CN115665880A

CN115665880A - Random access method and device applied to short-wave communication system

Info

Publication number: CN115665880A
Application number: CN202211164131.4A
Authority: CN
Inventors: 杨保峰; 沈庆国; 高西奇
Original assignee: Network Communication and Security Zijinshan Laboratory
Current assignee: Network Communication and Security Zijinshan Laboratory
Priority date: 2022-09-23
Filing date: 2022-09-23
Publication date: 2023-01-31

Abstract

The invention discloses a random access method and a random access device applied to a short-wave communication system, wherein the random access method comprises the following steps: sending a random access request signal determined according to the address identification of the device to be accessed to a central station; monitoring and receiving a random access response signal sent by a central station in an adjacent time slot, and if the random access response signal can be received and an address identifier of the pseudo-access device can be obtained by analyzing the random access response signal, the random access is successful; otherwise, the random access fails, and the random access request signal is sent to the central station again, and the random access response signal is monitored and received until the random access is successful or the maximum random access times are reached. The invention can complete the random access process by only two time slots at least by canceling the sending interval time slots between the messages, namely transmitting the random access request signal and the random access response signal in the adjacent time slots, thereby reducing the time required by the random access.

Description

Random access method and device applied to short-wave communication system

Technical Field

The invention belongs to the technical field of short-wave communication, and particularly relates to a random access method and a random access device applied to a short-wave communication system.

Background

The short-wave communication is mainly carried out in a mode of reflecting electromagnetic waves by an ionosphere, is a unique communication mode supporting over-long-distance information transmission of thousands of kilometers under the condition of no relay, and has the characteristics of wide coverage range, strong survivability, good autonomous communication capability and maneuverability and the like, so that the short-wave communication has irreplaceable value in the fields of emergency disaster relief, information service in oceans and remote areas, military communication, outsourced communication and the like, and is an indispensable emergency bottom-guaranteeing communication mode.

At present, the communication Link Establishment for the conventional short-wave communication system is mainly implemented by an Automatic Link Establishment (ALE) method. For the third generation ALE, a multi-user link establishment requires a plurality of timeslots, and as the number of users increases, the establishment time also increases, which is usually more than 4 seconds, which is equivalent to more than 5 timeslots on average.

For a high-speed short-wave communication system and a broadband short-wave communication system, the construction of the system is usually completed by adopting technologies such as Orthogonal Frequency Division Multiplexing (OFDM), and related innovations are mostly focused on physical layer technical research.

Random access is an uplink synchronization and establishment method used in a 4G/5G communication system, and relates to a physical layer, a Medium Access Control (MAC) layer, a Radio Link Control (RLC) layer, a Radio Resource Control (RRC) layer, and the like. In the prior art, a random access protocol has 2 modes based on competition and non-competition: in a contention-based mode, 4 messages including msg1, msg2, msg3 and msg4 are sequentially sent to complete a random access process; in the contention-free mode, a mode of sequentially sending 2 messages of msg1 and msg2 is adopted to complete the random access process. In these 2 modes, each message occupies one time slot, and after receiving the previous message, it takes several time slots to transmit the next message (the time slot length is 1 ms or less). If the above protocol is directly applied to short-wave communication with a long slot length (typically several hundred milliseconds), there is a problem in that the random access procedure is completed for a long time in any mode.

Disclosure of Invention

The invention aims to: aiming at the problems of more time slots and long establishment time in short wave communication application based on a competitive or non-competitive random access process in the existing 4G/5G technology, the invention provides a random access method and a random access device applied to a short wave communication system, which can complete the random access process of the short wave communication system by only two time slots at least and reduce the time required by random access.

The technical scheme is as follows: in order to achieve the purpose, the invention adopts the following technical scheme:

a random access method applied to a short-wave communication system comprises the following steps:

sending a random access request signal to a central station, wherein the random access request signal is determined according to an address identifier of a device to be accessed;

monitoring and receiving a random access response signal sent by a central station, and if the random access response signal can be received and the address identifier of the pseudo-access device can be obtained by analyzing the random access response signal, the random access is successful; otherwise, the random access fails, the random access request signal is sent to the central station again, and the random access response signal is monitored and received until the random access is successful or the maximum random access times are reached;

wherein, the random access request signal is sent, and the random access response signal is monitored and received in the adjacent time slot.

Further, the random access request signal satisfies:

the sum of the duration of the random access request signal, the duration of the guard time interval and the duration of the system receiving processing and transceiving switching time is equal to the duration of a single time slot of the short-wave communication system, wherein:

the duration of the guard time interval is used for meeting the requirement of a short-wave communication system on the propagation distance of the random access request signal;

the system receives the duration of the switching time between processing and transceiving, and is used for meeting the requirements of software and hardware of the short-wave communication system on detecting the random access request signal and switching time between receiving the random access request signal and sending the random access response signal.

Further, the random access request signal includes the following fields: a cyclic prefix and a preamble; wherein:

the lead code is determined according to the address identification of the device to be accessed;

the cyclic prefix is determined according to the lead code, and the duration of the cyclic prefix is greater than the maximum delay spread of a wireless channel of the short-wave communication system.

