CA2328078A1 - Increasing capacity in a cellular communications system by change of traffic channel rate - Google Patents
Increasing capacity in a cellular communications system by change of traffic channel rate Download PDFInfo
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- CA2328078A1 CA2328078A1 CA002328078A CA2328078A CA2328078A1 CA 2328078 A1 CA2328078 A1 CA 2328078A1 CA 002328078 A CA002328078 A CA 002328078A CA 2328078 A CA2328078 A CA 2328078A CA 2328078 A1 CA2328078 A1 CA 2328078A1
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- Prior art keywords
- rate
- traffic
- traffic channel
- channel
- communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/16—Performing reselection for specific purposes
- H04W36/22—Performing reselection for specific purposes for handling the traffic
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W28/00—Network traffic management; Network resource management
- H04W28/16—Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]
- H04W28/18—Negotiating wireless communication parameters
- H04W28/22—Negotiating communication rate
Abstract
The present invention dynamically increases the capacity of a cellular radio communications system to meet temporary high traffic demands effectively and economically. The current traffic load at a particular base station cell area is determined (14). If the determined traffic load exceeds a threshold (16), a higher rate traffic channel over which a dual rate mobile station is communicating is handed over to a lower rate traffic channel available in that cell area (18). A list is maintained for those dual rate mobile stations currently assigned to higher rate traffic channels. Before making the handover from the higher rate traffic channel to the lower rate traffic channel, it is determined whether a handover is permitted. If so, the intra-cell handover is preferably made to a traffic channel which is currently already supporting another lower rate call. Otherwise, any available lower rate traffic channel is assigned. At call setup, if the current traffic load in the cell area exceeds the threshold, a call request involving a dual rate mobile station is assigned a lower rate traffic channel (20). If the traffic load in the cell area decreases, a call intitially set up or subsequently handed over to a lower rate channel because of high traffic load may optionally be handed over to a higher rate channel (17).
Description
1NCREAS1NG TRAFFIC CAPACITY IN A CELLULAR COiVIiVIUNICATIONS
SYSTEM BY CHANGE OF TRAFFIC CHANNEL RATE
FIELD OF THE INVENTION
'The present invention relates to increasing traffic capacity in a cellular radio communications system, and more particularly, to increasing traffic capacity by changing a requested or initially selected traffic channel rate to a lower bit rate when extra traffic capacity is needed.
BACKGROUND AND SUMMARY OF THE INVENTION
In the Global System for Mobile communications (GSM), two bit rates for to speech coders are defined: full rate and half rate. Full rate corresponds to a bit rate of 13 kbits/s. and half rate corresponds to a bit rate of 6.5 kbits/s. A traffic channel in the GSM system can support one full rate speech call or two half rate speech calls. Speech ceding significantly lowers the bit rate over the radio interface (higher bit rates take up too much of the frequency spectrum) while still providing acceptable speech quality. In general, speech coding sends information about the speech (rather than the speech itsely from which the speech signal can be reconstructed at the receiver.
The GSM also employs time division multiple access (TDMA) with each radio fi-cquency carrier being divided into eight time slots (TS). One time slot in a TDMA
ii-ame is called a physical channel, and each duplex pair of frequency carriers includes Zo eight physical channels. Speech and other information are sent on logical traffic channels ('fCI-I) mapped onto the physical time slot channels. In full rate traffic channels. a user is assigned a single physical channel/time slot. For half rate traffic channels. two mobile stations share the same physical channel/time slot with each mobile station alternating use of the allocated time slot.
Mobile telephone system operators live in a highly competitive world. To be successful. a mobile telephone system operator must deliver:
~ Coverage -- a call can be set up anywhere ~ Capacity -- a call can be set up anytime s ~ Quality -- the call is clear, undisturbed, and uninterrupted.
The present invention addresses capacity.
'l~he traditional approach to increasing capacity is to equip base stations with as many transceivers as possible and to invest in high capacity base station controllers.
While this is a sound strategy in densely populated areas with evenly distributed traffic ~u demands over time, in areas where the traffic demand is high only during short periods.
e.g., certain streets during morning and evening rush hour, that strategy is less sound.
'I~he more difficult issue is how to satisfy temporary high traffic demands effectively and ccunomically.
'Thus, it is a primary object of the invention to dynamically increase system is capacity to meet temporary high traffic demands in an effective and economic fashion.
It is a further object of the invention to provide enhanced ability to provide service for connections requiring a full rate traffic channel.
Some percentage of mobile stations currently (and with increasing numbers in the future) are capable of transceiving at different bit rates. For purposes of explaining 2o the present invention, (and not in any way limiting the present invention), some mobile stations are assumed to be capable of transceiving on both full rate and half rate channels. Such mobile stations are referred to as having "dual rate"
capability. Dual rate mobiles indicate their dual rate capability to the cellular network via an initial channel request message or possibly in periodic registration messages. Higher rate -, channels may be used in favorable traffic conditions but half rate channels are employed during temporary high traffic conditions.
'1-he present invention increases the capacity in a cellular radio communications system in accordance with the following method. Initially, a higher rate traffic channel s is established for communication with a mobile station located in a particular cell area.
~'he current traffic load at that cell area is determined. If the determined tral~lic load exceeds a threshold, the higher rate traffic channel over which a dual rate mobile station is communicating is handed over to another lower rate traffic channel available in that cell area. For currently active traffic channels, a list is maintained for those dual rate ie~ mobile stations currently assigned to higher rate traffic channels.
Before making the handover from the higher rate traffic channel to the lower rate traffic channel, it is determined whether such a handover is permitted. If so, the intra-cell handover is preferably made to a traffic channel which is currently already Supporting another lower rate call. Otherwise, any available lower rate traffic channel t5 is assigned.
At call setup, if the current traffic load in the cell area exceeds the threshold, a call request involving a dual rate mobile is assigned a lower rate traff is channel. 1 I~ tim traffic load in the cell area decreases, a call initially setup or subsequently handed over to a lower rate channel because of high traffic load may be handed over to a higher rate channel.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, Features, and advantages of the invention will be apparent from the following description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are net necessarily to scale with emphasis bcin' placed upon illustrating the principles of the invention.
Hig. 1 is a flowchart illustrating a general "change channel rate" procedure in accordance with a first example embodiment of the present invention:
s Fig. 2 is a function block diagram of a GSM-type mobile radio communications system in which the present invention may be incorporated in accordance with a second example embodiment of the present invention;
Fig. 3 is a diagram conceptually depicting a traffic channel supporting a single full rate channel or two half rate channels;
io Fig. 4 are more detailed function block diagrams of specific blocks shown in Fig. 2: and Figs. ~A and ~B are t7owcharts illustrating example procedures in accordance with the second example embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
~s In the following description, for purposes of explanation and not limitation.
specitic details are set forth, such as particular embodiments, hardware, techniques, etc.
in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. For example, while a specific ~n embodiment of the present invention is described in the context of a GSM
cellular telephone network, those skilled in the art will appreciate that the present invention can be implemented in any cellular telephone system. In other instances. detailed WO 99!53700 PCT/SE99/00337 J
descriptions of well-known methods, interfaces, devices, and signaling techniques are omitted so as not to obscure the description of the present invention with unnecessary detai 1.
