CN112019292B - LTE downlink hybrid timing synchronization method and system - Google Patents

LTE downlink hybrid timing synchronization method and system Download PDF

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CN112019292B
CN112019292B CN202010816005.7A CN202010816005A CN112019292B CN 112019292 B CN112019292 B CN 112019292B CN 202010816005 A CN202010816005 A CN 202010816005A CN 112019292 B CN112019292 B CN 112019292B
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万显荣
但阳鹏
易建新
饶云华
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Wuhan University WHU
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Abstract

In order to solve the problems of time consumption and resource occupation faced by the LTE downlink timing search, the data rate is reduced through preprocessing, and the normalized sample detector and the normalized difference detector are combined, so that the time consumption and the resource occupation of the search can be effectively reduced, and the synchronization performance with excellent robustness is achieved. The invention discloses a method and a system for LTE downlink hybrid timing synchronization, which adopt a normalized sample detector to search all possible synchronization code positions and then utilize a normalized difference detector to determine a target cell peak value so as to realize downlink time slot synchronization and sector number judgment.

Description

LTE downlink hybrid timing synchronization method and system
Technical Field
The invention relates to the technical field of wireless communication, in particular to a method and a system for synchronizing LTE downlink hybrid timing.
Background
As a 4 th generation communication system popular around the world, Long Term Evolution (LTE) has the advantages of flexible bandwidth and spectrum configuration, high transmission data rate, small time delay, and the like, and includes two modes, frequency division multiplexing (FDD-LTE) and time division multiplexing (TDD-LTE). To ensure reliable communication, User Equipment (UE) frequently performs cell search to find and access the most suitable cell. Cell search aims to establish time, frequency synchronization with a target cell and identify a target cell ID, which is an indispensable function for the UE. In many cell search processes, time synchronization for determining the start of a time slot is the first step and is one of the most critical steps.
The inventor of the present application finds that the method of the prior art has at least the following technical problems in the process of implementing the present invention:
in the prior art, mainstream research has focused on reducing the complexity of a single search. However, since it is difficult to determine the starting point of the LTE downlink signal timeslot through a single timing search, the continuous search in the time domain consumes a lot of time and computation resources.
Therefore, the method in the prior art has the technical problems of long time consumption and high consumption of computing resources.
Disclosure of Invention
The invention provides an LTE (Long term evolution) downlink hybrid timing synchronization method and an LTE downlink hybrid timing synchronization system, which are used for solving or at least partially solving the technical problems of long time consumption and high calculation resource consumption in the method in the prior art.
In order to solve the above technical problem, the present invention provides an LTE downlink hybrid timing synchronization method, which includes:
s1: preprocessing downlink data;
s2: carrying out normalized sample detection according to the preprocessed data and the local synchronous code, eliminating useless secondary peaks from the first normalized sample detection result, and screening out the first L peak values and the corresponding time sequence number set phiLWherein, L is a positive integer;
s3: according to the time sequence number set phiLObtaining a corresponding first data vector and an interval N between the first data vector and the time sequence0The first data vector and the second data vector form an L pair of data vectors, and the L pair of data vectors are subjected to normalized differential detection to obtain a time sequence number corresponding to the maximum peak value;
s4: and finding out a third data vector according to the time sequence number corresponding to the maximum peak value, carrying out normalized sample detection according to the third data vector and all local synchronous codes to obtain the maximum value in a second normalized sample detection result, obtaining the synchronous code corresponding to the target cell according to the maximum value, and obtaining the sector number of the target cell according to the synchronous code.
