Received Pulse Shape Research Articles

Lack of Rotation Invariance in Short-Pulse Communication Between Broadband Circular-Polarization Antennas

There are many antenna designs capable of producing high quality circular polarization over very wide bandwidth. One of the beneficial attributes of circular polarization seen in narrowband applications is that one or both of the antennas in a link can be rotated around the boresight direction without significantly affecting the received signal. However, this does not apply to a broadband system, in which the received pulse shape will change under rotation. Calculations of maximum possible correlation between the rotated and unrotated pulse shapes as the antenna is rotated are presented, along with an experimental example. It is also shown that in general it is not possible to have the pulse shape and amplitude invariant under rotation for a broadband signal, even if completely general polarizations and antenna transfer functions are allowed.

Electromagnetic radiation from moving, pulsed source distributions: The 3D time-domain relativistic Doppler effect

The pulsed electromagnetic field radiated by distributed electric-current and magnetic-current sources in uniform translational motion is analyzed within the framework of the special theory of relativity. The relevant Lorentz transformations are used to exhibit the general structure of the field as it is experienced by a stationary observer. In particular, the differences in the transmitted and received pulse shapes are discussed, which are manifestations of the 3D time-domain relativistic Doppler effect. Applications are found in Doppler radar and spaceflight telemetry.

Optimization of a triangular PFDR antenna in a fully diffuse ow system influenced by background noise and multipath propagation

Optical wireless (OW) systems are generally impaired by multipath propagation and directional interference in the form of background noise. We present original results for a fully diffuse OW system that employs a novel triangular pyramidal fly-eye diversity receiver (PFDR). The received pulse shapes are evaluated at various locations on the communication floor and the background noise collected on the three faces of the pyramid is determined. It is demonstrated that, through optimization of the PFDR field-of-view, the directional background interference can be reduced and that the received pulse shape can be improved. The computed error probability shows a marked improvement when our optimized PFDR antenna is used instead of the conventional photodetector used in traditional diffuse optical wireless systems.

Ultra wideband channel model for indoor environments

This paper presents an in-depth study of a UWB indoor radio channel between 1 and 9 GHz, which was used for the subsequent development of a new statistical UWB multipath channel model, focusing on short range indoor scenarios. The channel sounding process was carried out covering different indoor environments, such as laboratories, halls or corridors. A combination of new and traditional parameters has been used to accurately model the channel impulse response in order to perform a precise temporal estimation of the received pulse shape. This model is designed specifically for UWB digital systems, where the received pulse is correlated with an estimated replica of itself. The precision of the model has been verified through the comparison with measured data from equivalent scenarios and cases, and highly satisfactory results were obtained.

Optical wireless multibeam transmitter with line strip, diamond, and uniform geometries

We propose and evaluate a novel configuration that employs a multibeam transmitter in an optical wireless system. Such a configuration borrows attractive features from diffuse and line-of-sight systems, resulting in great robustness and ease of use. A line strip multibeam transmitter placed on the communication floor is proposed to produce a line of diffusing spots on the middle of the ceiling. The results associated with the new structure show that a receiver SNR improvement of about 3.8 dB can be achieved compared to the conventional diffuse configuration. Other geometries including a diamond-shaped spot geometry and a uniform spot geometry are also considered. Power distribution, received pulse shapes, and a comparison with the conventional diffuse link are outlined. SNR results show that the proposed geometries are very attractive.

Closed-form expressions for ocean reverberation and signal excess with mode stripping and Lambert's law.

Closed-form expressions for two-way propagation and reverberation in variable depth ducts are derived for isovelocity water by using ray invariants and acoustic flux. These expressions include the transition to single mode propagation at long range. Three surface scattering laws are considered: Lambert, Lommel-Seeliger, and angle independent, and these are compared with a point target to give explicit signal-to-reverberation ratios. In particular, there is interesting and sometimes surprising behavior when the propagation obeys mode-stripping (the high angles are preferentially attenuated by bottom losses) whilst the scattering obeys Lambert's law (high angles are preferentially back-scattered). There may be conditions where the signal-to-reverberation ratio is independent of range so that there is no reverberation range limit. Bottom slope dependence of both target echo and reverberation is surprisingly weak. The implications of refraction are discussed. The angle dependence for a point or surface scatterer at a given range can be translated into arrival time, so it is possible to calculate the received pulse shape for one-way or two-way paths. Because the tail is exponential with a range-independent half-life that only depends on bottom reflection properties there is scope for extracting geoacoustic information from the pulse shape alone. This environmental time spread is also of use to sonar designers.

Performance evaluation of a triangular pyramidal fly-eye diversity detector for optical wireless communications

Background noise and multipath propagation are the major impairments in indoor optical wireless links. They can introduce heavy distortion in the received optical signal and can degrade the system performance. An investigation into the optical wireless system performance has been carried out for two configurations: a hybrid system, and a diffuse system with a single detector and a triangular pyramidal fly-eye diversity receiver (PFDR). Original results for both systems that employ a PFDR antenna, under different fields of view (FOVs), are presented. The design goal is to reduce the effect of signal spread and improve the signal-to-noise ratio when the system operates under the constraints of background noise and multipath dispersion. It is demonstrated that through PFDR FOV optimization the directional background interference can be reduced and the received pulse shape improved.