Further, the random access response signal includes the following fields: the subheader, the second back-off indication and the address identifier which is obtained by the central station through analysis from the random access request signal;

the subheader is used for indicating the subsequent content type of the byte and whether the subsequent content type is the last byte of the frame;

the second back-off indication is a back-off time interval of next random access given by the central station.

Further, the sending the random access request signal to the central station includes the following steps:

comparing the random access times with the maximum random access times, and if the random access times are more than or equal to the maximum random access times, the random access fails; if not, then,

generating the random access request signal according to the address identifier of the device to be accessed;

if the last random access is successful or the simulated access device is the first random access central station, the sending power is unchanged; if the random access is unsuccessful last time, increasing the transmission power;

and transmitting the random access request signal to a central station according to the transmission power.

Further, if the transmission power is increased and exceeds the transmission power range, the transmission power is set to the maximum transmission power.

Further, after the random access failure is determined, the method sends a random access request signal to the central station again, monitors and receives a random access response signal, and includes:

if the random access response signal can be received but the address identification of the device to be accessed cannot be obtained through resolution, then:

judging whether the random access times are less than the maximum random access times, if so, adding 1 to the random access times, delaying corresponding time slots according to a second backoff instruction in the random access response signal, and retransmitting the random access request signal to the central station, monitoring and receiving the random access response signal; if not, the maximum random access times is reached, and the random access fails;

if the random access response signal cannot be received:

judging whether the random access times are less than the maximum random access times, if so, adding 1 to the random access times, and retransmitting a random access request signal to a central station, monitoring and receiving a random access response signal; if not, the maximum random access times is reached, and the random access fails.

A random access apparatus applied to a short-wave communication system, comprising:

the sending module is used for sending a random access request signal to the central station, and the random access request signal is determined according to the address identifier of the device to be accessed;

the monitoring receiving module is used for monitoring and receiving a random access response signal sent by a central station, and if the random access response signal can be received and the address identifier of the pseudo-access device can be obtained by analyzing the random access response signal, the random access is successful; if not, the random access fails, the random access request signal is sent to the central station again, and the random access response signal is monitored and received until the random access is successful or the maximum random access times are reached;

wherein the random access request signal is transmitted and the random access response signal is monitored and received in adjacent time slots.

Further, the random access request signal satisfies:

Has the advantages that: compared with the prior art, the invention has the following beneficial effects:

on the basis of the existing contention-free random access process, a pseudo-access device firstly sends a random access request signal determined according to an address identifier of a central station to the central station in a certain time slot, then monitors and receives a random access response signal sent by the central station in the next adjacent time slot, and if the random access response signal can be received and the address identifier of the pseudo-access device can be obtained by analyzing from the random access response signal, the pseudo-access device succeeds in random access; otherwise, the random access of the access simulating device fails, and the random access request signal is sent to the central station again, and the random access response signal is monitored and received until the random access is successful or the maximum random access times are reached; the invention transmits the random access request signal and the random access response signal in the adjacent time slots, cancels the sending interval time slots between messages, can complete the random access process only by at least two time slots, and reduces the time required by the random access.

Drawings

Fig. 1 is a flowchart of a random access method in an embodiment of the present invention;

fig. 2 is a schematic diagram of two phases, two time slots and two handshakes of a random access method in an embodiment of the present invention;

fig. 3 is a block diagram of a random access request signal at a ue side according to an embodiment of the present invention;

fig. 4 is a block diagram of a random access response signal in an embodiment of the present invention;

fig. 5 is a flowchart illustrating a transmission of a random access request signal at a ue side according to an embodiment of the present invention;

fig. 6 is a time domain structure diagram of a time slot for transmitting a random access request signal at a ue side in an embodiment of the present invention;

fig. 7 is a time slot time domain structure diagram of a central station side random access request signal monitoring process in the embodiment of the present invention;

fig. 8 is a flowchart illustrating a receiving process of a random access response signal at a ue side according to an embodiment of the present invention;

fig. 9 is a slot allocation diagram of a random access procedure in the prior art;

fig. 10 is a block diagram of a random access apparatus according to an embodiment of the present invention.

Detailed Description

The present invention will be further described with reference to the accompanying drawings.

Example 1:

a random access method applied to a short-wave communication system, as shown in fig. 1, includes the following steps:

In this embodiment, the central station is a short wave device responsible for allocating and scheduling access resources (such as addresses and time slots) of all the pseudo access devices, and the pseudo access devices are pseudo network access user terminals. The user terminal includes but is not limited to a mobile phone, a tablet computer, a desktop computer, etc.

According to the rapid random access method of the short wave communication system, on the basis of the existing contention-free random access process, the random access request signal and the random access response signal are transmitted in adjacent time slots, the sending interval time slot between messages is cancelled, the random access process can be completed only by two time slots at least, and the time required by random access is shortened.

