A method for implementing an LTE-TETRA internet gateway for subways

Abstract

A subway-oriented LTE-TETRA Internet gateway and implementation method belong to the field of rail transit communication equipment: including power module, main control circuit, TETRA channel machine I, TETRA channel machine II, antenna I and antenna II; the power module supplies power for the main control circuit, TETRA channel machine I and TETRA channel machine II; the main control circuit is connected with TETRA channel machine I and TETRA channel machine II respectively; the TETRA channel machine I is connected with antenna I, and the TETRA channel machine II is connected with antenna II; the main control circuit is used for interacting with the AT command of TETRA channel machine I and TETRA channel machine II, SIP signaling analysis and audio processing; TETRA channel machine I and TETRA channel machine II are used for narrowband communication; the LTE wideband and TETRA narrowband can realize interconnection and intercommunication, and the stability of communication and the operation and maintenance of equipment in the complex environment of subway can be ensured.

Description

Technical Field

[0001] This invention relates to a method for implementing an LTE-TETRA Internet gateway for subways, belonging to the field of rail transit communication equipment technology. Background Technology

[0002] In subway communication systems, LTE broadband networks and TETRA narrowband networks often coexist on different lines; however, traditional interconnection equipment has revealed many shortcomings:

[0003] 1. Insufficient standard compatibility: Existing interconnection equipment is difficult to adapt to both the SIP signaling of LTE networks and the 800MHz frequency band communication of TETRA networks, resulting in low efficiency in establishing cross-system group calls and easy delays in the signaling conversion process.

[0004] 2. Limited interface functionality: There is a lack of dedicated interfaces for program upgrades and debugging expansions. When maintaining the device, it is often necessary to disassemble the device casing, which is a complicated process. In addition, the audio output path is singular and cannot meet the actual needs of real-time monitoring.

[0005] 3. Inadequate audio processing: Traditional audio processing typically uses a single buffer or queue, which is prone to blocking, and the buffer is usually a fixed-size circular buffer; existing interconnected devices generally adopt a centralized serial processing architecture, which has defects such as accumulated processing delay and poor timing synchronization accuracy.

[0006] 4. Complex control logic: Group call linkage between LTE and TETRA systems requires multiple protocol conversions and has a long signaling triggering link, which can easily lead to group call asynchrony in practical applications. Summary of the Invention

[0007] This invention addresses the interconnection and interoperability requirements of the LTE and TETRA systems in subways by providing an integrated method for implementing an LTE-TETRA internet gateway for subways.

[0008] The technical solution adopted in this invention is: an implementation method of LTE-TETRA Internet gateway for subway, in which broadband calls to narrowband perform the following operations: Step 1: The LTE system transmits SIP signaling and digital audio stream to the main control circuit of the Internet gateway via a wired communication network port to establish group call service;

[0009] Step 2: The main control circuit receives and parses the SIP signaling, generates the corresponding AT commands, and sends them to TETRA channel unit I and TETRA channel unit II.

[0010] Step 3: TETRA Channel Unit I and TETRA Channel Unit II receive AT commands from the main control circuit. The digital audio stream input from the LTE system is converted into an analog audio stream by the main control circuit and transmitted to TETRA Channel Unit I and TETRA Channel Unit II. The TETRA system group call is established, and the LTE system and the TETRA system conduct a call.

[0011] Narrowband calls broadband perform the following operations:

[0012] Step 1: The TETRA system initiates a group call and sends an analog audio stream. TETRA channel unit I and TETRA channel unit II send AT commands to the main control circuit to establish the group call service.

[0013] Step 2: The main control circuit receives and parses the AT commands and sends SIP signaling to the LTE system;

[0014] Step 3: The LTE system receives SIP signaling and successfully establishes a group call service. At the same time, the analog audio stream input by the TETRA system is converted into a digital audio stream by the audio processing module and transmitted to the LTE system. The LTE system establishes the group call and the LTE system and TETRA system conduct a call.

[0015] The method for transmitting SIP signaling and digital audio stream to the main control circuit of the Internet gateway in step one of broadband calling narrowband is as follows: SIP signaling is transmitted based on the TCP / IP protocol stack; the LTE core network sends SIP signaling to the Internet gateway through the communication network port; and the digital audio stream is encapsulated into IP data packets via the RTP real-time transmission protocol and transmitted to the Internet gateway.

