134 results about "Integer frequency offset" patented technology

Disclosed is a method, a computer program product and a device that includes a receiver for receiving a downlink signal transmitted into a cell. The receiver is operable to obtain time, carrier frequency and cell-specific preamble synchronization to the received signal and includes a plurality of synchronization units that include a first detector to detect a frame boundary using preamble delay correlation; a second detector to detect the frame boundary with greater precision using a conjugate symmetry property over a region identified by the first detector; a cyclic prefix correlator to resolve symbol boundary repetition; an estimator, using the cyclic prefix, to estimate and correct a fractional carrier frequency offset; an operator to perform a Fast Fourier Transform of an identified preamble symbol and a frequency domain cross-correlator to identify cell-specific preamble sequences and an integer frequency offset in sub-carrier spacing. The transmitted signal may be a downlink signal transmitted into the cell from a base station that is compatible with IEEE 802.16e (WiMAX).

The invention provides a synchronous processing method based on new CMMB (China Mobile Multimedia Broadcasting) synchronous signals. The CMMB synchronous signals comprise first training sequences and second training sequences; the first training sequences comprise CAZAC (Constant Amplitude Zero Auto Correlation) sequences, and the second training sequences comprise PN (Pseudo-Noise) sequences; in the synchronous processing method, the CAZAC sequences are utilized to achieve coarse symbol timing offset estimation and decimal frequency offset coarse estimation; the PN sequences are utilized to achieve the estimation of strongest path time delay in multipath, and the multipath is taken as coarse symbol timing positioning; the CAZAC sequences and the PN sequences are utilized to achieve the integer frequency offset estimation; the fast Fourier transform (FFT) is performed on the PN sequences to achieve the channel response estimation so as to estimate a first path time delay and achieve the fine symbol timing position estimation; and a maximum likelihood (ML) criterion is utilized to process the PN sequences in the second training sequences to obtain the decimal frequency offset fine estimation. The synchronous processing method can effectively improve the synchronous accuracy and can achieve better synchronization performance in the mobile communication environment with low signal-to-noise ratio.

A method and apparatus for performing time synchronization and an OFDMA receiver thereof are provided. The method preferably includes performing a differential phase correlation in a frequency domain based on one received sequence and one reference preamble and detecting an integer frequency offset based on a result of the differential phase correlation. The method and apparatus advantageously enable the use of one OFDM symbol to estimate ICFO and the use of a simple method to facilitate ICFO detection. Moreover, the performance of the integer frequency offset estimation becomes more robust in high noise and time-variant fading channels, with reduced hardware complexity.

The invention provides a TD-LTE (Time Division-Long Term Evolution) frequency offset estimation method for a relay system and relates to services or facilities suitable for a wireless communication network. The method comprises the following steps: obtaining positions of synchronizing signals and information about cell ID (Identity) number and cell group ID number inside a cell identification group from receiving signals at a relay end, so as to obtain a synchronizing signal sequence received by a relay; secondly, generating a local PSS (Primary Synchronization Signal) and an SSS (Secondary Synchronization Signal) according to the obtained relay-end cell ID number and cell group ID number relay end; thirdly, carrying out an integer-frequency-offset estimation process by using the PPS received at the relay end and the obtained relay locally-generated PSS; and finally, carrying out integer-frequency-offset adjustment on the receiving signals of the PSS/SSS at the relay end by using the obtained result epsilon I of the integer-frequency-offset estimation, and carrying out fine-frequency-offset estimation process by using a corresponding algorithm. Therefore, the problem of the frequency offset estimation at the relay end can be solved, and the sending frequencies of the signals received at the relay end and the signals at a base station end are synchronous.

The invention discloses a method for assessing an integer frequency offset of a TD-LTE (Long Term Evolution) system. According to the invention, the method comprises the following steps: assessing a timing fine synchropoint and a decimal frequency offset near a coarse synchronous position; performing decimal frequency offset compensation to time-domain signal; confirming an FFT (Fast Fourier Transform) initial window according to the timing fine synchropoint; filtering subcarrier outside a center band frequency of the frequency-domain signal by a filter after switching to the frequency domain; retaining the PSS frequency domain signal; and accessing the integer frequency offset according to the position where the maximal subcarrier data energy is positioned. The method provided by the invention can be effectively resistant to larger timing error, and has the advantages of more accurate calculating and lower calculation complexity.