Further, the random access request signal satisfies:

the sum of the duration of the random access request signal, the duration of the guard interval and the duration of the system receiving processing and transceiving switching time is equal to the duration of a single time slot of the short-wave communication system, wherein:

In this embodiment, by designing the time slot structure for transmitting the random access request signal, it is ensured that the central station can complete the receiving and analyzing of the random access request signal in one time slot, and at the same time, prepare for transmitting the random access response signal in the next time slot, that is, it is achieved that the random access request signal and the random access response signal are transmitted in adjacent time slots, and the transmission interval time slot between messages is cancelled.

comparing the random access times with the maximum random access times, and if the random access times are more than or equal to the maximum random access times, the random access fails; if not, then the mobile terminal can be switched to the normal mode,

generating the random access request signal according to the address identification of the access-intended device;

if the last random access is successful or the access-intended device is the first random access central station, the sending power is unchanged; if the random access is unsuccessful last time, increasing the transmission power;

judging whether the random access times are less than the maximum random access times, if so, adding 1 to the random access times, delaying corresponding time slots according to a second backoff instruction in the random access response signal, and retransmitting a random access request signal to a central station, monitoring and receiving the random access response signal; if not, the maximum random access times are reached, and the random access fails;

if the random access response signal cannot be received:

judging whether the random access times are smaller than the maximum random access times, if so, adding 1 to the random access times, and sending a random access request signal to the central station again, monitoring and receiving a random access response signal; if not, the maximum random access times are reached, and the random access fails.

Example 2:

the embodiment discloses a random access method applied to a short-wave communication system, wherein the frequency range of the short wave can be 1.6MHz-30MHz, and the method is applied to a two-stage fast random access method of the short-wave communication system by only adopting two messages msg1 and msg2 aiming at the problems of more required time slots and long establishment time in the short-wave communication application based on a competition or non-competition random access process in the prior art, and the msg1 and the msg2 are adjacent on the time slots, so that the required time in the random access process of the short-wave communication system is greatly reduced.

The fast random access method in this embodiment includes: on the basis of pre-configuration, namely parameter initialization, the random access process between the user terminal and the central station in the short-wave communication system is completed by adopting two time slots, two handshaking steps and two stages. As shown in fig. 2, namely:

the first stage is as follows: transmitting a random access request signal by adopting first handshake in a first time slot;

and a second stage: and transmitting the random access response signal by using the second handshake in the second time slot.

On the basis of the existing contention-free random access process, the embodiment can complete the random access process only by two time slots at least by a method of canceling the sending interval time slots between messages, namely, transmitting the random access request signal and the random access response signal in the adjacent time slots, thereby reducing the time required by the random access.

The above process is specifically explained as follows:

pre-configuration (parameter initialization)

The central station and the user terminal complete parameter initialization, specifically:

and the central station determines the lead code sequence rule according to the address identifications of all the user terminals and the number of all the user terminals, and configures the address identification of each user terminal and the determined lead code sequence rule to each user terminal in advance. The range and the specific numerical value of the address identifier of the user terminal are preset by the central station. The lead code sequence rule limits the one-to-one correspondence between the address identifier of each user terminal and the lead code generated according to the address identifier, the lead code corresponding to the address identifier of the user terminal is generated according to the lead code sequence rule, and the lead code should meet the characteristics of zero autocorrelation, low cross correlation, constant amplitude and low peak-to-average ratio and the like as far as possible, such as a ZC (Zadoff-Chu) sequence, a PN (Pseudo-Noise) sequence and the like, so that the purposes of identifying different lead codes and accurately acquiring the transmission time calibration value through correlation detection are conveniently realized at a receiving end.

When the random access process of a certain user terminal is triggered, the user terminal is a network access user terminal, and the network access user terminal initializes parameters such as a lead code sending count, a lead code maximum sending frequency, a power adjustment count, a first backoff indication and the like. Wherein:

the preamble transmission count is used to count the number of preamble transmissions, i.e., the number of random accesses.

The maximum lead code sending times are integers which are larger than or equal to zero and are used for determining the maximum lead code sending times in the random access process, the maximum lead code sending times are the maximum random access times, specific numerical values are related to factors such as the requirement of the short-wave communication system on the maximum time spent on random access, and the like, and particularly, when the maximum lead code sending times are zero, the fact that the user terminal is not allowed to access the current central station of the short-wave communication system currently is indicated;

the power adjustment counts are used to indicate the number of times the transmit power of the transmitted preamble is adjusted, and each power adjustment count corresponds to a transmit power, denoted as P _{Power adjust count} And the power adjustment count is increased, the corresponding transmission power is increased, and when the random access is not successful, the power adjustment count value is increased by 1, namely the transmission power is increased;

the first back-off indication is the back-off time interval of the next random access, and the values of the first back-off indications of different user terminals to be accessed to the network should be different usually, so that the random access success rate of the whole system can be improved by delaying the back-off time interval corresponding to the first back-off indication and then carrying out the random access.

The first stage is as follows: random access request signaling

At this stage, the user terminal intending to access the network sends a random access request signal to the central station, including the steps:

s101, comparing the preamble sending count with the maximum preamble sending times, and turning to S102 if the preamble sending count is smaller than the maximum preamble sending times; otherwise, ending the transmission flow of sending the random access request signal, and failing the random access;

s102, generating a lead code according to a lead code sequence rule determined by a central station and an address identification of the central station, and generating a random access request signal based on the lead code;

s103, determining whether the power adjustment count is increased by 1 according to whether the last random access is successful, if the last random access is successful, the power adjustment count is unchanged, if the last random access is unsuccessful, the power adjustment count is increased by 1, and the transmitting power is set to be P _{Power regulation counting} ；

And S104, the user terminal intending to access the network sends a random access request signal containing the lead code to the central station by the sending power in the step S103.

