WO2020145592A1

WO2020145592A1 - Synchronization method and apparatus for millimeter wave vehicle-to-vehicle communication

Info

Publication number: WO2020145592A1
Application number: PCT/KR2020/000178
Authority: WO
Inventors: 조용수; 박수호
Original assignee: 중앙대학교 산학협력단
Priority date: 2019-01-10
Filing date: 2020-01-06
Publication date: 2020-07-16
Also published as: KR102089206B1

Abstract

A synchronization method and apparatus for millimeter wave vehicle-to-vehicle communication are disclosed. According to the present invention, provided is a vehicle-to-vehicle synchronization device comprising a processor and a memory connected to the processor, wherein the memory includes one or more program commands, executed by the processor, so as to perform an initial access procedure with a base station by acquiring physical layer information about the base station through a base station synchronization signal including a new radio primary synchronization signal (NR PSS), estimate vehicle primary synchronization signal (V PSS) timing of a vehicle synchronization signal within a synchronization signal burst set period in which the base station synchronization signal is transmitted according to the completion of the initial access procedure with the base station, generate a V PSS of the vehicle synchronization signal so that same can be separated from a correlation between the vehicle synchronization signal and a time domain, and perform vehicle-to-vehicle synchronization by transmitting the vehicle synchronization signal including the generated V PSS to the other vehicle.

Description

Synchronization method and device for communication between millimeter wave vehicles

The present invention relates to a synchronization method and apparatus for communication between millimeter wave vehicles.

Recently, Vehicle to Infrastructure (V2I), Vehicle to Vehicle (V2V), and Vehicle to Everything (V2X) technologies are being developed for vehicle communication required for autonomous vehicles.

According to the standard of New Radio (NR) currently being developed for 3GPP 5G communication, a synchronization signal used in NR is called an SS/PBCH block, and is also called a Synchronization Signal Block (SSB), which means a synchronization signal block.

The SS/PBCH block is a 4-symbol length synchronization signal composed of a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a physical broadcast channel (PBCH), and a demodulation reference signal (DMRS).

In V2I, a method in which a vehicle communicates with a base station, there is no problem in synchronizing with an NR SS/PBCH block used by the base station. However, in V2V, which means inter-vehicle communication, a vehicle that transmits a synchronous signal can be regarded as a small base station, and problems may occur if the NR SS/PBCH block is used as it is in the small base station.

This is because a vehicle that wants to perform an initial access procedure cannot distinguish between a synchronization signal used by a base station and a synchronization signal used by another neighboring vehicle, and has to go through all the search processes for a myriad of synchronization signals received in the vicinity. .

In this case, even if the vehicle wishing to perform the initial access procedure synchronizes with the base station, the likelihood of synchronizing with the synchronization signal from another adjacent vehicle increases and it is impossible to select a desired communication method.

In order to solve the above-mentioned problems of the prior art, the present invention is to propose a synchronization method and apparatus for inter-vehicle communication between millimeter-waves that can quickly reduce the delay time by quickly dividing the source of the signal received during the initial access procedure.

In order to achieve the above object, according to an embodiment of the present invention, in the vehicle communication environment in the millimeter wave vehicle communication environment, a synchronization device, the processor; And a memory connected to the processor, wherein the memory acquires physical layer information of the base station through a base station synchronization signal including an NR New Radio Primary Synchronization Signal (PSS) and performs an initial access procedure with the base station. , V PSS (Vehicle Primary Synchronization Signal) timing of the vehicle synchronization signal within the synchronization signal burst set period in which the base station synchronization signal is transmitted according to the completion of the initial access procedure with the base station, estimates the V PSS of the vehicle synchronization signal One that is generated by the base station synchronization signal and the time domain to be distinguished from each other, and transmits the vehicle synchronization signal including the generated V PSS to another vehicle so that synchronization between vehicles is performed. An inter-vehicle synchronization device including the above program instructions is provided.

The V PSS may be generated by taking a conjugate complex number in the NR PSS.

The vehicle synchronization signal is transmitted by the number of beams of the vehicle, and the vehicle synchronization signal block index identifying the beam may be cyclically shifted in the time domain and included in the V PSS.

The program commands may determine whether the inter-vehicle communication environment is a sparse vehicle communication environment, and when the inter-vehicle communication environment is a interspersed communication environment, the V PSS may be generated using a cover code.

Whether the communication environment is interspersed is determined based on whether a maximum value of a difference in propagation delay between vehicles is greater than a preset threshold, and the preset threshold is a minimum time difference between detection timings that may occur in one symbol and OFDM It may be determined by at least one of the time period occupied by the CP (Cyclic Prefix).

The minimum time difference between detection timings that can occur in one symbol is one as the OFDM symbol length, the ratio at which detection timings can be shifted within one symbol when the number of RF chains is maximum, and the number of RF chains increases. V PSS in the symbol may be determined by at least one of the ratio.

