Bluetooth signal frequency offset estimation method and device based on reconstructed GFSK differential phase

Abstract

The invention discloses a frequency offset estimation method of a Bluetooth signal based on a reconstructed GFSK (Gaussian Frequency Shift Keying) differential phase. A Bluetooth receiver solves an actual differential phase on each sampling point of each Bluetooth symbol of a synchronization word or an access address in a Bluetooth receive signal and reconstructs a reference differential phase of each Bluetooth symbol of a synchronization word or an access address in a Bluetooth receive signal based on and calculates an initial of a Bluetooth receive signal and performing initial frequency offset compensation on the initial frequency offset estimation value. And the Bluetooth receiving end tracks the residual frequency offset of the Bluetooth receiving signal after the initial frequency offset compensation. According to the method, the frequency offset estimation precision can be effectively improved, the operand is greatly simplified, and the implementation complexity is reduced.

Description

Technical Field

[0001] The present application relates to a method for estimating frequency deviation of a Bluetooth signal. Background Art

[0002] In Bluetooth transmission systems, due to factors such as frequency deviation between the local crystal oscillator and the transmitter, as well as multipath effects, the received Bluetooth signal may exhibit significant frequency offset, significantly impacting Bluetooth demodulation performance. To address this issue, it is necessary to perform an initial frequency offset estimation of the Bluetooth signal and track the residual frequency offset during subsequent data processing. Both of these steps are considered part of the Bluetooth signal frequency offset estimation method.

[0003] An existing method for estimating the frequency offset of Bluetooth signals is to analyze the characteristics of the Bluetooth received signal. This method typically estimates the frequency offset based on the maximum and minimum values ​​of the differential phase. This method uses the transition rules between bits 0 and 1, as well as the signal characteristics of single and continuous bits, to determine the effective maximum and minimum values ​​and then average them to eliminate the effects of frequency offset. This method is described in detail in Liu Jia's 2018 Master of Engineering thesis, "Research and Design of Bluetooth Low Energy Digital Baseband Transceiver Circuits."

[0004] Another existing method for estimating the frequency offset of Bluetooth signals uses a correlation-based estimation algorithm to perform a correlation search among multiple possible frequency offset values ​​and select the frequency offset closest to the true differential phase as the current frequency offset estimate. This method is described in detail in the Chinese invention patent application "A Bluetooth Signal Frequency Offset Selection Method, Device, and Storage Medium," published on February 18, 2022, with application publication number CN114071442A.

[0005] The above two frequency offset estimation methods for Bluetooth signals both have the disadvantages of being complex to implement and consuming a lot of resources. Summary of the Invention

[0006] The technical problem to be solved by this application is: how to reduce the implementation complexity of frequency offset estimation of Bluetooth signals.

[0007] In order to solve the above technical problems, the present application proposes a frequency deviation estimation method for Bluetooth signals based on reconstructing GFSK differential phase, which includes the following steps. Step S1: The Bluetooth receiving end performs Bluetooth frame synchronization, and the Bluetooth receiving end finds the position of the synchronization word or access address in the data packet of the Bluetooth receiving signal. Step S2: The Bluetooth receiving end solves the phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal, and differentiates the phase to obtain the actual differential phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal. Step S3: The Bluetooth receiving end reconstructs the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal Step S3 and step S2 may be performed either before or simultaneously. Step S4: The Bluetooth receiving end uses the actual differential phase of each sampling point of each Bluetooth symbol of the Bluetooth received signal And the reference differential phase of each Bluetooth symbol of the reconstructed Bluetooth signal The DC component of the Bluetooth received signal is calculated, and the relationship between the frequency offset and the DC component is used to calculate an initial frequency offset estimate of the Bluetooth received signal. The Bluetooth receiving end performs initial frequency offset compensation on the I and Q signals of the Bluetooth received signal based on the initial frequency offset estimate. Step S5: The Bluetooth receiving end tracks the residual frequency offset of the Bluetooth received signal after the initial frequency offset compensation. For the first m-1 bits to be demodulated in the payload portion of the Bluetooth received signal, decision feedback equalization is directly performed to decode the decided bits. For the mth and subsequent bits to be demodulated in the payload portion of the Bluetooth received signal, the actual differential phase is calculated based on the decided bits in the payload portion of the Bluetooth received signal, the reference differential phase is reconstructed, the residual DC component is calculated and compensated, and the decided bits are decoded.

