GB2366695A - Control channel utilisation - Google Patents

Abstract

A cellular telecommunication system, such as GSM, utilises dedicated control channel (SDCCH) resources to relay, in-call, management information upstream from a subscriber unit to a base station sub-system and, ultimately, a switching centre. Call establishment procedures also initially utilise the dedicated control channel resources, such procedures generally requiring a complementary pair of dedicated control channels for the uplink and downlink directions. In instances where a BSS perceives that SDCCH capacity is impaired by SMS messaging or the relaying of management information, such as location updates, the BSS is configured to suppress access to dedicated control channel resources for management information purposes in favour of call-establishment procedures, especially when traffic channel resources are available for use in a call.

Description

2366695 CELLULAR COMMUNICATION SYSTEM AND METHOD OF CONTROL CHANNEL

UTILISATION THEREIN

Background to the Invention

5 This invention relates, in general, to a cellular communication system and method of control channel utilisation therein, and is particularly, but not exclusively, applicable to optimisation of dedicated control channel (SDCCH) resources in the management of subscriber equipment.

10 Summary of the Prior Art

As one way of addressing increasing demand for cellular services, communication systems (such as the Global System for Mobile communication, GSM) are now employing multi-layer cellular techniques in which an umbrella (or macro) cell overlays a plurality of smaller cells. Generally, the aim of this 15 particular configuration is to enhance capacity, to increase spectral efficiency and to reduce administrative overhead. In the first respect, capacity is increased through the ability of the smaller cells to use different traffic (and control) channel frequencies that additionally (and generally) benefit from a tighter reuse pattern than that used in the umbrella cell. In other words, successively 20 smaller cells are generally able to benefit from statistical frequency multiplexing to obtain tighter frequency re-use schemes. Multi-layer techniques therefore directly address the limited frequency spectrum available in the wireless domain by employing frequency re-use in ever increasingly tight frequency re-use patterns. However, increasing traffic capacity causes an associated and 25 proportional increase in management overhead and the use of dedicated control channels.

The deployment of such multi-layer cellular techniques is likely to remain prevalent in resolving capacity issues for present and proposed cellular systems, 30 including third generation systems such as UMTS (Universal Mobile Telecommunication System).

By way of elaboration of multi-layer cellular system operation, characteristics of (mobile) subscriber unit operation may be determined to assess whether the subscriber unit is better served by the umbrella cell or an underlying micro- (or pico-) cell. For example, to ensure call set-up, it is generally better to 5 communicate directly with a base station and associated control channel serving a macro-cell since boundary transitions and potential loss of the control channel are less likely. Once call set-up has been established, then handoff to a micro(or pico-) cell can occur to avoid traffic handling congestion within the macrocell. Of course, if the subscriber terminal is actually mobile, then its rate of 10 micro- (or pico-) cell boundary transitions may be such that administrative overhead (through the use of dedicated control channels and the actual time required for handover to take place) is significant within the system as a whole. In fact, increasing the number of handovers (and correspondingly the number of location updates) in a short amount of time decreases the call reliability (and 15 increases control overhead) and increases the number of breaks in communication, thus reducing the quality of communication and the perceived quality of the service. Indeed, in extreme cases of excessive handover, calls can be lost or blocked through the inability of the system to produce a stable communication channel environment or to adequately support control channel 20 demand, respectively. Fast moving mobile subscriber units therefore generally warrant a more stable call environment offered by the larger cell radius of the serving cell.

As will now be appreciated, a subscriber unit may therefore be located within 25 both a macro-cell and at least one of a micro-cell of pico-cell.

In one particular cellular system, a plurality of adjacent serviceable cells are assigned traffic channel carriers according to a regimented (or sequenced) frequency re-use pattern but no dedicated individual control channel carriers for 30 individual cells. In other words, a single broadcast control channel (BCCH) overlays a multitude of pico-cellular type traffic channels, with individual picocellular base station heads (having typical cell radii of less than one hundred metres) operating in a simulcast mode to transmit the BCCH control information.