The base station synchronization signal includes the NR PSS, a Secondary Synchronization Signal (SSS), a Physical Broadcast Channel (PBCH), and a Demodulation Reference Signal (DMRS), and the vehicle synchronization signals include the V PSS and the V Vehicle Secondary Synchronization Signal (SSS). ).

The program instructions receive a first vehicle synchronization signal of another vehicle received at the estimated V PSS timing to search for V PSS and V SSS, and the first vehicle ID and the first vehicle synchronization in the searched V PSS. Estimate the block index of the signal, the received beam ID of the first vehicle signal, estimate the second vehicle ID from the searched V SSS, and estimate the cell ID of the other vehicle through the first and second vehicle IDs can do.

According to another aspect of the present invention, as a vehicle-to-vehicle synchronization device in a millimeter-wave vehicle communication environment, a base station information acquisition unit that acquires physical layer information of the base station through a base station synchronization signal including an NR New Radio Primary Synchronization Signal (PSS) ; A timing estimator for estimating V PSS (Vehicle Primary Synchronization Signal) timing of a vehicle synchronization signal within a synchronization signal burst set period in which the base station synchronization signal is transmitted according to completion of an initial access procedure with the base station; And a V PSS generation unit generating the V PSS of the vehicle synchronization signal so as to be distinguished from the correlation between the base station synchronization signal and the time domain, and transmitting the vehicle synchronization signal including the generated V PSS to another vehicle. An inter-vehicle synchronization device for performing inter-vehicle synchronization is provided.

According to another aspect of the present invention, a method for synchronizing vehicles in a millimeter wave vehicle communication environment, comprising: obtaining physical layer information of the base station through a base station synchronization signal including an NR New Radio Primary Synchronization Signal (PSS); Estimating V PSS (Vehicle Primary Synchronization Signal) timing of a vehicle synchronization signal within a synchronization signal burst set period in which the base station synchronization signal is transmitted according to completion of an initial access procedure with the base station; Generating a V PSS of the vehicle synchronization signal to be distinguished from a correlation between the base station synchronization signal and the time domain; And transmitting the vehicle synchronization signal including the generated V PSS to another vehicle to perform vehicle-to-vehicle synchronization.

According to the present invention, it is possible to reduce the re-discovery process of the synchronization signal as much as possible by quickly distinguishing the source of the received signal during the initial access procedure. .

In addition, according to the present invention, the V SS block of the vehicle is composed of 2 symbols differently from the NR SS/PBCH block of the base station, so that even if a handover situation occurs due to the rapid movement of the vehicle, there is an advantage of being able to synchronize more quickly. .

Finally, it is possible to immediately check whether the base stations exist in the surrounding environment by simply going through the discovery process of the NR PSS, and if the base stations do not exist, the vehicles can perform V2V communication by using a side link to each other.

1 is a view showing the configuration of a millimeter wave inter-vehicle synchronization device according to an embodiment of the present invention.

2 illustrates propagation delay occurring in a V2X communication environment.

3 shows a synchronization signal arrangement in the time domain according to the present embodiment.

Figure 4 illustrates a V SS block transfer according to the number of RF chain N _RF.

5 shows an NR SS/PBCH block time frequency structure.

6 shows a V SS block time frequency structure.

7A and 7B show correlation characteristics between NR PSS and V PSS.

8A and 8B show V PSS used in a close vehicle communication environment.

It shows the correlation between.

9A and 9B are V PSSs used in a scattered vehicle communication environment.

It shows the correlation between.

10A and 10B are V PSS according to the present embodiment.

It shows the correlation between.

11 is a flowchart illustrating an initial access procedure for obtaining information of an adjacent base station and information about an adjacent vehicle for V2X communication.

12 shows a time domain V PSS correlation characteristic.

13 is a diagram for explaining a V PSS search process in a scattered vehicle communication environment.

14A and 14B are diagrams showing correlations between V PSSs having the same in a scattered communication environment.

15A and 15B are different in a scattered communication environment.

It is a diagram showing the correlation between V PSS with.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail.

However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The present invention proposes a vehicle synchronization signal and synchronization procedure of a millimeter wave (mmWave) inter-vehicle communication system in order to achieve V2V synchronization with a small latency in the initial access procedure of V2X. V2X communication is constructed by utilizing the system of NR in line with the development direction of New Radio (NR), which is currently being developed for 5G mmWave communication.

It is proposed to apply the beamforming technology in consideration of the conditions that may occur in the millimeter wave inter-vehicle communication environment, and to divide the environment according to the cell radius of the base station in consideration of the delay time to use a synchronization signal suitable for each characteristic.

1 illustrates a computing device installed in a vehicle, and may include a processor 100 and a memory 102.

The processor 100 may include a central processing unit (CPU) capable of executing a computer program or other virtual machines.

The memory 102 may include a non-volatile storage device such as a fixed hard drive or a removable storage device. The removable storage device may include a compact flash unit, a USB memory stick, and the like. The memory 102 may also include volatile memory, such as various random access memories.

