49 results about "Residual frequency offset" patented technology

The invention relates to the technical field of satellite internet, in particular to a low-orbit satellite communication system positioning method and a terminal. Comprising the following steps: a user terminal receives satellite broadcast to obtain ephemeris information at the current moment and position information of a wave position center point, and carries out initial time delay estimation and initial frequency offset estimation; then the user terminal carries out time-frequency pre-compensation processing on the PRACH signal according to the initial time delay and frequency offset estimation and sends the PRACH signal to a satellite; and after the satellite captures the PRACH signal, positioning the user terminal corresponding to the PRACH signal according to the residual time delay and the residual frequency offset carried in the PRACH signal and the position of the wave position center point. Therefore, under the condition of not depending on GNSS information, the satellite side can position the GNSS-free terminal.

The invention discloses a frequency offset estimation method and device, electronic equipment and a storage medium, and relates to the technical field of signal processing. In the invention, based on a data signal sent by a signal transmitting end and a local characteristic signal, a subsequent signal used for frequency offset estimation can be obtained, i.e., a fusion signal carrying frequency offset information is obtained; moreover, Chirp-Z transformation is carried out on the fusion signal in a limited residual frequency offset range of a data transmission channel, so that not only is spectrum information of the fusion signal meeting a fine frequency offset estimation requirement obtained, but also the calculation complexity is reduced to a certain extent as the residual frequency offset range is fine, and the accuracy of frequency offset estimation is improved. Namely, high-precision frequency offset estimation is completed under reasonable calculation complexity, so that the problem of insufficient timeliness of signal processing is solved; in addition, in the frequency offset estimation process, the frequency offset estimation precision is further improved by combining the frequency spectrum peak offset.

The invention relates to the technical field of satellite communication, and discloses a residual frequency offset compensation method, device and equipment, a storage medium and a computer program product, and the method comprises the steps: determining a linear interpolation phase step length according to frame header information in a data frame; calculating a phase offset estimation value and a phase change parameter based on the linear interpolation phase step length and interval data between any two pilots in the data frame; and when it is detected that the phase shift estimation value has a phase cross period, compensating the phase shift estimation value according to the phase change parameter to obtain modulation data phase information. Large residual frequency offset estimation and residual phase linear interpolation compensation can be carried out in each frame, the complexity of carrier fine synchronization and phase recovery is reduced, and the system phase recovery time under the condition of low symbol rate is greatly shortened.

The invention discloses an HRF signal synchronization method, device and system of a dual-mode carrier communication system, and belongs to the technical field of power line carrier communication. The method comprises the following steps: dividing a frequency offset range into a plurality of frequency offset hypothesis intervals based on an allowable maximum residual frequency offset range; performing frequency offset pre-compensation on the received signal according to each frequency offset hypothesis interval to obtain multiple paths of frequency offset compensation signals, and performing cross-correlation processing on the multiple paths of frequency offset compensation signals and a local reference sequence to obtain multiple paths of cross-correlation value sequences; in any cross-correlation value sequence, performing self-correlation processing on cross-correlation values of adjacent symbol intervals to obtain a corresponding self-correlation sequence; correlation peak values corresponding to the frequency offset hypotheses are extracted from the multiple paths of self-correlation sequences respectively, the maximum correlation peak value is determined from the correlation peak values, and if the maximum correlation peak value is larger than a synchronization judgment threshold value, the corresponding position is determined to be the synchronization position. According to the invention, high-precision wireless signal synchronization is realized, and high-quality signal transmission is ensured.

The invention discloses a method for tracking a signal with a large Doppler frequency change rate by using FFT (Fast Fourier Transform), which comprises the following steps of: S1, acquiring an input signal, and performing preliminary frequency offset compensation on the acquired input signal; s2, de-spreading the signal after the initial frequency offset, and performing phase correction on the de-spread signal; s3, performing FFT calculation on the signal after phase correction, and obtaining a residual frequency offset value; and S4, according to the residual frequency offset value, returning to S1 to circularly carry out frequency offset compensation on the input signal until the signal tracking is finished. According to the invention, an open-loop tracking mode is adopted, and the problem that a traditional three-order phase-locked loop cannot realize carrier tracking of a large Doppler frequency change rate of a short-time burst signal is solved.

