109results about How to "Reduce Intersymbol Interference" patented technology

Embodiments of the present invention are directed to acoustic data transmission using a spreading code. A system for acoustic data transmission includes an ingestible capsule and an acoustic receiver. The ingestible capsule includes a modulator, a spreader, and an acoustic transmitter. The modulator modulates data according to a modulation scheme. The spreader spreads the modulated data according to a spreading code. The acoustic transmitter acoustically transmits the modulated and spread data through a body of an animal. The acoustic receiver includes an acoustic transducer a de-spreader and a demodulator. The acoustic transducer receives the acoustically transmitted signal and forms an electrical signal therefrom. The de-spreader de-spreads the received signal in accordance with the spreading code. The demodulator demodulates the received and de-spread signal in accordance with the modulation scheme, wherein a phase of the spreading code is synchronized with the received signal whereby a signal-to-noise ratio of the received signal is increased.

A communication system is disclosed that allows high data-rate transmission of data between components. N-bit parallel data is transmitted in K-frequency separated channels on the transmission medium so as to fully take advantage of the overall bandwidth of the transmission medium. Additionally, a cross-channel interference filter in a receiver section corrects for cross-channel interference in the communication system. As a result, a very high data-rate transmission can be accomplished with low data-bit transmission on individual channels. A transmitter system and a receiver system are described for the communication system.

A transceiver system according to the present invention transmits data utilizing the baseband and one or more frequency separated transmission bands. A baseband transmitter is combined with one or more transmitters that transmit data into one of the frequency separated transmission bands. A baseband receiver is combined with one or more receivers that receive data from the frequency separated transmission bands. Any combination of modulation systems can be utilized (e.g. PAM for the baseband and QAM for the frequency separated bands). A transceiver circuit or chip according to the present invention includes a transmitter and a receiver and communicates with a corresponding transceiver chip. In some embodiments, one baseband PAM transmitter is combined with one frequency separated QAM transmitter.

The invention relates to a method and a system for estimating a symbol time error in a broadband transmission system, comprising: determination a timing error signal of an input-signal of a discrete Fourier-transformation block (5) in a data symbol stream on the basis of intersymbol correlation using a predetermined period in each received symbol, selecting as a predetermined period a number of samples of different useful data parts of a symbol, determining the time error value (ε) based on the intersymbol interference of the selected samples of the different parts of said symbol.

An apparatus for a wireless transmission of high data rate signals such as received from an optical interface including gigabit fiber channel or a sonet. The architecture combines direct detection of the optical signal with clock and data recovery circuit and a differential signal encoder which is preferably a differential quadrature phase shift encoder and modulator pair. A millimeter wave, local oscillator and up conversion chain converts the optical input signal to a microwave carrier. In the opposite direction, the down converted signal is non-coherently phase detected and fed to a pair of synchronized clock and data recovery circuits to recover I and Q channel signals. These recovered signals are then combined prior to re-timing before they are fed back to the optical transceiver.

The invention provides a neural network equalization method used for an indoor visible light communication system, and belongs to the visible light wireless communication technology field. The method includes the steps: utilizing a ceiling bounce model to calculate a VLC channel impulse response, carrying out photoelectric conversion for a visible light power signal received by a receiving end, and sending a sequence to a neutral network channel equalizer after amplification sampling; utilizing a heredity algorithm to optimize initialization weights and thresholds among neurons, establishing a neural network for training, and minimizing an error function; and judging an output, restoring the sent sequence, and finally achieving an equalization purpose. According to the scheme, interference among codes is obvious minimized, an error rate is reduced, the communication quality is further improved, a transmission rate that the system can reach is increased, the training time is shortened, and the system complexity is reduced.

A reception method and receiver structure that are relatively simple, that have close to optimum performance, and that use high order modulation combined with a low spreading factor are disclosed. The method receives a signal transmittal in the form of sequences of coded binary symbols comprising both predefined pilot symbols and date symbols multiplied by a spreading sequence. The method also includes a step of determining a channel estimate using received predefined pilot symbols. A system for receiving a signal transmitted on a multipath transmission channel using a spread spectrum technique and low spreading factor is also disclosed.

The invention discloses an automatic gain control method and an automatic gain control circuit which are suitable for an orthogonal frequency division multiplexing (OFM) system. The method comprises the following steps of: measuring a baseband signal; and adjusting gain. Slide window processing is performed during signal measuring so as to average signal energy in a window. A gain adjustment algorithm determines reasonable gain of the next adjustment period through conditions such as the gain of an upper frame, a measured value of the upper frame, the number of overflow sampling points, the receiving signal intensity indication on the current antenna and the like. Simultaneously, the gain of a radio frequency receiving chip is changed by circulating prefix time so as to track an OFDM symbol level.

A method equalizes a received signal in an optical communications system. The received signal is passed through an analog delay line where it is tapped to generate a set of delayed copies of the received signal. In a set of analog multipliers, each delayed copy of the received signal is multiplied by a corresponding weight to generate a set of weighted signals that are then summed to produce an output signal. The output signal is thresholded and subtracted from the output signal to produce an error signal, which is periodically sampled. In a digital weight updating circuit, the weights are produced from digitized versions of the sampled error signal and samples of the delayed copies of the received signal.

