Random access method and apparatus applied to short wave communication system

Abstract

This invention discloses a random access method and apparatus for shortwave communication systems, comprising: sending a random access request signal determined based on the address identifier of the intended access device to a central station; monitoring and receiving a random access response signal sent by the central station in adjacent time slots; if the random access response signal can be received and the address identifier of the intended access device can be parsed from the random access response signal, then the random access is successful; otherwise, the random access fails, and the random access request signal is resent to the central station, and the random access response signal is monitored and received again, until the random access is successful or the maximum number of random access attempts is reached. This invention reduces the time required for random access by eliminating the time slots between message transmissions, i.e., transmitting the random access request signal and the random access response signal in adjacent time slots, requiring only a minimum of two time slots to complete the random access process.

Description

Technical Field

[0001] This invention belongs to the field of shortwave communication technology, specifically relating to a random access method and apparatus for shortwave communication systems. Background Technology

[0002] Shortwave communication primarily relies on the reflection of electromagnetic waves from the ionosphere. It is the only communication method that can support ultra-long-distance information transmission over thousands of kilometers without relays. It features wide coverage, strong resilience, autonomous communication capabilities, and high mobility. Therefore, it has irreplaceable value in emergency rescue, information services in marine and remote areas, military communications, and diplomatic communications, and is an indispensable emergency backup communication method.

[0003] Currently, communication link establishment for traditional shortwave communication systems is mainly achieved using the Automatic Link Establishment (ALE) method. For third-generation ALE, multi-user link establishment requires multiple time slots, and the establishment time increases accordingly with the number of users, typically exceeding 4 seconds, equivalent to an average of more than 5 time slots.

[0004] For high-speed shortwave communication systems and broadband shortwave communication systems, technologies such as Orthogonal Frequency Division Multiplexing (OFDM) are typically used to construct the system, and related innovations are mostly focused on physical layer technology research.

[0005] Random access is an uplink synchronization and establishment method used in 4G / 5G communication systems, involving the physical layer, media access control (MAC) layer, radio link control (RLC) layer, and radio resource control (RRC) layer. Existing random access protocols have two modes: contention-based and contention-free. In contention-based mode, four messages (msg1, msg2, msg3, msg4) are sent sequentially to complete the random access process. In contention-free mode, two messages (msg1, msg2) are sent sequentially. In both modes, each message occupies one time slot, and after receiving the previous message, there is a several time slot interval before sending the next message (time slot length is 1 millisecond or less). If these protocols are directly applied to shortwave communication with longer time slot lengths (typically hundreds of milliseconds), both modes suffer from a long random access process completion time. Summary of the Invention

[0006] Purpose of the invention: To address the problems of numerous time slots and long setup times in shortwave communication applications based on contention- or contention-free random access procedures in existing 4G / 5G technologies, this invention proposes a random access method and apparatus for shortwave communication systems that can complete the random access process in shortwave communication systems with as few as two time slots, thereby reducing the time required for random access.

[0007] Technical solution: To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A random access method for shortwave communication systems includes:

[0009] Send a random access request signal to the central station, the random access request signal being determined based on the address identifier of the device to be accessed;

[0010] The system monitors and receives random access response signals sent by the central station. If the random access response signal can be received and the address identifier of the device to be accessed can be parsed from the random access response signal, then the random access is successful; otherwise, the random access fails, and the system resends the random access request signal to the central station and monitors and receives the random access response signal until the random access is successful or the maximum number of random access attempts is reached.

[0011] Among them, sending random access request signals and monitoring and receiving random access response signals occur in adjacent time slots.

[0012] Furthermore, the random access request signal satisfies:

[0013] The sum of the duration of the random access request signal, the duration of the protection time interval, and the duration of the system's receiving, processing, and transmitting / receiving conversion time is equal to the duration of a single time slot in the shortwave communication system, wherein:

[0014] The duration of the protection time interval is used to meet the propagation distance requirements of the shortwave communication system for the random access request signal;

[0015] The duration of the system's receiving and processing and transmit / receive conversion time is used to meet the requirements of the shortwave communication system's hardware and software for detecting the random access request signal and the conversion time between receiving the random access request signal and sending the random access response signal.

[0016] Furthermore, the random access request signal includes the following fields: a cyclic prefix and a preamble; wherein:

[0017] The preamble is determined based on the address identifier of the device to be accessed;

[0018] The cyclic prefix is ​​determined based on the preamble, and the duration of the cyclic prefix is ​​greater than the maximum delay spread of the wireless channel in the shortwave communication system.

[0019] Furthermore, the random access response signal includes the following fields: subheader, second backoff indication, and address identifier parsed by the central station from the random access request signal;

[0020] The subheader is used to indicate the type of content following this byte and whether it is the last byte of this frame;

[0021] The second backoff indication is the backoff time interval for the next random access given by the central station.

[0022] Furthermore, sending a random access request signal to the central station includes the following steps:

[0023] Compare the number of random access attempts with the maximum number of random access attempts. If the number of random access attempts is greater than or equal to the maximum number of random access attempts, then the random access attempt fails; otherwise,

[0024] The random access request signal is generated based on the address identifier of the device to be accessed;

[0025] If the previous random access was successful or the device to be accessed is accessing the central station for the first time, the transmission power remains unchanged; if the previous random access was unsuccessful, the transmission power is increased.

[0026] Based on the transmission power, the random access request signal is sent to the central station.

[0027] Furthermore, if the increase in transmission power exceeds the range of transmission power, then the transmission power is set to the maximum transmission power.

[0028] Furthermore, after determining that random access has failed, the system resends the random access request signal to the central station and monitors and receives the random access response signal, including:

[0029] If a random access response signal can be received, but the address identifier of the intended access device cannot be resolved, then:

[0030] Determine whether the number of random access attempts is less than the maximum number of random access attempts. If it is less, increment the number of random access attempts by 1, delay the corresponding time slot according to the second backoff indication in the random access response signal, resend the random access request signal to the central station, and monitor and receive the random access response signal. If it is not less than the maximum number of random access attempts, the maximum number of random access attempts has been reached, and the random access fails.

[0031] If a random access response signal is not received, then:

[0032] If the number of random access attempts is less than the maximum number of random access attempts, then the number of random access attempts is incremented by 1, and a random access request signal is resent to the central station, and the random access response signal is monitored and received. If the number of random access attempts is not less than the maximum number of random access attempts, then the maximum number of random access attempts has been reached, and the random access attempt fails.

