CN100361544C - A Realization Method of Trunking Service Based on GSM Public Network - Google Patents

Abstract

The present invention provides a method for implementing trunking services based on the GSM public network, the core of which is: the trunking mobile terminal determines the information carried in the system message of at least one trunking cell transmitted by the trunking base station subsystem through the channel resources of the GSM public network frequency band. The cluster cell where it resides, and performs cluster services in the cluster cell where it resides. The present invention superimposes the cluster network based on GSM technology on the GSM public network, so that the GSM public network can provide a unified cluster service for the cluster mobile terminal through the cluster network superimposed on it, so that the cluster network can have the same frequency band as the GSM public network , the same network number, so that the trunking mobile terminal always guarantees the preferred trunking cell when performing cell selection and cell reselection, so that the trunking mobile terminal can realize trunking services within the coverage of the trunking network, and outside the coverage of the trunking network Realize GSM public network service.

Description

A Realization Method of Trunking Service Based on GSM Public Network

technical field

The invention relates to the technical field of network communication, in particular to a method for realizing cluster services based on the GSM public network.

Background technique

With the development of wireless communication technology, the demand of group customers for trunking business is increasing day by day. At present, there are mainly two methods for providing cluster services to customers.

Method 1: Provide trunking services to the public through the public mobile digital network in GSM (Global System for Mobile Communications).

Due to the limited trunking services stipulated in the latest protocol of the GSM public network, and there are many GSM equipment manufacturers, the protocol versions of the GSM public network supported by each GSM equipment are inconsistent, so it is difficult to provide the public with a unified GSM latest protocol regulation through version upgrades The most basic cluster business, so the GSM public network cannot meet the growing demand for cluster services.

Method 2: Provide trunking services to trunking customers through a digital trunking network in GT (a trunking digital system based on the GSM system).

Based on the GSM technology system, GT digital trunking network is designed for professional trunking business characteristics and provides rich and powerful trunking functions. Trunking dispatching services specifically include: voice group call, voice broadcast, function number addressing, location-based routing, late entry, group call hold, dynamic grouping, group status display, group call merging, included call, careful monitoring, environmental monitoring, Remote opening and remote closing, area selection, priority call, preemption priority call, call restriction, control transfer, key remote destruction, open channel call and telephone supplementary services, etc. The trunking service it provides is far superior to the trunking service provided by the GSM public network in terms of business types and performance. However, because the GT digital trunking network needs to use a special frequency band and network number different from the GSM public network, it not only wastes valuable network resources, but also limits the application of the trunking mobile terminal to the trunking cell, which greatly limits the trunking The scope of use of mobile terminals.

Contents of the invention

The purpose of the present invention is to provide a method for implementing trunking services based on the GSM public network. By superimposing the trunking network based on GSM technology on the GSM public network, the trunking mobile terminal can realize the trunking service through the GSM public network.

In order to achieve the above object, a kind of trunking service realization method based on GSM public network provided by the present invention comprises:

The trunking mobile terminal determines the trunking cell where it resides based on the information carried in the system message of at least one trunking cell transmitted by the trunking base station subsystem through the channel resources of the GSM public network frequency band, and performs trunking services in the trunking cell where it resides.

The method further comprises:

a. The cluster base station subsystem and the GSM public network base station subsystem respectively transmit the system messages of the cluster cell and the GSM public network cell through the broadcast control channel of the GSM public network frequency band;

b. The trunking mobile terminal determines the trunking cell/GSM public network cell where it resides based on the information carried in the system message of at least one cell it receives, and performs corresponding trunking services/GSM public network services in the cell where it resides.

Described step a comprises:

Set the cluster cell ID;

Set the corresponding relationship between the cluster cell access prohibition flag, the cluster cell access prohibition permission flag, and the cell selection priority of the cluster cell;

The cluster base station subsystem carries the cluster cell identifier, the cluster cell access prohibition identifier, and the cluster cell access prohibition permission identifier in the predetermined field of the system message of the cluster cell, and transmits it through the broadcast control channel of the GSM public network frequency band;

The GSM public network base station subsystem carries the cell access prohibition identifier and the cell access prohibition permission identifier in the system message of the GSM public network cell, and transmits them through the broadcast control channel of the GSM public network frequency band.