[0008] Furthermore, in step S3, for classic Bluetooth technology, the Bluetooth receiving end reconstructs the reference differential phase of each Bluetooth symbol of the synchronization word; for low-power Bluetooth technology, the Bluetooth receiving end reconstructs the reference differential phase of each Bluetooth symbol of the access address.

[0009] Furthermore, in step S3, the reference differential phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal is reconstructed. Then the reference differential phase of all sampling points within a Bluetooth symbol is calculated. Accumulate and get the reference differential phase of the Bluetooth symbol

[0010] Furthermore, in step S3, the Bluetooth receiving end reconstructs the reference differential phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal. Among them, T S represents the sampling time; h represents the modulation index; a(n) represents the original bit of the Bluetooth signal, which takes a value of 0 or 1; b(n) represents the data after a(n) is mapped through binary phase shift keying (BPSK), which takes a value of -1 or 1; n represents the index or subscript of each bit of the Bluetooth signal; g(t) represents a Gaussian shaped pulse, and g(t) shifted by nT on the time axis is g(t-nT); T represents the Bluetooth symbol time.

[0011] Furthermore, in step S3, when three adjacent original bits am-1 ,a m ,a m+1 When the value of is 000, the middle bit a of the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 001, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 010, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 011, the middle bit a of the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 100, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 101, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 110, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 111, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point in, ln represents the natural logarithm function; B is the 3dB bandwidth of the Gaussian filter; erf() represents the error function; and t represents the time corresponding to each sampling point.

[0012] Furthermore, in step S3, the reference differential phase of each value corresponding to a Bluetooth symbol is The values ​​of the Bluetooth receive signal are made into a table, and the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receive signal is obtained by looking up the table. The numerical value of .

[0013] Furthermore, in step S4, the calculation formula of the DC component is Where L is the number of bits used to calculate the initial frequency offset; N is the number of sampling points in a Bluetooth symbol. The calculation formula for the initial frequency offset estimate is Among them, T S Indicates the sampling time.

[0014] Furthermore, in step S5, the process of tracking the residual frequency offset for the mth and subsequent bits to be demodulated in the payload portion of the Bluetooth received signal includes the following sub-steps: Step S51: The Bluetooth receiving end calculates the actual differential phase at each sampling point of the judged bit in the payload portion of the Bluetooth received signal. Step S52: The Bluetooth receiving end reconstructs the reference differential phase of the judged bits of the payload part of the Bluetooth received signal Step S52 and step S51 are either performed before or simultaneously. Step S53: The Bluetooth receiving end uses the actual differential phase at each sampling point of the judged bit in the payload part of the Bluetooth received signal and the reference differential phase of the judged bits of the payload portion of the reconstructed Bluetooth received signal Calculate the residual DC component DC' of the current bit to be demodulated in the payload portion of the Bluetooth received signal. Step S54: The Bluetooth receiving end performs a Kalman filter on the residual DC component DC' of the current bit to be demodulated in the payload portion of the Bluetooth received signal. Step S55: The Bluetooth receiving end indirectly eliminates the residual frequency offset based on the residual DC component DC" of the current bit to be demodulated in the payload portion of the Bluetooth received signal after Kalman filtering, and then uses decision feedback equalization to decode the bit to be demodulated.

[0015] Furthermore, in step S51 and step S52, the number of judged bits in the payload part of the Bluetooth received signal used to track the residual frequency deviation is L', and the actual differential phase and the reconstructed reference differential phase are calculated using the L' judged bits immediately preceding the bit to be demodulated.

