Double Sideband Suppressed Carrier Research Articles

Low phase noise millimetre-wave signal generation using a passively modelocked monolithic DBR laser injection locked by an optical DSBSC signal

The authors demonstrate an optical injection technique for stabilising the frequency and reducing the phase noise of the millimetre-wave signal generated by a passively modelocked monolithic DBR laser. The optical injection signal is obtained by externally modulating a CW laser using the double sideband suppressed carrier (DSBSC) modulation technique. A locking range of 170 MHz is achieved with an injection optical power of less than 50 µW.

A novel technique for double sideband suppressed carrier modulation of optical fields

We present a simple and efficient technique to produce double sideband suppressed carrier (DSBSC) modulation for coherent analog optical communications. When operating a Mach-Zehnder electro-optic modulator at the appropriate bias point the carrier exits one of the output ports while the information carrying sidebands exit the other output port. The absence of a strong carrier component in the DSBSC output allows the use of an optical amplifier immediately following the modulator where the light signals are still relatively strong hence preserving the high S/N. In our experiments using heterodyne detection at 1319 nm, we show a -28-dB carrier suppression using a commercial M-Z modulator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Detection of target distance in the presence of an interfering reflection using a frequency-stepped double side-band suppressed carrier microwave radar system

A technique for detecting the distance to a highly reflective target in the presence of an interfering reflection using a frequency-stepped double-sideband suppressed carrier (DSBSC) microwave-millimeter-wave radar system is analytically derived. The main result of the analysis shows that the measured group delays produced by the DSBSC system possess a periodicity inversely proportional to the difference between the time delays to the target and interferer, independent of the signal-to-interference ratio (SIR). Simulation results are presented in the context of electron plasma density range estimation using a block diagram communications CAD tool. A unique and accurate plasma model is introduced. A high-resolution spectral estimation technique, based on an autoregressive time series analysis is applied to the measured group delays, and it is shown that accurate target distance estimates may be obtained, independent of SIR.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pitch of unresolved, two-component complex tones.

Helmholtz [On the Sensations of Tone (Dover, New York, 1954), 2nd English edition] reported that the pitch of a two-component complex tone could be shifted slightly by increasing the amplitude of one component. The pitch was shifted toward the frequency of the more intense component. Helmholtz attributed the pitch shift to a variation in the instantaneous frequency of the two-tone complex. This laboratory has previously investigated the discriminability of pairs of two-component complex tones with identical small amplitude differences between the components of a pair. Discriminability seemed to depend upon the difference in their envelope-weighted instantaneous frequency fluctuations. In the study to be reported, four subjects matched a double-sideband suppressed-carrier (DSSC) signal to each member of pairs of two-component complex tones centered at frequencies from 500 to 4000 Hz. There were small, complementary amplitude differences between components of a pair of two-tone complex signals, while the amplitudes of the two components in the DSSC signal were equal. Listeners were also asked to discriminate between pairs of these complementary two-tone complexes. Data indicate that there is a relationship between the discriminability of the complementary two-component complexes and the perceived pitch of each complex. These data were used to test several variations of a (general) weighted time-average model to relate the pitch of each fluctuating two-tone complex to its averaged instantaneous frequency. In general, the model seems to hold for center frequencies below 4000 Hz where there are moderate frequency separations between the components of a complex. The model appears to be insensitive to the choice of weighting functions and the nature of the average.

Two Proposed Quadraphonic FM Broadcasting Systems

The Zenith Quadraphonic FM Broadcast Systems (NQRC designations, 2A, 3B) are capable of broadcasting four discrete audio signals and are compatible with existing monophonic and biphonic FM services as well as with the Subsidiary Communication Authorization (SCA) service presently in practice. Two additional subchannels are broadcast in addition to the monophonic channel and the biphonic subchannel to accommodate the additional audio signals. The first of these additional subchannels uses double sideband suppressed carrier (DSBSC) AM modulation and is broadcast in quadrature with the existing biphonic subchannel at 38 kHz. System 2A, utilizing upper single sideband suppressed carrier (SSBSC) AM, broadcasts the second additional subchannel at 76 kHz while system 3B, utilizing vestigial sideband suppressed carrier (VSBSC) AM, broadcasts the second additional subchannel at 90.25 kHz. Both systems provide the necessary spectrum for the existing SCA subchannel centered nominally around 67 kHz. Standard pre-emphasis is employed to broadcast the four discrete audio signals in the band from 50 Hz to 15 kHz. Both systems broadcast an additional pilot subcarrier (at 76 kHz for system 2A and at 90.25 kHz for system 3B) to provide automatic decoder operation for monophonic, biphonic or quadraphonic signals. Sufficient phase linearity is maintained in the baseband spectrum (50 Hz to 91 kHz for system 2A, 50 Hz to 93 kHz for system 3B) to assure adequate separation between the audio outputs.

