649 results about "Frequency domain equalization" patented technology

A modem receiver for receiving signals having a frequency domain equalizer training module (FTM) being responsive to a frequency channel response for processing the same to generate one or more frequency domain equalizer (FEQ) coefficients, said modem receiver being responsive to an input signal for processing the same to generate said frequency channel response, said input signal being generated from transmission of a transmitted signal, said frequency channel response for including one or more pilot tones, said FEQ coefficients for including one or more pilot tone FEQ coefficients, in accordance with an embodiment of the present invention. The modem receiver further includes an offset weight determination (OWD) module being responsive to said pilot tone FEQ coefficients for processing the same to generate one or more carrier weights, said modem receiver for using said carrier weights to generate a carrier offset, said OWD module for using said pilot tone FEQ coefficients to generate one or more timing weights, said modem receiver for using said timing weights to generate a timing offset, said modem receiver for reducing the effects of faded pilot tones on determination of said timing offset and said carrier offset between said transmitted signal and said input signal.

Joint equalization and decoding techniques to eliminate the division operations in the Frequency domain Equalizer (FEQ) of an Orthogonal Frequency Division Modulation (OFDM) receiver by incorporating the magnitude of the channel impulse response estimates into the decision metrics in the decoder. This includes methods for both hard-decision symbol-by-symbol detection and soft-decision decoding using the Viterbi algorithm. Further, Channel State Information (CSI) is incorporated to improve the performance of the receiver. The disclosure also introduces a computationally efficient bit-by-bit piecewise approximation technique incorporating CSI to implement decoder decision metrics. Finally, an efficient implementation technique for multiple receiver antennae using Maximum Ratio Combining (MRC) and Viterbi decoding with CSI is disclosed.

The invention provides a method and system for transmission and frequency domain equalization for wideband CDMA communications by providing at least one spread sequence portion, and inserting a cyclic redundancy to the spread sequence to form a transmitted baseband sequence. The invention further provides a method and system for converting a plurality of receive samples from at least one spread sequence portion into a plurality of frequency domain samples, determining a plurality of frequency domain equalization weights for the frequency domain samples, and determining a time domain signal estimate based on the frequency domain equalization weights and frequency domain samples.

An efficient method for calculating the step-sizes for a frequency-domain equalizer of a discrete-multitone communications system using signal power estimation and tone grouping (SPE-TG) while on-line. The SPE-TG method is used to calculate a plurality of subchannel step-sizes which are then stored in a lookup table. When on-line, the method uses signal power estimation to select step sizes for each tone, and uses these step sizes for frequency domain equalization. The SPE-TG method simplifies the calculations necessary for frequency domain equalization, thereby saving significant hardware and/or processing resources. The SPE-TG method is reliable and robust, and does not depend upon assumptions about the line, location, or channel.

A single integrated circuit multi-standard demodulator includes an adaptive inverse channel estimator for frequency domain equalization which employs a recursive least square cost function in estimating the inverse channel from the received signal and an error estimate. Utilizing a diagonal correlation matrix, the solution to may be determined utilizing fewer computational resources than required by conventional frequency domain equalizers, shifting from a computational intensive to memory intensive implementation. The memory requirement is fully satisfied by memory available within conventional OFDM decoders, and the necessary computational resources may be readily mapped to the resources available within such decoders, improving integrated circuit cost-effectiveness of the multi-standard demodulator.

An OFDM transceiver has a transmitter, a receiver, and a loopback switch. The loopback switch configured is for selectively establishing a physical connection between an output terminal of the transmitter and an input terminal of the receiver. The transmitter is configured for outputting to the output terminal an OFDM signal generated based on a local oscillator signal. The receiver is configured for demodulating the OFDM signal, received via the physical connection, using the local oscillator signal and determining amplitude and phase imbalance parameters based on performing frequency-domain estimation of amplitude and phase imbalances. Hence, the receiver is configured for performing imbalance compensation on a received wireless OFDM signal based on the determined amplitude and phase imbalance parameters. Hence, amplitude and phase imbalances can be estimated accurately despite channel fading and frequency variations encountered between the transmitter of the wireless OFDM signal and the receiver.

