CN105897304B - A kind of fast synchronization method of frequency-hopping communication system - Google Patents
A kind of fast synchronization method of frequency-hopping communication system Download PDFInfo
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- CN105897304B CN105897304B CN201610378129.5A CN201610378129A CN105897304B CN 105897304 B CN105897304 B CN 105897304B CN 201610378129 A CN201610378129 A CN 201610378129A CN 105897304 B CN105897304 B CN 105897304B
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
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Abstract
The invention discloses a kind of fast synchronization method of frequency-hopping communication system; the non-referenced synchronization slot for standing the uplink synchronizing signals sent to base station includes 1 protection interval, multiple homing sequences, multiple unique words and station information in the method; using more unique words and station information combination; carry out uplink synchronizing signals capture and parameter Estimation; in the case where easily there is collision using the competition method of synchronization, remain to effectively improve synchronization acquistion probability and acquisition speed；It can avoid interfering other users using protection interval, improve acquisition probability；Packet offset estimation is carried out to multi-hop homing sequence using fft algorithm and is averaging method again, the degree of accuracy of offset estimation can be improved, frequency calibration is carried out to synchronizing signal.
Description
Technical Field
The invention relates to a quick synchronization method of a frequency hopping communication system, belonging to the field of electronic communication.
Background
The frequency hopping communication system can be regarded as a synchronous communication system in nature, like a TDMA system, and requires a reference station for transmitting a "reference burst" signal, i.e. a system time reference, and the remaining stations are defined as non-reference stations, and each non-reference station receives the "reference burst" signal transmitted by the reference station and synchronizes to the reference station, thereby realizing synchronization of the frequency hopping communication system. The synchronization of the frequency hopping communication system is influenced by frequency hopping clock error, frequency source error, doppler frequency, transmitted signal power and the like between a reference station and a non-reference station besides reference time, and in order to realize the rapid synchronization of the system, the frequency hopping clock error, frequency difference (frequency offset) and signal power of receiving and transmitting need to be accurately and rapidly estimated, in particular to the frequency hopping clock error estimation. In addition, from the overhead of system resources, in order to reduce the use of common resources such as synchronization slots, etc., the ALOHA contention method is adopted for common slots such as synchronization slots and control slots.
The existing frequency hopping synchronization structure generally adopts a structure mode of 1 unique code, and because the receiving and transmitting frequency hopping clocks are not completely aligned during initial synchronization, the probability of correctly capturing the unique code is very low, and the synchronization time is slow; meanwhile, when a plurality of users synchronize simultaneously, mutual collision is easily caused, which causes that the unique code cannot be correctly captured, thereby affecting synchronization.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method solves the problems of low synchronous capture probability and low synchronous speed of the existing frequency hopping communication system, and provides a quick synchronization method of the frequency hopping communication system, aiming at a plurality of key parameters influencing the synchronization of the frequency hopping communication system: the method solves the problems of fast synchronization and synchronous capture probability of the frequency hopping communication system from two aspects of frame structure design and realization of the frequency hopping communication system.
