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The equations defining the amplitude of sidebands resulting from either frequency modulation or phase modulation by either square wave, sine wave, sawtooth or triangular modulating functions are presented. Spectral photographs and computer generated tables of modulation index vs. relative sideband amplitudes are also included.
This paper introduces a trellis coded modulation (TCM) scheme for non-coherent multiple full response M-ary CPFSK with modulation index 1/M. A proper branch metric for the trellis decoder is obtained by employing a simple approximation of the modified Bessel function for large signal to noise ratio (SNR). Pairwise error probability of coded sequences is evaluated by applying a linear approximation to the Rician random variable.
Phase-locked-loop phase modulator has the capability of generating a 6.8MHz carrier at modulation indexes as high as 2.5, with a distortion of the demodulated signal of less than 5 percent. These characteristics are obtained without the use of multipliers.
Modulation indexes for two-channel phase coherent communication system determining data rate yielding predetermined bit-error probability
It is well known that trellis codded modulation schemes using multidimentional constellations for MPSK and QAM have a number of advantages, such as improved performance, over the more common two dimensional schemes [1,2].
It is well known that trellis codded modulation schemes using multidimensional constellations for PSK and QAM have a number of advantages over the more common two dimensional schemes.
Video signal enhancement of signal component representing brightness of scene element in low contrast
A nonlinear analysis of a multifilter phase-lockloop (MPLL) by using the method of harmonic balance is presented. The particular MPLL considered has a low-pass filter and a band-pass filter in parallel. An analytic expression for the relationship between the input signal phase deviation and the phase error is determined for sinusoidal FM in the absence of noise. The expression is used to determine bounds on the proper operating region for the MPLL and to investigate the jump phenomenon previously observed. From these results the proper modulation index, modulating frequency, etc. used for the design of a MPLL are determined. Data for the loop unlock boundary obtained from the theoretical expression are compared to data obtained from analog computer simulations of the MPLL.
Using the S-band communications system, shuttle orbiter can communicate directly with the Earth via the Ground Spaceflight Tracking and Data Network (GSTDN) or via the Tracking and Data Relay Satellite System (TDRSS). The S-band frequencies provide the primary links for direct Earth and TDRSS communications during all launch and entry/landing phases of shuttle missions. On orbit, S-band links are used when TDRSS Ku-band is not available, when conditions require orbiter attitudes unfavorable to Ku-band communications, or when the payload bay doors are closed. the S-band communications functional requirements, the orbiter hardware configuration, and the NASA S-band communications network are described. The requirements and implementation concepts which resulted in techniques for shuttle S-band hardware development discussed include: (1) digital voice delta modulation; (2) convolutional coding/Viterbi decoding; (3) critical modulation index for phase modulation using a Costas loop (phase-shift keying) receiver; (4) optimum digital data modulation parameters for continuous-wave frequency modulation; (5) intermodulation effects of subcarrier ranging and time-division multiplexing data channels; (6) radiofrequency coverage; and (7) despreading techniques under poor signal-to-noise conditions. Channel performance is reviewed.
We describe a multilayered dielectric stack configuration designed specifically for use as a transmissive phase modulator for broadband optical signals. Applications for this device range from full aperture wavefront correction to nonmechanical beam steering arrays for free space optical communication links. Our implementation employs alternating GaAs and AlAs layers of varying thickness on a GaAs substrate to create a bandpass region of high average transmission centered about the one micrometer wavelength. Within this transmission bandpass, the phase component of the complex transmission coefficient varies in a near-linear fashion with respect to wavelength. The transmission bandpass is designed to have a bandwidth of 21.0 nm (or 6.3THz frequency bandwidth) and to have an edge-to-edge phase change of greater than 47T radians. Modification of the stack materials' optical properties causes the transmission profile to shift spectrally, resulting in a phase modulation for bands of transmitted frequencies. Our broadband phase modulator imparts up to a full-cycle of phase modulation with low loss and low group velocity dispersion. We identify several methods for implementing the requisite modulation, including refractive index modulation through free carrier injection and optical path length modulation through variation in angle of incidence. At least one sample comprising 91 alternating layers has been fabricated to exhibit the bandpass properties required for optical signal phase modulation. We experimentally characterize the sample using an interferometer and spectrometer to measure the transmitted signal spectrum and relative phase modulation. We compare the experimental data to computational predictions and discuss the results.
Using data from the Voyager 1 plasma wave instrument, a series of direction-finding measurements is presented for the intense 1992-93 heliospheric 2- to 3-kHz radio emission event, and several weaker events extending into 1994. Direction-finding measurements can only be obtained during roll maneuvers, which are performed about once every three months. Two parameters can be determined from the roll-induced intensity modulation, the azimuthal direction of arrival (measured around the roll axis), and the modulation index (the peak-to-peak amplitude divided by the peak amplitude). Measurements were made at two frequencies, 1.78 and 3.11 kHz. No roll modulation was observed at 1.78 kHz, which is consistent with an isotropic source at this frequency. In most cases an easily measurable roll modulation was detectable at 3.11 kHz. Although the azimuth angles have considerable scatter, the directions of arrival at 3.11 kHz can be organized into three groups, each of which appears to be associated with a separate upward drifting feature in the radio emission spectrum. The first group, which is associated with the main 1992-93 event, is consistent with a source located near the nose of the heliosphere. The remaining two groups, which occur after the main 1992-93 event, have azimuth angles well away from the nose of the heliosphere. The modulation indexes vary over a large range, from 0.06 to 0.61, with no obvious trend. Although the variations in the directions of arrival and modulation indicies appear to reflect changes in the position and angular size of the source, it is also possible that they could be caused by refraction or scattering due to density structures in the solar wind.