The invention relates to the technical field of satellite communication, and discloses a method, equipment and a program product for determining the influence of residual frequency offset on packet error rate performance, which are applied to an SC-FDMA communication system with channel coding, and the method comprises the following steps: under the condition of no frequency offset and different signal-to-noise ratio conditions, carrying out analogue simulation to obtain system packet error rates under different constellation mapping; under the condition of no frequency offset and the same signal-to-noise ratio, calculating a first symbol error rate of the system under different constellation mappings; under the condition of different residual frequency offsets, calculating a second symbol error rate of the system under different constellation mappings; according to a comparison result of the first symbol error rate and the second symbol error rate, calculating a noise variance required for reaching the system packet error rate when the residual frequency offset exists; and determining a prediction result of the residual frequency offset on system performance reduction according to the noise variance. Therefore, by combining theoretical calculation with simulation means, the influence of the residual frequency offset on the system performance can be accurately predicted, the system design is optimized, and the communication quality and reliability are improved.

The invention relates to an uplink and downlink time-frequency offset joint estimation compensation method, which comprises the following steps of: receiving ephemeris broadcasted by a satellite, and acquiring self position information; extrapolating the satellite position and speed at the downlink signal receiving moment according to the ephemeris, and calculating downlink frequency offset caused by satellite motion by combining the own position information; estimating downlink residual frequency offset and downlink sampling offset brought by the crystal oscillator according to the reference signal; calculating a frequency offset compensation value for the downlink signal according to the downlink frequency offset brought by the satellite motion and the downlink residual frequency offset brought by the crystal oscillator; and adjusting a received time domain signal by using the frequency offset compensation value of the downlink signal, and adjusting a received frequency domain signal by using the downlink sampling offset. According to the invention, the pre-compensation precision of the uplink frequency offset can be improved, and the estimation compensation of the downlink frequency offset and the sampling offset can be realized with lower complexity.

The invention relates to the field of satellite communication, and provides a spread spectrum signal real-time capturing method and device, electronic equipment and a storage medium, and the spread spectrum signal real-time capturing method comprises the steps: traversing Doppler frequency shift gears to carry out spread spectrum signal capturing, and determining an initial code phase and an initial frequency value; window sliding frequency measurement is carried out in an adjacent chip range of the initial code phase, and a residual frequency offset estimation value is determined; determining a coarse frequency estimation value according to the residual frequency offset estimation value and the initial frequency value; and performing spread spectrum signal capture again according to the coarse frequency estimation value to obtain a code phase value output by spread spectrum capture. According to the method and the device, search of three dimensions of code phase, frequency and code Doppler is reduced into search of two dimensions of phase and frequency, the method and the device are closer to engineering application of satellite communication, the problem of signal capture under the condition of large code Doppler can be solved, and the memory space in an existing capture scheme can be greatly reduced.

The invention relates to a Doppler frequency offset compensation method based on double-link cooperation and a satellite communication system. The Doppler frequency offset compensation method comprises the following steps that a UHF transmitter of a mobile platform terminal sends GPS information data of the mobile platform terminal to a UHF receiver of a satellite end; the UHF receiver of the satellite end receives GPS information data of the mobile platform terminal and transmits the GPS information data to the Ka receiver of the satellite end; a Ka receiver at the satellite end calculates UHF Doppler frequency offset by using the GPS information data of the mobile platform terminal and the position and speed of the satellite, and calculates Ka Doppler frequency offset based on the UHF Doppler frequency offset; injecting the Ka Doppler frequency offset into a local oscillator synthesizer of a Ka receiver at a satellite end to carry out Ka Doppler frequency offset pre-compensation; and compensating the pre-compensated residual frequency offset by using the phase-locked loop. According to the Doppler frequency offset compensation method, the time delay bottleneck of Ka link frequency offset compensation is highlighted, and the requirement that the end-to-end time delay of low-orbit satellite real-time services is smaller than or equal to 50 ms is met.

