Showing papers on "Continuous phase modulation published in 1987"

Mobile digital communications via tone calibration

Abstract: A new digital signaling technique that is particularly suited for channels impaired by multipath fading is presented. The proposed modulation scheme employs a continuous-wave (CW) tone to calibrate the mobile channel against the multipath-induced phase uncertainties. This technique is applicable to quaternary phase shift keying as well as to more complicated signal constellations such as M-ary phase shift keyed schemes. The advantages of tone calibration are: 1) robustness of the receiver and 2) elimination of the link dependent error floor. Furthermore, since the CW tone can also be used for coherent signal demodulation, carrier phase acquisition can be achieved within a bit time. This property is particularly attractive when a burst of data with a short burst length has to be detected. This radio technique is useful for both the terrestrial mobile and the newer satellite-aided mobile communication (SAMC) services.

Modulation and detection characteristics of optical continuous phase FSK transmission system

Abstract: The modulation and differential detection characteristics of optical CPFSK transmission systems are investigated both theoretically and experimentally. The error rate expressions of differentially detected CPFSK are derived by considering phase noise of LD's. It is clear that the linewidth requirement is less than 0.68 m percent of the bit rate, where m is modulation index. The performances of CPFSK are then experimentally presented at 400 Mbit/s using external optical feedback DFB LD's as the optical source. A beat spectral linewidth of less than 200 kHz for the transmitter and local oscillator LD's is achieved. The frequency response nonuniformity of frequency modulation efficiency is compensated by electrical circuits within 3 dB and 60°. To reduce IF thermal noise, a resonance-type preamplifier is used, with a 4.8 pA/ \sqrt{Hz} average input noise current density, and a receiver sensitivity 1.3 dB better than the conventional preamplifier. Differential detection of the 400-Mbit/s CPFSK modulation is performed. The generation of CPFSK is confirmed by good correlation between the output spectrum and theory. The average received optical power at a 10-9bit error rate is -49.9 dBm which improves direct detection by 10.3 dB. No additional power penalties due to 290-km transmission exist.

Circuit for extracting carrier signals

Abstract: In circuits for reproducing carriers for continuous phase modulation having a rational modulation index these signals are multiplied in a multiplier for producing a harmonic, with unique phases occurring due to phase addition irrespective of the information to be conveyed. This harmonic is selected by means of a bandpass filter and supplied to a divider for reprodu­cing the carrier signal. However, as the desired phases only occur at certain instants the effect of jitter in the reproduced carrier signal is undesirably high. Jitter suppression is considerably improved by supplying to the bandpass filter only the instan­taneous values of the virtually desired phases occurring at the specific instants.

Receiver Structures for Multi-h Signaling Formats

Abstract: A method of utilizing the available communication bandwidth efficiently is provided by multi- h phase coding. A receiver structure for joint estimation of data, carrier phase, and symbol timing is derived based on ML estimation techniques and subsequently assessed analytically and by means of Monte Carlo simulation procedures. Results indicate that the receiver structure, although not strictly optimum, yields near-optimum performance on the additive white Gaussian noise channel.

Carrier Phase and Clock Recovery for Continuous Phase Modulated Signals

Abstract: This paper presents an analysis of a synchronization circuit to be used for carrier-phase and symbol-timing recovery in continuous phase modulation systems. M -ary modulation formats with arbitrary pulse shaping and rational modulation indexes are assumed. Circuit performance is expressed in terms of variances of phase and timing errors. Numerical results are provided for some important cases, including minimum shift keying and tamed frequency modulation. Theoretical results are found in good agreement with computer simulations.

MSK-Type Reception of Continuous Phase Modulation: Cochannel and Adjacent Channel Interference

Abstract: For binary continuous-phase modulation with modulation index h = 1/2 (MSK being a rather familiar example), quadrature matched-filter reception is possible with only minor degradation relative to the maximum likelihood (trellis-based) receiver. Thus this class of modulations provides good spectral attributes together with reception techniques capable of being implemented simply at high speeds. As usual, the constant-envelope property is also present. We study here the effects of interfering signals with the same modulation format, located at the same frequency (cochannel interference), or at a nearby frequency (adjacent channel interference). Coherent reception is assumed, and we analyze two channel situations: both signals nonfading with additive Gaussian noise; and both signals independently Rayleigh fading, with additive Gaussian noise. As one would expect, the smoothed phase modulation schemes have larger tolerable adjacent channel levels, while there is little differentiation in the cochannel case. We also find that MSK filters are usable for other formats with negligible loss in performance relative to the optimal linear filters, provided the filter parameters are rescaled appropriately.