Because the application is applicable to any cellular telephone communications a systems, a first example embodiment of the present invention is now described in general terms. The flowchart in Fig. 1 outlines the steps of a Change Channel Rate routine (block 10). Assuming a light or moderate traffic load initially.
traffic channels are established for mobile calls in a particular cell, sector, or other location area at a first traffic rate (block 12) in accordance with normal channel request and assignment to procedures. The traffic load in the cell or location area is determined (block 14). A
decision is made in block 16 whether the traffic load for that cell or location area exceeds a threshold. i.e., whether there has been temporary increase in traffic demand.
If not, the mobile communications continue as set up (block 17). However, if the traffic load exceeds a threshold, a dual rate mobile communication being conducted over a is traffic channel at a first rate is handed over to another traffic channel where the communication is conducted a second lower rate (block 18). Moreover, new incoming calls for dual rate mobiles are set up as lower rate calls rather than higher rate calls until the traffic load decreases below the threshold. If the traffic load decreases significantly, calls may optionally be handed over from lower rate traffic channels to available higher 2o rate traff is channels (block 17).
'1'Irus, the present invention provides a temporary increase of the traff is capacity of a cell by utilizing lower rate capabilities of some dual rate mobile stations operating in the cell. Because the communication connections are moved within the serving cell, i.c., infra-cell handof~(s. there is no increase in interference Icvcl that might he experienced if inter-cell handoffs to other cells were employed. Another advantage of the: present invention is that no additional hardware is required. Reserve but often underutilized base station transceivers are not needed to ensure sufficient capacity for temporary high traffic demands. Yet another advantage of this invention is that a mobile communications network operator can control how the traffic demands of each cell are handled by changing the traffic load threshold to appropriate values.
An appropriately-valued threshold ensures that only a minimum number oi~ mohile stations s having dual rate capability are affected by intra-cell handovers to lower rate traffic channels during high traffic conditions. The present invention also selects the channel rate for a particular traffic channel at call setup based on a current cell traffic load level so that during periods of high traffic, communications involving dual rate mobile stations are established using lower rates to further increase traffic capacity.
A second example embodiment of the present invention will now be described as applied to a GSM-based cellular communications system. However, those skilled in the art will appreciate that the present invention is in no way limited to GSi~t-based cellular communications systems.
Reference is made to Fig. ? which illustrates in function block format a typical ~s GSM-based cellular communications system 30. A Gateway Mobile Switching Center (GMSC) 36 interfaces the cellular communications network with other telecommunications networks including the Public Switched Telephone Network (PSTN) 32, the Internet 34, other cellular networks, and other types of communications networks such as the Integrated Services Digital Network (ISDN). The Gateway zo Mobile Switching Center 36 connects to one or more Mobile Switching Centers (MSCs) 38. Each mobile switching center 38 is connected to one or more base station controllers (BSCs) 42. The BSC handles all radio related functions including administration and remote control of the base stations 44 as well as the handling of connections to mobile stations 46 including handovers. Each BSC 42 is connected to ?a plural base stations (BSs) 44 that communicate with mobile radio stations (MS) 46.
The aatewav MSC 36 is the interface point in the mobile radio network For calls to mobile subscribers. Although the GMSC 36 is shown as a separate node for clarity of illustration, it may be located with an MSC 38. Each mobile switching center 38 pcriorms telephony switching functions associated with calls involving a mobile station a (MS) 46 including interfacing with other telecommunications networks 3? and 34 and rc>utin'~ illObilc-originated calls.
Each MSC 38 is associated with a Visiting Location Register (VLR) 40 which includes a database containing temporary subscriber information needed by its associated MSC 3Ii to provide services to mobile stations in the MSC's service area.
io 'l~ypically. when a mobile station enters a visiting network or service area. it registers with the VLR 40 which then requests and receives data about the roaming mobile station from the mobile's Home Location Register (HLR) 41 and stores it. As a result.
when the visiting mobile station is involved in a call, the VLR 40 already has the information needed for call setup. While the VLR 40 may be a stand-alone node, it is is preferably integrated with its associated MSC to eliminate signaling between the two nuclcs.
The home location register (HLR) 41 is a database node that stores and manages subscriptions. For each "home" mobile subscriber, the HLR 41 contains permanent subscriber data such as the Mobile Station ISDN Number (MSISDN) which uniquely 2o identifies the mobile telephone subscription in a PSTN numbering plan, and an international mobile subscriber identity (IMSI), which is a unique identity allocated to cacti mobile subscriber and used for signaling for in the mobile network. All network-reiated subscriber information is connected to the IMSI. The HLR 41 contains a list of services which a mobile subscriber is authorized to use along with the current subscriber location number cocTesponding to the address of the VLR 40 currently servine the mobile subscriber.
' CA 02328078 2000-10-10 Once a serving MSCiVLR is identified (in the home or in a visiting network). a call intended for the mobile station 46 is routed by that serving MSC to a base Stliti()Il =~4 aSSOClatcd with the cell in which the called mobile station is currently located. Using well-known. established protocols and procedures documented in s various GSM standards, a call connection is established over the radio interface hctwecn the base station 44 and the mobile station 46.
During a call setup, a logical traffic channel is allocated to a radio connection between a base station and mobile station based on information about the available channel's characteristics. and in the present invention in particular, based on the mobile io stations capabilities. When the connection has been established over an assigned traffic channel, e.g., a TDMA time slot, signal strength and speech quality are monitored and forwarded to the BSC which may initiate a handover of the connection based on those reports.
When a call is initiated, it is the BSC that allocates an available traffic channel is (~~Ch1) to the mobile station. In current GSM systems, a traffic channel (TCH) can either support a single full rate communication such as shown at ~0 in Fig. 3 or two half rate communications as indicated at 22 and 24 in Fig. 3. An example full rate communication corresponds to a bit rate of l 3 kbits/s, and an example hal f rate communication corresponds to a bit rate of 6.5 kbits/s. It is understood that reference to 2o a full rate traffic channel means a traffic channel currently supporting a single lull rate call. and reference to a half rate traffic channel means a traffic channel currently supporting one or two half rate calls.
More detailed block diagrams of the BSC 42, base station 44, and a dual rate mobile station 46 are now described in conjunction with Fig. 4. For purposes of~
illustration and description only, function blocks arc shown. However. those Functions ' CA 02328078 2000-10-10 may be performed using any suitable electronic circuitry including DSP. AGIC, suitably programmed main processor, etc.
The traffic load in each base station's cell, sector, or location area is monitored by the BSC 42. However, this operation or function may be performed by other entities such as the MSC 38, each bases station. or other radio network control entity.
