404 results about "Symbol synchronization" patented technology

A cell search apparatus and method in an OFDM mobile communication system are provided. In the cell search apparatus, a symbol synchronization acquirer acquires OFDM symbol synchronization by performing CP correlation for a plurality of OFDM symbol intervals. A frame cell synchronization acquirer sorts received OFDM symbols according to the acquired OFDM symbol synchronization, and acquires frame cell synchronization by performing preamble correlation for a plurality of frame cell intervals. A pilot pattern detector sorts received frame cells according to the acquired frame cell synchronization, and detects a pilot pattern for identifying a base station by monitoring a plurality of frame cells.

In an OFDMA-based cellular system, a frame of a downlink signal includes a common slot and traffic slots. The common slot includes a synchronization preamble and a cell search preamble. The synchronization preamble has a structure for synchronizing time and frequency, and the cell search preamble has a cell search structure. The traffic slot includes pilot symbols provided on the time and frequency axes. A cyclic prefix is used to estimate initial symbol synchronization, and the initial symbol synchronization and the synchronization preamble are used to synchronize the frame. The synchronization frame and the cell search preamble are used to estimate time and frequency synchronization. The cell search preamble is used to search cells. When the initial synchronization is performed, the cyclic prefix is used to track the frequency, the synchronization preamble is used to track symbol synchronization, and the cell search preamble is used to track fine frequency synchronization.

A receiver determines a symbol synch time for recovering data from a symbol of signal samples generated in accordance with Orthogonal Frequency Division Multiplexing. Each symbol includes a guard period which carries data repeated from a data bearing part of the symbol and pilot signal samples. The receiver comprises a pilot assisted tracker which is operable to determine an adjustment to the symbol synch time from a pilot assisted channel impulse response estimate, a guard adapted filter processor comprising a filter and a filter controller operable to adapt the impulse response of the filter to the signal samples from the guard period. The controller is operable to excite the filter with the symbol signal samples to generate an output signal which provides a further representation of the channel impulse response. A symbol time adjustment estimator is operable to adjust the symbol synch time in accordance with the adjustment provided by at least one of the pilot assisted tracker and the guard adapted filter processor. The receiver provides an improved estimate of the symbol synch time by combining a pilot assisted tracker with a guard adapted filter processor. The pilot assisted tracker estimates the symbol synch time from a channel impulse response estimate generated from pilot signal samples. By combining the synch time adjustment estimated from the pilot assisted channel impulse response, with the adjustment estimated by the guard adapted filter processor, an ambiguity in a relative time of arrival of signal paths of the channel impulse response with respect to the main signal path is obviated.

An apparatus and method for OFDM demodulation establish symbol synchronization to minimize between-symbol interference even under an environment where multipath occurs.An incoming signal is an OFDM signal including a transmission symbol structured by a valid symbol period and a guard interval, and a predetermined synchronization symbol is included in the OFDM signal for every transmission frame. A correlator calculates how a signal generated by a synchronization symbol generator and the OFDM signal are correlated. A correlation calculator then calculates a correlation therefrom. An integrator integrates the calculated correlation by the guard interval. A timing determination device determines symbol timing from the integrated correlation. An FFT window generator outputs operation timing for Fourier transform from the determined symbol timing. Based on the signal outputted from the FFT window generator, the apparatus for OFDM demodulation extracts a signal in the valid symbol period from the transmission symbol for demodulation.

A receiver for detecting and recovering data from Orthogonal Frequency Division Multiplexed (OFDM) symbols. The receiver comprises a demodulator, symbol synchronization unit, frequency transform processor, and coarse frequency offset detector. The demodulator generates sampled symbols. The symbol synchronisation unit has correlators, which receives the sampled symbols, and a correlation detection processor. Each correlator auto correlates each sampled symbol, and the correlation detection processor determines a start point of each symbol. The frequency transform processor receives the sampled symbols and performs a frequency transform on each symbol. The coarse frequency offset detector includes a pilot data filter, which includes taps corresponding to a value and spacing of the pilot pattern of the symbols and arranged to receive as an input the frequency domain symbols from the frequency transform processor, and a coarse frequency offset detect processor, which is arranged to detect a coarse frequency offset output from the pilot data filter.

A modem, or a communication system, in its transmission section, has signal-formatting circuitry followed by circuitry for insertion of a sequence of pilot symbols into a sequence of data symbols outputted by the formatting circuitry. Placement of the insertion circuitry after the formatting circuitry permits a variety of formatting options without effecting the sequence of pilot symbols that serves as a time reference useful in detection of a signal transmitted by the modem. The reception section of the modem is equipped correspondingly to process a received composite signal of data symbols having a prescribed format and a sequence of pilot symbols. The reception section extracts the sequence of pilot symbols from the composite signal, and employs the pilot symbols to develop a time base for operation of circuitry for decoding the format of the received composite signal to extract data from the composite signal.