A Practical Receiver Structure for Multi-h CPM Signals

Abstract: Multi- h schemes are bandwidth-efficient CPM signaling formats which offer means of coding without explicit redundancy. However, the required (optimal) receiver structures tend to be very complex [1], [4], [8] requiring a large number of filters of correlators. Here a reduced complexity receiver for the joint estimation of M -ary data, carrier phase, and symbol timing is realized through the use of an approximate representation of the likelihood function. Evaluation of receiver performance indicates a fraction of a decibel degradation in coding gain and almost no loss in synchronization performance.

Nyquist 3 Pulse Shaping in Continuous Phase Modulation

Abstract: Continuous phase modulation (CPM) schemes, using Nyquist 3 pulse shaping and correlative codes, are popular candidates for mobile radio applications. This paper presents a detailed study of the effects of Nyquist 3 pulse shaping on the spectral characteristics of CPM schemes with a modulation index of 1/2. The influence of pulse parameters such as its shape, bandwidth, coding polynomial, and truncation length on spectral characteristics such as main lobe, fractional power bandwidths, and out-of-band power levels is thoroughly investigated; error performance is also briefly analyzed. Among uncoded schemes, a new scheme using a pulse satisfying both Nyquist 3 and Nyquist 2 criteria is pointed out as a promising candidate and as a good compromise between spectral and power efficiencies.

Carrier phase controller for a receiver of phase modulated signals

Abstract: A simplified carrier phase control apparatus used in a modem for demodulating a quadrature amplitude modulated data signal, to correct phase jitters of a carrier signal due to a 50 Hz or a 60 Hz frequency of the commercial power supply, and its harmonic wave frequency components. The carrier phase control apparatus has a predictive filter for predicting a carrier phase jitter, the predictive filter composed of band-pass filters with center frequencies of 50 Hz and 60 Hz, and a circuit where the output signals of the band-pass filters are multiplied by the coefficients and added linearly.

Method for transmitting digital data by means of continuous phase modulation

Abstract: A method for transmitting digital data by means of continuous phase modulation (CPM), wherein the transmission signal s(t) is generated by retrieving stored digital values, which are allocated to a continuous sequence of symbols ai present at the transmitter input, from storage in a memory. In contrast to the conventional method, these stored digital values are not calculated from a predetermined frequency-base-band pulse g(t) by linear superposition but are optimized with respect to the in-band power emitted by means of an iterative method. This non-linear method leads to distinctly improved spectral characteristics of the transmission signal s(t).

Determining and correcting for phase jumps

Abstract: A continuous phase magnetic field map is provided by dividing the field map of elements into regions; determining discontinuities in the regions and adding a constant modulo 2π to the phase values of each element of the region which results in a minimum difference between adjacent elements of the region. Then similarly joining the continuous regions to form continuous sections and the continuous sections to form continuous zones until substantially continuous phase magnetic field maps are obtained.

Respective Parts of the Carrier and of the Frequency Modulation in the Semantics of Distress Calls

Abstract: Distress calls are complex signals, i.e. they are made up of numerous harmonics. Their spectral composition suggests that there are two components: a carrier frequency and a modulating frequency. We have distinguished a primary modulation (slow increase or decrease of frequencies from the beginning to the end of the call) and an additional secondary modulation (fast frequency sweeps within a narrow bandwidth). We have attempted to examine the role of these different signal components in the semantics of distress. To resolve this problem, we have used digital synthesis methods. We have performed playback experiments in the field with starlings (Sturnus vulgaris). These experiments give the following results: a carrier frequency presented alone, without frequency modulation, does not elicit distress reactions. A signal with the carrier frequency only, modulated by a secondary modulation, gives the same results. But obvious distress reactions are observed if the carrier frequency is modulated by a signal which presents a slight increasing slope (primary modulation), be it with or without a secondary modulation. The primary modulation appears to be a very important parameter in the decoding of starlings distress calls. On the other hand, secondary modulation appears to be unnecessary for this decoding. We have demonstrated that distress calls, in spite of their complex structure, follow a very simple law of decoding.

1024-QAM and 256-QAM Coded Modems for Microwave and Cable System Applications

Abstract: Low redundancy FEC coded 1024-QAM modems, staggered 1024-QAM, and 256-QAM modems for spectrally efficient (up to 8.84 bits/s/Hz) microwave and cable systems applications are described. Such a high spectral efficiency is required for CEPT-1 (2.048 Mbit/s) rate digital transmission in a single analog supergroup (SG` band as well as for other emerging systems applications. Practical constraints of operational analog FDM systems are presented and taken into account in the choice of the low redundancy FEC codec and the coded 1024-QAM modem. Theoretical, computer simulation and experimental results of 256QAM modems have been extended to the feasibility study of 512-QAM, 961-QPRS, and 1024-QAM modems. Our experience with 256-QAM modems which have a T-1 (1.544 Mbit/s) rate in a 240 kHz analog supergroup (SG) band, i.e., an efficiency of 6.66 bits/s/Hz, demonstrates that a regenerative span over 1000 km is feasible over FDM radio systems. A significantly increased spectral efficiency of 8.84 bits/s/Hz is required for CEPT-1/SG system applications. Our R&D results, presented in this paper, demonstrate the feasibility of FEC coded 1024QAM modems, equipped with powerful digital adaptive equalizers, carrier phase noise, and symbol clock jitter cancellation subsystems, for the transmission of CEPT-1 rate signals in a single SG band.

Mean-Square Error Optimization of Quadrature Receivers for CPM with Modulation Index 1/2

Abstract: Detection of continuous phase modulation (CPM) signals can be accomplished using quadrature coherent detectors which include a pair of linear and time-invariant postdetection filters. Performance of the quadrature detectors is highly sensitive to the postdetection filters response. This paper presents a rigorous derivation of an optimum postdetection filter response. The derivation is based on minimizing the mean-square interference subject, to the constraint that the filter noise bandwidth is held constant. The amount of computations involved is fairly small and increases linearly with the receiver observation interval. Performance analysis results for several modulation techniques are presented.

Performance of Coherent Phase and Amplitude Digital Modulations with Carrier Recovery Noise

Abstract: A model of decision feedback carrier recovery noise is presented as a function of the number of symbols over which the carrier is derived. For this model, quantitative results for performance degradation in BPSK, QPSK, 8-phase, 16-QAM, 32-QAM, and 64-QAM coherent demodulators are presented. When the carrier is derived from only the last symbol, these results reduce to the performance for differential detection. Carrier integration over 100 symbols is shown to be adequate to provide performance quite close to ideal for all the modulations considered.

A power-efficient linear digital modulator and its application to an anti-multipath modulation PSK-RZ scheme

Abstract: This paper describes a new concept in modulation methods for high speed digital mobile communications. Linear modulation is introduced to allow amplitude variation in the modulated signal. This primarily brings the advantage that sharp cut-off band restriction can be performed to enhance the transmission efficiency. Also, we can adopt as a multipath strategy an amplitude-shift anti-multipath modulation technique, which is found to be more effective than its phase-shift counterpart. A linear modulation method is presented to meet the mobile radio requirement on power efficiency. We finally derive a narrow-band anti-multipath modulation scheme, with required bandwidth compatible with other narrow-band modulation techniques and with superior anti-multipath effect.

Error rate performance of narrowband multilevel CPFSK signals

Abstract: The paper presents a relatively simple method for analysing the effect of IF filtering on the performance of multilevel FM signals. Using this method, the error rate performance of narrowband FM signals is analysed for three different detection techniques, namely limiter-discriminator detection, differential detection and coherent detection followed by differential decoding. The symbol error probabilities are computed for a Gaussian IF filter and a second-order Butterworth IF filter. It is shown that coherent detection and differential decoding yields better performance than limiter-discriminator detection and differential detection, whereas two noncoherent detectors yield approximately identical performance.

On Optimum and Suboptimum Coherent Detection of Continuous Phase Modulation on a Two-Ray Multipath Fading Channel

Abstract: In this paper, the performance of continuous phase modulation (CPM) transmitted on a two-ray fading channel and received in white Gaussian noise is studied. The optimum coherent maximum likelihood (ML) detector and approximations thereof and their performance are studied by means of minimum Euclidean distance and simulated symbol error probability. A linear detector optimum at large signal-to-noise ratios is also studied and the performance is given by means of error probability. It is assumed that measurements on the channel provide information about the channel parameters. It is found that the loss in signal power due to the channel is small when an ML detector or an approximation thereof is used for binary schemes with modulation index h =1/2 . The loss for these schemes with a linear detector becomes significantly larger, especially when MSK is transmitted. The performance for this linear detector can, however, be improved significantly by using decision feedback, but still, the performance of the ML detector is superior.

CPFSK communication system employing nyquist-filtered modulator/demodulator

Abstract: An improved narrowband continuous phase modulation system incorporates a filtering mechanism in the transmitter and receiver sites that enables the radiated spectrum characteristic to have a substantially reduced response at frequencies other than the channel of interest and thereby achieve a significant reduction in unwanted adjacent channel interference. Each of the transmitter and receiver sites contains a square root Nyquist filter upstream and downstream of the modulator and demodulator, respectively. The output of the Nyquist filter in the receiver is coupled to an accumulator which sums successive samples of the demodulated data signals (including noise). The noise is reduced as a consequence of its inherent negative correlation properties (utilized in the accumulation of successive samples of the recovered signal).

Coherent detection of binary multi-h CPM

Abstract: In the paper receiver structures which minimise the bit error probability for coherent detection of multi-h binary continuous phase modulation (CPM) signals for arbitrary number of observation intervals are examined by means of the traditional union bound at high SNR and by using the concept of the average matched filter (AMF) at low SNR. Multi-h schemes are found by upper-bound minimisation as a function of observation intervals and received SNR. Explicit expressions for the performance of the AMF receiver are derived for three important subclasses of binary multi-h CPM. Optimum and suboptimum receiver structures are examined. Several numerical examples are given, and a comparison of our results with the available results on binary CPM is provided.

New Universal All-Digital CPM Modulator

Abstract: In this paper a new modulator for a broad class of continuous phase modulations (CPM) is proposed that is more flexible and less complex than conventional quadrature modulators, while achieving the same or better performance. Being all-digital it is more suitable for one-chip VLSI implementation. Some design parameters are also discussed and experimental results are presented.

Adaptive locally optimal detectors for CPFSK in non-Gaussian noise

Abstract: Performance of adaptive locally optimal Bayes' detectors (LOBD) for detecting Continuous Phase Frequency Shift Keyed (CPFSK) signals in impulsive non-Gaussian noise is investigated. Two models are used to characterize the noise process, the Johnson Su system of densities and a mixture of normals model. Analytic estimation of performance along with simulation results illustrate the robustness of these adaptive schemes.

Error probability analysis for CPM with linear detection on Gaussian and Rayleigh fading channels with multiple signal interference

Abstract: Binary continuous phase modulations with constant amplitude (CPM) with modulation index 1/2 have been shown to provide both good spectral and error probability properties. These modulations can also be detected with a very simple linear detector, which can be implemented simply at high speeds. This can be done with only a minor degradation in error performance. The linear detector can be implemented both as a serial and as a parallel detector, and these have slightly different sensitivity to errors in bit timing and phase synchronisation. In the paper we study the effects of multiple interfering signals on both these linear detectors for CPM. Coherent detection is assumed, and both Gaussian and slow Rayleigh fading channels are considered. Analytical formulas are derived on both channels, where only a single integral has to be calculated numerically. This formula can also easily be used for detector filters with impulse response of long time duration. It is shown that the difference in performance due to the number of interferers is small, when the total interference power is kept constant. Further, it is shown that the performance is improved by several decibels for the longer asymptotically optimum filters in adjacent channel interference. As one would expect, the smoothed phase modulations have significantly larger tolerances against adjacent channel interference, while the difference is small in cochannel interference. On the Rayleigh fading channel, the longer asymptotically optimum filters on the Gaussian channel lead to much lower irreducible error probabilities than does the MSK filter; a decrease by a factor of as much as 10 has been found.

Performance of GMSK and comparisons with the modulation methods of the 12PM3 class

Abstract: This paper shows that GMSK (Gaussian-filtered Minimum Shift Keying) modulation can be included in the 12PM3 (12-state Phase Modulation with correlation over 3 consecutive bits of the input stream) class, and compares its performance with that of other narrowband digital continuous-phase modulations. Performance comparisons are presented with reference to both AWGN channels, cochannel and adjacent channel interferences and the typical propagation conditions envisaged for SCPC/FDMA digital land mobile radio systems in urban environment. Two different receivers, coherent and frequency discrimination detection, have been considered. The sensitivity to channel distortions due to multipath propagation has been assessed by computing signature curves.

Features and Performance of 12PM3 Modulation Methods for Digital Land Mobile Radio

Abstract: A number of continuous-phase modulation methods suitable for digital and mobile radio applications has been grouped in a common class, which has been named 12PM3 (12-state, phase modulation with correlation over three consecutive bits). This paper introduces the definition of this class of modulation schemes, and presents some of its features. With reference to the scheme that gives the best spectral compactness, some effects of typical implementation imperfections of the modulation circuits are discussed. The performance of some 12PM3 modulators associated with a frequency discrimination receiver is then computed with reference to both AWGN (additive white Gaussian noise) channels and the typical propagation conditions envisaged for SCPC/FDMA digital land mobile radio systems in urban environment. The adopted pre and postdiscrimination filters of the receiver are optimized for the best performance. Different decision techniques are considered, namely 2-TH (2-threshold), 4-TH, mixed 2-TH/4-TH and MLSE (maximum-likelihood sequence estimation) techniques.

Communication System Design using M'ary Full and Partial Response Continuous Phase Modulation

Abstract: Continuous Phase Modulation (CPM), a constant envelope digital signaling technique, provides power efficient and/or bandwidth efficient performance Practical signal designs are selected by applying a trade-off between error probability performance and receiver complexity for a given occupied bandwidth An overall system architecture is presented incorporating the maximum likelihood sequence estimation demodulator coupled with phase and clock synchronization The size and cost of a digital receiver implementation is affected by the sampling rate and number of quantization levels When applied to CPM waveforms, these implementation parameters lead to reasonable design values with minimal performance degradation Finally, a hardware architecture is suggested for data rates on the order of megabits per second

Method for digital data transmission using continuous phase modulation

Abstract: Bei einem Verfahren zur Uebertragung von digitalen Daten mittels kontinuierlicher Phasenmodulation (CPM) wird das Sendesignal s(t) durch abgespeicherte Digitalwerte erzeugt, die einer fortlaufenden Folge von am Sendereingang anstehenden Symbolen a i zugeordnet und ausgespeichert werden. In a method for transmission of digital data by means of continuous phase modulation (CPM), the transmission signal s (t) generated by stored digital values, which are associated with a continuous sequence of pending at the transmitter input symbols a i and destaged. Im Unterschied zur herkommlichen Technik werden diese abgespeicherten Digitalwerte nicht durch lineare Superposition aus einem vorgegebenen Frequenz-Basisband-Impuls g(t) berechnet, sondern durch ein iteratives Verfahren bezuglich der abgegebenen In-Band-Leistung optimiert. In contrast to the conventional technique, these stored digital values ​​are not calculated by linear superposition of a predetermined frequency-base-band pulse g (t), but optimized by an iterative method with respect to the output in-band performance. Dieses nichtlineare Verfahren fuhrt zu deutlich verbesserten spektralen Eigenschaften des Sendesignals s(t). This nonlinear process leads to significantly improved spectral properties of the transmission signal s (t).

A partially coherent dynamic programming algorithm for CPM detection

Abstract: A dynamic programming algorithm for joint data detection and carrier phase estimation of continuous-phase-modulated signal is presented. The intent is to combine the robustness of noncoherent detectors with the superior performance of coherent ones. The algorithm differs from the Viterbi algorithm only in the metric that it maximizes over the possible transmitted data sequences. This metric is influenced both by the correlation with the received signal and the current estimate of the carrier phase. Carrier-phase estimation is based on decision guiding, but there is no external phase-locked loop. Instead, the phase of the best complex correlation with the received signal over the last few signaling intervals is used. The algorithm is slightly more complex than the coherent Viterbi algorithm but does not require narrowband filtering of the recovered carrier, as earlier appproaches did, to achieve the same level of performance.

Nmr signal receiving method

Abstract: Phase encoding of nuclear magnetic resonance (NMR) information is performed using rf pulse sequences. The rf pulse sequences produce a substantially continuous phase variation across the resonant frequency range of the atoms of an object in order to perform phase encoding. Some of the pulses may be tailored pulses, with each tailored rf pulse including frequencies which cover a bounded continuous frequency range. Either the phase or the amplitude of each tailored rf pulse varies with frequency across this continuous range. If the amplitude varies linearly across the range, the phase is constant, but if the phase varies linearly across the range, the amplitude is constant. The tailored rf pulses may be applied in the presence of pulsed magnetic gradient fields of the conventional type to produce the phase variation. Alternatively, rf pulses may be applied through rf field gradient coils providing a spatial variation which permits phase encoding of spatial information. The rf pulses may, in either case, be included in a sequence of pulses which also performs excitation of atoms in an object being imaged.

A 94 GHz Synchronized Oscillator-Chain for Fast, Continuous360° Phase Modulation

Abstract: A continuous phase shift of 0 to 360° has been achieved at 94 GHz by injection locking a 2nd harmonic mode Gunn-oscillator at its fundamental frequency. Phase shifting is achieved by varactor tuning the free running fundamental frequency within the locking range. The resulting phase shift between reference signal and the VCO output signal is +-90 degrees at the fundamental frequency and doubled to +-180 degrees at the 2nd harmonic frequency. The phase shifted signal as well as the reference signal each have output powers of more than 20 mW at 94 GHz.