CN107086896B

CN107086896B - Method for cell search and method for detecting receiving time of primary synchronization signal

Info

Publication number: CN107086896B
Application number: CN201610085647.8A
Authority: CN
Inventors: 张仲尧; 林专湖
Original assignee: Realtek Semiconductor Corp
Current assignee: Realtek Semiconductor Corp
Priority date: 2016-02-15
Filing date: 2016-02-15
Publication date: 2020-04-07
Anticipated expiration: 2036-02-15
Also published as: CN107086896A

Abstract

The present invention relates to a method for cell search and a method for detecting the reception time of a primary synchronization signal. The method for cell search is used in a mobile device in a wireless communication system, and the method comprises: performing a primary synchronization signal reception time detection procedure to obtain at least one possible reception time point of a primary synchronization signal; performing a primary synchronization signal assumption procedure to generate a first, second and third frequency domain primary synchronization sequence in a frequency domain according to three root indices corresponding to a first, second and third physical identifier respectively; and performing an auxiliary synchronization signal coherent detection procedure to calculate an auxiliary synchronization signal according to the at least one possible reception time point and the first, second and third frequency domain primary synchronization sequences respectively, and obtain a corresponding physical cell group.

Description

Method for cell search and method for detecting receiving time of primary synchronization signal

Technical Field

The present invention relates to a cell search method, and more particularly, to a cell search method for improving a cell search success rate through an assumption mechanism of an entity identifier and a determination mechanism of an auxiliary synchronization signal correlation operation output.

Background

In a wireless communication system, when a user equipment (ue) attempts network access, a cell search procedure is first performed to obtain a cell identifier, and then a synchronization procedure is performed with a cell. The ue should acquire the cell id as soon as possible in the cell search procedure to obtain synchronization with the cell, thereby reducing the time and frequency errors.

In the Long Term Evolution (LTE) system, 504 physical cell identifiers (are defined: (

physical-layer cell identity) consisting of 168 physical cell groups (

physical-layer-identity group) with 3 entity identifiers per group (

physical-layer identity).

The range of (a) is 0 to 167,

the range of (A) is 0 to 2,

can be expressed as

The physical cell identifier is carried by a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS), and therefore, the detection of the SSS is required to obtain the physical cell identifier.

The long term evolution system has Frequency Division multiplexing (FDD) and Time Division multiplexing (TDD) modes. Both PSS and SSS signals are repeated with a half radio frame (frame) period, i.e. a period of 5 ms. The cell search is a process in which a client detects cell signals by using the correlation between a PSS signal and an SSS signal and taking 5ms as a period to acquire downlink time domain and frequency domain synchronization, and is divided into PSS detection and SSS detection.

In detail, the PSS signal is composed of a length 63 Zadoff-Chu sequence corresponding to 31 subcarriers (subcarriers) on both left and right sides of a DC subcarrier in a frequency domain, and a PSS sequence d_u(n) may be represented as follows:

briefly, the PSS sequence d_u(n) is generated from the root index u. Referring to FIG. 1, listing entity identifiers

And the corresponding relation with the root index u. As can be seen from FIG. 1, entity identifiers

0. 1, 2 correspond to the root index u of the Zadoff-Chu sequence, respectively: 25. 29, 34. Therefore, the PSS sequence contains three sequences, distinguished by the root index u.