[0033] A random access device for use in a shortwave communication system, comprising:

[0034] The sending module is used to send a random access request signal to the central station, wherein the random access request signal is determined according to the address identifier of the device to be accessed;

[0035] The monitoring and receiving module is used to monitor and receive the random access response signal sent by the central station. If the random access response signal can be received and the address identifier of the device to be accessed can be parsed from the random access response signal, the random access is successful; otherwise, the random access fails, and the random access request signal is resent to the central station, and the random access response signal is monitored and received again until the random access is successful or the maximum number of random access attempts is reached.

[0036] Specifically, sending random access request signals and monitoring and receiving random access response signals occur in adjacent time slots.

[0037] Furthermore, the random access request signal satisfies:

[0038] The sum of the duration of the random access request signal, the duration of the protection time interval, and the duration of the system's receiving, processing, and transmitting / receiving conversion time is equal to the duration of a single time slot in the shortwave communication system, wherein:

[0039] The duration of the protection time interval is used to meet the propagation distance requirements of the shortwave communication system for the random access request signal;

[0040] The duration of the system's receiving and processing and transmit / receive conversion time is used to meet the requirements of the shortwave communication system's hardware and software for detecting the random access request signal and the conversion time between receiving the random access request signal and sending the random access response signal.

[0041] Furthermore, the random access request signal includes the following fields: a cyclic prefix and a preamble; wherein:

[0042] The preamble is determined based on the address identifier of the device to be accessed;

[0043] The cyclic prefix is ​​determined based on the preamble, and the duration of the cyclic prefix is ​​greater than the maximum delay spread of the wireless channel in the shortwave communication system.

[0044] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects:

[0045] Based on the existing contention-free random access process, this invention involves the proposed access device first sending a random access request signal, determined by its address identifier, to the central station in a specific time slot. Then, in the next adjacent time slot, it monitors and receives the random access response signal sent by the central station. If the random access response signal is received and the address identifier of the proposed access device can be parsed from it, the proposed access device successfully completes the random access; otherwise, the proposed access device fails to complete the random access and resends the random access request signal to the central station, monitoring and receiving the random access response signal again, until successful random access or the maximum number of random access attempts is reached. This invention transmits the random access request signal and random access response signal in adjacent time slots, eliminating the time slot between message transmissions. The random access process can be completed in as few as two time slots, reducing the time required for random access. Attached Figure Description

[0046] Figure 1 This is a flowchart of a random access method according to an embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of two stages, two time slots, and two handshakes in a random access method according to an embodiment of the present invention;

[0048] Figure 3 This is a diagram illustrating the structure of a random access request signal on the user terminal side in an embodiment of the present invention.

[0049] Figure 4 This is a diagram illustrating the structure of a random access response signal in an embodiment of the present invention.

[0050] Figure 5 This is a flowchart illustrating the transmission process of a random access request signal on the user terminal side in an embodiment of the present invention.

[0051] Figure 6 This is a time-slot time-domain structure diagram of random access request signal transmission on the user terminal side in an embodiment of the present invention;

[0052] Figure 7 This is a time-slot time-domain structure diagram of random access request signal monitoring and processing at a central station in an embodiment of the present invention;

[0053] Figure 8 This is a flowchart illustrating the process of receiving a random access response signal on the user terminal side in an embodiment of the present invention.

[0054] Figure 9 A time slot allocation diagram for the random access procedure in existing technologies;

[0055] Figure 10 This is a block diagram of a random access device according to an embodiment of the present invention. Detailed Implementation

[0056] The invention will now be further described with reference to the accompanying drawings.

[0057] Example 1:

[0058] A random access method applied to shortwave communication systems, such as Figure 1 As shown, it includes the following steps:

[0059] Send a random access request signal to the central station, the random access request signal being determined based on the address identifier of the device to be accessed;

[0060] The system monitors and receives random access response signals sent by the central station. If the random access response signal can be received and the address identifier of the device to be accessed can be parsed from the random access response signal, then the random access is successful; otherwise, the random access fails, and the system resends the random access request signal to the central station and monitors and receives the random access response signal until the random access is successful or the maximum number of random access attempts is reached.

[0061] Among them, sending random access request signals and monitoring and receiving random access response signals occur in adjacent time slots.

[0062] In this embodiment, the central station is a shortwave device responsible for allocating and scheduling access resources (such as addresses and time slots) for all devices intending to access the network. These devices are user terminals intending to join the network. User terminals include, but are not limited to, mobile phones, tablets, and desktop computers.

[0063] The fast random access method for a shortwave communication system described in this embodiment, based on the existing contention-free random access process, transmits random access request signals and random access response signals in adjacent time slots, eliminating the time slots for sending messages, and completing the random access process in as few as two time slots, thus reducing the time required for random access.

[0064] Furthermore, the random access request signal satisfies:

[0065] The sum of the duration of the random access request signal, the duration of the protection time interval, and the duration of the system's receiving, processing, and transmitting / receiving conversion time is equal to the duration of a single time slot in the shortwave communication system, wherein:

[0066] The duration of the protection time interval is used to meet the propagation distance requirements of the shortwave communication system for the random access request signal;

[0067] The duration of the system's receiving and processing and transmit / receive conversion time is used to meet the requirements of the shortwave communication system's hardware and software for detecting the random access request signal and the conversion time between receiving the random access request signal and sending the random access response signal.

[0068] This embodiment designs the time slot structure for transmitting random access request signals, ensuring that the central station can complete the reception and parsing of random access request signals within one time slot, while preparing for the transmission of random access response signals in the next time slot. This achieves the transmission of random access request signals and random access response signals in adjacent time slots, eliminating the time slot interval between message transmissions.

[0069] Furthermore, the random access request signal includes the following fields: a cyclic prefix and a preamble; wherein:

[0070] The preamble is determined based on the address identifier of the device to be accessed;

[0071] The cyclic prefix is ​​determined based on the preamble, and the duration of the cyclic prefix is ​​greater than the maximum delay spread of the wireless channel in the shortwave communication system.