Optimum Coherent Linear Demodulation

Presented is the performance analysis for four types of linear-modulated communication systems where the message to be transmitted comes from one of two classes of stochastic processes, and the additive channel noise is white and Gaussian. The two classes of stochastic processes which are used to modulate the transmitter are taken to be the maximally flat and asymptotically Gaussian processes. Demodulation is accomplished at the receiver by coherent frequency translation using a noisy replica of the carrier and filtering the result with one of two types of Wiener filters. These are commonly referred to as the zero-lag (realizable) and infinite-lag (nonrealizable) Wiener filters. The four types of modulation considered are: linear-modulation, double-sideband (DSB); linear-modulation, double-sideband, suppressed carrier (DSB/SC); linear-modulation, single-sideband (SSB); and linear-modulation, single-sideband, suppressed carrier (SSB/SC).

Phase-Inversion Tolerant Coding for PRK Data Links

Phase reversal keying (PRK) with coherent detection is becoming increasingly popular for use in binary data communication systems. Coherent detection of double sideband-suppressed carrier signals requires precautions to avoid inadvertent reinsertion of the local carrier 180° out of phase with the suppressed carrier, as this would convert every demodulated 1 to a 0 and vice versa. Some of the previous solutions to this 1-0 ambiguity problem are reviewed and a new solution based on properties of error correcting codes is outlined briefly. It is shown that the performance penalty imposed by the coding solution is negligible. Performance curves are presented to illustrate the efficiency of the scheme.

A communications engineer looks at conical scanning

The conical-scanning (con-scan) technique for automatic antenna control generates a double-side-band suppressed carrier (DSSC) signal, which must retain its absolute side-band-carrier phase and amplitude relationship for proper antenna operation. Definite passbands must be allowed in order to permit frequencies in the neighborhood of the nutation, or periodic movement, rate to pass through the system, unmodified by circuit characteristics. Signal-strength variations can cause serious deterioration of the tracking capabilities of the con-scan antenna, and total loss of track is not uncommon.

Double-Sideband Suppressed-Carrier Multiplex Equipment for Cable and Microwave Applications

Single-sideband suppressed-carrier modulation has been the backbone system for telephone multichannel carrier equipment for many years. However, particularly in recent years, a number of other modulation systems have been applied in lesser or greater degrees, with the emergence of new problems in telephone transmission. These problems are related to economics, bulk of equipment, power consumption, phase distortion as it is related to data, etc.

Optimum type of modulation

The conclusions reached in the paper by G.J. Kelley (ibid., vol, l. CS-6, pp. 14-21, June, 1958) are based on some assumptions for which there is little or no justification. The commentor provides a re-evaluation using the author's weighting factors that produces the conclusion that DSBSC (Double Sideband Suppressed Carrier) is no better than straight SSB (Single Sideband).

Choosing the Optimum Type of Modulation--A Comparison of Several Communication Systems

The engineer designing a new communications system often has available a choice between several different types of RF modulation. The four main methods considered here are standard amplitude (AM), double-sideband suppressedcarrier (DSBSC), single-sideband (SSB), and frequency (FM) modulations. Some of their basic system performance characteristics are evaluated on a comparative basis for the transmission of voice and pulsed data. Factors considered include: compatibility, effective range, bandwidth, signal-to-noise performance, interference rejection capabilities, distortion characteristics, required stability, required transmitter power, and resulting circuit complexity. The choice of the best type of modulation for a particular communications system requires the simultaneous consideration of many such factors evaluated for the basic requirements of that system. Because these factors vary with system parameters and because they may be of differing relative importance, it is not possible to say that any one type of modulation is best for all uses. The practical manner in which the choice may be made is illustrated by examples drawn from several types of communication systems.