[0016] The present application also proposes a frequency offset estimation device for a Bluetooth signal based on reconstructed GFSK differential phase, comprising a Bluetooth frame synchronization unit, an actual differential phase calculation unit, a reference differential phase reconstruction unit, an initial frequency offset estimation unit, and a residual frequency offset tracking unit. The Bluetooth frame synchronization unit is used to perform Bluetooth frame synchronization, allowing the Bluetooth receiving end to find the position of the synchronization word or access address in the data packet of the Bluetooth received signal. The actual differential phase calculation unit is used to solve the phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal, and to differentiate the phase to obtain the actual differential phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal. The reference differential phase reconstruction unit is used to reconstruct the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal. The initial frequency offset estimation unit is configured to use the actual differential phase at each sampling point of each Bluetooth symbol of the Bluetooth received signal And the reference differential phase of each Bluetooth symbol of the reconstructed Bluetooth signal The DC component of the Bluetooth received signal is calculated, and the relationship between the frequency offset and the DC component is used to calculate the initial frequency offset estimate of the Bluetooth received signal. The initial frequency offset compensation is performed on the Bluetooth received signal based on the initial frequency offset estimate. The residual frequency offset tracking unit is used to estimate and compensate for the residual frequency offset of the Bluetooth received signal after the initial frequency offset compensation. For the first m-1 bits to be demodulated in the payload portion of the Bluetooth received signal, decision feedback equalization is directly performed to decode the decided bits. For the mth and subsequent bits to be demodulated in the payload portion of the Bluetooth received signal, the actual differential phase is calculated based on the decided bits in the payload portion of the Bluetooth received signal, the reference differential phase is reconstructed, and the residual DC component is calculated and compensated to obtain the decided bits.

[0017] The technical effect achieved by this application is: it can effectively improve the frequency offset estimation accuracy, while greatly simplifying the amount of calculation and reducing the implementation complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of the Bluetooth signal frequency offset estimation method based on reconstructed GFSK differential phase proposed in this application.

[0019] Figure 2 yes Figure 1 FIG. 1 is a flow chart of a process for tracking the residual frequency offset of the mth bit to be demodulated (m≥5) in the payload part of the Bluetooth received signal in step S5.

[0020] Figure 3 This is a structural diagram of a Bluetooth signal frequency offset estimation device based on reconstructed GFSK differential phase proposed in this application.

[0021] Explanation of the reference numerals in the figure: Bluetooth frame synchronization unit 1, actual differential phase calculation unit 2, reference differential phase reconstruction unit 3, initial frequency offset estimation unit 4, residual frequency offset tracking unit 5. DETAILED DESCRIPTION

[0022] Bluetooth technology is divided into two categories: classic Bluetooth and Bluetooth Low Energy. Classic Bluetooth has two types: basic rate (BR) and enhanced data rate (EDR). Classic Bluetooth data packets contain an access code, which in turn contains a 64-bit synchronization word. BR-type classic Bluetooth uses GFSK (Gaussian frequency shift keying) as the modulation method. EDR-type classic Bluetooth uses GFSK as the modulation method for the synchronization word and π / 4DQPSK (π / 4 differential quadrature phase shift keying) or 8DPSK (8 differential phase shift keying) as the modulation method for the payload. Bluetooth Low Energy has three physical layer (PHY) types: LE 1M PHY, LE 2M PHY, and LE Coded PHY, all using GFSK as the modulation method. Bluetooth Low Energy data packets contain a 32-bit access address.

[0023] The frequency offset estimation method for Bluetooth signals proposed in this application is applicable to: initial frequency offset estimation of the synchronization word portion of BR type classic Bluetooth, EDR type classic Bluetooth, LE 1M PHY type low-power Bluetooth, and LE 2MPHY type low-power Bluetooth. A Bluetooth symbol refers to the smallest unit of a Bluetooth analog signal, while a bit represents the smallest unit of digital information. In the applicable scenarios of this application, one Bluetooth symbol corresponds to one bit.

[0024] This application does not apply to the payload portion of EDR-type Classic Bluetooth. LE Coded PHY-type Low Energy Bluetooth has a simpler initial frequency offset estimation method, so this application is not required. In theory, LE Coded PHY-type Low Energy Bluetooth can also use this application, in which case the Bluetooth symbol used to reconstruct the reference differential phase corresponds to a single encoded bit.

[0025] See also Figure 1The method for estimating the frequency offset of a Bluetooth signal based on reconstructing the GFSK differential phase proposed in this application includes the following steps. If a frequency offset exists between the Bluetooth receiver and transmitter, this is manifested as a DC offset in the GFSK-modulated differential phase signal. Therefore, frequency offset estimation of a GFSK-modulated signal by the Bluetooth receiver can be simply understood as calculating the DC component (DC) of the GFSK-demodulated Bluetooth received signal.