In one embodiment, S2 specifically includes:
s2.1: carrying out normalized sample detection on the preprocessed data and the local synchronous code according to the following formula:
Figure BDA0002632715540000021
wherein M isNRD[m]Represents the first normalized sample detection result, rm＝[sm,sm+1,…,sm+N-1]T+nmRefers to a received signal vector of length N, s, constructed using preprocessed datamRefers to a time domain downlink discrete signal,
Figure BDA0002632715540000022
reference to a local synchronization code, nmRefers to the noise vector, N refers to the OFDM data volume length, H refers to the Hermitian transformThe device is placed in a water tank,
Figure BDA0002632715540000023
a euclidean norm representing a vector;
s2.2: judging whether the l-th peak value falls on the position of the secondary peak of the m-th peak value or not according to the relative positions of the PSS autocorrelation main peak and the secondary peak, and if not, reserving two peak values; if so, comparing the difference value between the SMR ratio and the theoretical SMR ratio of the measured secondary peak to the main peak, if the difference value between the SMR ratio and the theoretical SMR ratio exceeds a threshold value, keeping two peak values, otherwise, removing the two peak values, and finally obtaining the previous L peak values and the corresponding time sequence number set phiL。
In one embodiment, S2.1 specifically includes:
when normalized sample detection is carried out according to the preprocessed data and the local synchronous code, the central symmetry of the LTE synchronous code PSS is calculated during each search
Figure BDA0002632715540000024
Namely, it is
r′m＝[rm，rm+1+rm+N-1，…，rm+N/2-1+rm+N/2+1，rm+N/2]T
Figure BDA0002632715540000026
By using
Figure BDA0002632715540000027
To replace
Figure BDA0002632715540000028
To save the molecular calculation amount, the iterative method is adopted to calculate the Euclidean norm
Figure BDA0002632715540000029
Ready to use
R1[m+1]＝R1[m]+|rm+N|2-|rm|2
And the denominator calculation amount is saved, and after the normalized sample detection is finished, the peak values and the corresponding time sequence number sets with the quantity larger than L are extracted from high to low.
In one embodiment, in S3, the normalized difference detection is performed on the data vector L to obtain the time sequence number corresponding to the maximum peak value, which specifically is:
Figure BDA0002632715540000031
wherein N is0Refers to the adjacent synchronous code interval, r, in the downlink discrete signalΦ,mAccording to the time sequence number set phiLA time series number of the acquired data vector,
Figure BDA0002632715540000032
is a is and rΦ,mInterval N0The corresponding data vector, H denotes the Hermitian transpose,
Figure BDA0002632715540000033
representing the euclidean norm of the vector.
In one embodiment, step S3 further includes:
the time number corresponding to the maximum peak value is used as the coarse timing position NcAnd carrying out time slot timing according to the coarse timing position to obtain a time starting point N of the time slot of the PSS1＝Nc-Nslot+N+k·N0In which N isslotIndicating the time slot length, N refers to the OFDM data body length, and k is a non-negative integer.
Based on the same inventive concept, a second aspect of the present invention provides an LTE downlink hybrid timing synchronization system, including:
the preprocessing unit is used for preprocessing the downlink data;
NRD detection and screening unit for performing normalized sample detection according to the preprocessed data and local synchronous code, eliminating useless secondary peaks from the first normalized sample detection result, and screening the former L peak values and corresponding time sequence number set phiLWherein L is a positive integer；
NDD detection and coarse timing unit for determining the time sequence number set phiLObtaining a corresponding first data vector and an interval N between the first data vector and the time sequence0The first data vector and the second data vector form an L pair of data vectors, and the L pair of data vectors are subjected to normalized differential detection to obtain a time sequence number corresponding to the maximum peak value;
and the synchronous code judging unit is used for finding out a third data vector according to the time sequence number corresponding to the maximum peak value, carrying out normalized sample detection according to the third data vector and all local synchronous codes, obtaining the maximum value in a second normalized sample detection result, obtaining the synchronous code corresponding to the target cell according to the maximum value, and obtaining the sector number of the target cell according to the synchronous code.
