阅读说明：本技术 一种蓝牙接收机coded模式下的高灵敏度接收方法 (High-sensitivity receiving method in coded mode of Bluetooth receiver ) 是由 刘德良 于 2021-09-07 设计创作，主要内容包括：本发明公开了一种蓝牙接收机coded模式下的高灵敏度接收方法,在同步捕获阶段,利用帧头格式中信号重复的特点检测到帧头,经过两次频偏估计获得总的频偏估计值,并确定随后的接入码位置；在同步跟踪阶段,利用蓝牙信号采用GMSK恒包络调制的特性,基于信号发送的伪随机特性提出了一种频偏跟踪环路进行残留频偏的跟踪,最终使接收机能够正确地对频偏进行补偿,从而使得接收机可以采用准相干解调来提高GMSK信号的解调性能。本发明可以在大频偏、低信噪比的场景下实现信号的同步捕获,即使信噪比低至0dB,也可以获得正确的频偏估计值和抽样位置估计值,并且在捕获到信号后,可以不断跟踪信号频率,为信号的解调奠定基础。(The invention discloses a high-sensitivity receiving method under a coded mode of a Bluetooth receiver, which comprises the steps of detecting a frame header by utilizing the characteristic of signal repetition in a frame header format in a synchronous capturing stage, obtaining a total frequency deviation estimated value through two times of frequency deviation estimation, and determining the position of a subsequent access code; in the synchronous tracking stage, a frequency offset tracking loop is provided for tracking residual frequency offset based on the pseudo-random characteristic of signal transmission by utilizing the characteristic that a Bluetooth signal adopts GMSK constant envelope modulation, and finally a receiver can correctly compensate the frequency offset, so that the receiver can improve the demodulation performance of the GMSK signal by adopting quasi-coherent demodulation. The invention can realize the synchronous capture of signals under the scenes of large frequency deviation and low signal-to-noise ratio, can obtain correct frequency deviation estimation value and sampling position estimation value even if the signal-to-noise ratio is as low as 0dB, and can continuously track the signal frequency after capturing the signals, thereby laying a foundation for the demodulation of the signals.)

1. A high-sensitivity receiving method under a coded mode of a Bluetooth receiver is characterized by comprising the following steps:

step one, sampling a received signal, detecting a frame header in a differential operation mode, and obtaining a differential summation operation result of a sampling point；

Setting the total frequency deviation estimated value asEstablishingThe composition of (A):

（1）

wherein the content of the first and second substances,t is the symbol transmission period, j may take the values-1, 0, + 1;

step three, respectively assuming that j takes the values of-1, 0 and +1, and performing frequency offset compensation on the received signal to obtain three frequency offset compensation results; construction of local training sequences，And Ts is the sampling period,represents a transmitted signal; performing correlation operation on the local training sequence and the three frequency offset compensation results respectively, taking a j value of the frequency offset compensation result corresponding to the maximum correlation value, and bringing the j value into the formula (1) to obtain a total frequency offset estimation value;

step four, determining the initial position of the access code;

and fifthly, performing frequency compensation on the received signal by using the total frequency offset estimation value obtained in the third step, performing error detection on the frequency-compensated signal to obtain a residual frequency offset estimation value, accumulating the residual frequency offset estimation value and the total frequency offset estimation value after filtering by a loop filter, updating the total frequency offset estimation value, performing frequency compensation by using the updated total frequency offset estimation value, and demodulating the frequency-compensated signal by using a quasi-coherent demodulation method.

2. The method for receiving with high sensitivity in coded mode of bluetooth receiver according to claim 1, wherein the method for detecting the frame header in the first step comprises:

let the transmitted signal be represented asThe received signal is represented asWhereinIs an additive white gaussian noise, and is,for frequency offset of both sides of the transceiver, setting the transmission period of the code element as T, the sampling number of each code element transmission period as L, and the sampling interval as Ts = T/L, calculating:

(2)

(3)

representing the result of a difference operation between two samples separated by a time of 8T,as an intermediate parameter, the parameter is,representing the number of samples participating in the difference operation, and defining the detection index as，

(4)

When the detection index exceeds the thresholdWhen the received signal contains frame head signal, recording the first time exceeding threshold。

3. The method for receiving high sensitivity data in coded mode of bluetooth receiver according to claim 2, wherein in step three, the method for calculating the frequency offset compensation result according to the hypothesis is:

respectively assuming that j takes the values of +1, -1 and 0, constructing a sequence with the length of K，

(5)

Wherein the content of the first and second substances,，

respectively using the sequencesAnd the following operation is carried out with the received signal:

(6)

respectively assuming a frequency offset of、Andand then performing frequency offset compensation.