[0026] Step S1: The Bluetooth receiving end performs Bluetooth frame synchronization. Bluetooth frame synchronization means that in Bluetooth communication, the Bluetooth receiving end correctly finds the location of the synchronization word or access address in the data packet of the Bluetooth received signal. For classic Bluetooth technology, the Bluetooth receiving end finds the location of the synchronization word. For low-power Bluetooth technology, the Bluetooth receiving end finds the location of the access address. Each bit of the synchronization word or access address in the Bluetooth received signal is known. The Bluetooth frame synchronization process does not require high frequency offset estimation accuracy, so the preamble in the Bluetooth received signal can be used for simple frequency offset estimation. The frequency offset estimation in this step belongs to the prior art and does not belong to the frequency offset estimation of Bluetooth signals based on reconstructed GFSK differential phase proposed in this application.

[0027] Step S2: The Bluetooth receiving end uses the CORDIC (coordinate rotation digital computer) algorithm to solve the phase of each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal, and differentiates the phase to obtain the actual differential phase of each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal.

[0028] Bluetooth receive signals are divided into in-phase and quadrature signals, referred to as I and Q signals, respectively. The phase of a Bluetooth signal refers to the phase of the I and Q signals. The differential phase of a Bluetooth signal is the difference between the phases of the I and Q signals—the phase at one moment minus the phase at the previous moment.

[0029] Step S3: The Bluetooth receiving end reconstructs the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal For classic Bluetooth technology, the Bluetooth receiver reconstructs the reference differential phase of each Bluetooth symbol of the synchronization word. For low-power Bluetooth technology, the Bluetooth receiver reconstructs the reference differential phase of each Bluetooth symbol of the access address.

[0030] There are N sampling points in each Bluetooth symbol, N = T ÷ T SWhere T represents the Bluetooth symbol time, that is, the transmission time of a Bluetooth symbol. For example, in BR type classic Bluetooth and LE 1M PHY type low power Bluetooth, the Bluetooth symbol time is 1μs. In LE 2M PHY type low power Bluetooth, the Bluetooth symbol time is 0.5μs. T S Indicates the sampling time. This step, for example, first reconstructs the reference differential phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal Then the reference differential phase of all sampling points within a Bluetooth symbol is calculated. Accumulate and get the reference differential phase of the Bluetooth symbol

[0031] a(n) represents the raw bits of the Bluetooth signal, which can be 0 or 1. n represents the index or subscript of each bit of the Bluetooth signal. If used with the LE Coded PHY type of Bluetooth Low Energy, a(n) represents the encoded data of the raw bits.

[0032] b(n) represents the data after a(n) is mapped using BPSK (binary phase shift keying). The value of b(n) is -1 or 1. b(n) is the Bluetooth signal before GFSK modulation.

[0033] The phase at each sampling point of each Bluetooth symbol of the Bluetooth signal after GFSK modulation Where t represents the current time. h represents the modulation index, a parameter used in GFSK modulation that determines the degree of frequency deviation. Classic Bluetooth typically uses a modulation index between 0.28 and 0.35, while Bluetooth Low Energy typically uses a modulation index between 0.45 and 0.55. g(t) represents a Gaussian-shaped pulse (also known as a Gaussian pulse). A time shift of g(t) by nT is g(t-nT). T represents the Bluetooth symbol time. In the above formula, the summation symbol Σ is used to accumulate n, and the integral symbol ∫ is used to integrate τ.

[0034] The reference differential phase reconstructed by the Bluetooth receiver at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal Among them, T S represents the sampling time, h represents the modulation index, and T represents the Bluetooth symbol time.

[0035] above The calculation formula involves the accumulation of n from -∞ to +∞, which is difficult to apply in practice. It can be simplified to Table 1. The left column of Table 1 shows the three adjacent original bits (a m-1 ,a m ,am+1 ), the right column of Table 1 represents the middle bit a among the three adjacent original bits. m The reference differential phase at each sampling point (corresponding to a Bluetooth symbol) The calculation formula of .

[0036]

[0037] Table 1: Reference differential phase at each sampling point within a Bluetooth symbol

[0038] In Table 1, ln represents the natural logarithm function, B is the 3dB bandwidth of the Gaussian filter, and T represents the Bluetooth symbol time. The 3dB bandwidth of the Gaussian filter refers to the bandwidth of the frequency domain corresponding to the Gaussian function, and the frequency range where its power spectrum density drops to half of its maximum value. erf() represents the error function (also known as the Gaussian error function). t represents the time corresponding to each sampling point. The calculation formula does not involve the accumulation from -∞ to +∞ and is suitable for practical applications.

