Showing papers on "Continuous phase modulation published in 1981"

Continuous Phase Modulation--Part I: Full Response Signaling

Abstract: The continuous phase modulation (CPM) signaling scheme has gained interest in recent years because of its attractive spectral properties. Data symbol pulse shaping has previously been studied with regard to spectra, for binary data and modulation index 0.5. In this paper these results have been extended to the M -ary case, where the pulse shaping is over a one symbol interval, the so-called full response systems. Results are given for modulation indexes of practical interest, concerning both performance and spectrum. Comparisons are made with minimum shift keying (MSK) and systems have been found which are significantly better in E_{b}/N_{0} for a large signal-to-noise ratio (SNR) without expanded bandwidth. Schemes with the same bit error probability as MSK but with considerably smaller bandwidth have also been found. Significant improvement in both power and bandwidth are obtained by increasing the number of levels M from 2 to 4.

Continuous Phase Modulation--Part II: Partial Response Signaling

Abstract: An analysis of constant envelope digital partial response continuous Phase modulation (CPM) systems is reported. Coherent detection is assumed and the channel is Gaussian. The receiver observes the received signal over more than one symbol interval to make use of the correlative properties of the transmitted signal. The Systems are M -ary, and baseband pulse shaping over several symbol intervals is considered. An optimum receiver based on the Viterbi algorithm is presented. Constant envelope digital modulation schemes with excellent spectral tail properties are given. The spectra have extremely low sidelobes. It is concluded that partial response CPM systems have spectrum compaction properties. Furthermore, at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained. This gain increases with M . Receiver and transmitter configurations are presented.

Continuous Phase Modulation-Part 11: Partial Response Signaling

Abstract: An analysis of constant envelope digital partial response continuous phase modulation (CPM) systems is reported. Coherent detection is assumed and .the channel is Gaussian. TPe receiver observes the, received signal over more than one symbol interval to make use of the correlative, properties of the transmitted signal. The systems are M-ary, and baseband pulse shaping over several symbol intervals is considered. An optimum receiver based on the Viterbi algorithm is presented. Constant envelope digital modulation schemes with excellent spectral tail properties are given. The spectra have extremely low sidelobes. .It is concluded that partial response CPM systems have spectrum compaction properties. Furthermore, at equal or even smaller bandwidth than minimum shift keying (MSK), a considerable gain in transmitter power can be obtained. This gain increases with M. Receiver and transmitter configurations are presented.

Correlative Phase Shift Keying--A Class of Constant Envelope Modulation Techniques

Abstract: Correlative phase shift keying (CORPSK) is described. CORPSK is a constant envelope modulation technique with smooth transitions between fixed phase positions with successive transitions correlated. A number of CORPSK members for 2 and 4 input levels are analyzed, including tamed frequency modulation (TFM). Main lobe bandwidth is the same or less than in other constant envelope modulation techniques such as MSK, QPSK, and CPFSK, but the out-of-band radiation is much lower. Carrier extraction can be realized with simple techniques, so that coherent detection with optimum receiver performance is practically feasible. Simulation results are presented for coherent as well as noncoherent detection. A power efficiency 2 dB better than four MSK and DQPSK can be obtained for CORPSK with no more than for phase positions. A wide variety of modulations exists within the CORPSK class, with ample opportunity for tradeoffs between power, bandwidth, and complexity. Practical results for TFM are reported.

Error rate performance of noncoherent detection of duobinary coded MSK and TFM in mobile radio communication systems

Abstract: Two continuous phase constant envelope modulation schemes are considered for use in digital mobile radio communication systems. These two schemes, duobinary coded minimum shift keying (MSK) and tamed frequency modulation (TFM), use partial response signaling to achieve efficient power spectrum. Therefore, they are suitable candidates for the application of digital data transmission via mobile radio where spectrum efficiency is an important consideration. The mobile communication channel is characterized by fast Rayleigh fading and cochannel interference resulting from the reuse of the channels. The error rate performance of duobinary coded MSK and TFM has been studied under these environments with noncoherent detection. A closed form expression for the probability of error of duobinary coded MSK with discriminator detection has been derived and evaluated for different cases of fast and slow fading and cochannel interference. The probability of error of duobinary coded MSK and TFM with differential detection has been calculated by numerical integrations for different cases of slow and fast fading and cochannel interference.