In one embodiment, the NRD detection and screening unit is specifically configured to:
carrying out normalized sample detection on the preprocessed data and the local synchronous code according to the following formula:
Figure BDA0002632715540000041
wherein M isNRD[m]Represents the first normalized sample detection result, rm＝[sm,sm+1,…,sm+N-1]T+nmRefers to a received signal vector of length N, s, constructed using preprocessed datamRefers to a time domain downlink discrete signal,
Figure BDA0002632715540000042
reference to a local synchronization code, nmRefers to the noise vector, N refers to the OFDM data volume length, H denotes the Hermitian transpose,
Figure BDA0002632715540000043
a euclidean norm representing a vector;
judging whether the l-th peak value falls on the position of the secondary peak of the m-th peak value or not according to the relative positions of the main peak and the secondary peak of the PSS autocorrelation, and if not, reserving two peak values(ii) a If so, comparing the difference value between the SMR ratio and the theoretical SMR ratio of the measured secondary peak to the main peak, if the difference value between the SMR ratio and the theoretical SMR ratio exceeds a threshold value, keeping two peak values, otherwise, removing the two peak values, and finally obtaining the previous L peak values and the corresponding time sequence number set phiL。
In one embodiment, the NDD detection and coarse timing unit includes a slot timing module configured to:
the time sequence number corresponding to the maximum peak value is used as a coarse timing position NcAnd timing the time slot according to the coarse timing position to obtain a time starting point N of the time slot of the PSS1＝Nc-Nslot+N+k·N0In which N isslotIndicating the time slot length, N refers to the OFDM data body length, and k is a non-negative integer.
One or more technical solutions in the embodiments of the present application have at least one or more of the following technical effects:
the invention provides a LTE downlink hybrid timing synchronization method, which comprises the steps of preprocessing downlink data; then, carrying out normalized sample detection according to the preprocessed data and the local synchronous code, eliminating useless secondary peaks from the first normalized sample detection result, and screening out the front L peak values and the corresponding time sequence number set phiLThen, carrying out normalized difference detection on the data vector according to L corresponding to the time sequence number set to obtain a time sequence number corresponding to the maximum peak value; and finally, acquiring the synchronous code and the sector number of the corresponding target cell according to the time sequence number corresponding to the maximum peak value.
All possible synchronization code positions can be searched by adopting normalized sample detection, unnecessary secondary peaks are removed, and the peak value of a target cell is determined by normalized differential detection, so that downlink time slot synchronization and sector number judgment are realized, the search time and resource occupation can be effectively reduced, and the synchronization performance of excellent robustness is realized.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a flow chart of an embodiment of the present invention;
fig. 2 is a schematic diagram of a frequency domain occupied subcarrier of an LTE synchronization code PSS according to an embodiment of the present invention;
fig. 3 is a diagram of a synchronization result of actually measured LTE downlink data 20181025151400 according to an embodiment of the present invention;
fig. 4 is a diagram of a synchronization result of the measured LTE downlink data 20180925161227 in the embodiment of the present invention.
Detailed Description
In order to solve the problems of time consumption and resource occupation faced by the LTE downlink timing search, the data rate is reduced through preprocessing, and the normalized sample detector and the normalized difference detector are combined, so that the time consumption and the resource occupation of the search can be effectively reduced, and the synchronization performance with excellent robustness is achieved.
The main concept of the invention is as follows:
the invention discloses an LTE downlink hybrid timing synchronization strategy, which adopts a method that a normalized sample detector is adopted to search all possible synchronization code positions, and then a normalized difference detector is utilized to determine a target cell peak value, so as to realize downlink time slot synchronization and sector number judgment.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example one
The embodiment of the invention provides an LTE downlink hybrid timing synchronization method, which comprises the following steps:
s1: preprocessing downlink data;
s2: carrying out normalized sample detection according to the preprocessed data and the local synchronous code, eliminating useless secondary peaks from the first normalized sample detection result, and screening the front L peak values and the corresponding peak valuesTime sequence number set phiLWherein, L is a positive integer;
s3: according to the time sequence number set phiLObtaining a corresponding first data vector and an interval N between the first data vector and the time sequence0The first data vector and the second data vector form an L pair of data vectors, and the L pair of data vectors are subjected to normalized differential detection to obtain a time sequence number corresponding to the maximum peak value;
s4: and finding out a third data vector according to the time sequence number corresponding to the maximum peak value, carrying out normalized sample detection according to the third data vector and all local synchronous codes to obtain the maximum value in a second normalized sample detection result, obtaining the synchronous code corresponding to the target cell according to the maximum value, and obtaining the sector number of the target cell according to the synchronous code.