In addition, the first and second substrates are,the SSS sequence is formed by interleaving two bit sequences with the length of 31 and corresponds to 31 subcarriers on the left side and the right side of a DC subcarrier on a frequency domain. The two sequences are generated by scrambling a scrambling sequence (scramblesequence) in a first step, and the method for generating the scrambling sequence and the entity identifier

In general, therefore, the receiving end needs to detect the PSS signal first to obtain the physical identifier

And using entity identifiers

The generated scrambling sequence is used to further detect the SSS signal. The transmission time of the SSS signal is in subframes (subframes) 0 and 5, and the SSS sequence may be represented as follows:

wherein n is more than or equal to 0 and less than or equal to 30. The four parameters of the above formula are index parameter m, sequence s, scrambling sequence c and sequence z, respectively, and are described as follows:

index m₀And m₁Can be grouped by physical cells

The derivation yields:

m₀＝m'mod 31

sequence of

And

consisting of m sequences (m-sequence)

Giving different cyclic shift (cyclic shift) m₀And m₁Comprises the following components:

and

related scrambling sequence c₀(n) and c₁(n) is composed of m sequences

Consists of the following components:

and sequence of

And

from m sequences

Consists of the following components:

referring to fig. 2, in the cell search procedure, the PSS signal is detected first, and then the SSS signal is detected according to the detected PSS type (three root indexes u). Firstly, because the PSS and SSS signals are 1.4MHz at the center of the LTE band, only a sampling frequency of 1.92MHz is needed, the received signals with different frequencies (30.72MHz, 23.04MHz …, 1.92MHz) are first down-converted to 1.92MHz by the down-conversion filter, and the client end uses three root indices u (corresponding to three indices u) at the receiving end

) Three time-domain 128-point PSS signals are generated, and correlation operation (correlation) is respectively carried out on the PSS signals and the frequency-reduced receiving signals. The correlation result of the PSS signal is outputted to a Non-Coherent-Combining Buffer (Non-Coherent-Combining Buffer) for Combining the correlation results of a plurality of half radio frames (5ms) to reduce the interference of background noise. The capacity of the non-coherent combining buffer is at least 28.8k samples (i.e. 3 non-coherent combining buffers x 9600 samples/group) calculated by 5ms of the transmission cycle of the PSS signal. Finding out the maximum value in three groups of buffers by Peak Search program (Peak Search) aiming at each receiving time point, comparing the maximum value with a preset threshold to judge whether the PSS signal is detected, if yes, judging the corresponding PSS signal is detected

And the receiving time point of the primary synchronization signal is sent to the SSS detection procedure for operation. The SSS detection process may use coherent or non-coherent detection: PSS signal receiving time point and entity identification code obtained by peak value searching procedure

Receiving signals in time domainThrough fast Fourier transform to frequency domain, the SSS sequences corresponding to 168 entity cell groups in the frequency domain are correlated, and the entity cell group corresponding to the maximum output value is selected from the 168 correlation results

Can identify the code according to the entity

And physical cell group

Calculating a physical cell identifier

However, the conventional cell search mechanism can be applied to a system with less strict frame synchronization requirements, such as frequency division multiplexing FDD-LTE mode, but cannot meet the time requirement of cell search for a system with strict frame synchronization requirements, such as time division multiplexing TDD-LTE mode. For example, in TDD-LTE mode, the requirement for small cell frame synchronization is 3us, and the OFDM symbol length is 66.67us, which means that synchronization signals (PSS signal and SSS signal) transmitted by different cells overlap at the receiving end (client), causing interference between the synchronization signals. In other words, a strong sync signal will seriously affect the probability that a weak sync signal will be successfully detected.

Disclosure of Invention

The invention solves the problem of low success rate of cell search caused by mutual interference of synchronous signals under frame synchronization.

The invention discloses a method for cell search, which is used in a mobile device of a wireless communication system, and the method comprises the following steps: performing a primary synchronization signal reception time detection procedure to obtain possible reception time points of the primary synchronization signal; performing a primary synchronization signal assumption procedure for generating a first, a second and a third frequency domain primary synchronization sequences in the frequency domain according to the three root indexes corresponding to the first, the second and the third entity identifiers, respectively; and performing a secondary synchronization signal coherent detection procedure for calculating secondary synchronization signals according to the possible receiving time points and the first, second and third frequency domain primary synchronization sequences, respectively, and obtaining corresponding physical cell groups.