Symbol Error Probability Bounds for Coherently Viterbi Detected Continuous Phase Modulated Signals

Abstract: Recently the minimum Euclidean distance and bandwidth properties of continuous phase modulated (CPM) signals have been considered. It has also been shown that, for rational modulation indexes, a state description of these signals is possible and that the Viterbi algorithm (VA) can be used for demodulation. In this paper the performance analysis of CPM systems is extended to obtain bounds on the symbol error probability when the VA is used. The calculation of these bounds is based on the transfer function technique, which has been generalized. From numerical comparisons of the upper and lower bounds, it is concluded that the minimum Euclidean distance is a good performance measure for a broad class of CPM signals, even when the symbol error probability is as large as 10-2.

Broad-Band Active Phase Shifter Using Dual-Gate MESFET

Abstract: This paper describes a broad-band, dual-gate MESFET phase shifter (vector generator), operating over the 4- 8-GHz frequency band and capable of a continuous phase shift and multiplicity of modulations including digital phase shift and amplitude modulation directly, and indirectly (with additional information processing circuits), single sideband modulation, frequency modulation, and phase modulation, etc. A dual-gate FET is used as a variable gain amplifier and phase shift is obtained by complex addition of two orthogonal variable vectors. The principle of the phase shifter and the experimental results are presented.

Demodulation and Carrier Synchronization of Multi-h Phase Codes

Abstract: Multi- h phase coding is a bandwidth-efficient modulation which offers substantial performance improvement over conventional digital modulations with little or no bandwidth expansion. This paper examines the demodulation of the multi- h signals, and in particular examines the behavior of a decision-directed carrier loop which utilizes the Viterbi algorithm decoder in the calculation of the loop error signal. Both analytic and simulation results are presented and the agreement between the two is shown to be very close.

Continuous Phase Chirp (CPC) Signals for Binary Data Communication--Part II: Noncoherent Detection

Abstract: Chirp (linear FM) signals provide an attractive wideband digital modulation scheme in applications where interference rejection is important. This paper evaluates the error rate (performance) of coherent binary continuous phase chirp (CPC) receivers operating on the additive white Gaussian noise (AWGN) channel and determines the improvement in performance made possible by multiple bit observation. In particular, it is shown that a receiver with two bit observation, giving up to 1.75 dB signal-to-noise ratio (SNR) improvement over the optimum single bit chirp receiver, provides a good compromise between SNR gain and system complexity. Furthermore, a simple, suboptimum, average matched filter (AMF) receiver is analyzed, and it is shown that a two-bit observation is optimum, giving a performance equivalent to that of antipodal phaseshift keying (PSK). An implementation of this receiver in the form of in-phase and quadrature demodulators is also derived.

Comments on Transmission System Using Pseudonoise Modulation of Linear Chirps

Abstract: The combination of phase shift keying (PSK) with different chirp waveforms is investigated in respect to its signal form and spectrum shape. A reasonable compromise for low probability of exploitation and jam sensitivity is found for a system where the chirp bandwidth is in the vicinity of the bitrate of the pseudonoise code.

A compact spectrum constant envelope digital phase modulation

Abstract: A digital modulation system with compact spectrum and constant envelope is proposed, based on the results of theoretical and experimental studies. This modulation system is suitable for digital mobile communication, which generally is subject to deep and rapid fading. It is characterized with a possibility of practical and stable instrumentation. In the modulator, modulation signal parameters are read out of the memories, by which precise spectrum and waveform can be realized. For the modulator, an orthogonal phase modulation, whose parameters are stable, can be adopted by pertinent parameter design for the modulating signal stored in the memories. The experimental results agree well with the design.

A Continuously Variable Ku-Band Phase/amplitude Control Module

Abstract: A Ku-band microstrip phase shifter capable of continuous phase and amplitude control is described. Three dual-gate FET amplifiers provide variable amplitude vectors that are separated by 120/spl deg/ and summed through an arrangement of quadrature couplers. The described phase shifter provides a full 360/spl deg/ shift with an amplitude weighting capability of more than 20 dB.

Coordinated Power Modulation in Multiterminal HVDC Systems

Abstract: A comparison is made between linear decentralized power modulation and centrally coordinated modulation of multiterminal hvdc systems. The centralized method is based on a fast on-line dc load flow solution which recognizes the nonlinearities of converter operation. A computer simulation of an integrated ac/dc power system demonstrates that the centralized approach can utilize dc overload capacity more efficiently than decentralized modulation.