The invention provides a method and device for iterative hybrid time-frequency domain block equalization of signals received via a communication channel subject to multipath interference. The equalization method includes frequency-domain equalization of blocks of received signals in a forward path, and time-domain inter-block echo correction and intra-block cyclic echo addition in the feedback path. The invention can be used for equalizing signals transmitted without cyclic prefix and subjected to multi-path interference with long delay spread.

The present invention relates to a signal generator and signal processor for single carrier wireless communication systems with frequency domain equalizer, which are operable to use pseudorandom-noise sequences as part of a preamble and possibly as cyclic prefix. The different arrangements and examples of said pseudorandom-noise sequences could be used for coarse timing synchronization, channel estimation, carrier synchronization, signal-noise-ratio estimation and channel equalization.

A system and method for a transceiver structure, where Different Known Guard Intervals (DKGI) are appended to multiple, consecutive data blocks and are then used in combination with Channel State Information (CSI) to restore cyclic convolution in the time domain. Once restored, the CSI and cyclic convolution are transformed into the frequency domain by FFT processing to facilitate equalization of the channel through Frequency Domain Equalization (FDE). Through performance of time domain channel estimation, there is no need for pilot signals and related overhead, thus channel capacity is enhanced.

Channel estimation of block signals containing pilot frequency and balanced method characterizes in containing side channels of force and after of a main channel component in a movable window to determine to get a correct channel estimation interval again to get channel impulse response estimation with the length of N, M or M+2XN, then to take position of home and end of the said window as the positioning information needed by circular convolution of the signal and channel inputs response structure and process the data block via channel transmission as the one after channel distortion via frequency domain balance offset or make time-domain over-sampling channel estimation in the sliding window interval to inerase time-domain resolution of channel estimation. The data block can be IDFT of OFDM or modulated by single carrier.

The system and method of the preferred embodiments may be directed to improving the signal-to-noise ratio in frequency spectrum regions where narrowband interference may be present. The system and method of the preferred embodiments includes reducing the narrowband interference by determining a noise estimate. In accordance with the noise estimate and output of a frequency domain equalizer, a noise-cancelled output may be obtained.

Methods and apparatus (100) for composing, generating and transmitting information-bearing optical signals are provided. An information-bearing electrical signal is composed (108) having desirable spectral properties, preferably configured to ensure that undesired interference between electrical spectral components generated in a square-law direct detection process (120) at a corresponding optical receiver (104) is substantially avoided. Predistortion (110) is advantageously applied to transmitted signals, in order to account for a nonlinear relationship arising in a modulation process (114) between electrical signal amplitude and corresponding optical field amplitude. Orthogonal frequency division multiplexing (OFDM) techniques may be applied to composed signals having the desired characteristics, and additionally may facilitate the application of frequency domain equalisation (128) in order to mitigate transmission impairments, including dispersion. Improvements in received signal quality, and/or transmission distance, may thereby be achieved, along with simplification of receiver configuration and operation.

A DTV receiver includes a tuner, a demodulator, a known sequence detector, and a frequency domain equalizer. The tuner initially receives a broadcast signal including valid data in which a known data sequence is periodically repeated. The demodulator demodulates the broadcast signal, and the known sequence detector detects the known data sequence from the demodulated signal. The frequency domain equalizer compensates channel distortion of the demodulated broadcast signal in a frequency domain using the detected known data sequence. In addition, the DTV receiver may further include a time domain equalizer which compensates channel distortion of the time domain signal, or a noise canceller which removes a predicted noise from the time domain signal.

A system and method for estimating a channel spectrum. The method includes: (a) receiving an input signal from a channel, where the input signal includes one or more major echoes and zero or more minor echoes introduced by the channel; (b) identifying the one or more major echoes present in the input signal; (c) identifying the minor echoes from a filtered autocorrelation function of the input signal in response to a determination that there is only one major echo; (d) identifying the minor echoes from a filtered power spectrum of the input signal in response to a determination that there is more than one major echo; (e) computing a channel spectrum estimate from the major echoes and minor echoes; where the channel spectrum estimate is usable to remove at least a portion of the one or more major echoes and one or more minor echoes from the input signal.

