Cross-correlation Receiver Research Articles

Design of Ultra-Wideband Monopulse Receiver

In this paper, we propose a novel amplitude-comparison monopulse receiver architecture for ultra-wideband radars. This monopulse receiver consists of four ridged-horn antennas placed in a square-feed configuration, a comparator circuit that generates the monopulse sum and difference signals, cross-correlation receivers that detect the monopulse signals, and an amplitude-comparison monopulse processor that determines the target's angular position. The derived monopulse sum and difference signals are verified through measurements. The derived sum and difference patterns are compared with measured patterns, and they show good agreements-measured 3-dB beamwidth=6.4deg(derived=6deg), measured unambiguous tracking range=plusmn5deg(derived=plusmn5deg), and measured sum pattern sidelobe level=-6 dB (derived=-8 dB)

Extended-Time Multitaper Frequency Domain Cross-Correlation Receiver-Function Estimation

This article documents a method that successfully yields frequency-domain cross-correlation receiver functions without losing amplitude at long time lags and without sacrificing any of the advantages of the method. After a description of this method, an analysis of synthetics of transition zone structure shows that it provides a way to investigate mantle structure from the surface through the transition zone and deeper.

Ultra-Wideband Transmitted Reference Systems

This paper derives optimal receiver structures for an ultra-wideband transmitted reference (UWB TR) system in multipath environments, based on the average likelihood ratio test (ALRT) with Rayleigh or lognormal path strength models. Several suboptimal receivers are obtained by either applying an approximation to the log-likelihood function without any specific channel statistical models or by approximating two ALRT optimal receiver structures. It is shown that the generalized likelihood ratio test optimal receiver is one of the suboptimal receiver structures in the ALRT sense. Average bit error probabilities of ALRT receivers are evaluated. Results show that ALRT optimal and suboptimal receivers derived from Rayleigh and lognormal models can perform equally well in each other's environments. This paper also investigates ad hoc cross-correlation receivers in detail, and discusses the equivalence between cross-correlation receivers and one theoretically derived ALRT suboptimal receiver. Results show that the noise /spl times/ noise term in a cross-correlation receiver can be modeled quite accurately by a Gaussian random variable when the noise time/spl times/bandwidth product is large, and cross-correlation receivers are suboptimal structures which have worse performance than ALRT receivers.

Adaptive Pulse Optimization for Improved Sonar Range Accuracy

Using the theory of optimal receivers, the range accuracy of echolocating systems can be expressed as a function of pulse bandwidth and SNR through the well-known Woodward equation. That equation, however, was developed in the limit of very high SNRs and assumes that the correct peak of the cross-correlation function is known a priori. We show that for increasing levels of noise, the accuracy of the cross-correlation receiver undergoes a sharp transition from the Woodward equation for a coherent receiver to a modified Woodward equation for a semicoherent receiver. Since this transition appears at different SNRs for pulses with different center frequencies and bandwidths, it is possible to choose the optimal pulse for any given SNR. We show that the adaptive method we propose outperforms the classical cross-correlation receiver for low SNRs. The same ideas can be applied to the case of a fixed broadband signal, by performing the cross correlation at the receiver end separately in a set of frequency bands with the appropriate center frequencies and bandwidths.

Range estimation by echolocation in the bat Eptesicus fuscus: trading of phase versus time cues.

Bats of the species Eptesicus fuscus have been trained to discriminate a stationary simulated target from a target with a virtual distance that jitters from sound to sound. Similar to Simmons [Science 207, 1336-1338 (1979)], a jitter-detection threshold below 1 microsecond was found. However, Simmons' decreased performance at a time delay jitter of 30 microseconds could not be replicated, a critical feature used to postulate the idea that bats employ a coherent cross-correlation receiver for ranging. Such a receiver uses all phase information in the signal for delay estimation and therefore will be biased by phase manipulations. To test for such a bias, a phase jitter of +/- 45 degrees and a time jitter in the echo were overlaid. It was not found that there was a combination of both where their effects canceled. Full phase information is thus not used in delay estimation. However, bats were able to detect a pure phase jitter, e.g., polarity inversion of the signal. Bats could also detect phase jitter in the presence of randomized time jitter and vice versa. Phase jitter and time jitter, therefore, are separable features for a bat. The underlying physiological mechanism is not clear.

