Showing papers on "Continuous phase modulation published in 1998"

Linear amplification systems and methods using more than two constant length vectors

Abstract: An input signal of varying amplitude and varying phase is converted into more than two signals of constant amplitude and controlled phase. Each of the more than two signals of constant amplitude and controlled phase is then separately amplified in separate amplifiers. The separately amplified more than two signals of constant amplitude and controlled phase are then combined to produce an output signal that is an amplification of the input signal at the desired power level. When converting the input signal into more than two signals, the phase of each of the more than two signals of constant amplitude and controlled phase is controlled to produce the output signal that is an amplification of the input signal at the desired power level. According to another aspect, a signal of varying amplitude and varying phase is generated from a plurality of constant amplitude varying phase signals, the sum of which is the signal of varying amplitude and varying phase. An IQ waveform generator generates a cosine carrier modulation waveform I(t) and a sine carrier modulation waveform Q(t) from the signal of varying amplitude and varying phase. A function generator generates a complimentary waveform Q′(t) from the cosine carrier modulation waveform I(t) such that the sum of squares of I(t) and Q′(t) is constant. A first modulator modulates a cosine carrier signal with I(t) to obtain a first modulated cosine carrier. A second modulator modulates a sine carrier signal with Q′(t) to obtain a first modulated sine carrier. A circuit such as a butterfly circuit forms the sum and difference of the first modulated cosine carrier and the first modulated sine carrier to obtain the constant amplitude varying phase signals.

Comparison of single-carrier and multitone digital modulation for ADSL applications

Abstract: Single-carrier modulation such as quadrature amplitude modulation (QAM) or carrierless amplitude modulation-phase modulation (CAP), and DMT are alternative techniques for providing digital communication in a variety of applications, in particular ADSL for communication over the telephone company subscriber lines. Although theory predicts comparable performance under ideal implementations, a definitive comparison of performance over a wide range of conditions will require more experience from field trials. Similarly, accurate comparison of implementation costs must await the greater availability of commercial-grade devices. However, enough is now known about these modulation schemes to compare their inherent similarities and differences in performance and cost. Overall, a present view of single-carrier and multitone modulation indicates comparable performance with some differences depending on the type of degradation. Costs should also be approximately equal, with multitone having some advantage in digital processing, but requiring greater cost in analog circuitry.

Method and apparatus for improved ranging

Abstract: A high resolution ranging method is described utilizing a novel modulated waveform, hereafter referred to as coherent burst modulation. In the coherent burst method, high frequency modulation of an acoustic or electromagnetic transmitter, such as a laser, is performed at a modulation frequency. This modulation frequency is transmitted quasi-continuously in the form of interrupted bursts of radiation. Energy from the transmitter is directed onto a target, interacts with the target, and the returning energy is collected. The encoded burst pattern contained in the collected return signal is detected coherently by a receiver that is tuned so as to be principally sensitive to the modulation frequency. The receiver signal is processed to determine target range using both time-of-flight of the burst envelope and phase shift of the high frequency modulation. This approach effectively decouples the maximum unambiguous range and range resolution relationship of earlier methods, thereby allowing high precision ranging to be conducted at arbitrarily long distances using at least one burst of encoded energy. Performance of such method and apparatus is significantly improved through use of phase alternation methods that compensate for non-ideal behavior of the ranging apparatus or of the target and its environment. Such phase alternation methods may be achieved by varying the phase of the transmitter or receiver channels. Moreover, methods for reduction of potential uncertainty in absolute range measurement are taught that make use of coherent signal components at twice the nominal modulation frequency.

Feedforward carrier frequency estimation with MSK-type signals

Abstract: We propose a non-data-aided technique for the estimation of the carrier frequency offset in minimum-shift keying (MSK)-type modulations. The proposed algorithm has a feedforward structure and is suited for burst-mode transmissions. Computer simulations are used to assess its performance and make comparisons with other existing methods in terms of estimation accuracy and minimum operating signal-to-noise ratio (threshold). Numerical results are provided for modulation schemes of practical interest such as MSK and Gaussian MSK.

Noncoherent sequence detection of continuous phase modulations

Abstract: In this paper, noncoherent sequence detection (NSD) proposed Colavolpe and Raheli (see Proc. IEEE Int. Conf. Commun. (ICC '97), Montreal, p.21-5, 1997, IEEE Commun. Lett., 1998, and Proc. IEEE Intern. Conf. Commun. (ICC '98), Atlanta, GA, USA, p.438-43, 1998) is extended to continuous phase modulation (CPM). CPM is treated here jointly with linear modulations with intersymbol interference (ISI) since it is mathematically equivalent to a sum of ISI-affected linearly modulated components, according to Laurent (1986) representation. We first consider combined noncoherent sequence detection and decoding of coded linear modulations in the presence of ISI. The results we then extended to the case of M-ary CPM signals. The proposed sub-optimal detection schemes have a performance which approaches that of coherent detection with an affordable level of complexity. The robustness of noncoherent sequence detection schemes to phase noise is also demonstrated.

Adaptive modulation system

Abstract: PROBLEM TO BE SOLVED: To prevent a signal transmission efficiency from being deteriorated by making a modulation signal the most likelihood estimation in a receiver side without transmitting any control signal in a transmitter side in an adaptive modulation system that is applicable to a mobile communication system or the like and where only a modulation index is changed based on a channel power gain especially. SOLUTION: A modulation index estimate section 110 calculates a square error of a minimum distance among respective distances between respective signal points to be received in a modulation index for every modulation index and signal points of a received signal. A reception power measurement device 109 measures a reception power level of the received signal. The modulation index estimation section 110 calculates a value obtained by calculating a weight calculated from a switching power level to switch the modulation figure and the reception power level for the square error calculated for the every modulation index as a likelihood value for the every modulation index. Then, the modulation index estimate section 110 estimates a modulation index corresponding to the most likelihood value among the likelihood values for the every modulation index as the modulation index of the received signal.

A comparison of CAP/QAM architectures

Abstract: Recently CAP modulation (Carrierless Amplitude and Phase modulation) has been of wide interest to industry because of its simplicity, bandwidth efficiency and zero dc component. This paper compares CAP versus QAM modulation and highlights some practical implementation issues. In addition, three different CAP-like architectures are compared according to A/D sampling-rates, A/D resolutions and jitter requirements.

Optical disk with a groove for defining serial data modulated into a signal using phase and frequency modulation

Abstract: In an optical disc manufacturing method and an optical disc device, when serial data are subjected to phase modulation and then subjected to frequency modulation to trace a groove, in modulated signals based on phase modulation corresponding to the first half portion and the last half portion of each bit of the serial data, the phase modulation is performed so that the period of the logic “1” and the period of the logic “0” are equal to each other. In the modulated signals based on the frequency modulation, the number of the frequency cycles corresponding to the respective logic levels are equal to each other.

Carrier phase derived symbol timing

Abstract: A method and apparatus for symbol timing initialization in a multi-carrier receiver. The method uses phase measurements from a plurality of the individual carriers to make an initial determination of the symbol boundary. The method measures the phases of two carriers, preferably the pilot carrier and one adjacent carrier, and, after compensating for phase distortion associated with modulation of data onto the carrier and phase distortion imposed on the carriers by the channel, determines the symbol timing based on the phase difference between the two carriers. Because a sampling offset results in a phase offset from bin to bin of a DFT, an examination of the extent of the phase offset between two known symbols yields the sampling offset, and thus the symbol frame index.

Noncoherent sequence detection of CPM

Abstract: Schemes in which noncoherent sequence detection based on the Viterbi algorithm are proposed for linearly modulated signals transmitted over additive white Gaussian noise channels, have recently been proposed by the authors. These schemes are attractive because their performance closely approaches that of coherent receivers with acceptable complexity, and they avoid the drawbacks of phase-locked loops. The authors extend these results to M-ary continuous phase modulation (CPM) signals.

Optimal and suboptimal symbol-by-symbol demodulation of continuous phase modulated signals

Abstract: In applications requiring soft-decision metrics, eg, systems with interleaved coded modulation, symbol-by-symbol detection is preferred to sequence detection This paper develops the optimum soft-output algorithm (OSA) for the demodulation of continuous phase modulated (CPM) signals Since this optimum detector is computationally complex, a class of suboptimum symbol-by-symbol detectors, called the reduced state soft-output algorithm (RS-SOA) is developed By varying certain parameters, the RS-SOA offers an effective tradeoff between performance and complexity, as measured by arithmetic operation count and the number of integrators required Additionally, some simple complexity reduction schemes can be used in conjunction with the OSA and the RS-SOA The properties of the OSA and the RS-SOA, and the various complexity reduction schemes are explored in an extensive simulation study

Coarse frequency synchronization in multicarrier systems

Abstract: A method and apparatus provide coarse frequency synchronization compensating for a carrier frequency deviation from an oscillator frequency in a demodulation system capable of demodulating a signal having a frame structure with at least one useful symbol and a reference symbol which is an amplitude-modulated sequence. A received and down-converted signal undergoes amplitude-demodulation to generate an envelope that is correlated with a predetermined reference pattern to determine the carrier frequency deviation. Finally, the oscillator frequency is controlled based on the carrier frequency deviation. The reference symbol may comprise two identical sequences. In this case, the envelope obtained by the amplitude-demodulation has two portions which are based on the identical sequences. One of the portions of the envelope is correlated with the other one of the portions in order to determine the carrier frequency deviation. The oscillator frequency is controlled based on the determined carrier frequency deviation.

A joint Viterbi algorithm to separate cochannel FM signals

Abstract: This paper presents a method for separating cochannel FM signals. We show that the Viterbi algorithm, traditionally limited to estimation of digital sequences, can jointly track analog FM signals by separately quantizing the derivatives of their instantaneous frequencies. We employ per-survivor processing in the trellis to estimate unknown channel effects. The approach works well when the signal to interference ratio (SIR) is less than or equal to zero, in contrast to conventional interference suppression algorithms that degrade as the SIR approaches zero and fail catastrophically when the SIR<0. Comparisons of mean squared error (MSE) between the estimates and the true signals are given for varying SIR, SNR, Doppler offsets, and frequency deviations. The same approach can also be used for any other continuous phase modulation scheme, such as continuous-phase frequency-shift keying (CPFSK).

Modulation and processing gain tradeoffs in DS-CDMA spread spectrum systems

Abstract: Continuous phase modulation (CPM) schemes are examined for use in DS-CDMA spread spectrum systems. Since the power spectra of CPM schemes are narrower than BPSK schemes, a larger processing gain can be used for the same overall bandwidth after spreading. The processing gain, relative to BPSK, that can be used with CPM is calculated. As an example, it is shown that the performance of an MSK system is better than a BPSK system for an equivalent overall bandwidth.

Multi-frequency S2FTIR PA spectral depth profiling by use of sinusoidal phase modulation and harmonic demodulation up to 2250 Hz (10th harmonic)

Abstract: Multi-frequency phase modulation for step-scan Fourier transform infrared photoacoustic spectroscopy (S2FTIR PAS) is demonstrated using a single frequency sinusoidal modulation of the interferometer movable mirror with modulation amplitude 5.2 λHe-Ne. A digital signal processing (DSP) lock-in amplifier is used to demodulate the photoacoustic response at the fundamental phase modulation frequency and its harmonic frequencies. Because the phase modulation is sinusoidal and of the appropriate amplitude, all the even and odd harmonics (up to the 10th harmonic) can be detected with good signal-to-noise ratio (SNR). Applications of this multi-frequency phase modulation approach for photoacoustic depth profiling are demonstrated by the study of a simple two-layered polymer sample. The sampling depth multiplexing advantage (as compared to that obtained with other types of phase modulation) is clearly demonstrated with the analysis of the phase and magnitude of signals at the fundamental frequency and all the harmonic frequencies. This is the first report of using the sinusoidal phase modulation method to easily obtain multi-frequency and high-frequency light modulation for FTIR PAS depth profiling. Although these data have been obtained sequentially, it would be possible (with considerable economy of time) to obtain them simultaneously by use of the internal digital signal processing capability of the instrument.

Detection of CPFSK signals using per survivor processing

Abstract: The use of per survivor processing (PSP) is considered in the detection of a continuous phase frequency shift keying (CPFSK) signal. It is shown that PSP can enable the use of a trellis structure for the demodulation that is different from the trellis structure used to generate the CPFSK signal. This allows one to select a receive trellis structure with fewer phases, resulting in a reduced state sequence estimation algorithm. Results are presented using a receive trellis of 3 states to receive binary CPFSK signals with a modulation index, h, of 7/10. The complexity of the receiver is reduced by a factor of 3.3 with minimal performance degradation. An application of this PSP technique is also discussed which enables one to perform maximum likelihood sequence estimation (MLSE) of a digital FM signal, where the modulation index is only approximately known. Results presented for the binary case show this technique to provide a significant detection efficiency advantage over conventional techniques such as limiter-discriminator detection or non-coherent detection.

System and apparatus for designing and producing signalling waveforms for direct-sequence code division multiple access communications

Abstract: A method of identifying direct sequence CDMA pulse shapes which optimize a cost function subject to various constraints. The cost function may either be an acquisition SNR or an interference power. The method may be applied to both full-response pulse shapes and partial-response pulse shapes. The constraints include a quasi-constant envelope constraint, a continuous phase constraint, a spectral nulls constraint, and an ISI-free constraint. The Fourier transform of a desired pulse shape is expressed in terms of a finite sum of prolate spheroidal wave functions. The cost function and the constraints are also expressed in terms of this finite sum. Numerical methods software determines the optimal solution. This may be used to produce finite impulse response filters which generate the desired pulse shape.

On noncoherent sequence detection of continuous phase modulations

Abstract: Based on Laurent (1986) decomposition of a multilevel continuous phase modulation (CPM) as a sum of linearly modulated components, we derive new noncoherent sequence detection algorithms for M-ary CPM signals transmitted over additive white Gaussian noise (AWGN) channels. Noncoherent sequence detection based on the Viterbi algorithm (.) has been proposed for linearly modulated signals. These schemes are attractive because they closely approach the performance of coherent receivers with acceptable complexity. This paper extends previous results and proposes a general structure for noncoherent sequence detection of CPM signals. The robustness of noncoherent sequence detection schemes to phase noise and frequency offset is also demonstrated.

Blind equalization and source separation with MSK inputs

Abstract: Channel equalization and identification appear as key issues in improving wireless communications. It is known that the linearization of the GMSK modulation leads to a continuous phase OQPSK which can be considered as a Minimum SHift Keying (MSK) modulation. Thus methods of equalization and identification when the channel is input by MSK modulated signals is worth to look at. Most algorithms consider MSK signals as two independent white binary PAM staggered signals; this is not the case in our approach. Here, MSK signals are seen, after sampling at baud rate, as colored complex discrete signals. Even if this view of MSK modulation is quite simple, it has never been utilized with purpose of blind equalization. The particular statistics of such signals are studied, yielding an original closed-form analytical solution to blind equalization, both in the monovariate case and in the source separation problem. Simulations show a good behavior of the algorithms in terms of bit error rate as a function of SNR, both in the case of blind equalization and source separation.

Noncoherent sequence detection of M-ary CPM

Abstract: New suboptimal noncoherent sequence detection schemes are proposed for continuous phase modulation (CPM). CPM is treated here as a sum of linearly modulated components, according to Laurent representation.

Blind detection of CPM signals transmitted over frequency-flat fading channels

Abstract: We propose a novel detection scheme for continuous-phase modulation (CPM) signals transmitted over frequency-flat fading channels. Its most significant feature is that it operates without statistical information on the fading channel, and for this reason it is nicknamed "blind detector." Its error-rate performance is assessed with minimum shift keying (MSK) and Gaussian MSK (GMSK) schemes and compared with the performance of other decoders.

Simulation of phase modulation in EDFAs using an extended model

Abstract: Nowadays, erbium-doped fiber amplifiers are described by the rate equations for the population densities and the evolution equations of the optical power propagation in the fiber. Since only the power is considered, phase effects like phase modulation and dispersion are not addressed. Here, we present an extended model using a slowly varying envelope approximation that takes into account dispersion and phase modulation. The phase modulation shifts the carrier frequency to a higher frequency. Due to this effect the impulse experiences in a single-mode fiber a different dispersion and, therefore, it should be included for numerical simulations.

Pulse driven Gaussian minimum shift keying

Abstract: A modification to the classical GMSK waveform is presented. The new waveform, called pulse driven GMSK (PDGMSK), differs from the classical definition in that it converges to SDPSK or DPSK for large filter bandwidths. This allows a trade of spectral efficiency for demodulator complexity. After describing the salient features of PDGMSK, some of its spectral properties are given. It is shown how the bandwidth of the modulated signal remains nearly constant as the symbol rate changes. Some performance results of using PDGMSK with the simplified demodulator structures are given.

Precoded nonlinear constant-envelope modulations

Abstract: Nonlinear constant-envelope digital modulation schemes are attractive in applications where high power efficiency is required. When used in high-rate, band-restricted applications, intersymbol interference (ISI) results and must be compensated to obtain satisfactory error performance. Tomlinson-Harashima precoding has proven attractive in applications with linear modulations such as that in the V.34 standard for high-rate wireline modems. This paper presents results on new techniques for precoding and their performance analysis in additive noise and fading channels. Substantial performance improvement is obtained over systems without precoding and systems with the Tomlinson type of precoding.

Method and device for processing signal and carrier recovery circuit

Abstract: PROBLEM TO BE SOLVED: To provide the improved carrier recovery method and its device that is proper to a format for the quadrature amplitude modulation(QAM), the quadrature phase shift key(QPSK) and other wide variety of modulation systems SOLUTION: The carrier recovery circuit 300 estimates a phase error (denoting a frequency error) between received symbols by means of any of a plurality of technologies A phase and/or a frequency of a received carrier signal is adjusted by using the estimated frequency error and frequency lock is attained This method and device are easily integrated with an existing carrier recovery design thereby supplementing the existing frequency and/or phase error correction technology, and frequency locking is attained in a smaller time in comparison with the case with employing only the known technology and/or in comparison with that a conventional phase detector provides an output of only a comparatively smaller DC component regardless of the presence of a comparatively large frequency offset

Binary PRCPM with differential phase detection and maximal ratio combining diversity in fading channels

Abstract: We derive a formula for the bit-error probability (BEP) of binary partial-response continuous-phase modulation (PRCPM) with N-bit differential phase detection (DPD) in a Rician fading channel subject to L-branch maximum ratio combining (MRC) diversity. We compute the BEP for minimum-shift keying (MSK), Gaussian MSK (GMSK), and 2 RC (2-b-duration raised cosine) frequency signals as a function of the energy-to-noise ratio per bit E/sub b//N/sub 0/ and other system and channel parameters [N=1 and 2 and L=1, 2, and 3, Rician factor K=-/spl infin/, 0, 6, 10, and /spl prop/ dB, Doppler frequency shift f/sub D/T=0, 0.01, and 0.02, Gaussian premodulation filter bandwidth B/sub g/T=/spl infin/, 0.5, 0.25, and the presence or absence of a Doppler frequency tracking loop (DFTL) in the receiver]. In all cases, the BEP is significantly reduced by diversity.

Modulator for modulating digital signals

Abstract: Digital signals are commonly transmitted using the single-carrier method or the multicarrier method, for example. Both methods use one carrier frequency per transmission channel or subchannel of predetermined bandwidth. According to the invention, at least two carrier frequencies (f1, f2, f3) are used to increase the transmission capacity of a channel. The distance between two carrier frequencies is less than the absolute value of a carrier frequency (f1, f2, f3) by a factor of, e.g., 500. The beat frequency resulting from the combination (ADD) of several carrier frequencies (f1, f2, f3) in a channel is negligible, particularly if the transmitted carrier frequencies (f1, f2, f3) are in phase at the start of oscillations. By the combination (ADD) of several carrier frequencies (f1, f2, f3), equal resulting carrier frequencies can be obtained for different bit streams (DATA1, DATA2, DATA3). A suitable distinguishing feature is, for example, the amplitude, the angle setting, or the assignment to additional carrier frequencies.

A receiver for continuous phase modulation in Walsh signal space

Abstract: Many continuous phase modulation schemes, besides the constant envelope feahue, are very attractive for their hi& efficiency both in powa and kquency requirements. However, they are difficult to employ in practice. The main reason is the unacceptable complexity of their receiver. The optimum receiver for CPM requires in general a bank of matched filters. As a consequence? except for certain simple schemes, this makes the receiver too complicated to implernent. In this thesis, a simple yet near-optimum coherent receiver structure for genefal CPM signals traasmitted over an AWGN channel has been developed. The receiver is constmcted based on observing the received signal in the Walsh signal space. By doing so, the requirement of matched filters is elllninated and the fiont end of the receiver is simplified to the hea r receiver structure which is widely used in PSK-type receivers. The pnce paid for the simplification is an increase of sampling rate (2-4 times that of the symbol rate) and more signal processing in the Viterbi decoder. The symbol timing and carrier phase synchronization, a problem associated with any coherent receiver, has also been investigated for the proposed Walsh receiver. A simple, efficient, yet near-optimum algorithm for both separate and joint estimation of symbol timing and carrier phase is developed. It aims to optimize the tracking performance of a synchronizer. The algorithm does not require computation of the derivative of the likelihood hc t ion for the symbol timing estimate and it exhibits excellent steady state performance. In two-dimensional Walsh space, it almost reaches the optimum for binary CPM schemes of practical interest, and is close to optimum for quaternary schemes. The algorithm can dso be used in any other signal space CPM

Multicarrier modulator and demodulator

Abstract: PROBLEM TO BE SOLVED: To provide a multicarrier modulator and demodulator which can improve performance of a reference carrier reproduction, needed for decoding an information carrier. SOLUTION: A data modulation wave I of a multicarrier signal, a main pilot carrier II which is phase synchronized with a reference carrier frequency of the data modulation wave and is in a frequency area different from a frequency band of a data modulation wave, and a sub-pilot carrier III of a frequency twice as large as that of the main pilot carrier II are multiplexed, transmitted and received. The sub-pilot carrier is phase synchronized with the reference carrier frequency. Even under multipath environment in which a direct wave and a multipath wave of the main pilot carrier are in mutually opposite phases relation, the direct wave and the multipath wave of the sub-pilot carrier are in a phase relationship which reinforces each other.