Program instructions executable by the processor 100 are stored in the memory 102.

The program instructions according to this embodiment acquire physical layer information of the base station through a base station synchronization signal including an NR New Radio Primary Synchronization Signal (PSS) and perform an initial access procedure with the base station.

In addition, the program instructions estimate the V PSS (Vehicle Primary Synchronization Signal) timing of the vehicle synchronization signal within a synchronization signal burst set period in which the base station synchronization signal is transmitted upon completion of the initial access procedure with the base station.

In this embodiment, the V SS block, which is a vehicle synchronization signal, is composed of 2 symbols of V PSS and V SSS, unlike the NR SS/PBCH block of the base station, and the V SS block is included in the data field of the existing NR specification.

According to this embodiment, the V PSS is generated by taking a conjugate complex number of the NR PSS so that the V PSS of the vehicle synchronization signal can be distinguished from the correlation between the NR PSS of the base station synchronization signal and the time domain. This will be described in detail below.

Thereafter, the program instructions transmit the vehicle synchronization signal including the generated V PSS to another vehicle to perform synchronization between vehicles.

The inter-vehicle communication environment according to the present embodiment transmits a vehicle synchronization signal through a plurality of beams, and the vehicle synchronization signal block index for beam identification of the vehicle is cyclically shifted in the time domain and included in the V PSS.

In addition, the inter-vehicle communication environment is divided into a close vehicle communication environment and a scattered vehicle communication environment, and in a scattered communication environment, a cover code is applied to V PSS to prevent errors. The threshold for whether the inter-vehicle communication environment is close will be described below.

In the above, it has been described that program instructions stored in the memory 102 connected to the processor 100 are synchronized between vehicles through an initial access procedure.

However, without being limited thereto, the base station information acquisition unit acquires physical layer information of the base station through a base station synchronization signal including an NR New Radio Primary Synchronization Signal (PSS), and the base station synchronization signal upon completion of an initial access procedure with the base station. A timing estimator for estimating V PSS (Vehicle Primary Synchronization Signal) timing of a vehicle synchronization signal and a V PSS of a vehicle synchronization signal within a synchronization signal burst set period in which the transmission is performed can be distinguished from the correlation between the base station synchronization signal and the time domain. V PSS generation unit to be generated is provided in a separate chip format, they may be included in the scope of the present invention to perform synchronization between vehicles under the control of the processor.

Hereinafter, assumptions, data structures, correlations, and the like in the present invention will be described in detail with reference to the drawings.

The environments assumed in the present invention are as follows.

Vehicles requiring initial access preferentially obtain physical layer information through a search process for an adjacent base station and perform synchronization using a base station synchronization signal. At this time, other vehicles that have already completed the initial access procedure around the base station transmit a vehicle synchronization signal including physical layer information of each vehicle based on the base station synchronization signal transmission time.

That is, the V2X vehicle having an initial connection first synchronizes with the base station using the synchronization signal of the base station to obtain information, and then obtains information of the vehicle through a search process for surrounding vehicles using the synchronization signal of the adjacent vehicle.

In the present invention, since the synchronization signals of all vehicles adjacent to the base station are transmitted based on the timing of the synchronization signal transmitted from the base station, the size of the cell operated by the base station is very important.

If the size of the cell of the base station in which the V2X is operated is small, since propagation delay of a signal transmitted within the cell is small, all vehicles receive a signal with a negligibly small difference in delay. However, if the size of the cell operated by the base station is large, the signal transmitted from the base station arrives at each vehicle with a different propagation delay time, and the synchronized vehicles transmit their synchronization signals based on different times. Therefore, the present invention proposes different synchronization signals to prepare for both of the above cases and describes the operation method thereof.

2 illustrates propagation delay occurring in a V2X communication environment.

In Figure 2

Is the propagation delay time for the signal from the transmitter to reach the receiver. When the first vehicle (Vehicle 0) performs an initial access procedure, the base station signal

It is received with a delay. Also

The synchronization signal of the second vehicle (Vehicle 1) transmitted based on the synchronization signal of the base station delayed by the first vehicle

It is received with a delay.

Therefore, a difference in propagation delay between signals transmitted from the surroundings occurs to the first vehicle for which the initial access procedure is to be performed. Difference in propagation delay between vehicles

Define. Maximum difference in propagation delay between vehicles that can occur in the cell

Is a predetermined threshold

Dense vehicle environment when smaller,

When larger, it is defined as a sparse vehicle communication environment.

The conditions of will be described in detail again below.

As described above, even if a vehicle that wants to perform an initial access procedure wants to synchronize with a base station, the possibility of synchronizing with a synchronization signal of another adjacent vehicle increases.

To solve this, in this embodiment, the vehicle synchronization signal is defined as a V (Vehicle) SS block.