In step S103, if the random access is the first random access, that is, there is no last random access, the power adjustment count is not changed.

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

The random access request signal in a single time slot consists of two parts: the corresponding time lengths of the cyclic prefix CP and the lead code Sequence are respectively T _CP And T _SEQ . A structure of a random access request signal transmitted by a user terminal is shown in fig. 3.

Cyclic prefix CP duration T _CP Should be greater than the maximum delay spread of the wireless channel. The multipath delay spread of a short-wave communication system is dependent on the cell radius and the propagation environment of the radio channel, but as long as the maximum delay spread is smaller than the cyclic prefix CP duration T _CP Integer waveforms of each subcarrier under each path in an integration interval of a receiving end can be guaranteed, so that intersymbol interference and inter-subcarrier interference (ICI) caused by multipath are eliminated, and the cyclic prefix CP is realized by performing cyclic shift on the lead code.

The preamble Sequence should satisfy the characteristics of zero autocorrelation, low cross correlation, constant amplitude, low peak-to-average power ratio, and the like, such as ZC Sequence, PN Sequence, and the like, as far as possible, so as to facilitate the identification of different preambles and the accurate acquisition of the calibration value of transmission time at the receiving end through correlation detection.

In the time slot, after the time occupied by the random access request signal, a period of guard time should be included, and no signal transmission is performed in the guard time. The protection time is divided into a protection time interval GP and a system receiving processing and transceiving conversion time IDLE, and the corresponding duration is T respectively _GP And T _IDLE Thus a single time slot duration T _{Single time slot} ＝T _CP +T _SEQ +T _GP +T _IDLE 。

The guard time interval GP is mainly used to overcome propagation delay in the access slot and other user terminal link interference, its time length T _GP Determining the maximum propagation distance smax of the supportable cells, wherein the relationship between the maximum propagation distance smax and the maximum propagation distance smax = T _GP X c/2 (c is the speed of light), thus protecting the duration T of the time interval GP _GP The larger the supported cell propagation distance, and therefore the guard time interval GP duration T _GP The transmission distance of the short-wave communication system should be satisfiedThe requirements of (2).

The system receiving processing and transceiving switching time IDLE is mainly used for the central station terminal to receive and process the lead code, complete transceiving switching and the like so as to ensure that the central station can complete the receiving processing of the random access request signal before the end of the first time slot and can send out the random access response signal on time when the next time slot begins, so the system receiving processing and transceiving switching time IDLE is long in time T _IDLE The requirements of software and hardware of the short-wave communication system on the time for detection, transceiving conversion and the like of the lead code in the random access request signal can be met.

To sum up, under the condition that the time length of a single time slot of the short wave communication system is fixed, each part in the random access request signal satisfies:

cyclic prefix CP duration T _CP Greater than the maximum delay spread of the wireless channel;

cyclic prefix CP duration T _CP Preamble Sequence duration T _SEQ Satisfies the following conditions: time length T of single time slot _{Single time slot} ＝T _CP +T _SEQ +T _GP +T _IDLE Wherein the guard time interval GP is of duration T _GP The requirements of the short-wave communication system on the propagation distance are met, and the IDLE duration T of the receiving processing and receiving-transmitting conversion time of the system _IDLE The requirements of software and hardware of the short-wave communication system on the time for detection, transceiving conversion and the like of the lead code in the random access request signal are met.

In this embodiment, a time slot structure (a cyclic prefix CP duration, a guard time interval GP duration, a system receiving processing and transceiving conversion time IDLE duration) for transmitting a random access request signal is designed, so that a central station can complete receiving and analyzing of the random access request signal in one time slot, and meanwhile, a preparation is made for sending a random access response signal in a next time slot.

And a second stage: random access response signaling

When the central station obtains the ADDRESS identifiers ADDRESS _ ID of one or more user terminals requesting random access in the current time slot from the preamble in the transmission phase of the random access request signal, the central station sends a random access response signal to all the user terminals in the next time slot, and simultaneously, the user terminal intending to access the network enters the receiving phase of the random access response.

The random access response signal MAC PDU sent by the central station is composed of a plurality of bytes, including the sub-header, the second backoff indicator, the address identifier, the data, and the like, and the specific configuration rule is as shown in fig. 4.

The subheader is used to indicate the content type following the byte and whether the content type is the last byte of the frame. The content types include:

and a second backoff indicator BI, which is a backoff time interval for the next random access given by the central station. In this embodiment, the central station may give a backoff time interval for the next random access according to the number of current user terminals intending to access the network or other criteria, wherein the central station may determine the number of current user terminals intending to access the network according to the received random access request signal;

ADDRESS identification ADDRESS _ ID, which is one or more user terminal ADDRESS identifications requesting random access blindly detected by the central station within IDLE time of a random access request signal transmission phase;

DATA, which is DATA content (such as Timing Advance (TA)) sent by the central station to the user terminal requesting random access.

In the random access response signal MAC PDU, the content type of each address mark is followed by the content type of a data, which represents the data content sent to the user terminal corresponding to the address mark.

