71 results about "Carrier frequency synchronization" patented technology

The invention relates to a synchronization and channel response estimation method which is applicable to an OFDM system, the technical proposal is as follows: a maximum likelihood criterion ML-based cost function for the symbol timing synchronization, the carrier frequency synchronization and the channel parameter joint estimation is proposed by using an OFDM system model under a frequency selective fading channel and against the requirements on the accuracy of the transmission of high-quality information of the next generation of wireless communication system and the existing OFDM wireless communication system. A system architecture and a strategy of joint estimation symbols of timing offset Theta, carrier frequency offset Epsilon and channel impulse response h are derived from the cost function. The method comprises the following steps of carrying out the coarse synchronization and the channel response estimation and carrying out the fine synchronization and the calculation of a channel estimated value. The method can realize the balance between the calculation precision and the calculation complexity, increase or reduce the times of the iteration of the fine synchronization according to an actual system, reduce the interference during the wireless transmission, further improve the reliability of the system and improve the availability of the system.

The invention provides a synchronized method of an orthogonal frequency division multiplexing (OFDM) system. The invention discloses an associated synchronized method of frame synchronization, carrier frequency synchronization and sampling clock synchronization. Carrier frequency offset estimation, channel estimation and fine estimation of symbol timing offset are performed again after sampling clock offset correction is finished, thereby avoiding influences of sampling clock offset on the carrier frequency offset estimation, the channel estimation and the fine estimation of the symbol timing offset, compensating phase deflection caused by the residual carrier frequency offset and the sampling clock offset simultaneously, greatly improving the synchronized performance, and meeting the demands of a high-order modulated system. In addition, due to aiming at a low time-varying channel, the channel estimation is required to be performed once only, thereby reliving the complexity of the system.

An apparatus and method for carrier frequency synchronization in an Orthogonal Frequency Division Multiplexing (OFDM) system are provided for correcting an initial carrier frequency offset in the OFDM system. A metric generator for frequency estimation performs a first accumulation process for a value computed by multiplying a Phase Reference Symbol (PRS) generated from a reception stage by a Fast Fourier Transform (FFT) output signal for an OFDM symbol in a PRS position within a frame, acquires a differential symbol from a product of adjacent FFT output symbols, performs a second accumulation process for a real part extracted from the differential symbol, and outputs a metric value for the frequency estimation. A maximal value-related index generator compares metric values for initial frequency estimation within a predetermined frequency offset estimation range, and selects and outputs a maximal metric value as a frequency offset estimate.

An apparatus (300) for and method of synchronizing OFDM signals utilizes a single baud to provide synchronization in time, frequency, and per-subcarrier rotation (201). Timing and fractional subcarrier frequency synchronization may be obtained from either a known or unknown (e.g., data symbol) baud having known symmetry properties. Because all three synchronization tasks may be accomplished utilizing a single sync baud, the present invention is spectrally efficient. A differential correlation metric is utilized to efficiently provide integer subcarrier frequency synchronization and per-subcarrier rotation synchronization.

While a clock generated by a built-in clock generator is used as a reference signal for determining a carrier frequency of a transmit signal, carrier frequency synchronization is achieved between base stations. A base station device is configured to perform wireless communication with a terminal device. In the base station device, accuracy of a carrier frequency of an OFDM signal is affected by accuracy of a clock frequency generated by a built-in clock generator 18. The base station device receives an OFDM signal transmitted from another base station device while transmission to the terminal device is stopped, estimates a carrier frequency offset of the OFDM signal, and corrects a carrier frequency of an OFDM signal to be transmitted to the terminal device.

The invention discloses a method for realizing synchronization of a carrier and a sampling clock. The method comprises the steps of: determining a carrier frequency deviation and a sampling clock frequency deviation according to the received downlink signal; carrying out carrier frequency compensation according to uplink to-be-sent data; and carrying out sampling clock frequency compensation according to the uplink to-be-sent data. The invention also provides a user site device, which comprises a carrier frequency deviation measuring unit, a frequency deviation compensating unit, a sampling clock frequency deviation measuring unit and a clock sampling frequency compensating unit. According to the invention, the problem of synchronization of medium-short distance messaging systems based on control is solved, especially, the problem of synchronization when uplink multiple users are accessed in parallel is solved. The synchronization of the time and the frequency is mainly completed by an STA according to a downlink synchronization precursor, the deviation of the frequency and the sampling clock frequency is preprocessed, the synchronization problem is simplified to the signal-user synchronization problem, so that multiple access interference is eliminated without a complicated algorithm when a receiving end separates data of multiple users.

