Showing papers on "Continuous phase modulation published in 1982"

Analysis of the phase unwrapping algorithm.

Abstract: Several workers have recently proposed digital techniques for high-resolution imaging through the turbulent atmosphere. The basic concept of these algorithms is to calculate and average phase angles of a series of image Fourier transforms to suppress the unwanted atmospheric effects on image resolution. Since computed phase angles contain the ambiguities of integral multiples of 2 pirad, it is necessary to obtain continuous phase curves without the ambiguities before averaging. This process of eliminating the ambiguities is called phase tracking or unwrapping. A similar problem has been discussed by Oppenheim and Schafer and Tribolet in the context of realization of a certain homomorphic signal processing system.

On the minimum Euclidean distance for a class of signal space codes

Abstract: The minimum Euclidean distance for a class of constant envelope phase modulation codes is studied. Bandwidth and power efficient signals with continuous phase are considered. The information carrying phase varies piecewise linearly and the slopes are cyclically changed for successive symbol time intervals, yielding the so-called multi- h signals. It has previously been shown that this class of signals contains bandwidth and power efficient signals when coherent maximum likelihood sequence detection is used. Bounds on the achievable Euclidean distance for signals in the above class are given. Upper bounds are calculated as well as minimum distance results for specific multilevel multi- h signals. It is concluded that quaternary and octal muiti- h schemes considerably outperform the binary schemes. Furthermore in the important small modulation index region, 2-h codes gain the maximum 3 dB. Larger gains are not available by increasing the number of h values.

Partially Coherent Detection of Digital Full Response Continuous Phase Modulated Signals

Abstract: Recently bandwidth efficient constant envelope digital modulation schemes have been shown also to he power efficient, if detected coherently. In this paper the performance of such systems is analyzed for an optimum noncoherent or partially coherent detector, at large signal-to-noise ratios. The considered schemes are M -ary with arbitrary pulse shaping over one symbol interval (full response). The performance is analyzed by means of a parameter called equivalent minimum Euclidean distance, mathematically playing the same role as the minimum Euclidean distance used for coherent detectors. It is shown that noncoherent detectors perform as well as coherent, although the observation interval must be increased.

Minimum Euclidean Distance and Power Spectrum for a Class of Smoothed Phase Modulation Codes with Constant Envelope

Abstract: A class of smoothed phase modulation codes is analyzed in terms of power spectral density and error probability for large signal-to-noise ratios. The signals have constant envelope and the information-carrying phase function is of multi- h partial response continuous phase type. A cyclic variation of modulation index from symbol time interval to symbol time interval is introduced. Coherent transmission and an additive white Gaussian channel are assumed. Both power- and bandwidth-efficient signals are to be found in the above class. Comparisons are made between fixed- h and multi- h systems both for the binary and multilevel cases. Tradeoff is performed between bandwidth and error probability performance for large signal-to-noise ratios. It is concluded that quaternary and octal systems always seem preferable. Increasing the number of modulation indexes from one in the fixed- h case to two in the simplest multi- h case gives performance advantages at the expense of increased system complexity.

System for demodulation of phase-shift keying signals

Abstract: in a system for demodulation of phase shift keying signals with a bandpass filter (6a) adapted to regenerate a carrier wave from a phase shift keying signal, there are provided means (8) for detecting phase variations in the regenerated carrier wave from the demodulated signal (e 1 , e 2 ), and means (8, 6a) for controlling the phase of the carrier wave being passed through the filter (6a) on the basis of the detection output (e c ) of the phase variation detecting means (8).

Error probability of partial-response continuous-phase modulation with coherent MSK-type receiver, diversity, and slow Rayleigh fading in Gaussian noise

Abstract: This paper considers a class of constant-amplitude modulation schemes with good spectral main lobe and tail behavior. Detection is assumed to be coherent and the receiver is of offset-quadrature type, i.e., minimum shift keying (MSK) type, consisting of a linear filter in each quadrature arm followed by simple processing. Analytical error-probability formulas are derived for various modulation schemes and receiver filters for ideal diversity with maximal-ratio and selection combining. Independent slow Rayleigh fading in Gaussian noise is assumed and several numerical examples are given. Asymptotic behavior of the error probability for large signal-to-noise ratios is derived, and the relationship between the degree of smoothing in the partial-response continuous-phase modulation and the asymptotic error probability is shown for fading channels with and without diversity.

PSK Demodulation system having carrier frequency variation compensation

Abstract: A system for demodulation of phase shift keying signals with a bandpass filter tracked to input carrier frequency variation. This system provides means for detecting phase variations in the regenerated carrier wave from the demodulated signal, and means for controlling the phase of the regenerated carrier wave to compensate for the demodulation error owing to input carrier frequency variation.

A method of coding for correlative transmission systems and its application to a continuous phase modulation system

Abstract: To transmit data reliably over band-limited channels, several correlation digital transmission techniques such as continuous phase FSK, and partial response signaling have been developed. The reliability of correlative transmission systems can further be enhanced by utilizing the error correcting codes. However, it is very important to select a coding scheme that is suitable for a given transmission system. This paper proposes an encoding scheme using block code to improve the performance of certain correlative transmission systems whose transmitters' states can be represented by a simple shift register. The Viterbi algorithm is used in the decoding. The detection of symbols and the soft decision for the decoding of the proposed scheme are combined into a single process. The performance of the proposed method is demonstrated through its application to a duobinary FSK system with modulation index h = 0.5. The results indicate that the proposed scheme outperforms the MSK scheme in both the power spectral distribution and the error rate.

AM transmitter with carrier control - using residual carrier value with characteristic value as function of lever for control

Abstract: The amplitude modulated transmitter has a carrier control using the residual carrier value. The value of the carrier is only changed to a given minimum carrier value in the same sense as the level of the modulation signal. This effects an energy saving and improves the characteristics of the transmitter. The carrier is controlled using a characteristic of the carrier value as a function of the level. The characteristic varies from a straight line through the two points where the carrier residual value-level is zero and the maximum carrier value- maximum permissible level. The variation is such that a smaller value is allocated in the range of the most frequently occuring level.

Variable phase system in demodulator

Abstract: PURPOSE:To attain a simple demodulation of a phase modulating wave of the pi/4 system, by multiplying the phase modulating wave by a carrier different from the carrier of the modulation wave by 45 deg. in phase to attain the demodulation, in demodulating the phase modulation wave of the pi/4 system. CONSTITUTION:The differential phase modulating wave (B system input signal) of the pi/4 system corresponding information to a phase difference of an odd number multiple of pi/4 is inputted to multipliers 10, 11. Further, a signal in which shifted by each 45 deg. in phase is applied to the carrier of the transmission side at the other input of the multipliers 10, 11 at the point of time of discrimination. For example, cosine and sine waves of the signal in 1,650Hz (C) is applied to the multiplier to a transmission carrier 1,800Hz (B). The output of the multipliers 10, 11 is discriminated at the discriminating section 14 and the original signal is obtained. In such a way, the demodulation is attained the same as the case of pi/2 system corresponding the phase difference being an integral number multiple of pi/2 to the information.

Relation between power spectrum and phase spectrum of oscillators

Abstract: The single-sideband to carrier power ratio L(f) and the phase fluctuations spectral density Sδϕ(f) are two convenient means of characterising the spectral purity of oscillators, and, for low-modulation indices, numerically Sδϕ = 2L, the letter briefly reviews the fundamental concepts and extends the above relationship to any modulation depth. Theoretical results for frequency modulation by bandlimited white Gaussian noise are presented. Computations are discussed and dimensional aspects have been checked experimentally.

Continuous phase fsk modulation system

Abstract: PURPOSE:To facilitate the application of viterbi algorithm to a demodulating method by making binary input data information correspond to the phase state of a modulated waveform in 1:1 proportion by making its transition into a multiple Markov chain. CONSTITUTION:A binary input data signal is converted into an l-multiple Markov chain on a transmission line and initial phase states of modulated waveforms are made to correspond to the 2 obtained states in 1:1 proportion; and the extent of the frequency shift of each time slot is controlled according to the transition of the input signal so that the phase varies continuously between adjacent time slots. Consequently, error rate characteristics and converging characteristics of an electric power spectrum are both improved and even when an optional modulation index is selected, the number of phase states of modulated waveforms is constant invariably. Further, pieces of information on l elements preceding the initial phase state are obtained, so viterbi algorith is applied easily to a demodulating method.

A Simplified Approach to Direct Sequence Carrier Modulation and its Selection

Abstract: Direct sequence modulated spread spectrum systems are quite similar in many ways to more conventional digital communications systems They employ some form of phase shift amplitude shift frequency shift keying to modulate their carriers and provide the desired spread bandwidth A key consideration, however, is the choice of carrier modulation to provide maximum antijamming margin while operating in nonlinear processing, plus minimizing impact on synchronization and cost/complexity of the modulators, demodulators, and synchronizers required This paper examines the relationships that exist between the various candidate waveforms and shows their common roots Also defined are the criteria that affect the choice of a waveforms, where various implementations are possible

An All Digital Maximum a Posteriori based Synchronizer for MSK

Abstract: A digital joint maximum a posteriori (MAP) symbol synchronizer and phase estimator is realized for minimum shift keying (MSK) modulation. This development permits direct digital implementation of closed loop synchronization and coherent demodulation. Advantages derived from this approach are parameter stability and accuracy with system flexibility and reliability.

Addressing and Modulation for Frequency-Hopping Multiple Access

Abstract: This paper describes the common structure of a large class of frequency-hopping multiple-access address sequences of the so-called "one-coincidence" type. We show methods for expanding the address sets to great size without compromising performance, and compare frequency and phase modulation methods. We also describe methods for dealing with unsynchronizable signalling alphabets, which arise as a result of expanding the MFSK sets.

The design and implementation of Biphase Costas Loop

Abstract: At present, transmitting data or digital message in carrier band via digital modulation such as digital radio has become more and more popular, and the various digital modulation techniques most oftenly employed almost invariably involve changing the carrier phase in some particular way according to the baseband message entering the modulator. These can be grossly termed “phase shift keying” (PSK). Phase shifted keyed carrier band signal must be detected “coherently”, i. e. at the receiver a locally generated carrier whose phase closely tracks the phase of the carrier signal at the transmitter is required. The process of generating such a local, phase coherent carrier is usually called “carrier recovery”. Since it has been well known that the quality of recovered carrier has a profound effect on the whole PSK receiver system performance (e. g. the bit error rate, etc.), carrier recovery circuit must be analyzed and designed carefully. In this paper, the “Costas loop”—one of the most efficient and...