[0039] Then the reference differential phase of all sampling points in each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal is calculated. Accumulate, that is, add the formula results of each row in Table 1 according to the number of sampling points N contained in a Bluetooth symbol, and get the cumulative value of the reference differential phase of all sampling points in a Bluetooth symbol, which is called the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal.

[0040] Assuming that π is represented by 1024 in hardware implementation and the sampling frequency is 12MHz, the lookup table of the reference differential phase of different Bluetooth symbols is shown in Table 2. The left column of Table 2 represents the three adjacent original bits (a m-1 ,a m ,a m+1 ), the right column of Table 2 represents the middle bit a among the three adjacent original bits. m (corresponding to one Bluetooth symbol) Specific value of .

[0041]

[0042] Table 2: Reference differential phase for each Bluetooth symbol

[0043] Table 2 stores the reference differential phase of each Bluetooth symbol in advance The value of no longer needs to be calculated through formulas, which not only takes up less storage space but also only requires table lookup operations, saving computing resources and is particularly suitable for hardware implementation.

[0044] There is no strict restriction on the order of step S3 and step S2, and they can be performed either before or simultaneously.

[0045] Step S4: The Bluetooth receiving end uses the actual differential phase of each sampling point of each Bluetooth symbol of the Bluetooth received signal And the reference differential phase of each Bluetooth symbol of the reconstructed Bluetooth signal The DC component of the Bluetooth received signal is calculated, and the relationship between frequency offset and DC component is used to calculate the initial frequency offset estimate of the Bluetooth received signal. The Bluetooth receiver then performs initial frequency offset compensation on the I and Q signals of the Bluetooth received signal based on the initial frequency offset estimate. This initial frequency offset estimation (also known as coarse frequency offset estimation) is part of the frequency offset estimation of Bluetooth signals based on reconstructed GFSK differential phase, as proposed in this application.

[0046] The calculation formula of the DC component of the Bluetooth received signal is, for example: Where L represents the number of bits used to calculate the initial frequency offset. For Classic Bluetooth, L is typically the length of the synchronization word. For Bluetooth Low Energy, L is typically the length of the access address. N represents the number of sampling points within a Bluetooth symbol. As previously explained, in the applicable scenarios of this application, one Bluetooth symbol corresponds to one bit.

[0047] The calculation formula of the initial frequency offset estimate is, for example: Among them, T S Indicates the sampling time.

[0048] Step S5: After initial frequency offset compensation, residual frequency offset still exists in the I and Q signals. The Bluetooth receiver needs to track the residual frequency offset in real time when demodulating the payload data of the Bluetooth received signal. The Bluetooth receiver tracks the residual frequency offset of the Bluetooth received signal after initial frequency offset compensation (i.e., estimates and compensates for the residual frequency offset) as follows.

[0049] For the first m-1 (e.g., first 4) bits to be demodulated in the payload portion of the Bluetooth received signal, since the initial frequency offset compensation has just been performed and the residual frequency offset is small, the first m-1 bits to be demodulated are directly subjected to decision feedback equalization (DFE) to decode the original bits (i.e., the bits after the decision).

[0050] For the mth and subsequent bits to be demodulated (e.g., from the 5th bit onwards) in the payload portion of the Bluetooth received signal, the actual differential phase is calculated based on the judged bits in the payload portion of the Bluetooth received signal, the reference differential phase is reconstructed, the residual DC component DC' (i.e., the DC component corresponding to the residual frequency offset) is calculated and compensated, and the original bits (i.e., the judged bits) are decoded. Figure 2 ,The tracking process of this part of the residual frequency offset includes the following ,sub-steps.

[0051] Step S51: The Bluetooth receiving end calculates the actual differential phase at each sampling point of the judged bit of the payload part of the Bluetooth received signal Each bit after determination corresponds to a Bluetooth symbol. This step uses the same calculation method as step S2.

[0052] Step S52: The Bluetooth receiving end reconstructs the reference differential phase of the judged bits of the payload part of the Bluetooth received signal This step adopts the same processing method as step S3.