The BSC 42 includes a traffic load detector 50 which, in this simplified example.
monitors the traffic load in area X serviced by a base station 4=1. The BSC 42 performs similar tasks for each such area for each base station under its control. Traffic load detector 50 includes a comparator 52 and a busy full rate traffic channel (TCH} counter 5~.
io Counter 54 is incremented and decremented to track a current total number of busv traffic channels for that call area "X". A traffic channel is considered busv if it is unavailable to support a full rate call, i.e.. the channel is partly or completely allocated for circuit-switched or packet-switched traffic. The output of counter 5~ is input to comparator 52 alon;= with a threshold value ~ T~ which may correspond to a certain ~s number of traffic channels set by the mobile network operator. When the output of the counter exceeds the threshold, the comparator generates a traffic load signal which may be used to set a high load flag in controller 56 for cell area X. Preferably, the threshold value ~ T~ incorporates hysteresis to minimize undesired channel rate switching. Thus, controller 56 receives channel requests from various base stations 4=I and issues channel zo assignments for various mobile communications to the base stations.
Controller 56 accesses a memory 58 to store a list of dual rate capable mobile stations currently assigned to a full rate traffic channel. In executing various channel assignments and channel drops, controller 56 increments and decrements, respectively, the busy full rate TCH counter 54 for each base station area.
Each base station 4~1, such as the base station shown for cell area X, includes numerous transceivers used to establish and maintain various channels over the; radio interface with mobile stations =~6 being serviced in area X. A simplified example of a base station transceiver shown in block 44 includes baseband processing circuitry 60 switchablv connected via switch 62 to one of a full rate encoder/decoder 64 and a half rate encoder/decoder 66 also switchablv connected at an opposite terminal via switch 70 a to transceiving circuitry 72 and antenna 76. A base station controller 74 performs a number of base station control operations including setting the position of swiichcs 6?
and 70 depending on whether a particular communication is to be conducted over a traffic channel at full rate or half rate.
The dual rate mobile station 46 shown in Fig. 4 includes. among other elements.
io baseband processing circuitry 80 switchably connected via switch 82 to one of a full rate encoder/decoder 84 and a half rate encoder/decoder 86 also switchably connected at their respective output terminals via switch 88 to transceiving circuitry 90 and antenna 94. A dual rate mobile station controller 92 performs a number of control functions including controlling the position of switches 82 and 88 depending upon is whether a full rate or a half rate channel assignment (initially or as a result of a handover) is received by the mobile station.
The operation of the second e:cample embodiment of the present invention is now described in conjunction with the flowchart illustrated in Fig. 5A. It is understood that change of channel rate is supported and permitted by the base station as well as by 2o at least some of the mobile stations currently being served by that base station. Change of channel rate may be blocked if it is not supported or permitted. For example, certain types of calls such as data calls which are initially assigned to a full rate call may not in some instances be permitted to be changed to a half rate call after the call is initially set up as a full rate connection.
The first step is for the traffic load detector to determine the traffic load corresponding in this second embodiment to the number of currently-assigned.
lull rate traffic channels (block l00) using the output from the busy full rate counter >=I, the threshold input. and the comparator ~2 in the traffic load detector ~0. A
decision is made in block 102 whether the current traffic load exceeds the threshold (which preferably incorporates a hvstcresis value}. If not, control loops back to block ! ()0 to s monitor the traffic load with no change of channel rate being necessary at this time.
I f the traffic load in this cell area exceeds the threshold, the BSC
controller s6 generates a list 58 of dual rate mobile stations in this cell area X that are currently assigned to a full rate traffic channel that are permitted to use a half rate traffic channel if necessary (block 106). A decision is made in block 108 by controller s6 whether io there are any dual rate mobile stations included in the list. If not, control returns back to block 100 to repeat the above procedures.
However, if there are dual rate mobile stations currently assigned to a full rate traffic channel entered on the list, another decision is made in block I 10 whether any traffic channel associated with the base station for area X has one hat f~
rate connection n idle. As described above in conjunction with Fig. 3, a traffic channel can support two half rate traffic channel connections. It is more efficient to fully occupy that traffic channel with two half rate calls. A handover of the current call on the foil rate traffic channel for the dual rate mobile station at the top of the list is handed over to the remaining idle half rate connection (block 112). The handover frees up a full rate traffic ?o channel for other call requests some of which may require a full rate traffic channel during this high traffic demand period. Alternatively, the freed up full rate channel may he used to support two new hat l~ rate call connections.
The BSC controller 56 generates the necessary handover commands for the base station controller 74 and mobile station controller 92. When the mobile station -~6 initially sends a ''channel request" message to its serving base station, the base station includes the channel request message with a "channel required" message sent to the WO 99153700 PC'T/SE99/00337 BSC. A portion of the channel request indicates the types of channels over which the mobile station can communicate, e.g., full rate, half rate, etc. A ''channel assignment"
command is then sent to the mobile station from the BSC via the serving base station containing a channel description of an initial or a new half~rate traffic channel for which the gall is to be established or handed over. The base station activates the new hal(~rate traffic channel. For handovers. when the new traffic channel is acknowledged.
the BSC
controller 56 sends a message to the mobile station via the old full rate traffic channel with information about the new half rate traffic channel frequency, time slot.
and output power. The mobile station tunes to the new frequency and sends handover access bursts io on the appropriate time slot. Once those bursts are detected and acknowledged. a handover complete message is transmitted by the mobile, and the old full rate traffic channel is deactivated making it available for assignment to other communications. .
On the other hand, if there are no traffic channels supporting a current half rate connection with the other half rate connection idle, a decision is made in block 1 I ~.
is ~.vhether there is any traffic channel with both half rate channel connections idle, i.e., a traflic channel that is available to support one lull rate connection or two hall~ratc connections. If not, then the list of dual rate mobile stations ~8 is cleared (block l22).
and the process repeats at block 100. On the other hand, if there is an available half rate channel connection, a handover is executed for the mobile station at the top of list 58 'o tcom a current full rate connection to a new half rate connection on the idle traffic channel identified in block I 14 (block 116). When the handover is performed in either blocks 1 12 or 1 16. the mobile station entry at the top of the list 58 is removed (block 1 18). A decision is then made in block 120 whether the traffic load is less than the threshold by a hysteresis amount. If not, if the cell is still experiencing high traffic conditions and may add additional capacity by changing the channel tale from lull rate to half rate connections. On the other hand, if the traffic load has decreased sufficiently WO 99/53'700 PCT/SE99/00337 beneath the threshold, the list is cleared in block 'Z2, and the process repeated starting at block 100.
ll~thc traffic load exceeds the threshold in decision hl~cl: 102. the: 13~C' controller ~6 also attempts to increase capacity by assigning half rate traffic channels where permittedipossibIe for new call requests, see flags A in Fio. ~A. and described in the flowchart illustrated in Fig. ~B. For a high traffic load condition. each new channel request is received (block I 30), and the rate capability of the mobile station associated with the channel request is determined (block 132) based on the indication of what kinds of channels the mobile station can handle contained in the channel request io message. If a full rate traffic channel is required. (for whatever reason).
the channel setup is continued to assign a full rate traffic channel assuming that one is available.
