38 results about "Non data aided" patented technology

A system and method of timing estimation for use in a digital receiver within a communication system. An algorithm calculates the timing offset by evaluating the spectral component at the symbol clock frequency. The spectral component is generated using a nonlinearity operation. However, the maximum likelihood non-data-aided timing estimation equation reveals an alternative approximation for the logarithm of the hyperbolic cosine function present in the maximum likelihood equation, which offers a compromise between implementation complexity and variance performance. The estimated timing offset is then fed to a timing correction unit, which calculates the data samples corresponding to the sampling clock phase and removes the redundant samples. The ideal sampled signal is then forwarded to additional synchronization and functional units for further processing.

A class of non data-aided cyclic based robust estimators for frequency offset estimation of multi-carrier systems is disclosed. The use of sufficient statistics provides a minimum variance unbiased (MVU) estimate of the frequency offset under complete knowledge of timing offset error. The Neyman-Fisher factorization theorem and Rao-Blackwell-Lehmann-Scheffe theorem are used to identify the sufficient statistic and appropriate mapping functions. It is shown that there is but one function of the sufficient statistics which results in the minimum variance estimate among the possible class of cyclic-based estimators. Also, a moment estimator of frequency offset is provided to obtain a consistent estimate of carrier offset under uncertain symbol timing error. The moment estimator does not rely on any probabilistic assumptions. Thus, its performance is insensitive to the distribution of the additive noise. A unified structure characterizing both the MVU and moment estimators, as well as a maximum likelihood estimator of a related, copending application is disclosed.

A WLAN (Wireless Local Area Network) receiver is provided that provides at least two acquisition units and at least two tracking units. The acquisition units perform a synchronization acquisition process, and the tracking units perform a synchronization tracking process. The acquisition units are arranged for being operated sequentially while the tracking units are arranged for being operated simultaneously. In an embodiment, frequency and phase error correction may be performed separately, and those units that operate at higher sampling rates may be located before lower-rate units. The synchronization process may include data-aided as well as non data-aided algorithms.

The invention provides a non-data aided OQPSK (Offset Quadra Phase Shift Keying) signal closed loop carrier synchronization method. The square spectrum characteristics of an OQPSK signal are utilized, a square spectrum estimation based carrier frequency offset coarse estimation algorithm is adopted, and accordingly the range of the frequency of the signal can be effectively reduced. A carrier synchronization loop is of a dot product and cross product frequency discriminator and phase discriminator combined cross ring structure and accordingly the speed and the accuracy of the carrier synchronization can be ensured simultaneously. A proportional integral filter is adopted as a loop filter to enable the synchronization loop to be a second-order loop and accordingly the stable loop dynamic response can be implemented under the conditions that the direct current gain is infinite and the frequency offset is a constant. According to the non-data aided OQPSK signal closed loop carrier synchronization method, the frequency offset can be accurately estimated, the accuracy and the speed of the carrier synchronization can be ensured, and the recruitments of a communication system can be met through the combined utilization of a dot product and cross product frequency discriminator and phase discriminator on the basis of the square spectrum frequency offset coarse estimation.

The invention discloses a non-data auxiliary frequency offset estimation method applicable to amplitude phase shift keying and relates to the technology of digital communication system receiving end processing. Frequency offset estimation and compensation are carried out on APSK signals by a receiving end. According to the method, the precision of carrying out the frequency offset estimation and compensation on the APSK signals by the receiving end is improved. The method comprises the steps of processing receiving signals by a rooted raised cosine filter and carrying out synchronization processing on the signals, wherein the synchronization processing comprises timing synchronization, frequency synchronization and phase synchronization processing. According to the method, for the frequency synchronization processing, frequency offset coarse estimation is carried out through utilization of an M&M algorithm according to a frequency range of the APSK signals, a frequency offset range is reduced, n times of frequency offset fine estimation is carried out through selective utilization of a Fitz algorithm according to a precision demand, and finally a precise frequency offset value is obtained. After the synchronization processing is carried out, judgment, constellation graph demapping and output are carried out. The invention provides an effective solution scheme for the APSK signal frequency offset estimation and compensation.

The invention provides an optical OFDM system adopting a non data aided frequency offset estimation algorithm. The optical OFDM system comprises an OFDM sending end, up-conversion, a DAC, optical modulation, optical fiber transmission, a variable optical attenuator, an optical detector, an ADC and an OFDM receiving end, the OFDM sending end generates a baseband OFDM signal; the OFDM receiving end comprises down-conversion, frequency offset estimation, secondary down-conversion, channel estimation and baseband frequency offset compensation, the frequency offset estimation divides a baseband OFDM time domain signal after the down-conversion with an absolute value to obtain a frequency offset factor containing sign bit influence, the frequency offset factor containing the sign bit influence is squared to eliminate the sign bit influence so as to obtain a 2 frequency-doubled frequency offset factor, an autocorrelation function of the frequency offset factor is figured out to eliminate the noise influence, a phase angle of the autocorrelation function is averaged to obtain a frequency offset estimator, the sampling frequency is adjusted, the down-conversion is carried out eliminate the envelope of frequency offset of up-conversion and down-conversion, and then channel estimation and frequency offset compensation are carried out. The optical OFDM system disclosed by the invention estimates the frequency offset without data assistance, and thus improving the data utilization rate.

Novel non-data-aided maximum likelihood estimators for the delays and the attenuations in an ultra-wide bandwidth channel are proposed. Numerical results show that these new estimators outperform the previous non-data-aided maximum likelihood channel estimators derived in the literature. Moreover, in some cases, the performances of the new non-data-aided estimators approach those of the data-aided estimators, enabling us to reduce the overhead expense of pilot symbols.

The invention discloses a non-data-aided parallel clock synchronizing method and system. The method comprises S1, caching received data; S2, performing parallel clock error detection on the cache data to obtain a sampling clock skew; S3, according to the sampling clock skew, performing parallel interpolation control on the cache data; S4, performing interpolation on the paralleled data to complete sampling clock error compensation; S5, outputting the interpolated paralleled data to achieve clock synchronization.

A method for non-data aided frequency offset determination for MPSK demodulation is accomplished by receiving a stream of K symbols and providing the symbol stream to a delay line of L symbols in length with L greater than 1. The symbol stream and an output of the delay line is taken at each increment of L and then multiplied and the output of the multiplier is raised to the M power to remove modulation. The result is accumulated over K symbols and the argument of 1/K2πMLT times the accumulated result is determined as a frequency offset. L is then incremented and the calculation repeated. The calculated frequency offsets are then summed for a final frequency offset determination.

The invention relates to the field of communication, in particular to a frequency synchronizing method and device. The frequency synchronizing method comprises the following steps: extracting a burst head from a burst signal; performing frequency deviation estimation and phase deviation estimation on the burst head; performing frequency deviation compensation on a received burst signal by using the frequency deviation estimation, and performing phase deviation compensation on the received burst signal by using the phase deviation estimation; extracting unique characters from the burst signal subjected to the phase deviation compensation; performing phase fuzzy elimination on the burst signal subjected to phase compensation by using the unique characters, and synchronizing the frequency. The frequency synchronizing device comprises a first extracting module, an estimating module, a first compensating module, a second extracting module and a processing module. By adopting the frequency synchronizing method and the device, the frequency and phase deviation estimation are performed by using a non-data-aided method without using the unique characters, so that the problem of low estimation accuracy in case of a small quantity of unique characters is solved.

The invention relates to a non-data aided phase noise blind estimation method for QAM signal, an M-th power algorithm based on improvement is provided, the algorithm can correct the frequency deviation and the phase deviation caused by the phase noise, a power estimation algorithm is adopted without any other data information for the frequency deviation and the phase deviation in the signal, a more precise output information is obtained through gradually correcting the estimation error, the estimation process is simplified, and the computation complexity is greatly reduced; according to the invention, in a condition that has no need to have the help of signal-to-noise ratio and auxiliary data information, the method represents good estimation performance, and a simple and efficient solution is provided for the high-speed wireless optical communication QAM signal phase estimation problem.