The cell selection priority of the cluster cell includes: normal cell selection priority, low cell selection priority, and forbidden cell selection priority.

The cell selection priority corresponding to the cell access prohibition flag and the cell access prohibition permission in the system message of the cluster cell is set to prohibit;

And the cell selection priority of the cluster cell is higher than the corresponding cell selection priority of the GSM public network cell.

The predetermined field of the system message is: a free field of system message 3 or system message 4.

Said step b further comprises:

The cluster mobile terminal determines all suitable cells according to the GSM protocol, and judges whether the system information of each suitable cell carries a cluster cell identifier;

If the system message of the appropriate cell carries the cluster cell identifier, obtain the cluster cell access prohibition identifier and the cluster cell access prohibition permission identifier from the system message;

If the system information of the appropriate cell does not carry the cluster cell identifier, obtain the cell access prohibition identifier and the cell access prohibition permission identifier from the system information;

determining the priority of each cell according to the identifiers obtained from the system message;

The cluster mobile terminal determines the cell to camp on according to the priority of each suitable cell, and camps on;

The trunking mobile terminal performs corresponding trunking service/GSM public network service in the cell where it resides as required.

Said step a also includes:

a1. Set the corresponding relationship between the cluster cell access prohibition flag, the cluster cell access prohibition permission flag, and the cell reselection state of the cluster cell;

a2. Determine the adjacent GSM public network cells and the cluster cells of the trunked digital system based on the GSM system, and store the adjacent cell information in the broadcast control channel frequency allocation table.

The cell reselection state of the cluster cell includes: the cell reselection state is normal, and the cell reselection state is forbidden.

Described step a2 comprises:

Configure cluster neighbors in the broadcast control channel frequency point allocation table of the GSM public network cell;

Configure the GSM public network neighbor cell in the broadcast control channel frequency allocation table of the cluster cell.

Said step a also includes:

Setting the cluster cell reselection offset parameter in the cluster mobile terminal;

And the step b includes:

The trunking mobile terminal measures the downlink signal strength of the broadcast control channel of each neighboring cell according to the broadcast control channel frequency point allocation table carried in the system message of the cell where it resides, and determines a predetermined number of downlink signal strengths of the broadcast control channel according to the measured downlink signal strength of the broadcast control channel. Neighborhood;

The cluster mobile terminal respectively calculates and determines the C2 values of the predetermined number of neighboring cells according to the cluster cell reselection offset parameter and the cluster cell identification carried in the system message of the corresponding neighboring cell;

When the cluster mobile terminal determines that cell reselection needs to be performed according to the calculated C2 value, the reselected cell status of the cluster cell, and the cell reselection trigger criterion of the GSM protocol, according to the cluster cell reselection offset parameter, the corresponding adjacent cell The cluster cell identifier carried in the system message determines the reselection priority of each neighboring cell;

The cluster mobile terminal determines the reselection target cell according to the reselection priority of each neighboring cell, and resides there;

The trunking mobile terminal performs corresponding trunking service/GSM public network service in the reselection target cell where it resides as required.

The steps for determining the C2 value of each neighboring cell are specifically:

When the penalty time PENALTY_TIME is not equal to 11111: C2=C1+TCF×GT_CELL_RESELECT_OFFSET+CELL_RESELECT_OFFSET-TEMPORARY_OFFSET×H(PENALTY_TIME-T);

When the penalty time PENALTY_TIME is equal to 11111: C2=C1+TCF*GT_CELL_RESELECT_OFFSET-CELL_RESELECT_OFFSET;

Among them: TCF is the cluster cell identifier, and when the adjacent cell is a GSM public network cell, TCF is 0, and when the adjacent cell is a cluster cell, TCF is 1;

GT_CELL_RESELECT_OFFSET is the cluster cell reselection offset parameter;

CELL_RESELECT_OFFSET is the GSM public network cell reselection offset parameter;

TEMPORARY_OFFSET is a temporary offset parameter;

H(PENALTY_TIME-T) is a function of H(x), and T is the duration of the corresponding neighboring cell becoming a predetermined number of neighboring cells. When x>0, H(x)=0, when x≤0, H (x)=1.