In this stage, the receiving method of the random access response signal at the pseudo-access user terminal side is as follows:

s201, after the transmission of the random access request signal is finished, starting to monitor a random access response signal sent by the central station in a next time slot:

if the random access response signal is received, go to step S202;

if the random access response signal is not received, go to step S204;

s202, setting the first backoff indicator as a second backoff indicator BI field in the random access response signal;

judging whether the random access response signal contains the ADDRESS _ ID of the random access response signal, if so, simultaneously receiving the subsequent DATA content and considering that the random access is successful, otherwise, considering that the random access is failed, and going to the step S203;

s203, judging whether the sending count of the lead code is less than the maximum sending times of the lead code, if so, adding 1 to the sending count of the lead code, delaying the backoff time interval corresponding to the first backoff indication, returning to the step S103 of the random access request signal sending transmission stage at the user terminal side, and continuing to execute the subsequent random access request signal sending transmission step; otherwise, the random access is considered to be failed;

s204, setting the first backoff indicator to 0, determining whether the preamble transmission count is less than the maximum preamble transmission frequency, if so, adding 1 to the preamble transmission count, delaying a backoff time interval corresponding to the first backoff indicator (since the first backoff indicator is set to 0, there is no actual delay), returning to step S103 of the random access request signal transmission phase at the user terminal, and continuing to perform the subsequent random access request signal transmission step; otherwise, the random access is considered to be failed.

Example 3:

in order to make the technical scheme and advantages of the present invention more clearly understood, the present embodiment further describes the present invention in detail by using a great circle with the south beijing as the center and the south beijing as the radius as the network coverage. It should be understood that the present embodiment is only for explaining the present invention, and is not intended to limit the present invention.

1. Pre-configuration-parameter initialization

The main parameters involved in the present embodiment include, but are not limited to, the following:

ADDRESS _ ID: address identification of the short wave terminal, namely the user terminal;

PREAMBLE _ TRANSMISSION _ COUNTER: a preamble transmission count;

PREAMBLE _ transition _ MAX: maximum transmission times of the lead code;

PREAMBLE _ POWER _ ramp _ COUNTER: power adjustment counting;

PREAMBLE _ BACKOFF1: a first backoff indicator.

Wherein, ADDRESS _ ID is the unique ADDRESS identifier of the user terminal, the range is 000-837, and the ADDRESS _ ID is set by the central station in advance.

Meanwhile, the central station generates a preamble sequence rule according to the address identifiers and the number of all the user terminals, in this embodiment, the preamble sequence rule is as follows:

mapping the ADDRESS identifier ADDRESS _ ID of the user terminal into a one-to-one corresponding u value according to a mapping table, wherein the range of the u value is 1-838;

and generating a Zadoff-Chu sequence (hereinafter referred to as ZC sequence) with the length of 839 by taking the u value as a root, wherein the ZC sequence is the lead code corresponding to the address identifier of the user terminal.

The mapping table of this embodiment may be as shown in table 1, but the corresponding relationship between ADDRESS _ ID and u is not limited to table 1:

TABLE 1 mapping table between ADDRESS_ID and u

Wherein, generating a ZC sequence with the length of 839 by taking the u value as a root by the following formula:

x _u [n]＝exp[-jπun(n+1)/N _ZC ](1)

wherein x is _u For the generated ZC sequence, N _ZC Is the length of the ZC sequence, where N _ZC ＝839，n＝0,1,…,N _ZC -1,exp represents an exponential function with a natural constant e as base, j is the imaginary sign and π is the circumferential ratio.

PREAMBLE maximum TRANSMISSION number PREAMBLE _ TRANSMISSION _ MAX is an integer greater than or equal to zero, and is used to determine the maximum number of PREAMBLEs that can be transmitted in the random access procedure, and the specific value is related to the maximum time taken by the system for random access, and the like, where PREAMBLE _ TRANSMISSION _ MAX =3 is initialized.

User transmission power P _{PREAMBLE_POWER_RAMPING_COUNTER} Usually, the low, medium and high power three-gear (P) _{Is low with} 、P _In 、P _{High (a)} ) When the user terminal performs preamble transmission, the power is usually low from P _{Is low with} And starting transmission, and increasing the transmission power to the maximum when the random access is not successful. Therefore, the POWER adjustment count range is 1-3 corresponding to three stages of low, medium and high POWER, and the initialization value of the POWER adjustment count PREAMBLE _ POWER _ ramp _ COUNTER is 1, i.e. the initialization value P _{PREAMBLE_POWER_RAMPING_COUNTER} ＝P ₁ ＝P _{Is low in} 。

The central station configures the address identifications of all the user terminals to each user terminal in advance. Assuming that the number of the user terminals to be accessed to the network is 32, and the ADDRESS _ ID of the user terminals to be accessed to the network is 000-031, the corresponding u values and preambles of the 32 user terminals to be accessed to the network can be obtained according to the mapping table shown in table 1 and the formula (1). For the central station and each access-intended user terminal, the formula (1) and the mapping table are known, which means that only one of the ADDRESS _ ID, the u value and the preamble of the access-intended user terminal needs to be known, and the other two items can obtain unique corresponding content.

When a random access process of a certain network user terminal is triggered, the network user terminal sets a PREAMBLE TRANSMISSION count PREAMBLE _ TRANSMISSION _ COUNTER to 0, sets a PREAMBLE maximum TRANSMISSION time PREAMBLE _ TRANSMISSION _ MAX to 3, sets a POWER adjustment count PREAMBLE _ POWER _ RAMPING _ COUNTER to 1, and sets a first BACKOFF indicator PREAMBLE _ BACKOFF1 to 0.

