than a threshold number of idle traffic channels.

11. The base station as in claim 9 wherein the control module is further operating to select that certain second transceiver of the plurality of second transceivers having a same type as the first fransceiver with as many idle traffic channels as possible.

12. The base station as in claim 11 wherein the same type comprises a second transceiver having the same number of logical channels as the first transceiver.

13. The base station as in claim 11 wherein the confrol module is further operating to select that certain second transceiver of the plurality of second transceivers having a different type as the first fransceiver with as many idle fraffic channels as possible.

14. The base station as in claim 9 wherein the confrol module is further operating to restore a prior configuration and frequency of the second transceiver following termination of the first fransceiver related blocking.

15. A method for control channel reconfiguration, comprising the steps of: responding to a blocking of a control channel supported by a first fransceiver in a base station by finding a second fransceiver in the base station supporting more than a threshold number of idle traffic channels; replacing a configuration and frequency of the second fransceiver with a configuration and frequency of the first transceiver; and deblocking the control channel which is now supported by the second fransceiver.

16. The method as in claim 15 further including the step of blocking the traffic channels previously supported by the second transceiver.

17. The method as in claim 15 further including the step of first attempting a recovery of the blocked control channel before finding the second transceiver.

18. The method as in claim 15 wherein the step of finding the second transceiver comprises the step of finding a second transceiver having the same number of logical channels as the first transceiver.

19. The method as in claim 15 further including the step of restoring the configuration and frequency of the second transceiver following termination of the first fransceiver related blocking.

20. A base station for a cell, comprising: a first transceiver supporting a confrol channel of the cell; a plurality of selectively tunable second transceivers each supporting at least one fraffic channel of the cell; and a control module operating in response to a blocking of the confrol channel to select a certain one of the plurality of selectively tunable second fransceivers having more than a threshold number of idle traffic channels and reconfigure support of the control channel to the certain second fransceiver by having the certain second transceiver adopt a configuration and frequency of the first fransceiver.

21. The base station as in claim 20 wherein the control module is further operating to select that certain second fransceiver of the plurality of second transceivers having the same number of logical channels as the first transceiver.

22. The base station as in claim 20 wherein the control module is further operating to restore a prior configuration and frequency of the second fransceiver following termination of the first transceiver related blocking.