The cluster cell reselection offset parameter is greater than the sum of the maximum value of the C2 values corresponding to each neighboring cell and the cell reselection offset parameter.

The steps of determining the reselection priority of each neighboring cell according to the cluster cell reselection offset parameter and the cluster cell identifier carried in the system message of the corresponding neighboring cell are specifically as follows:

The C2 values corresponding to the neighboring cells are sorted according to the sequence from large to small, and the reselection priority of each neighboring cell is determined according to the sorting of the C2 values.

Through the description of the above technical solution, it can be clearly known that the present invention distinguishes the cluster cell system message received by the cluster cell system message through the setting of the cluster cell system message, the cluster mobile terminal through the channel resource transmission of the GSM public network frequency band, and the transmission of the GSM public network cell. The incoming system message enables the cluster network and the GSM public network to use the same frequency band and the same network number; by setting T_CBQ, T_CBA, the cell selection priority of the cluster cell and the cell selection priority of the GSM public network in the system message, When the cluster mobile terminal is performing cell selection, the cluster cell is preferred; by setting the cluster cell reselection offset parameter and the reselection cell calculation method in the cluster mobile terminal, the cluster mobile terminal is preferably cluster cell when performing cell reselection; By setting the CBQ and CBA in the system message of the cluster cell, the common mobile terminal will not use the cluster cell as the object of cell selection and cell reselection; thus the technical solution provided by the present invention realizes superposition based on GSM technology on the GSM public network trunking network, so that the GSM public network can provide unified trunking services for trunking mobile terminals through the trunking network superimposed on it, so that trunking mobile terminals can realize trunking services within the coverage of the trunking network, and outside the coverage of the trunking network GSM public network services can be realized within the coverage of GSM public network, which effectively saves valuable network resources, enriches the functions of trunking mobile terminals, and expands the use range of trunking mobile terminals.

Description of drawings

Fig. 1 is the flow chart of cell selection of the cluster mobile terminal of the present invention;

Fig. 2 is a flow chart of cell reselection of the cluster mobile terminal in the present invention.

Detailed ways

The core of the present invention is: the cluster mobile terminal determines the cluster cell where it resides according to the information carried by the system message of at least one cluster cell transmitted by the cluster base station subsystem through the channel resource of the GSM public network frequency band, and determines the cluster cell where it resides. Carry out group business.

The technical solution provided by the present invention will be further described below based on the core idea of the present invention.

In the present invention, mobile terminals are divided into trunking mobile terminals and ordinary mobile terminals according to whether trunking services can be realized, and ordinary mobile terminals are various mobile terminals used by mobile users on the GSM public network, and trunking mobile terminals are mobile terminals capable of realizing trunking services .

The trunking SIM card in the trunking mobile terminal is a SIM card registered with the trunking service. The main difference between the trunking SIM card and the ordinary SIM card in the ordinary mobile terminal is that the trunking SIM card includes a trunking function parameter TRUNK_FLAG (trunk identification). The trunking mobile terminal runs in the trunking mobile terminal state only after reading the trunking function parameter in the trunking SIM card. Since there is no trunking function parameter in the common SIM card, when the trunking mobile terminal does not read the trunking function parameter, it runs in the normal mobile terminal state.

If a trunking SIM card is placed in an ordinary mobile terminal, the trunking function parameter is ignored when the ordinary mobile terminal reads the trunking SIM card. Therefore, regardless of whether a trunking SIM card or a common SIM card is placed in the common mobile terminal, the common mobile terminal can only operate in the normal mobile terminal state to realize the services provided by the GSM public network.

The present invention first needs to add three identifications in the system information 3 and system information 4 of the cluster cell transmitted by the cluster base station subsystem, namely TCF (cluster cell identification), T_CBA (cluster cell access prohibition identification), T_CBQ (cluster cell access Entry Prohibition Allow Identifier). TCF, T_CBA, and T_CBQ occupy 1 bit in system information 3 or system information 4 respectively.