2. First phase-random Access request signalling

Assuming that all the ues in the network use the same clock, all the ues in the network switch frequencies at the same time and know the frequencies and timeslots of other ues in the network.

The user terminal side random access request signal sending and transmitting method of the network-access-intended user terminal comprises the following steps:

if the PREAMBLE _ TRANSMISSION _ COUNTER is greater than or equal to PREAMBLE _ TRANSMISSION _ MAX, ending the TRANSMISSION flow of the random access request signal TRANSMISSION, and the random access fails; otherwise:

the user terminal of the network access is mapped with the ADDRESS identification ADDRESS _ ID of the user terminal of the network access as u according to the table 1, then a ZC sequence with the length of 839 is generated according to the formula (1), and a random access request signal is generated based on the generated ZC sequence, namely a lead code;

the user terminal of the network access simulation determines whether PREAMBLE _ POWER _ RAMPING _ COUNTER is added with 1 according to whether the last random access is successful or not, if the last random access is successful or the first random access is performed, the PREAMBLE _ POWER _ RAMPING _ COUNTER is unchanged, if the last random access is unsuccessful, the PREAMBLE _ POWER _ RAMPING _ COUNTER is added with 1, and the sending POWER is set as P _{PREAMBLE_POWER_RAMPING_COUNTER} If the power adjustment count is increased by 1 and then becomes larger than 3, the transmission power is set to be P as it is _{PREAMBLE_POWER_RAMPING_COUNTER} ＝P ₃ ；

Sending power P by user terminal of virtual network _{PREAMBLE_POWER_RAMPING_COUNTER} A random access request signal is transmitted to the central station.

The random access request signal transmission flow is shown in fig. 5.

Assuming that the short-wave communication system is designed in an OFDM manner, the parameters may be: nominal bandwidth BW =48khz, number of fft (fast fourier transform) samples 1024, number of subcarriers 624, baseband sampling rate f _S =73728, sample interval T _S ＝1/f _S 0.0136ms, subcarrier spacing delta f =72Hz, and the number of OFDM symbols N in a single time slot _sym In the range of =14, the length of each OFDM symbol is 14.9740ms, 14.8655ms 14.8655ms, 14.9740ms, 14.8655ms, 14.86 ms55ms, 14.8655ms, the time length of a single slot is equal to the sum of the lengths of 14 OFDM symbols in the single slot, namely T _{Single time slot} ≈208.334ms。

The structure of random access request signal in single time slot is composed of two parts, cyclic prefix CP and lead code Sequence, corresponding sampling point number is N _CP And N _SEQ With a corresponding time duration of T _CP And T _SEQ . In the time slot, after the time occupied by the random access request signal, a period of protection time is also included, the protection time is divided into a protection time interval GP and a system receiving processing and transceiving conversion time IDLE, and the corresponding sampling points are respectively N _GP And N _IDLE Respectively having a corresponding duration of T _GP And T _IDLE 。

Wherein:

the lead code Sequence is completed by the method for generating the ZC Sequence with the length of 839, and the corresponding number of sampling points N _SEQ =12288, duration T _SEQ ＝N _SEQ *T _s ＝N _SEQ /f _s ＝12288/73728≈166.6667ms。

Cyclic prefix CP duration T _CP Should be greater than the maximum delay spread of the wireless channel. The multipath time delay expansion of the short wave communication system is related to the cell radius and the wireless channel propagation environment, and the integral waveform of each subcarrier under each path contained in the receiving end integral interval can be ensured as long as the maximum time delay expansion is less than the CP duration, so that the intersymbol interference and the inter-subcarrier interference (ICI) caused by multipath are eliminated. When short wave sky-wave communication is carried out, part of signals in the signals transmitted by the transmitting terminal reach the receiving terminal only through one-time reflection of an ionized layer; part of the signals are reflected to the ionosphere again after being reflected to the ground through the ionosphere and reach a receiving end through the second reflection of the ionosphere; some signals even need to reach the receiving end after three to four reflections from the ionosphere. The multipath phenomenon is generally 2, 3, 4 paths, and the occurrence probability is 85%, wherein the case of 3 paths is the most. In addition, through a large amount of data statistics: in medium-long distance transmission systems, the majority of multipath delays are between 0.2 and 5ms, but rarely the maximum delay is 8ms. In the general case of the above-mentioned,99.5% of the multipath time delay is not less than 0.5ms,50% of the multipath time delay is not less than 1.4ms, and only 0.5% of the multipath time delay exceeds 5ms. Accordingly, the number of CP sampling points N in the present embodiment _CP =792, corresponding duration T _CP ＝N _cp /f _s And (4) the value of =792/73728 ≈ 10.7422ms, so that the requirement of being larger than the maximum delay spread of a wireless channel is met.

The guard time interval GP is mainly used to overcome propagation delay in the access time slot and interference of other user terminal links, and its length determines the cell propagation distance that can be supported. Guard time interval GP duration T _GP The larger the supported cell propagation distance. When the Nanjing-Beijing short wave sky wave propagation mode is adopted, the ground distance is about 1000km, and the propagation distance is about 1500km (due to the influence of an ionosphere, the propagation distance is related to the year, the season, the day and night and the like). In this embodiment, the number of sampling points N in the time interval GP is protected _GP =1488, corresponding duration T _GP ＝N _GP /f _s And the supported propagation distance is 20.1823 × 0.001 × 3 × 10^8/2=3027.345km, and the coverage of the system on the propagation distance in the current Nanjing-Beijing sky wave propagation mode is met.

