CN1145371C - Method and device for allocating communication channels in communication system - Google Patents

Abstract

A communication system (115) receives a paging signal (103) from a mobile station (100) requesting service and, if the paging signal (103) contains information identifying the service request as an emergency (502), a communication channel in a base transceiver station (105, 107, 109) is directly allocated to service the mobile station (100). If a communication channel is not immediately available, the communication system (115) will try to make a communication channel available. A distinct aspect of the communication system (115) is that it monitors an indicator (600) representative of the emergency call traffic on the communication system (115). Based upon the status of the indicator (600), the communication system (115) takes appropriate measures (440) to provide priority service for those mobile stations (100) having a priority access class. By providing priority service in this manner, the communication system (115) efficiently allocates the communication resource to the mobile stations (100) with priority access classes which need those resources urgently.

Description

Method and device for allocating communication channels in communication system

The present invention relates generally to communication systems, and more particularly to a method and apparatus for providing priority access service in a wireless telephone system.

Wireless communication systems are well known and consist of a variety of types including land mobile radios, cellular radiotelephones, personal communication systems (PCS) and other communication systems. For example in a cellular radiotelephone communication system, a number of communication units served by a base transceiver station (BTS) are usually linked to a base station controller (BSC) which constitutes a base station system (BSS). The BSCs are then linked to a Mobile Switching Center (MSC) which provides the connection between the BSS and the Public Switched Telephone Network (PSTN) and the interconnection of the BSSs. A mobile communication device (or mobile station) (MS) operating within range of a communication unit utilizes wireless communication to send and receive signals of a serving BSS. These signals are processed by the BTS, BSC and MSC to perform communication services with other MSs, or sent to a landline telephone subscriber via the PSTN.

In a special type of radiotelephone communication system, for example, in a Global System for Mobile Communications (GSM) radiotelephone communication system, the BSS continuously sends a signal to all MSs within its signal range via the Broadcast Control Channel (BCCH) . This signal contains the information necessary to allow an MS to access the system. Of special significance within this signal is the information on the access classes that the BSS allows access to the system.

GSM Recommendation 4.08 defines three access levels: normal access, emergency access and special service access levels. There are 10 normal access classes (randomly from 0 to 9), one emergency access class (10) and 5 special service access classes (11-15). In the future, when more and more emergency access levels and special service access levels are involved, they will be called "priority access levels" to distinguish them from normal access levels.

In a typical MS call origination sequence, the MS will enter a communication cell, accept the BCCH and determine if it has the appropriate class of access to be served by the BSS within that cell. If so, the MS requests service at the BSS with a one-byte information signal, commonly referred to as a Random Access Burst (RAB), which is sent to the BSS on the Random Access Channel (RACH). If the MS cannot receive a response to the RAB from the BSS within a time interval, the MS shall pause and issue a second RAB. For security, the RAB contains little information and no information about the specific identity of the MS requesting service. Therefore, the BSS cannot identify that the second RAB is from the same MS as the first RAB, and will attempt to service both requests when in fact only one needs to be served. As a result, the allocation efficiency of communication resources in such a system is very low.

This phenomenon is particularly problematic in situations where an MS user requests priority access, eg, in an emergency situation where the user may need immediate access to the system. Although a byte of RAB has no information about the MS specific identity, it contains a single bit called the Emergency Word (EW), which, when enabled, will identify the request as a Emergency access request. EW may be enabled in one of three ways: the MS has an emergency access class (10); the MS has a normal access class but is attempting to make an emergency call (ie 911); or the MS has a special service access level and are attempting to make an emergency call such as 911. Although the service request is identified as an emergency by the EW, the specific identity of the MS remains unknown. So, the case of multiple RABs leading to inefficient loading of the BSS still holds. The result is that when the user needs the fastest BSS service, the work of the BSS is inefficient.

Accordingly, there is a need for a method and apparatus for providing rapid access to a radiotelephone communications system to service preferred incoming calls without unduly loading the system and without losing the security provided by current RAB architectures.

