A direct RF sampling GPS receiver front-end is presented in a 130nm BiCMOS process, occupying less than 2mm2 of die area. Downconversion of the GPS L1 signal is achieved by subsampling rather than by mixing. The number of building blocks and the complexity of the subsampling receiver are lower than of a conventional heterodyne GPS receiver with comparable performance metrics. The total power consumption from a supply voltage of 1.2V is less than 9mW. The total receiver NF is 3.8dB, the lowest reported NF of a subsampling receiver at this level of power consumption. The NF penalty due to subsampling is less than 1dB.

A RF filter architecture is presented in a 130nm BiCMOS process, serving as replacement of the off-chip Surface Acoustic Wave filter in a GPS receiver front-end. The on-chip RF filter achieves a 3dB bandwidth of less than 12MHz at the GPS L1center frequency of 1575.42 MHz. It exhibits a steep roll-off characteristic resulting in more than 30dB attenuation at frequencies greater than 30MHz away from the center frequency, matching the performance of most commercial off-chip SAW filters. It is implemented as a single cascode stage and achieves a low power consumption of 8.7mW.

In 2005, the planet Mars was illuminated 56 times for 20 min each by an unmodulated 75-cm wavelength circularly polarized wave transmitted from the SRI International 46-m antenna in the Stanford foothills. The direct signal and a Martian surface echo, separated by differential Doppler frequency shifts, were received simultaneously at the Mars Odyssey orbiter. The surface echoes exhibit both fluctuating amplitude and varying spectral width, which are responses to surface reflectivity and roughness variations along the surface track, described by a surface scattering function. We analyze the echo data using quasi-specular scattering theory and exploit high-resolution Mars orbiter laser altimeter topographic maps to model the scattering surface in 3-D at positions along the specular track of the echo, assuming a two-scale classical scattering model. We solve for a surface scattering function via regularized matrix inversion using the measured data and our surface scattering model. Optimizing the matrix inversion regularization over the course of each experiment requires consideration of the changing properties of the surface echoes caused by different viewing geometries. At one extreme the echoes appear as a strong narrowband signal, but on the other extreme the echo signals are weak and have a wide bandwidth. In this paper, we describe a scheme for determining a set of regularization constants that result in physically plausible scattering functions over the full range of echo types.

For signal-based design of orthonormal (ON) wavelets, an optimization of a cost function over an N-dimensional angle space is required. However: (1) the N-dim space includes both smooth and non-smooth wavelets; (2) many of the smooth wavelets are similar in shape. A more practical approach for some applications may be to construct a library of smooth ON wavelets in advance-a library that consists of representative wavelet shapes for a given filter length. Existing ON wavelet libraries (Daubechies, nearly-symmetric, Coiflets) provide only one wavelet for each filter length. We construct ON wavelet libraries using local variation to determine wavelet smoothness and the discrete inner product to discriminate between wavelet shapes. The relationship between library size and the similarity threshold is investigated for various filter lengths. We apply an entropy-based wavelet selection algorithm to an example signal set, and investigate compactness in the wavelet domain as a function of library size.

Biorthogonal bases of compactly-supported wavelets are characterized by the FIR perfect-reconstruction filterbanks to which they correspond. We develop explicit representations of all such filterbanks, allowing us to generate every possible biorthogonal compactly-supported wavelet basis. For these filterbanks, the product /spl Hscr/(z)=H(z)H/spl tilde/(z) of the two lowpass filters must have N/spl ges/2 zeros at z=-1. There are N+1 minimal-length filterbanks for each N. The filterbanks associated with standard orthogonal and symmetric biorthogonal wavelet bases are found as a special case by using appropriate factorizations of symmetric /spl Hscr/(z) with even N; other filterbanks lead to novel biorthogonal bases.