[0072] Furthermore, the random access response signal includes the following fields: subheader, second backoff indication, and address identifier parsed by the central station from the random access request signal;

[0073] The subheader is used to indicate the type of content following this byte and whether it is the last byte of this frame;

[0074] The second backoff indication is the backoff time interval for the next random access given by the central station.

[0075] Furthermore, sending a random access request signal to the central station includes the following steps:

[0076] Compare the number of random access attempts with the maximum number of random access attempts. If the number of random access attempts is greater than or equal to the maximum number of random access attempts, then the random access attempt fails; otherwise,

[0077] The random access request signal is generated based on the address identifier of the device to be accessed;

[0078] If the previous random access was successful or the device to be accessed is accessing the central station for the first time, the transmission power remains unchanged; if the previous random access was unsuccessful, the transmission power is increased.

[0079] Based on the transmission power, the random access request signal is sent to the central station.

[0080] Furthermore, if the increase in transmission power exceeds the range of transmission power, then the transmission power is set to the maximum transmission power.

[0081] Furthermore, after determining that random access has failed, the system resends the random access request signal to the central station and monitors and receives the random access response signal, including:

[0082] If a random access response signal can be received, but the address identifier of the intended access device cannot be resolved, then:

[0083] Determine whether the number of random access attempts is less than the maximum number of random access attempts. If it is less, increment the number of random access attempts by 1, delay the corresponding time slot according to the second backoff indication in the random access response signal, resend the random access request signal to the central station, and monitor and receive the random access response signal. If it is not less than the maximum number of random access attempts, the maximum number of random access attempts has been reached, and the random access fails.

[0084] If a random access response signal is not received, then:

[0085] If the number of random access attempts is less than the maximum number of random access attempts, then the number of random access attempts is incremented by 1, and a random access request signal is resent to the central station, and the random access response signal is monitored and received. If the number of random access attempts is not less than the maximum number of random access attempts, then the maximum number of random access attempts has been reached, and the random access attempt fails.

[0086] Example 2:

[0087] This embodiment discloses a random access method for shortwave communication systems, wherein the frequency range of the shortwave can be 1.6MHz-30MHz. Addressing the problems of numerous time slots and long setup times in existing contention- or contention-free random access procedures for shortwave communication applications, this embodiment proposes a two-stage fast random access method for shortwave communication systems using only two messages, msg1 and msg2. Furthermore, msg1 and msg2 are adjacent in time slot, significantly reducing the time required for the random access process in shortwave communication systems.

[0088] The fast random access method described in this embodiment includes: based on pre-configuration, i.e., parameter initialization, using two time slots, two handshakes, and two stages to complete the random access process between the user terminal and the central station in the shortwave communication system. For example... Figure 2 As shown, that is:

[0089] Phase 1: In the first time slot, the random access request signal is transmitted using the first handshake.

[0090] Phase Two: In the second time slot, random access response signal transmission is performed using a second handshake.

[0091] Based on the existing contention-free random access procedure, this embodiment eliminates the message transmission interval time slot, that is, transmits the random access request signal and the random access response signal in adjacent time slots. The random access procedure can be completed in as few as two time slots, reducing the time required for random access.

[0092] The specific details of the above process are as follows:

[0093] Pre-configuration (parameter initialization)

[0094] The central station and user terminals have completed parameter initialization, specifically:

[0095] The central station determines the preamble sequence rule based on the address identifiers of all user terminals and the total number of user terminals. The address identifier and the determined preamble sequence rule for each user terminal are pre-configured to each terminal. The range and specific values ​​of the user terminal's address identifier are preset by the central station. The preamble sequence rule defines a one-to-one correspondence between each user terminal's address identifier and the preamble generated based on that address identifier. A preamble corresponding one-to-one with the user terminal's address identifier is generated according to the preamble sequence rule. Furthermore, the preamble should, as far as possible, satisfy characteristics such as zero autocorrelation, low cross-correlation, and constant amplitude with a low peak-to-average power ratio, such as the ZC (Zadoff-Chu) sequence or the PN (Pseudo-Noise) sequence. This facilitates the identification of different preambles and the accurate acquisition of transmission time calibration values ​​at the receiving end through correlation detection.

[0096] When a user terminal's random access procedure is triggered, that user terminal becomes the proposed network access user terminal. This proposed network access user terminal initializes parameters such as the preamble transmission count, maximum preamble transmission count, power adjustment count, and first backoff indication. Among these:

[0097] The preamble transmission count is used to count the number of times the preamble is transmitted, which is equivalent to the number of random access attempts.

[0098] The maximum number of preamble transmissions is an integer greater than or equal to zero, used to determine the maximum number of preamble transmissions during the random access process. The maximum number of preamble transmissions is the maximum number of random access attempts. The specific value is related to factors such as the shortwave communication system's requirement for the maximum time spent on random access. In particular, when the maximum number of preamble transmissions is zero, it means that the user terminal is not allowed to access the current central station of the shortwave communication system.

[0099] The power adjustment counter is used to indicate the number of times the transmit power for transmitting the preamble has been adjusted. Each power adjustment counter corresponds to one transmit power, denoted as P. 功率调整计数Furthermore, as the power adjustment count increases, the corresponding transmission power increases. When a random access fails, the power adjustment count is incremented by 1, thus increasing the transmission power.

[0100] The first backoff indication is the backoff time interval for the next random access. The value of the first backoff indication should usually be different for different user terminals intending to access the network. Therefore, delaying the backoff time interval corresponding to the first backoff indication before random access can improve the random access success rate of the entire system.

[0101] Phase 1: Transmission of Random Access Request Signals

[0102] During this stage, the user terminal intending to join the network sends a random access request signal to the central station, including the following steps:

[0103] S101. Compare the preamble transmission count with the maximum number of preamble transmissions. If the preamble transmission count is less than the maximum number of preamble transmissions, proceed to step S102; otherwise, end the random access request signal transmission process and the random access fails.

[0104] S102. Generate a preamble based on the preamble sequence rules set by the central station and its own address identifier, and generate a random access request signal based on the preamble;

[0105] S103. Based on whether the previous random access was successful, determine whether to increment the power adjustment counter by 1. If the previous random access was successful, the power adjustment counter remains unchanged; if the previous random access was unsuccessful, the power adjustment counter is incremented by 1, and the transmission power is set to P. 功率调整计数 ;

[0106] S104. The user terminal intending to join the network sends a random access request signal containing a preamble to the central station at the transmission power in step S103.