Each vehicle does not use the synchronization signal used in the NR, and allows the vehicle (receiver) to perform the initial access procedure to distinguish the initial access procedure from the adjacent base station and the vehicle by using a different synchronization signal.

Through this, the receiver can reduce the number of repetitions of an initial search procedure for finding a base station or a vehicle, and can synchronize only with a synchronization signal of a desired search target.

In addition, the presence or absence of an adjacent base station is also quickly determined so that the receiver can immediately recognize whether it is an environment capable of performing V2I or an environment capable of performing only V2V.

The SS/PBCH block is set to transmit once during a predetermined time called an SS burst set periodicity. That is, during the SS burst set periodicity, a portion in which SS blocks are transmitted and a portion in which they are not transmitted are divided. Therefore, the vehicle synchronization signal is intended to be transmitted by avoiding the position of the NR synchronization signal. Since receiving the NR sync signal is very important in the V2X initial access procedure, the vehicle sync signal is transmitted using a different position to avoid interference with the position of the NR sync signal.

3 shows signals that can be received in an initial access procedure in chronological order.

Referring to FIG. 3, in the NR SS Burst Set (base station synchronization signal), all SS blocks are transmitted within 5 ms, which is a half frame, and the SS burst set is no longer transmitted within the SS burst set periodicity.

Therefore, to avoid interference with the NR sync signal, a vehicle SS burst set (vehicle sync signal) is transmitted after a half period of burst periodicity. The NR SS block (base station synchronization signal) and V SS block (vehicle synchronization signal) are allocated to different beams and transmitted. Maximum number of beams at NR

As many as NR SS/PBCH blocks are transmitted.

Therefore, the SS/PBCH block index starts from 0 in the order of each SS/PBCH block.

Up to -1 is allocated.

In addition, the V SS block is also the maximum number of beams in the vehicle.

As many as the index is 0

Up to -1 is allocated. V SS block index

Expressed as

The V SS block consists of 2 symbols. Unlike the NR SS/PBCH block, which is composed of 4 symbols in total, the V SS block shortens two symbols occupied by the PBCH and DMRS to obtain faster initial synchronization. Therefore, in order to load the SS/PBCH block index provided by the existing PBCH and DMRS in a vehicle synchronization signal composed of 2 symbols, a method of transmitting the index information to the V PSS is proposed.

4 shows the number of RF chains

V SS block transmission according to FIG.

According to this embodiment, the maximum number of RF chains that can be possessed in the V2X communication antenna of the vehicle is maximum.

You can choose up to one. Therefore, the number of RF chains selected by the vehicle

Depending on the V SS block can be transmitted at the same time as shown in FIG.

Figure 4

When is 8, it shows the transmission of the V SS block.

V SS block index according to the transmission scheme of FIG. 4

Can be expressed as the following equation.

As you can see from Equation 1,

As the number of increases, the number of V SS blocks that can be transmitted in one symbol position increases. Indicating the index of the symbol position

Is, to distinguish the index of each RF chain that sends the V SS block

to be.

5 shows an NR SS/PBCH block time frequency structure.

Referring to FIG. 5, the NR SS/PBCH block is composed of four symbols contiguous in the time domain and 240 consecutive subcarriers in the frequency domain.

Among them, NR PSS is located in the first symbol, and NR SSS is present in the third symbol. In addition, NR PBCH and NR DMRS wrap the NR SSS from the second to the fourth.

The NR PSS consists of m-sequences, and the NR SSS consists of a gold sequence of two m-sequences combined.

NR DMRS is also a gold sequence, and NR PBCH is composed of data created by applying a polar coding technique. In addition, NR PSS and NR SSS have a total of 127 lengths ranging from 56 to 182 based on subcarrier indexes sequentially defined in the frequency domain. In addition, NR PBCH and NR DMRS have 240 lengths from subcarrier indices 0 to 239 in the

time domain symbols

1 and 3, and occupy subcarrier indices from 0 to 47 and 192 to 239 in the second symbol.

NR physical layer cell ID (base station cell ID) is

It can be represented by, and can have 1008 independent IDs from 0 to 1007.

The

Wow

It can be divided into two IDs, and the relationship is as follows.

For convenience in this specification

The first base station ID,

Is defined as the second base station ID.

Of these, NR PSS

It is a signal that contains information. NR SSS

NR PBCH and NR DMRS respectively contain 3 bits MSB (Most Significant Bit) and 3 bits LSB (Least Significant Bit) of the SS/PBCH index. Accordingly, if all of NR PSS, NR SSS, NR PBCH, and NR DMRS are searched, the cell ID and SS/PBCH block index of the corresponding NR base station can be determined.

6 shows a V SS block time frequency structure.

As shown in FIG. 6, the V SS block is composed of two symbols contiguous in the time domain and 240 consecutive subcarriers in the frequency domain. In order to use subcarrier resources such as the NR SS/PBCH block, 56 to 182 subcarrier indexes among the 240 subcarriers are used.

Among them, V PSS is located in the first symbol and V SSS is located in the second symbol.