[0016] In step two of the broadband-to-narrowband call process, the main control circuit receives and parses SIP signaling as follows: the main control chip receives SIP signaling messages sequentially through the network interface unit and the communication port, and calls the built-in sipEventThread function as the signaling processing thread to parse the received messages. According to the SIP protocol specification, this thread identifies and executes corresponding call, right-of-sale, right-of-sale, and hang-up operations for different types of SIP messages, including but not limited to "INVITE", "OPTIONS", "MESSAGE", and "BYE".

[0017] The method for generating the corresponding AT command and sending it to TETRA channel machine I and TETRA channel machine II in step two of the broadband call to narrowband is as follows: the main control chip of the main control circuit creates a serial port thread_serial and sends a handshake message to TETRA channel machine I and TETRA channel machine II for communication. Then, it calls the at_tx_process function to send the AT command to TETRA channel machine I and TETRA channel machine II through serial ports ttyS4 and ttyS8.

[0018] In the narrowband-to-broadband call process, the method for the main control circuit to receive and parse AT commands in step two is as follows: the main control chip of the main control circuit receives AT commands from TETRA channel device I and TETRA channel device II through a serial port thread, creates a serial port thread_serial, calls the at_rx_process function to process the AT commands, and passes the data to the upper-layer command parser at_cmd_process function; the parser will identify the specific command type from the string, and then search in a pre-registered command processing function mapping table msg_handlers to match the processing function corresponding to the command, and generate the final response result.

[0019] The method for sending SIP signaling to the LTE system in step two of the narrowband-to-broadband call process is as follows: the main control chip of the main control circuit calls the command processing function, embeds the generated SDP message as the message body into the SIP INVITE request, adds the necessary SIP header fields, including From, To, Call-ID, CSeq, Contact, and Content-Type fields, and sends the complete SIP INVITE request to the LTE system through the communication network port to establish a media session channel and realize cross-system voice communication between the narrowband TETRA terminal and the broadband LTE terminal.

[0020] In step three of the broadband call to narrowband, the method for converting the digital audio stream input to the LTE system into an analog audio stream via the main control circuit is as follows: a dual-channel adaptive audio scheduling method is used for processing. An independent state machine is maintained for each audio channel, including playback state, ready state, and buffer state. The dual-channel hybrid, single-channel A, or single-channel B working mode is dynamically selected according to the state combination. A dynamic buffer threshold triggering mechanism is introduced, and the ready state is automatically switched when the amount of buffered data reaches a preset threshold.

[0021] In the narrowband call broadband process, the method for converting the analog audio stream input to the TETRA system into a digital audio stream via the audio processing module is as follows: a distributed timing preservation method is adopted, which maintains independent sequence number generators and local timestamps based on the number of samples for the audio streams of TETRA channel I and TETRA channel II respectively, so as to realize the integrity and isolation of the timing information of each channel.

[0022] An LTE-TETRA internet gateway for subways includes a power module, a main control circuit, a TETRA channel unit I, a TETRA channel unit II, an antenna I, and an antenna II. The power module provides power to the main control circuit, TETRA channel unit I, and TETRA channel unit II. The main control circuit is connected to TETRA channel unit I and TETRA channel unit II respectively. TETRA channel unit I is connected to antenna I, and TETRA channel unit II is connected to antenna II. The main control circuit is used for AT command interaction with TETRA channel unit I and TETRA channel unit II, SIP signaling parsing, and audio processing. TETRA channel unit I and TETRA channel unit II are used for narrowband communication.