Specifically, to implement downlink synchronization, the present embodiment first performs preprocessing, such as filtering, decimation, etc., on downlink data.
S2 is to perform normalized sample detection to obtain a first normalized sample detection result, i.e., the NRD value refers to a result obtained by performing normalized sample detection calculation on any input signal. And then screening the first normalized sample detection result, and screening the first L peak values meeting the conditions and the corresponding time sequence numbers. The normalized sample detection is achieved by a normalized sample detector and the normalized differential detection is achieved by a normalized differential detector.
S3 is based on S2, carry on the normalized difference to detect, find the time sequence number that the maximum peak value corresponds to, the calculation mode is:
Figure BDA0002632715540000061
Figure BDA0002632715540000062
that is, the maximum peak value, after the time sequence number corresponding to the maximum peak value is known, S4 performs normalized sample detection according to the time sequence number corresponding to the maximum peak value, and finds out the second normalized sample detection resultThe maximum NRD value corresponds to the synchronization code of the target cell, and the calculation method is as follows:
Figure BDA0002632715540000063
Figure BDA0002632715540000064
for the synchronous code of the target cell corresponding to the maximum NRD value, corresponding data vectors and local 3 kinds of LTE synchronous codes are used
Figure BDA0002632715540000065
The NRD calculation (normalized sample detection) is performed and the synchronization code of the target cell will correspond to the largest NRD calculation.
Accordingly, sector numbers corresponding one-to-one to the synchronization codes are also available.
According to the definition of TS 36.211, the three types of LTE synchronization codes correspond to three sectors, that is, the PSS with ZC root indexes of 25,29 and 34 corresponds to sectors with sector numbers of 0, 1 and 2, respectively, and the corresponding sector numbers can be determined after the PSS type is known.
In one embodiment, S1 specifically includes:
s1.1: filtering the downlink data;
s1.2: and performing aliasing-free extraction on the filtered data.
Specifically, the downstream data may be filtered by a pre-designed Low Pass Filter (LPF), and when aliasing-free extraction is performed, the extraction rate is D.
In one embodiment, S2 specifically includes:
s2.1: carrying out normalized sample detection on the preprocessed data and the local synchronous code according to the following formula:
Figure BDA0002632715540000071
wherein M isNRD[m]Represents the first normalized sample detection result, rm＝[sm,sm+1,…,sm+N-1]T+nmRefers to a received signal vector of length N, s, constructed using preprocessed datamRefers to a time domain downlink discrete signal,
Figure BDA0002632715540000072
reference to a local synchronization code, nmRefers to the noise vector, N refers to the OFDM data volume length, H denotes the Hermitian transpose,
Figure BDA0002632715540000073
a euclidean norm representing a vector;
s2.2: judging whether the l-th peak value falls on the position of the secondary peak of the m-th peak value or not according to the relative positions of the PSS autocorrelation main peak and the secondary peak, and if not, reserving two peak values; if so, comparing the difference value between the SMR ratio and the theoretical SMR ratio of the measured secondary peak to the main peak, if the difference value between the SMR ratio and the theoretical SMR ratio exceeds a threshold value, keeping two peak values, otherwise, removing the two peak values, and finally obtaining the previous L peak values and the corresponding time sequence number set phiL。
Specifically, S2.1 adds the uncorrelated local synchronization codes and inputs them with the preprocessed data into the NRD for normalized sample detection.
In S2.2, since the relative positions of the secondary peak and the main peak are known, the SMR in the measured data can be obtained by dividing the NRD value of the secondary peak by the NRD value of the main peak. In practice, the PSS temporal autocorrelation has 6 secondary peaks on the left and right sides of the main peak, and the position and ratio of each secondary peak to the main peak are [ + -3, + -26, + -51, + -77, + -102 ], [0.2256,0.1782,0.2865,0.3080,0.1782], respectively.
