CN1893312A - Method for defining available signal by terminal under direct connection mode and communication method - Google Patents

Abstract

The present invention provides a method for a terminal to determine an available signal in a direct mode, by pre-establishing a dedicated code table for a code word used by a transponder, and storing the operating frequency point of the transponder and the dedicated code table in the terminal respectively; Then receive the signal at the working frequency point of the transponder; and compare the code word in the code word analyzed in the received signal with the code word in the special code table to judge whether there is a transponder at present; when there is a transponder , parsing the message sent by the forwarder, and determining an available forwarder according to the parsed message. The present invention can quickly search for available transponders or calling terminals in the current system, and further perform synchronization to the transponders or calling terminals.

Description

Method for Terminal to Determine Available Signals and Communication Method in Direct Mode

technical field

The present invention relates to the application technology of TD-SCDMA in a dedicated network, in particular to a method for terminal synchronization of TD-SCDMA in direct mode, especially a method for terminal to determine available signals during the synchronization process.

Background technique

The private network system has high requirements on reliability, but the private network system is often small in scale and cannot achieve continuous nationwide coverage. If the terminal enters an area that cannot be covered by the network, or the current network cannot provide communication services due to failures, Then the terminal can communicate through the direct mode. The direct mode refers to a mode in which terminals communicate directly or through transponders without performing signal transfer between terminals through network equipment.

The applicant of the present invention proposes the technology of using TD-SCDMA technology in a private network, so as to realize the terminal communication in the direct mode in the private network.

In TD-SCDMA, the basic direct mode is that a calling terminal transmits a signal, and all other called terminals synchronize to the calling terminal and receive the signal sent by the calling terminal. In order to increase the communication distance in direct mode, in some cases a repeater device is placed in the center of the communication area. In the case of using a repeater, all terminals are synchronized to the repeater, and transmit and receive signals with the repeater. The transponder receives the service data and signaling sent by a calling terminal, and forwards the data and signaling to all called terminals; at the same time, the transponder also receives the signaling sent by the called terminal, and forwards it to the calling terminal .

As mentioned above, in the direct mode, when the terminals communicate directly, the called terminal must synchronize with the calling terminal; when the calling terminal communicates with the called terminal through a transponder, the called terminal must The transponders are kept synchronous, therefore, to achieve synchronous communication, it is necessary to solve the problem of how to determine the calling terminal or transponder in communication in the current system.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for the terminal to determine the available signal and its communication in the direct mode, which can quickly search for the available transponders or calling terminals in the current system, and further send information to the transponders or calling terminals. The terminal is synchronized.

In order to solve the above technical problems, the present invention provides a method for a terminal to determine an available signal in a direct mode, including steps:

1) establishing a dedicated code table for the code word used by the transponder, and storing the operating frequency point of the transponder and the dedicated code table in the terminal respectively;

2) receiving signals at the working frequency of the transponder;

3) comparing the codewords analyzed in the received signal with the codewords in the dedicated code table to determine whether there is a transponder at present;

4) When there is a transponder, parse the message sent by the transponder, and determine the available transponder according to the parsed message.

Wherein, when there is no available transponder at the current frequency point, it also includes: performing step 2) and step 3) according to the operating frequency point of the transponder stored in step 1).

Wherein, the code word includes: downlink pilot code, uplink pilot code, scrambling code and basic midamble, and the downlink pilot code, uplink pilot code, scrambling code and basic midamble belong to the same code group.

The present invention also discloses a method for a terminal to determine an available signal in a direct mode, including steps:

41) Establishing a dedicated code table for the codewords used by each calling terminal, and storing the dedicated code table and the operating frequency points used by the calling terminal in the terminal;

42) receiving signals at the working frequency of the calling terminal;

43) Comparing the codeword parsed from the received signal with the codeword in the dedicated code table, judging whether the calling terminal is currently stored;

44) If there is a calling terminal, analyze the message sent by the calling terminal, and determine the available calling terminal according to the message

Wherein, the step 41) further includes: establishing a dedicated code table for the code word used by the transponder, and storing the operating frequency point of the transponder and the dedicated code table in the terminal respectively;

The step 42) also includes before: determining whether there is an available transponder according to the following steps:

A) receiving signals at the working frequency of the transponder;

B) comparing the codewords analyzed in the received signal with the codewords in the dedicated code table, judging whether there is a transponder at present;

When there is no available transponder, step 42) is performed.