Vehicle physical layer cell ID

Can be represented by, NR physical layer cell ID

Likewise, you can have 1008 independent IDs from 0 to 1007.

Degree

Wow

Can be divided into two IDs.

For convenience in this specification

The first vehicle ID,

Is defined as the second vehicle ID.

The relationship is as follows.

Like the SS/PBCH block index transmitted by the NR PBCH and NR DMRS, the V SS block index is carried on each V SS block and transmitted. In the process of searching for the NR SS/PBCH block index, the search process of the DMRS and the search process of the PBCH must be performed independently, and the overhead occupied by the process is large.

In addition, the SS/PBCH block of NR occupies 4 symbols. However, this overhead is not desirable in a V2X communication environment that wants to reduce latency as much as possible.

Accordingly, the present invention proposes a method using V PSS to transmit a V SS block index according to a V2X communication environment.

Although the synchronization signal of the existing NR occupies 4 symbols, V SSS block index information is transmitted to the V PSS together to reduce the overhead due to the separate discovery process of DMRS and PBCH. Unlike NR PSS, V PSS

Wow

It contains the information of, and the expression can be expressed as follows.

And, as in Equation 5, V PSS frequency domain signal

Is the time domain signal

Can be obtained by DFT. The V PSS defined in the time domain is converted into a signal in the frequency domain as shown in Equation 5, and is mapped and transmitted from subcarrier indexes 56 to 182 as shown in FIG. 6.

Time domain V PSS in Equation 4

The time domain NR PSS

By taking a complex number of digits, they can be distinguished in correlation between each other in the time domain.

And NR PSS

like

Distinguish between different phase rotation degrees. V SSS to V SS block index

It uses a cyclic shift in the time domain to load. To indicate the degree of cyclic shift

Is defined as follows.

In the time domain

On by

This parallel shift means that the detection timing in the time domain is also shifted. One symbol position

V SS block index that can be simultaneously transmitted in

It is a dog.

Equation 4

Is defined as the cover code,

The detection timing error is prevented from occurring due to the cyclic shift in the time domain. In a close vehicle communication environment, the degree of shift is not so large that it can be neglected in the search process, so the cover code

Do not use That is, V PSS in a close vehicle communication environment can be redefined as follows.

However, in a scattered vehicle communication environment, the time domain shifts

It does not distinguish at all, so a cover code is required.

In order to minimize the overhead of applying and removing cover codes in the process, the cover codes are used in the present invention.

It is proposed to use m-sequence (Maximum length sequence) as.

Since m-sequence is a binary sequence, multiplying a signal by m-sequence means that only sign conversion is required. Compared to multiplying nonbinary sequences of other common complex numbers, the overhead incurred in the calculation process is considerably smaller. In addition, removing the m-sequence is also simple because the m-sequence only needs to be coded once more. Therefore, V PSS in a scattered vehicle communication environment can be redefined as follows.

In the present invention, V PSS is set to be distinguished from NR PSS in the time domain correlation detection process. Also, unlike NR PSS, since V PSS adds V SS block index information, a correlation characteristic changes according to the information.

Hereinafter, various correlation characteristics of the previously proposed V PSS will be grasped. Using the detected correlation characteristic, it is possible to estimate how V PSS information can be searched when a signal is subsequently received. In the following, time lag

In this case, the cyclic correlation property set so that the maximum value is 1 will be checked.

7A and 7B show correlation characteristics between NR PSS and V PSS.

In the correlation where the maximum value of the correlation is normalized to 1, the result value is mostly 0.2 or less. Therefore, it can be seen that there is little similarity between NR PSS and V PSS in the correlation in the time domain.

In addition, V PSS used in a close vehicle communication environment

When the correlation between the two is confirmed, it is as shown in FIGS. 8A and 8B.

In Figures 8a and 8b

Wow

The same in the correlation between

It can be seen that V PSSs having a have a direct delta function form as in NR PSS. However, V SS block index

The maximum value of the correlation is

Shifted by Also, similar to the correlation in NR PSS,

The correlation between V PSSs having a time lag

It has a certain value except. This is also the V SS block index

According to the size of

Shifted by

V PSS used in scattered vehicle communication environments

When the correlation between the two is confirmed, it is shown in FIGS. 9A and 9B.

9A and 9B show V PSS used in a scattered vehicle environment.

It shows the correlation between.

The

Unlike the cover code

This is multiplied form.

therefore

It can be seen that the effect of the shift in the time domain appearing in is removed. However, under the influence of the cover code,

Wow

Have any other information

It can be confirmed that there is no peak in the correlation between. This characteristic may appear to increase the number of reference signals that must be generated when detecting in V PSS. However, in the description of the search process, it is possible to confirm a method of removing the cover code while taking the number of reference signals the same as before.

Hereinafter, a mathematical analysis of the correlation of V PSS defined in Equation 7 will be described. To derive the equation, convert the expression of V PSS defined in Equation 7 into the form of a vector, and can be summarized as follows.

