GB2322520A

GB2322520A - Method for Allocating a Communications Resource for a Group Call

Info

Publication number: GB2322520A
Application number: GB9703743A
Authority: GB
Inventors: Andrew John Aftelak; Matthew Quinton Bridle; Douglas Gray
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1997-02-22
Filing date: 1997-02-22
Publication date: 1998-08-26
Anticipated expiration: 2017-02-22
Also published as: GB2322520B; GB9703743D0

Abstract

A method is provided for allocating at least one communications resource for a group call based service in a cellular based radio system having a plurality of cells and a plurality of mobile stations operating within the cells. The method comprises the steps of determining a distribution of group call users among the mobile stations in the cells and allocating at least one communications resource for the group call based service based on the distribution.

Description

METHOD FOR ALLOCATING A COMMUNICATIONS RESOURCE FOR A GROUP CALL BASED SERVICE Field of the Invention This invention relates in general to a method for allocating a communications resource in a cellular radio communications system, and more particularly, to a method of allocating a communications resource for a group call based service in a radio cellular communications system.

Background to the Invention Wide area radio systems use multiple sites or cells to provide coverage across a required area. A technique used in cellular radio systems to provide more capacity is to make the area covered by each site smaller and to introduce more sites. Because the same frequencies are re-used geographically throughout the system, using smaller cells allows the frequencies to be used more often and hence the capacity of the system can be increased.

However, decreasing cell size is not necessarily helpful for all aspects of a communications system. In particular, in systems that provide wide area group calls, the concept of decreasing the cell size to increase capacity does not work once the area over which the members of the group are distributed is comparable with the area covered by each cell. Once the group is distributed across more than one cell a channel resource has to be used at each cell in which a member of the group is registered.

Even when the members of a group are physically within the nominal coverage area of a single cell, the effects of shadowing can mean that some members of the group are registered at adjacent sites.

An additional problem for wide-area group calls is grade of service in terms of the blocking probability or call set-up delay. Trunking systems are designed to offer a certain probability of blocking or queuing during the busy hour. The higher the number of cells used in the group call the higher the probability that the call will be blocked or delayed, since the call will not be able to proceed until a channel resource is available at each of the required cells.

In some cellular systems there is a feature called busy override that may be used. If a channel is not immediately available at all the sites at which members of the group are registered, the user receives a "busy" indication. Selected users are able to generate a busy override either manually or automatically. A call will then be set-up at all sites that have a channel available provided that "critical sites" have a channel available and/or sites at which a "critical user" is registered have a channel available. Members of the group registered at "noncritical" sites at which no channel is currently available are not included in the call. Critical sites and users are set by the system manager on a per talk group basis. This solution helps to reduce the traffic loading on the system, but is aimed mainly at reducing the call set-up delay. It is not desirable for instances when it is imperative that all members of the group must communicate in a group call.

In other communications systems, there is a feature called "Preferred Site Operation". This allows a site to be stored in a subscriber radio as a preferred site. A preferred site will always be used, provided the signal strength is above a minimum level, in preference to adjacent sites, even if the adjacent sites provide a higher quality signal. This feature is aimed at minimising the number of channels used for a group call. Although sometimes useful, a problem with this feature is that preferred sites are not linked to the current location of the group. Thus, the preferred site may in fact give poor quality of service. A poor quality communication is unacceptable in most communications systems, particularly in public safety markets.

Other cellular system solutions for group calls do not guarantee any number of members will be included in the group call. Thus, there is a desire, in cellular systems to have a group call service feature that allows a certain number of expected members of the group to be able to effectively communicate in a group call as desired.

Summarv of the Invention According to the present invention, a method is provided for allocating at least one communications resource for a group call based service in a cellular based radio system having a plurality of cells and a plurality of mobile stations operating within the cells, the method comprising the steps of determining a distribution of group call users among the mobile stations in the cells; and allocating at least one communications resource for the group call based service based on the distribution.

Brief Description of the Drawing FIG. 1 shows cellular radio communications system having a plurality of cells and a plurality of group call user mobile stations distributed among the cells.

FIGs. 2-4 each show a flow chart according to different embodiments of the present invention.

Detailed Description of the Preferred Embodiment This invention is described with reference to a cellular radio communications system having a plurality of cells 1-4 and a plurality of mobile stations 10, 20, 30, 40 as shown in FIG. 1. If a group call, including the mobile stations as shown, is requested to be set up then a method according to the present invention may be used. The present invention allocates at least one communications resource, or channel, for a group call based service in a cellular based radio system by determining a distribution of group call users among the mobile stations in the cells and allocating at least one communications resource for the group call based service based on the distribution.