The invention provides a channel quality estimation method for VDES satellite communication, and belongs to the technical field of wireless communication. The method comprises the following steps of: performing rectification and integration on a baseband sampling signal output by a filter, and calculating a received signal strength index; compensating the phase of the baseband sampling signal of the CPM spread spectrum; the non-CPM spread spectrum phase is compensated; and according to the obtained baseband sampling synchronization word sequence, the calculated SNR passes through a mean filter, and a final SNR result is output. The MPART phase estimation compensation method is designed according to the maximum residual frequency offset, the chip rate, the chip length and the least square method, it is guaranteed that the input data phase of the ML algorithm is stable, the influence of the frequency offset on ML estimation is reduced, the dynamic range of SNR estimation is greatly widened, the robustness and accuracy of SNR detection are improved, and the method is suitable for popularization and application. And algebraic operation is simplified through the lookup table, so that the calculation amount is reduced.

The invention provides a frequency offset determination method and device and a processor readable storage medium, and relates to the technical field of communication. The method comprises the following steps: obtaining a first frequency offset estimation value between a first pilot signal and a second pilot signal, and a first sending signal on each target symbol; the target symbols are symbols except a first symbol where the first pilot signal is located and a second symbol where the second pilot signal is located; for each target symbol, performing frequency offset compensation on the first sending signal according to each residual frequency offset value in the plurality of residual frequency offset values to obtain a second sending signal corresponding to each residual frequency offset value; the residual frequency offset value is determined according to a pilot symbol interval between the first symbol and the second symbol; and for each target symbol, determining a target frequency offset value of a transmission signal on each target symbol according to the second sending signal corresponding to each residual frequency offset value. According to the invention, the problem that the estimable frequency offset range of the current frequency offset estimation method is limited can be solved.

The invention relates to the technical field of wireless communication, and discloses a novel channel estimation method based on residual frequency offset elimination, which comprises the following steps of: despreading descrambled pilot frequency data to obtain a channel estimation value after noise smoothing, and transmitting the channel estimation value to an FIR (Finite Impulse Response) filter to generate a noise suppression channel estimation signal; phase-frequency response of the noise suppression channel estimation signal is obtained through calculation, conjugate multiplication and smoothing are conducted on the phase-frequency response of the noise suppression channel estimation signal and the phase-frequency response of the FIR filter, a residual frequency offset estimation signal for suppressing the noise influence is obtained and compensated to the noise suppression channel estimation signal output by the FIR filter, and a noise suppression channel estimation value for eliminating the residual frequency offset influence is obtained. And balancing with the service de-spreading signal compensated by the residual frequency offset estimation signal to obtain a final output signal. According to the method, the phase-frequency response characteristics of the filter are deeply analyzed, the FIR filter is used for improving the signal-to-noise ratio, meanwhile, the residual frequency offset is estimated through the phase-frequency characteristics of the FIR filter, finally, the phase error is compensated for, an accurate channel estimation value is obtained, and the signal detection precision is improved.

An operation method of a wireless communication device includes receiving a first signal including a first reference signal group, calculating a first residual frequency offset based on the first signal, receiving a second signal that is subsequent to the first signal and includes a second reference signal group, compensating a phase of the second signal based on the first residual frequency offset, estimating a first channel based on first channel characteristics, the first reference signal group, and the first signal, estimating a second channel based on second channel characteristics, the second reference signal group, and the second signal of which the phase is compensated, and calculating a second residual frequency offset based on the first channel estimation and the second channel estimation.

The application relates to a UWB preamble signal receiving processing method, which comprises the following steps: receiving a discrete digital signal obtained through sampling conversion after front-end processing; in a coarse acquisition stage, a locally reproduced preamble sequence is used to perform convolution processing on the discrete digital signal, coherent accumulation and fast Fourier transform are performed on the signal after convolution processing to obtain a first processing signal, a preamble is detected according to the strongest peak value response of the first processing signal, and frequency offset coarse estimation and CMR coarse estimation are performed when the preamble is detected; in an accurate receiving stage, the signal after convolution processing is subjected to frequency offset coarse compensation processing by using the frequency offset coarse estimation to obtain a compensation signal, interpolation processing is performed by taking the compensation signal as input, coherent accumulation and fast Fourier transform are performed on the signal after interpolation processing to obtain a second processing signal, residual frequency offset estimation and CMR accurate estimation are performed on the second processing signal. The application can improve the reliability of preamble detection and acquisition.