[0023] The beneficial effects of this invention are as follows: This invention achieves interconnection between LTE broadband and TETRA narrowband networks. It uses a main control chip as its core, integrating a power module and two 800MHz narrowband channel units, and incorporating various types of interfaces. The main control chip can parse SIP group call signaling sent by the LTE system and control the TETRA system channel units to initiate group calls by generating AT commands. Through hardware-level signaling conversion and direct interaction, the group call setup time is significantly shortened (≤300ms). A dual-channel adaptive audio scheduling method and a lock-free ping-pong buffer synchronization method are introduced, avoiding the blocking problem of traditional single-buffer queues. By replacing mutex locks with atomic operations on status flags, thread synchronization overhead is reduced by more than 60%, ensuring efficient and unblocked flow of audio data production and consumption. Its audio processing module supports audio conversion, encoding / decoding, and path switching, and has an independent audio monitoring channel, ensuring sound quality and switching efficiency in the complex environment of the subway. The multi-interface design improves the ease of equipment maintenance, and group call linkage ensures real-time performance through hardware interrupts, thereby effectively improving communication stability and equipment maintainability. Attached Figure Description

[0024] Figure 1 The connection block diagram for implementing the Internet gateway circuit of this invention;

[0025] Figure 2 To realize the main control circuit connection block diagram of this invention;

[0026] Figure 3 To implement the group call linkage flowchart of the LTE system and TETRA system of this invention;

[0027] Figure 4 To implement the external interface connection block diagram of this invention;

[0028] Figure 5 Flowchart for broadband to narrowband call implementation;

[0029] Figure 6 Flowchart for enabling narrowband to broadband calls. Detailed Implementation

[0030] like Figure 1 As shown, an LTE-TETRA internet gateway for subways includes a power module, a main control circuit, TETRA channel unit I, TETRA channel unit II, antenna I, and antenna II. The power module supplies power to the main control circuit, TETRA channel unit I, and TETRA channel unit II. The main control circuit is used for AT command interaction, SIP signaling parsing, and audio processing with TETRA channel unit I and TETRA channel unit II. TETRA channel unit I and TETRA channel unit II are used for narrowband communication. Both TETRA channel unit I and TETRA channel unit II operate in the 800MHz frequency band. Antenna I and antenna II work together with TETRA channel unit I and TETRA channel unit II to realize the reception and transmission of wireless signals.

[0031] like Figure 2 As shown, the main control circuit includes a main control chip of model NUC980DK63YC, an audio processing module of model TLV320AIC3106, a storage module of model SDINBG4-8G, TETRA channel receiver I interface unit I, TETRA channel receiver II interface unit II, a network interface unit, and a debugging interface unit. The main control chip is connected to the audio processing module, the storage module, TETRA channel receiver I interface unit I, TETRA channel receiver II interface unit II, the network interface unit, and the debugging interface unit, respectively.

[0032] The main control chip is used to realize the interconnection and interoperability of broadband LTE and narrowband TETRA communication systems; the audio processing module is used to realize the digital-to-analog conversion, encoding and decoding operations and path switching functions between digital audio of the broadband LTE system and analog audio of the narrowband TETRA system; the storage module is used to persistently store the application logs, kernel logs and system event logs generated during the operation of the main control chip; TETRA channel machine I interface unit I is used to connect the main control chip with TETRA channel machine I; TETRA channel machine II interface unit II is used to connect the main control chip with TETRA channel machine II; the network interface unit is used for the main control chip to realize network port communication; the debugging interface unit is used for debugging the main control chip.

[0033] The audio processing module adopts a hardware acceleration architecture based on the TLV320AIC3106 chip. This chip integrates a programmable digital signal processor (DSP) and a high-performance audio codec (CODEC), possessing the following key functions: Digital-to-Analog Conversion: Decodes the digital audio stream from the LTE side and converts it into an analog signal via a digital-to-analog converter (DAC). The sampling rate is adapted to the 8kHz requirement of the TETRA network. Codec Adaptation: It is compatible with the audio encoding formats of both LTE and TETRA systems, ensuring no loss of sound quality during audio conversion. Path Switching: A hardware switch enables rapid switching of the audio output path, effectively avoiding latency issues that may arise from software switching. Furthermore, the synchronization error between the two outputs (i.e., the audio output to the channel receiver and the audio output to the monitoring interface) can be controlled within a very small range (≤50ms).

[0034] like Figure 3 As shown, in the LTE system, the LTE handheld radio communicates with the LTE core network wirelessly, and the LTE core network communicates with the Internet gateway by sending SIP signaling through the communication network port; in the TETRA system, the Internet gateway communicates with TETRA Channel I and TETRA Channel II by exchanging AT commands, and TETRA Channel I and TETRA Channel II communicate with the TETRA handheld radio via wireless communication to make group calls.