The technical solution of the invention is as follows: a method for fast synchronization in a frequency hopping communications system, the frequency hopping communications system including a reference station and a plurality of non-reference stations, the method comprising the steps of:
(1) The reference station sends a downlink synchronous signal to the non-reference station, wherein the downlink synchronous signal comprises time reference information;
(2) The non-reference station captures a downlink synchronous signal, after the downlink synchronous signal is successfully captured, frequency offset estimation is carried out on the downlink signal, time reference information is extracted, and link delay is estimated;
(3) The non-reference station calibrates local time according to the received time reference information and the link delay estimated value, adjusts the phase of a local frequency hopping clock to complete initial synchronization with a frequency hopping clock of the reference station, and corrects the uplink carrier frequency according to the downlink frequency offset estimation result;
(4) The non-reference station sends an uplink synchronous signal to the reference station, wherein the uplink synchronous signal comprises 1 guard interval, X guide sequences, X unique codes and X station information, the X station information of the same non-reference station is the same, the X unique codes are different from each other, the corresponding unique codes of different non-reference stations are the same, and X is greater than 1;
(5) The base station receives the uplink synchronous signal, performs frequency hopping clock error, power and frequency offset estimation and analysis on the received whole frame uplink synchronous signal, performs frequency hopping clock error validity judgment, inserts the estimated frequency hopping clock error, power value and frequency offset information and station information of the non-base station into a downlink state time slot when the frequency hopping clock error is valid, and sends the time slot to the non-base station, otherwise inserts the invalid identifier and the station information of the non-base station into the downlink state time slot and sends the time slot to the non-base station;
(6) Extracting effective uplink frequency hopping clock phase error, frequency offset, power and station information from the downlink state time slot by the non-reference station, and correcting the frequency hopping clock phase, frequency and power;
(7) And (5) circularly executing the step (4) to the step (6) until the phase error, the frequency offset and the power of the frequency hopping clock meet the system requirements, and completing the synchronization of the frequency hopping communication system.
The frame format of the uplink synchronization signal is shown in the following table:
wherein:
the protection interval is used for avoiding mutual interference of signals between stations, the occupied time is longer than the maximum link delay estimation error between the non-reference station and the reference station, and no signal is sent in the protection interval;
the guide sequence is used for frequency offset estimation and consists of a string of characters with '1' and '0' alternately arranged;
unique codes 1-X used for frequency hopping clock error estimation, each unique code being different from each other;
station information for identifying different non-reference stations, the same non-reference station using the same station information.
The reference station receives the uplink synchronous signal, and the frequency hopping clock error estimation method comprises the following steps: and performing parallel correlation operation on the X local unique codes and the input signal to obtain X unique code correlation values, when the Y unique code correlation values are larger than a preset threshold, Y is larger than or equal to 1, the acquisition is considered to be successful, a frequency hopping clock error is extracted from any unique code correlation operation result and is used as the frequency hopping clock error of the reference station, otherwise, the acquisition is considered to be unsuccessful, and when waiting for the arrival of the next downlink synchronous signal frame, the frequency hopping clock error is estimated again.
The method for estimating the power of the reference station comprises the following steps:
(4a) When the symbol rate of the uplink synchronous signal is f c When, use 4 xf c Obtaining a sampling value I of the uplink synchronous signal k And Q k ；
(4b) To I k And Q k Is added to the square of to obtain a signal energy value P K Accumulating the energy values of 4N continuous signals, wherein N is the symbol number of the synchronous signals;
(4c) Averaging the IQ square sum accumulated value obtained by calculation in the step (4 b);
(4d) And (4) carrying out dB conversion on the average value obtained by calculation in the step (4 c) to obtain a power estimation value.
The frequency offset estimation method for the reference station comprises the following steps: firstly, performing frequency offset estimation on a signal in a pilot sequence of each hop in a synchronous time slot, and then averaging the frequency offset estimated by each hop of signal to obtain an uplink frequency offset estimation, wherein the specific implementation process is as follows:
(5a) When the symbol rate of the uplink synchronous signal is f c When, use 4 xf c Obtaining a sampling value of the uplink synchronous signal at the sampling rate;
(5b) Carrying out demodulation processing on the pilot sequence signal;
(5c) Extracting a sampling value of a one-hop guide sequence signal as a frequency offset estimation sequence, and increasing the number of points of the frequency offset estimation sequence by adopting a zero-padding interpolation method to ensure that the number of points is not less than N fft ，Wherein, Δ f is the frequency offset estimation precision required by the system;
(5d) Performing FFT operation on the frequency offset estimation sequence;
(5e) Performing square sum operation on the imaginary part and the real part of the FFT operation result to obtain a power spectrum of the jump pilot sequence signal;
(5f) Searching the maximum value in the jump guide sequence signal power spectrum and the position k where the maximum value is located;
(5g) Using the position k of the maximum and the estimated frequency f e The frequency value is converted by the relation between the frequency value and the frequency offset value to obtain the frequency offset value of the hopping pilot sequence signal, and the relation is as follows:
(5h) And (5) repeating the steps (5 c) to (5 g) to obtain a multi-hop frequency offset estimation value, and averaging the multi-hop frequency offset estimation value to obtain an uplink frequency offset estimation value.