Equation (9)

Means a cyclic downshift matrix. V SS block index of cyclic downshift matrix

It means that it is cyclically shifted in the time domain.

size

Cyclic downshift matrix of

Each element of

The definition is as follows.

Equation (9)

Is the phase rotation matrix,

Is used to represent the phase rotation in the time domain. size

of

The definition of is as follows.

Equation (9)

Means IDFT matrix, and size

DFT matrix

Is defined as follows.

And in Equation 9

The parts of are arranged in the reverse order in the frequency domain by the conjugate plural number property among the properties of the DFT. The characteristics are expressed as follows.

Since the frequency domain component of the NR PSS is m-sequence, only the real component exists, so that the complex conjugate of the frequency domain is not shown in Equation (9).

Hereinafter, the correlation using Equation (9) will be summarized by Equation, and is expressed as follows to simplify Equation (9).

The correlation to be obtained can be summarized as follows by using Equation (14).

Equation 15 is developed by using the following several characteristics.

Since the absolute value is used in the correlation analysis, the equation (15)

Becomes 1 and can be ignored. And, as shown in Equation 15

in

Ramen

Is considered 1 and can be ignored. if so

The

Can be expressed like

here,

Back side

As a result,

You can think like In other words,

Wow

In the condition of being

You can confirm that On the other hand

In a situation

Back side

The

Can be expressed like,

In the condition of being

Can be calculated. therefore

Wow

In the condition of being

You can confirm that

Equation (15)

On condition

Seems to add two m-sequences with different shift values. This is a sequence having the same m-sequence but different shift values due to the shift-and-add characteristic of the m-sequence. Because

Is an IDFT of a specific m-sequence. Therefore, a specific m-sequence plus two m-sequences is a signal in the frequency domain.

If you define

The

It's like getting

Therefore, in order to solve the equation that IDFTs the m-sequence, the DFT of the auto-correlation of the m-sequence is to be solved using the point that PSD (Power Spectral Density). The m-sequence PSD is defined as

Therefore, the process of deriving the m-sequence PSD is as follows.

Equation 20 provides a signal in a specific m-sequence frequency domain.

When defined as, we can see that the absolute value of the time domain is

Therefore, in Equation 20

To

Because it can be thought of as the same value,

The absolute value of Equation 20 under the condition of

When

,

When

You can confirm that

Summarizing the results so far, the two obtained through Equation 20

The absolute value of the correlation of can be summarized as follows.

10A and 10B are diagrams for comparing the mathematical results obtained from Equation 22 with the simulation results.

Figure 10a

Indicates the situation.

If it is, it can be confirmed that the value is 1. Also

When, that is, when the time lag exists, there are some values due to the limitations of the simulation tool, but it can be confirmed that the value is almost zero.

Figure 10b

Indicates the situation.

If it is, the value is 0.007874

Is the same as

If it is, the value is 0.08908

You can see that it matches

Referring to FIG. 11, essential information to be obtained while performing an initial access procedure are cell ID, synchronization signal index, and received beam ID information. When all of this information is obtained, the basic preparation for wireless communication is complete. In the present invention, it is assumed that the base station exists in the V2X environment.

First, essential information of a base station using the NR communication standard must be obtained. When the initial access procedure starts, the NR PSS of the base station is searched first. The vehicle (receiver) utilizes all of its received beams, while different signals are received through each beam.

The correlation signal is compared with the reference signal generated by. The time position of the NR PSS received based on the highest result value through the correlation signal characteristic

, Estimate the beam ID of the receiver.

Estimated through SSS after the above process

And estimated through PSS

Cell ID by combining

Can be estimated. In addition, the NR SS/PBCH index can be obtained through the discovery process of DMRS and PBCH. The timing of the V PSS can be estimated using the estimated NR information. Vehicles adjacent to the base station that have already undergone initial synchronization transmit the V SS burst set from half of the SS burst set periodicity based on the start position of the NR SS burst set. Accordingly, the timing of the NR PSS and the information of the SS/PBCH block index make it possible to estimate the V PSS location.

Using the estimated position V SSS

And V SS block index

, It is possible to estimate the vehicle reception beam ID. Then using V SSS

Estimating

Wow

Combined with the vehicle cell ID

Can be estimated. Thus, the V2X communication vehicle ends the initial access procedure by determining the neighbor base station, the neighbor vehicle cell ID, the received beam ID, and the SS block index.

I explained earlier

Is given as follows.

Equation 23 is

Wow

The minimum value

It means

Indicates a minimum time difference between detection timings that can occur in one symbol.

Denotes the ODFM symbol length,

Is a ratio in which the detection timing can be shifted within one symbol when the number of RF chains is the maximum.

Also,

Is the number of RF chains

As it increases, it means that many V PSSs are included in one symbol. Also,

Is a period of time occupied by CP (Cyclic Prefix).