Drawings

FIG. 1 is a table of entity identifiers versus Zadoff-Chu root indices.

Fig. 2 is a flow chart of cell search.

Fig. 3 is a schematic diagram of a communication device according to an embodiment of the invention.

FIG. 4 is a schematic diagram of a process according to an embodiment of the present invention.

Fig. 5 is a flowchart of a cell search according to an embodiment of the invention.

FIG. 6 shows a receiving time detection procedure of a primary synchronization signal according to an embodiment of the present invention.

Fig. 7 is a flowchart of a cell search according to an embodiment of the invention.

Fig. 8 shows a successive interference cancellation procedure according to an embodiment of the present invention.

Detailed Description

Fig. 3 is a diagram of a communication device 30 according to an embodiment of the invention. The communication device 30 may be a client, and includes a processing device 300, a storage unit 310, and a communication interface unit 320. The processing device 300 may be a microprocessor or an Application Specific Integrated Circuit (ASIC). The storage unit 310 may be any type of data storage device for storing the program code 314 and reading and executing the program code 314 via the processing device 300. The communication interface unit 320 may be a wireless transceiver, which exchanges wireless signals with a network (e.g., a base station) according to the processing result of the processing device 300.

FIG. 4 is a flow chart of a process 40 according to an embodiment of the present invention. The process 40 can be applied to the communication device 30 to reduce the cell search time and improve the success probability. The process 40 can be compiled into the program code 314 and stored in the storage unit 310, which includes the following steps:

step 400: and starting.

Step 410: a receiving time detection procedure of a primary synchronization signal is performed to obtain at least one receiving time point of a primary synchronization signal.

Step 420: a primary synchronization signal assumption procedure is performed to generate a first, second and third frequency domain primary synchronization sequences in a frequency domain according to three root indexes corresponding to a first, second and third entity identifiers, respectively.

Step 430: performing an assisted synchronization signal coherent detection procedure to calculate an assisted synchronization signal according to each of the at least one receiving time points and the first, second and third frequency domain primary synchronization sequences, and obtaining a corresponding physical cell group.

Step 440: and (6) ending.

According to the process 40, in the primary synchronization signal reception time detection procedure, only the possible reception time points of the PSS signal are found, and the physical identifier of the PSS signal is identified

Then, after obtaining the receiving time point of the PSS signal without making a judgment, three possible entity identifiers are used

Detecting SSS signals and physical cell groups by performing a matched detection with a received-time-point-input-assisted synchronization signal coherent detection procedure

Referring to fig. 5, the cell search process according to the present invention includes a primary synchronization signal reception time detection procedure, a primary synchronization signal assumption procedure, and a secondary synchronization signal coherence detection procedure. The following is a detailed description of each procedure:

1. primary synchronization signal reception time detection procedure:

referring to fig. 6, a diagram of a master synchronization signal reception time detection procedure 60 according to an embodiment of the invention is shown. After receiving the signal, the client down-converts the received signal to 1.92MHz (step 601), and then associates the three PSS sequences in the time domain (according to the three root fingers)Number u: 25. 29, 34, respectively) are generated and correlated (step 602). At each receive time (i.e., 9600 samples), the largest of the three sets of correlation results is selected (step 603) and output to the non-coherent combining buffer for combining over half a radio frame (step 604). Then, based on the 5ms capacity of the half-radio frame buffer, the stored value is compared with a predetermined threshold to find out the possible receiving time point n of the PSS signal_i(step 605), these possible reception time points n are finally assigned_iOutput to the assisted synchronization signal coherent detection procedure. It should be noted that the PSCH time detection procedure 60 does not determine the physical identifier, and therefore only one set of non-coherent combining registers (9600 samples) is required, and the register capacity of 2/3 is saved (see above, in the conventional cell search process, 3 sets of non-coherent combining registers are required to store 28.8k samples).