[0107] In step S103, if it is the first random access, that is, there is no previous random access, then the power adjustment count remains unchanged.

[0108] In step S103, if the power adjustment count exceeds the range of the power adjustment count after incrementing by 1, the transmission power is directly set to the transmission power corresponding to the maximum value of the power adjustment count.

[0109] The random access request signal within a single time slot consists of two parts: a cyclic prefix (CP) and a preamble (Sequence), with corresponding durations T and T, respectively. CP and T SEQ The structure diagram of the random access request signal sent by the user terminal is as follows: Figure 3 As shown.

[0110] Cyclic prefix CP duration T CPIt should be greater than the maximum delay spread of the wireless channel. The multipath delay spread of a shortwave communication system is related to the cell radius and the wireless channel propagation environment, but it is acceptable as long as the maximum delay spread is less than the cyclic prefix (CP) duration T. CP This ensures that each subcarrier within the integration interval of the receiver has an integer waveform under each path, thereby eliminating inter-symbol interference and inter-subcarrier interference (ICI) caused by multipath. The cyclic prefix CP is achieved by cyclically shifting the preamble.

[0111] Preamble sequences should, as far as possible, satisfy characteristics such as zero autocorrelation, low cross-correlation, and constant amplitude with low peak-to-average power ratio, such as ZC sequences and PN sequences. This facilitates the identification of different preamble sequences and the accurate acquisition of transmission time calibration values ​​at the receiver through correlation detection.

[0112] Within this time slot, after the time occupied by the random access request signal, a protection period should also be included, during which no signal transmission should occur. The protection period consists of the protection interval GP and the system reception processing and transmit / receive conversion time IDLE, with corresponding durations T and T, respectively. GP and T IDLE Therefore, the duration of a single time slot T 单时隙 =T CP +T SEQ +T GP +T IDLE .

[0113] The protection time interval (GP) is mainly used to overcome propagation delay in the access time slot and interference from other user terminal links; its duration is T. GP The maximum propagation distance smax that can be supported by the cell is determined, and the relationship between the two is smax = T. GP ×c / 2 (where c is the speed of light), therefore the protection time interval GP is the duration T. GP The larger the value, the greater the supported cell propagation distance; therefore, the protection interval GP duration T... GP It should meet the propagation distance requirements of shortwave communication systems.

[0114] The system receive processing and transmit / receive conversion time (IDLE) is mainly used by the central station terminal to receive and process the preamble and complete the transmit / receive conversion, ensuring that the central station can complete the random access request signal reception and processing before the end of the first time slot and can send the random access response signal on time at the beginning of the next time slot. Therefore, the system receive processing and transmit / receive conversion time (IDLE) duration T is... IDLE The system should meet the time requirements of shortwave communication system hardware and software for detecting the preamble in the random access request signal and for transmitting and receiving conversion.

[0115] In summary, given a fixed single-slot duration in a shortwave communication system, the components of the random access request signal satisfy the following:

[0116] Cyclic prefix CP duration T CP Greater than the maximum delay spread of the wireless channel;

[0117] Cyclic prefix CP duration T CP Preamble Sequence Duration T SEQ Satisfy: Single time slot duration T 单时隙 =T CP +T SEQ +T GP +T IDLE Among them, the protection time interval GP duration T GP To meet the propagation distance requirements of shortwave communication systems, the system's receiving, processing, and transmit / receive switching time (IDLE duration T) must be maintained. IDLE It meets the time requirements of shortwave communication system hardware and software for detecting the preamble in the random access request signal and for transmitting and receiving conversion.

[0118] This embodiment designs the time slot structure (Cyclic Prefix (CP) duration, Guard Interval (GP) duration, and System Receive Processing and Transmit / Receive Switching (IDLE) duration) for transmitting random access request signals, ensuring that the central station can complete the reception and parsing of random access request signals within one time slot, while preparing for the transmission of random access response signals in the next time slot.

[0119] Phase Two: Transmission of Random Access Response Signals

[0120] When the central station obtains the address identifier (ADDRESS_ID) of one or more user terminals requesting random access in the current time slot from the preamble during the random access request signal transmission phase, the central station sends a random access response signal to all user terminals in the next time slot, and the user terminals intending to join the network enter the random access response reception phase.

[0121] The random access response signal (MAC PDU) sent by the central station consists of multiple bytes, including a header, a second backoff indication, an address identifier, and data. The specific rules for its composition are as follows: Figure 4 As shown.

[0122] The sub-header indicates the type of content following this byte and whether it is the last byte of the frame. Content types include:

[0123] The second backoff indication BI is the backoff time interval for the next random access given by the central station. In this embodiment, the central station can give the backoff time interval for the next random access based on the number of user terminals currently intending to join the network or other standards. The central station can determine the number of user terminals currently intending to join the network based on the received random access request signal.

[0124] The address identifier ADDRESS_ID is one or more user terminal address identifiers requesting random access that are blindly detected by the central station during the IDLE time of the random access request signal transmission phase.

[0125] Data refers to the data content (such as Timing Advance, TA) sent by the central station to user terminals requesting random access.

[0126] In the random access response signal MAC PDU, each address identifier's content type is followed by a data content type, indicating the data content sent to the user terminal corresponding to that address identifier.

[0127] In this phase, the method for receiving the random access response signal on the terminal side of the user intending to join the network is as follows:

[0128] S201. After the random access request signal transmission is completed, the monitoring center station will begin sending the random access response signal in the next time slot:

[0129] If a random access response signal is received, proceed to step S202;

[0130] If no random access response signal is received, proceed to step S204;

[0131] S202, Set the first backoff indication to the second backoff indication BI field in the random access response signal;

[0132] Determine whether the random access response signal contains its own ADDRESS_ID. If it does, receive the subsequent DATA content and consider the random access to be successful. Otherwise, consider the random access to be unsuccessful and proceed to step S203.

[0133] S203. Determine whether the preamble transmission count is less than the maximum number of preamble transmissions. If so, increment the preamble transmission count by 1, delay the backoff time interval corresponding to the first backoff indication, return to step S103 of the random access request signal transmission stage on the user terminal side, and continue to execute the subsequent random access request signal transmission steps; otherwise, consider the random access to fail.