Effectively, therefore, a single wide-area BCCH services a plurality of cellular capsules, with the BCCH transmitted in the downlink from, effectively, a global base station. This form of system design is relatively easy to implement, 5 especially in an indoor environment, and is not wasteful of frequency resources that would otherwise be required in the provision of individual BCCHs in individual cells according to a BCCH frequency re-use pattern. However, access to control channel resources is clearly limited.

10 From an administrative perspective, therefore, subscriber management (both in terms of handoff and call set-up and control) is significant, with it being preferably to avoid such things as repeated handovers during on-going calls in order to maintain availability of control channel resources.

15 As will be understood, BCCH (and complementary uplink control channel CCCH) control information is actually associated with many aspects of a cellular call, including channel allocation and handover. Moreover, a conventional BCCH/CCCH channel is actually part of a control channel (CC) multiframe, with each CC frame being time division multiplexed (TDM) into eight time slots (in the 20 specific instance of GSM) and wherein the BCCH/CCCH is generally assigned to time slot zero (TS-0s). Turning to the BCCH/CCCH in more detail, the BCCH and up-link CCCH multiframes are constructed from a cyclic transmission of fifty-one (or sometimes, and more appropriately, one hundred and two) TS- 0 information bursts in contiguous CC frames. Within the BCCH/CCCH 25 multiframe, various TS-0 bursts (each of 0.577 millisecond duration) are assigned to specific management and control tasks. These bursts may be packaged so that several successive bursts each relate to a particular management or control function.

30 The BCCH is, in fact, realised by a combination of bursts in successive CC frames made up from: i) the frequency correction channel (FCCH) that addresses the correction of a receiving unit's internal time base; ii) the synchronisation (SCH) channel for time slot synch ro n isation; iii) the common control channel (CCCH), i.e. the PCH (paging control channel) and the AGCH (access grant control channel), for controlling call origination and call -paging functions; iv) the standalone dedicated control channel (SDCCH) that supports 5 the transfer of data to and from a subscriber unit during call set-up and location up-date; and v) the slow associated control channel (SACCH) that conveys power control and timing information. The SDCCH and SACCH are assigned both to the same time slot within each frame and to the same BCCH/CCCH carrier frequency, although the SDCCH and SACCH are distinguishable in time.

10 The SDCCH can, in fact, be transmitted on any time slot.

In a complementary sense, the uplink CCCH multiframe supports a predominant SDCCH and SACCH arrangement in additional to three presently unassigned (idle) bursts. The uplink CCCH is a logical channel (and separate channel to the 15 random access control channel, RACH). The 51-frame uplink SDCCH multiframe takes two repetitions to complete an entire (GSM-compliant) sequence.

In the context of the BCCH, its CCCH (i.e. PCH and AGCH) should not be 20 confused with the up-link CCCH multiframe.

A large proportion of call set-up procedures take place whilst a subscriber unit, such as a mobile, has access to (is on) a SDCCH. It is therefore imperative that the dimensioning of SDCCHs in a cell is carefully considered during any 25 planning process. The three principal factors that effect SDCCH dimensioning are:

i) to support call set-up in a cell; ii) the requirement to support the GSM defined short message service (SMS) feature; and 30 iii) to enable location update.

As will be appreciated, the SDDCH multiframe (for the uplink) should always be open to a subscriber during a call, with the SDCCH providing call control information (e.g. triggered by function selection by the subscriber) and measurement information (such as location update information based on either 5 the BA list or currently visible base stations). Moreover, with the scarcity of paired SDCCH resources, the bi-directional SDCCH path is released shortly after call establishment and other SDCCH pairings established, in call, on a need-driven basis. For the avoidance of doubt, the SDCCH multiframe should not be confused with the SACCH channel that is time mulitplexed into the uplink 10 traffic channel (TCH) for reporting, for example, quality of service metrics for mobile assisted handover and the like.