[0035] like Figure 4 As shown, the external interfaces include a communication network port, an OTG programming interface, a USB interface, a debugging network port, a listening port I, a listening port II, a debugging serial port, a TETRA channel device I programming interface I, and a TETRA channel device II programming interface II.

[0036] Regarding the communication interface: the communication network port is a 100 Mbps Ethernet interface, used to realize wired connection with the LTE system network; regarding the debugging interface: the debugging network port is a 100 Mbps Ethernet interface, and the debugging serial port adopts the RS232 standard with a communication rate set to 115200 bps, mainly used for configuring Internet gateway parameters and querying status.

[0037] The TETRA Channel Unit I programming interface I and TETRA Channel Unit II programming interface II use a dedicated bus, supporting flexible configuration of the channel unit's frequency within the 800MHz band. For expansion interfaces: an OTG programming interface is specifically designed for updating device firmware; this design eliminates the need to disassemble the device casing, greatly improving the convenience of device maintenance; a USB interface supports external storage devices, facilitating the import of device configuration files and allowing temporary connection of debugging tools to meet diverse device debugging needs; for audio interfaces: monitoring ports I and II use 3.5mm jacks with specific output levels and impedances. This interface is independent of the channel unit's audio path, specifically providing maintenance personnel with the ability to monitor call content in real time.

[0038] Example 1: The Internet gateway uses SIP and serial communication to achieve initialization, AT command interaction, and group call service establishment and management. The entire process is guaranteed to be real-time through a hardware interrupt mechanism.

[0039] The method for broadband to call narrowband is as follows: Figure 5 As shown: Step 1, the broadband LTE handheld radio (Group I, Group No. 1649001; Group II, Group No. 1649002) initiates a group call, presses PTT to occupy the talk right and speaks, the generated SIP signaling is transmitted based on the TCP / IP protocol stack, the LTE core network sends the SIP signaling to the Internet gateway through the communication network port, and the output digital audio stream is encapsulated into IP data packets via the RTP real-time transmission protocol and transmitted to the Internet gateway to establish the group call service;

[0040] Step 2: The main control chip receives SIP signaling messages through the communication network port and calls the built-in sipEventThread function as the signaling processing thread to parse the received SIP signaling messages. According to the SIP protocol specification, this thread identifies different types of SIP messages, including but not limited to "INVITE", "OPTIONS", "MESSAGE", and "BYE", and executes corresponding call, right-of-sale, right-of-sale, and hang-up operations. Then, a serial port thread thread_serial is created and a handshake message is sent to TETRA channel I and TETRA channel II for communication. The at_tx_process function is called to send AT commands (e.g., ATD1938801) to TETRA channel I and TETRA channel II through serial ports ttyS4 and ttyS8.

[0041] Step 3: TETRA channel unit I and TETRA channel unit II receive the AT command. The digital audio stream input to the LTE system is converted into an analog audio stream by the audio processing module. During this conversion, a dual-channel adaptive audio scheduling method is used. An independent state machine is maintained for each audio channel, including playback, ready, and buffering states. Based on the state combination, the system dynamically selects between dual-channel hybrid, single-channel A, or single-channel B operating modes. A dynamic buffering threshold trigger mechanism is introduced; when the buffered data volume reaches a preset threshold, the ready state is automatically switched. A TETRA system group call is established, and the TETRA handheld radio receives the group call and initiates communication.

[0042] The method for narrowband to broadband calls is as follows: Figure 6 As shown: Step 1, the TETRA handheld radio initiates a group call. TETRA channel unit I (group number 1938801, individual number 1932201) and TETRA channel unit II (group number 1938802, individual number 1932202) establish a group call service and send AT commands and analog audio streams to the main control chip.