I-Iowever, if a full rate traffic channel is not required for the current call request, a half rate traffic channel is assigned (block 136) and control returns to block 100 in Fig. 5.
When the traffic load is detected to have decreased sufficiently, an optional procedure is to permit ongoing half rate calls to be selectively handed over to available full rate ~i~,mncls.
Consider the following simple example. Assume that the base station ~4 has a total of four transceivers where each transceiver includes eight time slot channels.
accordingly, the base station includes a total of thirty-two time slots of which three arc ~o used for control channel signaling leaving twenty-nine time slots for traffic channels.
Again. all base station transceivers are assumed to be capable of carrying full rate and half rate channels. Half of the mobile stations arc assumed to be capable of dual rate communications with the other half being capable of full rate communication only. The traffic load threshold is set to seventy-five percent with a hysteresis of five percent.
Translated to a number of traffic channels for this example, the threshold is twenty-two busy traffic channels with a hysteresis of one traffic channel. Thus. a high load flay is 1=t set when twenty-three or more traffic channels are currently busy. and is reset when-less than nventv-one traffic channels are currently busy.
Assume that the traffic channels are currently used as Follows: two traffic channels are allocated as packet data channels, ten traff is channels are occupied by n~obiEc stations capable of full rate only. one traffic channel is occupied by two haifrutc calls. two traffic channels are occupied by one half rate call per each traffic channel, seven traffic channels are occupied by dual rate mobile stations currently using a full rate connection. In total, riventy-two traffic channels are busy, and therefore, the high traffic load flaa is not set.
~o Suppose another full rate call is established for a dual rate mobile station. The high traff c load flag is then set. The base station controller 56 generates a list of dual rate mobile stations that are candidates for handovers. The list includes eight entries corresponding to the eight dual rate mobile stations currently using full rate connections. These full rate connections are handed over one at a time to a hal f rate ~s channel until the high load situation is alleviated. For etample, a first full rate connection is moved to an idle half rate connection on one of the partially-allocated traftic channels already carrying one half rate call connection. After this first handover, the number of busy traffic channels equals twenty-two, assuming that no new calls have been established, which is not low enough to reset the high load flag. A
second ?o connection is moved to the idle part of the second of the partially-allocated traffic channels. The number of busy traffic channels is reduced to twenty-one which again is not low enough to reset the high load flag. A third full rate connection is moved to a halfrate channel on one of the idle full rate channels. A fourth connection is moved to the other available half rate connection on that same traffic channel.
I3v transforming the four full rate connections to four new half rate connections, the number of busy traffic channels is reduced from twenty-three to twenty. As a result, four additional traffic channels are made available to service other calls at a relatively minimal cost of performing for intra-cell handoffs. Surges in traffic demands are efficiently met in dynamic fashion without additional base station transceivers.
While the present invention has been described with respect to particular c~nhc~diments, those skilled in the art will recognise that the present invention is n«t limited to the specific embodiments described and illustrated herein.
Different formats, embodiments, and adaptations besides those shown and described, as well as many variations, modifications, and equivalent arrangements may also be used to implement the invention. Therefore, while the present invention has been described in relation to io its preferred embodiments, it is to be understood that this disclosure is only illustrative and e~cemplary of the present invention and is merely for the purposes of providing a full and enabling disclosure of the invention. Accordingly, it is intended that the invention be limited only by the spirit and scope of the claims appended hereto.
SYSTEM BY CHANGE OF TRAFFIC CHANNEL RATE
FIELD OF THE INVENTION
'The present invention relates to increasing traffic capacity in a cellular radio communications system, and more particularly, to increasing traffic capacity by changing a requested or initially selected traffic channel rate to a lower bit rate when extra traffic capacity is needed.
BACKGROUND AND SUMMARY OF THE INVENTION
In the Global System for Mobile communications (GSM), two bit rates for to speech coders are defined: full rate and half rate. Full rate corresponds to a bit rate of 13 kbits/s. and half rate corresponds to a bit rate of 6.5 kbits/s. A traffic channel in the GSM system can support one full rate speech call or two half rate speech calls. Speech ceding significantly lowers the bit rate over the radio interface (higher bit rates take up too much of the frequency spectrum) while still providing acceptable speech quality. In general, speech coding sends information about the speech (rather than the speech itsely from which the speech signal can be reconstructed at the receiver.
The GSM also employs time division multiple access (TDMA) with each radio fi-cquency carrier being divided into eight time slots (TS). One time slot in a TDMA
ii-ame is called a physical channel, and each duplex pair of frequency carriers includes Zo eight physical channels. Speech and other information are sent on logical traffic channels ('fCI-I) mapped onto the physical time slot channels. In full rate traffic channels. a user is assigned a single physical channel/time slot. For half rate traffic channels. two mobile stations share the same physical channel/time slot with each mobile station alternating use of the allocated time slot.
Mobile telephone system operators live in a highly competitive world. To be successful. a mobile telephone system operator must deliver:
~ Coverage -- a call can be set up anywhere ~ Capacity -- a call can be set up anytime s ~ Quality -- the call is clear, undisturbed, and uninterrupted.
The present invention addresses capacity.
'l~he traditional approach to increasing capacity is to equip base stations with as many transceivers as possible and to invest in high capacity base station controllers.
While this is a sound strategy in densely populated areas with evenly distributed traffic ~u demands over time, in areas where the traffic demand is high only during short periods.
e.g., certain streets during morning and evening rush hour, that strategy is less sound.
'I~he more difficult issue is how to satisfy temporary high traffic demands effectively and ccunomically.
'Thus, it is a primary object of the invention to dynamically increase system is capacity to meet temporary high traffic demands in an effective and economic fashion.
It is a further object of the invention to provide enhanced ability to provide service for connections requiring a full rate traffic channel.
Some percentage of mobile stations currently (and with increasing numbers in the future) are capable of transceiving at different bit rates. For purposes of explaining 2o the present invention, (and not in any way limiting the present invention), some mobile stations are assumed to be capable of transceiving on both full rate and half rate channels. Such mobile stations are referred to as having "dual rate"
capability. Dual rate mobiles indicate their dual rate capability to the cellular network via an initial channel request message or possibly in periodic registration messages. Higher rate -, channels may be used in favorable traffic conditions but half rate channels are employed during temporary high traffic conditions.
'1-he present invention increases the capacity in a cellular radio communications system in accordance with the following method. Initially, a higher rate traffic channel s is established for communication with a mobile station located in a particular cell area.
~'he current traffic load at that cell area is determined. If the determined tral~lic load exceeds a threshold, the higher rate traffic channel over which a dual rate mobile station is communicating is handed over to another lower rate traffic channel available in that cell area. For currently active traffic channels, a list is maintained for those dual rate ie~ mobile stations currently assigned to higher rate traffic channels.
