Programmable Matched Filters Research Articles

First demonstration of correlation in a niobium superconductive programmable binary-analog matched filter

A complete prototype superconductive programmable binary-analog matched filter for a 2-Gchip/s spread-spectrum modem has been operated for the first time and has performed correlation. We had previously demonstrated functionality of each individual element of the filter. The analog samplers had captured signals with bandwidths in the order of 10 GHz; the binary weighted taps, which utilize the unique quantum mechanical properties of superconductive circuits, had exhibited nondestructive readout as required; and the two digital shift registers, one that stores the binary code pattern and one that controls sampling of the input analog signal in the bank of track-hold cells, had functioned at 2 GHz. Now all of these elements have been operated together in low-frequency tests. A 7-bit (or "chip" in spread-spectrum terminology) pseudo-noise (pn) code sequence was loaded into the reference shift register in each of the seven possible positions while an analog version of the pn code with its amplitude varied over the full bipolar dynamic range of the filter was used as the incoming signal. The filter response peaked as expected when the analog signal and the binary reference were aligned. The peak and sidelobe responses agreed quantitatively with those predicted from calibration measurements made with uniform signals instead of pn codes.

Mixed analog-digital niobium superconductive circuits for a 2-gigachip-per-second spread-spectrum modem

This paper describes the architecture and operation of a superconductive programmable matched filter that provides rapid synchronization information and data demodulation for a 2-GHz spread-spectrum modem. Results are reported for the first circuit fabrication runs using a new doubly planarized process. With the exception of circuits containing layout errors, all circuits have performed as intended and with characteristics that match well the predictions of JSIM simulations. The MVTL digital components and the buffer between the digital and analog circuits have been demonstrated for the first time. The seven-stage MVTL shift register in a complete prototype filter was operated at 1 GHz. In addition, combinations of (1) the MVTL digital shift register and the buffer and (2) the buffer and the T/H cell have been operated successfully, demonstrating that all of the components in the filter core will work together.

A comparison of analog and digital circuit implementations of low power matched filters for use in portable wireless communication terminals

In this paper, analog and digital circuit realizations of a parallel programmable matched filter are examined. Through wide variations of the design space parameters, the general trend that is observed is that short, fast circuits tend to favor an analog implementation, while longer, slower circuits make a digital implementation more appropriate. A methodology is provided for choosing the preferable circuit-implementing technology when power consumption-as a function of data precision, filter length, operating frequency, technology scaling, and the maturity of the fabrication process-is used as the primary metric of comparison. It is shown that neither the analog nor the digital matched filter implementation is universally more power efficient than the other. Rather, a surface is mapped in the multidimensional design space where, on one side of this surface, a digital solution is preferable, while on the other side of the surface, an analog circuit is appropriate. Equations are given which delineate the position of this transitional surface in terms of the design space parameters, and example calculations and plots depicting the regions of dominance for the digital and analog matched filters for specific process and system parameters are presented.

Mathematical modeling and performance analysis for a two-stage acquisition scheme for direct-sequence spread-spectrum CDMA

Acquisition of synchronism is considered for DS/SS CDMA systems. For large systems with large timing uncertainties, it has been shown previously that acquisition in the presence of multiple-access interference may impose a significant limitation on capacity. This leads the authors to consider a system in which timing uncertainties are relatively small and to propose an acquisition scheme which exploits this to reduce complexity and acquisition overhead. The proposal may be appropriate for a microcellular environment for personal communications in which CDMA packet transmission is employed for both voice and data. Packetized transmission would imply that the overhead available for acquisition is small, and the large number of microcells would restrict the cost of the acquisition scheme used in the receiver in each microcell. The acquisition time required for a simple serial search scheme may therefore be unacceptably large. On the other hand, while acquisition using a passive matched filter is fast, the filter length required for reliable acquisition is liable to be excessive in terms of cost and complexity. Motivated by these considerations, the authors propose a two-stage acquisition scheme which employs a short programmable matched filter for initial detection, followed by a correlator for verification. Numerical results based on an approximate analysis of acquisition performance in the presence of multiple access interference are employed to compare the scheme with conventional acquisition schemes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Automated site characterization for robotic sample acquisition systems

A mobile, semiautonomous vehicle with multiple sensors and on-board intelligence is proposed for performing preliminary scientific investigations on extraterrestrial bodies prior to human exploration. Two technologies, a hybrid optical-digital computer system based on optical correlator technology and an image and instrument data analysis system, provide complementary capabilities that might be part of an instrument package for an intelligent robotic vehicle. The hybrid digital-optical vision system could perform real-time image classification tasks using an optical correlator with programmable matched filters under control of a digital microcomputer. The data analysis system would analyze visible and multiband imagery to extract mineral composition and textural information for geologic characterization. Together these technologies would support the site characterization needs of a robotic vehicle for both navigational and scientific purposes.