The reason defined as Equation 23 is as follows.

In the present invention, a vehicle that performs an initial access procedure first undergoes a synchronization process after searching for information of the base station, and estimates the synchronization signal timing of another vehicle based on the timing. In this process

this

Smaller means that there is no problem in searching for the vehicle's synchronization signals in the correct symbol unit, and the V SS block index is also provided through time domain correlation inside the symbol.

It means that it can operate without error in searching for.

On the other hand

this

If it is larger, it is difficult to estimate the symbol unit, so only the rough timing estimation of the vehicle synchronization signal is possible. For this reason, the process of exploring V PSS

The maximum value of the difference in propagation delay between vehicles that can occur in the cell based on the value of

It is necessary to distinguish whether it is larger or smaller.

The following describes what search process is performed according to the close or scattered communication environment and compares the results.

The close vehicle communication environment means'the maximum value of the difference in propagation delay between vehicles.

'this

It means when it is smaller. This means that other V SS block index detection that can be detected in one symbol is an environment that is not affected by a difference in propagation delay between vehicles. In addition, since the delay of the signal itself is small, it is possible to estimate the symbol unit timing of V PSS using information obtained from NR. Maximum number of beams the vehicle can send

And the number of RF chains

Depending on the

It is possible to estimate as many as V PSS symbols.

V PSS symbol index shown in equation (1)

Depending on the symbol signal received

Can be expressed as

V PSS received signal at the estimated position in a close vehicle communication environment

And equation (7)

The information of the V PSS is searched through the cyclic correlation between them. The equation is as follows.

As shown in Equation 24, the reference signal

The

Phosphorus signal is used. As described in Figure 8,

Depending on the

By using as many parallel movements

Is to estimate.

By searching conditions that have the maximum value among the results of Equation (24), information to be obtained in the V PSS search process can be obtained.

Equation (25)

Wow

Through the

Can be calculated. certain

Which can appear in

The number of

It is a dog. Therefore, the time lag of the correlation obtained through Equation 25

May appear depending on the value of

Estimated some of the candidates

It can be understood through Figure 12 whether to adopt as.

For example, in FIG. 4

,

In case, as shown in FIG. 12, two V SS block indexes at one V PSS symbol position

Can have If the propagation delay difference between vehicles

Without this,

When

There will be a maximum at the phosphorus position. Likewise

When

There will be a maximum at the phosphorus position. But the difference in propagation delay between vehicles

Is the basis for

There may be a maximum at a later time.

Therefore, considering the delay time of the signal, a range is set as shown in FIG. 12, and when the correlation maximum value of Equation 24 falls within the corresponding range, the V SS block index accordingly

To estimate.

The scattered vehicle communication environment means that the maximum value of the difference in propagation delay between vehicles.

'this

It means when it is bigger. This is the difference in propagation delay between vehicles when a signal is searched like a close vehicle communication environment.

By

It is very likely that the estimation is not correct. Therefore, in a scattered vehicle communication environment, as in Equation (8),

Cover code to remove shift effect of time domain by

To utilize.

In a scattered vehicle communication environment, it is difficult to estimate V PSS in units of symbols. Based on the information obtained from NR, a candidate time for which V PSS can exist is set. Since the candidate time spans multiple symbols, it is impossible to perform cyclic correlation search between symbols used in a close communication environment. In this case, the reference signal used in the scattered communication environment can be defined as follows.

The reference signal in a scattered environment is as long as Equation (26).

Is the number of samples of one symbol length

see

As long as The reference signal of Equation 26 is made based on a signal defined in a close environment. The general correlation between the received signal and the reference signal is the cover code sent by the transmitting end

Can not eliminate the influence of. Therefore, in a scattered communication environment, the total sum is not performed immediately after the multiplication between the components of the received signal and the reference signal.

Cover code to match the corresponding position

After multiplying by, the total sum is performed for each cover code length.

As in the case of calculating the existing correlation, after multiplying the received signal and the conjugate complex number of the existing signal, and not summing all the elements, after multiplying the conjugate complex existing signal and the received signal, each V SS block index

Add a cover code to the location. This has the effect of removing the cover code that the existing received signal had in the time domain. The received beam ID and V SS block index that collect the different correlation values thus obtained and make the maximum value among them

,

Estimating the information of V PSS search is completed. This is expressed as follows.

The simulation results searched through the search process described above will be described below. In order to generalize the correlation so that the maximum value is 1, a received signal is used that removes the effects of channel and beamforming and removes noise.

The two graphs of FIGS. 14A and 14B have their maximum values at different X-axis values. The above simulation is a sample lag

V PSS was set to exist at the phosphorus point. X axis sample lag

Is the movement of the reference signal based on the sample of the received signal, so even if V PSSs in the same position are searched, the V PSS blocks index

If is different, the maximum correlation can be obtained at different locations. Therefore, the estimated V SS block index

And estimated estimated sample time lag

According to the following equation, timing information of the actual V PSS

Can be estimated.

