Fractionally-spaced Decision Feedback Equalizer Research Articles

Mud pulse signal demodulation based on support vector machines and particle swarm optimization

Mud pulse telemetry is the most commonly used communication technology in measurement-while-drilling or logging-while-drilling systems. During the drilling process, the flowing drilling mud is the communication channel that carries the mud pulse signal to surface. Compared with the relatively benign conditions in the wireline communication method, the mud communication channel encounters high signal attenuation, low bandwidth, and numerous sources of noise. The harsh and volatile conditions of the mud channel make it difficult to demodulate the mud pulse signal. In this study, a novel signal demodulation technique based on support vector machines (SVM) is proposed. Meanwhile, the particle swarm optimization (PSO) algorithm is applied for selecting both the penalty parameter and the kernel parameter for the SVM classifier. To overcome the small training set problem and increase the demodulation accuracy, we introduce a training set expansion scheme which is implemented by enlarging the training set with correctly demodulated data based on the error detection method. Field experiment results prove the effectiveness of the training set expansion scheme and the superiority of the proposed methodology compared with the conventional adaptive fractionally-spaced decision-feedback equalizer (FS-DFE). Moreover, the computational time for the whole SVM demodulation procedure is much less than the signal duration. The proposed PSO–SVM method could be a potential solution for mud pulse signal demodulation in mud pulse telemetry systems.

Blind equalization based on T/4 fractionally spaced decision feedback equalizer with RLS algorithm

To further improve the performance of blind equalization based on T/4 fractionally spaced decision feedback equalizer, RLS algorithm is adopted to update the weights of equalizer according to simplified constant modulus algorithm (CMA) cost function. CMA cost function is simplified to meet second norm form in this work, and then the forward filter of equalizer with T/4 fractionally-spaced updates by RLS algorithm and the feedback filter of equalizer with symbol-spaced updates by gradient descent algorithm. Computer simulation results show that the algorithm proposed in this work has faster convergence rate and lower mean square error compare with blind equalization based on symbol-spaced and T/4 fractionally-spaced decision feedback equalizer based on gradient descend algorithm. DOI: http://dx.doi.org/10.11591/telkomnika.v11i6.2156 Full Text: PDF

A Low-Complexity Adaptive Multi-Beam Space-Time Receiver for CCI/ISI Cancellation over Frequency Selective MultipathChannels

A space-time (ST) receiver is proposed for combating the cochannel interference (CCI) and intersymbol interference (ISI) in a frequency-selective multipath environment. The scheme involves two stages. First, a set of adaptive beamformers pointed at a prescribed angular sector in space is constructed on an oversampled antenna array, each providing effective suppression of CCI and reception of desired signals. Second, a fractionally-spaced decision feedback equalizer (DFE) follows to eliminate the ISI left in beamformer outputs. In particular, both the beamformers and DFE can be realized in the form of a generalized sidelobe canceller (GSC) with the aid of channel estimation, and partial adaptivity is incorporated for reduced complexity processing and improved convergence. The proposed ST receiver can be employed as a multi-beam smart antenna system which is suitable for cellular communications. Computer simulations demonstrate that it can achieve nearly the same performance as the optimal ST minimum mean square error (MMSE) DFE with a much lower implementation complexity.

Timing-offset independent equalization techniques for robust indoor reception of ATSC DTV receivers

This paper presents a fractionally-spaced decision feedback equalizer with Stop-and-Go algorithm for robust indoor reception of ATSC DTV receivers. Many short delay echoes exist in an indoor environment and they can generate large symbol timing offsets. The conventional decision feedback equalizer performs poorly when large symbol timing offset occurs. But the proposed fractionally-spaced decision feedback equalizer with Stop-and-Go algorithm is independent of large symbol timing offsets. Therefore, the proposed equalizer outperforms the conventional decision feedback equalizer in the area of short delay echoes.