For an in-building cellular system, adequate provisioning for the first two factors (with respect to SDCCH resource availability) is vital in view of location update 15 being less important as mobiles (and subscribers generally) within a building are associated with a single (and known) base station controller (BSC). However, mobile units may still perform periodic location updates regardless of mobile movement, with such uplink data transmission used for management purposes.

20 One drawback with the use of a single BCCH overlaying a plurality of traffic cells is that there is clearly a limitation in the number of available SDCCHs, with this having an associated limiting effect on SDCCH allocation in the uplink. As previously described, it is usual for the logical SDCCH channel to be subsumed/combined within the BCCH/CCCH, although it is feasible to consider 25 the multiplexing of eight SDCCHs onto a single dedicated time slot; the latter respect is, however, considered wasteful of resources and would significantly reduce the capacity of a system in its entirety. As will now be appreciated, the combination of the logical SDCCH into a (simulcast) BCCH limits the availability of the logical SDCCH to four groups of four time slot bursts in every fifty-one 30 BCCH multiframes and eight time slot bursts in every fifty-one CCCH multiframes. A time occupancy of the four (4) SDCCHs in the BCCH multiframe (in GSM) represents 9.23ms in every 235.365ms (or a utilisation of 3.92%), or 18.46ms (7.84%) for eight (6) SDCCHs in the uplink CCCH multiframe. A similar access issue arises with SACCHs, although there is access to only four distinct SACCHs in every fifty-one CCCH multiframe (and two SACCHs in every fiftyone BCCH frames).

Unfortunately, in high capacity applications, overload of the control channel can occur, and this is certainly the case in multi-layer cellular environments where there is a periodic migration of subscribers into a particular service area. Although this capacity issue can be addressed by using more frequencies or by 10 assigning individual control channels to small underlaid cells, the associated costs and increase in design complexity seldom warrant the provision of a permanent solution that, in any event, may run in an inefficient manner for a majority of the operating time. Consequently, system operators are left to resolve the viability of providing additional channel resources that may be 15 seldom used (rendering the system less commercially attractive), or in operating a system that can stall at peak times when overload of the control channel causes either blocking of call set-up requests or refusal of a call set-up process in its entirety. In both latter events, a subscriber therefore perceives a lower standard of service.

In relation to capsule-based cellular system (especially) in which traffic cells are administered by a single BCCH, it is preferable to have the SIDCCH sent on a simulcast carrier, although this unfortunately leads to an arrangement in an inbuilding cellular system, for example, having an insufficient SDCCH capacity. It would therefore be desirable to increase the availability to SDCCHs within frame structures of existing (and future) cellular communications standards, such as GSM and UIVITS, without adversely affecting system capacity, with the increase in SIDCCH capacity associated with at least the uplink CCCH.

30 The issue of adequately provisioning SIDCCH resources is applicable to all cellular environments, although it becomes increasingly relevant with high cell loading, e.g. resulting from the use of multi-layer techniques. Indeed, in instances where there are no SIDCCH's available, a system operator loses revenue because they are unable to initiate calls on traffic channel resources that may, in fact, be vacant and available for use.

5 Summary of the Invention

According to a first aspect of the present invention there is provided a cellular communication system having at least one cell having by a base station subsystem administering control channel resources therein, the cellular communication system comprising: means for determining control channel 10 utilisation within the at least one cell; and means for suppressing transmission of non-call establishment control channel messages by denying access to control channel resources.

Preferably, the means for suppressing is operationally responsive to a threshold 15 level. The means for suppressing may also or alternatively be operationally responsive to an availability of traffic channel resources within the at least one cell.

Generally, the means for suppressing transmission denies access to control 20 channel resources on a cell-by-cell basis, although it is preferred that access control channel resources be denied within the at least one cell.

In a second aspect of the present invention there is provided a controller for administering allocation of control channel resources in a cell, the controller 25 comprising: means for determining control channel utilisation within the at least one cell; and means for suppressing transmission of non-call establishment control channel messages by denying access to control channel resources.