Phase evaluation in hypothetical receivers simulating ranging in bats.

Echo delay discrimination by the bat Eptesicus fuscus had been investigated in an experiment with simulated targets jittering in range (Simmons 1979). The dip in the resulting psychometric curve was used by Simmons to suggest the neuronal implementation of a coherent cross-correlation receiver in the auditory system of bats. By computer simulation it is shown here that the dip may be even more pronounced and less susceptible to noise with alternative receiver configurations which not necessarily evaluate signal phase information coherently, e.g., a bank of neuronal filters with envelope-processing. New behavioral experiments are suggested to critically test such model hypotheses.

Accuracy of distance measurement in the bat Eptesicus fuscus: theoretical aspects and computer simulations.

Behavioral experiments of Simmons [J. Acoust. Soc. Am. 54, 157-173 (1973) and Science 204, 1336-1338 (1979)] on the ranging accuracy in the bat Eptesicus fuscus have led to far-reaching postulates on the existence of optimal and phase-conserving processing mechanisms in the bat. In this paper, the results of computer simulations of these experiments are presented. Two receiver types are investigated: the fully coherent cross-correlation receiver and the cross-correlation receiver with envelope processing (semicoherent). It is shown that Simmons' experiments cannot be treated as a simple estimation of distance, but require at least two (range difference experiment; see Simmons, 1973) or four (range jitter experiment; see Simmons, 1979) echolocation sounds for one decision. The performance of the bat in both experiments is much worse than predicted for a coherent and a semicoherent receiver type. The bat's accuracy in Simmons' range difference experiment is at least 18 dB worse than predicted for an optimal receiver. The results of the jitter experiment cannot be interpreted in a simple way as proof that bats are able to evaluate phase information as in a fully coherent cross-correlation receiver.

Comments on "Some Pitfalls In Millimeter-wave Noise Measurements Utiking A Cross-correlation Receiver

In the above paper, 1 Sutherland and van der Ziel analyze some problems encountered during noise measurements at very low temperatures with a cross-correlation receiver. It is shown that, if a hybrid junction is used to split the noise signal from the device under test (DUT) into the two receiver channels, the correlation between the receiver input signals, which contains the useful information, vanishes if the remaining port of the hybrid is resistively terminated at a temperature equal to that of the DUT. The same effect occurs for a pure reactive termination, if the isolators used to decouple the receiver channels are also cooled down to the temperature of the DUT.

Some Pitfalls in Millimeter-Wave Noise Measurements Utilizing a Cross-Correlation Receiver

It is shown that the use of a hybrid junction as the power splitter in a cross-correlation receiver for millimeter-wave (94-GHz) noise measurements at low temperature (2 K) introduces an unwanted source of noise which defeats the purpose of the measurements. The same is the case when isolators are introduced to prevent cross-coupling of the noise from the two receiver channels.

Some Observations on the Statistics of Beyond-the-Horizon Transionospheric Propagation from a Satellite

The HF signals radiated (from heights above <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_{2}h_{max}</tex> ) by the first satellite orbited by the Peoples Republic of China (1970-34A) were monitored at a ground site in Florence, Italy. Beyond-Beyond-the-horizon reception with distances up to antipodality were repeatedly observed. Path loss improvement with respect to free space was typically 4 dB for distances of 12 000 km and 8 dB for distances of 20 000 km (antipodal focusing). A cross correlation receiver, designed to detect the most frequent tone (784 Hz) contained in the musical theme ("The East is Red") emitted by the satellite, provided a processing gain of 27 dB and made possible reliable reception for input SNR as low as -13 dB.