2. Primary sync hypothesis procedure and secondary sync coherence detection procedure:

referring to fig. 7, a flowchart of cell search according to an embodiment of the invention is shown. At the time of receiving n from the master synchronization signal receiving time detecting program 60_i(0≤n_i< 9600), the primary synchronization signal assumption program 70a will assign three possible entity identifiers

The auxiliary synchronization signal coherent detection process 70b is sequentially inputted for detection. Further, as shown in fig. 7, at the reception time point n_iThen a parameter initial will be set to 1, so that the PSCH assumption procedure 70a will be initiated

Is 0.

It is noted that, in order to eliminate the Interference between the synchronization signals, the present invention proposes a complete frequency domain Interference cancellation (SIC) procedure. As shown in fig. 7, first, the client determines that it is at the reception time point n_iWhether a cell was detected (i.e., a physical cell identifier was obtained)

) If yes, proceeding with the successive interference cancellation procedure 70c, and then proceeding with the secondary synchronization signal coherent detection procedure 70 b; otherwise, the SSCH coherent detection process 70b is performed directly. If the client is at the receiving time point n_iWhen no cell is detected, a secondary synchronization signal coherent detection procedure 70b is performed.

The signal coherence detection process 70b is described in detail as follows: the client end detects the receiving time point n of the primary synchronization signal provided by the measuring process 60 according to the receiving time of the primary synchronization signal_iTaking 128 sampling points on the time domain to perform fast Fourier transform to the frequency domain:

and taking 31 subcarriers at the left side and the right side of DC on the frequency domain to obtain:

Y_pss(k),k＝-31,-30,...,-1,1,2,...,31

the PSS signal receiving time point n provided by the primary synchronization signal receiving time detection process 60_iAccording to the TDD-LTE mode, the SSS signal leads the PSS signal by two OFDM symbol times, and the receiving time point n 'of the SSS signal is calculated'_iTaking 128samples in the time domain to perform fast Fourier transform to the frequency domain:

Y_sss(k),k＝-31,-30,...,-1,1,2,...,31

presume value of entity identifier based on primary synchronization signal of program 70a

Generating PSS sequences in the frequency domain:

and (3) performing channel estimation of the PSS signal:

applying channel estimation result and Y of PSS signal_sssPerforming coherent combination operation to obtain:

wherein Re {. means a real number part, n represents a mark on a time axis,

then a coherent combining buffer with a capacity of 3x62 sample points. And performing correlation operation on the result of the coherent combination operation and the SSS sequence:

representing a given physical cell group

With entity identifiers

Later, the sequence of the SSS signal in the frequency domain:

since the SSS sequence is composed of m-sequences, the correlation operation of the SSS sequence can be calculated by Fast-hadamard Transform (FHT) to reduce the complexity of hardware implementation.

Since the present invention finds out the time that the PSS signal may appear only in the time domain, and does not make a judgment with respect to the type of the PSS sequence, the embodiment of the present invention provides a detection program 70d to determine whether the cell is detected in the correlation operation result of the SSS sequence. Taking the maximum value in the correlation operation result of the SSS sequence as the basis:

defining the detection threshold Q as:

wherein q is the sum of energies:

q should satisfy Q ≦ 1, and if Q is greater than a predetermined threshold, e.g., 0.8, it is determined that a new cell is detected and calculated

. The parameter initial is then set to 1, meaning that the entity identifier is assumed by the primary synchronization signal assumption program 70a

Is reset to zero upon detection

The successive interference cancellation procedure is performed, and then the secondary synchronization signal coherent detection procedure 70b is performed. Otherwise, the assumed entity identifier is discarded

Is set to 0, so that in primary synchronization signal assumption routine 70a, parameter initial is set to 0

I.e. try the next entity identifier

Assumed value of (so on)

Try to

) And re-executes the secondary synchronization signal coherent detection process 70 b. If, three possible entity identifiers

The ssc coherent detection procedure 70b is performed and no new cell is detected, the detection of the secondary psc reception time point is finished, and the psc hypothesis procedure 70a and the ssc coherent detection procedure 70b are performed at the next reception time point.

