Binary Phase Code Research Articles

Reconfigurable optical interconnects by a combined computer-generated hologram and spatial light modulator method

A new method for implementing electrically addressed dynamic optical interconnects is presented. In this approach a phase spatial light modulator (SLM) is combined with a computer-generated hologram (CGH). The phase SLM is used to change the phase of the wave front that illuminates the CGH. Binary orthogonal phase codes are used to address the SLM. The CGH is designed with iterative discrete on-axis encoding so that different wave fronts direct light to different locations. High efficiency can be achieved because of the large number and the small dimensions of pixels in the CGH. The dynamic aspects result from the use of an SLM that may have a relatively small number of relatively large pixels. In this manner a high-efficiency programmable interconnect system with fast reconfiguration time based on current technology devices may be implemented. The CGH-SLM method yields connection efficiencies significantly higher than previous methods that are based on the use of thin optical elements. Simulation results indicate that for switch sizes in the range from 1 × 2 to 1 × 8, connection efficiencies of higher than 1/ √N (where N is the number of possible destinations) are feasible.

Good multi-T phase codes under bandwidth and complexity constraints

Multi-T phase codes are an equivalent realization of multi-h phase codes within the class of continuous phase modulations (CPM). The authors present, in the form of code tables, the results of a systematic search for binary and quaternary multi-T phase codes which maximize the free Euclidean distance under given bandwidth and complexity constraints. >

Simulated annealing searches for long binary phase codes with application to radar remote sensing

We apply the technique of simulated annealing to search for long discrete codes with special autocorrelation and ambiguity function properties, suitable for radar applications. This technique provides access to codes which are far too long for exhaustive search, and to codes whose correlation properties do not lend themselves to algebraic investigation. We illustrate the process with two new kinds of binary phase codes.

Generation of uniform amplitude complex code sets with low correlation sidelobes

The performances of generated test code sets are compared to other phase coding and theoretical limits. The results presented show that the generation algorithm produces uniform amplitude complex code sets with low autocorrelation sidelobes and low cross-correlation outputs. The mainlobe to peak sidelobe ratio (MPSR) gains over binary codes could lead to significant performance improvements in both communication and radar systems that require multiple codes. The Doppler characteristics of the generated codes are comparable to those of binary phase codes. Although the generation times are long, they are not impractical given current and projected processing technology. >

Fine structure variability of acoustic signals propagating to two convergence zones.

The influence of propagation to two convergence zones on active sonar signals was investigated by transmitting a wavetrain consisting of a 100-ms, 400-Hz-wide LFM and a 10-s binary phase code. The center frequency of both signals was 1-kHz. The wavetrain was received and recorded over a period of 14 h on a surface vessel two convergence zones removed from the transmitting vessel. The received signals were examined by matched filtering of the LFM and binary phase code and by spectral analysis of the LFM and the carrier frequency of the phase code. Statistically significant variation over time in the signal was observed both in which of the four predicted multipaths were actually detected and in the delay structure within particular arrivals. The spectrum of deep refracted LFM signals showed the expected fading at selected frequencies but which frequencies were attenuated varied dramatically from ping to ping. Corresponding variability in the matched filter output was also observed. Variability in the total multipath structure of the received signal ranged from clear presence of all four predicted arrivals to clear presence of only one, which was interpreted as the deep refracted arrival.

Signal processing and data analysis in middle atmosphere radar

Use of signal‐processing and data analysis methods in radar studies of middle atmospheric motions is examined. Detection of weak Doppler‐shifted signals from thin atmospheric regions in a noise background requires an optimum receiver. It is noted that the optimum receiver is implemented in successive stages using matched‐filter and correlator structures for locating targets distributed in range and a filter bank for estimating their Doppler shifts. Effectiveness of coherent integration in reducing high data rates, and as an efficient but crude low‐pass filter, is discussed. Use of noiselike binary phase codes and decoding in improving range resolution is outlined. Spectral analysis of radar signals using a time‐averaged periodogram and the autoregressive model is briefly reviewed. Methods of reducing undesirable artifacts in spectral analysis of nonstationary signal components, using windows and trend removal, are delineated. Estimation of signal parameters through spectral moments and least squares estimation is summarized. Finally, simple ad hoc data‐editing methods for suppressing outliers and interference are outlined.

Performance of a Pseudorandom Binary Phase Code with Errors and Doppler-Shifted CW

The effects that various code imperfections have on the peak of the mainlobe and on the time sidelobes of the compressed coded signal are described. The imperfections considered are finite pulse rise time, timing errors, code integration mismatch, and Doppler shift of the coded signal.

Finite-length binary phase codes for digital pulse compression

Binary phase codes for radar pulse compression giving compression ratios greater than 13 (the maximum-length Barker code) must generally be found by trial and error on a digital computer. Formulas are derived for the maximum number of codes of given length which have different autocorrelation functions, and it is shown how redundant codes can be recognised without evaluating the autocorrelation functions.

The Operation of Acoustic Surface Wave Delay Lines in a Nuclear Environment

The operation of three types of surface wave acoustic devices; a lithium niobate delay line, a quartz pulse-compression filter and a quartz binary-phase-coded (BPC) delay line, in a nuclear environment are investigated. Neutron irradiation up to 5 × 1015 N/cm2 (E>10 keV) and exposure to 4 × 108 rads of 60Co gamma rays results in no changes. Transient ionizing radiation, occurring at the time when an electrical signal is being converted to acoustic energy, decreases the amplitude and changes the phase of the signal. Once the signal is transmitting in the device as acoustic energy it is generally unaffected by ionizing radiation up to 1011 rad(Si)/sec. However, in the case of the BPC device, functional operation is impaired above levels of 4 × 108 rad(Si)/sec.

Effects of Random Implementation Errors in Matched Filters for Binary Phase Code Pulse Signals

The effects of implementation errors in tapped delay line filters on the peak-to-sidelobe ratio and the signal-to-noise ratio of binary PSK pulse compression codes are considered. As error model the delay elements and weighting factors of such filters are assumed to have an error distribution with known mean and variance.

A new technique for short-pulse compensation in phased-array scanning

A new technique is briefly described for wide-angle scanning when the spatial pulsewidth is smaller than the length of the phased array. The concept obviates the need for the long-time delayers used with subarrays; it employs a binary phase code on the array-element modulo-2π phase shifters and a decoder matched to this phase code.