The reference station judges the effectiveness of the error of the frequency hopping clock by adopting a method of joint judgment of power value and unique code capture, namely: and after the unique code is successfully captured, judging whether the power estimation value is greater than a set threshold, if so, considering the frequency hopping clock error estimation value to be effective, otherwise, considering the frequency hopping clock error estimation value to be invalid.
Compared with the prior art, the invention has the following advantages:
(1) In the synchronous initial stage of the frequency hopping communication system, as a large frequency hopping clock error exists (the frequency hopping time between a reference station and a non-reference station is not consistent), the invention adopts a mode of combining multiple unique codes and station information to carry out acquisition and judgment on uplink synchronous signals, and solves the problems of low synchronous acquisition and low synchronous speed caused by the non-alignment of receiving and transmitting frequencies;
(2) The invention adopts a structure of multiple unique codes to overcome the problem that a plurality of user stations can carry out synchronization at the same time and the collision probability is higher when the synchronization is carried out in a competition mode, and correctly captures the synchronization signal;
(3) According to the invention, the guard interval is set in the frame structure of the uplink synchronous signal, so that interference to other users is avoided, and the capture probability is improved;
(4) The method adopts a square sum averaging mode to estimate the power, judges whether a signal appears according to the power value and the unique code capturing joint judgment, judges whether the signal appears according to the power estimation, if the power estimation value is smaller, the unique code capturing is successful, at the moment, the capturing condition is probably mistaken, the capturing is confirmed to be correct only if the power reaches a preset threshold and the unique code capturing is successful, the accuracy of synchronous capturing is improved, false synchronization is avoided, and the synchronization speed is improved;
(5) The invention adopts the FFT algorithm to carry out the grouping frequency offset estimation on the multi-hop guide sequence and then carries out the frequency offset estimation by an averaging method, thereby improving the accuracy of the frequency offset estimation and carrying out the frequency calibration on the synchronous signal.
Drawings
FIG. 1 is a flow chart of a fast synchronization method of a frequency hopping communication system of the present invention;
FIG. 2 is a schematic diagram illustrating a process of estimating and adjusting the frequency hopping clock error according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a power estimation and adjustment process according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a frequency offset estimation and adjustment process according to an embodiment of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and the specific embodiments.
Fig. 1 is a flow chart of a fast synchronization method of a frequency hopping communication system. As can be seen from the figure, the method comprises the following steps:
(1) And the reference station inserts time reference information into the downlink synchronous time slot and sends downlink synchronous signals to the non-reference station according to a preset frequency hopping pattern at the frequency with the concentrated synchronous frequency.
The time reference information is represented by a multi-bit binary number. If the time reference information is calculated for 1000 hops/second, corresponding to 1ms of time accuracy, and calculated for 30 years of operation, the time reference information is represented as a 40-bit binary number, (1000 × 3600 × 24 × 365 × 30=946080000000 =0xdcz46c 32800, corresponding to 40-bit binary data).
(2) The non-reference station captures a downlink synchronous signal with time reference information at a certain frequency of the synchronous frequency set, after the downlink synchronous signal is successfully captured, frequency offset estimation, time reference information extraction and link delay estimation are carried out on the downlink signal, the link delay can be obtained by dividing the distance between the reference station and the non-reference station by the speed of light, the non-reference station can obtain the longitude and latitude of the non-reference station through a GPS or a Beidou positioning system, and therefore the distance between the non-reference station and the reference station is determined according to the longitude and latitude.
(3) And the non-reference station calibrates the local time according to the received time reference information and the link delay estimated value, adjusts the frequency hopping clock to complete initial synchronization with the frequency hopping clock of the reference station, and corrects the uplink carrier frequency according to the downlink frequency offset estimation result.
And the uplink carrier frequency correction value is obtained by multiplying the ratio of the uplink frequency to the downlink frequency by the downlink frequency offset estimation value. For example: if the current transmission frequency is f, the downlink estimated frequency difference is Δ f, the uplink-downlink frequency ratio is ρ (for example, 2GHz downlink, 3GHz uplink, ρ =3GHz/2ghz = 1.5), and the adjusted transmission frequency is f + ρ × Δ f.
(4) The uplink synchronization signal of the non-reference station is sent to the reference station according to an uplink frequency hopping pattern, the uplink synchronization signal comprises 1 guard interval, X guide sequences, X unique codes and X station information, wherein the X station information of the same non-reference station is the same, the X unique codes are different from each other, the corresponding unique codes of different non-reference stations are the same, and X >1.
(5) The method comprises the steps that a reference station carries out frequency hopping clock error, power and frequency offset estimation on received uplink synchronous signals of each whole frame and analyzes station information of a non-reference station, frequency hopping clock error validity judgment is carried out, when the frequency hopping clock error is valid, the uplink frequency hopping clock error, the power value and the frequency offset information and the station information of the non-reference station are inserted into a downlink state time slot and sent to the non-reference station, otherwise, an invalid identifier and the station information of the non-reference station are inserted into the downlink state time slot and sent to the non-reference station, the frequency hopping clock error refers to the phase difference of time frequency hopping clocks of the non-reference station and the reference station, and the invalid identifier is 0xFF.
(6) The non-reference station analyzes the downlink state time slot to obtain station information, a frequency hopping clock error, frequency offset and power, judges whether the frequency hopping clock error of the station is effective or not, and if the frequency hopping clock error is effective, the step (7) is carried out; and if the frequency hopping clock error is invalid, adjusting the transmission time of the frequency hopping clock and the uplink synchronous time slot signal, sliding backwards for 1/4 frequency hopping clock period, and repeatedly executing the steps (4) to (6).
(7) The non-reference station judges whether the frequency hopping clock error is smaller than a preset threshold value, if so, the non-reference station switches to a synchronous tracking state, and executes the step (8); otherwise, correcting the sending time of the frequency hopping clock and the uplink synchronous time slot signal according to the frequency hopping clock error, and repeatedly executing the step (4) to the step (7).
(8) The non-reference station judges whether the frequency deviation is smaller than a preset frequency deviation threshold, if the frequency deviation is smaller than the threshold, the non-reference station enters a frequency tracking state, and the step (9) is executed; otherwise, correcting the sending frequency of the uplink synchronous signal according to the extracted uplink frequency offset, and repeatedly executing the step (4) to the step (8).
(9) The non-reference station judges whether the power value reaches a preset system required value, if so, the non-reference station enters a power holding state, and the steps (4) to (9) are repeated; otherwise, correcting the transmission level of the uplink synchronous signal according to the extracted uplink power, and repeatedly executing the step (4) to the step (9).
Table 1 shows a basic structure of an uplink signal frame of a fast synchronous frequency hopping communication system, where an uplink signal is a synchronization signal transmitted from a non-reference station to a reference station, and is composed of a synchronization slot (ranging slot), a control slot, and a service slot. See table below:
table 1 basic structure of uplink signal frame
The synchronous time slot is used for synchronizing and tracking the frequency hopping communication system and is specially used for signals of synchronous parameter estimation;
the control time slot is used for the transmission of control and signaling information of calling, network entering, network leaving and the like of a non-reference station (subscriber station);
the traffic time slot is used for communication between non-reference stations (subscriber stations), and each frame is composed of 1 or more traffic time slots, and each traffic time slot is the minimum unit used by a subscriber.
Table 2 shows a basic structure of a downlink signal frame of the fast synchronous frequency hopping communication system. The downlink signal is a signal transmitted from the reference station to the non-reference station. The downlink signal frame is composed of four parts of a synchronous time slot, a control time slot, a state time slot and a service time slot. See table below:
table 2 downlink signal frame basic structure
The reference station receives the synchronous time slot signal to estimate parameters such as frequency hopping clock error, power and frequency deviation of different users, and inserts the estimated value and the analyzed station information into a state information time slot in a downlink frame, wherein the station information of different non-reference stations is inconsistent, and the non-reference stations identify whether the group of parameter values is of the station according to the station information.
The basic structure of the uplink synchronization timeslot signal frame is shown in table 3 below:
TABLE 3 basic structure of uplink synchronous timeslot signal frame
a. Guard interval
In order to avoid this phenomenon, a certain time gap needs to be left as a guard time (i.e., a guard interval) when the frequency hopping communication system performs synchronization.
The guard interval is used for avoiding mutual interference of signals between stations, the time occupied by the guard interval is larger than the maximum link delay estimation error between the non-reference station and the reference station, and no signal is transmitted in the guard interval.
b. Boot sequence
The pilot sequence is used for assisting frequency offset estimation and is composed of a special sequence. In this embodiment, the leader sequence is a sequence of 48 length, which is "1" and "0" alternately arranged, and may be a "1010 \ 823010" sequence or a "0101 \ 823001" sequence. The method is used for frequency offset estimation of uplink synchronous signals, and the design advantages and disadvantages of the method can influence the precision of the frequency offset estimation, so that the synchronization speed and the synchronization effect are influenced.
c. Unique code 1-unique code X
The unique codes 1-X are used for frequency hopping clock error estimation (namely frequency hopping clock phase difference), and are the core of the whole frequency hopping communication system synchronization.
In order to ensure that the system can work normally, the length of the unique code in the synchronous signal is determined according to the demodulation threshold of the system, the unique codes used by different non-reference stations are the same, the unique codes 1-X in the synchronous time slot are different, and the self-correlation characteristic and the cross-correlation characteristic are better, so that the acquisition probability of the system can be improved, and the false alarm probability can be reduced.
Designs that employ multiple different unique codes have several advantages as follows:
(1) when the frequency hopping communication system is in an initial synchronization stage, after the non-reference station completes downlink synchronization, a clock error (namely, the receiving and transmitting synchronous frequency is not aligned) still exists between the frequency hopping clock and the frequency hopping clock of the reference station, and if only a mode of 1 unique code and station information is adopted, the missed detection probability is higher; by adopting a plurality of unique codes and station information, the synchronous capture probability can be effectively improved, namely the error estimation of the fast frequency hopping clock is realized;
(2) the ALOHA competition mode adopted by the frequency hopping communication system is synchronous, so that a plurality of user stations can be synchronized at the same time, the collision probability is high, the system synchronization is influenced, and the use of the whole system is influenced. By adopting a plurality of unique code structures, if collision occurs (namely, the frequency hopping clock between user stations has errors), the system only needs to capture more than 1 unique code to finish the error estimation of the frequency hopping clock, therefore, the influence on the system synchronization is little, and the system synchronization speed is improved.
(3) Assuming that the error rate of the baseband signal is P b The length of the unique code is G, the correlation threshold is Q, and the correct detection probability is P d If Y unique codes are captured successfully, the synchronous capture probability is P c The capture probability is increased by a factor of T.
The synchronization acquisition probability is improved by T times.
If: the error rate of the baseband signal is 0.12, the length of the unique code is 32, the threshold is more than 28, X is 4, Y is 1, a single unique code method is adopted, and the capture probability is P d =0.4544, the method of the invention for multiple unique codes has an acquisition probability P c =0.9921, the capture probability is significantly improved.
d. Station information
The station information is used for identifying different user stations, the used bit number is determined by the number of stations supported by the system and is coded.
