National Telecommunications and Information Administration

The Institute for Telecommunication Sciences (ITS) has developed an objective video quality assessment system that emulates human perception. The perception-based system was developed and tested for a broad range of scenes and video technologies. The 36 test scenes contained widely varying amounts of spatial and temporal information. The 27 impairments included digital video compression systems operating at line rates from 56 kbits/sec to 45 Mbits/sec with controlled error rates, NTSC encode/decode cycles, VHS and S-VHS record/play cycles, and VHF transmission. Subjective viewer ratings of the video quality were gathered in the ITS subjective viewing laboratory that conforms to CCIR Recommendation 500-3. Objective measures of video quality were extracted from the digitally sampled video. These objective measurements are designed to quantify the spatial and temporal distortions perceived by the viewer. This paper presents the following: a detailed description of several of the best ITS objective measurements, a perception-based model that predicts subjective ratings from these objective measurements, and a demonstration of the correlation between the model's predictions and viewer panel ratings.

Propagation properties of suspended water and ice particles which make up atmospheric haze, fog, and clouds were examined for microwave and millimeter-wave frequencies. Rates of attenuation alpha (dB/km) and delay tau (ps/km) are derived from a complex refractivity based on the Rayleigh absorption approximation of Mie's scattering theory. Key variables are particle mass content and permittivity, which depends on frequency and temperature both for liquid and ice states. Water droplet attenuation can be estimated within a restricted (10+or-10 degrees C) temperature range using a simple two-coefficient approximation. Experimental data on signal loss and phase delay caused by fog at four frequencies (50, 82, 141, and 246 GHz) over a 0.81-km line-of-sight path were found to be consistent with the model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Many organizations have focused on developing digital video quality metrics which produce results that accurately emulate subjective responses. However, to be widely applicable a metric must also work over a wide range of quality, and be useful for in-service quality monitoring. The Institute for Telecommunication Sciences (ITS) has developed spatial-temporal distortion metrics that meet all of these requirements. These objective metrics are described in detail and have a number of interesting properties, including utilization of (1) spatial activity filters which emphasize long edges on the order of 10 arc min while simultaneously performing large amounts of noise suppression, (2) the angular direction of the spatial gradient, (3) spatial-temporal compression factors of at least 384:1 (spatial compression of at least 64:1 and temporal compression of at least 6:1, and 4) simple perceptibility thresholds and spatial-temporal masking functions. Results are presented that compare the objective metric values with mean opinion scores from a wide range of subjective data bases spanning many different scenes, systems, bit-rates, and applications.

Millimeter wave communication systems in the 21.5 to 29.5 GHz band are being developed in the United States and Canada for use in a local multipoint distribution service (LMDS). This paper summarizes radiowave propagation impairments for the LMDS and reports measurement data for small cells. Results include area coverage estimates over a range of basic transmission losses for 0.5-, 1.0- and 2.0-km suburban cells with foliated trees. Multipath, signal attenuation, depolarization, and cell to cell coverage also are discussed. Data indicates a high probability of non-line-of-sight paths due to trees which can cause signal attenuation and signal variability when wind is present. Signal variability was studied using k factors and compared to the Rician cumulative distribution function. Depolarization caused by vegetation and other signal scatterers was found to be an order of magnitude greater than rain-induced depolarization. A simple tapped delay line model is presented to describe multipath for three channel states.

article Free Access Share on A method of univariate interpolation that has the accuracy of a third-degree polynomial Author: Hiroshi Akima U.S. National Telecommunications and Information Administration, U.S. Dept. of Commerce, Boulder, CO U.S. National Telecommunications and Information Administration, U.S. Dept. of Commerce, Boulder, COView Profile Authors Info & Claims ACM Transactions on Mathematical SoftwareVolume 17Issue 3Sept. 1991 pp 341–366https://doi.org/10.1145/114697.116810Published:01 September 1991Publication History 66citation1,251DownloadsMetricsTotal Citations66Total Downloads1,251Last 12 Months74Last 6 weeks6 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my Alerts New Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

This report describes the results of interference tests and measurements that have been performed on radar receivers that have various missions in several spectrum bands. Radar target losses have been measured under controlled conditions in the presence of radio frequency (RF) interference. Radar types that have been examined include short range and long range air traffic control; weather surveillance; and maritime navigation and surface search. Radar receivers experience loss of desired targets when interference from high duty cycle (more than about 1–3%) communication-type signals is as low as −10 dB to −6 dB relative to radar receiver inherent noise levels. Conversely, radars perform robustly in the presence of low duty cycle (less than 1–3%) signals such as those emitted by other radars. Target losses at low levels are insidious because they do not cause overt indications such as strobes on displays. Therefore operators are usually unaware that they are losing targets due to low-level interference. Interference can cause the loss of targets at any range. Low interference thresholds for communication-type signals, insidious behavior of target losses, and potential loss of targets at any range all combine to make low-level interference to radar receivers a very serious problem.