Wherein the threshold value can be set as the case may be.
In one embodiment, S2.1 specifically includes:
when normalized sample detection is carried out according to the preprocessed data and the local synchronous code, the central symmetry of the LTE synchronous code PSS is calculated during each search
Figure BDA0002632715540000074
Namely, it is
r′m＝[rm，rm+1+rm+N-1，…，rm+N/2-1+rm+N/2+1，rm+N/2]T
Figure BDA0002632715540000076
By using
Figure BDA0002632715540000081
To replace
Figure BDA0002632715540000082
To save the molecular calculation amount, the iterative method is adopted to calculate the Euclidean norm
Figure BDA0002632715540000083
Ready to use
R1[m+1]＝R1[m]+|rm+N|2-|rm|2
And the denominator calculation amount is saved, and after the normalized sample detection is finished, the peak values and the corresponding time sequence number sets with the quantity larger than L are extracted from high to low.
In one embodiment, in S3, the normalized difference detection is performed on the data vector L to obtain the time sequence number corresponding to the maximum peak value, which specifically is:
Figure BDA0002632715540000084
wherein N is0Refers to the adjacent synchronous code interval, r, in the downlink discrete signalΦ,mAccording to the time sequence number set phiLA time series number of the acquired data vector,
Figure BDA0002632715540000085
is a is and rΦ,mInterval N0The corresponding data vector, H denotes the Hermitian transpose,
Figure BDA0002632715540000086
representing the euclidean norm of the vector.
In one embodiment, step S3 further includes:
the time number corresponding to the maximum peak value is used as the coarse timing position NcAnd carrying out time slot timing according to the coarse timing position to obtain a time starting point N of the time slot of the PSS1＝Nc-Nslot+N+k·N0In which N isslotIndicating the time slot length, N refers to the OFDM data body length, and k is a non-negative integer.
Specifically, NslotCorresponding to a duration of 0.5ms, N1Is one of the coarse synchronization search results and can be used for subsequent fine synchronization search.
Based on the same inventive concept, the embodiment of the invention also provides a system corresponding to the synchronization method of the embodiment, which is detailed in embodiment two.
Example two
The embodiment provides an LTE downlink hybrid timing synchronization system, which includes:
the preprocessing unit is used for preprocessing the downlink data;
NRD detection and screening unit for performing normalized sample detection according to the preprocessed data and local synchronous code, eliminating useless secondary peaks from the first normalized sample detection result, and screening the former L peak values and corresponding time sequence number set phiLWherein, L is a positive integer;
NDD detection and coarse timing unit for determining the time sequence number set phiLObtaining a corresponding first data vector and an interval N between the first data vector and the time sequence0The first data vector and the second data vector form an L pair of data vectors, and the L pair of data vectors are subjected to normalized differential detection to obtain a time sequence number corresponding to the maximum peak value;
and the synchronous code judging unit is used for finding out a third data vector according to the time sequence number corresponding to the maximum peak value, carrying out normalized sample detection according to the third data vector and all local synchronous codes, obtaining the maximum value in a second normalized sample detection result, obtaining the synchronous code corresponding to the target cell according to the maximum value, and obtaining the sector number of the target cell according to the synchronous code.
Specifically, the preprocessing unit can reduce the data rate under the condition of no aliasing, and the NRD detection and screening unit comprises an NRD detector module and an interference peak eliminating module and is used for acquiring a plurality of effective peak values and corresponding time sequence numbers. The NDD detection and coarse timing unit includes an NDD detector module and a slot timing module for determining a synchronization peak from a target cell in the NRD peak. The synchronization code determination unit is used for determining the sector number of the target cell.
Referring to fig. 1, the system of the present invention includes a preprocessing unit, an NRD detecting and screening unit, an NDD detecting and coarse timing unit, and a synchronization code determining unit. The NRD detection and screening unit comprises an NRD detector module and an interference peak rejection module; the NDD detection and coarse timing unit comprises an NDD detector module and a time slot timing module.