Fig. 2 is a schematic diagram illustrating a process of estimating and adjusting an error of a frequency hopping clock, which is mainly implemented as follows:
the uplink frequency hopping clock error estimation of the frequency hopping communication system is realized mainly by searching the unique code of the uplink signal to determine the position (namely the frequency hopping clock phase) of the uplink signal in the frequency hopping signal, the reference station inserts the estimated frequency hopping clock error and other parameter information into the downlink state time slot and transmits the parameter information back to the non-reference station, and the non-reference station adjusts the frequency hopping clock phase according to the frequency hopping clock error.
The method comprises the steps that a reference station receives uplink synchronous signals, parallel correlation operation is carried out on unique codes 1-X and input signals to obtain X unique code correlation values, when Y unique code correlation values are larger than a preset threshold, the unique codes are considered to be successfully captured, frequency hopping clock errors are extracted from any one unique code correlator to serve as frequency hopping clock errors of the reference station, then the effectiveness of the frequency hopping clock error estimation value is judged according to a power estimation value, if the power estimation value is small and the unique codes are successfully captured, the situation of error capture is possible at the moment, the fact that the frequency hopping clock error estimation value is effective is confirmed only when the power is larger than the preset threshold and the unique codes are successfully captured, and otherwise, the frequency hopping clock error estimation value is considered to be invalid. Thus, the synchronization acquisition accuracy can be improved, false synchronization can be avoided, and the synchronization speed can be improved. When the frequency hopping clock error estimation value is effective, inserting the error into a downlink state time slot, sending the error to a non-reference station in the state time slot, extracting the frequency hopping clock error by the non-reference station and then judging, when the frequency hopping clock error is smaller than a preset threshold value, finishing uplink synchronous capture, entering a tracking state, performing frequency offset and power adjustment, and otherwise, continuously adjusting the sending time of an uplink signal.
In this embodiment, the number of symbols of the synchronization time slot after the guard interval is removed is 960, which is composed of 6 hops, each hop is 160 symbols, wherein the pilot sequence is 48 symbols, the unique code is 32 symbols, and the station information is 80 symbols (after coding), the correlation peak value of the unique code is on the 80 th symbol of each hop under complete synchronization, and at this time, the frequency hopping clock error is 0; if the correlation peak value of the unique code is on the 75 th symbol, the frequency hopping clock error is-5 at the moment; if the correlation peak of the unique code is on the 85 th symbol, the frequency hopping clock error is 5 at this time, and the system frequency hopping clock error threshold value takes 1/160 frequency hopping clock period.
Fig. 3 is a schematic diagram of a power estimation and adjustment process, in which the power estimation process includes 4 steps:
(3a) When the symbol rate of the uplink synchronous signal is f c When, use 4 xf c Sampling rate of, I, Q for up synchronous signalsSampling is carried out on the way to obtain I k And Q k ；
(3b) To I, pair k And Q k Is added to the square of to obtain a signal energy value P K Accumulating the energy values of 4N continuous signals, wherein N is the symbol number of the synchronous signals;
(3c) Averaging the IQ square sum accumulated value obtained by calculation in the step (3 b);
(3d) And (4) carrying out dB conversion on the average value obtained by calculation in the step (3 c) to obtain a power estimation value.
In this embodiment, the dB conversion is represented by 8 bits in a table lookup manner, the power accuracy is 0.1dB, and the range that can be represented is 25.6dB.
The method comprises the steps that a reference station carries out power estimation on an uplink signal, when a power value is larger than a set threshold, frequency hopping clock error estimation is effective, the power value is sent to a non-reference station in a downlink state time slot, the non-reference station carries out power adjustment on the uplink signal according to the power estimation value, when the power estimation value is consistent with system design power, namely the power value reaches a preset power value, the power adjustment is finished, a power maintaining state is entered, and closed-loop power control is achieved.
In this embodiment, when no signal is input, the estimated power value is 0dB, and therefore, the power threshold value for determining whether a signal is input is set to 5dB at the initial synchronization stage; after the frequency hopping clock error and the frequency offset are adjusted, the level required by the system work is 15dB, and the power threshold value is set to be 15dB at the moment.