The invention discloses a carrier phase error extraction system applied to MAPSK modulation and relates to the field of satellite communication. The system comprises a multiplier, a first filter, a frequency detector, a numerical control oscillator, a second filter, a phase detector and a clock recovery module. The system can be applied to both a non-data assistant scene and a data assistant scene. The system focuses on solving residual carrier phase error extraction of fine synchronization. According to the system, through utilization of a constellation characteristic of MPSK/MAPSK signals ina satellite communication system, constellation diagram simplification and segmentation are carried out on signals of different modulation modes, so complex computing of carrying out the carrier error signal extraction through direct utilization of an original constellation diagram is avoided, engineering realization flexibility is greatly improved, and rapid realization of a product is facilitated. According to the system, components related to a phase are extracted from received signals of different modes, so carrier tracking and locking are realized.

An apparatus for cooperative multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) is provided. The apparatus uses a new carrier assignment scheme (CAS) called generalized interleaved CAS, along with non-data-aided timing synchronization. With the generalized interleaved CAS, random OFDM signals are formed into patterns similar to unequal period synchronization patterns (UPSPs), and a corresponding non-data-aided timing synchronization scheme is set. With the help of majority vote refinement (MVR), the present invention achieves better timing synchronization and enhances the quality of signal demodulation.

In the invention, a simple and robust method for clock offset compensation is proposed using an equalizer with time-varying signal windowing for which the timing information needed is obtained by an existing non-data-aided (NDA) timing estimator. Instead of interpolating the received signal, the proposed method compensates clock offset by using a moving signal window for equalizer. Since no interpolation is needed, the timing information required for the proposed method need not be so accurate as required for interpolation methods. Rather than the exact time drift due to clock offset, the proposed method requires only the timing points where the time drift accumulates to a pre-defined threshold. By applying an existing non-data-aided (NDA) timing estimator, the needed timing information can be obtained easily. Moreover, thanks to robustness of the NDA timing estimator, the proposed method is inherently robust and simple in implementation.

The present disclosure is directed at a method and apparatus for generating a metric for use in any one or more of lock detection, SNR estimation, and modulation classification. To generate the metric, an input angle in the form of a symbol phase or a difference in symbol phases is used to evaluate a base function. The base function relates possible metrics to possible input angles using a triangle wave having its maxima or minima at ideal input angles, and the other of its maxima or minima at angles midway the ideal input angles. Described are embodiments that are one or more of non-data aided; that may be implemented relatively efficiently in hardware; that can function using one sample/symbol; that can achieve relatively good detection certainty using relatively few estimates; and that can be used to implement modulation classifiers, lock detectors, and SNR estimators that are resilient to imperfections in automatic gain control.

The invention provides a non data aided-error vector magnitude (NDA-EVM) adaptive modulation method under a fast time-varying channel. The method comprises the steps of firstly, performing modulation by adopting QAM (Quadrature Amplitude Modulation), then estimating the coherence time of the channel by a receiving end, and collecting the statistics on the number of symbols sent within the coherence time; secondly, according to the data symbol of the current modulation order, calculating NDA-EVM values of all modulation orders and the bit error rate corresponding to the NDA-EVM of each modulation order under the current channel; and finally, under the condition of a specified bit error rate, selecting the current optimal modulation order, and returning to execute next modulation order adjustment. Compared with SNR-AM (Signal to Noise Ratio based-Adaptive Modulation) and DA-EVM-AM (Data Aided Error Vector Magnitude based-Adaptive Modulation), the NDA-EVM-AM method can improve the timeliness and accuracy of channel quality assessment and modulation order selection and then improve the spectrum efficiency of a system, wherein the spectrum efficiency can be improved to 0.82bit/s/Hz and 0.53bit/s/Hz to the highest degree.