The embodiment elaborates an LTE downlink hybrid timing synchronization method. The carrier frequency of the downlink frequency division multiplexing LTE (FDD-LTE) signal adopted by the embodiment is 1.8675GHz, and the bandwidth is 15.36 MHz. Fig. 2 is a schematic diagram of a frequency spectrum of a synchronization code PSS of FDD-LTE, where PSS subcarriers only occupy 31 subcarriers on both sides of a dc carrier, and besides, two 5 subcarriers on the left and right of the PSS spectrum are respectively used for a guard band. The pass band and stop band frequencies of the LPF are respectively 0.54 MHz and 0.96MHz, and the order is 139 orders; the decimation rate D is 12, which is exactly the quotient of the baseband sampling rate (23.04MHz) and the minimum sampling rate (1.92 MHz); the number of maximum values of NRD is L9. The timing synchronization results of the two sets of preprocessed data 20181025151400 (denoted as data a) and 20180925161227 (denoted as data B) are shown in fig. 3 and 4. In fig. 3, the timing peak of the target cell of the NRD and NDD is stronger than the peak of the neighboring cell, the synchronization code peak of the PSS 29 type is strongest, the corresponding sector number is 1, and the corresponding coarse time starting point is 1.312 ms; in fig. 4, the adjacent cell timing peak of the NRD within 5-12 ms is equivalent to the target cell peak, so the target cell PSS needs to be determined by the timing result of the NDD, which reflects the necessity of combining the NRD and the NDD. The PSS 34 type of synchronization code in fig. 4 has the strongest peak value, corresponding to sector number 2, and the corresponding coarse time starting point is 3.049 ms. Let the downlink signal length be L0The complex multiplication of the conventional cross-correlation algorithm requires L0N times, complex addition requires L0(N-1); the complex multiplication of the hybrid timing coarse synchronization strategy proposed by the embodiment requires L0(N+12D)/2D2The complex addition requires L0(N+D)/D2That is, the complex multiplication and addition of the hybrid timing strategy is 1/2D which is almost the complex multiplication and addition of the traditional cross-correlation algorithm2、1/D2. In summary, the hybrid timing strategy not only has low computational complexity, but also has excellent robustness.
In one embodiment, the preprocessing unit includes a filtering module and a decimation module, where the filtering module is configured to perform filtering processing on downlink data; and the decimation module is used for performing aliasing-free decimation on the filtered data.
In one embodiment, the NRD detection and screening unit is specifically configured to:
carrying out normalized sample detection on the preprocessed data and the local synchronous code according to the following formula:
Figure BDA0002632715540000101
wherein M isNRD[m]Represents the first normalized sample detection result, rm＝[sm,sm+1,…,sm+N-1]T+nmRefers to a received signal vector of length N, s, constructed using preprocessed datamRefers to a time domain downlink discrete signal,
Figure BDA0002632715540000102
reference to a local synchronization code, nmRefers to the noise vector, N refers to the OFDM data volume length, H denotes the Hermitian transpose,
Figure BDA0002632715540000103
a euclidean norm representing a vector;
judging whether the l-th peak value falls on the position of the secondary peak of the m-th peak value or not according to the relative positions of the PSS autocorrelation main peak and the secondary peak, and if not, reserving two peak values;if so, comparing the difference between the ratio (SMR) of the actually-measured secondary peak to the main peak and the theoretical SMR ratio, if the difference between the actually-measured SMR ratio and the theoretical SMR ratio exceeds a threshold value, keeping two peak values, otherwise, removing the two peak values, and finally obtaining the first L peak values and the corresponding time sequence number set phiL。
In one embodiment, the NDD detection and coarse timing unit includes a slot timing module configured to:
the time sequence number corresponding to the maximum peak value is used as a coarse timing position NcAnd timing the time slot according to the coarse timing position to obtain a time starting point N of the time slot of the PSS1＝Nc-Nslot+N+k·N0In which N isslotIndicating the time slot length, N refers to the OFDM data body length, and k is a non-negative integer.