[0043] Step 2: The main control chip creates a serial port thread (thread_serial) to receive AT commands from TETRA channel receiver I and TETRA channel receiver II. It calls the at_rx_process function to process the AT commands and passes the data to the upper-layer command parser (at_cmd_process function). The parser identifies the specific command type (e.g., +CTICN) from the string and searches a pre-registered command processing function mapping table (msg_handlers) to match the corresponding processing function (e.g., handle_CTICN), generating the final response result. Then, the main control chip calls the command processing function to embed the generated SDP message as the message body into the SIP INVITE request, adding necessary SIP header fields, including From, To, Call-ID, CSeq, Contact, and Content-Type fields. The complete SIP INVITE request is then sent to the LTE system through the communication network port.

[0044] Step 3: The LTE core network receives SIP signaling and successfully establishes a group call service. At the same time, the analog audio stream input from the TETRA side is converted into a digital audio stream by the audio processing module. During this conversion process, a distributed timing preservation method is adopted to maintain independent sequence number generators and local timestamps based on the number of samples for the audio streams of TETRA channel I and TETRA channel II, so as to achieve the integrity and isolation of the timing information of each channel. The LTE handheld radio receives the group call and conducts communication.

[0045] The fact that the LTE handheld radio and the TETRA handheld radio can play audio and make calls normally indicates that the interconnection function is normal.

Claims

1. A method for implementing an LTE-TETRA Internet gateway for subway systems, characterized in that, Broadband calls to narrowband perform the following operations: Step 1: The LTE system transmits SIP signaling and digital audio streams to the main control circuit of the Internet gateway via a wired communication network port to establish group call service; Step 2: The main control circuit receives and parses the SIP signaling, generates the corresponding AT commands, and sends them to TETRA channel unit I and TETRA channel unit II. Step 3: TETRA Channel Unit I and TETRA Channel Unit II receive AT commands from the main control circuit. The digital audio stream input from the LTE system is converted into an analog audio stream by the main control circuit and transmitted to TETRA Channel Unit I and TETRA Channel Unit II. The TETRA system group call is established, and the LTE system and the TETRA system conduct a call. Narrowband calls broadband perform the following operations: Step 1: The TETRA system initiates a group call and sends an analog audio stream. TETRA channel unit I and TETRA channel unit II send AT commands to the main control circuit to establish the group call service. Step 2: The main control circuit receives and parses the AT commands and sends SIP signaling to the LTE system; Step 3: The LTE system receives SIP signaling and successfully establishes a group call service. At the same time, the analog audio stream input by the TETRA system is converted into a digital audio stream by the audio processing module and transmitted to the LTE system. The LTE system establishes the group call and the LTE system and TETRA system conduct a call.

2. The method for implementing an LTE-TETRA Internet gateway for subways according to claim 1, characterized in that, The method for transmitting SIP signaling and digital audio stream to the main control circuit of the Internet gateway in step one of broadband calling narrowband is as follows: SIP signaling is transmitted based on the TCP / IP protocol stack; the LTE core network sends SIP signaling to the Internet gateway through the communication network port; and the digital audio stream is encapsulated into IP data packets via the RTP real-time transmission protocol and transmitted to the Internet gateway.

3. The method for implementing an LTE-TETRA Internet gateway for subways according to claim 1, characterized in that, In step two of the broadband-to-narrowband call process, the main control circuit receives and parses SIP signaling as follows: the main control chip receives SIP signaling messages sequentially through the network interface unit and the communication port, and calls the built-in sipEventThread function as the signaling processing thread to parse the received messages. According to the SIP protocol specification, this thread identifies different types of SIP messages, including "INVITE", "OPTIONS", "MESSAGE", and "BYE", and performs corresponding call, occupy talk rights, release talk rights, and hang-up operations.

4. The method for implementing an LTE-TETRA Internet gateway for subways according to claim 1, characterized in that, The method for generating the corresponding AT command and sending it to TETRA channel machine I and TETRA channel machine II in step two of the broadband call to narrowband is as follows: the main control chip of the main control circuit creates a serial port thread_serial and sends a handshake message to TETRA channel machine I and TETRA channel machine II for communication. Then, it calls the at_tx_process function to send the AT command to TETRA channel machine I and TETRA channel machine II through serial ports ttyS4 and ttyS8.