[0134] S204. Set the first backoff indication to 0, determine whether the preamble transmission count is less than the maximum number of preamble transmissions, if so, increment the preamble transmission count by 1, delay the backoff time interval corresponding to the first backoff indication (since the first backoff indication is set to 0, there is actually no delay here), return to step S103 of the random access request signal transmission stage on the user terminal side, and continue to execute the subsequent random access request signal transmission steps; otherwise, consider the random access to fail.

[0135] Example 3:

[0136] To make the technical solution and advantages of the present invention clearer, this embodiment will use a large circle centered on Nanjing and with a radius of Nanjing-Beijing as the network coverage area to further describe the present invention in detail. It should be understood that this embodiment is merely illustrative of the present invention and is not intended to limit the present invention.

[0137] I. Pre-configuration – Parameter Initialization

[0138] The main parameters involved in this embodiment include, but are not limited to, the following parameters:

[0139] ADDRESS_ID: The address identifier of the shortwave terminal, i.e., the user terminal;

[0140] PREAMBLE_TRANSMISSION_COUNTER: Preamble transmission count;

[0141] PREAMBLE_TRANSMISSION_MAX: Maximum number of preamble transmissions;

[0142] PREAMBLE_POWER_RAMPING_COUNTER: Power adjustment count;

[0143] PREAMBLE_BACKOFF1: First backoff instruction.

[0144] ADDRESS_ID is the unique address identifier of the user terminal, ranging from 000 to 837, and is set in advance by the central station.

[0145] Meanwhile, the central station generates a preamble sequence rule based on the address identifiers and quantities of all user terminals. In this embodiment, the preamble sequence rule is as follows:

[0146] The address identifier ADDRESS_ID of the user terminal is mapped to a corresponding u value according to the mapping table, and the u value ranges from 1 to 838.

[0147] A Zadoff-Chu sequence (hereinafter referred to as the ZC sequence) with a length of 839 is generated with u as the root. The ZC sequence is the preamble of the address identifier of the corresponding user terminal.

[0148] In this embodiment, the mapping table can be as shown in Table 1, but the correspondence between ADDRESS_ID and u is not limited to Table 1:

[0149] Table 1 Mapping table between ADDRESS_ID and u

[0150]

[0151]

[0152]

[0153]

[0154] The ZC sequence of length 839 is generated with u as the root, and the generation formula is as follows:

[0155] x u [n] = exp[-jπun(n+1) / N] ZC (1)

[0156] Where, x u For the generated ZC sequence, N ZC N is the length of the ZC sequence. ZC =839, n=0,1,…,N ZC -1, exp represents an exponential function with the natural constant e as the base, j is the imaginary number, and π is the value of pi.

[0157] The maximum number of preamble transmissions, PREAMBLE_TRANSMISSION_MAX, is an integer greater than or equal to zero. It is used to determine the maximum number of preamble transmissions during the random access process. The specific value is related to factors such as the maximum time the system spends on random access. Here, PREAMBLE_TRANSMISSION_MAX is initialized to 3.

[0158] User transmits power P PREAMBLE_POWER_RAMPING_COUNTER It typically has three power settings: low, medium, and high (P). 低 P 中 P 高 When a user terminal transmits a preamble, it typically starts from a low-power P... 低 Start sending; if random access fails, increase the transmission power up to the maximum. Therefore, the power adjustment count range here is 1-3, corresponding to low, medium, and high power levels, and the power adjustment count PREAMBLE_POWER_RAMPING_COUNTER is initialized to 1, i.e., P is initialized... PREAMBLE_POWER_RAMPING_COUNTER =P1=P 低 .

[0159] The central station pre-configures the address identifiers of all user terminals for each user terminal. Assuming the number of user terminals to be connected to the network is 32, and the address identifiers (ADDRESS_ID) of the user terminals to be connected to the network are 000 to 031, the corresponding u-values ​​and preambles of the 32 user terminals to be connected to the network can be obtained according to the mapping table shown in Table 1 and formula (1). For the central station and each user terminal to be connected to the network, formula (1) and the mapping table are known, which means that only one of the address identifier (ADDRESS_ID), u-value, and preamble of the user terminal to be connected to the network needs to be known, and the other two can be uniquely matched.

[0160] When a random access procedure for a user terminal intending to join the network is triggered, the user terminal intending to join the network sets the preamble transmission count PREAMBLE_TRANSMISSION_COUNTER to 0, the maximum number of preamble transmissions PREAMBLE_TRANSMISSION_MAX to 3, the power adjustment count PREAMBLE_POWER_RAMPING_COUNTER to 1, and the first backoff indication PREAMBLE_BACKOFF1 to 0.

[0161] II. First Phase – Transmission of Random Access Request Signals

[0162] Assume that all user terminals in the network use the same clock, all user terminals switch frequencies simultaneously, and the frequency and time slot of other user terminals in the network are known.

[0163] The method for transmitting the random access request signal on the user terminal side of the user terminal intending to join the network is as follows:

[0164] If PREMBLE_TRANSMISSION_COUNTER is greater than or equal to PREMBLE_TRANSMISSION_MAX, the random access request signal transmission process ends, and random access fails; otherwise:

[0165] The user terminal intending to join the network maps its own user address identifier ADDRESS_ID to u according to Table 1, and then generates a ZC sequence of length 839 according to Equation (1), and generates a random access request signal based on the generated ZC sequence, i.e., the preamble.

[0166] The user terminal intending to join the network determines whether to increment PREMBLE_POWER_RAMPING_COUNTER by 1 based on whether the previous random access was successful. If the previous random access was successful or it was the first random access, PREMBLE_POWER_RAMPING_COUNTER remains unchanged. If the previous random access was unsuccessful, PREMBLE_POWER_RAMPING_COUNTER is incremented by 1, and the transmit power is set to P. PREAMBLE_POWER_RAMPING_COUNTERIf the power adjustment counter increments by 1 and then exceeds 3, the transmission power is directly set to P. PREAMBLE_POWER_RAMPING_COUNTER =P3;

[0167] The user terminal to be connected to the network will transmit power P PREAMBLE_POWER_RAMPING_COUNTER Send a random access request signal to the central station.

[0168] The random access request signal sending process is as follows: Figure 5 As shown.

