Showing papers on "Continuous phase modulation published in 1990"

Influence of the modulation method on the conduction and switching losses of a PWM converter system

Abstract: The authors explore the dependency of the conduction losses of a bridge leg of a pulsewidth modulation (PWM) power converter system with a high pulse rate on the shape of the phase modulation functions. This is done for modulation methods that are optimized with respect to minimum harmonic current RMS values. The results are compared to the results gained for simple sinusoidal modulation. Besides conduction losses, the switching losses of the electric valves are calculated. The main topic is the determination of those power loss components of a PWM converter system that can be (besides the harmonic losses) influenced by the modulation method selected. As the calculations show, these modulation methods allow a significant increase of the effective switching frequency. The optimal modulation as calculated leads to a reduction of the harmonic power loss in the upper modulation region. Furthermore, due to the frequency modulation the spectrum is spread out to a wider frequency band as compared to operation with constant pulse frequency. >

Theory and design of the liquid crystal TV as an optical spatial phase modulator

Abstract: An expression is derived for the complex amplitude transmittance of the liquid crystal TV (LCTV) and verified experimentally. It is shown that spatial phase modulation is realizable with good linearity, high transmission efficiency, and small intensity distortion. Although the commercial LCTV does not provide a sufficiently large dynamic range for continuous phase modulation, a dynamic range of 2'rr can be obtained by making appropriate changes in the design.

Maximum likelihood sequence estimation of CPM signals transmitted over Rayleigh flat-fading channels

Abstract: A method for the sequential updating of log-likelihood functions for maximum-likelihood sequence estimation is presented. It is shown that, in a general case, this method can be implemented using Kalman filtering techniques. For the special case of Rayleigh flat fading and continuous phase modulation (CPM) signaling, this approach is shown to lead to an attractive receiver structure. This type of receiver, called the linear predictive receiver, can be implemented in the form of the Viterbi algorithm with the trellis updates being computed using a bank of finite pulse response (FIR) filter and square operations. Simulation results are presented that demonstrate the superiority of the linear predictive receiver over receivers employing differential detection, in the presence of fast fading. It is shown that the optimal linear predictive receiver does not possess an irreducible error rate for a class of Rayleigh fading channels used to model terrestrial mobile channels. >

On the spectral efficiency of CPM systems over real channel in the presence of adjacent channel and cochannel interference: a comparison between partial and full response systems

Abstract: In all the new radio systems to be designed-for example, local radio networks or portable communication systems-a crucial point is determination of the actual spectral efficiency obtainable. To this end, the fundamental role played by adjacent and cochannel interference must be considered. The computer program implemented allows general analysis of continuous phase modulation (CPM) systems with limiter-discriminator detection and symbol-by-symbol regeneration, the combined effects of intersymbol interference, noise, and adjacent channel or cochannel interference have been tested to give the design criteria of the transmission system. To emphasize the role played by interference, an ideal multipath-free channel has been considered: with reference to a binary case, Gaussian minimum-shift keying (GMSK) systems have been investigated and compared with full-response CPM systems to obtain a suitable tradeoff between spectral efficiency (connected to channel spacing at radio frequency) and signal-to-noise ratio with fixed bit-error probability. The numerical results presented emphasize the performance obtainable with full- and partial-response techniques for varying system parameters such as phase deviation index, receiver filter bandwidth, and spectral efficiency. >

Modulation and coding for satellite and space communications

Abstract: Several modulation and coding advances supported by NASA are summarized. To support long-constraint-length convolutional code, a VLSI maximum-likelihood decoder, utilizing parallel processing techniques, which is being developed to decode convolutional codes of constraint length 15 and a code rate as low as 1/6 is discussed. A VLSI high-speed 8-b Reed-Solomon decoder which is being developed for advanced tracking and data relay satellite (ATDRS) applications is discussed. A 300-Mb/s modem with continuous phase modulation (CPM) and codings which is being developed for ATDRS is discussed. Trellis-coded modulation (TCM) techniques are discussed for satellite-based mobile communication applications. >

