Showing papers on "Continuous phase modulation published in 1997"

Symbol-by-symbol MAP demodulation of CPM and PSK signals on Rayleigh flat-fading channels

Abstract: Demodulation using the symbol-by-symbol maximum a posteriori probability (MAP) algorithm is presented. The algorithm is derived for the case of continuous phase modulation (CPM) signals transmitted over Rayleigh flat-fading channels, and a corresponding receiver structure is specified. It is shown that the MAP algorithm requires computing, for each trellis branch, the sum of the products of the weights of all paths through the trellis which pass through that branch, and that this generic computational problem can be solved efficiently by an approach that uses a forward and backward recursion through the trellis. Simulation results are presented which show both the hard and soft decision performance of the MAP receiver to be robust, even in the presence of fade rates of up to 30% of the symbol rate. The application of the receiver concept to phase-shift keying (PSK) signals is also discussed, and then evaluated via simulation. The concept of joint demodulation and decoding using iterative processing techniques is introduced. It is shown that the MAP receiver is well suited for iterative processing applications due to its use of a priori symbol probabilities and its production of optimal soft decisions. Simulation results for the reception of quaternary PSK (QPSK) show that the bit error rate (BER) performance of the iterative MAP receiver can approach that of a receiver operating with perfect knowledge of the fading process.

GMSK modulator formed of PLL to which continuous phase modulated signal is applied

Abstract: A Gaussian Minimum Shift Keying modulator that provides direct modulation of a carrier signal, produced by a single microwave high power voltage controlled oscillator. A continuous phase frequency shift keyed modulated signal with a modulation index of 0.5 is produced at the desired output frequency using a full 360 degree linear continuous phase modulator, controlled by a linear baseband signal that is the integral of the binary baseband information signal. This modulated signal is used as the reference signal for a phase locked high power voltage controlled oscillator. The phase locked loop provides frequency tracking and Gaussian spectral shaping to the modulated output signal.

Reduced-complexity detection and phase synchronization of CPM signals

Abstract: Based on an extension of Laurent (1986) decomposition of continuous phase modulation (CPM) signals into a sum of linearly modulated components, we derive a class of reduced-complexity maximum-likelihood (ML) coherent detection and closed-loop phase synchronization schemes. The complexity of the resulting detection schemes, expressed in terms of the number of matched filters and states of a Viterbi algorithm, is significantly reduced with respect to that of optimal coherent receivers with negligible performance loss. This result extends a known one valid for the binary case to multilevel CPM. The proposed synchronization schemes do not require an increased number of matched filters, and are perfectly suitable to be used in conjunction with these receivers. Based on the phase-locked loop (PLL) equivalent linear model, a method for optimizing the parameters of digital second-order PLL's is presented. Numerical examples, based on theoretical analysis and computer simulation, are provided for two specific formats in the CPM class: tamed frequency modulation (TFM) and a quaternary raised-cosine (RC) modulation.

Symbol rate estimation by the wavelet transform

Abstract: Demodulation of a digital modulated waveform requires the symbol rate of a received signal. This parameter may not be known a priori and may need to be estimated in the receiver. This paper studies the use of wavelet transform to estimate the symbol rate of an M-ary phase shift keying (PSK) signal. The idea is to use wavelet transform to locate the transients produced from phase changes. The separation between transients gives a symbol rate estimate. Previous work uses the transform coefficients in a single scale to estimate symbol rate. This paper improves the performance of the estimator by combining the coefficients at several scales before estimation. The accuracy of the estimator is shown to be within 3-6dB of the CRLB, when the sampling rate is four times the carrier frequency and the carrier-to-noise ratio is greater than 7 dB.

Joint phase and timing recovery with CPM signals

Abstract: We describe joint carrier phase and timing recovery algorithms for CPM signaling. They may be employed with any CPM format, and with either full or reduced state detectors. Their implementation is fully digital, and involves a limited computational complexity. Simulation results show that these algorithms have excellent tracking performance. When operated in their simplest form, however, they may exhibit false locks. In particular, this occurs with multilevel and partial response formats. A simple solution to the false lock problem is proposed.

Transmitter for qam encoded data

Abstract: Quadrature Amplitude Modulated signals are generated from data bits by using a first Quadrature Phase Shift Keying (QPSK) modulator for encoding a first pair of the data bits into one of four carrier signal phases, thereby producing a firs QPSK signal. A second QPSK modulator encodes a second pair of the data bits into one of four carrier signal phases, thereby producing a second QPSK signal. The first QPSK signal is amplified to a first power level, and the second QPSK signal is amplified to a second power level. The first and second amplified signals are then combined to produce a signal in which four data bits are encoded. In another aspect of the invention, a new type of modulation, called Offset Quadrature Phase Shift Keying (OQPSK), is used in place of the first and second QPSK modulators, so that an Offset Quadrature Amplitude Modulation (OQAM) transmitter is formed. An OQPSK modulator encodes data bits by encoding a first sub-group of the data bits into a real part of a complex signal at an odd instant of a clock, and by encoding a second sub-group of the data bits into an imaginary part of the complex signal at an even instant of the clock. OQPSK modulation provides the benefit of having all signal transitions being constrained to trajectories around constant radius circles, thereby producing spectral efficiency.

Joint phase and timing recovery with CPM signals

Abstract: We describe an algorithm for joint timing and carrier phase recovery with CPM signaling. The proposed method may be employed with any CPM format and with either full or reduced state detectors. It can be implemented in digital form with a limited computational complexity. Simulation results show that its tracking performance is excellent. However, when operated in its simplest form, it may exhibit false locks during acquisition. In particular, this happens with multilevel partial response formats. A simple solution to false locks is proposed.

MLSE and soft-output equalization for trellis-coded continuous phase modulation

Abstract: This paper presents two equalizer structures for trellis-coded continuous phase modulation (TC-CPM) on multipath fading intersymbol interference (ISI) channels. An equivalent discrete-time (DT) model is developed by combining the tapped-delay-line (TDL) model of the frequency-selective channel and by oversampling at the receiver. The (noninterleaved) fractionally spaced maximum-likelihood sequence estimation (MLSE) equalizer performs continuous phase modulation (CPM) demodulation, trellis-coded modulation (TCM) decoding, and channel equalization by exploiting the finite state nature of the ISI-corrupted TC-CPM signal. Both simulation and analytical results show diversity-like improvement when performing joint MLSE decoding and equalization. For the interleaved soft-output equalizer, the soft symbol metric is delivered to the TCM decoder by using a forward and backward recursion algorithm. Three variants of the soft-output equalizer are examined. We conclude that the backward recursion is essential to partial response CPM schemes, and with moderate complexity, the soft-output equalizer can have a substantial advantage over a noninterleaved MLSE equalizer.

Comparison of Phase Rotation, Phase Spectrum, and Two-Dimensional Correlation Methods in Step-Scan Fourier Transform Infrared Photoacoustic Spectral Depth Profiling

Abstract: This paper compares three photoacoustic phase-related analytical approaches for spectral depth profiling of heterogeneous materials, particularly in conjunction with step-scan Fourier transform infrared spectroscopy. The three approaches compared are (1) the phase rotation method, (2) the direct analysis of the phase spectrum, and (3) the calculation of two-dimensional (2D) frequency correlation maps. The experimental data for a representative two-layer sample consisting of a 12-μm-thick layer of ethylene−vinyl acetate on a 60-μm-thick polypropylene substrate are compared for the three approaches. Similar/identical phase difference information can be obtained from either the continuous phase rotation plot or the phase spectrum. However, the phase spectrum method provides more accurate, direct, and efficient results with a higher depth resolution than does the phase rotation method. Qualitative agreement between the 2D correlation analysis and the photoacoustic phase analysis is observed, although the 2D a...

Frequency discriminator and method and receiver incorporating same

Abstract: Apparatus and method for digital frequency discrimination are provided that only require one sample per data symbol (e.g. one bit for BPSK or 2 bits for QPSK). This is accomplished by determining the difference between the carrier phase error on successive data symbols. The difference in phase error is then used as an approximation to the derivative of the phase error, which is the frequency error between the carrier and the local oscillator of the receiver. An important advantage of this apparatus and method is that they allow the maximum symbol rate to be processed by the receiver for a given digital technology. In other words, maximum symbol rate can now be equal to the maximum clock rate of the digital technology, if so desired by the user. In contrast, conventional digital frequency discriminators limit the maximum symbol rate to one-half or one-fourth of the maximum clock rate for a given digital technology. A key feature is the use of a threshold apparatus and method that allows the discriminator to ignore phase shifts that are due to data modulation, and only use phase shifts that are due to carrier frequency errors. Thus, when successive data symbols are identical, frequency error information can be obtained for carrier recovery. When successive data symbols are different, no updates are made to the carrier recovery. This allows a carrier recovery loop to operate at a rate of one sample per data symbol.

Digital frequency synthesizer/modulator for continuous-phase modulations with slow frequency hopping

Abstract: This paper gives a description of a modulator for burst-by-burst carrier frequency hopping in time-division multiple-access (TDMA) systems. The architecture consists of a digital frequency synthesizer/modulator for continuous-phase modulations (CPMs) and a fast frequency settling RF synthesizer consisting of one phase-locked loop (PLL). The performance of the digital frequency synthesizer/CPM modulator has been analyzed theoretically and simulated by a computer program. The analyses show that the proposed digital frequency synthesizer/CPM modulator achieves 2.5-W lower power consumption and 18-dB lower spurious levels than the fast frequency hopping systems synthesizing digitally a full frequency band. In the computer simulations the effect of the digital frequency synthesizer/CPM modulator parameters on the power spectrum and the phase error is investigated.

Method and apparatus for performing digital data signal modulation

Abstract: The present invention includes a method for generating a GMSK modulating signal from a serial digital data bit stream whereby the GMSK modulating signal modulates a carrier frequency signal associated with a GMSK transmitter of a digital communications system. Specifically, the method includes converting each set of m consecutive data bits of the bit stream into a parallel symbol, whereby there are 2 m possible symbols. Each symbol is generally defined as (B - (m-1). . . B 0 ), where B 0 is the current data bit and B - (m-1) is the mth previous data bit with respect to B 0 . Next, a corresponding phase advance is assigned to each of the 2 m symbols, each phase advance being substantially equivalent to a percent phase advance contributed by the m consecutive data bits of each symbol. Also, four corresponding accumulated phases are assigned to each of the 2 m symbols, each accumulated phase being derived from a multiple of 90 degrees. Still further, digitally represented waveform portions are stored in a memory unit, each waveform portion respectively representing a time varying waveform that advances in phase by an amount respectively equal to each of the four accumulated phases. Next, the phase advance assigned to the current symbol is added to the phase advance accumulated from the previous symbol to yield a current accumulated phase for the current symbol. The memory unit is searched for the waveform portion that corresponds to the current accumulated phase and the portion is then outputted from the memory unit. The adding, searching and outputting steps are performed for each data bit of the digital data bit stream to form a digital representation of the GMSK modulating signal.

Laboratory experimental results of an adaptive modulation/TDMA/TDD for wireless multimedia communication systems

Abstract: This paper reports laboratory experimental results of a time division multiple access/time division duplex (TDMA/TDD) based adaptive modulation system to verify feasibility and its usefulness for future wireless multimedia communication systems. The developed system employs a symbol rate and modulation level controlled adaptive modulation in which the modulation scheme is selected from full-rate 64-ary quadrature amplitude modulation (64 QAM), full-rate 16 QAM, full-rate quaternary phase shift keying (QPSK), 1/2-rate QPSK, 1/4-rate QPSK, 1/8-rate QPSK and no transmission according to the expected channel condition for the transmitted signal. The experimental results confirm that the developed system is very effective in achieving high quality and high bit rate transmission of around 1 Mbit/s without any special anti-frequency selective fading techniques even under frequency selective fading conditions with its d delay spread of less than 250 ns and f/sub d/ of less than 10 Hz.

Synchronization algorithms for wireless data transmission using orthogonal frequency division multiplexing (ofdm)

Abstract: Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation method which provides efficient bandwidth utilization and robustness against multipath delay spread. In an OFDM system, finding the symbol timing, the carrier frequency offset, and the sampling rate offset at the receiver is important in the recovery of the signal. Synchronization methods are needed which will work well for signals passing through frequency selective channels with large delay spreads. This thesis presents methods to acquire synchronization for either a continuous stream of data as in a broadcast application or for a burst of data as in a wireless local area network. The ratio of the number of overhead bits for synchronization to the number of message bits must be kept to a minimum, and low-complexity algorithms and rapid acquisition are needed. The carrier frequency offset can be many subcarrier spacings, so a large carrier frequency acquisition range is necessary. A general method using two training symbols is presented and analyzed. First the symbol/frame timing is found by searching for a symbol in which the first half is identical to the second half in the time domain. Then the carrier frequency offset is partially corrected, and a correlation with a second symbol is performed to find the carrier frequency offset. This carrier frequency offset estimate is shown to approach the Cramer-Rao lower bound for variance. The symbol timing estimate can be refined after the frequency correction by using matched filtering in the time domain to determine the channel impulse response. Simulations are presented over three types of channels to compare several symbol timing estimators. The maximum likelihood estimator for the sampling rate offset is presented. This can be used if there will be a large enough offset to cause a degradation in the received signal. Another contribution is a synchronization method requiring no training data. This could be useful for systems with simple constellations such as QPSK.

Direct 2nd derivative synthesis method for controlling sidelobe energy in an MSK modulated signal

Abstract: A method for generating minimum shift keying (MSK) modulation signals with relatively reduced energy sidelobes relative to known methods. In one embodiment, a second derivative of the phase waveform is taken and convolved with a selectable smoothing function and integrated twice to generate a smooth phase waveform S2D -- MSK (i)=where .o slashed. (i)=π i d(i)/2T. In the alternate embodiment, the sidelobe energy can be varied by simply changing the smoothing function, which can be stored in a lookup table. In the embodiment, the MSK modulation signal has a constant amplitude envelope allowing it to be transmitted using class C amplifiers. Since the embodiment provides continuous phase derivatives, the frequency and thus the sidelobe energy is sufficiently reduced to minimize interference with cosite equipment and nearby communication channels bands.

Cochannel Receivers for CPM Signals Based Upon the Laurent Representation

Abstract: In this paper, we develop optimum and suboptimum receivers for jointly detecting two cochannel continuous phase modulated (CPM) signals. These receivers are based upon Laurent’s representation of binary CPM as the sum of a finite number of pulse amplitude modulated signals. We also provide a review of the Laurent representation and its application to the design of optimum and suboptimum single-channel receivers.

Method of and apparatus for modulation of FSK carrier in a very narrow band

Abstract: A method and a transmitter system is provided for modulating binary information on a frequency shift keying carrier in a very narrow band. Phase reversal keying is initially used to create a carrier. The transmitter of the present invention generates a carrier signal by modulating a reference signal and a control signal having two frequencies representing the binary data to be transmitted. The resulting phase reversal carrier signal is processed by high order filtering such that the output of the transmitter provides a frequency shift keyed carrier at very close frequencies. The resulting carrier signal may, at the receiver, be processed by very narrow band filtering so as to create a communication system which will use only a small part of the available spectrum.

Continuous phase modulation digital communication system

Abstract: A digital communication system having a transmitter and a receiver. The receiver transmits a radio-frequency (RF) signal that is continuous phase modulated by digital data. The receiver having a converter, a differential detector, and a sequential decoder. The receiver receives the RF signal. The RF signal is converted into a baseband signal by the converter. The baseband signal is received by the differential detector wherein the continuous phase modulation of the baseband signal is detected. The detected signal is received and the digital data is decoded by the sequential decoder. The sequential decoder has a Viterbi decoder to compensate for intersymbol interference caused by the differential detector. The Viterbi decoder performs reduced Viterbi decoding utilizing a feedback loop (FB) for reducing computing inaccuracies due to the reduction of the number of trellis states.

Blind receivers for nonlinearly modulated signals in multipath

Abstract: Classical blind channel equalization methods may not be suitable for systems with nonlinear modulation (e.g. continuous phase modulated signals) because the input to the channel may not be i.i.d. due to the modulator's memory. Moreover, the nonlinear characteristics of the modulator further complicates the channel estimation task. In this paper, we derive blind maximum likelihood channel estimation algorithms for nonlinearly modulated signals, using a hidden Markov model formulation. The novel algorithm is based on a modified Baum-Welch procedure. The proposed method implements a stochastic maximum likelihood approach and is well suited for short data records, appearing in TDMA systems. Cramer-Rao bounds are derived, and some illustrative simulations are presented.

A 2 V 100 MHz CMOS vector modulator

Abstract: For digital wireless communications, precise phase and amplitude control in carrier modulation is essential to achieve efficient spectrum utilization. In contrast to the conventional I-Q vector modulator, this phase-amplitude vector modulation method can generate a high intermediate-frequency (IF) modulated carrier. A high IF carrier mitigates the design specifications for the radiofrequency (RF) front-end of a heterodyne radio transceiver. This type of modulation is especially suitable for circuit realization of constant-envelope phase modulation schemes that do not require amplitude modulation, such as the Gaussian filtered minimum shift keying (GMSK). The authors present a modulator chip implementing this technique. This chip uses a standard 0.6 /spl mu/m single-poly, double-metal digital CMOS process, and operates with a single 2 V supply.

Transient deformation measurement using dual-pulse addition ESPI

Abstract: An electronic speckle pattern interferometry system based on a frequency-doubled twin Nd:YAG laser emitting dual pulses at a TV camera field rate (50 Hz) was developed to analyze addition fringes generated by transient deformation of a test object. The main advance has been the automatic, quantitative analysis of dual-pulsed addition ESPI data by the introduction of carrier fringes and the application of Fourier methods. The carrier fringes are introduced between dual pulses by tilting the reference beam with a mirror driven by a galvanometer. The resulting deformation-modulated addition fringes are enhanced with a variance filter before evaluation of the phase distribution using a Fourier transform method with bandpass filtering. From the wrapped phase distribution, a continuous phase map is reconstructed using an iterative weighted least- squares unwrapper. The linear phase distribution associated with the carrier fringes is removed by evaluating it with a least-squares fitting algorithm. Preliminary results obtained for a thin plate submitted to an acoustic shock show the suitability of the system for the quantitative evaluation of transient deformation fields.

A design technique for spectral shaping in CPM systems

Abstract: We describe a technique of pulse shaping able to control the power spectral density of a full-response CPM signal in various frequency ranges, under the constraint of a prescribed minimum Euclidean distance. Some examples illustrating the potentialities of the method and some comparisons with standard pulses are presented.

High data rate UHF satcom

Abstract: Users of UHF satcom require higher data rates to support today's sophisticated C4I mission planning and execution methods that are associated with the digital battlefield of the war fighter. Unfortunately, the UHF satcom channel has characteristics which prevent the implementation of advanced modulation techniques developed in the commercial industry. As an example, the QAM modulation format of cable modems cannot be transmitted through the limiters in the UHF satellites because it does not have a constant waveform envelope. For optimum UHF satellite transponder performance, the modulation must have a constant envelope. This paper discusses modulation formats that have a constant envelope and a bits/Hertz performance much closer to Shannon's (1949) limit than the current waveforms on UHF satcom. A set of waveforms is presented which is compatible with the UHF satcom specifications and provides the desired data rate improvement without requiring additional bandwidth. These waveforms allow a doubling of the current data rates without requiring additional bandwidth. In many applications these increased data rates are available without increased transmitter power.

Optimal Chip Waveforms for DS-CDMA with Generalized OQPSK Modulation

Abstract: The effect of chip waveform shaping on both the error and spectral performance of DS-CDMA communication systems using generalized offset quadrature modulation formats is investigated A solution to the problem of optimizing the chip waveform shape to achieve minimum multiple access interference variance at a given in-band power bandwidth occupation and with a continuous phase constraint is presented Several design examples with various bandwidth occupancies are used to illustrate the gains achieved by the optimized chip waveforms over other conventional modulation schemes such as OQPSK and MSK

Reduced-complexity detection and phase synchronization of CPM signals

Abstract: Based on an extension of Laurent (1986) decomposition of continuous phase modulation (CPM) signals into a sum of linearly modulated components, we derive a class of reduced-complexity maximum-likelihood (ML) coherent detection and closed-loop phase synchronization schemes. The complexity of the resulting detection schemes is significantly reduced with respect to that of optimal coherent receivers with negligible performance loss. This result extends a known one valid for the binary case to multilevel CPM. The proposed synchronization schemes are perfectly suitable to be used in conjunction with these receivers.

Power line carrier communication system, power line carrier communication equipment used for the system, frequency mutual converter and power line characteristic detector

Abstract: PROBLEM TO BE SOLVED: To provide a power line carrier communication system in which different frequencies are communicated even when communication is made to pluralities of power line carrier communication equipments in different carrier frequencies in matching with the frequency characteristic of power lines. SOLUTION: The system is provided with a frequency mutual converter 1 that is placed between a power line carrier communication equipment 2 that applies narrow band modulation (phase modulation and amplitude modulation or the like) to communication data and makes communication at a frequency f1 via a power line and other power line carrier communication equipment 3 that applies narrow band modulation (phase modulation and amplitude modulation or the like) to the communication data and makes communication at a frequency f2 via a power line and communication can be executed by converting the signal in the carrier frequency f1 into the signal in the frequency f2 and the signal in the carrier frequency f2 into the signal in the frequency f1. COPYRIGHT: (C)1999,JPO

Efficient estimation of continuous phase modulation with unknown carrier phase

Abstract: An efficient algorithm is presented for the estimation of continuous phase modulation (CPM) sequences over the Gaussian channel with unknown carrier phase. It operates on the excess phase trellis like the Viterbi algorithm, except that it is not a maximum-likelihood (ML) estimator. Its decision metric for survivor selection at each node is chosen so that it achieves the node error event probability of coherent ML estimation in the limit as the carrier phase remains constant over a long interval, so that the observation interval for forming the metric can be made large. It is shown for the case of minimum-shift-keying (MSK) that the bit-error probability (BEP) of perfectly coherent ML estimation is attained.

A decision-feedback phase-tracking receiver for continuous phase modulation

Abstract: In this letter, a new recursive structure of a decision-feedback (DF) phase-tracking receiver for continuous phase modulation (CPM) is derived. This receiver uses the previously detected symbols to continuously estimate the initial phase in the current symbol and thus makes optimum coherent detection. The theoretical and simulation analyses of the error performance are given. It is shown that the BER performance of binary continuous phase frequency-shift keying (2CPFSK) and raised cosine (2RC) with a small modulation index is very close to the ideal bound, and the BER performance of GMSK is better than any previously known noncoherent detection.

Laser phase conversion using continuous distributed phase plates

Abstract: Energy-efficient laser phase conversion, using fully continuous distributed phase plates, has been achieved for solid-state laser drivers in ICF. Optical lithography has been demonstrated to be an excellent means of generating deep, continuous surface-relief structures in photosensitive materials that subsequently are replicated with embossing or etching techniques. In addition, the method of simulated annealing has been shown to be a superior technique for designing continuous phase plates to control the focal-plane profile.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Polynomial minimum shift keying modulation: simplified decoding of CPM signals

Abstract: In this work we introduce the so called polynomial minimum shift keying (PMSK) modulation as a particular case of continuous phase modulations (CPM), the standard used in GSM or DECT systems. The demodulation is based on the high order ambiguity function and leads to simple implementations essentially based on FFT. The most important feature of the demodulation process of PMSK signals is Doppler tolerance and the capability, under some bandwidth constraints, for blind equalization for transmissions over multipath fading channels. The price paid is essentially in terms of oversampling and increased modulation indices to obtain satisfactory performance.