On the other hand, if there is a detected cell (i.e. get the physical cell identifier)

) The client proceeds with a successive interference cancellation procedure 70 c. Referring to fig. 8, a flowchart of a successive interference cancellation procedure 80 according to an embodiment of the present invention is shown. The client end groups the physical cells according to the detected

With entity identifiers

Separately generating PSS sequences X in frequency domain_pssWith SSS sequence X_sss. Channel estimation of the SSS signal is then performed:

reconstructing received signals of the PSS and the SSS by using channel estimation of the SSS signals:

removing corresponding reconstruction signals from the received PSS and SSS signals respectively:

PSS and SSS signals Y 'after continuous interference elimination program execution'_pss、Y′_sssReplace the original PSS and SSS reception signal Y_pss、Y_sssThe auxiliary synchronization signal coherent detection process 70b is inputted for detection. The above operations of the entire successive interference cancellation procedure are completely completed in the frequency domain, and there is no need to switch to the time domain to re-detect the existence of the weaker PSS signal, thereby saving the time of cell search. It should be noted that, in order to eliminate the interference among the synchronization signals, the ue switches to the time domain and then performs the successive interference cancellation procedure after detecting the cell and acquiring the physical cell identifier. However, this approach may cause the ue not to perform the successive interference cancellation procedure in the current frame of the detected cell, and the ue must perform the successive interference cancellation procedure in the next frame, which causes a time delay for the ue to synchronize with the cell.

All the steps can be implemented by hardware, firmware (i.e. combination of hardware device and computer instruction, data in the hardware device is read-only software data), or electronic system. The hardware may include analog, digital, and hybrid circuits (i.e., microcircuits, microchips, or silicon chips). The electronic system may include a System On Chip (SOC), a system in package (Sip), a Computer On Module (COM), and the communication device 30.

In summary, the cell search procedure provided by the present invention can solve the problem that when a plurality of primary synchronization signals exist in the time domain in the frame synchronization system at the same time, the mutual synchronization interference cannot be reduced through the non-coherent combining operation, and therefore, a weaker primary synchronization signal cannot be detected. The invention can confirm whether there is a cell by the detection mechanism of the main synchronous signal hypothesis procedure and the auxiliary synchronous signal correlation operation result in the frequency domain, further adopts the full frequency domain continuous interference elimination procedure to eliminate the interference of the stronger cell and combines the synchronous combination of different frames, thereby greatly improving the probability of detecting the weaker signal cell.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Description of the symbols

Entity identifier

Physical cell group

Physical cell identifier

u root index

n_iReceiving time point

30 communication device

300 processing device

310 storage unit

320 communication interface unit

314 program code

40 flow path

400 to 440, 601 to 605

60 Primary synchronization signal reception time detection procedure

70a Primary Sync Signal assumption procedure

70b assisted Sync Signal coherent detection procedure

70c, 80 successive interference cancellation procedure

70d detection program.

Claims

1. A method of cell search in a mobile device in a wireless communication system, the method comprising:

performing a primary synchronization signal reception time detection procedure for obtaining at least one possible reception time point of a primary synchronization signal;

performing a primary synchronization signal assumption procedure for generating a first, second and third frequency domain primary synchronization sequence on a frequency domain according to three root indexes corresponding to a first, second and third entity identifiers, respectively; and

performing an SSCH coherent detection procedure to calculate an SSCH according to the at least one possible receiving time point and the first, second and third frequency domain PSCHs respectively, so as to obtain a corresponding physical cell group.