Since the normally assumed white Gaussian interference is the most destructive in terms of minimizing channel capacity, substantial improvement can usually be obtained if the real-world interference environment (non-Gaussian) is properly taken into account. In this paper, the performance of the locally optimum Bayes detector (LOBD) is compared to the performance of various ad hoc nonlinear detection schemes. The known results are reviewed, and then it is demonstrated that these theoretical results may be misleading due to the assumptions that are required in order to derive them analytically. For a particular type of broad-band impulsive noise, the critical assumptions of "sufficiently" small signal level and large number of samples (large time-bandwidth product so that the central limit theorem applies) are removed; the first analytically, and the second by computer simulation. The thus-derived performance characteristics are then compared, especially as the signal level increases. One result is that there are situations where the bandpass limiter outperforms the LOBD as the signal level increases; that is, the locally optimum detector may not remain "near optimum" in actual operational situations.

This report describes the 3.5 GHz Study. It explains the assumptions, methods, analyses, and system characteristics used to generate the revised exclusion zones for small-cell commercial broadband systems to protect federal radar operations (ship and land based) from aggregate interference in the band 3550–3650 MHz. The 3.5 GHz Study’s exclusion zones are compared with the exclusion zones that were generated in the Fast Track Report, which considered macro-cell operations. This report was reissued in March 2016 to correct typographical errors.

The intent of H.264 (MPEG-4 Part 10) was to achieve equivalent quality to previous standards (e.g., MPEG-2) at no more than half the bit-rate. H.264 is commonly felt to have achieved this objective. This document presents results of an HDTV subjective experiment that compared the perceptual quality of H.264 to MPEG-2. The study included both the coding-only impairment case and a coding plus packet loss case, where the packet loss was representative of a well managed network (0.02% random packet loss rate). Subjective testing results partially uphold the commonly held claim that H.264 provides quality similar to MPEG-2 at no more than half the bit rate for the coding-only case. However, the advantage of H.264 diminishes with increasing bit rate and all but disappears when one reaches about 18 Mbps. For the packet loss case, results from the study indicate that H.264 suffers a large decrease in quality whereas MPEG-2 undergoes a much smaller decrease.

Continuous wave (CW) propagation experiments were conducted at 912, 1920, and 5990 MHz simultaneously using a narrowband system consisting of a fixed transmitter and a mobile receiver. The goal of the experiments was to quantify building penetration losses at various frequencies to determine the viability of indoor coverage using street microcells with base antenna heights below the roof level of nearby buildings. Statistical analysis included the computation of mean building penetration losses, standard deviations, cumulative probability distribution functions, and correlation coefficients.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Time-domain free-field measurements comprised the dielectric properties of several common building materials using dual-ridged guide antennas and 1 mtimes1 m samples placed on an optical table covered with an absorber. The samples are polycarbonate, gypsum, plywood, a brick wall, and a concrete wall. Time gating and deconvolution are used to isolate a sample's front and back surfaces to obtain the measured reflection coefficients (RCs) and transmission coefficients. Theoretical reflection and transmission equations were generated from a plane-wave model. Relative permittivity is obtained by varying the parameters in the Kirkwood-Fuoss equation until a best fit between the theoretical and measured reflection and transmission coefficients is obtained.

We present time-domain techniques for modeling, characterizing, and measuring anechoic and semi-anechoic chambers used for emission and immunity testing of digital devices. The finite difference time-domain (FDTD) approach is used to model and characterize these chambers. In the FDTD model presented here, we discuss methods used to eliminate the need to spatially resolve the fine detail of the absorbing structures; present a differential-operator approach for incorporating both frequency-dependent permittivity and permeability into the time domain; and discuss the effects of gaps and holes in ferrite-tile absorbers on both absorber and chamber performance. Comparisons of the FDTD chamber model with measured data for different chamber sizes are presented. Finally, we discuss and illustrate how time-domain techniques can be used to characterize chambers, predict performance, and diagnose problems with both absorbers and chambers. With time-domain and frequency-domain techniques, we show how the performance of chambers can be significantly altered with only small changes in the type of absorbing structure used, and we illustrate how undesirable modal field distributions can occur inside a chamber when a nonoptimal absorber is used.

In response to proposals to introduce new radio systems into 3550–3650 MHz radio spectrum in the United States, the authors have performed measurements and analysis on effects of interference from a variety of radar waveforms to the performance of a Long Term Evolution (LTE) base station receiver. This work has been prompted by the possibility that LTE base station receivers may eventually share spectrum with radar operations in this spectrum range. The base station receiver that was tested used time division duplex (TDD) modulation. Radar pulse parameters used in this testing spanned the range of both existing and anticipated future radar systems in the 3100–3650 MHz spectrum range. LTE base station receiver data throughput rates, block error rates (BLER), and internal noise levels have been measured as functions of radar pulse parameters and the incident power level of radar pulses in the base station receiver. The authors do not determine the acceptability of radar interference effects on LTE base station performance. Rather, these data are presented for the use of spectrum managers and engineers who can use this information as a building block in the construction of frequency-and-distance separation curves for radar transmitters and LTE base station receivers, supporting possible future spectrum sharing at 3.5 GHz. Note: This report was reissued in May 2014 to correct the duty cycles of four radar interference waveforms that were misstated in the original version of this report. The error was due to a mistake in the equations on page 8, now corrected, in which a pulse repetition rate (PRR) variable was used instead of a pulse repetition interval (PRI) variable. The waveforms’ pulse widths, pulse repetition rates, and chirp bandwidths were correctly reported.