5. The method for implementing an LTE-TETRA Internet gateway for subways according to claim 1, characterized in that, In the narrowband-to-broadband call process, the method for the main control circuit to receive and parse AT commands in step two is as follows: the main control chip of the main control circuit receives AT commands from TETRA channel device I and TETRA channel device II through a serial port thread, creates a serial port thread_serial, calls the at_rx_process function to process the AT commands, and passes the data to the upper-layer command parser at_cmd_process function; the parser will identify the specific command type from the string, and then search in a pre-registered command processing function mapping table msg_handlers to match the processing function corresponding to the command, and generate the final response result.

6. The method for implementing an LTE-TETRA Internet gateway for subways according to claim 1, characterized in that, The method for sending SIP signaling to the LTE system in step two of the narrowband-to-broadband call process is as follows: the main control chip of the main control circuit calls the command processing function, embeds the generated SDP message as the message body into the SIP INVITE request, adds the necessary SIP header fields, including From, To, Call-ID, CSeq, Contact, and Content-Type fields, and sends the complete SIP INVITE request to the LTE system through the communication network port to establish a media session channel and realize cross-system voice communication between the narrowband TETRA terminal and the broadband LTE terminal.

7. The method for implementing an LTE-TETRA Internet gateway for subways according to claim 1, characterized in that, In step three of the broadband call to narrowband, the method for converting the digital audio stream input to the LTE system into an analog audio stream via the main control circuit is as follows: a dual-channel adaptive audio scheduling method is used for processing. An independent state machine is maintained for each audio channel, including playback state, ready state, and buffer state. The dual-channel hybrid, single-channel A, or single-channel B working mode is dynamically selected according to the state combination. A dynamic buffer threshold triggering mechanism is introduced, and the ready state is automatically switched when the amount of buffered data reaches a preset threshold.

8. The method for implementing an LTE-TETRA Internet gateway for subways according to claim 1, characterized in that, In the narrowband call broadband process, the method for converting the analog audio stream input to the TETRA system into a digital audio stream via the audio processing module is as follows: a distributed timing preservation method is adopted, in which independent sequence number generators and local timestamps based on the number of samples are maintained for the audio streams of TETRA channel I and TETRA channel II respectively, so as to realize the integrity and isolation of the timing information of each channel.

9. An LTE-TETRA Internet gateway employing the implementation method of the LTE-TETRA Internet gateway for subways as described in claim 1, characterized in that: It includes a power module, a main control circuit, TETRA channel unit I, TETRA channel unit II, antenna I, and antenna II; the power module provides power to the main control circuit, TETRA channel unit I, and TETRA channel unit II; the main control circuit is connected to TETRA channel unit I and TETRA channel unit II respectively; TETRA channel unit I is connected to antenna I, and TETRA channel unit II is connected to antenna II; the main control circuit is used for AT command interaction with TETRA channel unit I and TETRA channel unit II, SIP signaling parsing, and audio processing; TETRA channel unit I and TETRA channel unit II are used for narrowband communication.

10. The LTE-TETRA Internet gateway of the method for implementing an LTE-TETRA Internet gateway for subways according to claim 9, characterized in that: The main control circuit includes a NUC980DK63YC main control chip, a TLV320AIC3106 audio processing module, an SDINBG4-8G storage module, a TETRA channel receiver I interface unit I, a TETRA channel receiver II interface unit II, a network interface unit, and a debugging interface unit. The main control chip is connected to the audio processing module, the storage module, the TETRA channel receiver I interface unit I, the TETRA channel receiver II interface unit II, the network interface unit, and the debugging interface unit, respectively. The main control chip is used to realize the interconnection between broadband LTE and narrowband TETRA communication systems. The audio processing module is used to implement digital-to-analog conversion, encoding / decoding operations, and path switching functions between digital audio in the broadband LTE system and analog audio in the narrowband TETRA system; the storage module is used to persistently store application logs, kernel logs, and system event logs generated during the operation of the main control chip; the TETRA channel machine I interface unit I is used for the connection between the main control chip and TETRA channel machine I; the TETRA channel machine II interface unit II is used for the connection between the main control chip and TETRA channel machine II; the network interface unit is used for the main control chip to implement network port communication; and the debugging interface unit is used for debugging the main control chip.

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