Sensitivity assessment of a three-segment pyramidal fly-eye detector in a semidisperse optical wireless communication link

A pyramidal fly-eye diversity detection configuration is presented for wireless infrared communication in small and middle-sized office rooms. It is demonstrated that the configuration combats the sensitivity degradation imposed by multipath dispersion and ambient noise in a semidisperse environment. The improvement is especially notable when the threshold level is set to its optimum value with regard to the maximum collected level of ambient noise and multipath dispersion. As the number of photodetectors in the configuration is limited, the penalty paid for an increase in performance is a limited increase in complexity. The applied simulation method used to determine the received pulse shapes and the detected level of ambient noise is outlined. Original analytical details are provided which enable the evaluation of the system sensitivity, for any detected pulse shape and any fixed threshold level.

Signal separation using fractional sampling in multiuser communications

Described is a decorrelating filter that separates signals in a multiuser environment by relying on the relative delays to be sufficiently distinct. The input signal is fractionally sampled to allow for the differentiation of the user delays. Both zero-forcing and minimum mean-square-error versions of this filter are derived and probability of error expressions are given. The algorithm successfully separates unknown digital signals by using the known received pulse shapes and the symbol rate. A delay-division multiple-access (DDMA) scheme based on this signal decorrelator is proposed that will allow signals to be transmitted without spreading the signal spectrum. It is shown that in a noisy environment the signal-to-noise ratio penalty for DDMA can be severe yet the bandwidth advantage is very pronounced compared to spread-spectrum systems and is similar to other bandwidth efficient schemes. The performance of a code-division multiple-access (CDMA) system using this signal decorrelator is also given. The decorrelator can be used as a blind multiuser detector or as a preprocessor to enhance the performance of a CDMA system.

Rapid numerical estimation of soil thermal properties for a broad class of heat-pulse emitter geometries

The recently developed dual-probe heat-pulse technology permits the rapid, automatic monitoring of soil volumetric heat capacity, thermal diffusivity, and conductivity. The method relies on parameter fits of equations describing received pulse shape. These, in turn, depend on the particular geometric model assumed to characterize the sensor system. This paper describes an estimation procedure applicable to a wide class of sensor geometries. Key attributes of the method are that: (1) it replaces multidimensional, parameter space searches with a single, univariate optimization; (2) no derivatives are required for point estimates; (3) except for a one-time-only table precalculation, computational requirements are independent of model complexity; and (4) it computes its own initial estimates from the data. A computer implementation of the method is presented along with fits of finite and infinite line source emitters to temperature data from laboratory dual-probe heat-pulse experiments. The results show the new method gives answers identical to the commonly used Marquardt algorithm.

Optically preamplified pulse-position modulation for fibre-optic communication systems

A Chernoff bound is applied, by means of a recently developed moment-generating function (MGF), to the error probability of an optically preamplified pulse-position-modulation (PPM) receiver assuming Gaussian received pulse shapes. Sensitivity results are presented for various length PPM words and also bit-error-rate curves. The results are compared with those obtainable from an equivalent on–off keyed nonreturn-to-zero (OOK NRZ) system and show a possible benefit of 7.1 dB. The work demonstrates the potential of such an optically preamplified PPM receiver by giving results which surpass the fundamental sensitivity limit of an optically preamplified OOK NRZ receiver and approach the sensitivity of coherent detection systems. In particular, the analysis suggests that, at the STM-4 bit rate of 622 Mbit/s, a sensitivity of 25.27 photon/bit is attainable. In addition, a Gaussian approximation is developed from the variance obtainable from the MGF and the results obtained from the Chernoff bound are compared with those obtainable from the approximation.

Performance of a suboptimum PPM presynchronization filtering network

AbstractAn optimum presynchronization filter for the pulse‐position‐modulation (PPM) signal is derived and shown to be comprised of a matched filter in cascade with a derivative network. An original investigation of the performance of the filtered PPM system is presented. The matched filter is realized from a time‐domain specification on the received pulse shape and an RC combination derivative network is used to shape the pulse. The results demonstrate that there exists an optimum value of the differentiating capacitor resulting in performance that is close to the true derivative. The results obtained illustrate a significant improvement in both the timing variance and jitter wrong slot error (JWSE) probability compared to that for the matched filter. © 1995 John Wiley & Sons, Inc.