The invention relates to a united synchronized method based on the two-dimensional short sliding self correlation, comprising: firstly, the receiving end processes the two-dimensional short sliding self correlation for the receiving serial; secondly processing the circulated frame synchronization by using the result of the self correlation operation; then, processing the timing frequency synchronization and the carrier frequency synchronization by using the frequency bias estimation and the carrier frequency bias estimation. The invention also relates to a corresponding receiving end of the united synchronized method. The technical solution of the invention provides the united synchronized method and the receiving end thereof, which can offer reliable and precise synchronization under the bad transmitting condition; the invention is suitable for the transmitting system having the part circulated characteristic for all the transmitting serials.

The invention discloses a carrier frequency synchronous circuit and method of an OFDM (Orthogonal Frequency Division Multiplexing) system. The carrier frequency synchronous circuit comprises a decimal fraction frequency offset estimation circuit, a decimal fraction frequency offset compensation circuit, an integer frequency offset estimation circuit, an integer frequency offset compensation circuit and other circuits; correspondingly, the method comprises the following steps of decimal fraction frequency offset estimation, decimal fraction frequency offset compensation, integer frequency offset estimation and integer frequency offset compensation; a cross-correlation value of two adjacent synchronous sequences to be sampled of a frequency domain is subjected to normalization treatment to obtain a decimal fraction frequency offset estimation value, and decimal fraction frequency offset compensation correction is carried out by utilizing the estimation value; then, the high energy carrier sign bit of each OFDM sign subjected to fast Fourier transform (FFT) treatment is subjected to self-correlation computation, the self-correlation of a plurality of OFDM signs is subjected to summation computation to obtain an integer frequency offset estimation value, and then integer frequency offset compensation is carried out according to the integer frequency offset estimation value. By adopting the synchronous circuit and method, the computational burden can be reduced, the influence of noise to frequency offset estimation can be lowered, and low-power equipment is favorably designed and realized.

A method and sytem for achieving carrier frequency synchronization in a high speed receiver. A feedback loop in a carrier recovery system is operated at a down-sampled rate until carrier lock is detected. The output of a phase accumulator, operating at the down-sampled rate, is then extrapolated to provide extrapolated outputs to provide outputs at the original symbol rate. Addresses for a look-up table are then generated from the combined phase accumulator outputs and extrapolated outputs, such that the frequency and phase compensation offsets provided to a phase derotator and slicer are at the original symbol rate. The total pipeline delay as seen by the carrier recovery system is thus reduced. This in turn allows for more efficient correction of residual carrier frequency errors present in a complex baseband signal.

The invention discloses a carrier frequency synchronization method suitable for a millimeter wave inter-satellite link, and belongs to the field of inter-satellite communication systems. The method includes firstly, constructing a millimeter wave inter-satellite link communication scene, and any two satellites transmitting information through an inter-satellite link; next, launching the satellitefor the current time, the high-frequency wireless frame reaching a receiving end of another satellite through a millimeter wave inter-satellite link, obtaining a digital signal with carrier frequencyoffset after sampling, extracting an STF sequence rstf [n] of the current wireless frame, demodulating the sequence rstf [n] , extracting a phase difference, and obtaining a coarse frequency offset estimated value of the current wireless frame; and finally, carrying out fine estimation on the frequency offset estimation value again and compensating to the current wireless frame to realize carrierfrequency synchronization of the current frame; and sequentially selecting a next wireless frame, repeatedly extracting the STF sequence rstf [n], carrying out coarse estimation and fine estimation offrequency offset, and compensating a final estimation value to each frame, thereby realizing carrier frequency synchronization of each frame. According to the method, a more stable and accurate frequency offset estimation value can be obtained, so that the system performance is effectively improved.