15A and 15B are different in a scattered communication environment.

It is a diagram showing the correlation between V PSS with.

15A and 15B are different

Shows the correlation for signals with. V SS block index

Regardless of

When correlated with different signals, there are no peaks, so

You can see that you can distinguish.

The above-described embodiments of the present invention have been disclosed for purposes of illustration, and those skilled in the art having various knowledge of the present invention will be able to make various modifications, changes, and additions within the spirit and scope of the present invention. It should be regarded as belonging to the following claims.

Claims

As a vehicle-to-vehicle synchronization device in a millimeter wave vehicle communication environment,

Processor; And

It includes a memory connected to the processor,

The memory,

Acquire physical layer information of the base station through a base station synchronization signal including an NR PSS (New Radio Primary Synchronization Signal), and perform an initial access procedure with the base station,

Estimate the V PSS (Vehicle Primary Synchronization Signal) timing of the vehicle synchronization signal within a synchronization signal burst set period in which the base station synchronization signal is transmitted according to the completion of the initial access procedure with the base station,

V PSS of the vehicle synchronization signal is generated so as to be distinguished from the correlation between the base station synchronization signal and the time domain,

The vehicle synchronization signal including the generated V PSS is transmitted to another vehicle so that synchronization between vehicles is performed.

An inter-vehicle synchronization device comprising one or more program instructions executed by the processor.
According to claim 1,

The V PSS is a vehicle-to-vehicle synchronization device that is generated by taking a conjugate complex number in the NR PSS.
According to claim 1,

The vehicle synchronization signal is transmitted by the number of beams of the vehicle,

The vehicle synchronization signal block index identifying the beam is cyclically shifted in a time domain to be included in the V PSS.
According to claim 1,

The program instructions,

It is determined whether the vehicle-to-vehicle communication environment is a sparse vehicle communication environment,

A vehicle-to-vehicle synchronization device that generates the V PSS using a cover code when the vehicle-to-vehicle communication environment is a scattered communication environment.
According to claim 4,

Whether the communication environment is interspersed is determined through whether the maximum value of the difference in propagation delay between vehicles is greater than a preset threshold,

The preset threshold is an inter-vehicle synchronization device determined by at least one of a minimum time difference between detection timings that may occur in one symbol and a time period occupied by a cyclic prefix (CP) of OFDM.
The method of claim 5,

The minimum time difference between detection timings that can occur in one symbol is one as the OFDM symbol length, the ratio at which detection timings can be shifted within one symbol when the number of RF chains is maximum, and the number of RF chains increases. The inter-vehicle synchronization device determined by at least one of the ratios of V PSS in the symbol.
According to claim 1,

The base station synchronization signal includes the NR PSS, Secondary Synchronization Signal (SSS), Physical Broadcast Channel (PBCH) and Demodulation Reference Signal (DMRS),

The vehicle synchronization signal is a vehicle synchronization device including the V PSS and V SSS (Vehicle Secondary Synchronization Signal).
The method of claim 7,

The program instructions,

Search for V PSS and V SSS by receiving the first vehicle synchronization signal of another vehicle received at the estimated V PSS timing,

In the searched V PSS, a first vehicle ID, a block index of the first vehicle synchronization signal, and a received beam ID of the first vehicle signal are estimated,

Estimating the second vehicle ID from the searched V SSS,

A vehicle-to-vehicle synchronization device for estimating the cell ID of the other vehicle through the first and second vehicle IDs.
As a vehicle-to-vehicle synchronization device in a millimeter wave vehicle communication environment,

A base station information acquisition unit configured to acquire physical layer information of the base station through a base station synchronization signal including an NR PSS (New Radio Primary Synchronization Signal);

A timing estimator for estimating V PSS (Vehicle Primary Synchronization Signal) timing of a vehicle synchronization signal within a synchronization signal burst set period in which the base station synchronization signal is transmitted according to completion of an initial access procedure with the base station; And

It includes a V PSS generating unit for generating the V PSS of the vehicle synchronization signal to be distinguished from the correlation between the base station synchronization signal and the time domain,

An inter-vehicle synchronization device that performs inter-vehicle synchronization by transmitting a vehicle synchronization signal including the generated V PSS to another vehicle.
As a method for synchronization between vehicles in a millimeter wave vehicle communication environment,

Obtaining physical layer information of the base station through a base station synchronization signal including an NR PSS (New Radio Primary Synchronization Signal);

Estimating V PSS (Vehicle Primary Synchronization Signal) timing of a vehicle synchronization signal within a synchronization signal burst set period in which the base station synchronization signal is transmitted according to completion of an initial access procedure with the base station;

Generating a V PSS of the vehicle synchronization signal to be distinguished from a correlation between the base station synchronization signal and the time domain; And

And transmitting the vehicle synchronization signal including the generated V PSS to another vehicle to perform vehicle-to-vehicle synchronization.