Before making the handover from the higher rate traffic channel to the lower rate traffic channel, it is determined whether such a handover is permitted. If so, the intra-cell handover is preferably made to a traffic channel which is currently already Supporting another lower rate call. Otherwise, any available lower rate traffic channel t5 is assigned.
At call setup, if the current traffic load in the cell area exceeds the threshold, a call request involving a dual rate mobile is assigned a lower rate traff is channel. 1 I~ tim traffic load in the cell area decreases, a call initially setup or subsequently handed over to a lower rate channel because of high traffic load may be handed over to a higher rate channel.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, Features, and advantages of the invention will be apparent from the following description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are net necessarily to scale with emphasis bcin' placed upon illustrating the principles of the invention.
Hig. 1 is a flowchart illustrating a general "change channel rate" procedure in accordance with a first example embodiment of the present invention:
s Fig. 2 is a function block diagram of a GSM-type mobile radio communications system in which the present invention may be incorporated in accordance with a second example embodiment of the present invention;
Fig. 3 is a diagram conceptually depicting a traffic channel supporting a single full rate channel or two half rate channels;
io Fig. 4 are more detailed function block diagrams of specific blocks shown in Fig. 2: and Figs. ~A and ~B are t7owcharts illustrating example procedures in accordance with the second example embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
~s In the following description, for purposes of explanation and not limitation.
specitic details are set forth, such as particular embodiments, hardware, techniques, etc.
in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. For example, while a specific ~n embodiment of the present invention is described in the context of a GSM
cellular telephone network, those skilled in the art will appreciate that the present invention can be implemented in any cellular telephone system. In other instances. detailed WO 99!53700 PCT/SE99/00337 J
descriptions of well-known methods, interfaces, devices, and signaling techniques are omitted so as not to obscure the description of the present invention with unnecessary detai 1.
Because the application is applicable to any cellular telephone communications a systems, a first example embodiment of the present invention is now described in general terms. The flowchart in Fig. 1 outlines the steps of a Change Channel Rate routine (block 10). Assuming a light or moderate traffic load initially.
traffic channels are established for mobile calls in a particular cell, sector, or other location area at a first traffic rate (block 12) in accordance with normal channel request and assignment to procedures. The traffic load in the cell or location area is determined (block 14). A
decision is made in block 16 whether the traffic load for that cell or location area exceeds a threshold. i.e., whether there has been temporary increase in traffic demand.
If not, the mobile communications continue as set up (block 17). However, if the traffic load exceeds a threshold, a dual rate mobile communication being conducted over a is traffic channel at a first rate is handed over to another traffic channel where the communication is conducted a second lower rate (block 18). Moreover, new incoming calls for dual rate mobiles are set up as lower rate calls rather than higher rate calls until the traffic load decreases below the threshold. If the traffic load decreases significantly, calls may optionally be handed over from lower rate traffic channels to available higher 2o rate traff is channels (block 17).
'1'Irus, the present invention provides a temporary increase of the traff is capacity of a cell by utilizing lower rate capabilities of some dual rate mobile stations operating in the cell. Because the communication connections are moved within the serving cell, i.c., infra-cell handof~(s. there is no increase in interference Icvcl that might he experienced if inter-cell handoffs to other cells were employed. Another advantage of the: present invention is that no additional hardware is required. Reserve but often underutilized base station transceivers are not needed to ensure sufficient capacity for temporary high traffic demands. Yet another advantage of this invention is that a mobile communications network operator can control how the traffic demands of each cell are handled by changing the traffic load threshold to appropriate values.
An appropriately-valued threshold ensures that only a minimum number oi~ mohile stations s having dual rate capability are affected by intra-cell handovers to lower rate traffic channels during high traffic conditions. The present invention also selects the channel rate for a particular traffic channel at call setup based on a current cell traffic load level so that during periods of high traffic, communications involving dual rate mobile stations are established using lower rates to further increase traffic capacity.
A second example embodiment of the present invention will now be described as applied to a GSM-based cellular communications system. However, those skilled in the art will appreciate that the present invention is in no way limited to GSi~t-based cellular communications systems.
Reference is made to Fig. ? which illustrates in function block format a typical ~s GSM-based cellular communications system 30. A Gateway Mobile Switching Center (GMSC) 36 interfaces the cellular communications network with other telecommunications networks including the Public Switched Telephone Network (PSTN) 32, the Internet 34, other cellular networks, and other types of communications networks such as the Integrated Services Digital Network (ISDN). The Gateway zo Mobile Switching Center 36 connects to one or more Mobile Switching Centers (MSCs) 38. Each mobile switching center 38 is connected to one or more base station controllers (BSCs) 42. The BSC handles all radio related functions including administration and remote control of the base stations 44 as well as the handling of connections to mobile stations 46 including handovers. Each BSC 42 is connected to ?a plural base stations (BSs) 44 that communicate with mobile radio stations (MS) 46.
The aatewav MSC 36 is the interface point in the mobile radio network For calls to mobile subscribers. Although the GMSC 36 is shown as a separate node for clarity of illustration, it may be located with an MSC 38. Each mobile switching center 38 pcriorms telephony switching functions associated with calls involving a mobile station a (MS) 46 including interfacing with other telecommunications networks 3? and 34 and rc>utin'~ illObilc-originated calls.
Each MSC 38 is associated with a Visiting Location Register (VLR) 40 which includes a database containing temporary subscriber information needed by its associated MSC 3Ii to provide services to mobile stations in the MSC's service area.
io 'l~ypically. when a mobile station enters a visiting network or service area. it registers with the VLR 40 which then requests and receives data about the roaming mobile station from the mobile's Home Location Register (HLR) 41 and stores it. As a result.
when the visiting mobile station is involved in a call, the VLR 40 already has the information needed for call setup. While the VLR 40 may be a stand-alone node, it is is preferably integrated with its associated MSC to eliminate signaling between the two nuclcs.
The home location register (HLR) 41 is a database node that stores and manages subscriptions. For each "home" mobile subscriber, the HLR 41 contains permanent subscriber data such as the Mobile Station ISDN Number (MSISDN) which uniquely 2o identifies the mobile telephone subscription in a PSTN numbering plan, and an international mobile subscriber identity (IMSI), which is a unique identity allocated to cacti mobile subscriber and used for signaling for in the mobile network. All network-reiated subscriber information is connected to the IMSI. The HLR 41 contains a list of services which a mobile subscriber is authorized to use along with the current subscriber location number cocTesponding to the address of the VLR 40 currently servine the mobile subscriber.
' CA 02328078 2000-10-10 Once a serving MSCiVLR is identified (in the home or in a visiting network). a call intended for the mobile station 46 is routed by that serving MSC to a base Stliti()Il =~4 aSSOClatcd with the cell in which the called mobile station is currently located. Using well-known. established protocols and procedures documented in s various GSM standards, a call connection is established over the radio interface hctwecn the base station 44 and the mobile station 46.