[0169] Assuming the shortwave communication system is designed using OFDM, its parameters can be: nominal bandwidth BW = 48kHz, FFT (Fast Fourier Transform) sampling points 1024, subcarrier number 624, and baseband sampling rate f. S =73728, sampling interval T S =1 / f S ≈0.0136ms, subcarrier spacing Δf=72Hz, number of OFDM symbols N in a single time slot sym =14, and the lengths of each OFDM symbol are 14.9740ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.9740ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms, 14.8655ms. Therefore, the duration of a single time slot is equal to the sum of the lengths of the 14 OFDM symbols within that single time slot, i.e., T. 单时隙 ≈208.334ms.

[0170] The structure of a random access request signal within a single time slot consists of two parts: a cyclic prefix (CP) and a preamble (Sequence), with corresponding sampling points of N. CP and N SEQ The corresponding duration is T. CP and T SEQ Within this time slot, after the time occupied by the random access request signal, a protection period should also be included. This protection period consists of the protection time interval GP and the system reception processing and transmit / receive conversion time IDLE, corresponding to N sampling points respectively. GP and N IDLE The corresponding durations are T GP and T IDLE .

[0171] in:

[0172] The preamble sequence is generated using the method described above for generating a ZC sequence of length 839, corresponding to the number of sampling points N. SEQ =12288, duration T SEQ=N SEQ *T s =N SEQ / f s =12288 / 73728≈166.6667ms.

[0173] Cyclic prefix CP duration T CP The multipath delay spread should be greater than the maximum delay spread of the wireless channel. The multipath delay spread of shortwave communication systems is related to the cell radius and the wireless channel propagation environment. As long as the maximum delay spread is less than the CP duration, it can guarantee that each subcarrier within the receiver's integration interval has an integer waveform under each path, thereby eliminating inter-symbol interference and inter-subcarrier interference (ICI) caused by multipath. In shortwave skywave communication, some signals transmitted by the transmitter reach the receiver after only one reflection from the ionosphere; some signals are reflected back to the ground by the ionosphere and then reflected again to the ionosphere, reaching the receiver after a second reflection; some signals even require three to four reflections from the ionosphere to reach the receiver. Multipath phenomena typically involve 2, 3, or 4 paths, with a probability of 85%, with 3 paths being the most common. Furthermore, extensive statistical data shows that in medium- and long-distance transmission systems, the majority of multipath delays are between 0.2 and 5 ms, but in rare cases, the maximum delay reaches 8 ms. Generally, 99.5% of multipath propagation delays are no less than 0.5ms, 50% are no less than 1.4ms, and only 0.5% exceed 5ms. Therefore, in this embodiment, the number of cyclic prefix (CP) sampling points N is... CP =792, corresponding duration T CP =N cp / f s =792 / 73728≈10.7422ms, which meets the requirement of being greater than the maximum delay spread of the wireless channel.

[0174] The protection time interval (GP) is primarily used to overcome propagation delays in access time slots and interference from other user terminal links. Its duration determines the supported cell propagation distance. The GP duration is T. GP The larger the value, the greater the supported cell propagation distance. When using the Nanjing-Beijing shortwave skywave propagation mode, the ground distance is approximately 1000km, and the propagation distance is around 1500km (due to ionospheric influence, it is related to the year, season, day / night cycle, etc.). In this embodiment, the number of GP sampling points N during the protection time interval is... GP =1488, corresponding duration T GP =N GP / f s=1488 / 73728≈20.1823ms, the supported propagation distance is 20.1823*0.001*3*10^8 / 2=3027.345km, which meets the system's coverage range for propagation distance in the current Nanjing-Beijing skywave propagation mode.

[0175] The system receive processing and transmit / receive conversion time (IDLE) is mainly used for the time spent by the central station receiving and processing the preamble and for the transmit / receive conversion. In this embodiment, the number of sampling points for the system receive processing and transmit / receive conversion time (IDLE) is N. IDLE =792, corresponding duration T IDLE =N IDLE / f s =792 / 73728≈10.7422ms, which fully meets the time requirements of the current system hardware and software for detecting and transmitting / receiving a preamble of length 839.

[0176] And the above T CP +T SEQ +T GP +T IDLE ≈T 单时隙 It meets the requirements of each part of the random access request signal.

[0177] The time-domain structure diagram of the random access request signal transmission on the user terminal side of the proposed network access within a single time slot is as follows: Figure 6 As shown.

[0178] The central station is in the T during the transmission of the random access request signal. CP T SEQ and some T GP During the specified time period, it remains in a listening state. If it receives a random access request signal from the terminal of a user intending to join the network, it will then... GP (Users whose propagation distance is less than the maximum supported propagation distance of the cell) and T IDLE Within a time period, blind detection and identification of the preamble codes corresponding to the u values ​​of 32 users who intend to join the network are completed. If a preamble code is detected, the reverse mapping from the preamble code to the u value and from the u value to the user terminal address identifier is further completed according to Table 1 and Formula (1) above. One or more user terminal address identifiers that request random access in the current time slot are obtained. At the same time, the transmit and receive conversion is completed and the signal transmission is prepared.

[0179] The time-domain structure diagram of random access monitoring processing of the central station within a single time slot is as follows: Figure 7 As shown.

[0180] III. Second Phase – Transmission of Random Access Response Signals

[0181] When the central station obtains the address identifiers (ADDRESS_ID) of one or more user terminals requesting random access in the current time slot during the random access request signal transmission phase, it sends a random access response signal to all user terminals in the next time slot. At the same time, the user terminal side intending to join the network enters the random access response signal reception phase.

[0182] The central station's random access response signal MAC PDU consists of multiple bytes, including:

[0183] The sub-header is used to indicate the type of content following this byte and whether it is the last byte of this frame. For example, BI is the backoff interval for the next random access given by the central station based on the number of user terminals currently intending to join the network. The more user terminals currently intending to join the network, the longer the backoff interval for the next random access. ADDRESS_ID is the address identifier of one or more user terminals requesting random access that the central station blindly detects during part of the GP and IDLE time during the random access request signal transmission phase. DATA is the data content sent by the central station to the user terminal (such as timed advance TA, etc.).

[0184] The method for receiving the random access response signal on the user terminal side of the user terminal intending to join the network is as follows:

[0185] After the random access request signal transmission ends, the monitoring center station will start sending the random access response signal in the next time slot.