2. The method of claim 1, wherein the PSCH detection procedure comprises the steps of:

receiving a wireless signal from the wireless communication system;

down-converting the received signal to the frequency of the primary synchronization signal;

performing a correlation operation on the down-converted signal and a primary synchronization sequence corresponding to the primary synchronization signal, wherein the primary synchronization sequence comprises a first, a second and a third time domain primary synchronization sequences, which are generated by the mobile device in a time domain according to a first, a second and a third indices, respectively;

selecting the maximum output value from the first, second and third correlation operation results at each sampling time point in the primary synchronization signal transmission cycle for performing a non-coherent combining operation to generate an operation result; and

comparing the operation result with a default value to determine whether the primary synchronization signal is detected.

3. The method of claim 1 wherein the SSC coherent detection process comprises a primary synchronization signal channel estimation operation, a coherent combining operation, and a fast Hadamard transform operation.

4. The method of claim 3, further comprising:

performing a detection procedure for determining whether the secondary synchronization signal is detected, wherein the detection procedure comprises: when the fast Hadamard transform operation result is larger than a preset threshold value, judging that an auxiliary synchronization sequence is detected and acquiring a corresponding entity cell group; and

and when the fast Hadamard transform operation result is smaller than the threshold value, judging that an auxiliary synchronization signal is not detected.

5. The method of claim 4, further comprising:

calculating an entity cell identifier corresponding to a cell according to the obtained entity cell group and a first, second or third entity identifier corresponding to a first, second or third frequency domain primary synchronization sequence used for performing the secondary synchronization signal coherent detection procedure; and

performing a successive interference cancellation procedure for canceling interference of a synchronization signal received from the cell, wherein the successive interference cancellation procedure comprises the steps of:

generating a first primary synchronization sequence and a first secondary synchronization sequence in a frequency domain according to the entity cell group and a first, second or third entity identifier for the secondary synchronization signal;

performing a channel estimation operation of the auxiliary synchronization sequence;

respectively reconstructing a second primary synchronization signal and a second auxiliary synchronization signal received by the mobile device by using a channel estimation operation result of the auxiliary synchronization sequence and the first primary synchronization sequence and the first auxiliary synchronization sequence; and

and removing the reconstructed second main synchronous signal and the reconstructed second auxiliary synchronous signal from the main synchronous signal and the auxiliary synchronous signal respectively to obtain a third main synchronous signal and a third auxiliary synchronous signal after interference elimination.

6. The method of claim 4, further comprising:

when the secondary synchronization signal is not detected, determining whether a first receiving time point of the at least one possible receiving time point and the first, second and third frequency domain primary synchronization sequences have been subjected to the secondary synchronization signal coherent detection procedure;

performing the secondary synchronization signal coherent detection procedure using a second one of the at least one possible reception time point and the first, second, and third frequency domain primary synchronization signals if the first reception time point and the first, second, and third frequency domain primary synchronization signals have been performed the secondary synchronization signal coherent detection procedure; and

if the first receiving time point and the first, second and third frequency domain primary synchronization signals have not been subjected to the secondary synchronization signal coherent detection procedure, continuing to perform the secondary synchronization signal coherent detection procedure at the first receiving time point and the first, second or third frequency domain primary synchronization signals that have not been subjected to the secondary synchronization signal coherent detection procedure.

7. A method for detecting a primary synchronization signal reception time in a mobile device in a wireless communication system, the method comprising:

receiving a wireless signal from the wireless communication system;

down-converting the received signal to the frequency of a primary synchronization signal;

comparing the operation result with a default value to obtain at least one possible receiving time point of the primary synchronization signal and determining whether the primary synchronization signal is detected.

8. The method of claim 7, further comprising:

performing an SSCH coherent detection procedure to calculate an SSCH according to each of at least one possible receiving time point and the first, second and third frequency domain PSCHs respectively, so as to obtain a corresponding physical cell group.

9. The method of claim 8 wherein the SSC coherent detection process comprises a primary synchronization channel estimation operation, a coherent combining operation, and a fast Hadamard transform operation.

10. The method of claim 9, further comprising: