Showing papers on "Continuous phase modulation published in 2000"

Method and system for detecting and classifying the modulation of unknown analog and digital telecommunications signals

Abstract: Disclosed is a unique system and method for recognizing the type of modulation embedded in an unknown complex baseband signal, comprising a receiver section for extracting the complex baseband signal from a modulated signal having a carrier frequency, and comprising an orderly series of signal processing functions for (a) estimating the bandwidth of the unknown signal, (b) removing the out-of-band noise and correcting gross carrier frequency errors, (c) discriminating between constant envelope and irregular envelope signals, (d) estimating and correcting residual carrier frequency errors, (e) classifying a constant envelope signal into one of the following modulation formats: {Continuous Wave (CW), Frequency Modulation (FM), Frequency Shift Keying (FSK)}, and (f) classifying an irregular envelope signal into one of the following modulation formats: {Amplitude Modulation (AM), Double Sideband Suppressed Carrier (DSB-SC), Binary Shift Keying (BPSK), Quaternary Phase Shift Keying (QPSK), π/4-shifted QPSK, M-ary PSK (MPSK), and OTHER classes}.

Wave-front sensing and deformable-mirror control in strong scintillation

Abstract: Recent studies of coherent wave propagation through turbulence have shown that under conditions where scintillation is significant a continuous phase function does not in general exist, owing to the presence of branch points in the complex optical field. Because of branch points and the associated branch cuts, least-squares approaches to wave-front reconstruction and deformable-mirror control can have large errors. Branch-point reconstructors are known to provide superior performance to least-squares reconstructors, but they require that branch points be explicitly detected. Detecting branch points is a significant practical impediment owing to spatial sampling and measurement noise in real wave-front sensors. Branch points are associated with real zeros in an optical field, and hence information about the phase of the field is encoded in the amplitude of the wave. We present a new wave-front-sensor processing algorithm that exploits this observation in the wave-front-reconstruction and deformable-mirror-control process. This algorithm jointly processes three intensity measurements by using light from the beacon field to develop a set of deformable-mirror actuator commands that are maximally consistent with three intensity measurements: (1) the entire wave-front-sensor image, (2) a pupil intensity image, and (3) a conventional image. Owing to the nonlinear nature of the resulting algorithm, we have used a simulation to evaluate performance. We find that in a focused laser beam projection paradigm that uses a point-source beacon, the new algorithm provides significantly improved performance over that of conventional Hartmann sensor least-squares deformable-mirror control based on centroid processing of wave-front-sensor outputs. The performance of the new algorithm approaches, the performance of an idealized branch-point reconstructor that requires pointwise phase differences for operation.

Power and bandwidth efficient serially concatenated CPM with iterative decoding

Abstract: Serially concatenated continuous phase modulation (SCCPM) with iterative decoding is analyzed and simulated. Earlier results on outer rate 1/2 convolutional codes combined with inner binary and quaternary CPM systems are extended to rate 2/3 and 3/4 codes with low-complexity octal and hexadecimal CPM systems, having the 2RC and 3RC frequency pulses. Analysis and simulations show that-among the evaluated systems-the octal 2RC systems provide the highest power/bandwidth efficiency. As an example, rate 2/3-coded octal 2RC with modulation index 1/4 provides a 5.7 dB gain over uncoded minimum shift keying at a bit error rate of 10/sup -3/ and an input delay 4096 bits, without any bandwidth expansion.

A quasi-optimum receiver for continuous phase modulation

Abstract: A simple receiver structure for any continuous phase modulation (CPM) scheme is introduced. Its front end is just the ordinary linear receiver followed by a subinterval sampler, eliminating the need for the standard analog matched filters. Its design is based on the decomposition of the CPM signal in the Walsh signal space. This brings the hardware requirement to a minimum, and near-optimum performance can be easily obtained.

Description and performance results for a multi-h CPM telemetry waveform

Abstract: Multi-h continuous phase modulation (CPM) offers significant improvements over both legacy telemetry waveforms (PCM/FM) and the newly-introduced waveform (Feher (International Telemetering Conference, Las Vegas,p.27-30, 1997) patented FQPSK) in terms of spectral containment and detection efficiency, while retaining a constant envelope characteristic. This paper describes the theoretical and measured performance of the multi-h CPM waveform as well as the implementation of a suitable trellis demodulator.

Parallel concatenated turbo codes for continuous phase modulation

Abstract: There are several ways to use iterative decoding techniques with coded continuous phase modulation (CPM). This paper presents a method using parallel concatenation of convolutionally-coded CPM. All CPM schemes can be decomposed into a ring convolutional code and a memoryless signal mapper. This allows a properly designed convolutional code trellis to be combined with the CPM trellis, producing the joint trellis of a constituent code. Parallel concatenation of such constituent codes combined with iterative decoding yields very good performance. We present the results of code searches for two binary CPM schemes, each using bit interleaving and symbol interleaving. Simulation results using various length interleavers are also provided. Low complexity encoders are shown to perform better using bit interleaving, whereas encoders with higher complexity perform better with symbol interleaving.

Trellis termination in CPM

Abstract: A technique is presented for terminating the encoder of continuous phase modulation (CPM) into a known trellis state. This is useful when block-wise a posteriori probability processing is employed, e.g. in iterative ("turbo") receivers for serially concatenated CPM.

Noncoherent sequence detection in frequency nonselective slowly fading channels

Abstract: A new class of noncoherent sequence detection (NSD) algorithms for combined demodulation and decoding of any coded linear and continuous phase modulations, transmitted over additive white Gaussian noise (AWGN) channels, has been previously presented. In this paper, this class is generalized to the case of frequency nonselective Rayleigh or Rice slowly fading channels, in the presence or absence of channel state information. Coded linear modulations, namely M-ary phase shift keying (M-PSK) and quadrature amplitude modulation (M-QAM), are considered. The proposed detection schemes have a performance which approaches that of coherent detectors, are very robust to phase and frequency instabilities, and compare favorably to other solutions previously proposed in the technical literature.

Method for designing arbitrary two-dimensional continuous phase elements

Abstract: We propose a method for designing arbitrary two-dimensional continuous phase elements. The phase anomalies that are due to amplitude zeros that occur in conventional design methods can be avoided completely with this method. Therefore the method is also useful for designing holographic elements that are free from amplitude zeros. The method is based on an iterative Fourier-transform algorithm. In the iteration process the method operates on the unwrapped phase. Consequently, a subsequent continuation step is not needed.

Data aided symbol timing system for precoded continuous phase modulated signals

Abstract: Data aided carrier phase and symbol timing synchronizers are implemented at baseband as digital modulators isolating input signal inphase and quadrature component signals fed into inphase and quadrature Laurent transforms that function as data detector to provide odd and even data bit multiplexed output data signal while cross coupling the inphase and quadrature transformed outputs for removing data modulation in error signals to correct phase errors and timing errors in the received signal so as to provide reliable data demodulation of noisy received signals having dynamic carrier phase and symbol timing errors as found in continuous phase modulation communications systems such as Gaussian minimum shift keying communications systems.

Soft-output detection of CPM signals in frequency flat, Rayleigh fading channels

Abstract: Symbol-by-symbol detection algorithms are useful in systems in which soft-decision metrics are important, e.g., systems with interleaved coded modulation. A soft-output algorithm for the detection of continuous phase modulated (CPM) signals transmitted over frequency flat, Rayleigh fading channels is developed. Since the optimum detector is computationally too complex for any practical implementation, some suboptimal detectors which give near optimal performance are proposed. Some theoretical approximations for the performance of the interleaved coded system are given. The performance of the soft-output algorithms is also extensively characterized by means of Monte-Carlo simulations.

Coding CPFSK for differential demodulation

Abstract: A model is developed for finding codes for differentially demodulated continuous phase frequency-shift keying with modulation index h=1/M, where M is the size of the symbol alphabet The results of codes searches show that there is very little loss in squared Euclidean distance when comparing differential codes with coherent codes

A wideband carrier-recovery system for multilevel QAM signals

Abstract: A decision-directed carrier-recovery technique for coherent demodulation of quadrature amplitude modulated (QAM) signals is proposed. This system adaptively tracks both the carrier frequency and phase of the received QAM signal's modulated carrier. The acquisition time of the proposed system is shown to be faster than that of conventional carrier-recovery schemes, especially when the initial carrier-frequency offset is relatively large, i.e. beyond a small fraction of the symbol rate. Also, the proposed method has a wider acquisition range compared to conventional techniques.

Data aided carrier phase tracking system for precoded continuous phase modulated signals

Abstract: Data aided carrier phase and symbol timing synchronizers are implemented at baseband as digital modulators isolating input signal inphase and quadrature component signals fed into inphase and quadrature Laurent transforms that function as data detector to provide odd and even data bit multiplexed output data signal while cross coupling the inphase and quadrature transformed outputs for removing data modulation in error signals to correct phase errors and timing errors in the received signal so as to provide reliable data demodulation of noisy received signals having dynamic carrier phase and symbol timing errors as found in continuous phase modulation communications systems such as Gaussian minimum shift keying communications systems.

Phase state analyzing method for equiphase stripes

Abstract: PROBLEM TO BE SOLVED: To improve the precision of a phase state analysis in an observation region by applying a masking process to portions corresponding to regions where no stripe information exists in the phase distribution applied with a phase unlapping process in the analyzing method for the phase state of a checked body having an observation region split into multiple portions by separation bands where no stripe information exists. SOLUTION: In this phase state analyzing method, stripes scanning is applied in four steps to a checked face split into multiple observation regions by separation bands (S1). The phase distribution of the checked face is obtained from four interference stripes intensities obtained by the stripes scanning (S2). The phase distribution is folded between -π and π, thus phase unlapping is applied by the phase unlapping method, and the continuous phase distribution is obtained (S3). A masking process is applied to portions having 0 modulation corresponding to the separation bands (S4). Finally, an inclination correction is made to the continuous phase distribution applied with the masking process by the method of least squares (S5).

Effect of polarization mode dispersion on optical heterodyne CPFSK system

Abstract: An analytical approach is developed to determine the impact of signal phase distortion due to polarization mode dispersion (PMD) on the bit error rate (BER) performance of optical heterodyne continuous phase FSK (CPFSK) system with delay demodulation receiver. The computed results at a bit rate of 10 Gb/s show that the CPFSK system suffer a significant amount of power penalty due to the effect of PMD. At a modulation index of 0.5, the penalty at a BER of 10/sup -9/ is found to be 1.0 dB, 1.8 dB and 2.8 dB when the differential group delay is 10 ps, 50 ps and 100 ps respectively for fiber length of 100 km. At modulation index of 1, the penalty is approximate 3.75 dB for differential group delay of 10 ps.

Iterative joint channel estimation and detection of coded CPM

Abstract: The serial concatenation of continuous phase modulations and convolutional codes has proven to perform well at low SNR when iteratively detected. The iterative detection algorithm assumes that the channel state is known at the receiver end. In this paper, the expectation-maximization (EM) algorithm is used as an alternative to pilot symbol aided channel estimation. The EM channel estimation is associated with the iterative detection and requires no increase in decoding complexity.

Phase tracking apparatus and method for continuous phase modulated signals

Abstract: A method establishes a phase reference signal for trellis demodulating CPM modulated received signals by using phase reference signals and symbol timing estimates. Branch metrics signals representing the highest-probability path through the trellis are calculated to produce beat estimates of the modulation data. The branch metrics signals are phase shifted to produce phase shifted branch metrics (PSBM) for each path. At each symbol interval, the highest probability PSEM (HPPSBM) signal for the path is selected. The selected phase shifted branch metric adjusts the value of the phase reference signals. Another method estimates the transmitted signal from at least the estimated data and the phase reference signal. The estimated transmitted signal is phase shifted to produce phase shifted estimated transmitted signals, which are correlated with the received data signals to produce phase error signals, which are smoothed and correct the phase reference signal.

Performance analysis of blind carrier phase estimators for general QAM constellations

Abstract: Large quadrature amplitude modulation (QAM) constellations are currently used in throughput-efficient high-speed communication applications such as digital TV. For such large signal constellations, carrier phase synchronization is a crucial problem because for efficiency reasons the carrier acquisition must often be performed blindly, without the use of training or pilot sequences. The goal of the present paper is to provide thorough performance analysis of the blind carrier phase estimators that have been proposed in the literature and to assess their relative merits.

Non-data-aided frequency offset and symbol timing estimation for binary CPM: performance bounds

Abstract: The use of (spectrally efficient) CPM modulations may lead to a serious performance degradation of the classical non-data-aided (NDA) frequency and timing estimators due to the presence of self noise The actual performance of these estimators is usually much worse than that predicted by the classical modified Cramer-Rao bound We apply some well known results in the field of signal processing to these two important problems of synchronization In particular we propose and explain the meaning of the unconditional CRB in the synchronization task Simulation results for MSK and GMSK, along with the performance of some classical and previously proposed synchronizers, show that the proposed bound (along with the MCRB) is useful for a better prediction of the ultimate performance of the NDA estimators

Detection of linear modulations in the presence of strong phase and frequency instabilities

Abstract: The previously proposed noncoherent sequence detection (NSD) algorithms have a performance which approaches that of coherent detectors and are robust to phase negligible performance loss in the presence of a frequency offset, provided this offset does not exceed an order of 1% of the signaling frequency. For higher values, the performance rapidly degrades. In this paper, two detection schemes are proposed, characterized by high robustness to frequency offsets and capable of tolerating offset values up to 10% of the signaling frequency. More generally, these detection schemes are very robust to rapidly varying phase and frequency instabilities. The general case of coded linear modulations is addressed, with explicit reference to M-ary phase shift keying (M-PSK) and quadrature amplitude modulation (M-QAM).

Modulation/demodulation method for multi-value digital modulation signal and orthogonal frequency division multiplex system

Abstract: PROBLEM TO BE SOLVED: To further simplify the circuit configuration of a transmitter and a receiver. SOLUTION: A differential phase encoder 15 of a transmitter 10 applies differential modulation to a phase of each symbol, where a same subcarrier is consecutive in the OFDM system without changing amplitude of the symbol, and the transmittar 10 transmits a multi-value digital modulation signal to a radio channel 1. A receiver 30 receives the multi-value digital modulation signal sent via the radio channel 1, and a differential phase decoder 38 of the receiver 30 demodulates the phase of each consecutive symbol in the same subcarrier and applies coherent processing to the amplitude.

Blind self-noise-free frequency detectors for a subclass of MSK-type signals

Abstract: Frequency offset due to Doppler shift and/or oscillator instabilities degrade the receiver performance. A family of frequency detectors for frequency offset estimation and compensation in digital receivers is introduced. The proposed detectors are best suited for frequency offset compensation of a subclass of binary continuous phase modulation with h=1/2 that includes modulation schemes with nonnegative frequency pulses. For the considered modulation schemes, the modulation-induced self-noise term is absent from the variance of the frequency estimate. The estimator is nondata- and nontiming-aided and its estimation range is either half or a quarter of the bit rate (R). With larger frequency offsets, the estimators that have a /spl plusmn/R/2 estimation range introduce a frequency ambiguity of R that is of no relevance to the performance of a differential detection based receiver.

New modulation scheme for integrated single side band lightwave source allowing fiber transport up to 256 QAM over 38 GHz carrier

Abstract: A new modulation scheme for the integrated SSB source is presented allowing now to address 256 QAM modulation format on a 38 GHz millimetric carrier while yielding very low phase noise Moreover, this scheme presents 10 dB gain for both carrier and signal modulation power

Adaptable Viterbi detector for a decomposed CPM model over rings of integers

Abstract: A novel, practical and flexible way of implementing continuous phase modulation (CPM) using a decomposed model and a Viterbi detector is presented. The decomposed CPM modulator, comprising a continuous phase encoder (CPE) and a memoryless modulator (MM), is implemented and can be concatenated with a ring convolutional encoder (CE) such that the detector may be readily adapted to the ring of integers over which the CE/CPE operates. A partial-response CPM system is simulated over additive white Gaussian noise (AWGN) and Rayleigh flat fading (RFF) channels, and results, in terms of the bit error rate (BER) against the signal to noise ratio (SNR), are presented, discussed and evaluated.

Performance of a frequency-hop system with turbo trellis-coded modulation in partial-band interference

Abstract: We describe a frequency-hop (FH) packet radio system that employs parallel concatenated trellis coding, or turbo trellis coding, and continuous-phase modulation. This system is spectrally efficient and performs well at low signal-to-noise ratios. When combined with interleaving, turbo coding also provides a FH system with resistance to partial-band interference. We present simulation results for the turbo trellis-coded FH system with noise and partial-band interference. In particular, we study the probability of packet success for different packet sizes and levels of interference. Results show that this turbo trellis-coded system provides three times the capacity of SINCGARS in an AWGN channel and compares favorably with a block-coded system in partial-band interference.

Analytical evaluation of the effect of self-phase modulation on coherent optical CPFSK system

Abstract: An analytical approach is presented to evaluate the effects of self-phase modulation (SPM) on the bit error rate performance of an optical heterodyne CPFSK transmission system. The signal phase distortion induced by SPM at the output of the fiber is determined by using the beam propagation method (BPM). The bit error rate performance is evaluated by using Gauss quadrature rule using the moments of the random phase fluctuations at the receiver output. The results show that the performance of a heterodyne CPFSK system is highly degraded due to the effect of fiber dispersion and self-phase modulation and the power penalty increases with the increase in input power level. Compared to direct detection CPFSK, the effect of SPM is found to be more pronounced in case of heterodyne receiver.

The performance of simplified maximum-likelihood sequence detector for continuous phase modulation scheme

Abstract: Continuous phase modulation (CPM) signals, which can be written as a sum of amplitude modulated pulses (AMP), are optimally demodulated using maximum-likelihood sequence detection (MLSD). It has been shown that CPM signals can be approximated by a single amplitude modulated pulse. This approximation reduces the complexity of MLSD. We examine the performance of this simplified receiver. The performance criterion used in this paper is the symbol error probability, which is a function of the minimum Euclidean distance (d/sub min//sup 2/)/spl middot/d/sub min//sup 2/ of the simplified receiver is compared to d/sub min//sup 2/ of the optimum receiver both asymptotically and for each observation interval.

Liquid Crystal Phase Shifter for Optically Generated RF-Signals

Abstract: In this paper we present a phase shifter for optically generated RF-signals including a liquid crystal amplitude modulator. The light is intensity modulated by a Mach-Zehnder modulator and split into two paths. One path exhibits a fixed ?RF/4 delay and a liquid crystal light valve to vary the transmitted amplitude of this path. In the proposed experimental setup the resulting phase ?RF of the modulated signal can be adjusted from 0° to 45°. The method can be used for a continuous phase shift up to 360° with only four light valves.