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.

Systems, methods, apparatuses, and computer program products for physical layer specification support for the reduction of reference signal resource overhead for time-and frequency tracking reference signal. For example, some example embodiments may include a method comprising receiving, by a user equipment, at least one indication comprising at least one symbol configuration associated with at least one reference signal; and determining, by the user equipment, based on the received indication, at least one of residual frequency offset or residual phase offset based on the at least one reference signal.

The invention provides a low-orbit satellite Doppler frequency offset compensation method, device and equipment and a medium, and the method comprises the steps: dividing a coverage area into a plurality of continuous frequency offset subareas based on the real-time orbit parameters of a low-orbit satellite and the geographical range information of the coverage area; for each frequency offset partition, according to the partition characteristic parameters of the frequency offset partition, adjusting the beam forming parameters of the low-orbit satellite so as to perform Doppler frequency offset compensation on the frequency offset partition; selecting a part of terminals from each frequency offset partition, and obtaining residual frequency offset information fed back by the part of terminals; and dynamically adjusting the beam forming parameters of the corresponding frequency offset partitions according to the residual frequency offset information fed back by part of the terminals. According to the embodiment of the invention, the influence of terminal movement and track disturbance on compensation precision can be effectively suppressed, deep coupling of beam regulation and frequency offset characteristics is realized, the frequency offset fluctuation in the beam is stabilized in a traceable range of a terminal phase-locked loop, and continuous and reliable communication of the terminal in a high-speed movement process is ensured.

The present specification relates to the technical field of satellite internet, and particularly relates to a low-orbit satellite communication system positioning method and a terminal. The method comprises the following steps: a user terminal receives satellite broadcast to obtain ephemeris information at a current time and position information of a wave position center point, and performs initial time delay estimation and initial frequency offset estimation; then the user terminal performs time-frequency pre-compensation processing on a PRACH signal according to the initial time delay and frequency offset estimation, and sends the PRACH signal to a satellite; after the satellite captures the PRACH signal, the user terminal corresponding to the PRACH signal is positioned according to residual time delay and residual frequency offset carried in the PRACH signal and the position of the wave position center point. Thus, the positioning of the satellite side for the GNSS terminal is realized without relying on GNSS information.

This application relates to the field of intelligent conditioning technology for grating filter sensing signals, and discloses a grating filter sensing signal conditioning method based on machine learning. The invention acquires observation response characterization data and conditional constraint state quantities, first performs spectral axis registration processing based on a preset reference frequency window to eliminate the influence of measurement coordinate offset, then performs residual frequency offset decoupling processing on the preset target frequency band to extract residual frequency offset characterization quantities, and constructs a residual dynamic state sequence by combining historical control states, further utilizes a preset time-series inference model to output voltage compensation quantity and conditioning reliability results, and finally determines the final control voltage through reliable gating conditioning and local spectrum scanning verification, thereby effectively distinguishing pseudo offset from the preset target frequency band true offset, and reducing the interference of original observation signal fluctuations, environmental changes and uneven internal electric field distribution on the control results.

The invention discloses a short baseline synthetic aperture passive positioning method and system based on Chirp-Z spectrum estimation, and mainly solves the problem of large positioning error and frequency estimation error caused by residual frequency deviation in the prior art. According to the implementation scheme, the method comprises the steps that a geometric scene comprising a reconnaissance plane, two short baseline antennas and an unknown radiation source is built; obtaining signals of the radiation source received by the two short baseline antennas on the reconnaissance plane according to the geometric scene; performing down-conversion and correlation method processing on the received signal to obtain a single-frequency signal sequence; a Chirp-Z spectrum estimation algorithm is adopted for the single-frequency signal sequence to obtain a frequency estimation value, and the coordinates of the radiation source are calculated according to the frequency estimation value. According to the invention, frequency measurement is carried out by using a Chirp-Z spectrum estimation method, and Z transformation is converted into an FFT processable form through convolution operation, so that the operation complexity and spectrum estimation errors are reduced, phase ambiguity and signal coherence dependence are avoided, the reliability of the model is improved, and the method is suitable for large-scale popularization and application. The method can be used for an unknown signal source which has a short baseline and does not have a periodic discontinuous short signal sequence.