Selecting smoothing pulses for partial-response digital FM

Abstract: In recent years, it has been demonstrated that partial-response continuous-phase modulation (sometimes also referred to as partial-response digital FM) is a spectrally efficient constant-envelope digital-modulation method. If maximum-likelihood sequence detection (e.g. the Viterbi detector) is used, these schemes can also be made power efficient. System complexity grows exponentially with the length of the baseband pulse that introduces the memory in the partial-response scheme. The smoothness and the length of this pulse determines the spectral properties. The paper considers binary systems based on short pulses of length ?2 symbol intervals. New spectrum formulas are given for modulation schemes based on pulses with an increasing number of continuous derivatives. It is demonstrated how the spectral mainlobe and the spectral tails are affected by the shape of the pulse. Comparisons are made with binary full-response systems. The tradeoff between error probability and bandwidth is demonstrated.

Active phase shifters at X band using GaAs MESFETs

Abstract: This report will describe a X-band active phase shifter with 140° continuous phase variation and associated gain of 30dB. The circuit consists of pre-and post-amplifying FETs, connected with a dual-gate FET as a phase-shifting element. Noise figure is better than 4.9dB at 12GHz.

Modulation/demodulation techniques for satellite communications. Part 4: Appendices

Abstract: The use of the Viterbi algorithm in a general context is examined. The generalized transfer function bounds are given which permit the following applications to be carried out: maximum likelihood demodulation of such bandwidth modulations as minimum-shift-keying and continuous phase frequency-shift-keying, demodulation of intersymbol interference and partial response signals, estimation and smoothing, and simultaneous phase synchronization, and data detection. Sufficient conditions are reviewed for tightening Chernoff and Rhattacharyya bounds.

Demodulator for continuous-phase modulated signals, and transmission system involving such a demodulator

Abstract: 1. Demodulator of signals modulated in accordance with a continuous phase modulation for the transmission of binary data at a rhythm F, characterized in that it comprises : - means (600) for the determination and sampling of the phase of the modulated signal ; - means (700) for the determination of a value (ai ) of a bit from the phase values of two successive samples ; - means (13) for estimation of the value of the value of the bit (a'i ) that has been most probably transmitted, as a function of the phase values of two successive samples (phi i-1 , phi i ) received for this bit, these phase values being corrected by means of stored data being characteristic of the average effects of the distortion on the phase corresponding to sequences of p bits (p being a fixed integer equal to or exceeding 2) the first bit of which is formed by the preceding bit (a i-1 ) ; - means (12) for the estimation of these characteristic data, and determining for each sample the difference between the phase (phi i ) determined by the means (600) for the determination and sampling of the phase of the modulated signal and a theoretical phase (theta i ) computed from the theoretical phase (theta i-1 ) computed for the preceding sampling and from the value (ai-1 ) of the preceding bit, the latter being determined by the means (700) for the determination of the value of a bit, from the phase values of two successive samples, said means estimating, from the thus determined distortion values, data which are characteristic of the average effects of the distortion on the phase for all possible sequences of p bits, and storing these characteristic data.

Transmitter for a navigation system

Abstract: In navigation transmitters it is important that the phase difference between the carrier waves of a carrier signal and the carrier waves of sideband signals be held at a constant value. To accomplish this, the carrier waves are maintained constant relative to a reference signal in a known manner. A phase meter measures the phase difference between the carrier waves of the sideband signals and the reference signal and between the carrier waves of the carrier signal and the reference signal. The measure values are used to determine the phase difference between the carrier signal and sideband signals which are compared with a desired value. Depending on the deviation from the desired value, a controllable phase shifter controls the phase of the carrier waves of the sideband signals. Since the measurements are made on a time-division multiplex basis, little circuitry is required. Any measuring errors do not affect the formation of the desired phase difference.

Method and apparatus for demodulating quadriphase differential transmissions

Abstract: A method and apparatus for synchronizing a digital data demodulator to a received phase modulation carrier signal (42) in which the carrier signal is phase shifted during each modulation period of the carrier to represent one of four pairs of binary bits or dibits. A dibit clock (76) is adjusted to the phase of a reference dibit clock (66, RDCL) whose output is used to synchronize the demodulator in establishing the location of the modulation period of the incoming carrier. In order to overcome errors found in the decoding of the carrier signal, the adjustment of the dibit clock is suppressed when the dibits 00 and 10 are being decoded.