[0186] If a random access response signal is received, then:

[0187] Set PREMBLE_BACKOFF1 as a BI field;

[0188] If the random access response signal contains its own ADDRESS_ID, then the subsequent DATA content is received and the random access is considered successful; otherwise:

[0189] If PREMBLE_TRANSMISSION_COUNTER ≥ PREMBLE_TRANSMISSION_MAX, then random access is considered to have failed; otherwise, PREMBLE_TRANSMISSION_COUNTER is incremented by 1, PREMBLE_BACKOFF is delayed by 1 time slot, and the user terminal returns to the random access request signal transmission stage. The user terminal intending to access the network determines whether to increment PREMBLE_POWER_RAMPING_COUNTER based on whether the previous random access was successful. If the previous random access was successful or it was the first random access, PREMBLE_POWER_RAMPING_COUNTER remains unchanged; if the previous random access was unsuccessful, PREMBLE_POWER_RAMPING_COUNTER is incremented by 1, and the transmission power is set to P. PREAMBLE_POWER_RAMPING_COUNTER If the power adjustment counter increments by 1 and then exceeds 3, the transmission power is directly set to P. PREAMBLE_POWER_RAMPING_COUNTER =P3” and continue to execute the subsequent random access request signal transmission steps;

[0190] If no random access response signal is received, then:

[0191] Set PREMBLE_BACKOFF1 to 0. If PREMBLE_TRANSMISSION_COUNTER ≥ PREMBLE_TRANSMISSION_MAX, random access is considered to have failed; otherwise, PREMBLE_TRANSMISSION_COUNTER is incremented by 1. Delay PREMBLE_BACKOFF1 time slots and return to the user terminal side during the random access request signal transmission phase. The user terminal intending to access the network determines whether to increment PREMBLE_POWER_RAMPING_COUNTER based on whether the previous random access was successful. If the previous random access was successful or it was the first random access, PREMBLE_POWER_RAMPING_COUNTER remains unchanged; if the previous random access failed, PREMBLE_POWER_RAMPING_COUNTER is incremented by 1, and the transmission power is set to P. PREAMBLE_POWER_RAMPING_COUNTER If the power adjustment counter increments by 1 and then exceeds 3, the transmission power is directly set to P. PREAMBLE_POWER_RAMPING_COUNTER =P3” and continue to execute the subsequent random access request signal transmission steps.

[0192] The random access response receiving process on the terminal side of the user intending to join the network is as follows: Figure 8 As shown.

[0193] In this embodiment, due to the good autocorrelation and cross-correlation of the ZC sequence, the central station can easily complete the analysis and identification of random access request signals from 32 user terminals within part of the GP and IDLE time. Therefore, under normal circumstances, only two time slots (approximately 416ms) are needed to complete the random access process of 32 user terminals, achieving synchronous networking.

[0194] This method employs a contention-based random access procedure containing four messages (msg1, msg2, msg3, and msg4) from existing 4G / 5G technology, assuming that the interval between each message is minimized. For specific time slot allocation details, please refer to [link to relevant documentation]. Figure 9 In this implementation, after the msg1 message is sent, the msg2 message is sent after a two-slot interval. After the msg2 message is sent, the msg3 message is sent after another two-slot interval. After the msg3 message is sent, the msg4 message is sent in the next time slot. In the ideal scenario, random access is successful immediately after the msg4 message is sent, requiring at least 8 time slots. Similarly, using the existing non-contention-free random access procedure containing two messages (msg1 and msg2), and assuming the minimum interval between messages, the msg2 message is sent after the msg1 message, after a two-slot interval. In the ideal scenario, random access is successful immediately after the msg2 message is sent, requiring at least 4 time slots. The shortwave communication system random access method used in this embodiment requires significantly fewer time slots to establish a shortwave communication link than the random access procedure used in existing 4G / 5G technologies, thus greatly shortening the access success time.

[0195] Example 4:

[0196] This embodiment discloses a random access device applied to a shortwave communication system, such as... Figure 10 As shown, it includes:

[0197] The sending module sends a random access request signal to the central station, the random access request signal being determined based on the address identifier of the device to be accessed.

[0198] The monitoring and receiving module monitors and receives the random access response signal sent by the central station. If the random access response signal can be received and the address identifier of the device to be accessed can be parsed from the random access response signal, the random access is successful; otherwise, the random access fails, and the random access request signal is resent to the central station, and the random access response signal is monitored and received again until the random access is successful or the maximum number of random access attempts is reached.

[0199] Among them, sending random access request signals and monitoring and receiving random access response signals occur in adjacent time slots.

[0200] Furthermore, in the sending module, the random access request signal satisfies:

[0201] The sum of the duration of the random access request signal, the duration of the protection time interval, and the duration of the system's receiving, processing, and transmitting / receiving conversion time is equal to the duration of a single time slot in the shortwave communication system, wherein:

[0202] The duration of the protection time interval is used to meet the propagation distance requirements of the shortwave communication system for the random access request signal;

[0203] The duration of the system's receiving and processing and transmit / receive conversion time is used to meet the requirements of the shortwave communication system's hardware and software for detecting the random access request signal and the conversion time between receiving the random access request signal and sending the random access response signal.

[0204] Furthermore, in the sending module, the random access request signal includes the following fields: a cyclic prefix and a preamble; wherein:

[0205] The preamble is determined based on the address identifier of the device to be accessed;

[0206] The cyclic prefix is ​​determined based on the preamble, and the duration of the cyclic prefix is ​​greater than the maximum delay spread of the wireless channel in the shortwave communication system.

[0207] Furthermore, in the monitoring receiving module, the random access response signal includes the following fields: subheader, second backoff indication, and address identifier parsed by the central station from the random access request signal;

[0208] The subheader is used to indicate the type of content following this byte and whether it is the last byte of this frame;

[0209] The second backoff indication is the backoff time interval for the next random access given by the central station.

[0210] Furthermore, in the sending module, sending a random access request signal to the central station includes the following steps:

[0211] Compare the number of random access attempts with the maximum number of random access attempts. If the number of random access attempts is greater than or equal to the maximum number of random access attempts, then the random access attempt fails; otherwise,

[0212] The random access request signal is generated based on the address identifier of the device to be accessed;

[0213] If the previous random access was successful or the device to be accessed is accessing the central station for the first time, the transmission power remains unchanged; if the previous random access was unsuccessful, the transmission power is increased.