Fig. 4 is a schematic diagram of a frequency offset estimation and adjustment process, which is mainly implemented as follows:
in this embodiment, after the frequency offset estimation is performed after the synchronization of the frequency hopping clock, the frequency offset estimation is performed on the bootstrap sequence signal of each hop, and then the frequency offset estimated by each hop signal is averaged, so as to improve the uplink frequency offset estimation accuracy, and the frequency offset estimation process is divided into 8 steps:
(5a) When the symbol rate of the uplink synchronous signal is f c When, use 4 xf c Obtaining a sampling value I of the uplink synchronous signal k And Q k ；
(5b) Performing demodulation processing on the pilot sequence signal, for example, performing square calculation on two paths of input I and Q respectively by using a demodulation processing method of a BPSK modulation mode;
(5c) Extracting a sampling value of a one-hop pilot sequence signal as a frequency offset estimation sequence, wherein when the system requires the frequency offset estimation precision to be delta f, the number of points of FFT operation is not less than N fft At the moment, the point number of the frequency offset estimation sequence is increased by adopting a zero-filling interpolation method, wherein
(5d) Performing FFT operation on the frequency offset estimation sequence to obtain a signal frequency spectrum of the guide sequence;
(5e) Performing square sum operation on the imaginary part and the real part of the FFT operation to obtain a power spectrum of the pilot sequence signal;
(5f) Searching the maximum value in the power spectrum and the position k where the maximum value is located;
(5g) Using the position k of the maximum and the estimated frequency f e The frequency value conversion is carried out by the relation between the following components:
(5h) And (5) repeating the steps (5 c) to (5 g) to obtain a multi-hop frequency offset estimation value, and averaging the multi-hop frequency offset estimation value to obtain an uplink frequency offset estimation value.
In this embodiment, the tolerable frequency offset for system operation is 2KHz, and therefore, in order to satisfy normal operation of the system, the frequency offset threshold is set to 1KHz. The pilot sequences used for frequency offset estimation are respectively sent in 6-hop signals and are divided into 6 groups in total, each group comprises 48 '101010' \ 8230 '. The' symbol is 192 sampling points after sampling, the number of FFT operation points is 256, 64 '0's are complemented, if the frequency offset is 30KHz at the moment, the frequency offset estimation is respectively 31KHz, 29KHz, 30KHz, 31KHz and 29KHz after 6 times of frequency offset estimation, and finally the frequency offset value is estimated to be 30KHz.
The invention is not described in detail and is within the knowledge of a person skilled in the art.
Claims (5)
1. A fast synchronization method of frequency hopping communication system is characterized by the following steps:
(1) The reference station sends a downlink synchronous signal to the non-reference station, wherein the downlink synchronous signal comprises time reference information;
(2) The non-reference station captures a downlink synchronous signal, after the downlink synchronous signal is successfully captured, frequency offset estimation is carried out on the downlink signal, time reference information is extracted, and link delay is estimated;
(3) The non-reference station calibrates local time according to the received time reference information and the link delay estimated value, adjusts the phase of a local frequency hopping clock to complete initial synchronization with a frequency hopping clock of the reference station, and corrects an uplink carrier frequency according to a downlink frequency offset estimation result;
(4) The non-reference station sends an uplink synchronous signal to the reference station, wherein the uplink synchronous signal comprises 1 guard interval, X guide sequences, X unique codes and X station information, the X station information of the same non-reference station is the same, the X unique codes are different from each other, the corresponding unique codes of different non-reference stations are the same, and X is greater than 1;
(5) The base station receives the uplink synchronous signal, carries out frequency hopping clock error, power and frequency offset estimation and analysis on the received whole frame uplink synchronous signal, carries out frequency hopping clock error validity judgment, inserts the estimated frequency hopping clock error, power value and frequency offset information and station information of the non-base station into a downlink state time slot to send to the non-base station when the frequency hopping clock error is valid, or inserts an invalid identifier and the station information of the non-base station into the downlink state time slot to send to the non-base station;
(6) Extracting effective uplink frequency hopping clock phase error, frequency offset, power and station information from the downlink state time slot by the non-reference station, and correcting the frequency hopping clock phase, frequency and power;
(7) And (5) circularly executing the step (4) to the step (6) until the phase error, the frequency deviation and the power of the frequency hopping clock meet the system requirements, and completing the synchronization of the frequency hopping communication system.