The invention provides a method for estimating integer frequency offset with timing error during the communication synchronization, which comprises the following steps: a constant-amplitude Chu sequence with ideal autocorrelation characteristics is selected as a frequency domain difference sequence C(k),a first element S(0) in a frequency domain training sequence is defined to be equal to 1, the frequency domain training sequence S(k) with a length of N is obtained according to the recursion formula S(k)=C(k-1)S(k-1), and the S(k) is transformed into a time domain training sequence s(n) through an IFFT; after a receiving sequence finishes the fractional frequency offset compensation, two sections of receiving sequences with a length of N are taken out according to a coarse timing sequence, and two sections of receiving sequences are added to obtain a receiving sequence r(n) with a length of N; the frequency domain of the sequence r(n) is transformed into R(k) through FFT, the formula D(k)=R(k+1)(R(k))<*> is utilized to calculate a receiving frequency domain difference sequence D(k), the cyclic shift correlation is performed through the conjugation of the received sequence D(k) and the sequence C(k), and a related peak value corresponds to the integer frequency offset estimation epsilon int of a system, as shown in the right formula. The method strengthens the frequency offset estimation performance and improves the transmission efficiency of the system on the premise of not affecting the timing synchronous performance.

The invention discloses a joint estimation method for synchronizing frames, frequencies and fine symbols for orthogonal frequency division multiplexing (OFDM). The method comprises the following steps: carrying out autocorrelation operations of small point length and big point length on base band data sequences at the receiving terminal in parallel; jointly determining the frame synchronization position in real time and in parallel according to the small point autocorrelation peak and the big point autocorrelation peak; computing integer frequency offset coarse estimation value and decimal fraction frequency offset coarse estimation value according to the small point autocorrelation peak and the big point autocorrelation peak; estimating the final frequency offset detection value from the integer frequency offset coarse estimation value and the decimal fraction frequency offset coarse estimation value with a frequency offset dereferencing decision device; carrying out frequency offset correction on the base band data sequences according to the estimated final frequency offset detection value; and carrying out cross-correlation on the corrected base band data sequences and the local data sequences and determining the accurate fine symbol synchronization position through the cross-correlation peak. The contradiction of complex system measure function hardware design in the traditional time-domain joint estimation systems is solved by using the method.

The invention provides a method for synchronizing a downlink time and a frequency of an OFDM system, which comprises that: a sending end sends a training symbol for marking different cells, wherein the training symbol consists of two identical subsymbols and a cyclic prefix in a time domain, the time length of each subsymbol is Tuus, and the time length of the cyclic prefix is Tgus; a receiving end carries out autocorrelation calculation on a received signal and searches an autocorrelation platform in an autocorrelation value of the received signal; after the effective autocorrelation platform is detected, an initial position of the autocorrelation platform is determined as a time synchronization position, and a decimal frequency offset can be calculated by using the autocorrelation value of the autocorrelation platform. The invention further can intercept the received signal to carry out mutual correlation with the local training symbol from the time synchronization position acquired by the method, more accurately determines the time synchronization position and an integer frequency offset according to a double correlation peak generated by the structure of the training symbol, and at the same time can finely adjust the decimal frequency offset and distinguish different cells.

The implementation mode of the invention provides a time and frequency synchronization method in a wireless communication system, which comprises the steps of carrying out the symbol timing estimation and the fine frequency estimation on received signals based on the Orthogonal Frequency Division Multiplexing (OFDM) technique; carrying out the timing estimation on the Packet Switching Service (PSS) through the matched filtering of the received signals; determining at least two continuous OFDM symbols as candidate OFDM symbols containing the PSS; shifting the candidate OFDM symbols compensated by the fine frequency estimation into a frequency domain; carrying out the cyclic shift channel estimation on the corresponding sub-carriers of each candidate OFDM symbol of the at least two candidate OFDM symbols; shifting the cyclic shift channel estimation result of each candidate OFDM symbol into a time domain; figuring out the energy value of each sampling point according to the time-domain channel impulse response of each integer-frequency-offset value; and determining the OFDM signals containing the PSS and the calculated value of the integer-frequency-offset value based on the energy maximum principle.

A frequency synchronization apparatus and method for OFDM systems. The frequency synchronization apparatus is comprised of a digital mixer, a first synchronizer and a second synchronizer. The digital mixer acquires a baseband signal by means of a local frequency and adjusts the local frequency in response to an integer frequency offset and a fractional frequency offset. The first synchronizer takes a sequence of received samples derived from the baseband signal in a time domain to estimate the fractional frequency offset. The fractional frequency offset is fed back to the digital mixer. After that, the second synchronizer takes a sequence of demodulated symbols derived from the baseband signal in a frequency domain. The second synchronizer yields the integer frequency offset through a coarse search stage and a fine search stage. Then, the integer frequency offset is fed back to the digital mixer.