During a call setup, a logical traffic channel is allocated to a radio connection between a base station and mobile station based on information about the available channel's characteristics. and in the present invention in particular, based on the mobile io stations capabilities. When the connection has been established over an assigned traffic channel, e.g., a TDMA time slot, signal strength and speech quality are monitored and forwarded to the BSC which may initiate a handover of the connection based on those reports.
When a call is initiated, it is the BSC that allocates an available traffic channel is (~~Ch1) to the mobile station. In current GSM systems, a traffic channel (TCH) can either support a single full rate communication such as shown at ~0 in Fig. 3 or two half rate communications as indicated at 22 and 24 in Fig. 3. An example full rate communication corresponds to a bit rate of l 3 kbits/s, and an example hal f rate communication corresponds to a bit rate of 6.5 kbits/s. It is understood that reference to 2o a full rate traffic channel means a traffic channel currently supporting a single lull rate call. and reference to a half rate traffic channel means a traffic channel currently supporting one or two half rate calls.
More detailed block diagrams of the BSC 42, base station 44, and a dual rate mobile station 46 are now described in conjunction with Fig. 4. For purposes of~
illustration and description only, function blocks arc shown. However. those Functions ' CA 02328078 2000-10-10 may be performed using any suitable electronic circuitry including DSP. AGIC, suitably programmed main processor, etc.
The traffic load in each base station's cell, sector, or location area is monitored by the BSC 42. However, this operation or function may be performed by other entities such as the MSC 38, each bases station. or other radio network control entity.
The BSC 42 includes a traffic load detector 50 which, in this simplified example.
monitors the traffic load in area X serviced by a base station 4=1. The BSC 42 performs similar tasks for each such area for each base station under its control. Traffic load detector 50 includes a comparator 52 and a busy full rate traffic channel (TCH} counter 5~.
io Counter 54 is incremented and decremented to track a current total number of busv traffic channels for that call area "X". A traffic channel is considered busv if it is unavailable to support a full rate call, i.e.. the channel is partly or completely allocated for circuit-switched or packet-switched traffic. The output of counter 5~ is input to comparator 52 alon;= with a threshold value ~ T~ which may correspond to a certain ~s number of traffic channels set by the mobile network operator. When the output of the counter exceeds the threshold, the comparator generates a traffic load signal which may be used to set a high load flag in controller 56 for cell area X. Preferably, the threshold value ~ T~ incorporates hysteresis to minimize undesired channel rate switching. Thus, controller 56 receives channel requests from various base stations 4=I and issues channel zo assignments for various mobile communications to the base stations.
Controller 56 accesses a memory 58 to store a list of dual rate capable mobile stations currently assigned to a full rate traffic channel. In executing various channel assignments and channel drops, controller 56 increments and decrements, respectively, the busy full rate TCH counter 54 for each base station area.
Each base station 4~1, such as the base station shown for cell area X, includes numerous transceivers used to establish and maintain various channels over the; radio interface with mobile stations =~6 being serviced in area X. A simplified example of a base station transceiver shown in block 44 includes baseband processing circuitry 60 switchablv connected via switch 62 to one of a full rate encoder/decoder 64 and a half rate encoder/decoder 66 also switchablv connected at an opposite terminal via switch 70 a to transceiving circuitry 72 and antenna 76. A base station controller 74 performs a number of base station control operations including setting the position of swiichcs 6?
and 70 depending on whether a particular communication is to be conducted over a traffic channel at full rate or half rate.
The dual rate mobile station 46 shown in Fig. 4 includes. among other elements.
io baseband processing circuitry 80 switchably connected via switch 82 to one of a full rate encoder/decoder 84 and a half rate encoder/decoder 86 also switchably connected at their respective output terminals via switch 88 to transceiving circuitry 90 and antenna 94. A dual rate mobile station controller 92 performs a number of control functions including controlling the position of switches 82 and 88 depending upon is whether a full rate or a half rate channel assignment (initially or as a result of a handover) is received by the mobile station.
The operation of the second e:cample embodiment of the present invention is now described in conjunction with the flowchart illustrated in Fig. 5A. It is understood that change of channel rate is supported and permitted by the base station as well as by 2o at least some of the mobile stations currently being served by that base station. Change of channel rate may be blocked if it is not supported or permitted. For example, certain types of calls such as data calls which are initially assigned to a full rate call may not in some instances be permitted to be changed to a half rate call after the call is initially set up as a full rate connection.
The first step is for the traffic load detector to determine the traffic load corresponding in this second embodiment to the number of currently-assigned.
lull rate traffic channels (block l00) using the output from the busy full rate counter >=I, the threshold input. and the comparator ~2 in the traffic load detector ~0. A
decision is made in block 102 whether the current traffic load exceeds the threshold (which preferably incorporates a hvstcresis value}. If not, control loops back to block ! ()0 to s monitor the traffic load with no change of channel rate being necessary at this time.
I f the traffic load in this cell area exceeds the threshold, the BSC
controller s6 generates a list 58 of dual rate mobile stations in this cell area X that are currently assigned to a full rate traffic channel that are permitted to use a half rate traffic channel if necessary (block 106). A decision is made in block 108 by controller s6 whether io there are any dual rate mobile stations included in the list. If not, control returns back to block 100 to repeat the above procedures.
However, if there are dual rate mobile stations currently assigned to a full rate traffic channel entered on the list, another decision is made in block I 10 whether any traffic channel associated with the base station for area X has one hat f~
rate connection n idle. As described above in conjunction with Fig. 3, a traffic channel can support two half rate traffic channel connections. It is more efficient to fully occupy that traffic channel with two half rate calls. A handover of the current call on the foil rate traffic channel for the dual rate mobile station at the top of the list is handed over to the remaining idle half rate connection (block 112). The handover frees up a full rate traffic ?o channel for other call requests some of which may require a full rate traffic channel during this high traffic demand period. Alternatively, the freed up full rate channel may he used to support two new hat l~ rate call connections.
The BSC controller 56 generates the necessary handover commands for the base station controller 74 and mobile station controller 92. When the mobile station -~6 initially sends a ''channel request" message to its serving base station, the base station includes the channel request message with a "channel required" message sent to the WO 99153700 PC'T/SE99/00337 BSC. A portion of the channel request indicates the types of channels over which the mobile station can communicate, e.g., full rate, half rate, etc. A ''channel assignment"
command is then sent to the mobile station from the BSC via the serving base station containing a channel description of an initial or a new half~rate traffic channel for which the gall is to be established or handed over. The base station activates the new hal(~rate traffic channel. For handovers. when the new traffic channel is acknowledged.
the BSC
controller 56 sends a message to the mobile station via the old full rate traffic channel with information about the new half rate traffic channel frequency, time slot.
and output power. The mobile station tunes to the new frequency and sends handover access bursts io on the appropriate time slot. Once those bursts are detected and acknowledged. a handover complete message is transmitted by the mobile, and the old full rate traffic channel is deactivated making it available for assignment to other communications. .