4. The method as claimed in claim 3, wherein in step three, the correlation operations are performed by setting the phases to be、And 0, the values of the corresponding elements are selected from the setWhile the elements with the phase at the other values are forced to be zero,is taken fromThen the following correlation operations are carried out:

(7)

in thatSearching for the maximum correlation value in equation (7) within the range,the frequency offset compensation value corresponding to the maximum correlation value is the correct frequency offset estimation value.

5. The method for receiving with high sensitivity in coded mode of bluetooth receiver according to any of claims 1 to 4, characterized in that, in the fourth step, according to the approximate position of the frame header, the position of the access code is determined by using the anti-interference high precision signal synchronization method based on the access code, so as to complete the signal synchronization acquisition.

6. The high-sensitivity receiving method in coded mode of bluetooth receiver according to any of claims 1 to 4, wherein in step five, the method for obtaining the estimated value of residual frequency offset by error detection is:

let the phase of the modulated Bluetooth signal be represented as ，The phase of the received signal is represented asResidual frequency deviation ofThe residual frequency offset estimation value is，

（8）

Wherein the content of the first and second substances,is the first of transmissionnA code element, which takes the value of +1 or-1;his a modulation index, and the value of the modulation index is 0.5;the response of a rectangular pulse with the length of a code element period through a Gaussian filter is satisfied；

NT represents the integration time length, the value of NT is calculated from equation (9),

（9）

neglecting the effect of noise, there are:

（10）

estimated from equations (9) and (10):

（11）

calculating a residual frequency offset estimation valueI.e. the result of the error detection.

7. The method of claim 6, wherein if the samples of the received signal are oversampled, then formula (11) is calculated by summing instead.

8. The method for receiving with high sensitivity in coded mode of a bluetooth receiver according to any of claims 1 to 4, wherein the loop filter is a first or second order loop filter.

9. The high-sensitivity receiving method in coded mode of bluetooth receiver according to any of claims 1 to 4, characterized in that in step five, the signal after frequency compensation is demodulated by using decision-based 1-bit differential demodulation or by using quasi-coherent demodulation based on source decomposition.

10. A bluetooth receiver comprising a processor, a memory and a software program stored in the memory and executable by the processor, the software program when executed by the processor being operable to implement a method of high sensitivity reception in coded mode of the bluetooth receiver as claimed in any one of claims 1 to 9.

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to a high-sensitivity receiving method in a coded mode of a Bluetooth receiver.

Background

Compared with the unicoded mode, the bluetooth 5.0 coded mode is an extended transmission distance, and formats of a Preamble (hereinafter, referred to as a frame header) part and a PDU part are modified. The Preamble part consists of 10 repeated symbol sequences of '00111100', and the PDU part is added with error correction coding with code rate of 1/8 or 1/2. For this reason, a receiving method different from the unicoded mode is required to improve the sensitivity of the receiver and extend the communication distance. How to solve the problem that the sensitivity of a receiver is influenced by the strength reduction of a distance extension receiving signal and the reduction of a signal-to-noise ratio under the condition of the same transmitting power is a technical difficulty faced by a Bluetooth 5.0 coded mode.

Disclosure of Invention

The purpose of the invention is as follows: in order to solve the problem that the sensitivity of a Bluetooth receiver in a 5.0 coded mode is poor in the prior art, the invention provides a high-sensitivity receiving method in the coded mode of the Bluetooth receiver.