Since the system described in the second embodiment of the present invention is a system used for implementing the hybrid timing synchronization method in the first embodiment of the present invention, a person skilled in the art can understand the specific structure and the modification of the system based on the method described in the first embodiment of the present invention, and thus the detailed description is omitted here. All systems adopted by the method of the first embodiment of the present invention are within the intended protection scope of the present invention.
Overall, the advantages or advantageous technical effects of the invention are as follows:
the invention has the following advantages:
1. hardware overhead is saved, time consumption of searching is shortened, and coarse synchronization performance is excellent;
2. the method is suitable for two modes of FDD (frequency division duplex mode) and TDD (time division duplex mode);
3. the method has the advantages of high efficiency, robustness and high accuracy, and is suitable for real-time implementation.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Claims (5)

1. An LTE downlink hybrid timing synchronization method is characterized by comprising the following steps:
s1: preprocessing downlink data;
s2: carrying out normalized sample detection according to the preprocessed data and the local synchronous code, eliminating useless secondary peaks from the first normalized sample detection result, and screening out the first L peak values and the corresponding time sequence number set phiLWherein, L is a positive integer;
s3: according to the time sequence number set phiLAcquiring a corresponding first data vector and having an interval N with the first data vector0The first data vector and the second data vector form an L pair of data vectors, and the L pair of data vectors are subjected to normalized differential detection to obtain a time sequence number corresponding to the maximum peak value;
s4: finding out a third data vector according to the time sequence number corresponding to the maximum peak value, carrying out normalized sample detection according to the third data vector and all local synchronous codes to obtain the maximum value in a second normalized sample detection result, obtaining the synchronous code corresponding to the target cell according to the maximum value, and obtaining the sector number of the target cell according to the synchronous code;
wherein, S2 specifically includes:
s2.1: carrying out normalized sample detection on the preprocessed data and the local synchronous code according to the following formula:
Figure FDA0003047882300000011
wherein M isNRD[m]Represents the first normalized sample detection result, rm＝[sm,sm+1,…,sm+N-1]T+nmRefers to a received signal vector of length N, s, constructed using preprocessed datamRefers to a time domain downlink discrete signal,
Figure FDA0003047882300000012
reference to a local synchronization code, nmRefers to the noise vector, N refers to the OFDM data volume length,h denotes the Hermitian transpose,
Figure FDA0003047882300000013
a euclidean norm representing a vector;
s2.2: judging whether the l-th peak value falls on the position of the secondary peak of the m-th peak value or not according to the relative positions of the PSS autocorrelation main peak and the secondary peak, and if not, reserving two peak values; if so, comparing the difference value between the SMR ratio and the theoretical SMR ratio of the measured secondary peak to the main peak, if the difference value between the SMR ratio and the theoretical SMR ratio exceeds a threshold value, keeping two peak values, otherwise, removing the two peak values, and finally obtaining the previous L peak values and the corresponding time sequence number set phiL；
In S3, performing normalized difference detection on the L pair data vectors to obtain a time sequence number corresponding to the maximum peak value, specifically:
Figure FDA0003047882300000021
wherein N is0Refers to the adjacent synchronous code interval, r, in the downlink discrete signalΦ,mAccording to the time sequence number set phiLA time series number of the acquired data vector,
Figure FDA0003047882300000022
is a is and rΦ,mInterval N0The corresponding data vector, H denotes the Hermitian transpose,
Figure FDA0003047882300000023
representing the euclidean norm of the vector.
2. The LTE downlink hybrid timing synchronization method according to claim 1, wherein S2.1 specifically includes:
when normalized sample detection is carried out according to the preprocessed data and the local synchronous code, the central symmetry of the LTE synchronous code PSS is calculated during each search
Figure FDA0003047882300000024
Namely, it is
Figure FDA0003047882300000025
Figure FDA0003047882300000026
By using
Figure FDA0003047882300000027
To replace
Figure FDA0003047882300000028
To save the molecular calculation amount, the iterative method is adopted to calculate the Euclidean norm
Figure FDA0003047882300000029
Ready to use
R1[m+1]＝R1[m]+|rm+N|2-|rm|2
And the denominator calculation amount is saved, and after the normalized sample detection is finished, the peak values and the corresponding time sequence number sets with the quantity larger than L are extracted from high to low.
