19 - Digital modulation

Nowadays, in order to improve the quality of signal transmission and reduce the signal attenuation and noise interference, the transmission digital baseband signal modulation become mainstream in today's signal transmission. For the digital baseband signal transmission performance of research helps us to understand the process of digital signal transmission. Firstly, using shift registers to produce m sequence, used to simulate the data signal and the pseudo random noise signal. Then, to design a low pass filter, used to simulate the channel. Data signal transmission in the channel was carried with additive random noise interference, we can measure signal interference by observing eye pattern at the receiving terminal. If to Manchester encoding of data signal, the receiver decoding output data signal can be extracted using the synchronous clock circuit to get the clock signal to synchronize, and display the eye pattern, which is used to evaluate the performance of the transmission system. And we put forward the optimization scheme of the digital baseband signal transmission performance through the research.

In the UWAC system, the information signal is usually a digital baseband signal. These signals often contain a rich low-frequency component and even direct current components. UWA channels are bandwidth-limited. Due to the influence of transmission loss on signal attenuation, the high-frequency band and low-frequency band are limited by environmental noise and transmitting transducers. A digital baseband signal cannot be transmitted directly in a channel with such bandpass transmission characteristics. It requires modulation techniques to shift the spectrum of its baseband signal to the appropriate frequency band for effective transmission. Therefore, modulation has a great impact on the effectiveness and reliability of the UWAC system. What modulation and demodulation are used will directly affect the performance of the communication system.

1 - Basic television

A conventional differential line (DL), commonly used on typical digital circuit boards for transmitting high-speed digital data, has fundamental limitations on the maximum signal bandwidth (~10 GHz), mainly due to signal skew, multiple line coupling, and EM interference. Therefore, to support super-high-speed digital data transmission, especially for beyond 5G communications, a practical high-performance transmission structure for digital signals is required. Balanced lines (BLs) can transmit the differential signals with multiple advantages of ultra-wide bandwidth, common-mode rejection, reduced crosstalk, phase recovery, and skew reduction, which enable super-high-speed transmission. In order to utilize the BLs in the DL-based digital circuit, connecting structures between a DL and BLs are required, but the DL-to-BL transition structures dominate the operating bandwidth and signal properties. Therefore, in this paper, properties, and design methods for two ultra-wideband DL-to-BL transitions, i.e., DL-to-CPS (coplanar stripline) and DL-to-PSL (parallel stripline) transitions, are presented. Both implemented DL-to-CPS and DL-to-PSL transitions provide high-quality performance up to 40 GHz or higher, significantly enhancing the frequency bandwidth for the transmission of digital signals while providing compatibility with the DL-based PCBs. The fabricated DL-to-CPS transition performs well from DC to 40 GHz with an insertion loss of less than 0.86 dB and a return loss of more than 10 dB, and the fabricated DL-to-PSL transition also provides good performance from DC to 40 GHz, with an insertion loss of less than 1.34 dB and a return loss of more than 10 dB. Therefore, the proposed DL-to-BL transitions can be applied to achieve super-high-speed digital data transmission with over 40 GHz bandwidth, which is more than four times the bandwidth of the DL, supporting over 200 Gbps of digital data transmission on PCBs for the next generation of advanced communications.

In this article, the propagation of digital and analog signals through media which, in general, are both dissipative and dispersive is modeled using the one-dimensional telegraph equation. Input signals are represented using impulsive, Heaviside unit step, Gaussian, rectangular pulse, and both unmodulated and modulated sinusoidal pulse type boundary data. Applications to coaxial transmission lines and freshwater signal propagation, for both digital and analog signals, are included. The analysis presented here supports the finding that digital transmission in dispersive media is generally superior to that of analog. The boundary data (input signals) give rise to solutions of the telegraph equation which contain propagating discontinuities. It is shown that the magnitudes of these discontinuities, as a function of distance, can be found without the need of solving the governing equation. Thus, for digital signals in particular, signal strength at a given distance from the input source can be easily determined. Furthermore, the magnitudes of these discontinuities are found to be independent of both the dispersion coefficient k and the elastic coefficient b. In addition, it is shown that, depending on the algebraic sign of k, one of two distinct forms of dispersion is possible and that for small-time intervals, solutions are approximately independent of k.