Systems and methods for wide offset frequency synchronization in OFDM communications. Frequency domain OFDM bursts include training symbols having known transmitted values in known frequency domain positions. Received values at the known training symbol positions are correlated from burst to burst. The magnitudes are used to establish and correct small integer frequency offsets as measured in frequency domain symbol widths. The phase of the correlation result is used to determine and correct integer frequency offsets that exceed the training tone spacing. Use of the phase to correct large frequency offsets greatly extends the acquisition range required for low cost analog components.

The invention relates to a united integer frequency offset estimation method and device through utilization of an inter-multi-symbol pilot. The method comprises the following steps of finishing synchronization by a system, thereby determining a position of a cyclic prefix CP of each OFDM (Orthogonal Frequency Division Multiplexing) symbol; calculating decimal frequency offset through the cyclic prefixes in a time domain and correcting the decimal frequency offset in a receiving signal; in a frequency domain, carrying out conjugate multiplication on local pilot subcarriers and receiving subcarriers at different initial positions, thereby obtaining sequence signals, carrying out self-correlation conjugate multiplication on the adjacent sequence signals, thereby obtaining self-correlation sequences, and carrying out summation on the self-correlation sequences, thereby obtaining maximum likelihood self-correlation values; determining an initial position of a pilot index according to the maximum likelihood self-correlation values of multiple symbols; and subtracting the initial position of the pilot index from a receiving end pilot position to obtain the integer frequency offset, and extracting all subcarrier information according to an integer frequency offset value and direction in the frequency domain. According to the method and the device, the integer frequency offset estimation is carried out through unity of the inter-multi-symbol and maximum likelihood conjugate correlation, so the accuracy is greatly improved.

The invention discloses an SC-FDM (single-carrier Frequency-division multiple) system time frequency synchronizer and a synchronization method, mainly solving the problems of a low energy utilization rate, a small frequency offset estimation scope and low estimation precision in the prior art. The synchronizer comprises a delay correlation selection module, a fine frequency compensation module, a coarse frequency compensation module and a time refinement processing module. The synchronization method comprises the following steps: (1) employing Chu sequence with a communication system to construct SC-FDM signal frame; (2) processing the signal to obtain a time coarse synchronization position; (3) carrying out phase extraction and fractional frequency offset compensation treatments on a signal coarse synchronization point; (4) obtaining integer frequency offset of the signal and carrying out integer frequency offset compensation treatment on the received signal; (5) utilizing local training sequence to process the signal and obtain a precise beginning time of the signal. The synchronization method provided in the invention has the advantages of a high energy utilization rate, a large frequency offset estimation scope and high estimation precision, and is suitable for the uplink of a high speed mobile communication system in an LTE (Long Term Evolution) standard.

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.

The invention discloses a method and a device for estimating integer frequency offset; the method comprises the steps: fast Fourier transformation is carried out to a plurality of time-domain positions which receive signals and comprise timing synchronization positions so as to obtain multiple groups of frequency domain data; the frequency domain data are correlated with local pilot sequences respectively in the searching range of the integer frequency offset so as to obtain multiple groups of correlation values; peak search is carried out to the multiple groups of correlation values; and the integer frequency offset corresponding to the highest value among the correlation values is taken as the integer frequency offset estimation. With the adoption of the method and the device in the embodiment, a frequency domain correlation is carried out in a plurality of positions around the timing synchronization position, and the integer frequency offset corresponding to the highest value among the correlation values is taken as the integer frequency offset estimation, thereby increasing the accuracy of the integer frequency offset estimation and reducing the influence on the integer frequency offset estimation by unsatisfied timing synchronization.

The invention discloses a frequency domain joint estimation method of integer frequency offset and fine symbol synchronization. The method comprises the following steps of: carrying out circular shifting and differential modulation on a frequency domain training sequence of a transmitting end; then carrying out cross-correlation on the frequency domain training sequence processed by the circular shifting and the differential modulation and a frequency domain training sequence processed through differential modulation of a receiving end; obtaining a corresponding circular shifting bit through detecting the peak value of a cross-correlation result so as to obtain an integer multiple frequency offset estimation value; and meanwhile, solving for a fine symbol synchronization result through taking a phase angle of the cross-correlation result. By utilizing the invention, the integer multiple frequency offset estimation and the fine symbol synchronization can be carried out simultaneously, the problem that the integer multiple frequency offset estimation and the fine symbol synchronization are not accurate and mutually influence in the traditional time frequency joint estimation method is solved, and the accuracy of the integer multiple frequency offset estimation and the fine symbol synchronization is improved.