3. The LTE downlink hybrid timing synchronization method of claim 1, wherein the step S3 further includes:
the time number corresponding to the maximum peak value is used as the coarse timing position NcAnd carrying out time slot timing according to the coarse timing position to obtain a time starting point N of the time slot of the PSS1＝Nc-Nslot+N+k·N0In which N isslotIndicating the time slot length, N refers to the OFDM data body length, and k is a non-negative integer.
4. An LTE downlink hybrid timing synchronization system, comprising:
the preprocessing unit is used for preprocessing the downlink data;
NRD detection and screening unit for performing normalized sample detection according to the preprocessed data and local synchronous code, eliminating useless secondary peaks from the first normalized sample detection result, and screening the former L peak values and corresponding time sequence number set phiLWherein, L is a positive integer;
NDD detection and coarse timing unit for determining the time sequence number set phiLAcquiring a corresponding first data vector and having an interval N with the first data vector0The first data vector and the second data vector form an L pair of data vectors, and the L pair of data vectors are subjected to normalized differential detection to obtain a time sequence number corresponding to the maximum peak value;
the synchronous code judging unit is used for finding out a third data vector according to the time sequence number corresponding to the maximum peak value, carrying out normalized sample detection according to the third data vector and all local synchronous codes to obtain the maximum value in a second normalized sample detection result, obtaining the synchronous code corresponding to the target cell according to the maximum value, and obtaining the sector number of the target cell according to the synchronous code;
the NRD detection and screening unit is specifically used for:
carrying out normalized sample detection on the preprocessed data and the local synchronous code according to the following formula:
Figure FDA0003047882300000031
wherein M isNRD[m]Represents the first normalized sample detection result, rm＝[sm,sm+1,…,sm+N-1]T+nmRefers to a received signal vector of length N, s, constructed using preprocessed datamRefers to a time domain downlink discrete signal,
Figure FDA0003047882300000032
reference to a local synchronization code, nmRefers to the noise vector, N refers to the OFDM data volume length, H refers to HThe result of the transposition of the hermitian,
Figure FDA0003047882300000033
a euclidean norm representing a vector;
judging whether the l-th peak value falls on the position of the secondary peak of the m-th peak value or not according to the relative positions of the PSS autocorrelation main peak and the secondary peak, and if not, reserving two peak values; if so, comparing the difference value between the SMR ratio and the theoretical SMR ratio of the measured secondary peak to the main peak, if the difference value between the SMR ratio and the theoretical SMR ratio exceeds a threshold value, keeping two peak values, otherwise, removing the two peak values, and finally obtaining the previous L peak values and the corresponding time sequence number set phiL；
The NDD detection and coarse timing unit performs normalized differential detection on the L pair of data vectors to obtain a time sequence number corresponding to the maximum peak value, and the method specifically comprises the following steps:
Figure FDA0003047882300000034
wherein N is0Refers to the adjacent synchronous code interval, r, in the downlink discrete signalΦ,mAccording to the time sequence number set phiLA time series number of the acquired data vector,
Figure FDA0003047882300000035
is a is and rΦ,mInterval N0The corresponding data vector, H denotes the Hermitian transpose,
Figure FDA0003047882300000036
representing the euclidean norm of the vector.
5. The LTE downlink hybrid timing synchronization system of claim 4, wherein the NDD detection and coarse timing unit comprises a slot timing module configured to:
the time sequence number corresponding to the maximum peak value is used as a coarse timing position NcAnd timing the time slot according to the coarse timing position to obtain a time starting point N of the time slot of the PSS1＝Nc-Nslot+N+k·N0In which N isslotIndicating the time slot length, N refers to the OFDM data body length, and k is a non-negative integer.
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