The controller is preferably associated with a base station controller, although it 30 could be associated with a switch or an operations and maintenance centre.

In another aspect of the present invention there is provided a method of allocating control channel resources in a cell, the method comprising: determining control channel utilisation within the at least one cell; and suppressing transmission of non-call establishment control channel messages 5 by denying access to control channel resources.

Suppressing non-call establishment control channel messages is preferably operationally responsive to at least one of a threshold level of control channel resource utilisation and an availability of traffic channel resources within the at 10 least one cell.

Suppressing transmission denies access to control channel resources on a cellby-cell basis and preferably within the at least one cell.

15 The method may further include attempting to acquire control channel resources through re-transmission of a RACH request. In another embodiment, retransmission of a RACH request may result in an acquisition of control channel resources from a secondary base station in a cell adjacent to a serving cell for a call. In a particular embodiment, access to control channel resources results in 20 notification of at least management information to the secondary base station when a primary base station of the serving cell denies access to traffic channel resources.

Advantageously, the present invention therefore provides a system that can vary 25 its capacity in handling call set-up messages (especially in the context of SIDCCH in GSIVI) without resorting to additional, preallocated time slot utilisation and derivatives thereof. The preferred embodiment of the present invention can be easily integrated into existing systems, since the invention can be controlled by a software upgrade (provided, for example in the form of a computer program 30 product or by way of modulated applets) to install the requisite system functionality; hardware remains essentially unaffected although operational capabilities are altered.

Consequently, deployment of the underlying inventive algorithm does not generally compromise system performance, but enhances system operation and improves operator revenue and subscriber satisfaction.

Brief Description of the Drawings

An exemplary embodiment of the present invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 illustrates inter-relationships between time slots, frames and a multi 10 frame in a conventional time division multiplex (TDM) communication system, such as GSM; FIG. 2 illustrates a combined uplink multiframe for GSM showing control channel allocation; FIG. 3 is representative of a multi-layer cellular communication system 15 employing an overlaid control channel (BCCH) and a plurality of traffic serving cells; FIG. 4 is a block diagram of a cellular communication system that may be adapted to support the concepts of the preferred embodiment of the present invention; 20 FIG. 5 is a flow diagram of an operating methodology employed by a preferred embodiment of the present invention in re-allocating SDCCH resources; and FIG. 6 is a flow diagram of an uplink RACH request for SIDCCH allocation according to a preferred embodiment of the present invention.

Detailed Description of a Preferred Embodiment

Referring briefly to FIG.1, this diagram illustrates inter-relationships between time slots 10-24, frames 26-30 and a multi-frame 32 in a conventional time division multiplex (TDM) communication system, such as GSM. The specific 30 structure has already been discussed above, with the diagram more clearly demonstrating the construction of a BCCH multi-frame. It is worthy to note the groupings of time slot bursts to construct SDCCHs (DO-D3) and SACCHs (AO-Al) in the exemplary fifty-one time-slot multiframe 32. A contiguous multi frame generally follows an identical structure, although optionally third (A2) and fourth (A3) logically independent SACCHs take the place of the SACCHs AO and 5 Al.

FIG. 2 illustrates a combined uplink control channel multiframe 40 for GSM showing burst allocation therein. Essentially, the combined uplink control channel multiframe of FIG. 2 is used in instances where traffic density is low, 10 perhaps in a rural cell with few RF carriers and (usually) only a light traffic load, as is provided for illustrative purposes. Consequently, the combined multiframe contains a mixture of RACH, SDCCH and SACCH bursts; the latter two forming logical control channels.

15 Turning to FIG. 3, there is shown a multi-layer cellular communication system 80 employing an overlaid control channel (BCCH) 82 and a plurality of traffic serving cells 84-128; this system may be adapted to support the concepts of the present invention. The cellular system includes at least one base transceiver station (BTS) (head) controller 130-132 coupled to provide operational control 20 and synchronisation to transceiver heads (such as head 136 in pico- cell 106) in each of the cells 84-128. If multiple BTS (head) controllers 120-132 are implemented in the cellular communication system, then interconnection of the heads through, typically, a wireline or optical interface ensures that consistent system operation is maintained, as will be readily appreciated. Each transceiver 25 head 136, which typically has limited signal processing functionality to reduce head size and complexity, is coupled to a serving BTS (head) controller 130-132 through a suitable communication resource (again typically realised by a wireline connection, such as a coax, optical fibre, twisted pair or local area network). The BTS (head) controller(s) 130-132 is/are coupled, ultimately, into an MSC or the 30 like and then into a comprehensive telecommunications network, such as an extended cellular network, a broadband network (e.g. an asynchronous transmission mode (ATM) domain) or a trunked network. The term "head" should be construed in a broad sense to encompass a device that has a considerable range to functionality, including that of a fully configured base station.

5 In deployment, the pico-cellular configuration of cells could, for example, be arranged to service a particular floor or floors of a shopping complex or building, or a commercial group within an office suite. As regards operation, the transceiver heads 136 of each cell generally operate in a simulcast mode of operation to establish the single control channel coverage indicated in the diagram. Generally, as will be appreciated, each transceiver head has a low power output both in terms of the control channel and associated traffic channels, with the network of pico-cells 84-128 co-operating to produce. a merging of service areas (both traffic and control) at adjacent cell boundaries to provide area specific coverage. Interactions, such as call set-up procedures handover, between subscriber units within the cellular system 80 and the transceiver heads 136 (as well as functional partitioning between the transceiver heads 130 and the BTS (head) controller for signal processing requirements) will be readily appreciated by the skilled addressee.

FIG. 4 illustrates a conventional communication network 150 that may be adapted to support the underlying principles of the present invention.

Essentially, the network 150 comprises a plurality of adjoining cells 152172 that form a coverage area of a cellular communication system. Each cell 152- 172 (which may support, for example, macro- or micro-cellular communication) includes a base station sub-system (BSS) 174-190 comprising a base site controller (BSC) 192 coupled to at least one base transceiver station (BTS) 194.

Typically, each BSC 192 will control operation of three or more (plus redundant) BTSs, perhaps configured to provide sectorised coverage. Each BSC 194 has a controller 196 and associated memory 198, with each BSC coupled (generally via a transcoder, not shown) to a mobile switching centre 200-202. Subject to design considerations, multiple MSCs may be interconnected to provide an extensive (far-reaching) cellular network, as will be appreciated. Each MSC 200- 202, in conventional fashion, is coupled to a storage facility providing visiting (VLR, 204) and home-location register (HLR, 206) facilities. The MSC also provides a gateway to a PSTN (or the like) 206, which PSTN may in itself provide access to an internet domain 208. An operations and maintenance 5 centre (OMC) 209 is coupled to the MSC 200-202.

As regards each BTS 194, transceiver circuitry 210-211 supports the establishment and connection of radio communication channels to subscriber units 210-220, including fixed but predominantly mobile units, serviceable by an 10 in-range BTS. The subscriber units 212-220 therefore have complementary transceiver apparatus 222 (if configured for bi-directional communication) controlled by a suitable micro-controller 224 that executes operational commands typically stored in memory 226.

15 Although only a few subscriber units 212-220 are shown distributed through the cells, each BSS is likely to be providing simultaneous service to many subscriber units. The subscriber units 212-220 will, in conventional fashion, undergo hand-off between cells and call establishment from idle mode operation. Indeed, with all cellular systems, roaming subscriber units will be 20 serviceable through appropriate registration with respective VLRs and HLRs.

To address the periodic increase in control channel utilisation, the preferred embodiment of the present invention contemplates the re-assignment of SDCCH resources for call establishment purposes only. Re-assignment is preferably 25 actioned on a cell-by-cell basis, subject to instantaneous loading. More specifically, since the SDCCH is generally not only used for call establishment but also to report, for example, management information (such as location up dates), non-critical management information is suppressed (within a cell) by the control architecture of the present invention only allowing SDCCH usage for call 30 establishment.

Present systems are configured such that servicing of subscriber units within a particular cell could, at times, result in all SDCCHs being assigned for reporting management purposes when, in fact, the servicing BSS has available traffic channel resources which a new subscriber unit wishes to access/make use of.

5 The present invention is therefore geared to ensure that service is established when traffic resources are available. Consequently, management reports (generally non-critical to system operation but which use uplink and downlink SIDCCH capacity) are ignored, delayed or suppressed whilst subscriber units wishing to obtain system access are registered with the BSS using a SDCCH 10 prioritorisation scheme.

An exemplary form of management information that is suppressed from using the SIDCCH in times of restricted SIDCCH availability is location information either: i) periodically sent to the BSS for updating the HLRNLR; or ii) arising 15 from a change in base station environment as a consequence of subscriber unit movement.

In a preferred embodiment, since a base station controller is aware (as a consequently of its current operational status) of its immediate traffic channel 20 resource pool and SDCCH usage, the BSC determines whether it is appropriate to allocate SIDCCH resources to tasks other than call establishment procedures. From an implementation perspective, an indication of current operational status is generally stored in memory 198 or internal cache accessible to the controller 196). In view of the release of the SIDCCH shortly after call establishment, 25 RACH requests by subscriber units are inherently not associated with call establishment but rather management information which must be communicated on a new uplink SDCCH; the controller therefore being able to react accordingly, subject to SIDCCH utilisation If the RACH transmitted by the subscriber unit is ignored, the subscriber unit will simply time-out and either RACH again or select 30 another cell to attempt a management information download, e.g. a location update. Clearly, if the initial RACH is successful, then management information may be relayed over the subsequent assigned SIDCCH of the serving BSS. A RACH that secures access only to a secondary BSS (other than its serving BSS) results in the subscriber unit being able to communicate the management information into the system through the secondary BSS, if available, even though its serving BSS is potentially fully congested (with no perceived SDCCH 5 capacity). Of course, any failed RACH attempt may result in the management information being temporarily stored in memory 226, or disregarded by the subscriber unit in favour of subsequently obtained management information.

As regards downlink establishment of SDCCH in-call, then the BSC operates on 10 the basis of a paging request (on the PCH), which paging request causes an addressed subcriber unit to RACH to establish the bidirectional SDCCH resources.

The present invention allows for optimisation of a cellular system in terms of 15 traffic channel utilisation and specifically call establishment procedures which generate revenue for the cellular operator. The present invention therefore simplifies an operator's decision on dimensional split between TCH and SDCCH (in their limited radio frequency resources) by allowing a greater proportional utilisation of TCHs. In other words, the present invention improves trunking 20 capacity for voice and data traffic, i.e. more subscribers or a better service is provided for a nominal allocation of channel resources.

FIG. 5 is a flow diagram of an operating methodology 300 employed by a preferred embodiment of the present invention in re-allocating SDCCH 25 resources. Whilst it is preferred that the controller 196 of the BSC is arranged to determine 302 SDCCH occupancy, it is contemplated that this and subsequent functional steps could be orchestrated within the MSC 200-202. The preferred embodiment has a load occupancy thresholddetermined by the operator, which load occupancy threshold is selected within a range of between 0 and 100%.

30 Load occupancy is basically usage of the SDCCH for non-call establishment procedures/reports. A decision is then taken as to whether 304 the current load occupancy exceeds the load occupancy threshold. In the negative 306, the SIDCCH is assigned (typically in response to a RACH request) and the system is set to accept 308 management information/SIVIS messaging (or the like). The BSC assigns 310 the SIDCCH and communication between the subscriber unit and BSS follows 312. After termination of the SIDCCH communication, the 5 SDCCH is released 314. An affirmative path 316 from decision block 304 leads to a determination as to whether 318 traffic channel resources are available. If there are no available TCHs, then limitation of SDCCH functionality is pointless and flow proceeds back to step 308 (and onward therefrom). If traffic channel resources are available 320, then the non-call establishment SDCCH request is 10 suppressed and the RACH ignored 322.

From a subscriber unit perspective (FIG. 6), the present invention causes the subscriber unit to RACH 350 for SDCCH allocation for SIVIS, call establishment or management information upload. The subscriber unit then looks to see 15 whether an SIDCCH is assigned 352, subject to the process of FIG. 5. With an assigned SDCCH, data is communicated 312. In the event that the SDCCH allocation is not forthcoming (either by time-out or explicit refusal), the subscriber unit may decide 354 whether the data for uplink transmission can be dropped. In the affirmative 356, the requirement (and hence the data) for uplink 20 communication us dropped and the process ends 358. A negative path 360 from decision block 354 results in a re-RACH 362 and a determination as to whether an SIDCCH is assigned 364. On the basis that the serving BSS is able to communicate to other BSSs in the BA list, then the re-RACH attempt may be serviced by a secondary (in-range) BSS in an adjacent cell (which could be an 25 underlying or overlying cell). Of course, the re-RACH could result in an SIDCCH being assigned from the serving cell if load occupancy (step 304) has changed.

If the re-RACH yields assignment of an SIDCCH, data is communicated between the BSS-subscriber unit. In the negative 366, data is stored 368 and flow proceeds to decision block 354 or straight to the re-RACH request, as desired.

30 Clearly, if data is of transitory relevance, then re-RACH attempts are pointless and the data can be dropped and the process ended.

Accordingly, the preferred embodiment of the present invention allows the BSC to make the decision on whether it will accommodate uplink location updates or solely voice/data call origination requests on SDCCH resources. Furthermore, the present invention can be extended to defer transmission of SMS messages 5 since data transmissions are not subject to time sensitive transmissions for coherent data recovery. The present invention preferably forces a subscriber unit in idle mode to look to another serviceable location (i.e. adjacent cell BSS) to relay management control information. The present invention also provides additional capacity at cells adjacent to a boundary, since such cells are 10 statistically less likely to have location information communicated upstream to the BSC in an SDCCH transmission.

The present invention therefore advantageously supports an increase in control channel handling capacity, especially in relation to SDCCH. Indeed, in the 15 preferred embodiment, the increase in capacity has been obtained without requiring an additional, dedicated channel (although nonessential management information is delayed or ignored which could momentarily detract from optimal system performance).

20 Alternative embodiments of the invention may be implemented as a computer program product for use with a processor-based system. Such implementation may include a series of computer instructions fixed either on a tangible medium, such as a computer readable media (e.g. a diskette, CD-ROM, or fixed disk, magneto-optical disks, ROMs, EEPROMs, flash memory or magnetic or optical 25 cards), or fixed in a computer data signal embodied in a carrier wave that is transmittable to a computer system via a modem or other interface device, such as a communications adapter connected to a network over a medium. The medium may be either a tangible medium (e.g. optical or analog communications lines) or a medium implemented with wireless techniques (e.g.

30 microwave, infrared or other transmission techniques). The series of computer instructions embodies all or part of the functionality previously described herein with respect to the system.

Software embodiments of the invention may be implemented in any conventional computer programming language. For example, preferred embodiments may be implemented in a procedural programming language (e.g.

5 "C") or an object oriented programming language (e.g. "C++"). Furthermore, such instructions may be stored in any memory device, such as semiconductor, magnetic, optical or other memory devices, and may be transmitted using any communications technology, such as optical, infrared, microwave, or other transmission technologies. It is expected that such a computer program product 10 may be distributed as a removable medium with accompanying printed or electronic documentation (e.g. shrink wrapped software), preloaded with a computer system (e.g. on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the network (e.g. the Internet, World Wide Web or through a radio frequency channel resource).