The TCF is used to judge whether the cell is a cluster cell, and if the TCF is 1, it indicates a cluster cell.

T_CBA and T_CBQ are used to indicate the cell selection priority and cell reselection status of the cluster cell. The cell selection priority and cell reselection status corresponding to T_CBA and T_CBQ in the cluster cell can be set according to the network planning requirements, as shown in Table 1:

Table 1

Cluster cell access prohibition and permission (T_CBQ) Trunk Cell Access Barring (T_CBA) cell selection priority Cell reselection status 0 0 normal normal 0 1 prohibit prohibit 1 0 Low normal 1 1 Low normal

The settings in CBQ and CBA in system message 3 and system message 4 of the GSM public network cell are shown in Table 2:

Table 2

Cell access barring permission (CBQ)   Cell Access Barring (CBA) Cell selection priority Cell reselection status 0 0 normal normal 0 1 prohibit prohibit 1 0 Low normal 1 1 Low normal

The cell selection priority and cell reselection status in the above two tables have the same meanings as those specified in the GSM system. For example, when the cell selection priority corresponding to a cell is normal, it means that the cell can As the object of cell selection, when the corresponding cell reselection status of a certain cell is prohibited, the cell cannot be used as the object of cell reselection. For example, according to the needs of cluster network optimization, when a cluster cell prohibits cluster mobile terminals from camping, T_CBA and T_CBQ in the system information 3 and system information 4 of the cluster cell are set to 1 and 0 to realize that the cluster cell prohibits the cluster mobile terminal from camping.

CBA and CBQ in system information 3 and system information 4 of the cluster cell can be fixedly set to 1 and 0.

After receiving the system information 3 and system information 4 of the GSM public network cell, the ordinary mobile terminal extracts the relevant parameters CBA and CBQ of the cell selection priority and the cell reselection state, interprets these parameters according to the original definition of the GSM system, and according to the GSM The cell selection and cell reselection methods originally defined by the system are used to realize cell selection and cell reselection.

After receiving the system message 3 and system message 4 of the trunking message, the ordinary mobile terminal ignores TCF, T_CBA, T_CBQ, and still only extracts CBA and CBQ. Since CBA and CBQ are always defined as 0 and 1 in system message 3 and system message 4, According to the original definition of the GSM system, the cell selection priority and the cell reselection state are prohibited, thus ensuring that ordinary mobile terminals will not use the cluster cell as a suitable cell and a suitable cell to reside in, and can only reside in a GSM public network cell, accepting Services provided by the GSM public network.

Considering the existing functions currently implemented by ordinary mobile terminals and trunking mobile terminals, the three identifiers of TCF, T_CBA, and T_CBQ can be filled with idle bits in system information 3 and system information 4. In this way, it is equivalent to the existing GSM Based on the upward evolution of the protocol, the backward compatibility of the GSM protocol version is guaranteed, thus ensuring that the functions supported by the existing common mobile terminals and trunking mobile terminals are not affected by the three identifiers added in the system message.

The present invention also needs to configure GSM public network adjacent area and cluster adjacent area in BA1 (broadcast control channel frequency allocation table) of each GSM public network sub-district, configure cluster adjacent area and GSM public network adjacent area in BA1 of each cluster sub-district .

After the above settings are made, the trunking mobile terminal determines a suitable cell according to the suitable cell determination conditions defined in the GSM protocol.

The suitable cell judgment conditions defined by the GSM protocol are as follows:

1. The cell belongs to the selected network. The network comprises an overlay network of the GSM and trunked networks of the present invention.

2. The cell selection priority of the cell is not "forbidden".

3. The cell is not in a prohibited domestic roaming location area.

4. The wireless path loss between the mobile terminal and the BTS (base station) is within the threshold set by the network, satisfying the criterion of wireless path loss C1>0. The calculation formula of C1 is the same as the definition in the GSM protocol.

When a cell satisfies the above four judging conditions at the same time, the cell is a suitable cell.

For all suitable cells including GSM public network cells and cluster cells, the cluster mobile terminal can determine the suitable cell with the highest priority according to the cell selection priority of each suitable cell, and determine the suitable cell with the highest priority as its camping district.