1 generally depicts a block diagram of a cellular radiotelephone communications system adapted to embody priority access services in accordance with the present invention;

Figure 2 depicts an example flow diagram illustrating an embodiment of a prior art call processing sequence for a normal access service request.

Figure 3 generally depicts a block diagram of a radiotelephone communications system embodying priority access service features in accordance with the present invention.

Figure 4 provides an example flow diagram illustrating an embodiment of a priority access service according to the present invention;

Figure 5 generally depicts an example of the RAB structure as defined in GSM Recommendation 4.08; and

Figure 6 generally depicts the relationship between flags and a ratio of the number of emergency service requests received to the number of communication channels available within the communication system.

A communication system 115 receives a paging signal 103 requesting service from a mobile station 100, and if the paging signal 103 contains information determining that the service request is an emergency 502, a communication channel in a base transceiver station 105, 107, 109 is directly assigned to serve the mobile station 100. If a communication channel is not immediately available, the communication system 115 will attempt to form an available communication channel. A distinctive feature of the communication system 115 is that it monitors a sign 600 representing emergency call traffic on the communication system 115 . Depending on the state of the flag 600, the communication system 115 employs an appropriate method 440 to provide priority service to those mobile stations 100 having a priority access class. By providing priority service in this manner, the communication system 115 efficiently allocates communication resources to mobile stations 100 with a priority access class that are in urgent need of resources.

The present invention includes a communication system 115 that assigns a communication channel in the system to a user 100 requesting emergency services 502 . Communications system 115 accomplishes this by first receiving a signal 103 from user 100 containing emergency services information 502 . Depending on the status of the emergency services information 502 contained in this signal 103, the communications system 115 will directly assign a communications channel to service the emergency services request rather than wasting time through the standard call processing sequence of FIG. In the event that a communication channel is not immediately available, the communication system 115 will allocate a control channel to temporarily place the emergency service request while simultaneously releasing a voice channel, thereby creating a new available communication channel. A new available communication channel is then assigned to the emergency service request.

Another feature of the communication system 115 is that at the moment of emergency 404, it proactively restricts access to those users having a priority access class. The communication system 115 accomplishes this by receiving a plurality of signals 103 from a plurality of users 100 corresponding to priority access levels; monitoring a flag 600 representing emergency call traffic on the communication system 115, and When thresholding, access to the communication system 115 is denied to all other users except those users with a priority access class 440 . Therefore, in accordance with the claimed invention, another improvement over the prior art is that the communication system 115 will track the flag 600, which represents the emergency access load on the communication system 115, and in accordance with reaching a threshold, except for priority access requests 440 Additionally, it will deny all requests to provide optimal service to those users.

The present invention is described in terms of an embodiment relating to a Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA) radiotelephone communications system. Those skilled in the art will appreciate that the present invention is applicable to any type of radiotelephone communication system, such as analog, Code Division Multiple Access (CDMA) or other TDMA type. Referring to FIG. 1, there is depicted a block diagram of an example cellular radiotelephone communications system suitable for embodying priority access services in accordance with the present invention. Illustrated in FIG. 1 is a radiotelephone communications system which includes a plurality of base transceiver stations (BTS) 105-109 served by a base station controller (BSC) 111, which form a base station system (BSS) 115. BSC 111 is connected to a Mobile Switching Center (MSC) 120 which in turn is connected to a Public Switched Telephone Network (PSTN) 130 . Mobile stations, one of which is shown as MS 100, operate in communication cells served by BTS 105-109 and communicate with one of BTS 105-109 via radio frequency (RF) signals 103 in a known manner. Calls originating or terminating on MS 100 are routed through MSC 120 to a wireless telephone subscriber linked to PSTN 130 or to other wireless telephone communication system subscribers served by MSC 120 or other MSCs (not shown).

In a preferred embodiment, mobile stations (MS) 100 served by BSS 115 are assigned access classes to manage access to the BSS. To request the service of the BSS 115, the MS 100 will send a signal 103, commonly called a paging, to all BTSs 105-109. In the preferred embodiment, the paging signal is called a Random Access Burst (RAB), which is an 8-bit (one byte) signal sent by the MS 100 to all BTSs 105-109 within range of the BSS 115 requesting service information. Of special significance within the RAB is the Emergency Word (EW), which, in effect, will identify the service request as an emergency call.