[0053] In order to track the residual frequency deviation of the payload data of the Bluetooth received signal in real time, the number of bits used to track the residual frequency deviation should not be too large; at the same time, in order to suppress the influence of noise, the number of bits used to track the residual frequency deviation should not be too small. For example, the number of bits L' after the decision of the payload part of the Bluetooth received signal used to track the residual frequency deviation can be set to 4. In this case, the actual differential phase is calculated using the 4 bits after the decision immediately preceding the bit to be demodulated. and reconstructed reference differential phase

[0054]

[0055] There is no strict restriction on the order of step S52 and step S51 , and they can be performed either before or simultaneously.

[0056] Step S53: The Bluetooth receiving end uses the actual differential phase at each sampling point of the judged bit in the payload part of the Bluetooth received signal and the reference differential phase of the judged bits of the payload portion of the reconstructed Bluetooth received signal Calculate the residual DC component DC' of the current bit to be demodulated in the payload portion of the Bluetooth received signal. This step uses the same processing method as step S4. The calculation formula for the residual DC component is, for example:

[0057] Step S54: the Bluetooth receiving end performs Kalman filtering on the residual DC component DC' of the bit to be demodulated in the payload portion of the Bluetooth received signal to smooth the noise and make the residual DC component more accurate.

[0058] Step S55: The Bluetooth receiving end indirectly eliminates (indirectly compensates for) the residual frequency offset based on the residual DC component DC″ after Kalman filtering of the current bit to be demodulated in the payload portion of the Bluetooth received signal, and then uses decision feedback equalization to decode the original bit of the current bit to be demodulated (i.e., the bit after the decision).

[0059] In step S5, the Bluetooth receiver continuously tracks the subsequent bits to be demodulated in the payload portion of the Bluetooth received signal, i.e., it continuously estimates and compensates for the residual frequency offset. This residual frequency offset estimation (also known as fine frequency offset estimation) is part of the frequency offset estimation method for Bluetooth signals based on reconstructed GFSK differential phase, as proposed in this application.

[0060] See also Figure 3 The frequency offset estimation device for Bluetooth signals based on reconstructed GFSK differential phase proposed in this application includes a Bluetooth frame synchronization unit 1, an actual differential phase calculation unit 2, a reference differential phase reconstruction unit 3, an initial frequency offset estimation unit 4, and a residual frequency offset tracking unit 5. Figure 3 The device shown corresponds to Figure 1 The method shown.

[0061] The Bluetooth frame synchronization unit 1 is used to perform Bluetooth frame synchronization, so that the Bluetooth receiving end can correctly find the location of the synchronization word or access address in the data packet of the Bluetooth receiving signal.

[0062] The actual differential phase calculation unit 2 is used to solve the phase of each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal, and perform phase differentiation to obtain the actual differential phase of each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal.

[0063] The reference differential phase reconstruction unit 3 is used to reconstruct the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal.

[0064] The initial frequency offset estimation unit 4 is configured to use the actual differential phase at each sampling point of each Bluetooth symbol of the Bluetooth received signal And the reference differential phase of each Bluetooth symbol of the reconstructed Bluetooth signal The DC component of the Bluetooth received signal is calculated, and the relationship between the frequency offset and the DC component is used to calculate the initial frequency offset estimate of the Bluetooth received signal. The initial frequency offset compensation is performed on the Bluetooth received signal according to the initial frequency offset estimate.

[0065] The residual frequency offset tracking unit 5 is used to estimate and compensate for the residual frequency offset of the Bluetooth receive signal after initial frequency offset compensation. For the first m-1 bits to be demodulated in the payload portion of the Bluetooth receive signal, decision feedback equalization is directly performed to decode the decided bits. For the mth and subsequent bits to be demodulated in the payload portion of the Bluetooth receive signal, the actual differential phase is calculated based on the decided bits in the payload portion of the Bluetooth receive signal, the reference differential phase is reconstructed, and the residual DC component is calculated and compensated to obtain the decided bits.

[0066] This application performs initial frequency offset estimation and residual frequency offset tracking based on the reference differential phase of the Bluetooth symbol and the actual differential phase of each sampling point of the Bluetooth symbol. Kalman filtering is used to effectively suppress noise in the residual frequency offset tracking stage. Compared with existing frequency offset estimation schemes for Bluetooth signals, this application does not require mean filtering and determination of effective maximum and / or minimum values, does not require correlation operations and extreme value searches, and does not require FFT (Fast Fourier Transform) operations and amplitude square calculations; the amount of computation is greatly reduced and the processing speed is significantly improved.