Disclosed is a symbol synchronization method in an OFDM-based communication system which includes multiple access nodes supporting wireless connection of terminals, supports multi-connection of each terminal for the access nodes and performs synchronization by means of a cyclic prefix. The symbol synchronization method includes monitoring connection of a new access node; setting a number of times by which the new access node transmits equal symbols and a number of times by which at least one existing access node transmits the equal symbols when the connection of the new access node is detected; transmitting the equal symbols by the determined number of times by each access node; and performing synchronization by means of the symbols received from the access nodes by the terminal.

A rectangular-to-polar-converter receives a complex input signal (having X0 and Y0 components) and determines an angle φ that represents the position of the complex signal in the complex plane. The rectangular-to polar-converter determines a coarse angle φ1 and a fine angle φ2, where φ=φ1+φ2. The coarse angle φ1 is obtained using a small arctangent table and a reciprocal table. These tables provide just enough precision such that the remaining fine angle φ2 is small enough to approximately equal its tangent value. Therefore the fine angle φ2 can be obtained without a look-up table, and the fine angle computations are consolidated into a few small multipliers, given a precision requirement. Applications of the rectangular-to-polar converter include symbol and carrier synchronization, including symbol synchronization for bursty transmissions of packet data systems. Other applications include any application requiring the rectangular-to-polar conversion of a complex input signal.

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 discloses a multi-carrier synchronizing system and a multi-carrier synchronizing method which are applied to an OFDM multi-carrier system. The multi-carrier synchronizing system comprises a symbol synchronizing module and a frame synchronizing module, wherein the symbol synchronizing module carries out related calculation on a received sequence and a local sequence and determines the symbol synchronizing position by detecting the related peak value of a continuous symbol window, the frame synchronizing module calculates the cumulative sum of the differentials between a phase of a current symbol and an average phase of former symbols, compares the cumulative sum with a preset judgment threshold and finds out the frame synchronizing position after judgment. The multi-carrier synchronizing method comprises the steps of carrying out related calculation on received signals and the local sequence after average filtering is carried out on the received signals, determining the symbol synchronizing position by detecting the related peak value of the continuous window, and judging whether frames are synchronized by calculating the phase differential of two continuous symbols according to the symbol synchronizing position. Compared with the existing synchronizing technology, the multi-carrier synchronizing system and the multi-carrier synchronizing method have the advantages of being low in complexity, high in accuracy and capable of being achieved easily through hardware.

The invention discloses a GFSK baseband digital receiver and a baseband synchronization and demodulation method of the GFSK baseband digital receiver. The receiver comprises a phase difference detection module, a frequency shift estimation module, a frequency shift compensation module, a matched filtering module, a direct current component estimation and removing module, a selector and a synchronization and demodulation module. According to the receiver and the method, DFT operation of a specific frequency point is carried out on code element envelope signals output through phase difference detection; whether there are leader sequence signals or not is judged; moreover a corresponding frequency shift is calculated; frequency compensation and matched filtering are carried out on follow-up baseband signals; code element envelope is output through difference detection; and at this time, the direct current component estimation and removing module and the synchronization and demodulation module of the backward stage start working. The receiver is equipped with a frequency shift estimation and compensation circuit, thus improving the performance of the receiver; signal demodulation and code element judgment are carried out in a phase domain; the symbol synchronization and sampling clock synchronization of the receiver are realized based on a counter; and the receiver is simple and reliable in structure and can adapt to various different data rates.

In an OFDM receiver, a synchronisation pulse for defining a Fast Fourier Transform window is generated by examining the output of a correlator to find a sub-interval within which there is maximum correlation between samples of the symbol separated by the length of the useful part of the symbol. The synchronisation pulse is generated during this sub-interval (102). Adjustments to the timing of the synchronisation pulse are made only if the current error is significant and persistent. A signal representing the amount of adjustment is used to determine phase rotations applied to the output of the FFT circuit.

One aspect provides an optical communication system. The system includes an optical-to-digital converter, a frequency estimator and a symbol synchronizer. The optical-to-digital converter is configured to receive an optical OFDM bit stream including an OFDM symbol bearing payload data and a symbol header preceding the OFDM payload data. The frequency estimator is configured to determine a carrier frequency offset of the payload data from the symbol header. The symbol synchronizer is configured to determine a starting location of the payload data within the bit stream by cross-correlating a synchronization pattern within the symbol header with a model synchronization pattern stored by the symbol synchronizer.

A synchronization apparatus and method for an OFDM system includes four portions: delay conjugate multiplication, phase processing, delay moving sum and minimum value detection. The invention performs the correlation phase operation and finds out the location of abnormal change for the phase difference of the output signal. The location is used for the reference of symbol synchronization. It overcomes the problems of incorrect judge about synchronization location due to the channel fading or noise. The invention can be applied to wire / wireless communications or digital video broadcasting-terrestrial systems, specialized in symbol synchronization at a receiving end.