Referring to FIG. 5, an example of an 8-bit RAB 500 structure is shown, which identifies a 3-bit EW 502 within the RAB 500. EW 502 may be enabled in one of three ways: MS 100 has an emergency access class; MS 100 has a normal access class but is attempting to make an emergency call (i.e. 911); MS 100 has a special services access level and are attempting to make an emergency call, such as 911. So, although BSS 115 is not aware of the special identity of MS 100, when EW 502 contained in RAB 500 is enabled, it knows that the service request is an emergency. In the preferred embodiment, when EW 502 is enabled, as identified above, it will be set to a logic state "1" and conversely, when disabled, it will be set to a logic state "0".

Referring to Figure 2, a flow diagram of an embodiment of the prior art is shown. It specifies the call processing sequence for normal access service requests. Under the condition of normal call, when MS 100 requests access on BSS 115, it will send a signal 103 requesting normal service (that is, EW is prohibited), shown in step 200, and in step 202, BSS 115 will allocate An available control channel gives MS 100 to respond to this random service request, and signal MS 100: BSS 115 has accepted its service request 206. However, since a control channel cannot handle audio calls it can only be used for signaling purposes. So in step 208, when MS 100 temporarily camps on the control channel, BSS 115 will signal to MSC 120 that BSS 115 has an incoming call from MS 100, so in step 210, MSC 120 can determine whether to request audio service, and control Unlike channels, the communication channel is capable of handling audio calls and signaling information, and at step 212, the control channel will handle the call 220 if the MSC 120 determines that the communication channel is not required. On the other hand, when it is determined that a communication channel is needed at step 212, then MSC120 will notify BSS115 at step 214 that a communication channel is requested. In step 216, the BSS 115 will determine which communication channel to allocate and notify the MS 100 via the control channel to tune to a specific frequency to access the communication channel 218, then release the control channel.

Within the scope of the preferred embodiment of the GSM communication system, the control channel will hereinafter be referred to as a separate dedicated control channel (SDCCH) and the communication channel will be referred to as a traffic channel (TCH).

Referring to FIG. 3, there is shown a typical example of a block diagram of a radiotelephone communication system embodying the features of priority access service according to the present invention. In this embodiment, a signal 103 comprising RAB 500 is sent from MS 100 to BTS 105-109 antenna 302. Received signal 103 is coupled via amplifier 304 to channel equalizer/detector 306 which detects the presence of RAB 500 within signal 103. The communication channel determination/allocation means 310 then determines whether the RAB 500 has an active EW 502 in the input signal 103, and if so, it will allocate the MS 100 to an available TCH. If BTS 105-109 does not have an available TCH, then communication channel determination/allocation means 310 determines whether SDCCH is available, and if so, then it is allocated to MS 100 while removing a TCH for MS 100 to use. If the communication channel determination/assignment means 310 determines that the SDCCH is not available, it will adjust a flag 600 to indicate an emergency call request in anticipation of future call requests. Once the TCH is available, the TCH will operate in a known manner 308, 312, 330, 320, 318, 316 and 314. The communication channel determination/assignment means 310 is only used to determine whether the TCH is available, and if so, allocate it to the MS while constantly tracking the number of emergency service requests received by the BSS in the form of tokens 600 .

Figure 4 provides an example flow diagram illustrating an embodiment of a priority access service in accordance with the present invention. In step 400, the BSS 115 will receive a signal 103 from the MS 100 containing the RAB 500. In an emergency call origination sequence, at step 402, the BSS 115 will determine that the EW 502 of the RAB 500 sent by the MS 100 will be enabled, and after adjusting the flag 404, the request will be made immediately by any available TCH 408-412 Processing, the latter will signal to the MS 100: BSS 115 has accepted its request, thereby providing the highest priority access for this urgent request. Therefore, an improvement of the prior art that the present invention carries out is: when BSS 115 receives RAB 500 with valid EW 502 to indicate an emergency service request, this request will be processed immediately by any available TCH There is no SDCCH processing, thus minimizing the time required to complete the originating call.