Current models for the 2-3 kHz emissions observed by the Voyager spacecraft in the outer heliosphere involve 2f(p) radiation generated near the termination shock or the heliopause. Radio wave scattering by solar wind density irregularities strongly affects observed sources of f(p) and 2f(p) emission in the inner heliosphere and the characteristics of astrophysical sources. In particular, the angular size, brightness temperature, and time variability of the source are strongly affected by scattering, thereby having major implications for the inferred size, energy budget, time variability, location, and nature of the source if scattering is ignored. This paper addresses whether scattering is important for interpreting the Voyager 2-3 kHz emissions. Quantitative calculations (with and without diffraction) are performed for the angular broadening of an outer heliospheric source as a function of path length, radiation frequency relative to f(p) and the spectrum of density irregularities. The effects of scattering in both the solar wind and the heliosheath are considered. Predictions for radial gradients in the source's apparent angular size and in the source's modulation index are presented. The calculations are compared with observations and the results discussed. First estimates suggest that scattering plausibly dominates the observed source size. The observed trend in modulation index with heliocentric distance is consistent with scattering being important and the source being in the outer heliosphere. Additional arguments for scattering being important are summarized.
The effect of a noisy reference carrier on the performance of International Comet Explorer (ICE) Sequential decoder is analyzed. Ideal reference models for frame deletion probability are given for the Telemetry Processing Assembly (TPA) and the Linkabit (LS4815) sequential decoders. Based on these ideal reference models the deletion probability in the presence of noisy reference carrier is computed for both the high and the low data rate cases. A medium data rate performance model is then derived using an interpolation method. The derived medium rate performance model depends on the phase locked loop bandwidth-integration time product. Results are obtained for frame length 1024 bits, data bit rates of 1024 bps and 512 bps, modulation index of 60 deg, and threshold loop bandwidths of 10 Hz and 3 Hz. The medium rate model agrees with experimental data to within measurement uncertainty. For the 10 Hz loop bandwidth and modulation index of 60 deg at frame deletion rate of 0.0001, the required total received power to noise ratio is 36 dB. The analysis given is general and applicable to any sequential decoder, provided that the ideal reference model of the decoder is available.
Signals from phase-modulated satellite transmitters usually exhibit some degree of incidental amplitude modulation. The effects of incidental AM are analyzed when this type of signal is demodulated by a phase-lock receiver which does not employ a limiter preceding the loop phase detector. The presence of incidental AM causes a reduction in the receiver output signal-to-noise ratio. The tolerable level of AM decreases in proportion to the phase modulation index Beta. For a square-wave modulating signal, a 1 db reduction results at the receiver PM channel output when Beta = 1 radian and the percentage of AM = 23, Beta = 1.2 radians and the percentage of AM = 16, or Beta = 1.5 radians and the percentage of AM = 4. Although only the PM channel of the receiver is used ordinarily, utilizing both the AM and PM channel by summing offers an improvement in S/N relative to the S/N ratio of the PM channel if the percentage of incidental AM is greater than fifteen.
Converter can be used for automatic spectrum analysis. Automatic gain amplifier digitizes RF amplitude, and amplifier gain is measured by binary counter. Amount of gain corresponds to signal level and is proportional to count in counter. System can be used to calculate AM and FM modulation index and other parameters of pulse-modulated FM waves.
Currently, ranging for deep space missions is performed by turning around the uplink ranging modulation and remodulating it onto the downlink carrier. This method results in about 1.5 MHz of noise also being modulated onto the downlink, severely degrading the received ranging SNR on the ground. This degradation must be compensated for by either increasing the integration time of the received signal, which increases the length of time for the track, or increasing the downlink ranging signal's modulation index, which decreases the power available for the telemetry modulation. A method for the regeneration on the spacecraft of a pseudo noise (PN) ranging signal has been developed. This method allows for an increase of up to 30dB in the received downlink ranging power. The increased power can be used to decrease the measurement uncertainty, reduce the time of the measurement, or increase the power allocated to the downlink telemetry. This system was implemented in the Spacecraft Transponding Modem that was developed by JPL for NASA.
A solution to the lock-in detection method, which is valid for arbitrary values of the modulation frequency, is described. The theory for determining frequency modulation of a single frequency laser is presented. The theoretical predictions for the optimum modulation index are compared to experimental solutions for the quasi-static regime. Signal line shapes for first, second, and third harmonic generations are derived and examined. It is noted that there is good correlation between experimental and quasi-static theory data for the relation between small modulation frequency and resonance linewidth.
The performance of deep space telemetry signals that employ a residual carrier modulation technique is compared in the presence and absence of a subcarrier. When the subcarrier is present, the performance for the resulting pulse-coded modulation/phase-shift keyed/phase-modulated (PCM/PSK/PM) scheme is evaluated for both sine wave and square wave subcarriers and non-return-to zero (NRZ) data. When the subcarrier is absent, the performance for the resulting PCM/PM technique is evaluated for both the NRZ and the bi-phase data format. The comparison is based on telemetry performance as well as bandwidth efficiency. The first criterion is characterized in terms of the symbol error rate (SER) as a function of symbol SNR, loop bandwidth-to-data rate ratio, and modulation index. The bandwidth efficiency is characterized by the occupancy factor. The results of both the analysis and measurements show that when the interference-to-carrier ratio (ICR) is less than -15 dB, the performance degradation in the absence of a subcarrier is negligible. Various combinations of loop bandwidth-to-data rate ratios and modulation indices that achieve this performance are derived and listed. Bandwidth occupancy comparison indicates that PCM/PM/NRZ is the most efficient in this regard. Therefore, by eliminating the subcarrier and using the PCM/PM/NRZ scheme, many advantages can be realized without any sacrifice in performance.