The invention provides a synchronous acquisition method and receiving end equipment of an OFDM (orthogonal frequency division multiplexing) signal. The synchronous acquisition method comprises the following steps of multiplying the front or rear half of the OFDM signal, which has a length of N, by a pseudo noise sequence at a receiving terminal to calculate a timing metric function; multiplying the radication of a power factor by a splicing sequence to obtain a training sequence in the OFDM signal, wherein a front son sequence multiplies by the pseudo noise sequence to obtain the splicing sequence; searching the maximum value when the timing metric function exceeds a reserved threshold, wherein a sampling point which corresponds to the maximum value is a timing estimation point; determining a decimal frequency deviation estimated value at the timing estimation point, and carrying out decimal frequency deviation compensation on the sequence which is behind the timing estimation point and has the length of N in the OFDM signal; and carrying out circulating shift cross-correlation on the sequence subjected to decimal frequency deviation compensation and the training sequence in a time domain, searching for a maximum value to obtain an integer frequency offset estimated value. The synchronous acquisition method and the receiving end equipment provided by the invention have the advantages that the exact and rapid synchronous acquisition is realized.

The invention relates to a synchronous method used for a digital audio broadcasting receiver. The method comprises the following steps: fractional frequency offset estimation, fractional frequency offset correction, integer frequency offset estimation and timing offset estimation are performed to data received at the acquisition phase, frequency offset correction is performed according to the fractional frequency offset estimation and the integer frequency offset estimation, and time offset correction is performed according to the timing offset estimation; the fractional frequency offset estimation and the timing offset estimation are performed to data received at the tracking phase, frequency offset correction is performed according to the fractional frequency offset estimation, time offset correction is performed according to the timing offset estimation, and the timing offset estimation is selfadaptive according to the signal-to-noise ratio. The method is applied to the digital audio broadcasting receiver of a mobile terminal, when the signal is weaker, the program is received at the mobile terminal for a long term, or the acceleration motion and the deceleration motion are performed at the mobile terminal suddenly at high speed, high quality audio broadcasting signals can be demodulated, and further the satisfying reception effect can be obtained.

The invention relates to a frequency offset estimation method and a frequency offset estimation system for a frequency domain strong interference environment of an OFDM (Orthogonal Frequency DivisionMultiplexing) system. The frequency offset estimation method comprises the following steps: receiving and performing interference cancellation on an FFT (Fast Fourier Transform)-transformed subcarriersignal; performing integer frequency offset calculation and integer frequency offset adjustment on the subcarrier signal after the interference cancellation; and performing fractional frequency offset calculation on the subcarrier signal adjusted by the integer frequency offset according to the phase difference between the inter-symbol pilots to perform fractional frequency offset adjustment. Thefrequency offset estimation method and frequency offset estimation system provided by the invention directly perform interference cancellation on the FFT-transformed subcarrier signal firstly, then perform integer frequency offset calculation and adjustment on the interference-canceled subcarrier signal, and perform fractional frequency offset calculation on the subcarrier signal adjusted by theinteger frequency offset according to the phase difference between the inter-symbol pilots so as to perform fractional frequency offset adjustment, which is more accurate in calculation by using own characteristics of the OFDM system with no need to separately set a interference cancellation device, and saves resources and computational complexity.

The invention belongs to the technical field of the wireless communication, and discloses a OFDM synchronization method under a high-dynamic environment. The OFDM synchronization method under the high-dynamic environment comprises the following steps: performing transformation on a frequency domain ZC sequence; performing IFFT on the transformed frequency domain ZC sequence; performing timing synchronization by a receiving end according to a lead sequence structure of a sending end, and acquiring an accurate timing point according to a timing metric function; performing trice iterative fractional part of frequency offset estimation; estimating to obtain the fractional part of frequency offset and performing frequency offset compensation on a signal; performing integer frequency offset estimation by use of the shifting characteristic of the ZC sequence and compensating, thereby accomplishing the synchronization at the receiving end. A symbol sample count in the OFDM system adopted by the method disclosed by the invention is less, so that the entire complexity is low, the synchronization acquisition can be fast accomplished; and meanwhile, the length of the lead sequence can be added or deleted according to system demands, and the flexibility is high; the synchronization method disclosed by the invention can be used for OFDM synchronization acquisition in a remote-measuring system and like high-dynamic environment.