The invention belongs to the technical field of fiber communication and optical network transmission signal equalization treatment, and particularly discloses a single-sideband modulated single carrier frequency-domain equalization technology-based fiber communication system. In a transmission system of fiber communication, by using a DSP equal high-speed digital signal processing mode, single-sideband modulated electrical signals received by direct detection are transformed to a frequency domain from a time domain by adopting FFT transformation, an equalization module designed aiming at a transmission link is adopted for performing equalization compensation in the frequency domain, and finally the signals processed by the equalization module are transformed to the time domain from the frequency domain through IFFT to acquire the final equalization signal. The fiber communication system can improve the transmission quality of the signals, and has the signal equalization compensation capacity of the self-adaptive fiber transmission link.

Joint equalization and decoding techniques to eliminate the division operations in the Frequency domain Equalizer (FEQ) of an Orthogonal Frequency Division Modulation (OFDM) receiver by incorporating the magnitude of the channel impulse response estimates into the decision metrics in the decoder. This includes methods for both hard-decision symbol-by-symbol detection and soft-decision decoding using the Viterbi algorithm. Further, Channel State Information (CSI) is incorporated to improve the performance of the receiver. The disclosure also introduces a computationally efficient bit-by-bit piecewise approximation technique incorporating CSI to implement decoder decision metrics. Finally, an efficient implementation technique for multiple receiver antennae using Maximum Ratio Combining (MRC) and Viterbi decoding with CSI is disclosed.

A DHT-based OFDM transmitter and receiver use discrete Hartley transform to implement multicarrier transmission. A transmission terminal (or a receiving terminal) of a transmitter and receiver comprises two IDHT (or DHT) processors and a diagonal processing device. The two IDHT processors make the DHT-OFDM system transmit the 2D modulation signal to increase the bandwidth efficiency. The diagonal processing device is used to diagonalize the circulant channel matrix into discrete memoryless subchannels, and thus only one-tap frequency domain equalizer can compensate the channel effects. Besides, the proposed DHT-OFDM transmitter and receiver are also compatible with a conventional DFT-OFDM system, and they can flexibly works with the conventional DFT-OFDM transmitter and receiver.

The invention relates to a time- and frequency-domain unified single carrier modulation (TFU-SCM) signal transmission method, and belongs to the technical field of digital information transmission. The method comprises that: information generated by a sending end is subjected to source coding, channel coding and constellation mapping in turn to form mapped information; the mapped information is subjected to time- and frequency-domain unified single carrier modulation FU-SCM modulation, and a plurality of modulated symbols form a frame signal to be sent; the received frame signal is split into a TFU-SCM modulation symbols in a corresponding composition mode; and the modulation symbols are subjected to TFU-SCM demodulation to form serial data, and the serial data is subjected to constellation inverse mapping, channel decoding and source decoding in turn to form the original information. The method maintains the advantage of low complexity of the sending end of the single carrier frequency domain equalization (SC-FDE) technology, the number of UW in the pilot frequency can be flexibly selected according to requirement on system performance, operation such as synchronization, channel estimation, balance and the like can be convenient to carry out at a receiving end by operating the pilot frequency in the frequency domain, the processing efficiency of the system is improved, and the method is more suitable for a broadband wireless mobile communication system.

The invention provides a block balancing method for an orthogonal frequency division multiplexing (OFDM) system on the condition of a fast time variant channel. The method comprises the following: at a sending terminal, a bit signal subjected to cyclic redundancy codification is subjected to channel codification, interlacement, symbol map, serial/parallel conversion and IFFT conversion to be converted to a time domain signal; the time domain signal which is subjected to serial/parallel conversion and is inserted with a cyclic prefix is sent to a radio channel; at a receiving terminal, the signal is received by a traditional first-order frequency domain equalizer, and the signal guess value is checked after the signal is subject to serial/parallel conversion, demap, deinterlacement and signal path decoding; if the check is correct, the signal is outputted; if the check is not correct, the block balancing process is performed, during which, firstly, a time domain OFDM sending signal is restructured; secondly, the received time domain OFDM symbol is divided into a plurality of equilong signal receiving subblocks, the loop restructuring and the interference removing processes are performed by a time domain OFDM restructured signal; and finally, each subblock is subjected to frequency domain balance, the balanced guess values of sub blocks are merged to obtain the block balance output serving as the input of the serial/parallel conversion.