摘要:
An apparatus and method for jointly equalizing a return to zero (RZ) signal and detecting timing errors in the RZ signal, using values or indices from equalizer taps, including a set reference tap that does not shift. A timing error detector detects a timing error based on a group delay measured from the equalizer tap information, and then adjustment circuitry modifies samples of the received RZ signal prior to their equalization to offset that timing error. Methods of modifying the samples to offset the timing error include adjusting the timing of the sampler, or adjusting the sampled data using intermediate, interpolated samples generated by a timing interpolation filter.
摘要:
An equalizer for return-to-zero (RZ) signals comprises: (a) an equalizer core for equalizing the received signal; (b) a decision corrector for detecting and correcting misplaced pulses and double pulses in the equalized signal using known characteristics and properties of the RZ signal itself; and (c) an error calculator that generates an error signal for updating tap values based on the initial outputs of the equalizer core and the corrected outputs of the decision corrector. The decision corrector comprises a zero assertion counter that generates a clock synchronized with the timing of the received signal, and corrects the equalized signal by forcing zeroes in those portions of the equalized signal that the synchronized clock indicates should be “RZ” zeroes (as opposed to “data” zeroes or “data” symbols “1” or “−1”). The decision corrector further comprises a misplaced pulse detector for detecting misplaced pulses and double pulses based on both the output of the zero assertion counter and coding in the RZ signal, and corrects the equalized signal by moving the misplaced pulse or doubled portion of the pulse forward or backward in time in accordance with the principles of the RZ coding scheme used. The equalizer can further comprise interpolators for generating a plurality of signals based on the equalized signal, to provide a greater diversity of information for the decision corrector.
摘要:
A physical channel estimator for a communication system using pilot symbols and an equalizer uses a model of the system in which the impulse response of the physical channel is considered separately from the impulse responses of the pulse shaping filters in the transmitter and receiver of the communication system. The system is modeled as if the signals were propagated first through both pulse shaping filters and then through the physical channel. To estimate the physical channel impulse response, known pilot symbols are transmitted and then sampled. The pilot symbol samples and the known impulse responses of the pulse shaping filters are then used to estimate the physical channel impulse response. In one embodiment, the physical channel impulse response is considered time-invariant over the estimation period and a sufficient number of pilot symbol samples are taken so that the system is overdetermined. A least squares method is then used to estimate the physical channel impulse response from the pilot symbol samples and the known responses of the pulse shaping filters. Further refinements include conditioning the estimated physical channel impulse response to improve performance in low SNR conditions and estimating a DC offset incurred from demodulating the received signal.
摘要:
The invention provides a synchronizer incorporating a Δ-Σ modulator (i.e. a bit stuffing command generator), coupled in series with a frequency offset measurement block and a frequency-locked loop, to synchronize the data rate of an output data stream to that of an input data stream such that jitter energy is shifted up in frequency, simplifying attenuation of the jitter energy when the output data stream is desynchronized (demapped). Placement of the Δ-Σ modulator outside the frequency-locked loop allows selectable adjustment of the frequency offset measurement block's frequency. A mapper incorporating the Δ-Σ modulator interprets the pulse train output by the Δ-Σ modulator as stuff/null/de-stuff commands.
摘要:
A system for linearly transmitting an amplified output signal using predistortion whereby a straight inverse modeling scheme is used to more easily and accurately determine the inverse of the distortion caused by a power amplifier of a RF transmitter. The "inverse" of the power amplifier is directly modeled by considering the power amplifier as a signal processing block with the input and output ports reversed. As a result, the computationally intensive inversion required by conventional schemes is avoided. The predistorter system stores complex coefficients in a predistorter LUT, which are then used as the tap weights of a digital filter implementing the predistorter. The predistortion is done by a non-linear filter which incorporates both instantaneous and average envelope power or magnitude effects. The predistortion LUT is addressed as a function of the instantaneous envelope power or magnitude and past power or magnitude envelopes. This scheme takes into account the instantaneous envelope power or magnitude of the current sample and a profile of the envelope power or magnitude of previous samples to accurately compensate for modulation envelope memory effects of the power amplifier. The past powers or magnitudes provide an indication of the trajectory of the power or magnitude leading to the current power or magnitude, which enables the predistorter to more accurately compensate for the power amplifier distortion. The predistorter LUT is updated with values that are indexed as a function of the powers or magnitudes of past samples and the power or magnitude of the current sample.