The system reception processing and transmission/reception conversion time IDLE is mainly used for the central station to perform reception processing of the preamble, transmission/reception conversion, and the like. In this embodiment, the system receives and processes and receives and dispatches the number of IDLE sampling points N _IDLE =792, corresponding duration T _IDLE ＝N _IDLE /f _s And (4) the length of the preamble is not less than 792/73728 ≈ 10.7422ms, so that the time requirements of the current system software and hardware on detection, transceiving conversion and the like of the preamble with the length of 839 are completely met.

And the above-mentioned T _CP +T _SEQ +T _GP +T _IDLE ≈T _{Single time slot} And the requirements of all parts in the random access request signal are met.

Fig. 6 shows a time domain structure diagram of a time slot for transmitting a random access request signal at a ue intended to access a network in a single time slot.

T of central station in random access request signal transmission _CP 、T _SEQ And part T _GP In the monitoring state in time, if receiving the random access request signal sent from the terminal side of the user intending to access the network, in the part T _GP (propagation distance)<User with maximum propagation distance supported by cell) and T _IDLE And (2) completing blind detection and identification work of lead codes of u values corresponding to 32 network access users in time, if a certain lead code is detected, further completing inverse mapping from the lead code to the u value and from the u value to a user terminal address identifier according to the table 1 and the formula (1), obtaining one or more user terminal address identifiers requested to be randomly accessed by the current time slot, and simultaneously completing transceiving conversion and preparing for transmitting signals.

The time-domain structure diagram of the time slot for the central station random access listening process within a single time slot is shown in fig. 7.

3. Second phase-random access response signalling

When the central station obtains one or more user terminal ADDRESS identifiers ADDRESS _ ID requested to be randomly accessed in the current time slot in the random access request signal sending and transmitting stage, the central station sends random access response signals to all user terminals in the next time slot, and meanwhile, the user terminal side which is to be accessed to the network enters the random access response signal receiving stage.

The central station random access response signal MAC PDU is composed of a plurality of bytes, wherein:

the subheader is used to indicate the content type following the present byte and whether it is the last byte of the present frame. If the BI is the backoff time interval of the next random access given by the central station according to the number of the current network access user terminals, the more the number of the current network access user terminals is, the longer the backoff time interval of the next random access is; ADDRESS _ ID is one or more user terminal ADDRESS identifiers requesting random access blindly detected by the central station in part of GP and IDLE time of a random access request signal transmission phase; and the DATA is DATA content (such as Timing Advance (TA) and the like) which is issued by the central station to the user terminal.

The method for receiving the random access response signal at the user terminal side of the user terminal to be accessed into the network comprises the following steps:

after the random access request signal is sent and transmitted, starting to monitor a random access response signal sent by the central station at the next time slot;

if a random access response signal is received:

setting PREAMBLE _ BACKOFF1 as a BI field;

if the random access response signal contains the ADDRESS _ ID of itself, the subsequent DATA content is received at the same time and the random access is considered to be successful, otherwise:

if PREAMBLE _ TRANSMISSION _ COUNTER is more than or equal to PREAMBLE _ TRANSMISSION _ MAX, then the random access is considered to be failed, otherwise, the PREAMBLE _ TRANSMISSION _ COUNTER is added with 1, the PREAMBLE _ BACKOFF is delayed by 1 time slot, the user terminal side random access request signal TRANSMISSION stage is returned, the user terminal to be accessed to the network determines whether the PREAMBLE _ POWER _ RAMPING _ COUNTER is added with 1 according to whether the last random access is successful or the first random access, if the last random access is successful or the first random access, the PREAMBLE _ POWER _ RAMPING _ COUNTER is not changed, if the last random access is unsuccessful, the PREAMBLE _ POWER _ RAMPING _ COUNTER is added with 1, and the TRANSMISSION POWER is set as P _{PREAMBLE_POWER_RAMPING_COUNTER} If the power adjustment count is increased by 1 and then becomes larger than 3, the transmission power is set to be P _{PREAMBLE_POWER_RAMPING_COUNTER} ＝P ₃ "and continue to execute the subsequent transmission step of sending random access request signal;

if no random access response signal is received:

setting PREAMBLE _ BACKOFF1 to 0, if PREAMBLE _ TRANSMISSION _ COUNTER is more than or equal to PREAMBLE _ TRANSMISSION _ MAX, then considering that random access fails, otherwise, PREAMBLE _ TRANSMISSION _ COUNTER is added with 1, delaying PREAMBLE _ BACKOFF1 time slot, returning to the sending and TRANSMISSION stage of random access request signal at user terminal side, determining whether PREAMBLE _ POWER _ RAMPING _ COUNTER is added with 1 according to whether last random access is successful, if last random access is successful or first random access, then PREAMBLE _ POWER _ RAMPING _ COUNTER is not changed, if last random access is unsuccessful, PREAMBLE _ POWER _ RAMPING _ COUNTER is added with 1, and setting the sending POWER as P _{PREAMBLE_POWER_RAMPING_COUNTER} If the power adjustment count is increased by 1 and then becomes larger than 3, the transmission power is set to be P _{PREAMBLE_POWER_RAMPING_COUNTER} ＝P ₃ And proceeds to perform a subsequent random access request signaling transmission step.