This report describes the methodology and results of an investigation into the source, mechanism, and solutions for radiofrequency (RF) interference to WSR-88D Next-Generation Weather Radars (NEXRADs). It shows that the interference source is nearby base stations transmitters in the Broadband Radio Service (BRS) and the Educational Broadband Service (EBS) and that their out-of-band (OOB) emissions can cause interference on NEXRAD receiver frequencies. The methodology for determining interference power levels and mitigation solutions is described. Several technical solutions that can mitigate the problem are shown to be effective. Trade-offs between effectiveness, difficulty, and costs of various solutions are described, but it is shown that there is always at least one effective technical solution. The report shows that careful planning and coordination between communication system service providers and Federal agencies operating nearby radars is important in the implementation of these interference-mitigation techniques. A number of the report’s interference mitigation options have already been implemented in several United States cities served by a BRS/EBS licensee, at licensee WiMAX stations where NEXRAD radar operations are located nearby. As of the date of this report’s release, interference from the licensee’s WiMAX links to NEXRAD receivers in those markets has been successfully mitigated using the techniques described herein.

We investigate the way in which errors arise in photocount-limited, coherent imaging systems and how such errors fundamentally limit the quality of images formed. To reflect the best possible imaging performance with a given optical system, we utilize a continuous-photodetection model to describe the operation of the image-recording mechanism, in which the image-plane camera records the exact x and y positions of each photodetection event produced by the detected coherent field intensity. Using this continuous-detection model and well-known statistical properties of. laser-speckle patterns, we compute the signal-to-noise ratio of the complex Fourier amplitudes estimated by the detected coherent image. With the help of computer-simulated coherent imagery, we illustrate how this expression can be used to characterize the effective resolving power of multiple-snapshot coherent imaging systems.

Ground wave propagation is analyzed for a two-section path on a spherical earth. Each section can be a two-layer medium which is characterized by a surface impedance. Specific calculations for a land-to-sea path indicate that the well-known recovery effect in amplitude and phase is more extreme at higher frequencies but is reduced for elevated observer heights. Calculations for a sea-to-sea ice path indicate a brief recovery because of the excitation of the trapped surface wave over sea ice. At greater distances from the boundary, the field may be seriously degraded due to the sea ice.

Impulse response radiowave propagation measurements from an urban area of Denver, CO, are described. The basic transmission loss and delay spread are used to characterize the mobile communications environment. These metrics are quantified using path loss slope and delay spread statistics. By analyzing the results versus carrier frequency, the relative propagation impairments at 430, 1350, 2260, and 5750 MHz are compared. It was found that the path loss slope increased on average by 11 dB/dec and the median delay spread decreased from 0.7 to 0.3 /spl mu/s over the decade of frequencies measured.

In response to proposals to introduce new Long Term Evolution (LTE) microcell Citizens Broadband Service (CBS) radio systems into 3550–3650 MHz (3.5 GHz) radio spectrum in the United States, the authors have performed measurements and analysis on effects of LTE interference on the performance of a type of radar receiver that might eventually share spectrum with such systems. LTE and Gaussian noise interference were injected into a radar receiver; Gaussian noise was a proxy for aggregated interference sources and one type of LTE. Interference was injected into a radar receiver so as to appear coincident with synthetic radar targets on the radar’s display. The targets’ baseline (non-interference) probability of detection (Pd) was 90 percent. With interference present, the targets’ Pd was measured and recorded as a function of LTE signal (both on-tuned and off-tuned) and Gaussian noise interference levels. Additional data presented in this report include: the radar receiver’s antenna radiation pattern, RF front end frequency response, IF-stage frequency response, noise figure, and RF overload response up to an input power of -4.6 dBm. A measured LTE emission spectrum is also provided. Using these data, spectrum management personnel can perform electromagnetic compatibility (EMC) analyses for possible future spectrum sharing between LTE transmitters and this type of radar receiver.

Ground wave propagation is analyzed for a path where sea water is covered by a uniform layer of sea ice. The source is taken to be a vertical electric dipole on or above the ice layer. The solution indicates that a trapped surface wave is significant at short ranges while, at longer ranges, the usual ground wave modes are dominant. The resulting interference pattern may produce rapid variations of the field at intermediate ranges. These characteristics, as well as the height dependence of the observed field strength, are strongly dependent on the thickness of the ice layer.

We propose a model for rating behavior based on subject bias and subject error. Evidence for subject bias can be found in freely available subjective experiments. When subject bias is removed from ratings, the sensitivity of statistical comparisons between stimuli usually improves. According to our model, subject biases characterize the subject pool. These between-subject differences are important when analyzing and comparing people. On the other hand, it is advantageous to remove subject bias when analyzing mean opinion score. We conclude that bias acts like a random variable within ratings.