摘要:
An interpolator having a linear phase response has a first stage implemented with an IIR filter to achieve the narrow transition bandwidth with relatively few filter coefficients. Zero-stuffing and filtering are used to achieve the interpolation. A forward-backward filtering methodology is then used to achieve a linear phase response for the IIR filter. The input sequence to be interpolated is zero stuffed and passed through the IIR filter a first time. Then the time order of the resulting sequence is reversed and then passed through the IIR filter a second time. After that, the resulting output sequence is reversed again. Guard blocks are added to both ends of the input sequence, and then a block of zeros is appended to the zero-stuffed guarded input sequence. The appended zero block causes the startup and ending transient effect of the IIR filter's step response to be equal at both ends, which tends to improve the accuracy of the interpolation. Subsequent zero-stuffing and filtering by FIR filter stages are used to further increase the interpolation. A linear interpolator may also be included after the FIR filter stages.
摘要:
A pattern detector adapted for wireless communication systems includes an error calculator, a comb filter, an averager, and a threshold detector. The pattern to be detected is a sequence of pilot signal patterns whose error calculation is relatively invariant with respect to frequency offset introduced by Doppler and the local oscillator. The pattern detector processes received input samples y.sub.k to determine an error signal from the input samples y.sub.k and estimated input samples y.sub.k. The estimated input samples y.sub.k are determined using an estimated channel impulse response. When a vector of the received input samples is "aligned" with the expected header sync input samples, the level of the error signal is about equal to the level of the noise. The pattern detector determines the average level of the error signals for the last K error signals of each sample position E.sub.Kn within a pilot pattern, where K corresponds to the number of pilot patterns in a header sync pattern and n corresponds to the sample position. The pattern detector also determines the average level of the error signals E.sub.L corresponding to the last L received input samples, where L corresponds to the number of samples in a header sync sequence. When E.sub.Kn for a sample position is lower than a preselected threshold percentage of E.sub.L, the header sync pattern is deemed detected. Finally, the end of the header sync pattern is determined by the location of the minimum E.sub.Kn. This minimum is found by calculating, once the header is deemed detected, values for E.sub.Kn that are a certain number of samples past the last minimum.
摘要翻译:适用于无线通信系统的模式检测器包括误差计算器,梳状滤波器,平均器和阈值检测器。 要检测的模式是导频信号模式的序列,其误差计算相对于由多普勒和本地振荡器引入的频率偏移是相对不变的。 模式检测器处理接收到的输入样本+ E,ovs y + EE k,以从输入样本+ E,ovs y + EE k和估计输入样本+ E,cir y + EE k确定误差信号。 使用估计的信道脉冲响应确定估计输入样本+ E,cir y + EE k。 当所接收的输入采样的矢量与期望的报头同步输入采样“对准”时,误差信号的电平约等于噪声的电平。 模式检测器确定导频模式中每个采样位置EKn的最后K个误差信号的误差信号的平均电平,其中K对应于报头同步模式中的导频模式的数量,n对应于采样位置。 模式检测器还确定对应于最后L个接收输入采样的误差信号EL的平均电平,其中L对应于报头同步序列中的采样数。 当采样位置的EKn低于EL的预选阈值百分比时,认为检测到标题同步模式。 最后,头部同步模式的结束由最小EKn的位置决定。 通过计算找到该最小值,一旦检测到标题,则EKn的值超过了最后一个最小值的一定数量的样本。
摘要:
A linear transmitter (101) using predistortion includes a modulator (103), a predistorter (107), a digital quadrature modulator (111), an upconverter (113), a power amplifier (115), and an antenna (117). In addition, the transmitter (101) has a feedback loop including a coupler (119), a downconverter (123), a digital quadrature demodulator (125), and a trainer (131). The digital data to be transmitted is provided into the modulator (103), which converts the digital data into in-phase and quadrature component signals. The in-phase and quadrature component signals are then provided to the predistorter (107), which "predistorts" the component signals prior to amplification. The digital quadrature modulator (111) converts the component signals into a single analog signal. The upconverter (113) upconverts this signal from the predistorter (107) into the desired frequency of transmission, which is provided to the power amplifier (115) and the antenna (117) for amplification and broadcast. The coupler (119) provides a portion of the amplified signal to the analog downconverter (123), which lowers the frequency of this signal to a range that is easily processed. The signal is then provided to the digital quadrature demodulator (125), which outputs the in-phase and quadrature component signals of the signal. These in-phase and quadrature component signals are provided to the trainer (131) which analyzes them with the output signals from the modulator. The trainer (131) compares these signals and updates the predistorter (107) so that the digital quadrature demodulator (125) output signals are substantially equivalent to the modulator (103) output signals.