R. Neil Braithwaite

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This paper shows that digital predistortion (DPD) used to linearize an RF power amplifier (PA) can achieve wide bandwidth distortion cancellation using measurements obtained from a narrow bandwidth observation path. The DPD module creates a correction signal using a set of nonlinear basis waveforms, weighted by adjustable coefficients. The coefficients are(More)
This paper presents a new representation called " hierarchical Gabor filters " and associated novel local measures which are used to detect potential objects of interest in images. The " first stage " of the approach uses a wavelet set of wide-bandwidth separable Gabor filters to extract local measures from an image. The " second stage makes certain spatial(More)
wireless communications, CDMA, multi-access communication, intermodulation distortion This paper investigates the effects of Walsh code selection and baseband filtering on the statistical moments of the bandlimited forward-link CDMA signal. A normalized moment, the " power variance " , is proposed as a measure of the signal's sensitivity to nonlinear(More)
This paper describes algorithms used to improve linearity, efficiency, and peak power of a Doherty amplifier whose auxiliary transistor gate voltage is adjusted digitally as a function of the signal envelope. Two predistortion stages are used to compensate for high-order memoryless nonlinearities and low-order memory effects. The digital gate voltage(More)
A combined approach to digital predistortion (DPD) and crest factor reduction (CFR) is proposed. The new CFR is structured similar to DPD and is implemented by introducing a steady-state offset into the DPD coefficients. The DPD and CFR coefficients are estimated using separate adaptive processes but applied to the transmission path in a common module. The(More)
J.G. Daugman's (1988) neural network solution to the Gabor expansion of an image is reformulated as a steepest descent implementation. Nonlinear optimization theory is then applied to select an appropriate convergence factor. Two quasi-Newton-based nonlinear optimization techniques are applied to improve the convergence for certain types of lattice.
Recognition of aircraft in complex, perspective aerial imagery has to be accomplished in presence of clutter, occlusion, shadow, and various forms of image degradation. This paper presents a system for aircraft recognition under real-world conditions that is based on the use of a hierarchical database of object models. The particular approach involves three(More)
This paper develops an error bound for narrow band-width Gabor filters synthesized using multiple stages. It is shown that the error introduced by approximating narrow bandwidth Gabor kernels by a weighted sum of spatially offset, separable kernels is a function of the frequency offset and the reduction in bandwidth of the desired kernel compared to the(More)