The cell selection priority of GSM cells shall be determined according to CBA and CBQ in system information 3 or system information 4, and the cell selection priority of cluster cells shall be determined according to T_CBA and T_CBQ in system information 3 or system information 4.

When the present invention sets the cell selection priority of the cluster cell as the normal priority, its priority is the highest; when the cell selection priority of the cluster cell is low priority, its priority is next; the cell selection priority of the GSM public network cell is When it is the normal priority, its priority level is lower, and when the cell selection priority of the GSM public network cell is low priority, its priority level is the lowest.

According to the GSM protocol, only when a high-priority suitable cell does not exist, a low-priority suitable cell will be selected as its resident cell. This mechanism of GSM protocol for selecting a resident cell can ensure that the trunking mobile terminal is When selecting a cell, as long as there is a cluster cell in a suitable cell, the cluster mobile terminal will select the cluster cell as its camping cell instead of camping in the GSM public network cell.

The process of selecting a cell to camp on by the cluster mobile terminal will be described below with reference to FIG. 1 .

In Fig. 1, step 100, the trunking mobile terminal selects a PLMN (Public Land Mobile Network).

Going to step 110, the cluster mobile terminal searches for a suitable cell according to the suitable cell standard defined in the GSM protocol, and determines all suitable cells of the cluster mobile terminal.

Go to step 120, obtain the system message 3 or system message 4 of all suitable cells of the cluster mobile terminal, if the cell of the suitable cell is the cell of the GSM public network, then determine the priority of the cell according to the CBA and CBQ carried in the message, if the cell of the cell is The cluster cell determines the priority of the cell according to the T_CBA and T_CBQ carried in the message. According to the principle of normal cell selection priority of cluster cells > low cell selection priority of cluster cells > normal cell selection priority of GSM public network cells > low cell selection priority of GSM public network cells, the priority of each suitable cell Sort.

Going to step 130, the trunking mobile terminal selects a suitable cell with the highest priority as its camping cell.

From the above description of the cell selection process for the trunking mobile terminal, it can be clearly seen that within the coverage of the trunking network, the trunking mobile terminal preferentially accepts the trunking services provided by the trunking network, while outside the coverage of the trunking network, the trunking mobile terminal will Stay in the GSM public network community and accept the public network services provided by the GSM public network.

After the cluster mobile terminal resides in the cell, the cluster mobile terminal performs cell reselection according to the cell reselection trigger criteria defined in the GSM protocol. The invention needs to set the cluster cell reselection offset parameter GT_CELL_RESELECTION_OFFSET in the cluster mobile terminal.

The cluster cell reselection offset parameter may be set in the SIM card of the cluster mobile terminal, or in other storage media of the cluster mobile terminal.

The cell reselection trigger criteria defined by GSM are as follows:

1. The mobile terminal calculates that the C2 value of the cell belonging to the same location area as the current cell exceeds the C2 value of the current serving cell of the mobile terminal for 5 consecutive seconds.

2. The C2 value calculated by the mobile terminal for a cell that does not belong to the same location area as the current cell exceeds the sum of the C2 value of the mobile terminal's current serving cell and the cell reselection hysteresis value CELL_SELECTION_HYSTERESIS for 5 consecutive seconds.

3. The cell reselection status of the current serving cell of the mobile terminal is "forbidden".

4. The mobile terminal detects a downlink failure.

5. The C1 value of the current serving cell of the mobile terminal is less than 0 for 5 consecutive seconds.

The cell reselection process of the cluster mobile terminal is specifically as follows: after the cluster mobile terminal resides in the cell, it obtains the BA1 carried in the system message 3 or system message 4 of the cell it resides in, and measures the adjacent cell information according to the adjacent cell information stored in BA1. BCCH downlink signal strength, and determine the 6 neighbors with the strongest BCCH downlink signal strength.