In step 408, if the BSS 115 does not have an available TCH, it will allocate an available SDCCH 414-418, signal the MS 100 that the BSS 115 has accepted its request (just as in a normal random service request) and begin "Tear down" a TCH with 420 non-emergency calls. The "teardown" process closes the communication path between MS 100 and BSS 115, thereby freeing a communication channel. In a preferred embodiment, newly available TCHs will be used for MSs 100 temporarily camping on SDCCHs 422-424. So, another improvement to the prior art is that when no TCH is available except one SDCCH, the BSS 115 will temporarily place the MS 100 on the SDCCH (it will signal the MS 100 that the request has been accepted, thus preventing suspend/resend RAB problem) and initiates a "tear down" of lower priority calls, thereby minimizing the time taken to provide MS 100 requested service.

In step 416, when BSS 115 does not allocate SDCCH or TCH to an emergency call, MS 100 will not receive any response to its originating RAB 500. The MS 100 will pause waiting for the BSS 115 to respond, and in step 416 will issue another RAB 500. Therefore, the BSS 115 can receive multiple RABs 500 from the same MS 100. In this way, when a unit is highly utilized, several non-emergency calls can be terminated in an effort to release a TCH to a retransmitting emergency RAB 500.

Because it is likely that several MS 100 will strive for the same emergency call, BSS 115 will track a flag at step 426, which will provide an indication of the emergency call's level of service. When the flag reaches a threshold 426, the BSS 115 will first restrict access to the normal access class 432 in favor of the priority access class. So another improvement to the technology is that the present invention allows the BSS 115 to act on an emergency by anticipating the increased need for communication channels and maintaining those channels for several MSs 100 with priority access levels.

Finally, FIG. 6 depicts an example of a marker metric 600 with reference to the markers associated in step 426 . BSS can be used to track the load of emergency calls placed on a system. Specifically, FIG. 6 shows a signature 600 defined to relate a ratio of the number 602 of emergency service requests to the number 604 of communication channels available within a given BSS within a given period of time. Ratio.

In summary, the invention claimed herein provides two significant improvements over the prior art. First, when the communication system receives a page with emergency service information, any available communication channel immediately handles the request directly, rather than the normal BSS-MSC communication process exhibited by the prior art. Second, the communications system will keep track of a flag representing emergency call traffic placed on the system, and in the event of an emergency, it will initially deny access to the communications system to all users except those with a priority access class of service user. Together, these two improvements provide a much more responsive and effective communication system in emergency situations.

Claims (8)

1. A method for allocating communication channels in a communication system, the method comprising the steps of: receiving a signal from the first user containing an emergency services message; determining whether there is an available communication channel; and An available communication channel is assigned to the first user based on the status of the emergency services information. 2. The method according to claim 1, further comprising the steps of: determining whether an available control channel exists when no communication channel is available; and When it is determined that the control channel is available, the available control channel is allocated to the first user. 3. The method of claim 1, wherein the step of determining whether there is an available communication channel further comprises the step of removing second users without an emergency access level from a communication channel to create an available communication channel. 4. An apparatus for allocating communication channels in a communication system, the apparatus comprising: means for receiving a signal containing emergency services information from a first user; means for determining whether there is an available communication channel; and An available communication channel is allocated to the device of the first user. 5. The apparatus according to claim 4, further comprising: means for determining whether a control channel is available when no communication channel is available; and When it is determined that the control channel is available, the available control channel is allocated to the device of the first user. 6. The apparatus of claim 4, wherein the means for determining whether there is an available communication channel further comprises means for removing second users without an emergency access level from a communication channel to produce an available communication channel. 7. A method for providing a plurality of communication channels to corresponding plurality of users in a communication system, the method comprising the steps of: receiving a plurality of signals from a corresponding plurality of users; tracking a flag related to the number of received signals with priority access information; and When the mark reaches a certain threshold, access to the communication system is restricted to those users with priority access information. 8. A method according to claim 7, wherein the flag is a ratio of the total number of received signals with priority access information to the total number of communication channels in the communication system.

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