The invention relates to a carrier synchronization method in a UFMC system, comprising the following steps: first, generating two sets of orthogonal codes at a sender, inserting the orthogonal codes as pilot sequences into original data, and modulating, filtering and sending the original data through UFMC; then, performing time-domain zero filling and 2N-FFT transform at a receiver, extracting data on even bands, sending the data to a filter matching the sender, getting the estimated value of data information using a zero forcing equalizer, extracting pilot signals and calculating the correlation between the two sets of pilot signals, and minimizing the correlation to achieve UFMC system carrier frequency synchronization; and finally, using an iterative algorithm to improve the accuracy of frequency offset estimation. According to the invention, the carrier frequency offset of the system is estimated by inserting a pilot frequency into each sub band of UFMC, so good properties of the UFMC system are maintained, and the accuracy and stability of frequency offset estimation are improved through iteration. Therefore, the bit error performance of the system is enhanced, the quality of communication is improved, and the design complexity of the filter in the UFMC system is reduced to a certain extent.

The invention provides a combined timing and frequency synchronization method based on a conjugated structure preamble. The method comprises following steps: 1. calculating a correlated signal r0(n, d) of a reception signal r(n) and a preamble signal c(n); 2. obtaining a difference correlation signal p(m, d) through calculation; 3. performing weighted accumulation on the difference correlation signal p(m, d) so as to obtain a weighted correlation function P(d); 4. normalizing the weighted correlation function P(d) by the use of the energy of the reception signal in a sliding window so as to obtain a normalized timing metric value M(d); 5. working out the maximum of the normalized timing metric value M(d) so as to obtain a timing offset estimated value epsilon-hat according to a formula shown in the description; 6. calculating a carrier wave frequency offset estimated value xi-hat of a decimal part; 7. compensating the reception signal by the use of the carrier wave frequency offset estimated value xi-hat of the decimal part so as to obtain the compensated reception signal r1(n, epsilon-hat); 8. calculating a carrier wave frequency offset estimated value q-hat of an integer part by the use of the reception signal compensated according to decimal frequency offset; and 9. working out the carrier wave frequency offset estimated value according to a formula that v-hat = q-hat + xi-hat. By employing the method, only one preamble signal having the conjugated structure is employed for combined signal timing and carrier wave frequency synchronization, and signal timing synchronization is not influenced by the frequency offset.

The invention relates to a frequency offset estimation method under a high-speed scene, and belongs to the field of the carrier frequency synchronization. The method comprises the following steps: computing frequency offset by using relativity between OFDM symbols located by a CRS in one sub-frame at first; and then performing frequency offset estimation by using CP-based frequency offset estimation algorithm; and finally modifying an estimation result of the frequency offset estimation algorithm based on CRS by using the estimation result of the CP-based frequency offset estimation result, thereby obtaining the final frequency offset. Under the condition of not additionally consuming frequency band resource and not performing symbol judgment, the estimation range of the frequency offset estimation algorithm based on a reference signal is enlarged to [-7.5KHZ, 7.5KHZ] from [-1KHZ, 1KHZ], so that the requirement of the high-speed scene is satisfied.

The invention relates to a method for synchronizing time and carrier frequency in a short-range wireless network, and belongs to the technical field of wireless communication. The method comprises the following steps of: obtaining the range of the tolerance of a receiving system to frequency deviation by tests; according to the maximum tolerance, performing phase deviation compensation of a local frequency-expanded modulation sequence, and obtaining a new local frequency deviation correlation value sequence; correlating the received correlation value sequence with the local correlation value sequences, and obtaining a group of correlation value sequences; and according to the position of the sequence corresponding to the maximum correlation value, realizing the decoding of the data. The time-frequency synchronizing method has the advantages of improving the time synchronization performance under the influence of the frequency deviation, making a receiver have lower energy consumption and higher receiving performance under the condition of bigger frequency deviation, improving an operational precision in the frequency deviation compensation and effectively improving the time synchronization performance of the receiver.