Carrier recovery system and digital phase demodulator

Abstract: A carrier recovery system combining a narrow band carrier phase estimator and a wide band carrier phase estimator, and a digital phase demodulator using this carrier recovery system. The narrow band carrier phase estimator extracts a carrier phase having a low pulse slip rate from received signal. This carrier phase, however, cannot track fast phase fluctuation due to fading. On the other hand, the wide band carrier phase estimator tracks fast phase fluctuation due to fading, and extracts a carrier phase from the received signal. From this carrier phase is subtracted the other carrier phase obtained by the narrow band carrier phase estimator, and the balance, after its fluctuating range is limited, is added to the carrier phase obtained by the narrow band carrier phase estimator, thereby making it possible to obtain a carrier phase which can track fast phase fluctuations due to fading without sacrificing the phase slip rate. By using the carrier phase obtained in this manner, there can be structured a digital phase demodulator suitable for mobile communication systems based on coherent detection. If carrier component is extracted by reversely modulating the received signal with reference signal obtained by subjecting to decision the signal demodulated by this digital phase demodulator, a carrier phase is recovered by filtering the extracted carrier component in a wide band, and the received signal is synchronously detected with this carrier phase, the error rate can be further reduced.

Optimum system design for CPFSK heterodyne delay demodulation system with DFB LDs

Abstract: An optimum system configuration for an optical continuous-phase frequency-shift-keying (CPFSK) heterodyne delay demodulation system with distributed feedback laser diodes (DFB LDs) is discussed. The optimum modulation index was determined by evaluating the LD phase noise effect and the IF noise effect. The IF noise effect was investigated in detail, considering the noise conversion effect through delay demodulation. In the case of 10-MHz IF beat spectral width, the modulation index m=1.5 is optimum for a 1.2-Gb/s system. With this optimum modulation index, a 204-km long-span transmission experiment, with -41.5 dBm receiver sensitivity, has been successfully performed. The feasibility of using stand-alone DFB LDs for a high-sensitivity CPFSK delay demodulation system has been confirmed through this experiment. >

Reduced state sequence detection of full response continuous phase modulation

Abstract: A reduced state sequence detector (RSSD) which combines decision feedback with Viterbi decoding is proposed for M-ary full response continuous phase modulation. The detector is analysed with minimum Euclidean distances and by simulations of the symbol error probability. It is shown that M-ary full response CPM schemes can be optimally decoded by a decoder with only two states when the modulation index is relatively small ( >

Probability of error analysis of digital partial response continuous phase modulation with two-bit differential detection and offset receiver diversity in fast Rayleigh fading channels

Abstract: The performance of constant envelope digital partial response continuous phase modulation (PRCPM) with two-bit differential detection and offset receiver diversity is theoretically analyzed in fast Rayleigh fading channels. A simple closed-form expression for the probability of error is derived and evaluated for cases of practical interest to researchers and designers of land mobile radio systems. It is shown that the dynamic bit error rate (BER) performance is considerably improved using the offset diversity scheme. Thus, many PRCPM signals having a compact power spectrum can be used in future digital mobile radio systems. >

Coded and uncoded M-PSK and CPM signals on nonlinear bandpass channels: an approach to a fair comparison

Abstract: The performances of several coded and uncoded M-ary phase-shift keying (M-PSK) schemes and two representative continuous-phase modulation (CPM) schemes are compared on a given nonlinear bandpass channel with adjacent channel interference (ACI). It is shown that, due to their constant envelope, the CPM schemes are not degraded by the nonlinearity and allow saturated operation of the high-power amplifier (HPA). In this case the only degradation is produced by ACI. The PSK schemes are assumed to be filtered with conventional square-root Nyquist filters and are very bandwidth efficient. The results of simulations are presented for 4-PSK, offset 4-PSK, coded and uncoded 8-PSK, minimum-shift keying (MSK), and a four-stage CPM scheme with smoothed frequency impulse (M=4, h=1/2, 3RC). It is shown that coded 8-PSK maintains or improves its gain over 4-PSK in the nonlinear channel, when the operating point of HPA is carefully optimized. MSK suffers mainly from ACI, and for narrow channels it is outperformed even by 4-PSK. The 3RC-CPM scheme shows nearly the same performance as coded 8-PSK. >

Two-wavelength infrared heterodyne transceiver with a continuous phase tracking system

Abstract: We describe the performance of an optical heterodyne sensor with a two‐wavelength coherent infrared beam, which is used to detect the motion of remote targets in a real environment with an unambiguous sensing of the instantaneous direction along the line‐of‐sight propagation path. The initial phase condition of maximum sensitivity of the transceiver is stabilized and held by an active feedback system which drives the phase of the optical field of the local oscillator. The experimental results show that this feedback is particularly useful in reducing the noise generated by low‐frequency environmental disturbances, leaving the signal unaffected when the respective frequency ranges are separated. Under certain circumstances, the signal can be recovered from the noise by the linearizing properties of the phase tracking on the interferometer response. The measurements reported show that the two‐wavelength infrared heterodyne transceiver generates signals which replicate the target vibration exactly up to ampl...