A method and apparatus for enhancing synchronization in a heterogeneous network, including transmitting an auxiliary synchronization signal by a base station in a pico cell, a transmission interval of the auxiliary synchronization signal being 10 ms or 5 ms, and the auxiliary synchronization signal being located in a 0th subframe and / or a 5th subframe of each transmission frame; and notifying by the base station to user equipment in a cell range extension (CRE) region to detect the auxiliary synchronization signal, so that the user equipment performs symbol synchronization and frame synchronization in accordance with the auxiliary synchronization signal in accessing to the pico cell, and high-layer signaling indication and a auxiliary synchronization signal are combined, user equipment in a CRE region of the pico cell may obtain synchronization, thereby not only ensuring compatibility but also satisfying requirements of the system performance with a relatively low time frequency resource overhead.

The invention relates to a symbol synchronization and Doppler compensation method for a mobile orthogonal frequency division multiplexing (OFDM) underwater sound communication signal. The method comprises the following steps of: obtaining rough estimation of a first OFMD symbol start position according to a frame header signal, extracting a symbol, then obtaining Doppler expansion rough estimation of the symbol according to a frequency measurement simple-frequency signal in the symbol, converting the symbol to a frequency domain according to Chirp-z conversion, searching a precise start moment and a Doppler expansion amount of the symbol by taking a pilot of the frequency domain and a relevant value of a local pilot as cost functions, presuming the start position of the next symbol according to the start position of the current symbol, extracting the next symbol, and repeating the operations till the end of a frame of signal. According to the Doppler measurement and compensation method, based on the Chirp-z conversion, the measurement and compensation precision is high; the Chirp-z conversion is implemented according to fast Fourier transformation (FFT); the practicability is high; according to the Doppler expansion search method which is in a manner that large step length is superior to small step length, so that the search efficiency is high; a Doppler measurement range is not limited; and the method can be used for constant-speed motion and variable-speed motion.

A signal reception device is disclosed that is capable of detecting symbol synchronization timing with high precision in accordance with a condition of a propagation path even in an environment involving multi-path interference. The signal reception device adopts an OFCDM transmission scheme or a multi-carrier transmission scheme. The signal reception device includes a received signal information calculation unit to calculate received signal information representing a signal reception condition of a received signal; an output combination unit to combine correlation values in a predetermined section obtained by correlation detection based on the received signal information; and a symbol timing detection unit to detect a symbol synchronization timing based on the combined value.

An apparatus for demodulating an analogue input signal comprises a hard limiter stage (4) for converting the signal to a two level signal, A digital down converter / low pass filter stage (6) converts the signal to a base band signal, and a symbol synchronization stage (8) extracts symbol timing. An instantaneous phase detector (10) calculates the instantaneous phase of the one or more symbols associated with the input signal. If the input signal has been modulated according to a pi / 4DQPSK, pi / 2DBPSK, GMSK, or a GFSK modulation scheme, a differential detector (12) determines a difference in the phase between adjacent symbols, a coarse frequency offset compensation stage (14) applies a compensation signal to compensate for frequency offset, and a frequency offset estimation stage (16) updates this compensation signal. A demapper (18) generates a demodulated output signal after compensation by the frequency offset compensation stage.

A communication system and method is disclosed that performs symbol boundary synchronization by generating a symbol alignment estimate from a partial signal correlation; and then refining the symbol alignment estimate via a carrier phase calculation. To generate the symbol alignment estimate, two methods are disclosed. After an estimate is determined, an embodiment provides for refining the symbol alignment estimate via a carrier phase calculation by determining a carrier phase of two adjacent carriers, determining a phase error as directly proportional to an offset from the start of a symbol, determining a phase difference contribution due to a communication channel and device hardware, and counter-rotating the determined carrier phase by an angle of a constellation point at a transmitter.

An apparatus for detecting symbol synchronization in a received signal including a first preamble and a second preamble which is consecutive to the first preamble, the apparatus including a first correlator calculating a first correlation value between the received signal and a first pattern of a first period among iterative patterns of the first preamble, a second correlator calculating a second correlation value between the received signal and a second pattern of a second period among iterative patterns of the second preamble, a third correlator calculating a third correlation value between the first correlation value and the second correlation value, and a detector detecting symbol synchronization from the third correlation value.

A mutually-operated emitting and receiving system of microwave is prepared as forming emission system by randomization module, channel coding module, interlacing module, modulation module, setting-frame module, IFFT conversion module, adding circulation prefix module, parallel / series conversion module, etc; forming receiving system by sampling-positioning module, A / D conversion module, symbol synchronization module, de-circulation prefix module, FFT conversion module, de-framing module, channel estimation module, balance module, decoding module, derandomization module, etc.

The circuit includes local reference conjugate sequencer, delayed conjugate correlator, selecting merger unit. Local reference conjugate sequencer stores conjugate values of local reference sequence samples in different time delays. Multiplication is carried out between the said conjugate values and OFDM data sequence received respectively. Delayed conjugate correlator delays the multiplied result. After taking conjugate operated result of previous step, Multiplication is carried out between the multiplied result and the delayed multiplied result. The result of multiplication in twice is accumulated and square summation is carried out. Selective merger is carried out for output values of multiple delayed conjugate correlators. Peak detection is carried out in order to select maximum. The position of the peas value is synchronous position. Before frequency synchronism and symbol synchronization, the circuit can find position of OFDM frame precisely without inference from frequency deviation and sampling clock.