An Aperture Synthesis Study of H I in the Irregular II Galaxy NGC 3077

The Cambridge Half-Mile telescope has been used in conjunction with a 160-channel cross-correlation receiver to map the neutral hydrogen emission in NGC 3077 with a synthesized beam of width |$1^{\prime} \cdot 5 \times 1^{\prime} \cdot 6.$| The H I distribution is found to be severely distorted, with the projected centroid lying about 4 kpc SE of the optical centre in a region where star formation may be occurring, and a streamer of H I extending ~ 10 kpc northwards. The observed H I mass is |$4 \cdot 1 \times 10^{8} M_{\odot}$| of which a quarter is in the streamer. A small gradient of radial velocity exists across the galaxy which, if interpreted as rotation, suggests an indicative mass of |$(6 \pm 2) \times 10^{9} M_{\odot}.$| A computer model is proposed to explain the distorted H I distribution in terms of tidal forces exerted during a close (12 kpc) encounter between NGC 3077 and M81, (2 to 6) × 108 yr ago.

Signal Processing Techniques for a Lunar Radar System

The NRL lunar radar system is being used to make long term, precision Earth-Moon distance measurements. A pulse compression ratio of 104 permits a high signal to noise ratio for a range resolution of 1.2 ?s (180 meters). The high pulse compression ratio is achieved through the use of a pseudorandom (P-N) code, phase reversal modulation of the carrier, and a multichannel cross-correlation receiver. The transmitted signal is phase modulated by the P-N code. This code has a correlation function which permits separation of the echo in range. In each correlator, the echo is multiplied by a replica of the code with an appropriate delay, and the product is passed through a narrow band filter. The correlator output measures the energy of the echo from a range interval corresponding to the delay chosen. A separate correlator is used for each of 40 adjacent range channels. The correlation circuitry consists of ring modulators, crystal filters, and envelope detectors. The ring modulators permit compact and economical packaging of the 40 correlators. The multiple outputs are recorded on magnetic tape for analysis and are also displayed in realtime.

Acoustic Signal Detection by Simple Correlators in the Presence of Non-Gaussian Noise. I. Signal-to-Noise Ratios and Canonical Forms

The detection of underwater acoustic signals by simple auto- and cross-correlation receivers in the presence of nonnormal, as well as normal background noise is examined on the basis of signal-to-noise ratios calculated from a generalized deflection criterion. Particular attention is devoted to the effects of impulse noise and mixtures of impulse and normal noise on system performance. Comparisons between system behavior vis-à-vis the two types of interference are made. For impulse noise equivalent in spectral distribution and average intensity to a Gaussian noise background it is found that the output signal-to-noise (power) ratios are related by the canonical expression (SN)I2 = (S/N)G21 + (1 − μ)Λ(S/N)G2, 0⩽μ⩽1, where Λ(⩾0) is the “impulse factor” and μ is the fraction (in average intensity) of the total noise background that is attributable to normal noise. Impulse noise always degrades system performance vis-à-vis normal noise in the autocorrelation reception of stochastic signals, characteristic of applications where passive receiving methods must be used. This degradation can be considerable [O(10 dB or more)] if the noise is highly impulsive (large Λ) and if large values of (S/N)out2(&amp;gt;0 dB) are required (for high accuracy of decision). On the other hand, when coherent (i.e., deterministic) signals are employed, so that cross-correlation reception is possible, the degradation may be reduced essentially to zero (i.e., Λ → 0) under realizable conditions of operation. It is observed for impulsive, as well as normal noise backgrounds, that cross-correlation receivers are linear in their dependence on signal-to-noise ratio, i.e., (S/N)out2∼(S/N)in2 if sufficiently strong injected signals are employed. The analysis is carried out largely in canonical form, so that the general results for (S/N)out2 can be applied to other, special types of nonnormal noise backgrounds. Specific relations are included, along with a detailed summary of the principal results, showing the dependence of (S/N)out2 on (S/N)in2, filtering, delay, noise and signal spectra, etc., for weak and strong inputs, little or heavy postcorrelation smoothing and for Gaussian as well as for impulse noise.

Detection of a Signal Specified Exactly with a Noisy Stored Reference Signal

This paper treats the optimization problem of detecting the presence of a signal in a background of white Gaussian noise, under the restriction that the signal is specified exactly but the receiver memory contains only a noisy version of the signal. The optimum receiver is specified. The performances of both the optimum receiver and the cross-correlation receiver with a noisy memory are calculated and compared for a special case.