A hybrid dense‐wavelength‐division‐multiplexing (DWDM) system using a combination of a Fabry–Perot (FP) laser diode, an optical circulator (OC), and a fiber Bragg grating (FBG), as well as half‐split‐band and WDM techniques, is demonstrated. It is a four‐wavelength system, in which two wavelengths are for AM–VSB video, one wavelength is for a 256‐QAM digital signal, and one wavelength is for OC‐48 digital baseband signal transmission. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 390–393, 2002.

A new method is presented to broadcast digital signals simultaneously with the existing analog frequency modulation (FM) radio in the same band. The method involves special signal design at the transmitter and analytic technique of separating two co-channel FM signals at the receiver side. The digital signal is first removed by adding/subtracting the received signal in an orthogonal frequency-division multiplexing (OFDM) symbol basis, resulting in two co-channel FM signals. Then, the two co-channel FM signals are separated within one of two possibilities. The phase ambiguity can be removed naturally by computing the distance between the estimates and the original received signal. After obtaining the FM signal estimates, the digital signals can be obtained by subtracting the estimated analog FM signals from the original received signals. Iterative methods can be adopted to further improve the system performance. Simulation results show that the bit error rate of the recovered digital signal does not depend on the power level difference between the host analog FM and the digital signal and is only 4-dB loss compared with clean OFDM digital systems.

In this chapter, various issues on pulse shaping waveform design for bandwidth efficient digital modulations will be addressed. Here what we concern about the pulse shaping waveforms is the physical appearances or shapes each information data bit or symbol take before carrier modulations. It is well known that the spectral characteristics of a carrier modulated signal can be uniquely determined by its baseband signal before modulation, and thus the waveform shape applied to pre-modulated signals is of ultimate importance to ensure overall bandwidth-efficiency of a wireless communication system. This chapter starts with an overview on the evolution of pulse shaping technologies from early digital modulation schemes to recently emerging new carrier modulations such as quadrature-overlapped modulations. The impact of the pulse shaping technologies on both bandwidth-efficiency and power-efficiency, which are two essential merit parameters of a digital modem, will also be discussed. The majority of the content in this chapter, however, is dedicated to the discussions on shaping pulse design methodology as well as performance analysis of a pulse-shaped digital modem, in which various shaping pulse design methods (including those commonly referred and those recently proposed in the literature) will be presented. To measure the effectiveness of the pulse-shaping techniques, different pulse shaped digital modulations will be evaluated and then compared in terms of their spectral characteristics, the sensitivity of their performance against synchronization timing jitter as well as their bit error rate performance, where the emphasis will be put on the pulse-shaped quadrature-overlapped (QO) modems under bandpass nonlinear channels, which usually exist in satellite and mobile cellular systems. Several new pulse shaped QO modulation schemes, which adopt various novel pulse shaping waveforms generated by time-domain convolution method, will be presented and their performance analysis will be carried out in comparison with other traditional digital modems, such as QPSK, OQPSK, MSK and so forth.

Radio over fibre (RoF) technology is currently receiving large attention due to its ability to provide simple antenna front ends, increased capacity, and multi radio wireless access coverage. In this paper, an all-photonic Digital Radio over Fibre (DRoF) link is proposed. By using this DRoF system, performance of an integrated transportation system, for transporting multi-types analogue, digital and baseband signals over single mode fibre is investigated. Simulation results proved that bit error rate (BER) of DRoF communication link is remarkably better than the analogue RoF (ARoF)