On the other hand, if there are no traffic channels supporting a current half rate connection with the other half rate connection idle, a decision is made in block 1 I ~.
is ~.vhether there is any traffic channel with both half rate channel connections idle, i.e., a traflic channel that is available to support one lull rate connection or two hall~ratc connections. If not, then the list of dual rate mobile stations ~8 is cleared (block l22).
and the process repeats at block 100. On the other hand, if there is an available half rate channel connection, a handover is executed for the mobile station at the top of list 58 'o tcom a current full rate connection to a new half rate connection on the idle traffic channel identified in block I 14 (block 116). When the handover is performed in either blocks 1 12 or 1 16. the mobile station entry at the top of the list 58 is removed (block 1 18). A decision is then made in block 120 whether the traffic load is less than the threshold by a hysteresis amount. If not, if the cell is still experiencing high traffic conditions and may add additional capacity by changing the channel tale from lull rate to half rate connections. On the other hand, if the traffic load has decreased sufficiently WO 99/53'700 PCT/SE99/00337 beneath the threshold, the list is cleared in block 'Z2, and the process repeated starting at block 100.
ll~thc traffic load exceeds the threshold in decision hl~cl: 102. the: 13~C' controller ~6 also attempts to increase capacity by assigning half rate traffic channels where permittedipossibIe for new call requests, see flags A in Fio. ~A. and described in the flowchart illustrated in Fig. ~B. For a high traffic load condition. each new channel request is received (block I 30), and the rate capability of the mobile station associated with the channel request is determined (block 132) based on the indication of what kinds of channels the mobile station can handle contained in the channel request io message. If a full rate traffic channel is required. (for whatever reason).
the channel setup is continued to assign a full rate traffic channel assuming that one is available.
I-Iowever, if a full rate traffic channel is not required for the current call request, a half rate traffic channel is assigned (block 136) and control returns to block 100 in Fig. 5.
When the traffic load is detected to have decreased sufficiently, an optional procedure is to permit ongoing half rate calls to be selectively handed over to available full rate ~i~,mncls.
Consider the following simple example. Assume that the base station ~4 has a total of four transceivers where each transceiver includes eight time slot channels.
accordingly, the base station includes a total of thirty-two time slots of which three arc ~o used for control channel signaling leaving twenty-nine time slots for traffic channels.
Again. all base station transceivers are assumed to be capable of carrying full rate and half rate channels. Half of the mobile stations arc assumed to be capable of dual rate communications with the other half being capable of full rate communication only. The traffic load threshold is set to seventy-five percent with a hysteresis of five percent.
Translated to a number of traffic channels for this example, the threshold is twenty-two busy traffic channels with a hysteresis of one traffic channel. Thus. a high load flay is 1=t set when twenty-three or more traffic channels are currently busy. and is reset when-less than nventv-one traffic channels are currently busy.
Assume that the traffic channels are currently used as Follows: two traffic channels are allocated as packet data channels, ten traff is channels are occupied by n~obiEc stations capable of full rate only. one traffic channel is occupied by two haifrutc calls. two traffic channels are occupied by one half rate call per each traffic channel, seven traffic channels are occupied by dual rate mobile stations currently using a full rate connection. In total, riventy-two traffic channels are busy, and therefore, the high traffic load flaa is not set.
~o Suppose another full rate call is established for a dual rate mobile station. The high traff c load flag is then set. The base station controller 56 generates a list of dual rate mobile stations that are candidates for handovers. The list includes eight entries corresponding to the eight dual rate mobile stations currently using full rate connections. These full rate connections are handed over one at a time to a hal f rate ~s channel until the high load situation is alleviated. For etample, a first full rate connection is moved to an idle half rate connection on one of the partially-allocated traftic channels already carrying one half rate call connection. After this first handover, the number of busy traffic channels equals twenty-two, assuming that no new calls have been established, which is not low enough to reset the high load flag. A
second ?o connection is moved to the idle part of the second of the partially-allocated traffic channels. The number of busy traffic channels is reduced to twenty-one which again is not low enough to reset the high load flag. A third full rate connection is moved to a halfrate channel on one of the idle full rate channels. A fourth connection is moved to the other available half rate connection on that same traffic channel.
I3v transforming the four full rate connections to four new half rate connections, the number of busy traffic channels is reduced from twenty-three to twenty. As a result, four additional traffic channels are made available to service other calls at a relatively minimal cost of performing for intra-cell handoffs. Surges in traffic demands are efficiently met in dynamic fashion without additional base station transceivers.
While the present invention has been described with respect to particular c~nhc~diments, those skilled in the art will recognise that the present invention is n«t limited to the specific embodiments described and illustrated herein.
Different formats, embodiments, and adaptations besides those shown and described, as well as many variations, modifications, and equivalent arrangements may also be used to implement the invention. Therefore, while the present invention has been described in relation to io its preferred embodiments, it is to be understood that this disclosure is only illustrative and e~cemplary of the present invention and is merely for the purposes of providing a full and enabling disclosure of the invention. Accordingly, it is intended that the invention be limited only by the spirit and scope of the claims appended hereto.
Claims (31)
1. A method for increasing capacity in a cellular communications system where mobile stations communicate over traffic channels, comprising the steps of:
establishing a first rate traffic channel for a communication with a mobile station located in a particular cell area;
determining a traffic load at the cell area; and if the traffic load at the cell area exceeds a threshold, changing the first rate traffic channel to a second rate traffic channel.
establishing a first rate traffic channel for a communication with a mobile station located in a particular cell area;
determining a traffic load at the cell area; and if the traffic load at the cell area exceeds a threshold, changing the first rate traffic channel to a second rate traffic channel.
2. The method in claim 1, further comprising:
if the traffic load at the cell area exceeds a threshold, setting up new second rate traffic channel in response to a channel request involving a mobile station in the cell area.
if the traffic load at the cell area exceeds a threshold, setting up new second rate traffic channel in response to a channel request involving a mobile station in the cell area.
3. The method in claim 2, further comprising:
determining whether the mobile stations identified in the channel requests have the capability to communicate over a second rate channel before the setting up step.
determining whether the mobile stations identified in the channel requests have the capability to communicate over a second rate channel before the setting up step.
4. The method in claim 1, wherein the first rate is a higher rate than the second rate.
5. The method in claim 1, further comprising:
determining whether the mobile station includes a dual rate capability to communicate using either one of the first and the second rates, wherein the changing step includes determining whether the mobile station has the dual rate capability.
determining whether the mobile station includes a dual rate capability to communicate using either one of the first and the second rates, wherein the changing step includes determining whether the mobile station has the dual rate capability.
6. The method in claim 5, further comprising:
for a dual rate capable mobile station, determining whether change to a second rate channel communication is permitted.
for a dual rate capable mobile station, determining whether change to a second rate channel communication is permitted.
7. The method in claim 1, wherein the changing step includes:
performing an intra-cell handover of the communication from the first rate traffic channel to the second rate traffic channel.
performing an intra-cell handover of the communication from the first rate traffic channel to the second rate traffic channel.
