J. Eric Salt

Quality of underwater source localization in a multipath environment

This paper investigates the accuracy of a passive underwater localization system using two submerged omnidirectional sensors in a multipath environment. Expressions for the variance and bias of localization error are developed for two sources of error: ocean noise and sensor perturbations. Expressions are also given for the variance of time delays obtained from the cross correlation of the two sensor signals. It is shown that the variance of localization error is very sensitive to vertical sensor perturbations. It is also shown that in the region where the time difference of arrival (TDOA) of the surface reflected paths is approximately equal to the TDOA of the direct paths, the localization error is very large.

On economical timing-error detectors for QAM receivers

This paper deals with timing jitter reduction in the timing recovery loop of a digital QAM receiver. The main contribution, which is derived analytically, is an economical prefilter to reduce the timing jitter in timing recovery loops containing either the early-late or the Gardner timing-error detector (TED). The proposed prefilter has the advantage of being an infinite impulse response filter that is placed inside the TED and runs at the symbol rate. For small roll off factors, it is shown with a computer simulation that a single-pole filter placed inside either the early-late or the Gardner detector is quite effective in reducing the timing jitter.

A Fast-Converging Equalizer for Upstream DOCSIS Channels

This paper proposes a method of increasing the efficiency of the CATV plant in the upstream direction. The general approach is to reduce the convergence time of the equalizer to allow a shorter training sequence. Specifically, the upstream channel is modeled as a postdetection filter. A short unique word is inserted near the beginning of the preamble to estimate the coefficients of the postdetection filter. The postdetection filter is then crudely inverted to estimate a few key tap weights of the equalizer. The equalizer is initialized with these estimated tap weights before adaptive updating is turned on. The method is evaluated for the echo-laden DOCSIS CATV upstream channel with a signal-to-noise ratio (SNR) of 25 dB. Plots of the probability of the modulation error ratio exceeding 19- and 22-dB values versus the length of the training sequence show that the performance is comparable to an unseeded equalizer with a training sequence that is about 50 symbols longer.

Precoder Design for BICM-MIMO Systems Under Channel Estimation Error

If properly designed, the use of a linear precoder can achieve the maximum coding gain and diversity order in bit-interleaved coded modulation with multiple-input multiple-output systems. However, such maximum coding gain and diversity order are compromised under the practical scenario of having imperfect channel state information (CSI) at the receiver. To alleviate the impact of imperfect CSI on the coding gain and diversity order, joint linear precoder and training pattern are designed in this paper. The design is carried out by considering both the pairwise error probability and the mean square error of the channel estimator. The effectiveness of the proposed design is illustrated by comparing its performance with the performance obtained when only the training pattern is designed for an precoder optimized under the perfect CSI. In particular, simulation results show that a

An Economical, ISI-Immune Frequency Offset Estimator for DOCSIS Upstream Channels

1.5

A Novel Iterative OFDMA Channel Estimation Technique for DOCSIS 3.1 Uplink Channels

1.5 dB gain is achieved by the proposed design.

Iterative Channel Estimation for DOCSIS 3.1 Uplink Channels

In this paper, the asymptotic performance of a precoded bit-interleaved coded modulation with multiple-input multiple-output (BICM-MIMO) system in a block-fading environment is first evaluated. Specifically, the asymptotic pairwise error probability is derived for imperfect channel state information (CSI) and of the minimum mean squared-error (MMSE) detector. The analysis is then used to evaluate the impact of two different training schemes. It is shown that inserting training symbols before precoder is a better option than multiplexing training symbols with data symbols after the precoder. The theoretical result is verified by simulation.

Soft iterative channel estimator for BICM-ID-SSD over time-varying flat fading channels

This paper discusses the design and implementation of frequency offset estimation algorithms for DOCSIS upstream channels. A cost-effective estimator which approaches the Cramer-Rao bound for high SNRs is derived. The effect of ISI generated by upstream micro-reflections in typical cable networks is considered, and a condition upon the transmitted preamble sequence which guarantees unbiased estimation is presented. It is shown that the proposed estimator is unbiased for a wide range of preamble sequences, which is generally not the case for burst frequency estimators. This flexibility may be utilized by selecting a broadband preamble which is suitable for performing channel estimation and frequency offset estimation simultaneously, thereby increasing the efficiency of the upstream channels.