The procedure of receiving the random access response at the ue of the intended access network is shown in fig. 8.

In this embodiment, because of the good auto-correlation and cross-correlation of ZC sequences, the central station can easily complete the analysis and identification of the random access request signals of 32 ues within a part of GP and IDLE time. Therefore, in general, only two time slots (about 416 ms) are needed to complete the random access process of 32 ues, so as to implement synchronous networking.

Adopting a competition-based random access process containing four messages of msg1, msg2, msg3 and msg4 in the existing 4G/5G technology, and assuming that the interval between the messages takes the minimum value, the specific time slot allocation is shown in FIG. 9, namely, msg2 messages are sent at intervals of 2 time slots after the msg1 messages are sent out, msg3 messages are sent at intervals of 2 time slots after the msg2 messages are sent out, msg4 messages are sent at next time slots after the msg3 messages are sent out, and under the optimal condition, random access is successful after the msg4 messages are sent out, so that at least 8 time slots are needed at the moment; similarly, a contention-free random access process including two messages, msg1 and msg2, in the prior art is adopted, and it is assumed that the interval between the messages takes the minimum value, that is, the msg2 message is sent at an interval of 2 slots after the msg1 message is sent out, and in the most ideal case, the random access is successful after the msg2 message is sent out, and a minimum of 4 slots are needed. The time slot spent by the short-wave communication system random access method used by the embodiment to complete the short-wave communication link establishment is far smaller than the time slot used in the random access process in the existing 4G/5G technology, and the access success time is greatly shortened.

Example 4:

the embodiment discloses a random access apparatus applied to a short-wave communication system, as shown in fig. 10, including:

the sending module is used for sending 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 receiving module is used for monitoring and receiving a random access response signal sent by the central station, and if the random access response signal can be received and the address identifier of the pseudo-access device can be obtained by analyzing the random access response signal, the random access is successful; if not, the random access fails, the random access request signal is sent to the central station again, and the random access response signal is monitored and received until the random access is successful or the maximum random access times are reached;

Further, in the sending module, the random access request signal satisfies:

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

Further, in the monitoring and receiving module, the random access response signal includes the following fields: the subheader, the second back-off indication and the address identifier which is obtained by the central station through analysis from the random access request signal;

Further, in the sending module, the sending a random access request signal to the central station includes the following steps:

Further, in the transmitting module, if the transmission power is increased and exceeds the range of the transmission power, the transmission power is set to the maximum transmission power.

Further, in the monitoring and receiving module, after the random access failure is determined, the method sends a random access request signal to the central station again, monitors and receives a random access response signal, and includes:

if the random access response signal cannot be received:

judging whether the random access times are less than the maximum random access times, if so, adding 1 to the random access times, and retransmitting a random access request signal to a central station, monitoring and receiving a random access response signal; if not, the maximum random access times are reached, and the random access fails.

The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.

Claims

1. A random access method applied to a short-wave communication system is characterized by comprising the following steps:

2. The random access method applied to the short wave communication system according to claim 1, wherein the random access request signal satisfies the following conditions:

3. A random access method applied to short wave communication system according to claim 1 or 2, wherein the random access request signal comprises the following fields: a cyclic prefix and a preamble; wherein:

the lead code is determined according to the address identification of the access-intended device;

4. The random access method applied to the short wave communication system according to claim 1, wherein the random access response signal comprises the following fields: the subheader, the second back-off indication and the address identifier which is obtained by the central station through analysis from the random access request signal;

5. A random access method applied to a short wave communication system according to claim 3, wherein the step of sending a random access request signal to the central station comprises the following steps:

if the last random access is successful or the access-intended device is the first random access central station, the sending power is unchanged; if the last random access is unsuccessful, increasing the transmission power;

6. The method as claimed in claim 5, wherein the transmission power is set to the maximum transmission power if the transmission power is increased beyond the range of the transmission power.

7. The random access method applied to the short-wave communication system of claim 1, wherein after the random access failure is judged, the random access request signal is re-transmitted to the central station, and the random access response signal is monitored and received, and the method comprises the following steps:

if the random access response signal cannot be received:

judging whether the random access times are smaller than the maximum random access times, if so, adding 1 to the random access times, and sending a random access request signal to the central station again, monitoring and receiving a random access response signal; if not, the maximum random access times is reached, and the random access fails.

8. A random access apparatus for use in a short-wave communication system, comprising:

the monitoring receiving module is used for monitoring and receiving a random access response signal sent by a central station, and if the random access response signal can be received and the address identifier of the pseudo-access device can be obtained by analyzing the random access response signal, the random access is successful; otherwise, the random access fails, the random access request signal is sent to the central station again, and the random access response signal is monitored and received until the random access is successful or the maximum random access times are reached;

9. The random access device applied to the short wave communication system according to claim 8, wherein the random access request signal satisfies:

10. A random access device applied to short wave communication system according to claim 8 or 9, wherein the random access request signal includes the following fields: a cyclic prefix and a preamble; wherein: