Showing papers on "Quadrature amplitude modulation published in 1970"

Binary PSK Error Probabilities with Multiple Cochannel Interferences

Abstract: Exact error probabilities are given for a binary phase-shift-keyed (PSK) signal which is transmitted over a nondistorting channel, but additively corrupted by Gaussian noise and cochannel interference. Both coherent detection and quasicoherent (noisy reference) detection are considered. The analysis admits a wide class of interferences, but numerical results are limited to interferences modeled by a sum of randomly phased sinusoids. This includes most extraneous analog frequencymodulation (FM), phase-modulation (PM), or digital PSK signals, or combinations of the same which are cochannel with the desired PSK signal.

DPSK Versus FSK with Frequency Uncertainty

Abstract: Expressions and curves of error probabilities of differential phase shift keying (DPSK) and noncoherent frequency shift keying (FSK) are obtained as a function of the pulse carrier frequency offset. These indicate that the frequency offset which causes the DPSK error probability to be larger than the FSK error probability is approximately \Delta\omegaT = 0.74. This crossover frequency appears to be a linear function of the signal-to-noise ratio over the range-4 dB to 14 dB. The crossover point is extended by sub-bit processing and the previous curves are modified for this case.

Communications Efficiency of Certain Digital Modulation Systems

Abstract: The efficiency as measured by data rate per unit bandwidth of certain digital modulation systems is compared. The systems considered are frequency modulation (FM), phase modulation (PM), and linear modulation. The achievable bits per cycle in digital PM and amplitude modulation (AM) at a given signal-to-noise ratio and error rate have been known for some time. In digital FM this quantity can be maximized, a fact apparently first realized by J. R. Pierce at Bell Telephone Laboratories. Rigorous optimizations were later carried out by Mazo, Rowe, and the author. In addition to the comparisons made with other systems, additional details related to the optimization problem in frequency-shift keying (FSK) are also furnished. Whereas previous treatments analyzed a frequency discrimination system, this paper treats the optimum detector. The results indicate very minor differences m efficiency attained by the two different models analyzed. Results are exhibited graphically, showing the relationships between the important system parameters.

Performance Characteristics of Adaptive/Self-Synchronizing PSK Receivers Under Common Power and Bandwidth Conditions

Abstract: An analytical and numerical investigation of the performance characteristics of partially coherent system techniques which consist of 1) the squaring-tracking loop, 2) the pilot-tone tracking loop, and 3) the differential phase-shift keying (DPSK) technique is discussed. Performance characteristics (error probabilities) are obtained under a unified receiving systems framework, with commonality expressed in terms of the receiver data and reference acquisition channel bandwidths and equal total transmitted power conditions. The modulation addressed is binary phase-shift keying (PSK), operating over a Gaussian noise channel with nonstationary phase characteristics. System performance is expressed analytically, computed numerically, and illustrated graphically with the following conclusions. The squaring-tracking loop technique provides the best performance and closely approximates coherent PSK performance when reference smoothing over several bauds is employed. The performance of the squaringtracking loop system and the DPSK system are comparable within a decibel for tracking loop averaging over 1 baud. Performance of the pilot-tone system depends critically upon the tracking loop bandwidth and the power allocation between pilot carrier and information sidebands. In no case considered does the pilot-tone system outperform the squaring-tracking loop system. On the basis of minimum error rate, the systems can be ranked as follows: 1) the squaring-tracking loop system, 2) DPSK, and 3) the pilottone system. At large signal-to-noise ratios, pilot-tone systems can outperform DPSK.

Mitigation of Non-linear Distortion Using PTS and IDAR Method for Multi-Level QAM-OFDM System

Abstract: The future satellite communication systems are required to support the higher transmission data rate for providing the multimedia services by employing the efficient modulation method such as multi-level QAM. The employment of single carrier transmission with multi-level QAM would cause the fatal degradation of signal quality due to the non-linear amplifiers located at the earth station and satellite. To overcome this problem, we have proposed the multilevel QAM-OFDM technique with IDAR (Improved Decision Aided Reconstruction) method designed for non-linear satellite channel. However, the proposed method could not mitigate the non-linear distortion sufficiently when modulation level becomes higher such as 64QAM. This paper proposes the combined scheme of partial transmission sequence (PTS) and OFDM-IDAR methods so as to enable the usage of higher multi-level QAM method, which can achieve the higher transmission data rate with keeping the better bit error rate performance in the non-linear satellite channel. The various computer simulations are conducted in this paper to verify the effectiveness of proposed method in the non-linear satellite channel.

Frequency Modulation Using Digital Filtering Techniques

Abstract: A simple unstable second-order digital filter with one variable multiplier can provide a source of frequency-modulated signals. This modulator is readily time-shared and should prove attractive when a large number of transmitters are required. A system consisting of a multiple installation of identical binary frequency-shift keying data transmitters is described and analyzed. A refinement which totally eliminates amplitude and phase discontinuities is also presented.

Cesium Beam Servo System Using Square Wave Frequency Modulation

Abstract: This paper describes a new modulation and servo system that is being tested in the NRC long-beam cesium-frequency standard. Square-wave frequency modulation is employed; it is introduced by switching between two separately generated frequencies. The synthesizer producing these frequencies and the problems caused by switching transients are described. Since in a laboratory standard systematic errors play a very important role these errors are discussed in the description of the servo system. The resulting systematic error as calculated from results of experiments on its components is less than 1 part in 1013.

A comparative analysis of frequency modulation threshold extension techniques

Abstract: FM threshold extension for system performance improvement, comparing impulse noise elimination, correlation detection and delta modulation signal processing techniques implemented at demodulator output

Power spectra of digital p.m. signals

Abstract: A formula of Shimbo et al. for the power spectrum of signals pulse-modulated in accordance with random sequences is specialised for Markov chains. In the analysis, z transform techniques are used rather than explicit matrix methods. The resulting expressions may be used to find the spectra of a wide class of digital signals obtained by pulse modulating the amplitude, frequency, phase, or any combination of these, of a radio-frequency carrier. Attention is directed to phase modulation and, in particular, to ideal phase reversal and signals which practical systems might produce as approximations to it. In the first such signal, amplitude modulation is introduced in addition to the phase modulation, while in the other there is a nonzero switching time between the two phase levels. The power spectra of these signals are determined and compared with the phase reversal spectrum.

Error rate for envelope-detected on--off keying in the presence of interference

Abstract: The effects of an interfering carrier and Gaussian noise on envelope-detected on--off keying are analysed. Optimum decision levels with their resulting error rates were found numerically and are presented for a range of interference and noise levels.

Balanced modulation and the exclusive OR function

Abstract: The EXCLUSIVE OR function of two square waves is shown to be identical with the output of a doubly balanced modulator subject to constant input amplitudes and constant output offset.

Spectral Density Functions of a Carrier Amplitude Modulated by a Biphase PCM Code

Abstract: The autocorrelation and power spectral density functions are given for a carrier signal that is coherently and noncoherently amplitude modulated by a biphase pulse-code modulation code.