Wherein, described step 1) also includes before:

The codewords are classified, wherein one type of codeword is used to identify the corresponding relationship with the transponder, and the other type of codeword is used to identify the corresponding relationship with the calling terminal.

Wherein, the classified codewords also include reserved class codes for backup.

Wherein, if there is no calling terminal available at the current frequency point, step 42) and step 43) are performed at the next working frequency point according to the working frequency point of the calling terminal stored in step 41).

In addition, the steps further include: if there is no calling terminal available at the current frequency point, performing steps A) to B) during manual intervention.

In addition, the method further includes the step of setting an analysis period, and when the analysis period is reached, steps 42) and 43) are performed.

The present invention also discloses a method for direct terminal communication, including

111) Determining available transponders according to claim 1;

112) Synchronize with the available transponder, and parse the message sent by the transponder;

113) Communicating through the available transponders according to the information.

Further, it also includes the step of: setting an analysis cycle, and when the analysis cycle is reached, the information sent by the transponder is analyzed.

The present invention also discloses a method for direct terminal communication, including:

131) Determine the available calling terminal;

132) Synchronize with the available calling terminal, and parse the message sent by the calling terminal;

133) Communicate with the calling terminal according to the information.

Wherein, the period is 160ms or 320ms.

Further, the steps also include:

The information sent by the calling terminal is analyzed, and when it is judged that the calling terminal is changed to another terminal, the timer of the receiver is adjusted to keep synchronization with the new calling terminal.

Compared with the prior art, the beneficial effect of the present invention is: when the terminal communicates through the transponder, the method for determining the available transponder provided by the present invention pre-establishes the dedicated code table of the transponder and the codeword, and transfers the dedicated code table The code tables are respectively stored in the terminal, and through the pre-stored special code table, the called terminal can quickly determine the currently available transponder, and then keep in sync with it for communication.

The method for determining the available calling terminal provided by the present invention, when directly communicating between the terminals, pre-establishes the special code table of the calling terminal and the code word, and stores it in the terminal in advance, and uses the pre-stored special code table Determine the available calling terminal, and then maintain synchronization with it for communication;

If there is a transponder in the current network, the present invention first determines whether there is an available transponder, and if there is no available transponder, then determines the available calling terminal. Further, the present invention classifies codewords in advance to limit The codeword used reduces the complexity of the search, improves the reliability of the search, and further shortens the search time.

In addition, the present invention also reserves reserved class codes to facilitate future business expansion and use.

In addition, the present invention sets the period for resolving available transponders or calling terminals, so as to achieve the purpose of saving terminal power.

Further, the present invention periodically judges the transfer of the calling right during the communication process, so that the determination of the currently available calling terminal or transponder is more reliable and effective.

In addition, the code word in the present invention adopts the downlink pilot code, uplink pilot code, scrambling code and basic intermediate code used in the original TD-SCDMA, which simplifies the design difficulty.

Description of drawings

FIG. 1 is a flow chart of the terminal determining available transponders in the direct mode according to the present invention;

Fig. 2 is a flow chart of the terminal determining the available calling terminal in the direct mode according to the present invention;

Fig. 3 is a flowchart of the first embodiment.

Detailed ways

At present, TD-SCDMA technology is mainly used in the public mobile communication network. All terminals must communicate through the base station. If the terminal wants to communicate with other terminals, it must send service data and signaling to the network and receive service data from the network at the same time. and signaling. The applicant of the present invention has designed a set of schemes that use TD-SCDMA technology for private networks (such as trunking communication systems used by public security agencies in various places). Private network systems have relatively high reliability requirements, but private network systems are often small in scale and cannot achieve continuous nationwide coverage. If the terminal enters an area that cannot be covered by the network, or the current network cannot provide communication services due to a failure, the terminal can enter the direct mode. At this time, the terminal no longer sends and receives signals with the network equipment, but directly communicates between the terminal equipment. Its basic communication mode is that a calling terminal transmits a signal, and all other called terminals synchronize to the calling terminal and receive signals from the calling terminal. In order to increase the communication distance in direct mode, sometimes a transponder is also placed in the center of the communication area. In the case of using a repeater, all terminals are synchronized to the repeater, and transmit and receive signals through the repeater. After the terminal enters the direct mode, it must be synchronized with the calling terminal or the transponder, because synchronization is the basic element of communication. Only when the receiver completes the synchronization with the transmitter can it correctly obtain the information sent by the transmitter, that is, the called terminal and the calling terminal The service data and signaling can be received correctly only after the terminal or transponder is synchronized. Since the terminal does not know whether the transponder is used in the current system after entering the direct mode, it should first try to search for available transponders. If no transponders are found or the IDs of all found transponders do not match Transponder ID, the terminal thinks that there is no transponder at present, and can enter the state of continuously searching for the calling terminal. .

The present invention proposes just at this problem. The core idea of the present invention is to pre-store in each terminal and/or transponder a codeword used to set the corresponding relationship between each transponder and each terminal, and determine to establish communication according to the pre-stored codeword when the terminal enters the direct mode transponder or calling terminal.

The present invention provides two methods for determining the available signal. The so-called available signal refers to the signal sent to the terminal by the available transponder, or the signal that a calling terminal is preparing or sending call information to the terminal.

The present invention firstly provides a method of how to determine the available transponder, that is, the transponder currently used when the called terminal establishes communication with the calling terminal. As shown in Figure 1, the specific method is: set up the special code table of the code word used by the transponder, and store the operating frequency point of the transponder and the special code table in the terminal respectively (S1); The operating frequency point of the transponder attempts to receive the signal sent by the transponder (S2); the code word analyzed in the signal is compared with the code word in the dedicated code table to determine whether there is a transponder currently (S3); When the parsed code word is consistent with the code word in the dedicated code table, it is considered that there is a transponder. Since the codeword corresponding to the transponder may have a group of codewords corresponding to multiple transponders, it is necessary to determine whether the current transponder is an available transponder, and the method is to further analyze the information sent by the transponder (S4), The parsed information includes the transponder ID, and at the same time, the terminal itself stores a list of available transponders, and can determine whether it is an available transponder according to the transponder ID.

The present invention also provides a method of how to determine the available calling terminal. In the direct mode, if the terminals communicate directly without passing through the transponder, it is necessary to determine the currently available calling terminal; In the case of transponders, an attempt should be made to search for available transponders first. If no available transponder is found, the terminal considers that there is no available transponder at present, and can enter a state of continuously searching for the calling terminal. The following two situations are described in detail.

Fig. 2 is a flowchart of determining an available calling terminal when there is no repeater. When there is no transponder in the direct mode, pre-establish a dedicated code table for the code word used by the calling terminal, and store the dedicated code table and the frequency point information used by the calling terminal in each terminal (S1) ; Receive the signal sent by the calling terminal according to the working frequency point (S2); analyze the signal sent by the calling terminal, and judge whether the current code word in the code word and the dedicated code table is stored according to the code word analyzed calling terminal (S3); if there is a calling terminal, then analyze the information sent by the calling terminal, and judge whether the main terminal is trying to establish a call with itself according to the called terminal identification contained in the information (S4) .

When there is a transponder in the direct mode, the terminal first determines whether there is an available transponder when it is turned on. The specific method is the same as the method for determining the available transponder described above. Whether there is currently an available calling terminal, the method is the same as the method for determining the available calling terminal when there is no transponder above. table, and pre-store the operating frequency point of the transponder and the dedicated code in the terminal.

In addition, as a further improvement of the present invention, when there is a transponder, the present invention classifies the codewords, wherein one type of codeword is used to identify the corresponding relationship with the transponder, and the other type of codeword is used to identify the corresponding relationship with the calling terminal. In addition, the rest of the codewords are used as reserved codewords for future use. The purpose of classifying the codewords and restricting the codewords used by the transponder and the calling terminal in advance is to reduce the complexity of the search and improve the reliability of the search. The search time will be prolonged due to incorrectly searching for a code that is not currently in use.

Further, when the available signal is an available transponder, the present invention also provides a method for the direct terminal to communicate using the determined available signal. First, use the above method to determine the available transponder; keep synchronization with the transponder; and analyze the transponder sent message to determine whether there is a call with the terminal as the call object, and since the information includes the identification of the called terminal, it joins the current call when it is judged that the identification is consistent with its own identification. In order to save power consumption, a signal receiving period may be set, and when the signal receiving period is reached, the signal is received and analyzed again. This is because if a transponder is found, it means that the current communication is carried out through the transponder. Since the transponder always keeps signaling, after the terminal is synchronized with the transponder, all calls related to the terminal will pass through the transponder conduct. If the terminal is not in the call state, it will analyze the information sent by the transponder to determine whether there is a call and the call. At the same time, since the calling terminal can correspond to multiple terminal groups, only when the called party belongs to this group is it allowed to join the call , if the called terminal wants to join the communication, it needs to first determine whether the current calling terminal is calling itself.

When the available signal is the calling terminal, the present invention also provides a method for the corresponding direct terminal to communicate using the determined available signal. First, the above method is used to determine the available calling terminal; There may be a group of codewords corresponding to multiple calling terminals, so it is necessary to determine whether the current calling terminal is an available calling terminal. The method is to analyze the information sent by the calling terminal, and according to the information in the information The called subscriber identity identifies the available calling terminals. In this case, the terminal does not directly communicate with the calling terminal through the transponder. Unlike the transponder, the calling terminal will only send out a signal when it needs to communicate, so the called terminal synchronizes with the calling terminal and joins a After calling, the called terminal will continue to analyze all signaling sent by the calling terminal.

Since the identity of the calling terminal may be transferred, that is, the identity of the calling terminal changes from one terminal to another, all called terminals can obtain the calling information called identity transfer. The new calling terminal will maintain the continuity of the frame number. The frame number is used to mark the wireless frame, and the wireless frame number will automatically increase by 1 every time the calling terminal sends a signal of a wireless frame. The radio frame number can be used for higher level synchronization. For example, it may be agreed to send specific information in a wireless frame corresponding to a specific wireless frame number. Keeping the continuity of the frame number can make it unnecessary for each slave terminal to reacquire the frame number of the signal sent by the new calling terminal.

In the above case, after the right to speak is transferred, all called terminals including the original calling terminal must re-synchronize to the new calling terminal. Because all the original called terminals are synchronized with the original calling terminal, and since there may be a certain distance between the new calling terminal and the original calling terminal, it takes The time (that is, the electromagnetic wave transmission time) may be different from the time it takes for the signal sent by the original calling terminal to reach the slave terminal. Therefore, the called terminal must adjust the local timer to ensure synchronization with the new calling terminal. In order to maintain continuous synchronization with the new calling terminal, the called terminal needs to adjust the timer of the receiver to keep synchronizing with the new calling terminal. And if the current communication is carried out through the transponder, since all terminals are synchronized with the transponder, when the identity of the calling terminal is transferred, each terminal is still synchronized with the transponder, and it is not necessary to adjust the timer of the receiver.

If the terminal can neither search for an available transponder nor find an available calling terminal on all direct frequency points after the terminal is turned on, the terminal will continue to try to search for the calling terminal. It is not necessary to search for the transponder because the transponder is continuously sending signals. If no currently available transponder can be found, it means that there is no available transponder in the current environment. Also in order to save power, a fixed search cycle can be set.

When there is no available transponder or calling terminal, the process of searching for transponders can also be triggered actively by the user.

In order to simplify the reference, the present invention uses the downlink pilot code (SYNC_DL), uplink pilot code (SYNC_UL), scrambling code (scrambling) and basic midamble (basic midamble) in the existing TD-CDMA to set up and transponder and each Correspondence between terminals. The length of these codes, the position in the frame, the generation method, etc. are the same as those of the public mobile communication network based on TD-SCDMA technology. The first embodiment is taken as an example below to describe in detail the determination of available transponders and the The implementation process of the calling terminal can be used.

Embodiment 1: In this embodiment, the codes involved in transmitting signals between the calling terminal and the transponder in direct mode include but are not limited to: downlink pilot code (SYNC_DL), uplink pilot code (SYNC_UL), scrambling code (Scrambling ), Basic midamble. The length, position in the frame, and generation method of these codes are the same as those of the public mobile communication network based on TD-SCDMA technology. There are 32 SYNC_DLs, located in the downlink pilot time slot; 128 SYNC_UL, located in the uplink pilot time slot. There are 128 Basic midambles in total, and Midamble codes can be generated as training sequences for regular time slots. These codes belong to 32 code groups, and the corresponding relationship is as follows code group corresponding code SYNC-DL ID SYNC-UL ID Scrambling CodeID Basic Midamble Code ID 1 0 0...7 0 0 1 1 2 2 3 3 2 1 8...15 4 4 5 5 6 6 7 7 ... 32 31 248...255 124 124 125 125 126 126 127 127

As shown in Fig. 3, in this embodiment, as a preferred embodiment, first, SYNC_DL, SYNC_UL, scrambling code, and basic midamble codes are respectively divided into three categories (S1), including the M-M category used for direct communication between terminals. It is used to identify the M-R class that the terminal communicates with the transponder, and the reserved class reserved for future business expansion. The specific classification method is: firstly retain the code group classification methods of SYNC_DL, SYNC_UL, scrambling code, and basic midamble Code used by terminals in the prior art, that is, there are 32 code groups in total, and each code group includes 1 SYNC_DL code, 8 There are 1 SYNC_UL code, 4 scrambling codes and 4 basic midamble codes, and the scrambling code corresponds to the basic midamble code one by one. On this basis, select one or more SYNC_DL codes as M-M SYNC_DL codes, select one or more SYNC_UL codes in the same code group as M-M SYNC_UL codes, and select one or more scrambling codes and basic midamble Codes as M-M codes Class scrambling code, basic midamble Code (S2). The unselected SYNC_UL, scrambling code, and basic midamble Code in the same code group are all reserved class codes for the use of new transponders in the future.

Similarly, select one or more SYNC_DL codes as M-R SYNC_DL codes, select one or more SYNC_UL codes in the same code group as M-R SYNC UL codes, and select one or more scrambling codes and basic midamble Codes as M-R types scrambling code, basic midamble Code. The unselected SYNC_UL, scrambling code, and basicmidamble Code in the same code group are used as reserved codes for future new terminals.

The remaining unselected SYNC_DL codes, as well as the SYNC_UL, scrambling code, and basic midamble Code that belong to the same code group as these SYNC_DL codes are all reserved class codes.

In the direct mode, after the terminal is turned on, it will first receive the signal at the working frequency of the supported transponder (S3), and judge whether there is a transponder according to the received signal (S4). The terminal uses the M-R type SYNC_DL, scrambling code, and basic midamble code to search through correlation operations and other methods, and uses the M-M type SYNC_DL, scrambling code, and basic midamble code to search for the calling terminal. The search method is the same as the process of starting the terminal to search for the network in the public network (commonly referred to as the initial cell search process of a TD-SCDMA terminal) are consistent. The search process is as follows:

First, according to the received signal strength, sort the frequency points that may have signals; and according to the characteristics of the frame structure, use the power feature window method to search for the approximate position of SYNC_DL; then use the correlation method to find out the exact position and code pattern of SYNC_DL (that is, which specific SYNC_DL code); then use SYNC to estimate the frequency deviation between the local receiver and the remote transmitter, and adjust the frequency deviation roughly; use channel estimation to determine the Basic midamble code, and therefore determine the Scrambling code; then use the Midamble code and data part for further fine-tuning Bias; look for the change pattern of the relative phase deviation between SYNC_DL and midamble, determine the S1 information (S1 is a specific relative phase deviation change pattern between SYNC_DL and midamble, which can indicate the synchronization of 20ms), and obtain 20ms synchronization; finally Receive broadcast information.

If the terminal searches for a transponder, it will analyze the information sent by the transponder. The information includes frame number, current call status, transponder ID and other information (S5). The terminal itself stores a list of available transponders, and according to the received transponder The transponder ID is used to determine whether the current transponder is available. If the transponder is available, the terminal will synchronize with the transponder, and periodically try to parse the message sent by the transponder, and judge whether there is a call and whether it needs to join the call according to the identifier of the called user in the message (S7). If the searchable transponder cannot be found, the signal is received at the working frequency of the calling terminal (S8), and whether there is an available calling terminal is judged according to the received signal (S9).

If the terminal searches for an available calling terminal, it will obtain synchronization with the calling terminal as soon as possible, and analyze the message sent by the calling terminal (S10). The calling message includes the identifier of the called user. If it matches the self-identity, it means that the user needs to join the call, and then joins the call initiated by the terminal (S7).

If the available transponders and calling terminals cannot be searched on all the direct frequency points after starting up, the terminal will repeatedly search for the calling terminal on the frequency points available for the calling terminal with a fixed period (such as 160ms, 320ms). Or the user actively triggers the process of searching for transponders, and the terminal searches for transponders and calling terminals according to the above-mentioned process of starting up and searching for transponders and calling terminals.

Once the terminal joins the call, it enters the connected state. In private network communication, the communication mode is one-to-one or one-to-many, that is, one calling terminal calls to another terminal, or one calling terminal calls to other multiple terminals. Only the calling terminal with the right to speak can speak to other terminals, and the terminal without the right to speak can only listen in the calling state. In this way, when a user finishes speaking, if other users need to speak, they must obtain the right to speak. That is, the transfer of the right to speak. When the identity of the calling terminal is transferred, the new calling terminal will maintain the continuity of the frame number. However, if the call does not involve a repeater, all terminals must adjust their receiver timing.

The above is the implementation process of determining the available signal when there is a transponder, and the following describes the implementation process of determining the available calling terminal when there is no transponder.

The second embodiment: In this embodiment, the code subclassification method in the first embodiment is still used, but only the M-M class codes are used, including downlink pilot code (SYNC_DL), uplink pilot code (SYNC_UL), scrambling The code (Scrambling) and the basic midamble (Basic midamble) are used as the special code words of the calling terminal.

In the direct mode, after the terminal is turned on, it will first receive the signal on the supported direct frequency, and judge whether there is a calling terminal according to the received signal.

If the terminal searches for the calling terminal, it will obtain synchronization with the calling terminal as soon as possible, and analyze the message sent by the calling terminal. The call message includes the identity of the called user. If the called identity matches its own identity, Then it indicates that the user needs to join the call (that is, the calling terminal is available), and then joins the call initiated by the terminal.

If no available calling terminal can be searched on all direct frequency points after starting up, the terminal will repeatedly search for the calling terminal on the working frequency points of the calling terminal with a fixed period (such as 160ms, 320ms).

Once the terminal joins the call, it enters the connected state. In private network communication, the communication mode is one-to-one or one-to-many, that is, one calling terminal calls to another terminal, or one calling terminal calls to other multiple terminals. Only the calling terminal with the right to speak can speak to other terminals, and the terminal without the right to speak can only listen in the calling state. In this way, when a user finishes speaking, if other users need to speak, they must obtain the right to speak. That is, the transfer of the right to speak. When the identity of the calling terminal is transferred, the new calling terminal will maintain the continuity of the frame number. All terminals shall adjust their receiver timing.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be It is regarded as the protection scope of the present invention.

Claims (15)

1. A method for a terminal to determine an available signal in a direct mode, comprising the steps of: 1) establishing a dedicated code table for the code word used by the transponder, and storing the operating frequency point of the transponder and the dedicated code table in the terminal respectively; 2) receiving signals at the working frequency of the transponder; 3) comparing the codewords analyzed in the received signal with the codewords in the dedicated code table to determine whether there is a transponder at present; 4) When there is a transponder, parse the message sent by the transponder, and determine the available transponder according to the parsed message. 2. The method for the terminal to determine the available signal in the direct mode according to claim 1, characterized in that, when there is no available transponder at the current frequency point, further comprising: performing the step according to the operating frequency point of the transponder stored in step 1) 2) and step 3). 3. The method for determining available signals by a terminal in direct mode according to claim 1, wherein the codewords include: downlink pilot codes, uplink pilot codes, scrambling codes and basic intermediate codes, and the downlink pilot codes The frequency code, the uplink pilot code, the scrambling code and the basic midamble belong to the same code group. 4. A method for a terminal to determine an available signal in a direct mode, comprising the steps of: 41) Establishing a dedicated code table for the codewords used by each calling terminal, and storing the dedicated code table and the operating frequency points used by the calling terminal in the terminal; 42) receiving signals at the working frequency of the calling terminal; 43) Comparing the codeword parsed from the received signal with the codeword in the dedicated code table, judging whether the calling terminal is currently stored; 44) If there is a calling terminal, analyze the message sent by the calling terminal, and determine the available calling terminal according to the message 5. The method for the terminal to determine the available signal in the direct mode according to claim 4, characterized in that the step 41) further comprises: establishing a dedicated code table for the code word used by the transponder, and adding the code word of the transponder The working frequency point and the dedicated code table are respectively stored in the terminal; The step 42) also includes before: determining whether there is an available transponder according to the following steps: A) receiving signals at the working frequency of the transponder; B) comparing the codewords analyzed in the received signal with the codewords in the dedicated code table, judging whether there is a transponder at present; When there is no available transponder, step 42) is performed. 6. The method for the terminal to determine the available signal in the direct mode according to claim 5, characterized in that before the step 1), it also includes: The codewords are classified, wherein one type of codeword is used to identify the corresponding relationship with the transponder, and the other type of codeword is used to identify the corresponding relationship with the calling terminal. 7. The method for determining available signals by a terminal in direct mode according to claim 6, characterized in that: the classified codewords further include reserved class codes for backup. 8. The method for determining the available signal by the terminal in the direct mode according to claim 4 or 6, characterized in that: if there is no available calling terminal at the current frequency point, the working frequency point of the calling terminal stored in step 41) Execute step 42) and step 43) at the next working frequency point. 9. The method for determining an available signal by a terminal in direct mode according to claim 6, wherein said step further comprises: if there is no available calling terminal at the current frequency point, when manual intervention is performed, step A) to step B). 10. The method for determining an available signal by a terminal in a direct mode according to claim 6, further comprising the step of: setting an analysis period, and when the analysis period is reached, performing steps 42) and 43). 11. A method for communicating directly through a terminal, comprising the steps of: 111) Determining available transponders according to claim 1; 112) Synchronize with the available transponder, and parse the message sent by the transponder; 113) Communicating through the available transponders according to the information. 12. The method for communicating with a direct terminal according to claim 11, further comprising the step of: setting an analysis period, and analyzing the information sent by the transponder when the analysis period is reached. 13. A method for communicating directly through a terminal, comprising the steps of: 131) Determine the available calling terminal; 132) Synchronize with the available calling terminal, and parse the message sent by the calling terminal; 133) Communicate with the calling terminal according to the information. 14. The method for communicating with a direct terminal according to claim 10, wherein the period is 160 ms or 320 ms. 15. The method for determining available signals by a terminal in direct mode according to claim 13, characterized in that said steps further comprise: The information sent by the calling terminal is analyzed, and when it is judged that the calling terminal is changed to another terminal, the timer of the receiver is adjusted to keep synchronization with the new calling terminal.

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