[0067] This application only involves simple table lookup, addition, subtraction and division operations when reconstructing the reference differential phase of the Bluetooth symbol, and does not involve complex correlation operations and Fourier transform operations. The division operation is slightly complicated, but it can be implemented by changing the division operation into multiplication and shift operations through an approximate method. This application only needs to add Kalman filtering in the residual frequency deviation tracking stage. The Kalman filter adopts a simple first-order filtering scheme, and the specific implementation also involves only table lookup, addition, subtraction and multiplication operations. The Kalman filter processing smoothes the noise of the residual frequency deviation, improves the overall frequency deviation estimation accuracy, and also has good residual frequency deviation estimation performance under low signal-to-noise ratio. Overall, the implementation complexity of this application is low, and the hardware implementation is simple.

[0068] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for estimating frequency offset of a Bluetooth signal based on reconstructing GFSK differential phase, characterized in that: The method includes the following steps: Step S1: The Bluetooth receiving end performs Bluetooth frame synchronization, and the Bluetooth receiving end finds the location of the synchronization word or access address in the data packet of the Bluetooth receiving signal; Step S2: The Bluetooth receiving end solves the phase of each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal, and differentiates the phase to obtain the actual differential phase of each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal. Step S3: The Bluetooth receiving end reconstructs the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receiving signal Step S3 and step S2 may be performed either before or simultaneously; Step S4: The Bluetooth receiving end uses the actual differential phase of each sampling point of each Bluetooth symbol of the Bluetooth received signal And the reference differential phase of each Bluetooth symbol of the reconstructed Bluetooth signal The DC component of the Bluetooth received signal is calculated, and an initial frequency offset estimate of the Bluetooth received signal is calculated using the relationship between the frequency offset and the DC component; the Bluetooth receiving end performs initial frequency offset compensation on the I and Q signals of the Bluetooth received signal based on the initial frequency offset estimate; Step S5: The Bluetooth receiving end tracks the residual frequency offset of the Bluetooth receiving signal after the initial frequency offset compensation; for the first m-1 bits to be demodulated in the payload part of the Bluetooth receiving signal, directly perform decision feedback equalization to decode the bits after the decision; for the mth and subsequent bits to be demodulated in the payload part of the Bluetooth receiving signal, calculate the actual differential phase based on the bits after the decision in the payload part of the Bluetooth receiving signal, reconstruct the reference differential phase, calculate the residual DC component and compensate for it, and decode the bits after the decision.

2. The method for estimating the frequency offset of a Bluetooth signal based on reconstructing the GFSK differential phase according to claim 1, wherein: In step S3, for classic Bluetooth technology, the Bluetooth receiving end reconstructs the reference differential phase of each Bluetooth symbol of the synchronization word; for low-power Bluetooth technology, the Bluetooth receiving end reconstructs the reference differential phase of each Bluetooth symbol of the access address.

3. The method for estimating the frequency offset of a Bluetooth signal based on reconstructing the GFSK differential phase according to claim 2, wherein: In step S3, the reference differential phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal is first reconstructed. Then the reference differential phase of all sampling points within a Bluetooth symbol is calculated. Accumulate and get the reference differential phase of the Bluetooth symbol 4. The method for estimating the frequency offset of a Bluetooth signal based on reconstructing the GFSK differential phase according to claim 3, wherein: In step S3, the Bluetooth receiving end reconstructs the reference differential phase at each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal. Among them, T S represents the sampling time; h represents the modulation index; a(n) represents the original bit of the Bluetooth signal, which takes a value of 0 or 1; b(n) represents the data after a(n) is mapped through binary phase shift keying (BPSK), which takes a value of -1 or 1; n represents the index or subscript of each bit of the Bluetooth signal; g(t) represents a Gaussian shaped pulse, and g(t) shifted by nT on the time axis is g(t-nT); T represents the Bluetooth symbol time.

5. The method for estimating the frequency offset of a Bluetooth signal based on reconstructing the GFSK differential phase according to claim 4, wherein: In step S3, when three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 000, the middle bit a of the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 001, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 010, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 011, the middle bit a of the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 100, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 101, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 110, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point When three adjacent original bits a m-1 ,a m ,a m+1 When the value of is 111, the middle bit a among the three adjacent original bits m The reference differential phase at each sampling point in, ln represents the natural logarithm function; B is the 3dB bandwidth of the Gaussian filter; erf() represents the error function; and t represents the time corresponding to each sampling point.