Wide-band packet radio for multipath environments

A direct-sequence spread-spectrum packet radio is described that has versatile signal-processing and local-control capabilities designed to support the functions required of a robust mobile communications network. Noteworthy capabilities include eleven selectable data rates with accurate range measurements in a fading multipath channel. The radio uses a hybrid analog/digital signal processor and nonrepeating spreading codes for suppression of intersymbol interference and jamming. It incorporates two sets of monolithic surface-acoustic-wave convolvers as programmable matched filters with time-bandwidth products of 64 and 2000. The analog matched filters are coupled with binary postprocessing for the functions of detection, RAKE demodulations and ranging measurements over a wide multipath spread. The data rate can be varied in response to channel conditions from 1.45 Mb/s down to 44 b/s with an almost ideal tradeoff in signal-processing gain from 18 dB up to 61 dB prior to multipath combining. >

An Application of SAW Convolvers to Spread-Spectrum Transmission of Packet Voice

Abstmcl-A spread-spectrum system for the transmission of packet voice is presented. A continuously variable slope delta (CVSD) modulator is used to encode speech signals at 16 kilobits per second (kbps). The resulting binary data stream is transmitted in bursts containing 1024 message bits. The bit rate within a burst is 84 kbps, with binary code shift keying (CSK) being employed for data representation. The spreading modulation is direct-sequence (DS) with a code rate of 21.4 MHz. The receiver signal processing is based on the application of SAW elastic convolvers to programmable matched filtering of the continuously changing code patterns. Synchronization is accomplished with the aid of an eleven-hit preamble preceding each data packet. Experimental results on the performance of the spread spectrum modem are presented and compared with theory.

A SAW filter for SSB waveform generation

Surface acoustic wave (SAW) devices are known to be capable of generating real-time Fourier transforms. This property has been successfully exploited in the past to enable implementation of so-called transform domain used primarily for interference rejection in spread spectrum communication systems. Filters designed in this manner have included programmable matched filters as well as adaptable notch filters. The same ideas, however, can be used to implement a filter in the Fourier domain which will allow simple and accurate generation of singlesideband (SSB) signals. This paper will describe in depth how the filtering technique works, and experimental results will be presented to demonstrate the procedure.

A SAW/CCD programmable matched filter

A charge-coupled device (CCD) has been integrated with a surface-acoustic-wave (SAW) piezoelectric delay line in a hybrid gap-coupled structure to produce an electronically programmable analog matched filter in which the filter function is controlled by the charge pattern clocked into the CCD. This device allows analog-analog correlation of SAW input signals of ≲40-MHz bandwidth and ≲3.5-μs duration. Programming time is 6 ms at a 100-kHz clock rate, and the reference holding time is 1 s for a 3-dB degradation of the correlation peak. Operation as a matched filter for a 3.25-μs-long 13-bit Barker-encoded signal yields a peak correlation level of −41 dB m.

Acoustoelectric convolvers for programmable matched filtering in spread-spectrum systems

Acoustoelectric convolvers for a spread-spectrum communication application age described with a 100-MHz bandwidth. The use of convolvers as programmable matched filters provides the ability to change the coding waveform from bit-to-bit, thus offering improved multipath performance, security against decoding, and protection against repeat jamming. In this paper, we describe design and performance details of a prototype convolver which processes signals of 10-µs duration with a 100-MHz bandwidth. A dynamic range of 50 dB is obtained, and error signals are 30 dB below the output signal with input signal levels of +14 dBm. A test circuit is described which creates typical spread-spectrum signals in which each bit is encoded into 512 chips and data is encoded by inverting the phase of an entire bit at a data rate of 100 kbits/s.

Programmable surface acoustic wave devices utilizing hybrid microelectronic techniques

Programmable matched filters can be realized using surface acoustic wave propagation in conjunction with external microelectronic circuitry. Here two devices, a programmable analogue matched filter and a diode convolver, are discussed, highlighting the similarities in constructional technique. Specific device requirements include an r.f. circuit which for 10 MHz signal bandwidth must possess a 310 μm pitch. Factors influencing the choice of the thin film hybrid microelectronic technique are outlined and the design, fabrication and performance details are described.