The cluster mobile terminal respectively obtains the system information 3 or system information 4 of the above six neighboring cells, according to the TCF carried in the system information 3 or system information 4 of each neighboring cell, and the cluster cell reselection offset parameter GT_CELL_RESELECTION_OFFSET set in the cluster mobile terminal In GSM, the C2 value of each neighboring cell is calculated separately, and the specific formula is as follows:

When the penalty time PENALTY_TIME is not equal to 11111: C2=C1+TCF×GT_CELL_RESELECT_OFFSET+CELL_RESELECT_OFFSET-TEMPORARY_OFFSET×H(PENALTY_TIME-T);

When PENALTY_TIME is equal to 11111: C2=C1+TCF*GT_CELL_RESELECT_OFFSET-CELL_RESELECT_OFFSET;

Among them: PENALTY_TIME is the penalty time, TCF is the cluster cell identifier, and when the adjacent cell is a GSM public network cell, TCF is 0, and when the adjacent cell is a cluster cell, TCF is 1;

GT_CELL_RESELECT_OFFSET is the cluster cell reselection offset parameter;

CELL_RESELECT_OFFSET is the GSM public network cell reselection offset parameter;

TEMPORARY_OFFSET is a temporary offset parameter;

PENALTY_TIME, CELL_RESELECT_OFFSET, TEMPORARY_OFFSET can be obtained from system message 3 or system message 4. T is the duration for the corresponding neighboring cell to become a predetermined number of neighboring cells, H(PENALTY_TIME-T) is a function of H(x), and when X>0, H(x)=0, when X≤0, H (x)=1.

T can be realized by a timer. For example, if the initial value of T is set to 0, when a certain cell is determined by the mobile terminal as one of the six neighboring cells with the strongest BCCH downlink signal strength, the timer corresponding to the cell starts timing. When the cell is no longer one of the six neighboring cells with the strongest BCCH downlink signal strength, the timer corresponding to the cell is reset.

Determine whether the cluster mobile terminal needs cell reselection according to the value of C2 corresponding to each adjacent cell calculated above, C1, downlink monitoring results, etc., and the cell reselection trigger criteria defined by GSM. If cell reselection is not required, this The secondary cell reselection process ends. If cell reselection is required, the neighbor cell corresponding to the calculated maximum C2 value is determined as the reselection target cell, and resides in the reselection target cell.

Since the cluster mobile terminal performs an optimal offset for the cluster cell according to GT_CELL_RESELECTION_OFFSET, as long as GT_CELL_RESELECTION_OFFSET is greater than maxmum(C2)+CELL_SELECTION_HYSTERESIS (cell reselection hysteresis), it can be guaranteed that: as long as there is a cluster cell in the adjacent cell, the cluster mobile terminal will not reselect To the GSM public network cell, that is, when the cluster mobile terminal resides in the GSM public network cell, as long as there are cluster cells in the adjacent cells of the six strongest signals tested by the cluster mobile terminal, the cluster mobile terminal can quickly reselect to the cluster cell ; When the cluster mobile terminal resides in the cluster cell, as long as there is a cluster cell in the adjacent areas of the six strongest signals tested by the cluster mobile terminal, the cluster mobile station will not reselect to the GSM public network cell.

The implementation process of the cluster mobile terminal reselecting a cell will be described below with reference to FIG. 2 .

In FIG. 2 , in step 200, the cluster mobile terminal starts a cell reselection process according to the actual network configuration.

Going to step 210, the cluster mobile terminal obtains the BA1 carried in the system message 3 or system message 4 of the cell it is camping on, and measures the BCCH downlink signal strength of all neighboring cells of the cell it is camping on according to the neighbor cell information stored in the BA1.

Going to step 220, the trunking mobile terminal sorts the measured BCCH downlink signal strengths of neighboring cells according to the signal strengths.

Go to step 230, determine the six cells with the strongest signal strength, and obtain their system information 3 or system information 4 respectively.

Go to step 240, according to the C2 calculation formula described in the above-mentioned embodiments, use the cluster cell reselection offset parameter, the TCF carried in the system message 3 or system message 4 to calculate C2, and calculate C2 according to the order from large to small value to sort.