The invention relates to the technical field of satellite communication, in particular to a satellite communication frequency offset estimation and synchronization method, a storage medium and a satellite communication terminal.The satellite communication frequency offset estimation and synchronization method comprises the steps that a satellite wireless signal containing a frequency correction channel burst and a broadcast control channel burst is received; detecting frequency correction channel burst to obtain coarse carrier frequency offset; positioning baseband data corresponding to a broadcast control channel burst in the satellite wireless signal; pre-compensating baseband data corresponding to the broadcast control channel burst by using coarse carrier frequency offset, and calculating residual frequency offset of a residual frequency offset signal; obtaining a total carrier frequency offset according to the coarse carrier frequency offset and the residual frequency offset; and performing complete compensation, demodulation and channel decoding on the baseband data corresponding to the broadcast control channel burst by using the total carrier frequency offset to obtain decoded data. According to the method, the coarse estimation of the FCCH and the fine estimation and verification mechanism of the BCCH are combined, and the synchronization reliability can still be ensured under the complex channel condition.

The application discloses a residual frequency offset estimation method based on multi-channel in-track interference, and belongs to the field of radio reconnaissance. The method comprises the following steps: arranging multiple detection antennas in front of and behind the flight direction; the detection antennas passively receive signals emitted by a radiation source target; and the received signals are processed. Since the multiple antennas pass through the same slant range course in sequence, interference processing is performed after compensating for the phase caused by time delay. In an ideal case, the interference phase between channels is 0. In the case that there is a residual frequency offset, the interference phase between channels is the phase generated by the joint action of time delay and the residual frequency offset. The residual frequency offset can be estimated according to the corresponding relationship between the residual frequency offset and the interference phase. The application can realize accurate estimation of the residual frequency offset in the case of non-cooperative reception, and eliminate the influence of the residual frequency offset on subsequent signal processing.

Systems, methods, apparatuses, and computer program products for physical layer specification support for the reduction of reference signal resource overhead for time-and frequency tracking reference signal. For example, some example embodiments may include a method comprising receiving, by a user equipment, from a network entity, at least one indication comprising at least one antenna port identifier associated with at least one reference signal; and determining, by the user equipment, based on the received indication, at least one of residual frequency offset or residual phase offset based on the at least one reference signal.

The invention discloses a short baseline synthetic aperture passive positioning method and system based on MUSIC spectrum estimation, and mainly solves the problem of large positioning error and frequency estimation error caused by residual frequency deviation in the prior art. According to the implementation scheme, the method comprises the steps that a geometric scene comprising a reconnaissance plane, two short baseline antennas and an unknown radiation source is built; obtaining signals of the radiation source received by the two short baseline antennas on the reconnaissance plane according to the geometric scene; performing down-conversion and correlation method processing on the received signal to obtain a single-frequency signal, and performing noise adding and sampling processing on the single-frequency signal to obtain discrete data; performing MUSIC spectrum estimation on the discrete data to obtain a frequency estimation value; and calculating the coordinates of the radiation source according to the frequency estimation value. Through the MUSIC spectrum estimation algorithm, the original positioning problem is converted into the frequency estimation problem of the signal to be measured, the spectrum estimation error can be reduced, the reliability of the model is improved, the high-precision, high-real-time and high-robustness frequency estimation of the single-frequency short signal is realized, and the method can be used for a discontinuous short signal sequence unknown signal source with a short baseline and without periodicity.

This invention discloses a method and system for suppressing distributed co-channel interference in a region-coexisting environment. The method includes: a desired signal node generating a desired signal and transmitting it through an antenna; distributed interference nodes generating interference signals and transmitting them through antennas; authorized receiving nodes receiving and processing the signals to obtain the down-converted received signal; converting the received distributed interference signal into real and imaginary parts, expanding it with respect to time error and residual frequency offset to obtain the interference signal expression after expansion with time error and residual frequency offset; merging the time-invariant coefficients before the real and imaginary parts of the interference signal into one term to obtain the reconstruction coefficient expression of the distributed interference; estimating the coefficients of the distributed interference suppression system model; reconstructing the interference signal; performing distributed interference suppression; and obtaining the desired signal. This invention achieves the reconstruction and suppression of distributed interference signals under constraints of time error, frequency offset, and IQ imbalance.