The invention discloses a detection and estimation method for fine synchronization of a downlink primary synchronization signal in an NB-IoT system. The method comprises the following steps: step (1),acquiring a time domain sampling sequence by an air interface receiver by adopting a sampling rate of 1.92MHz; step (2), performing NPSS coarse synchronization estimation by a terminal receiver; andstep (3), performing second fine synchronization at the sampling rate of 1.92Msps according to time offset and frequency offset results estimated in the course synchronization in step (2), and carrying out self-correlation operation by using an NPSS sequence and a local sequence, wherein the local sequence is generated by using integer frequency offset, and accurate time offset and the integer frequency offset are determined according to a peak position maximum value. The method of the invention has the following beneficial effects: the fine synchronization is that a correlation operation is carried out after an accumulation operation is carried out, so that the storage capacity is reduced; the fine synchronization adopts a pipeline structure based on two adders and one multiplier, so thatthe calculation amount and the storage size are reduced; and the fine synchronization frequency offset estimation stores a group of local sequences and performs iterative updating to replace multiplegroups of local sequences, so that the storage capacity is reduced.

The invention discloses a 5G waveform system synchronization method based on index modulation. The method comprises the following steps: dividing sending end parallel data of a filter orthogonal frequency division multiplexing system based on index modulation into index bit data and constellation modulation data, performing sub-band matching filtering processing, cyclic prefix removal and Fouriertransform at a receiving end, detecting the position of an activated sub-carrier, estimating an index bit, and demodulating constellation symbol information; establishing a training sequence based ona pseudo-random sequence and a Zadoff-Chu sequence, and performing timing and frequency offset estimation based on a pilot frequency data aided method; and completing timing estimation, performing fractional frequency offset estimation, performing integer frequency offset estimation by using the power difference between the activated subcarrier and the silent subcarrier, determining a receiving end Fourier transform starting window according to timing estimation information, determining a receiving end demodulation carrier frequency according to an estimated frequency offset value, and completing system synchronization. According to the invention, on the premise of not reducing the transmission efficiency, the influence of frequency offset on the system performance is effectively reduced.

The invention provides an integer frequency offset estimation method based on an OFDM preamble. The integer frequency offset estimation method comprises the following steps: firstly, obtaining an OFDM frequency domain preamble through FFT, circularly shifting the OFDM frequency domain preamble by d sampling positions and then performing conjugate multiplication on the circularly-shifted OFDM frequency domain preamble and a known frequency domain preamble at a receiving end to obtain signal; secondly, calculating difference correlation data, obtaining the absolute values of the difference correlation data and performing mean weighing accumulation on the absolute values to obtain a frequency offset estimation measure; and finally, obtaining the maximum value of the frequency offset estimation measure to obtain an integer frequency offset estimator. The integer frequency offset estimation method only requires one OFDM block preamble rather than using two preambles or inserting a pilot frequency in a data symbol; difference correlation is performed in the frequency domain of the OFDM signal to estimate the integer frequency offset and the estimation performance is not affected by the timing residual offset of the symbol; besides, an implementation structure of mean summation on Mo difference results is adopted to achieve a relatively low wrong detection probability under a multipath channel condition.

The invention relates to an OFDM (Orthogonal Frequency-Division Multiplexing) training sequence construction method and synchronization method, comprising the following steps: a PN (pseudo-noise) sequence is utilized to construct a sequence with a front and back repetition conjugate symmetric structure; weighting treatment is performed on the sequence, and a training sequence with a transmitting terminal used for synchronization is obtained; a receiving terminal defines a timing metric function, and symbol timing synchronization is finished by searching the maximum of the timing metric function; an estimation of fraction frequency offset is obtained by computing a phase difference of two front and back repetition parts of the received training sequence; an estimation of integer frequency offset is finished by utilizing the influence of integer frequency offset on correlated characteristics of a training sequence frequency domain. The OFDM training sequence construction method and synchronization method eliminates the influences of side peaks and peak platforms on synchronization, which are caused by symmetrical structure sequences and cyclic prefixes in a traditional synchronization method, so that the timing synchronization accuracy rate is higher, the estimation of synchronization frequency offset has a smaller error of mean square, and the OFDM training sequence construction method and synchronization method can be effectively used for time and frequency synchronization of an OFDM system in a multipath fading channel.