The technical scheme is as follows: a high-sensitivity receiving method under a coded mode of a Bluetooth receiver comprises the following steps:

step one, sampling a received signal, detecting a frame header in a differential operation mode, and obtaining a differential summation operation result of a sampling point；

Setting the total frequency deviation estimated value asEstablishingThe composition of (A):

（1）

wherein the content of the first and second substances,t is the symbol transmission period, j may take the values-1, 0, + 1;

step three, respectively assuming that j takes the values of-1, 0 and +1, and performing frequency offset compensation on the received signal to obtain three frequency offset compensation results; construction of local training sequences，And Ts is the sampling period,represents a transmitted signal; performing correlation operation on the local training sequence and the three frequency offset compensation results respectively, taking a j value of the frequency offset compensation result corresponding to the maximum correlation value, and bringing the j value into the formula (1) to obtain a total frequency offset estimation value;

step four, determining the initial position of the access code;

and fifthly, performing frequency compensation on the received signal by using the total frequency offset estimation value obtained in the third step, performing error detection on the frequency-compensated signal to obtain a residual frequency offset estimation value, accumulating the residual frequency offset estimation value and the total frequency offset estimation value after filtering by a loop filter, updating the total frequency offset estimation value, performing frequency compensation by using the updated total frequency offset estimation value, and demodulating the frequency-compensated signal by using a quasi-coherent demodulation method.

Further, the method for detecting the frame header in the first step comprises the following steps:

let the transmitted signal be represented asThe received signal is represented asWhereinIs an additive white gaussian noise, and is,for frequency offset of both sides of the transceiver, setting the transmission period of the code element as T, the sampling number of each code element transmission period as L, and the sampling interval as Ts = T/L, calculating:

(2)

(3)

representing the result of a difference operation between two samples separated by a time of 8T,as an intermediate parameter, the parameter is,representing the number of samples participating in the difference operation, and defining the detection index as，

(4)

When the detection index exceeds the thresholdWhen the received signal contains frame head signal, recording the first time exceeding threshold。

Further, in step three, the method for calculating the frequency offset compensation result according to the assumption is as follows:

respectively assuming that j takes the values of +1, -1 and 0, constructing a sequence with the length of K，

(5)

Wherein the content of the first and second substances,，

respectively using the sequencesAnd the following operation is carried out with the received signal:

(6)

respectively assuming a frequency offset of、Andand then performing frequency offset compensation.

Further, in step three, the phases of the correlation operations are respectively set to be、And 0, the values of the corresponding elements are selected from the setWhile the elements with the phase at the other values are forced to be zero,is taken fromThen the following correlation operations are carried out:

(7)

in thatSearching for the maximum correlation value in equation (7) within the range,the frequency offset compensation value corresponding to the maximum correlation value is the correct frequency offset estimation value.

And further, determining the position of the access code by adopting an anti-interference high-precision signal synchronization method based on the access code according to the approximate position of the frame header to finish signal synchronization acquisition.

Further, in step five, the method for obtaining the residual frequency offset estimation value through error detection comprises:

let the phase of the modulated Bluetooth signal be represented as ，The phase of the received signal is represented asResidual frequency deviation ofThe residual frequency offset estimation value is，

（8）

Wherein the content of the first and second substances,is the first of transmissionnA code element, which takes the value of +1 or-1;his a modulation index, and the value of the modulation index is 0.5;the response of a rectangular pulse with the length of a code element period through a Gaussian filter is satisfied；

NT represents the integration time length, the value of NT is calculated from equation (9),

（9）

neglecting the effect of noise, there are:

（10）

estimated from equations (9) and (10):

（11）

calculating a residual frequency offset estimation valueI.e. the result of the error detection.

Further, if the samples of the received signal are oversampled, then the summation is used in the calculation of equation (11).

Further, the loop filter employs a first or second order loop filter.

Further, in step five, the signal after frequency compensation is demodulated by adopting a 1-bit differential demodulation method based on decision or a quasi-coherent demodulation method based on source decomposition.

A bluetooth receiver comprising a processor, a memory and a software program stored in the memory and executable by the processor, the software program when executed by the processor enabling a high sensitivity receiving method in coded mode of the bluetooth receiver as described above.