The invention discloses a self-adaptive dual-threshold quick capture method and device in satellite communication and a medium. The method comprises the following steps: performing down-conversion mixing and residual frequency offset removal on IQ data and a local sweep frequency control carrier to obtain first data; performing AGC amplification processing on the first data to obtain second data with a predetermined amplitude; performing timing deviation removal on the second data to obtain third data; performing correlation accumulation on the third data to obtain fourth data; according to the fourth data, capturing and tracking are carried out based on a self-adaptive double-threshold mode, the position of a frame header is identified, and captured data are obtained; the self-adaptive double-threshold value is a double-threshold value capturing mode of capturing a high threshold value and tracking a low threshold value. The method has the advantages of high-probability capture and low-probability missed alarm.

This disclosure provides a fine timing method, apparatus, electronic device, storage medium, and chip, including determining the residual frequency offset of a first target frequency and a second target frequency in a detection sequence; wherein the first target frequency and the second target frequency are determined when the detection sequence is converted into a spectrum; determining the adjustment amount of the DC component at the first target frequency and the second target frequency based on the residual frequency offset; determining the phase of the first target frequency and the second target frequency based on the adjustment amount; and determining the fine timing adjustment amount based on the phase of the first target frequency and the second target frequency. Compared with related technologies, this disclosure, by determining the residual frequency offset, determining the adjustment amount of the first target frequency and the second target frequency based on the residual frequency offset, and determining the phase based on the adjustment amount, makes the fine timing adjustment amount obtained based on the phase more accurate, and makes the TOA estimate more accurate.

The invention discloses a modulation identification method based on phase entropy blind frequency offset compensation, and the method comprises the steps: carrying out the polar coordinate transformation of a complex baseband signal, and achieving the blind estimation and compensation of carrier frequency offset; extracting features such as high-order cumulant, skewness, peak ratio and power spectrum from the compensated signal, inputting the extracted feature vectors into a full-connection neural network for modulation classification, and outputting identification confidence; then, combining the phase entropy and the confidence coefficient to construct a dynamic uncertainty score, and calculating a sample selection probability for quantifying the residual frequency offset and confidence coefficient condition of the sample; and finally, incremental training is carried out on the selected sample by using weighted cross entropy loss, and online adaptive updating of a dynamic environment is realized, so that the accuracy and robustness of modulation identification are remarkably improved in a non-cooperative communication scene without pilot frequency and protocol information.

The embodiment of the invention provides a frequency offset compensation method, and the method comprises the steps: carrying out the time-domain frequency offset estimation and compensation of a PPDU (Physical Protocol Data Unit), and determining a first frequency offset compensation value of the time domain of the PPDU; and converting the frequency domain residual frequency offset compensation value of the signaling field of the PPDU into a second frequency offset compensation value of the time domain, and updating the first frequency offset compensation value according to the second frequency offset compensation value. According to the embodiment of the invention, the problem that the accuracy of the generated PPDU frequency offset compensation value is low in the related technology is solved, and the effect of generating the accurate frequency offset compensation value through the feedback mechanism of the frequency domain residual frequency offset is achieved.

The method for fine timing provided by the present disclosure comprises the following steps: acquiring residual frequency offset of a detection sequence determined according to a target signal point and a marker signal point in the detection sequence, wherein the target signal is a sampling point in the detection sequence except the marker signal; correcting the residual frequency offset according to the target signal and the marker signal to obtain a corrected detection sequence; determining phase values of a first target frequency point and a second target frequency point in the corrected detection sequence, wherein the first target frequency point and the second target frequency point are determined when the detection sequence is converted into a frequency spectrum; and determining a fine timing adjustment amount according to the phase values of the first target frequency point and the second target frequency point. By determining the residual frequency offset and correcting the residual frequency offset in the detection sequence, the phase values are calculated according to the corrected detection sequence, so that the fine timing adjustment amount based on the phase values is more accurate, and the accuracy of the estimated value of TOA is improved.