Differential detection of correlative encoded continuous phase modulation schemes using decision feedback

Abstract: The authors generalize a differential detection technique, which was introduced by A. Yongacoglu et al. (1988) for a Gaussian minimum shift-keying (GMSK) scheme, to include any correlative encoded continuous phase modulated (CECPM) signaling format. As in the previous work, the proposed symbol-by-symbol receivers use decision feedback to partially remove the effects of the destructive intersymbol interference (ISI), which corrupts the differentially detected CECPM signal. After achieving wider eyeopening with the decision feedback, the outputs of the two or more differential detectors are used together to further improve the performance. As a typical example of the CECPM family of signals, and because of its excellent spectral characteristics, the new receiver configurations using up to 3-b differential detectors have been applied to a tamed frequency modulation (TFM) signal. Bit-error rate performance evaluation results have indicated that performance improvements of more than 5 dB over the conventionally differential-detected TFM scheme are possible. >

M-algorithm decoding of convolutional code combined with CPM

Abstract: The performance of convolutional codes combined with continuous phase modulation schemes (CC/CPM) with M-algorithm decoding is evaluated by computer simulation. New CC/CPM schemes with a feedback convolutional encoder having, in some cases, better distances than previous CC/CPM which uses a feedforward encoder, are presented. Comparison of CC/CPM and CPM, constrained to the same complexity and bandwidth, shows that the former have a better performance. The simulation results also corroborate the fact that the M-algorithm is far more efficient than the Viterbi algorithm. >

New detection algorithm with reduced complexity

Abstract: A new algorithm for detecting and/or decoding of signals in communication system is presented. The advantage of the proposed suboptimum algorithm with respect to the classical maximum likelihood detection (MLSE) method lies in the significant reduction in computation complexity attainable by associating a reliable information to each received signal. At the same time, the error probability is maintained close to MLSE levels through the proper selection of the reliability information. We describe the application of the proposed algorithm to some interesting cases, such as the detection of continuous phase modulations with and without combined channel coding, detection of Ungerboeck codes, use in conjunction with the Viterbi algorithm. In all cases, a net reduction in computation complexity with respect to the classical MLSE algorithm is achieved.

A phase modulator with gain for microwave millimeter-wave systems

Abstract: A method of achieving phase modulation directly at microwave and millimeter-wave frequencies with concurrent signal amplification is presented. The modulation is achieved with a voltage-controlled oscillator and circulator. The technique is demonstrated experimentally with the generation of a bi-phase coded signal at Ku-band with a signal gain of 10 dB. By cascading multiple VCOs in an injection-locked chain, additional gain and continuous phase variability are possible. A reduction in microwave hardware may be achieved in phase-coding system applications. >

Linear-prediction-aided differential detection of CPM signals transmitted over Rayleigh flat fading channels

Abstract: A receiver structure, called linear-prediction-aided differential detection (LPADD), for detection of continuous phase modulation (CPM) signals with Nyquist III pulse shaping in fast Rayleigh flat-fading channels is presented. This technique was found to be capable of significantly reducing the bit error rate of conventional differential detection (CDD) at high signal-to-noise ratios. The algorithm reduces the phase noise power from the fading process at the differential detector. Therefore, performance benefits are only seen when the phase noise becomes the dominant source of degradation. Simulations showed that with practical predictor lengths the error floor of conventional differential detection can be reduced by more than a factor of 30. >

Frequency selective fading and adjacent channel interference performance of MSK and SFSK

Abstract: The performance of minimum-shift keying (MSK) and sinusoidal frequency-shift keying (SFSK) in adjacent-channel interference and frequency-selective fading is investigated analytically. The receiver system considered uses a sampling detector and hence is suboptimum. In addition to the above impairments, the system model incorporates other disturbances, namely stationary white Gaussian noise, quadrature channel interference, random timing misalignment, and random carrier phases of interfering signals. Results and comparisons are presented for both coupled effects and individual effects of frequency-selective fading, adjacent-channel interference, and quadrature-channel interference. >

Optimization of Optical Components for Optical Computer Systems

Abstract: We analyze several different methods of encoding and calculating optically thin periodic Fourier-transform binary phase gratings and multiple or continuous phase kinoforms for use as e.g. optical fan-out elements in all-optical computing systems. The construction of the gratings and kinoforms is equivalent to the phase retrieval problem which we formulate as a nonlinear optimization problem and solve using different numerical techniques. Typical gratings have very high diffraction efficiency (up to 95%) and high reconstruction accuracy.

Biphase modulaton circuit having continuous phase changes

Abstract: A BPSK modulation circuit for a digital communication transmitter comprising a data generator for generating data, a timing circuit for delaying the data produced from the data generator by timing the data in synchronism with a given pulse, a logic circuit for generating a timing pulse whenever the data from the data generator is inverted, a local oscillator for generating a local oscillating frequency, a phase shifter for shifting the local oscillating frequency to have a phase difference of 90°, a first double balanced mixer for modulating the delayed signal of the timing circuit in synchronism with the 90° phase-shifted signal of the phase shifter, a second double balanced mixer for modulating the timing pulse of the logic circuit in synchronism with the local oscillating frequency of the local oscillator, and a signal mixer (synthesizing circuit) for synthesizing the output signals of the first and second balanced mixers.

Generalized CPM and DPM: digital angle modulation schemes with improved bandwidth efficiency

Abstract: In digital angle modulation schemes the carrier is frequency modulated (continuous phase modulation) or phase modulated (digital phase modulation) by a waveform that is conventionally generated from the data sequence by a linear filtering operation. The concept is generalized by allowing a nonlinear dependence of the modulating signal on the data, making it possible to produce a signal with a narrower spectrum. The design procedure for the waveform is demonstrated for a signal with minimum out-of-band power. It is shown that the increase in bandwidth efficiency can be achieved without compromising the power efficiency of the signal. >

Method and apparatus for measuring phase accuracy and amplitude profile of a continuous-phase-modulation signal

Abstract: A method and apparatus for determining the phase and amplitude accuracy of continuous-phase-modulated signals is described. A modulated RF signal generated by a transmitter is down converted to a relatively low intermediate frequency which is filtered and sampled by a high sampling rate analog-to-digital convertor. a digital signal processor processes the digital signals to produce a measured amplitude function and a measured phase function corresponding to the modulated RF signal. From the measured amplitude and phase functions, an ideal phase function corresponding to the modulated RF signal is calculated and synthesized. The ideal phase function is compared to the measured phase function to determine the phase function from which the modulated RF signal phase error and frequency error are computed.

Viterbi differential detection for binary partial response continuous phase modulation with index 0.5

Abstract: A differentially coherent receiver which uses the Viterbi algorithm is presented. This receiver compensates for intersymbol interference (ISI) and avoids noise enhancement. A phase estimate which takes into account the presence of inherent ISI in the signal is derived. This phase estimate is then used in the decision metric of a coherent receiver. The resulting decision rule can be implemented using the Viterbi algorithm. The complexity of the resulting receiver increases with the duration of observation used by the implicit phases estimator. A simple four-state Viterbi receiver with good performance is obtained when the phase estimate is based on one observable. Simulation results are given. >

Neural net based continuous phase modulation receivers

Abstract: Feed-forward neural nets (NN) are proposed as receivers for partial-response CPM (continuous phase modulation) systems. The approach involves replacing the entire receiver structure, excluding timing recovery, with a neural-net unit whose inputs are time samples of the incoming baseband signals and whose outputs are the decoded symbols. The authors present simulation results for coherent and incoherent NN-based receivers, and compare their performance with the optimum maximum-likelihood (ML) receiver. A performance analysis of NN-based receivers at high signal-to-noise ratio (SNR) is presented. There is an excellent match between the predicted and actual noise in the network at high SNR. It is found that at high SNR the ratio between the output and input noise variance is a constant depending on the number of saturated nodes, the product of the input and output weights, and the temperature parameter of the nonlinearity. >

Coded continuous phase modulation combined with nonuniform mapping and multi‐h scheme

Abstract: The convolutional coding combined with continuous phase modulation (CPM) has been shown as a good tradeoff between coding and bandwidth. This paper proposes the coded CPM with the nonuniform signal constellation and the multi-h scheme to achieve further coding gains over the conventional uniform mapping single-h coded CPM. Using the minimum Euclidean distance, the number of merge events up to a certain depth in the state trellis and the average bandwidth as estimated criteria, the performance of the non-uniform multi-h coded CPM is analyzed. It is found that the nonuniform multi-h coded CPM achieves larger Euclidean distance and diminishes the number of merge events without expanding the bandwidth.