6. The method for estimating frequency offset of a Bluetooth signal based on reconstructing GFSK differential phase according to claim 5, wherein: In step S3, the reference differential phase of each value corresponding to a Bluetooth symbol is calculated. The values ​​of the Bluetooth receive signal are made into a table, and the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth receive signal is obtained by looking up the table. The numerical value of .

7. The method for estimating the frequency offset of a Bluetooth signal based on reconstructing GFSK differential phase according to claim 1, wherein: In step S4, the calculation formula of the DC component is Where L represents the number of bits used to calculate the initial frequency offset; N represents the number of sampling points in a Bluetooth symbol; The formula for calculating the initial frequency offset estimate is Among them, T S Indicates the sampling time.

8. The method for estimating frequency offset of a Bluetooth signal based on reconstructing GFSK differential phase according to claim 1, wherein: In step S5, the process of tracking the residual frequency offset for the mth and subsequent bits to be demodulated in the payload part of the Bluetooth received signal includes the following sub-steps: Step S51: The Bluetooth receiving end calculates the actual differential phase at each sampling point of the judged bit of the payload part of the Bluetooth received signal Step S52: The Bluetooth receiving end reconstructs the reference differential phase of the judged bits of the payload part of the Bluetooth received signal Step S52 and step S51 may be performed either before or simultaneously; Step S53: The Bluetooth receiving end uses the actual differential phase at each sampling point of the judged bit in the payload part of the Bluetooth received signal and the reference differential phase of the judged bits of the payload portion of the reconstructed Bluetooth received signal Calculate the residual DC component DC' of the bit to be demodulated in the payload portion of the Bluetooth received signal; Step S54: the Bluetooth receiving end performs Kalman filtering on the residual DC component DC' of the bit to be demodulated in the payload portion of the Bluetooth received signal; Step S55: The Bluetooth receiving end indirectly eliminates the residual frequency offset based on the residual DC component DC″ after Kalman filtering of the current bit to be demodulated in the payload part of the Bluetooth received signal, and then uses decision feedback equalization to decode the decided bit of the current bit to be demodulated.

9. The method for estimating frequency offset of a Bluetooth signal based on reconstructing GFSK differential phase according to claim 8, wherein: In step S51 and step S52, the number of judged bits in the payload part of the Bluetooth received signal used to track the residual frequency offset is L', and the actual differential phase and the reconstructed reference differential phase are calculated using the L' judged bits immediately preceding the bit to be demodulated.

10. A frequency offset estimation device for Bluetooth signals based on reconstructed GFSK differential phase, characterized in that: It includes a Bluetooth frame synchronization unit, an actual differential phase calculation unit, a reference differential phase reconstruction unit, an initial frequency offset estimation unit, and a residual frequency offset tracking unit; The Bluetooth frame synchronization unit is used to perform Bluetooth frame synchronization, allowing the Bluetooth receiving end to find the location of the synchronization word or access address in the data packet of the Bluetooth received signal; The actual differential phase calculation unit is used to solve the phase of each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal, and perform differential phase calculation to obtain the actual differential phase of each sampling point of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal. The reference differential phase reconstruction unit is used to reconstruct the reference differential phase of each Bluetooth symbol of the synchronization word or access address in the Bluetooth received signal. The initial frequency offset estimation unit is configured to use the actual differential phase at each sampling point of each Bluetooth symbol of the Bluetooth received signal And the reference differential phase of each Bluetooth symbol of the reconstructed Bluetooth signal Calculate the DC component of the Bluetooth received signal, and use the relationship between the frequency offset and the DC component to calculate an initial frequency offset estimate of the Bluetooth received signal, and perform initial frequency offset compensation on the Bluetooth received signal based on the initial frequency offset estimate; The residual frequency offset tracking unit is used to estimate and compensate for the residual frequency offset of the Bluetooth receive signal after initial frequency offset compensation; for the first m-1 bits to be demodulated in the payload part of the Bluetooth receive signal, decision feedback equalization is directly performed to decode the decided bits; for the mth and subsequent bits to be demodulated in the payload part of the Bluetooth receive signal, the actual differential phase is calculated based on the decided bits of the payload part of the Bluetooth receive signal, the reference differential phase is reconstructed, the residual DC component is calculated and compensated, and the decided bits are obtained.

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