Slot synchronization in optical‐fiber ppm systems with gaussian‐type received pulse shapes

AbstractThe problem of determining the precise slot boundaries is an essential one in optical‐fiber pulse position modulation (PPM) systems due to the temporal nature of the format. Here we present an original spectral characterization of the PPM process and establish the requirements to realize a discrete spectral slot rate component. In particular we show that this component is independent of the modulation index and data probability distribution. The dependence of the component on pulse shapes is investigated and examined for the important class of dispersed Gaussian‐type pulse shapes normally associated with optical‐fiber transmission. Original practical results, measured on a 128‐slot PPM system, are presented and shown to be in agreement with the theoretical predictions to within 1 dB. © 1993 John Wiley & Sons, Inc.

Sensitivity analysis of direct detection optical FDMA networks with OOK modulation

The authors analyze the sensitivity degradation in direct-detection optical FDMA networks as a result of signal filtering (both optical and electrical), interchannel crosstalk, channel beats (or nonlinear crosstalk), and intersymbol interference. The model used is valid for arbitrary linear time-invariant optical filters and received pulse shapes. The analysis is applied to on-off keying (OOK) systems using single-cavity Fabry-Perot filters and multistage Mach-Zehnder filters. >

Optical fibre digital pulse-position-modulation assuming a Gaussian received pulse shape

The abundance in bandwidth available in the best monomode fibres may be exchanged for improved receiver sensitivity by employing digital PPM. This paper presents a performance and optimisation analysis for a digital PPM coding scheme operating over a fibre channel employing a PIN-BJT receiver and assuming a Gaussian received pulse shape. We present original results for a 50 Mbit/s, 1.3 μm wavelength digital PPM system and conclude that, provided the fibre bandwidth is several times that of the data rate, digital PPM can outperform commercially available PIN-BJT binary PCM systems.

Experimental evaluation of the performance of pulsed two-color laser-ranging systems

Two-color laser-ranging systems can be used to estimate the atmospheric delay by measuring the difference in propagation times between two optical pulses transmitted at different wavelengths. This paper describes horizontal-path ranging experiments that were conducted using flat diffuse targets and cube-corner reflector arrays. Measurements of the timing accuracy of the cross-correlation estimator, atmospheric delay, received pulse shapes, and signal power spectra are presented. The results are in general agreement with theory and indicate that target speckle can be the dominant noise source when the target is small and is located far from the ranging system or when the target consists of a small number of cube-corner reflectors.

Beam wave two-frequency mutual-coherence function and pulse propagation in random media: an analytic solution

Pulse propagation in a random medium is determined by the two-frequency mutual coherence function which satisfies a parabolic equation. In the past, numerical solutions of this equation have been reported for the plane wave case. An exact analytical solution for the plane wave case has also been reported for a Gaussian spectrum of refractive-index fluctuations. Using the same approximation, an exact analytic solution for the more general case of an incident beam wave is presented. The solution so obtained is used to study the propagation characteristics of the beam wave mutual coherence function at a single frequency as well as at two frequencies. Simple expressions are obtained which qualitatively describe the decollimating and defocusing effects of turbulence on a propagating beam wave. The time variation of the received pulse shape, on and away from the beam axis, is studied when the medium is excited with a delta function input. The results are presented for both collimated and focused beams.

P-wave seismograms from continuously varying transition zones -- II. Elastic media

Summary. The P-wave response from a class of acoustic transition zones with exponential variation in the velocity is studied in the frequency and time domains by means of contour integration in the complex k plane and the fast Fourier transform (FFT). Interesting relationships between received pulse shapes and velocity gradients inside the transition zone are observed. It is suggested that the models could be of practical interest, e.g. in interpreting observations from explosion seismology. For one model the results from the contour integral method are compared with those from the reflectivity method of Fuchs.

Plane wave pulse propagation through random media

The theory of plane wave pulse propagation through a random medium, under the forward-scattering assumption is presented. Since pulse propagation characteristics are determined by two-frequency mutual coherence function <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Gamma</tex> , a set of normalized curves is given for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Gamma</tex> for different propagation parameters (operating frequency, propagation distance, turbulence strength or density of scatterers, etc.). From the curves one can obtain the coherence bandwidth of a wave for a variety of situations. A received pulse form due to an input delta function is given in a normalized form which is applicable to the whole range of strong fluctuation. The results are applied to optical pulse propagation in dense clouds. It is shown that the high data rate optical pulse communication through clouds may be limited due to a narrow coherence bandwidth of the order of megahertz. A good agreement between the theoretical prediction and the available experimental data has been demonstrated for both the received pulse shapes and the pulse durations of an optical pulse in clouds.

Photomultiplier Reception of Satellite Beacon Flashes

Experiments have been performed on the electrooptical detection of flashes from satellite-borne beacons for the purposes of establishing the time of flash at the observing site, measurement of received pulse shape, and relative measurement of received energy. Initial observations have been made of the beacons carried by the geodetic satellite GEOS-B. Time of flash has been obtained to a precision of 0.1 msec. Pulse shape and energy measurements have been made for various slant ranges and at various voltages on the photomultiplier circuits. Continued testing is directed toward microsecond timing of flash reception.