Although the steps of the preferred operating methodology are performed in software (e.g. general or specific-purpose processor or logic circuits programmed with suitable machine-executable instructions), the steps may be performed by a combination of hardware and software.

It will, of course, be appreciated that the above description has been given by way of example only and that modifications in detail may be made within the scope of the present invention. For example, the principals of the present invention can be employed within any cellular communication system, and

25 reference to SIDCCH should be construed in a broad sense to encompass functionally equivalent channels in complementary systems.

Claims (1)

1. Claims

   1. A cellular communication system having at least one cell having by a base station sub-system administering control channel resources therein, the cellular communication system comprising:

   5 means for determining control channel utilisation within the at least one cell; and means for suppressing transmission of non-call establishment control channel messages by denying access to control channel resources.

   10 2. The cellular communication system of claim 1, wherein the means for suppressing is operationally responsive to a threshold level.

   3. The cellular communication system of claim 1 or 2, wherein the means for suppressing is operationally responsive to an availability of traffic channel 15 resources within the at least one cell.

   4. The cellular communication system of any preceding claim, wherein the control channel resources are SDCCH resources.

   20 5. The cellular communication system of any preceding claim, wherein the means for suppressing transmission denies access to control channel resources on a cell-by-cell basis.

   6. The cellular communication system of any preceding claim, wherein the means for suppressing transmission denies access to control channel resources within the at least one cell.

   7. A controller for administering allocation of control channel resources in a cell, the controller comprising:

   30 means for determining control channel utilisation within the at least one cell; and means for suppressing transmission of non-call establishment control channel messages by denying access to control channel resources.

   8. The controller of claim 7, wherein the means for suppressing is 5 operationally responsive to a threshold level.

   9. The controller of claim 7 or 8, wherein the means for suppressing is operationally responsive to an availability of traffic channel resources within the at least one cell.

   10. The controller of claim 7, 8 or 9, wherein the control channel resources are SDCCH resources.

   11. The controller of claims 7 to 10, wherein the means for suppressing 15 transmission denies access to control channel resources on a cell-bycell basis.

   12. The controller of any of claims 7 to 11, wherein the means for suppressing transmission denies access to control channel resources within the at least one cell.

   13. A base station controller comprising the controller of any of claims 7 to 12.

   13. A method of allocating control channel resources in a cell, the method comprising: determining control channel utilisation within the at least one cell; and suppressing transmission of non-call establishment control channel messages by denying access to control channel resources.

   30 14. The method of claim 13, wherein suppressing non-call establishment control channel messages is operationally responsive to a threshold level of control channel resource utilisation.

   15. The method of claim 13 or 14, wherein suppressing non-call establishment control channel messages is operationally responsive. to an availability of traffic channel resources within the at least one cell.

   16. The method of claim 13, 14 or 15, wherein the control channel resources are SDCCH resources.

   17. The method of any of claims 13 to 16, wherein suppressing transmission 10 denies access to control channel resources on a cell-bycell basis.

   18. The method of any of claims 13 to 17, wherein suppressing transmission denies access to control channel resources within the at least one cell.

   15 19. The method of any of claims 13 to 18, further comprising attempting to acquire control channel resources through re-transmission of a RACH request.

   20. The method of claim 19, further comprising acquiring control channel resources from a secondary base station in a cell adjacent to a serving cell for a call.

   21. The method of claim 20, further comprising notifying at least management information to the secondary base station when a primary base station of the serving cell denies access to traffic channel resources.

   22. A computer program element containing computer program code to cause a controller to execute procedure according to any of claims 13 to 21.

   23. The computer program element of claim 22, embodied on a computer 30 program product.

   24. A cellular communication system substantially as hereinbefore described with reference to FIG. 4 to 5 of the accompanying drawings.

   25. A method of allocating control channel resources to a cell, substantially 5 as hereinbefore described with reference to FIG. 4 to 5 of the accompanying drawings.

   26. A cell controller substantially as hereinbefore described with reference to FIG. 4 to 5 of the accompanying drawings.