2. The fast synchronization method of the frequency hopping communication system according to claim 1, wherein the reference station receives an uplink synchronization signal, and the frequency hopping clock error estimation method comprises: and performing parallel correlation operation on the X local unique codes and the input signal to obtain X unique code correlation values, when the Y unique code correlation values are larger than a preset threshold, Y is larger than or equal to 1, the acquisition is considered to be successful, a frequency hopping clock error is extracted from any unique code correlation operation result and is used as the frequency hopping clock error of the reference station, otherwise, the acquisition is considered to be unsuccessful, and when waiting for the arrival of the next downlink synchronous signal frame, the frequency hopping clock error is estimated again.
3. The method of claim 1, wherein the power estimation performed by the reference station comprises:
(4a) When the symbol rate of the uplink synchronous signal is f c When, use 4 xf c Obtaining a sampling value I of the uplink synchronous signal k And Q k ；
(4b) To I, pair k And Q k Is added to the square of (c) to obtain a signal energy value P K Accumulating the energy values of 4N continuous signals, wherein N is the symbol number of the synchronous signals;
(4c) Averaging the IQ square sum accumulated value obtained by calculation in the step (4 b);
(4d) And (5) carrying out dB conversion on the average value obtained by calculation in the step (4 c) to obtain a power estimation value.
4. The method of claim 1, wherein the frequency offset estimation performed by the reference station comprises: firstly, performing frequency offset estimation on a signal in a pilot sequence of each hop in a synchronous time slot, and then averaging the frequency offset estimated by each hop of signal to obtain uplink frequency offset estimation, wherein the specific implementation process comprises the following steps:
(5a) When the symbol rate of the uplink synchronous signal is f c When, use 4 xf c Obtaining a sampling value of the uplink synchronous signal according to the sampling rate;
(5b) Carrying out demodulation processing on the pilot sequence signal;
(5c) Extracting a sampling value of a one-hop guide sequence signal as a frequency offset estimation sequence, and increasing the number of points of the frequency offset estimation sequence by adopting a zero-padding interpolation method to ensure that the number of points is not less than N fft ，Wherein, Δ f is the frequency offset estimation precision required by the system;
(5d) Performing FFT operation on the frequency offset estimation sequence;
(5e) Performing square sum operation on the imaginary part and the real part of the FFT operation result to obtain a power spectrum of the jump pilot sequence signal;
(5f) Searching the maximum value in the power spectrum of the jump guide sequence signal and the position k where the maximum value is located;
(5g) Using the position k of the maximum and the estimated frequency f e The frequency value is converted by the relation between the frequency value and the frequency offset value to obtain the frequency offset value of the hopping pilot sequence signal, and the relation is as follows:
(5h) And (5) repeating the steps (5 c) to (5 g) to obtain a multi-hop frequency offset estimation value, and averaging the multi-hop frequency offset estimation value to obtain an uplink frequency offset estimation value.
5. The method according to claim 1, wherein the reference station uses a power value and unique code acquisition joint decision method to determine the validity of the frequency hopping clock error, that is: and after the unique code is successfully captured, judging whether the power estimation value is greater than a set threshold, if so, considering that the frequency hopping clock error estimation value is effective, otherwise, considering that the frequency hopping clock error estimation value is ineffective.
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| CN113489511B (en) * | 2021-08-02 | 2022-10-21 | 福建友通实业有限公司 | Wireless frequency hopping networking method based on time slice rotation scheduling |
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