[0214] Based on the transmission power, the random access request signal is sent to the central station.

[0215] Furthermore, in the transmission module, if the transmission power increases beyond the transmission power range, the transmission power is set to the maximum transmission power.

[0216] Furthermore, in the monitoring and receiving module, after determining that random access has failed, it resends the random access request signal to the central station and monitors and receives the random access response signal, including:

[0217] If a random access response signal can be received, but the address identifier of the intended access device cannot be resolved, then:

[0218] Determine whether the number of random access attempts is less than the maximum number of random access attempts. If it is less, increment the number of random access attempts by 1, delay the corresponding time slot according to the second backoff indication in the random access response signal, resend the random access request signal to the central station, and monitor and receive the random access response signal. If it is not less than the maximum number of random access attempts, the maximum number of random access attempts has been reached, and the random access fails.

[0219] If a random access response signal is not received, then:

[0220] If the number of random access attempts is less than the maximum number of random access attempts, then the number of random access attempts is incremented by 1, and a random access request signal is resent to the central station, and the random access response signal is monitored and received. If the number of random access attempts is not less than the maximum number of random access attempts, then the maximum number of random access attempts has been reached, and the random access attempt fails.

[0221] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A random access method applied to a shortwave communication system, characterized in that, include: Send a random access request signal to the central station, the random access request signal being determined based on the address identifier of the device to be accessed; The system monitors and receives random access response signals sent by the central station. If the random access response signal can be received and the address identifier of the device to be accessed can be parsed from the random access response signal, then the random access is successful; otherwise, the random access fails, and the system resends the random access request signal to the central station and monitors and receives the random access response signal until the random access is successful or the maximum number of random access attempts is reached. Among them, sending random access request signals and monitoring and receiving random access response signals occur in adjacent time slots; The random access request signal satisfies: The sum of the duration of the random access request signal, the duration of the protection time interval, and the duration of the system's receiving, processing, and transmitting / receiving conversion time is equal to the duration of a single time slot in the shortwave communication system, wherein: The duration of the protection time interval is used to meet the propagation distance requirements of the shortwave communication system for the random access request signal; The duration of the system's receiving and processing and transmit / receive conversion time is used to meet the requirements of the shortwave communication system's hardware and software for detecting the random access request signal and the conversion time between receiving the random access request signal and sending the random access response signal.

2. The random access method for a shortwave communication system according to claim 1, characterized in that, The random access request signal includes the following fields: a cyclic prefix and a preamble; wherein: The preamble is determined based on the address identifier of the device to be accessed; The cyclic prefix is ​​determined based on the preamble, and the duration of the cyclic prefix is ​​greater than the maximum delay spread of the wireless channel in the shortwave communication system.

3. The random access method for use in a short wave communication system according to claim 1, characterized in that, The random access response signal includes the following fields: subheader, second backoff indication, and address identifier parsed by the central station from the random access request signal; The subheader is used to indicate the type of content following this byte and whether it is the last byte of this frame; The second backoff indication is the backoff time interval for the next random access given by the central station.

4. The random access method for use in a short wave communication system according to claim 2, characterized in that, Sending a random access request signal to the central station includes the following steps: Compare the number of random access attempts with the maximum number of random access attempts. If the number of random access attempts is greater than or equal to the maximum number of random access attempts, then the random access attempt fails; otherwise, The random access request signal is generated based on the address identifier of the device to be accessed; If the previous random access was successful or the device to be accessed is accessing the central station for the first time, the transmission power remains unchanged; if the previous random access was unsuccessful, the transmission power is increased. Based on the transmission power, the random access request signal is sent to the central station.

5. The random access method for use in a short wave communication system according to claim 4, characterized in that, If the increase in transmission power exceeds the range of transmission power, then the transmission power is set to the maximum transmission power.

6. The random access method for use in a short wave communication system according to claim 1, characterized in that, After determining that random access has failed, the system resends the random access request signal to the central station, monitors and receives the random access response signal, including: If a random access response signal can be received, but the address identifier of the intended access device cannot be resolved, then: Determine whether the number of random access attempts is less than the maximum number of random access attempts. If it is less, increment the number of random access attempts by 1, delay the corresponding time slot according to the second backoff indication in the random access response signal, resend the random access request signal to the central station, and monitor and receive the random access response signal. If it is not less than the maximum number of random access attempts, the maximum number of random access attempts has been reached, and the random access fails. If a random access response signal is not received, then: If the number of random access attempts is less than the maximum number of random access attempts, then the number of random access attempts is incremented by 1, and a random access request signal is resent to the central station, and the random access response signal is monitored and received. If the number of random access attempts is not less than the maximum number of random access attempts, then the maximum number of random access attempts has been reached, and the random access attempt fails.

7. A random access apparatus applied to a short wave communication system, characterized in that, include: The sending module is used to send a random access request signal to the central station, wherein the random access request signal is determined according to the address identifier of the device to be accessed; The monitoring and receiving module is used to monitor and receive the random access response signal sent by the central station. If the random access response signal can be received and the address identifier of the device to be accessed can be parsed from the random access response signal, the random access is successful; otherwise, the random access fails, and the random access request signal is resent to the central station, and the random access response signal is monitored and received again until the random access is successful or the maximum number of random access attempts is reached. Specifically, sending a random access request signal and monitoring and receiving a random access response signal occur in adjacent time slots; the random access request signal satisfies: The sum of the duration of the random access request signal, the duration of the protection time interval, and the duration of the system's receiving, processing, and transmitting / receiving conversion time is equal to the duration of a single time slot in the shortwave communication system, wherein: The duration of the protection time interval is used to meet the propagation distance requirements of the shortwave communication system for the random access request signal; The duration of the system's receiving and processing and transmit / receive conversion time is used to meet the requirements of the shortwave communication system's hardware and software for detecting the random access request signal and the conversion time between receiving the random access request signal and sending the random access response signal.

8. The random access device for use in a short wave communication system according to claim 7, characterized in that, The random access request signal includes the following fields: a cyclic prefix and a preamble; wherein: The preamble is determined based on the address identifier of the device to be accessed; The cyclic prefix is ​​determined based on the preamble, and the duration of the cyclic prefix is ​​greater than the maximum delay spread of the wireless channel in the shortwave communication system.

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