This disclosure is directed to systems and methods for positioning a FFT window using the noise power that is related to ISI By selecting a FFT window position that minimizes the noise power, ISI is reduced or eliminated The techniques can be used in coherent and non-coherent systems Further, noise associated with the Doppler effect is compensated for, allowing the use of these system and methods in time-varying environments, such as mobile applications.

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.

A method and apparatus for increasing in the data rate of a multiple-input and/or multiple-output system that has frequency selective fading by using training sequences with both low normalized auto-correlation and low normalized cross-correlation. Both 1) the sum of the square of the normalized auto-correlation of each training sequence over an auto-correlation window and 2) the sum of the square of the normalized cross-correlation of each pair of the training sequences over a cross-correlation window, are significantly less than unity. In one embodiment of the invention the training sequences are shifted versions of each other, and the low normalized cyclic-auto-correlation of cyclic sequences is significantly less than unity, with each cyclic sequence being N′, N′=N−L+1, symbols of one of the at least two training sequences. In another embodiment, the training sequences are ones where the trace of the inverse of the product of the matrix of training sequences' symbols and the conjugate transpose of this matrix is low. The matrix is a function of the number of symbols over which multipaths of significant power can arrive, the number of training sequences, and the number of symbols in a training sequence. More particularly the matrix is a block-toeplitzmatrix composed of the training symbols.

A method for non-orthogonal frequency division multiplexed communication through a non-linear transmission medium includes the steps of selecting at least one desired bandwidth, selecting a non-orthogonal pair of base frequencies within a first bandwidth of the at least one desired bandwidth, identifying where primary intermodulation products formed as a result of signal transmission on the pair of base frequencies fall within the first bandwidth. The method may also include the step of selecting a plurality of non-orthogonal interleaved frequencies adjacent at least one of the pair of base frequencies so as to be interleaved between the primary intermodulation products to form a frequency cluster which includes the at least one of the pair of base frequencies and the interleaved frequencies.

A variable-bit-rate communication system is described. The communication system includes a variable-bit-rate transmitter that generates digital data at a first or a second bit rate and a variable-bit-rate receiver that receives the digital data. The digital data comprises a sequence of signaling waveforms having a first or a second duty cycle, respectively, wherein each signaling waveform has the same shape.

The method includes following steps: through software, a radiotechnics is introduced into demodulator based on structure of limiter coupling with discriminator to make the angle resolution of demodulator is not limited by sampling rate; the reception matched filter adopts root raised cosine filter (RRCF) to make problem of which demodulator with structure of hardware limiter is sensitive to roll-off factor of root raised cosine filter is solved. The invention can be applied in PHS and PCS system, signal demodulation based on PSK modulation technology like satellite communication system.

Techniques for processing of symbols (e.g., orthogonal frequency division multiplexing (OFDM) or single carrier-frequency division multiple access (SC-FDMA) symbols) provide enhanced out-of-band (OOB) suppression of the symbols and also provide reduced inter-symbol interference (ISI) between a symbol and a subsequent symbol. Multiple frequency tones of a symbol may be divided into two or more subsets of tones. For example, subsets of tones associated with a head portion or a tail portion of an OFDM symbol may be processed with a relatively long weighted overlap-add (WOLA) weighting length or filtering length, and a subset of tones associated with a center portion of the OFDM symbol may be processed with a relatively short WOLA weighting length or filtering length. Such heterogeneous processing of tones within a symbol may provide enhanced inter-channel interference (ICI) and improved OOB suppression and also provide reduced ISI for the center tones of the symbol.

A filter circuit, method of configuring the filter circuit, and a bit pump and transceiver employing the circuit and method. In one embodiment, the filter circuit includes a noise prediction equalizer that generates a noise prediction equalizer coefficient during activation of the bit pump to reduce an intersymbol interference associated with a receive signal propagating along a receive path of the bit pump. The filter circuit also includes a decision feedback equalizer that generates a decision feedback equalizer coefficient during the activation of the bit pump to reduce the intersymbol interference associated with the receive signal. The noise prediction equalizer is concatenated with the decision feedback equalizer during showtime of the bit pump to form a precoder associated with a transmit path of the bit pump.

A radio transmitting apparatus and a radio transmitting method wherein the interference between codes can be reduced and the degradation of preamble detection capability can be prevented. According to these apparatus and method, a signature table storing part (103) that stores a table including a plurality of signatures obtained by classifying the magnitudes of propagation loss levels into levels in accordance with the distances from a base station, associating preamble detection window widths with those levels as classified, and by circularly shifting the pattern of a detection window signature #n corresponding to a signature #n to generate a signature #n+1. A signature selecting part (104) selects, based on the magnitude of a propagation loss level outputted by a propagation loss level determining part (102), one of the corresponding signatures from the signature table storing part (103) at random. A RACH signal generating part (105) uses the selected signature to generate a RACH signal.

A differential multiplexer includes a plurality of multiplexing circuits. Each multiplexing circuit inputs a corresponding differential input signal including a positive input signal and a negative input signal, and outputs positive and negative output signals. Each multiplexing circuit includes first, second, third and fourth transistors. The first and second transistors input the positive input signal. The third and fourth transistors input the negative input signal. Outputs of the first and third transistors are connected to the positive output signal. Outputs of the second and fourth transistors are connected to the negative output signal. The positive and negative output signals are controlled using gate voltages on the first and fourth transistors. The second and third transistors are turned off when the differential multiplexer is in use. The transistors are cross-coupled to make leakage between the positive and negative input signals common mode in the positive and negative output signals.