Has the advantages that: compared with the prior art, the invention can realize the synchronous capture of signals under the scenes of large frequency deviation and low signal to noise ratio, can obtain correct frequency deviation estimated values and sampling position estimated values even if the signal to noise ratio is as low as 0dB, and greatly reduces the operation complexity under the condition of correctly estimating the frequency deviation value. And after capturing the signal, a frequency offset tracking loop is provided for tracking residual frequency offset based on the pseudorandom characteristic of signal transmission, the signal frequency can be tracked at any time, so that the influence of frequency offset on the demodulation of the Bluetooth GMSK signal is reduced as much as possible, a foundation is laid for the demodulation of the signal, and a receiver can improve the demodulation performance of the GMSK signal by adopting quasi-coherent demodulation.

Drawings

FIG. 1 is a graph of timing synchronization performance affected by signal-to-noise ratio;

FIG. 2 shows a timing offset with a signal-to-noise ratio of 0 dB;

FIG. 3 is a graph of the performance of frequency offset estimation affected by signal-to-noise ratio;

FIG. 4 is a schematic flow chart of the method of the present invention.

Detailed Description

The invention is further explained below with reference to the figures and the specific embodiments.

A Bluetooth receiver includes a processor, a memory, and a software program stored in the memory and executable by the processor, and when the software program is executed by the processor, a high-sensitivity receiving method in a coded mode of the Bluetooth receiver described below can be realized.

The high-sensitivity receiving method in the coded mode of the bluetooth receiver, as shown in fig. 4, includes the following steps:

step one, sampling the received signal, because the frame header part is composed of 10 repeated symbol sequences of '00111100', the regular repetition of the frame header part can be utilized to detect the signal, so that the receiver can detect the information of the frame header part in the received signal. In the process of detecting the frame head, a sampling point differential summation operation junction can be obtainedFruit；

The method for detecting the frame header by the differential operation mode comprises the following steps:

let the transmitted signal be represented asSymbol period ofThen, then. Assuming that it is only affected by white noise, the received signal is represented asWhereinIs an additive white gaussian noise, and is,are frequency offsets of both the transmitting and receiving sides. Assuming that a symbol transmission period is T, the number of samples per symbol transmission period is L, and a sampling interval is Ts = T/L, the following is calculated:

(1)

(2)

whereinPresentation pairTaking conjugationAs a result of (a) the process of (b),representing the result of a difference operation between two samples separated by a time of 8T,representing the number of samples participating in the difference operation,for the intermediate parameter, defining the detection index as，

(3)

When detecting the indexExceeds a predetermined thresholdWhen the frame header signal is included in the received signal, the received signal is considered to contain the frame header signal. Recording the moment when the threshold is exceeded for the first time。

If the influence of noise is ignored due to the signal repeatability of the frame header part, it is assumed thatThe time is the time corresponding to the first sample value of the frame header part, namely the signal detection achieves the complete accuracy of the position, and the formula (1) can be simplified into

(4)

The step detects the frame head and obtains the result of sampling point difference summationAnd the frequency offset is used for the next frequency offset estimation.

Step two, considering phase ambiguity, if frequency deviationThen its estimated valueT is the symbol transmission period, otherwise. Order to，Then:

（5）

wherein the content of the first and second substances,，given the maximum frequency offset specification in the protocol, j may take the value-1, 0, or + 1. The value of j needs to be estimated next.

Step three, respectively assuming j to take the values of +1, 0 and-1, and constructing a sequence with the length of K，

(6)

Wherein the content of the first and second substances,. Obviously, the above sequences assume frequency offsets of、And。

then using the above sequences separatelyAnd the following operation is carried out with the received signal:

(7)

respectively assuming a frequency offset of、Andand then performing frequency offset compensation.

After three frequency offset compensation results are obtained, a local training sequence is constructed，And Ts is the sampling period,represents a transmitted signal; performing correlation operation on the local training sequence and the three frequency offset compensation results respectively, taking a j value of the frequency offset compensation result corresponding to the maximum correlation value, and bringing the j value into the formula (5) to obtain a total frequency offset estimation value;

because the sending signal of the bluetooth adopts a GMSK constant envelope modulation mode, the sequence constructed by the formula (7) is a complex value sequence, and the correlation operation can bring greater complexity. For this purpose, only phase approximations in the sequence may be taken、And 0 elements, respectively, having phases of、And 0, the values of the corresponding elements are selected from the setWhile elements with other values of phase are forced to zero. At this point in time,is taken fromSelecting. The following correlation is then performed:

(8)

although the position of the frame header is roughly found by means of detection in the step oneHowever, since the position is not exact, it is necessary to perform correlation operation in a certain range, for example, to limit a rangeSearching for the maximum correlation value in equation (8) within the range,the frequency offset compensation value corresponding to the maximum correlation value is the correct frequency offset estimation value. For example, in the present embodiment,if the maximum correlation value occurs, the total frequency offset estimation value is. The position at which the correlation peak occurs is recorded simultaneously as。

Step four, obtaining correct estimated value through step threeNext, the correct signal sampling location needs to be obtained, and the approximate location has been obtained in the context of the determination of the total frequency offset estimateFurther searching for more accurate locations is needed. Since the bluetooth communication protocol sends the access code after the frame header, the access code is known to both the transceiver and the access code has better randomness. Therefore, can be based on another patent of the present applicantPatent 2020111383050 entitled "anti-interference high-precision signal synchronization method based on access code in bluetooth receiver" uses access code to realize the search of the start and stop positions of the access code precisely, and realizes the synchronous capture of signals, thereby making full preparation for the following signal demodulation.

Fig. 1 shows the performance of timing synchronization under various signal-to-noise ratio conditions when the method is used for signal synchronization acquisition. Even with a signal-to-noise ratio as low as 0dB, the probability of false synchronization (missed synchronization and false synchronization) is only 3%. FIG. 2 shows the oversampling factorLThe distribution of timing deviation is shown in the case of 8. At a signal-to-noise ratio of 0dB, the vast majority of timing skew is controlled within two samples. Fig. 3 shows the performance of frequency offset estimation under various signal-to-noise ratios, and the vertical axis of the coordinate axis shows the root mean square error normalized with respect to the symbol rate. It can be seen that the root mean square error of the frequency offset estimation is basically controlled to be 2kWithin Hz.

Step five, from the above steps, the synchronous acquisition of the signal is realized, but from the view of the Bluetooth protocol, the maximum frequency drift rate of the Bluetooth signal in the transmission process can reach. Therefore, it is necessary to continuously track the frequency offset to reduce the influence of the frequency offset on the demodulation of the bluetooth GMSK signal as much as possible. To this end, a tracking method of a frequency offset tracking loop is provided.

And C, performing frequency compensation on the received signal by using the total frequency offset estimation value obtained in the step three, wherein certain residual frequency offset exists in the received signal after frequency offset compensation, and performing error detection on the signal after frequency compensation to obtain a residual frequency offset estimation valueResidual frequency offset estimationObtaining more accurate residual frequency offset estimation value through loop filter。

Specific acquisitionThe method comprises the following steps: let the phase of the modulated Bluetooth signal be represented asThe phase of the received signal isResidual frequency deviation ofThe residual frequency offset estimation value is

（9）

Wherein the content of the first and second substances,is the first of transmissionnA code element, which takes the value of +1 or-1;his a modulation index, and the value of the modulation index is 0.5;the response of a rectangular pulse with the length of a code element period through a Gaussian filter is satisfied；

Due to the fact thatIs a random + 1-1 sequence, therefore, based on the pseudo-random characteristic of Bluetooth signal transmission, the pair can be considered to be transmitted within a period of timeResult of integrationLet NT denote the integration time length, the value of NT is calculated from equation (10),

（10）

the receiving end ignores the influence of noise due to the existence of frequency offset, and then:

（11）

thus corresponding integration resultWhereinIndicating the residual frequency offset, i.e. the tracking error in the tracking phase.

Further calculating residual frequency deviation estimated value，

（12）。

If the samples of the received signal are oversampled, then the calculation of equation (12) may be replaced by a summation.

Residual frequency deviation estimated value detected by errorSending the signal into a loop filter to eliminate the influence of noise as much as possible and obtain a more accurate estimated value. The loop filter may employ a first or second order loop filter.

Residual frequency offset estimation valueFrequency offset estimation from previous timeAccumulating to obtain the frequency deviation estimated value of the current timeUsing updatedThe frequency compensation is carried out, demodulation can be carried out after the frequency offset compensation, and a 1-bit differential demodulation method based on judgment or a quasi-coherent demodulation method based on source decomposition and the like can be adopted for the demodulation of the GMSK signal.