An ultrasonic measuring method includes: (A) receiving a coded spread spectrum ultrasonic signal in at least two receivers, and generating at least two received signals; (B) performing an quadrature detection on the received signals using the carrier frequency, and producing I and Q components of the received signals; (C) performing phase difference processing on the I and Q components with a coding period synchronized with that of the carrier frequency, and obtaining I′ and Q′ components from which a phase shift caused by a Doppler shift has been canceled; (D) despreading the I′ and Q′ components signals using different codes at time intervals synchronized with the carrier frequency, and obtaining despread I″ and Q″ components; (E) computing the amplitude and phase information based on the I″ and Q″ components; and (F) calculating the propagation distance and/or orientation of the ultrasonic wave based on the amplitude and phase information.

Systems and methods are described for carrier-frequency synchronization for improved AM and TV broadcast reception. A method includes synchronizing a carrier frequency of a broadcast signal with a remote reference frequency. An apparatus includes a reference signal receiver; a phase comparator coupled to the reference signal receiver; a voltage controlled oscillator coupled to the phase comparator; and a radio frequency output coupled to the voltage controlled oscillator.

The invention belongs to the field of digital communication receivers, and relates to a tracking control method of digital communication receiver time and carrier frequency synchronization. The tracking control method comprises the following steps of: selecting a parameter of a PID (Proportion Integration Differentiation) controller; obtaining a decimal time deviation R(k) between the carrier frequency and a symbol; obtaining a residual deviation E(k) subjected to former deviation correction; carrying out following clinical value regulation on the decimal time deviation R(k): calculating a deviation correction value U(k) of the tracking control; and judging whether the U(k) is in the specified range, if not, resetting the parameter of the PID controller, if yes, carrying out carrier frequency and symbol time synchronization by using the correction value. The invention can better eliminate influences of steady-state errors, and is not sensitive to influence of quality of the tracking control to the control coefficient, thereby ensuring that the control coefficient is determined more simply and easily.

The present teachings include a method and computing apparatus for triggering synchronization of a satellite modem to a carrier frequency of a beam of a satellite, retrieving ephemeris information for the satellite and beam configuration information for the beam, calculating a velocity of the satellite per the ephemeris information, and adjusting the carrier frequency of the satellite modem when communicating via the beam to compensate for a doppler offset induced in the carrier frequency by the velocity. In the method, the satellite has a satellite type selected from a Geosynchronous Earth Orbit (GEO), Medium Earth Orbit (MEO) or Low Earth Orbit (LEO) type of satellite, and the satellite type is different than a satellite type of an immediately preceding synchronization.

The invention discloses a device and a method for adaptive compensation of SCO in an LTE system. When a DL subframe is normally received, if it is determined that CFO is equal to or greater than 7.5 kHz, then the value of the integer part which is obtained after dividing CFO by 7.5 kHz is acquired, synchronization adjustment of the sampling clock frequency and the carrier frequency is executed, then the value of CFO%7.5 kHz is obtained after modulus of CFO and 7.5 kHz, and SCO compensation is executed; if it is determined that CFO is smaller than 7.5 kHz, then the value of CFO%7.5 kHz which is acquired after modulus of CFO and 7.5 kHz is directly obtained, and SCO compensation is executed. Therefore, based on the technical scheme of the invention, the performance of the whole system is guaranteed to be stable during the SCO compensation process.

The method includes following steps and devices. At sending end, specific PN sequences are inserted into every other section of digital modulated communication signals and then the signals are sent. PN sequence is C=(v X u). At receiving end, matched filtering is carried out for baseband signal containing PN sequence with frequency being converted so as to output P pieces of signals in complex number. Using likelihood function and FFT transforms the said complex signals to frequency domain, from which coarse position omega 0 of max. amplitude is found. Using Chirp-Z transform finds position increment information omega1. quadratic interpolation is carried out for omega1 to obtain position increment omega, which is exact position of max. amplitude. Frequency shift fe is calculated from formula fe=fs.(omega+omega0 - M.P/2)/K.M.P. fe controls oscillation frequency of oscillator to reach frequency synchronism. The invention also includes receiver and transmitter for implementing the method.