Maximum likelihood carrier phase recovery for coherently orthogonal CPFSK signals

Abstract: ML estimation of carrier phase for coherently orthogonal continuous-phase frequency-shift-keying (COCPFSK) signals is considered. Although the estimator, in general is nonimplementable, its high and low signal-to-noise-ratio approximations both lead to linear readily implementable receiver structures. The high SNR approximation yields a DA receiver, whereas the low SNR approximation yields an NDA receiver. The performance of both receivers in term of bit error probability is analyzed. The existence of an unmodulated component in the sufficient statistical representation of a COCPFSK signal is pointed out, and it is shown how this component enters directly into maximum-like carrier recovery. This leads to interpretation of the NDA receiver as a generalization of the conventional matched-filter envelope-detector receiver. The insights gained here are useful to the problem of ML carrier recovery for Viterbi decoding of continuous phase modulation signals. >

Optimal multi-h phase codes for full response continuous phase signaling

Abstract: Multi-h full response CPM (continuous-phase modulated) signals are analyzed at preselected numbers of states in contrast to the standard method of analyzing them at preselected numbers of modulation indices. Optimal multi-h phase codes which produce the highest minimum Euclidean distance are presented according to the number of states. Three orders of multi-h signaling are considered in the optimal code search. Numerical results are presented for binary CPFSK (continuous-phase frequency shift keying) and binary 1RC (1 raised cosine) signals at number of states from four through 12. >

Data-aided synchronization of M>or=2-ary coherent CPM receivers

Abstract: Simple joint and nonjoint data-aided maximum-likelihood (ML) estimators are derived for the carrier phase and symbol timing at coherent continuous phase modulation (CPM) receivers, which implement 4- or 6-time-limited sinusoidal basis functions. It is shown that, due to the choice of proper basis functions for the signal space, the estimation of symbol timing becomes a special form of phase estimation and leads to a simple synchronizer and that the synchronizers based on this estimation structure work robustly in steady state, even at low signal-to-noise ratios (SNRs). Several approaches to solving the hang-up problem of symbol-timing tracking loops are discussed, and simulation results are presented to show both the steady-state and acquisition performances of the proposed synchronizers. >

Prediction/Cancellation Techniques For Fading Broadcasting Channels = Part I:

Abstract: In this two part paper, a novel approach for reducing the effects of multiplicative noise, such as fad- ing, on the performance of mobile broadcasting trans- mission systems is introduced. The proposed method is based on a noise prediction/cancellation technique and is applied here to Phase Shift Keying (PSK) signals. In a companion paper (I), a more general receiver which employs more than one sample per received symbol and deals with Continuous Phase Modulation (CPM) signalling formats is described. We consider bandlim- ited as well as constant envelope &phase (Quadrature) PSK (QPSK) schemes corrupted by various nonselec- tive, multiplicative fading channels, as is the typical environment in mobile radio applications. By exploit- ing the statistical characteristics of the multipath fad- ing signal and its strong correlation properties, we de- rive a novel sequential receiver structure employing a detection algorithm which identifies the most probable transmitted sequence in the maximum likelihood detec- tion sense. The algorithm has been obtained for both Rayleigth and Rician fading channels. Furthermore, by applying a truncation strategy on the maximum order of prediction employed within the algorithm, a reduced complexity detector is derived. Issues such as imple- mentation complexity versus performance are also dis- cussed. We have evaluated the proposed detection tech- nique for various QPSK schemes operated in channels corrupted by a combination of additive white Gaussian noise (AWGN) and fading. The obtained computer sim- ulation results show that by employing a relatively sim- ple receiver with a prediction algorithm of second or- der, considerable error floor reductions are achieved by the proposed receivers. Furthermore and as a direct re- sult of these error floor reductions substantial Bit Error Rate (BER) improvements (of more than three orders of magnitude) over conventionally detected schemes are obtained.

Frequency Modulation Of Short Laser Pulses As A Method Of Image Transfer

Abstract: It is shown, that the Fourier-processing based modulation of short laser pulses can be successfully used for all-optical image transfer. The proposed system contains a transmitter, where the transferred image modulates the frequency profile of the carrier pulse, and a receiver, where after the reverse processing is restored the original image. The main limitations are discussed. The transfer of binary amplitude and phase images is demonstrated.