Go to step 250, according to the C2 value calculated above, the TCF carried in system message 3 or system message 4, and the cell reselection status determined by CBA, CBQ, T_CBA, T_CBQ, etc., use the cell reselection criteria defined in the GSM protocol to judge the cluster Whether the mobile terminal needs cell reselection, if cell reselection is required, then go to step 260, the cluster mobile terminal selects the neighbor cell with the largest C2 value as the cluster cell/GSM public network cell where it resides, and resides. Going to step 200, the cluster mobile terminal starts the next cell reselection process according to the actual network configuration.

In step 250, if the cluster mobile terminal does not need cell reselection, go directly to step 200, and the cluster mobile terminal starts the next cell reselection process according to the actual network configuration.

From the above description of the cluster mobile terminal reselection process, it can be clearly seen that within the coverage of the cluster network, the cluster mobile terminal preferentially accepts the cluster services provided by the cluster network, while outside the coverage of the cluster network, the cluster mobile terminal It will stay in the GSM public network community and accept the public network services provided by the GSM public network.

While the invention has been described by way of example, those skilled in the art will appreciate that there are many variations and changes to the invention without departing from the spirit of the invention, and it is intended that such variations and changes be covered by the appended claims.

Claims (14)

1, a kind of trunking service realization method based on GSM public network, it is characterized in that comprising: The cluster mobile terminal determines the cluster cell where it resides based on the information carried in the system message of at least one cluster cell transmitted by the cluster base station subsystem through the broadcast control channel resources of the GSM public network frequency band, and performs cluster services in the cluster cell where it resides . 2. A method for realizing cluster services based on GSM public network as claimed in claim 1, characterized in that said method further comprises: a. The cluster base station subsystem and the GSM public network base station subsystem respectively transmit the system messages of the cluster cell and the GSM public network cell through the broadcast control channel of the GSM public network frequency band; b. The trunking mobile terminal determines the trunking cell/GSM public network cell where it resides based on the information carried in the system message of at least one cell it receives, and performs corresponding trunking services/GSM public network services in the cell where it resides. 3. A method for realizing cluster services based on GSM public network as claimed in claim 2, characterized in that said step a comprises: Set the cluster cell ID; Set the corresponding relationship between the cluster cell access prohibition flag, the cluster cell access prohibition permission flag, and the cell selection priority of the cluster cell; The cluster base station subsystem carries the cluster cell identifier, the cluster cell access prohibition identifier, and the cluster cell access prohibition permission identifier in the predetermined field of the system message of the cluster cell, and transmits it through the broadcast control channel of the GSM public network frequency band; The GSM public network base station subsystem carries the cell access prohibition identifier and the cell access prohibition permission identifier in the system message of the GSM public network cell, and transmits them through the broadcast control channel of the GSM public network frequency band. 4. A method for implementing a trunking service based on a GSM public network as claimed in claim 3, wherein the cell selection priority of the cluster cell includes: normal cell selection priority, low cell selection priority, and cell selection priority level prohibited. 5. A method for realizing cluster services based on the GSM public network as claimed in claim 3, characterized in that: In the system message of the cluster cell, the cell selection priority corresponding to the cell access prohibition identifier and the cell access prohibition permission is set to prohibition, and the cell access prohibition identifier and the cell access prohibition permission are respectively used to indicate the cell reselection status and cell selection priority; And the cell selection priority of the cluster cell is higher than the corresponding cell selection priority of the GSM public network cell. 6. A method for implementing a trunking service based on a GSM public network according to claim 3, wherein the predetermined field of the system message is an idle field of system message 3 or system message 4. 7. A method for realizing cluster services based on GSM public network as claimed in claim 3, characterized in that said step b further comprises: The cluster mobile terminal determines all suitable cells according to the GSM protocol, and judges whether the system information of each suitable cell carries a cluster cell identifier; If the system message of the appropriate cell carries the cluster cell identifier, obtain the cluster cell access prohibition identifier and the cluster cell access prohibition permission identifier from the system message; If the system information of the appropriate cell does not carry the cluster cell identifier, obtain the cell access prohibition identifier and the cell access prohibition permission identifier from the system information; determining the priority of each cell according to the identifiers obtained from the system message; The cluster mobile terminal determines the cell to camp on according to the priority of each suitable cell, and camps on; The trunking mobile terminal performs corresponding trunking service/GSM public network service in the cell where it resides as required. 