8. The method in claim 1, wherein the second rate is corresponds to a bit rate of 6.5 kbits/s and the first rate corresponds to a bit rate of 13 kbits/s.
9. The method in claim 1, wherein the second rate communication occupies one half of the capacity occupied by the first rate communication.
10. The method in claim 1, further comprising:
assigning the second rate communication to a traffic channel currently supporting another second rate communication.
assigning the second rate communication to a traffic channel currently supporting another second rate communication.
11. The method in claim 1, further comprising:
compiling a list of dual rate mobile stations having the capability to communicate using either the first rate and the second higher rate.
compiling a list of dual rate mobile stations having the capability to communicate using either the first rate and the second higher rate.
12. The method in claim 11, further comprising:
employing hysteresis in the determining step.
employing hysteresis in the determining step.
13. A method for increasing capacity in a cellular communications system where mobile stations in cell areas communicate with corresponding base stations over traffic channels, comprising the steps of:
in response to a request to establish a traffic channel for a communication with a mobile station in a cell area. determining a traffic channel rate capability of the mobile station;
determining a cell area traffic load; and if the cell area traffic load exceeds a threshold and if the mobile station has the capability to communicate using either a first higher rate and a second lower rate.
establishing a traffic channel for the mobile station communication at the second lower rate.
in response to a request to establish a traffic channel for a communication with a mobile station in a cell area. determining a traffic channel rate capability of the mobile station;
determining a cell area traffic load; and if the cell area traffic load exceeds a threshold and if the mobile station has the capability to communicate using either a first higher rate and a second lower rate.
establishing a traffic channel for the mobile station communication at the second lower rate.
14. The method in claim 13, wherein the second lower rate is corresponds to a bit rate of 6.5 kbits/s and the first higher rate corresponds to a bit rate of 13 kbits/s.
15. The method in claim 13, wherein the second lower rate communication occupies one half of a traffic channel and the first higher rate communication occupies a hull traffic channel.
16. The method in claim 13, further comprising:
switching the second lower rate communication to a traffic channel currently supporting another second lower rate communication.
switching the second lower rate communication to a traffic channel currently supporting another second lower rate communication.
17. The method in claim 13, further comprising:
compiling a list of mobile stations having the capability to communicate at both the second lower rate and the first higher rate.
compiling a list of mobile stations having the capability to communicate at both the second lower rate and the first higher rate.
18. The method in claim 13, further comprising:
if the traffic load at the cell area decreases below a threshold, establishing a traffic channel for the mobile station communication at the first higher rate.
if the traffic load at the cell area decreases below a threshold, establishing a traffic channel for the mobile station communication at the first higher rate.
19. The method in claim 18, further comprising:
employing hysteresis in the determining step.
employing hysteresis in the determining step.
20. The method in claim 13, further comprising:
if the traffic load at the cell area exceeds a threshold, examining first rate traffic channel connections and changing one of the first rate traffic channel connections to a second rate traffic channel.
if the traffic load at the cell area exceeds a threshold, examining first rate traffic channel connections and changing one of the first rate traffic channel connections to a second rate traffic channel.
21. In a cellular communications system where mobile stations communicate over traffic channels with base stations. each base station having a corresponding cell, a controller coordinating the setup of a first rate traffic channel for a communication with a mobile station being served by a base station, comprising:
a memory storing traffic channel rate capabilities of plural mobile stations served by the base station, and data processing circuitry, connected to the memory, programmed to perform the following tasks:
determining a traffic load at the cell corresponding to the base station, and if the traffic load at the cell exceeds a threshold, reassigning the communication to a second lower rate traffic channel.
a memory storing traffic channel rate capabilities of plural mobile stations served by the base station, and data processing circuitry, connected to the memory, programmed to perform the following tasks:
determining a traffic load at the cell corresponding to the base station, and if the traffic load at the cell exceeds a threshold, reassigning the communication to a second lower rate traffic channel.
22. The controller in claim 21, wherein the mobile station has the capability to communicate over first and second rate traffic channels.
23. The controller in claim 21, wherein the data processing circuitry executes an intra-cell handover of the communication from the first rate traffic channel to the second rate traffic channel.
24. The controller in claim 21, wherein the second rate is corresponds to a bit rate of 6.5 kbits/s and the first rate corresponds to a bit rate of 13 kbits/s.
25. The controller in claim 21, wherein the second rate communication occupies one half of the capacity occupied by the first rate communication.
26. The controller in claim 21, wherein the data processing circuitry assigns the second rate communication to a traffic channel currently supporting another second rate communication.
27. The controller in claim 21, wherein the memory stores a list of dual rate mobile stations having the capability to communicate using either the first rate and the second higher rate.
28. The controller in claim 21, wherein if the traffic load at the cell area exceeds a threshold, the data processing circuitry sets up new second rate traffic channels in response to channel requests involving mobile stations in the cell area.
29. The controller in claim 21, wherein the controller is located in a base station controller coupled to plural base stations.
30. The controller in claim 21, wherein the controller is located in a mobile switching center coupled to plural base stations.
31. The controller in claim 21, the data processing circuitry comprising:
a counter for counting the number of busy traffic channels, and a comparator for comparing an output from the counter to the threshold.
a counter for counting the number of busy traffic channels, and a comparator for comparing an output from the counter to the threshold.
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| US09/058,282 | 1998-04-10 | ||
| PCT/SE1999/000337 WO1999053700A1 (en) | 1998-04-10 | 1999-03-05 | Increasing traffic capacity in a cellular communications system by change of traffic channel rate |
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| ZA946674B (en) * | 1993-09-08 | 1995-05-02 | Qualcomm Inc | Method and apparatus for determining the transmission data rate in a multi-user communication system |
| US5649299A (en) * | 1993-10-27 | 1997-07-15 | Motorola, Inc. | Apparatus and method for adapting a digital radiotelephone system to increased subscriber traffic |
-
1999
- 1999-03-05 WO PCT/SE1999/000337 patent/WO1999053700A1/en active Application Filing
- 1999-03-05 CN CN 99807232 patent/CN1305687A/en active Pending
- 1999-03-05 DE DE19983107T patent/DE19983107T1/en not_active Withdrawn
- 1999-03-05 GB GB0026225A patent/GB2353188A/en not_active Withdrawn
- 1999-03-05 BR BR9909568-8A patent/BR9909568A/en not_active IP Right Cessation
- 1999-03-05 AU AU29664/99A patent/AU2966499A/en not_active Abandoned
- 1999-03-05 CA CA002328078A patent/CA2328078A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| BR9909568A (en) | 2000-12-19 |
| CN1305687A (en) | 2001-07-25 |
| AU2966499A (en) | 1999-11-01 |
| GB0026225D0 (en) | 2000-12-13 |
| DE19983107T1 (en) | 2001-05-10 |
| GB2353188A (en) | 2001-02-14 |
| WO1999053700A1 (en) | 1999-10-21 |
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