A parametric loudspeaker has been used for audio guidance to a specific area because it has a sharper directivity compared with the conventional electrodynamic loudspeakers. The parametric loudspeaker emits an ultrasound as a carrier wave, which is modulated with an audio signal and has large-amplitude. An audible sound is reproduced by the modulated ultrasound with large-amplitude distorted by the nonlinearity on the air. The conventional modulations have been proposed as the amplitude modulation and the frequency modulation. In the sound quality, the amplitude modulation is superior to the frequency modulation. However, in the sound pressure level, the frequency modulation is superior to the amplitude modulation. In the present paper, we especially focus on that the parametric loudspeaker will emit the speech signals for the audio guidance. Therefore, we propose new modulation method based on the combination of amplitude and frequency modulations, which are specialized for speech signals. More specifically, we apply the amplitude and frequency modulations to the divided frequency bands of speech signals, respectively. In order to confirm the effectiveness of the proposed method, we carried out evaluation experiments. As a result of evaluation experiments, we confirmed the effectiveness of the proposed method compared with conventional methods.

Recent studies on amplitude modulation (AM) detection for tones in noise reported that AM-detection thresholds improve when the AM stimulus is preceded by a noise precursor. The physiological mechanisms underlying this AM unmasking are unknown. One possibility is that adaptation to the level of the noise precursor facilitates AM encoding by causing a shift in neural rate-level functions to optimize level encoding around the precursor level. The aims of this study were to investigate whether such a dynamic-range adaptation is a plausible mechanism for the AM unmasking and whether frequency modulation (FM), thought to be encoded via AM, also exhibits the unmasking effect. Detection thresholds for AM and FM of tones in noise were measured with and without a fixed-level precursor. Listeners showing the unmasking effect were then tested with the precursor level roved over a wide range to modulate the effect of adaptation to the precursor level on the detection of the subsequent AM. It was found that FM detection benefits from a precursor and the magnitude of FM unmasking correlates with that of AM unmasking. Moreover, consistent with dynamic-range adaptation, the unmasking magnitude weakens as the level difference between the precursor and simultaneous masker of the tone increases.

Radio transmitters are evolving towards digital-intensive solutions to exploit reconfigurability and benefit from CMOS process scaling. Outphasing has been identified as a suitable candidate for digital wideband transmitters. However, with recent digital-intensive outphasing transmitters the achieved performance in terms of adjacent channel leakage ratio (ACLR) has been limited. This paper identifies the sampling images of the modulating phase signal as the main factor limiting the ACLR of digital outphasing transmitters. We present a new digital interpolating phase modulator architecture, capable of providing significantly better sampling image attenuation. When evaluated in outphasing configuration with a 100 MHz OFDM signal at the carrier frequency of 2.46 GHz, and 10-bit phase resolution, the proposed solution achieves an ACLR of $-$ 59 dBc, compared to $-$ 43 dBc achievable with the phase modulator architecture utilized in state-of-the-art digital outphasing transmitters. The proposed digital interpolating phase modulator is also capable of custom carrier generation, a straightforward method for generating an arbitrary carrier frequency up to 1.25 times the phase modulator sampling rate.

We analyse 38-month of contiguous short-cadence data, concentrating on mode multiplets induced by the star rotation and on frequencies forming linear combinations that show intriguing behaviors during the course of the observations. We find clear signatures that point toward nonlinear effects predicted by resonant mode coupling mechanisms. These couplings can induce various mode behaviors for the components of multiplets and for frequencies related by linear relationships. We find that a triplet at 5760\,$\mu$Hz, a quintuplet at 5287\,$\mu$Hz and a ($\ell>2$) multiplet at 5412\,$\mu$Hz, all induced by rotation, show clear frequency and amplitude modulations which are typical of the so-called intermediate regime of a resonance between the components. One triplet at 316\,$\mu$Hz and a doublet at 394\,$\mu$Hz show modulated amplitude and constant frequency which can be associated with a narrow transitory regime of the resonance. Another triplet at 519\,$\mu$Hz appears to be in a frequency lock regime where both frequency and amplitude are constant. Additionally, three linear combination of frequencies near 6076\,$\mu$Hz also show amplitude and frequency modulations, which are likely related to a three-mode direct resonance. The identified frequency and amplitude modulations are the first clear-cut signatures of nonlinear resonant couplings occurring in pulsating hot B subdwarf stars. However, the observed behaviors suggest that the resonances occurring in these stars usually follow more complicated patterns than the simple predictions from current nonlinear theoretical frameworks. These results should therefore motivate further work to develop the theory of nonlinear stellar pulsations, considering that stars like KIC~10139564 now offer remarkable testbeds to do so.

As an aid in evaluating technical control techniques, an emulation facility that automatically performs the status monitoring, performance assessment, and fault isolation technical control functions as they apply to a future, predominantly digital Defense Communications System (DCS) has been developed. This emulation facility is a multicomputer system which automatically monitors and isolates faults for digital transmission equipments (power generators, RF distributions, digital radios, second level multiplexers, first level multiplexers, submultiplexers, and key generator units). The status monitoring and performance assessment functions are performed by two processors, the adaptive channel estimator (ACE) and an LSI 11/03, the composite being referred to as the CPMAS-D unit. When the software residing in the CPMAS-D unit detects a monitor point transition (alarm to/from nonalarm), it transmits the monitor point information to the CPMAS emulator, a PDP 11/60 minicomputer. These messages, called exception reports, enable the CPMAS emulator to perform its prime mission: fault isolation. A unique fault isolation algorithm has been developed for test with this emulation facility. The algorithm consists of three discrete steps. First, the equipment alarms are mapped into their effect upon each transmission path (link, supergroup, group, or channel). Second, the stations with the faulty equipment are located by deleting the impact of sympathetic alarms. Third, the faulty equipment is identified using the equipment alarm status. Testing of the fault isolation algorithm is enhanced by an emulated network consisting of up to 16 stations, 2048 equipments, and two nodal control areas. Monitor point simulators and T1-4000 multiplexers, which provide simulated and real inputs to two CPMAS-D units, are also part of the emulation facility. Technical control terminals are provided to evaluate man-machine operation in an automated technical control environment. An adaptive channel estimator (ACE) field test was conducted at the Rome Air Development Center (RADC) test facilities so that the ACE development unit could be evaluated as a means of assessing performance of high-speed digital radio transmission systems. Also, the fault isolation algorithm was tested using the previously described emulation facility. The test data and subsequent technique evaluations are discussed in this paper.

ICITAL transmission systems of all types are of great current interest as we embark on the information age. For any new transmission system, the topology, components, and system parameters are determined by many and various techniques. They are chosen not only by explicit, deductive technical reasoning, but also by the art of engineering, the desire for continued product line compatibility, patents possessed or not possessed, and new technology. Nonetheless, most digital transmission systems are made up using one or more of the following components: a bandpass filter, low-pass filter, Nyquist filter, slope equalizer, cable equalizer, and transversal equalizer. These items are the subject of this article. It is ironic that digital transmission systems have a preponderance of such components-all necessary for analog signal conditioning of the digitally transmitted signal. In the myriad of digital transmission systems, two distinct approaches to filtering and equalization predominate: one for baseband systems and the other for frequency translated, or modulated, signal systems. This division results from the need to have a competitive system transmission efficiency to cost ratio: where transmission efficiency is transmitted bit rate/channel bandwidth (BR/BW). For baseband systems, as might be expected, the difficulties, and thus cost, of filtering and equalization increase with increased transmission efficiency. To obtain a favorable BR/BW to cost ratio, the bandwidth, an available quantity, is usually sacrificed to keep system costs low. Signal modulation is required when it is desired to simultaneously transmit several baseband signals over common transmission facilities using a frequency division multiplex scheme. A modulated signal system is also necessary when the transmission vehicle has a significant low-frequency limitation; as does, for example, the general customer premises-to-customer premises telephone connection. In such systems, costs start off high because of the additional modulation circuitry. Money can then be further spent on filtering and equalization to allow for increased transmitted bit rate in order to provide a more reasonable BR/BW to cost ratio. Based upon the above premise, the text expands further on the differences between filters and equalizers used for baseband and modulated digital transmission systems.