An embodiment of the present invention is shown in FIG. 2. In step 200 of FIG. 2, a distribution of the group across the cell pattern is determined. In particular, for the embodiment of FIG. 2, the number or percentage of group call users are determined for each cell. For example, in the distribution of FIG. 1 of group call users, 60% of the group call users or members are in cell 3, 20% are in cell 4, and 10% are in cells 1 and 2.

Referring back to FIG. 2, when a group call service request is initiated, or a best cell group call request, a communications resource is allocated to facilitate the group call in the cell which contains the highest number or percentage of users, step 202. Furthermore, a communications resource is also allocated in the cell of the call initiator of the request if different from the cell which contains the highest number or percentage of users, also step 202. Thus, for example, if a best cell group call request is made in a distribution as shown in FIG. 1, then a communications resource would be allocated in cell 3 because cell 3 has the highest number of group call users in it.

The best cell group call is set-up using only a communications resource at the cell at which the greatest number of group members are located, and the cell of the initiator, if different. Therefore, only one communications channel may be used for each group call and the system advantageously achieves the best possible spectrum efficiency. Although there is no guarantee of the number of group members included in the best cell, the system operator is guaranteed that only one, maybe two, channels will be used and could therefore offer this service at a lower cost than a conventional group call.

Another embodiment of the present invention is shown in the flow chart of FIG. 3. Similarly, a distribution of group call users are determined across a cell pattern in terms of the highest number or percentage of members in each cell as in step 300. However, upon receipt of a group call request, or percentage of group call request, a particular percentage of the group call users is requested, threshold percentage. The minimum number of cells are then determined as required to reach the threshold percentage of the group call users as in step 302. Communication resources are allocated only in the cells as determined to reach at least the threshold percentage of users, step 304. Thus, for example, if an 80% percent of the group call users is requested in a distribution as shown in FIG. 1, then a communications resource would be allocated in cells 3 and 4 because cells 3 and 4 are the minimum number of cells that together provide at least 80% of the group call users in it.

The threshold percentage could be predefined or selected by a user at call set-up. Using this service a user is guaranteed to reach a certain percentage of their group and at the same time the number of channels used for the call is likely to be less than in a conventional group call. A call charge rate could be linked to the number of cells used in the call or the percentage of the group selected.

A A further embodiment of the present invention is shown in the flow chart of FIG. 4. Similarly, a distribution of group call users are determined across a cell pattern in terms of the highest number or percentage of members in each cell as in step 400. The cell with the largest number or percentage of users is defined as the preferred site, step 402. The communications system then periodically transmits to the group call users the preferred site as determined above, step 404. The preferred site may be dynamically determined upon request and transmitted by the system.

The preferred site group call service requires that the infrastructure periodically checks to determine how many members of the group are currently registered at each site. The site at which the greatest number of group members are registered is marked as the preferred site. This preferred site is then broadcast at each site at which group members are registered. Each mobile station then knows to use the currently preferred site whenever possible. This "Dynamic Preferred Site Operation" service has the benefit of minimising the number of channels used for a group call but at the same time maximising the call quality for the majority of the group even if the location of the group moves across different sites. Similarly, the system could allocate two or more preferred sites dependent on the location density of group members.

The present invention offers a method to provide efficient and effective group call services in a cellular communications system. By using the method of the present invention the minimum number of resources are used as determined to have an effective group call.

Claims

1. A method of allocating at least one communications resource for a group call based service in a cellular based radio system having a plurality of cells and a plurality of mobile stations operating within the cells, the method comprising the steps of: determining a distribution of group call users among the mobile stations in the cells; and allocating at least one communications resource for the group call based service based on the distribution.

2. The method according to claim 1 wherein the step of determining further comprises the step of: determining from the distribution of group call users which cell has a largest percentage of group call users in it; and wherein the step of allocating includes allocating at least one communications resource from the cell determined to have the largest percentage of users in it.

3. The method according to claim 1 wherein the step of determining further comprises the step of: determining from the distribution of group call users a minimum number of cells required to meet a requested percentage of group call users; and- wherein the step of allocating includes allocating at least one communications resource from each of the minimum number of cells.

4. The method according to claim 1 wherein the step of determining further comprises the step of: determining from the distribution of group call users which single cell has the most users in it; and periodically transmitting to the group call users the single cell which has the most users in it as determined above.

5. The method of claim 4 wherein the step of determining from the distribution of group call users which single cell has the most users in it is dynamic.

6. A method of allocating at least one communications resource as substantially as herein described with reference to FIGs. 2-4 of the drawings.