8. A method for implementing trunking services based on the GSM public network according to any one of claims 3 to 7, characterized in that said step a further comprises: a1. Set the corresponding relationship between the cluster cell access prohibition flag, the cluster cell access prohibition permission flag, and the cell reselection state of the cluster cell; a2. Determine the adjacent GSM public network cells and the cluster cells of the trunked digital system based on the GSM system, and store the adjacent cell information in the broadcast control channel frequency allocation table. 9. A method for implementing a cluster service based on a GSM public network according to claim 8, wherein the cell reselection status of the cluster cell includes: the cell reselection status is normal, and the cell reselection status is prohibited. 10. A method for implementing trunking services based on the GSM public network as claimed in claim 8, characterized in that said step a2 comprises: Configure cluster neighbors in the broadcast control channel frequency point allocation table of the GSM public network cell; Configure the GSM public network neighbor cell in the broadcast control channel frequency allocation table of the cluster cell. 11. A method for implementing trunking services based on the GSM public network as claimed in claim 8, characterized in that said step a further comprises: Setting the cluster cell reselection offset parameter in the cluster mobile terminal; And the step b includes: The trunking mobile terminal measures the downlink signal strength of the broadcast control channel of each neighboring cell according to the broadcast control channel frequency point allocation table carried in the system message of the cell where it resides, and determines a predetermined number of downlink signal strengths of the broadcast control channel according to the measured downlink signal strength of the broadcast control channel. Neighborhood; The cluster mobile terminal respectively calculates and determines the C2 values of the predetermined number of neighboring cells according to the cluster cell reselection offset parameter and the cluster cell identification carried in the system message of the corresponding neighboring cell; When the cluster mobile terminal determines that cell reselection needs to be performed according to the calculated C2 value, the reselected cell status of the cluster cell, and the cell reselection trigger criterion of the GSM protocol, according to the cluster cell reselection offset parameter, the corresponding adjacent cell The cluster cell identifier carried in the system message determines the reselection priority of each neighboring cell; The cluster mobile terminal determines the reselection target cell according to the reselection priority of each neighboring cell, and resides there; The trunking mobile terminal performs corresponding trunking service/GSM public network service in the reselection target cell where it resides as required. 12. A method for realizing cluster services based on the GSM public network as claimed in claim 11, wherein the step of determining the C2 value of each neighboring cell is specifically: When the penalty time PENALTY_TIME is not equal to 11111: C2=C1+TCF×GT_CELL_RESELECT_OFFSET+CELL_RESELECT_OFFSET-TEMPORARY_OFFSET×H(PENALTY_TIME-T); When the penalty time PENALTY_TIME is equal to 11111: C2=C1+TCF*GT_CELL_RESELECT_OFFSET-CELL_RESELECT_OFFSET; Among them: TCF is the cluster cell identifier, and when the adjacent cell is a GSM public network cell, TCF is 0, and when the adjacent cell is a cluster cell, TCF is 1; GT_CELL_RESELECT_OFFSET is the cluster cell reselection offset parameter; CELL_RESELECT_OFFSET is the GSM public network cell reselection offset parameter; TEMPORARY_OFFSET is a temporary offset parameter; H(PENALTY_TIME-T) is a function of H(x), and T is the duration of the corresponding neighboring cell becoming a predetermined number of neighboring cells. When x>0, H(x)=0, when x≤0, H (x)=1. 13. A method for implementing cluster services based on the GSM public network according to claim 12, characterized in that the cluster cell reselection offset parameter is greater than the maximum value of the C2 values corresponding to each adjacent cell and the GSM public network cell Sum of reselection offset parameters. 14. A method for implementing cluster services based on the GSM public network according to claim 11, characterized in that each neighbor is determined according to the cluster cell reselection offset parameter and the cluster cell identifier carried in the system message of the corresponding neighbor cell. The specific steps for reselecting the priority of the district are as follows: The C2 values corresponding to the neighboring cells are sorted according to the sequence from large to small, and the reselection priority of each neighboring cell is determined according to the sorting of the C2 values.

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