A general modulation theory for single-phase Thyristor systems

Abstract: Amplitude Modulation (AM) and Phase Modulation (PM) processes of discrete form have been discussed in a previous associated paper. This present paper discusses discrete Frequency Modulation (FM) in power frequency circuits, highlighting their advantages compared with amplitude and phase modulations. Mixed modulation systems of both PM and FM nature are introduced to solve the disadvantages and undesirable features associated with pure FM modulation. A generalised equation of modulation is introduced to represent the various forms of power frequency modulation.

Singleephase ac signal phase detector

Abstract: PURPOSE:To prevent an error in a detected phase, by producing two-phase AC input signals from a single-phase AC input signal and using the two-phase signals to continuously perform phase comparison. CONSTITUTION:A signal eo (Eo) is picked out from a single-phase-to-two-phase converter 8 as one eod of two-phase sinusoidal input signals as the signal eo is not processed. On the other hand, the signal eo is processed through the phase shifter circuit 81, coefficient units 84, 85, 87, etc. of the converter 8 to pick out the other eoq of the two-phase signals. The two-phase sinusoidal signals eod.eoq can be represented by a formula I where thetao shows the phase difference between the signals eod, eoq. Two-phase sinusoidal signals e1d, e1q of unit amplitude can be represented by a formula II where Q1 shows the phase difference between the signals e1d, e1q. The phase difference DELTAtheta(=Qo-theta1) between both the pairs of the two-phase sinusoidal signals can be continuously calculated in accordance with a formula III. Continuous phase comparison is thus effected to provide a phase lock loop. This results in preventing an error in a detected phase.

Error rate performance of duobinary coded MSK and TFM with differential detection in land mobile communication systems

Abstract: Two continuous phase constant envelope modulation schemes are considered for use in digital mobile radio communication systems. These two schemes: duobinary coded MSK and tamed frequency modulation (TFM) use partial response signaling to achieve efficient power spectrum. Therefore, they are suitable candidates for the application of digital data transmission via mobile radio where spectrum efficiency is an important consideration. The mobile communication channel is characterized by fast Rayleigh fading and cochannel interference resulting from the reuse of the channels. The error rate performance of duobinary coded MSK and TFM has been studied under these environment with differential detection. The probability of error has been calculated by numerical integrations for different cases of slow and fast fading and cochannel interference.

Color reproducing device for double scanning television receiver

Abstract: PURPOSE:To perform accurate color demodulation, by obtaining continuous phase of each sub-carrier during each double speed scanning period, in a double speed scanning television receiver which twice scans signals substantially equal with each other obtained from signals during horizontal scanning period. CONSTITUTION:A double speed scanning signal S2 from a terminal 26 becomes a chroma signal SC1 through a band pass amplifier 9 and is connected to a contact (a) of a switch 29 and to a contact (b) via an inverter 30. The switch 29 is changed over at each 1H with a switching pulse PG applied to a terminal 27. Thus, the phase of sub-carrier of an output signal SC2 of the switch 29 is inverted at each 1/2H. On the other hand, a burst SB is picked up from the signal SC1, which drives a sub-carrier oscillator 17. Then, the phase of the sub-carrier is continuous in each scanning line and chroma signals R, G and B with correct demodulation can be obtained from a color reproducing circuit 25.

Precise T and F intercomparison via VLF phase measurements

Abstract: Continuous phase recording of the 16kHz transmission from GBR (UK) are being made and published midday phase data of GBR are received regularly from laboratories in the US, FGR, and UK. The local time scale (UTC, India), at the National Physical Laboratory in New Delhi, and those at the foreign laboratories are intercompared using the VLF phase data. A major factor which limits the accuracy of long term comparison is the seasonal variation in the VLF over delay over long paths. By taking into account the seasonal delay variations in a semiempirical way, the accuracy of time and frequency comparisons can be improved. Over a one year period, accuracy of a few parts in 10 to the 14th power in frequency and 1 to 2 micron sec in time were obtained. The relative frequency offset difference between UTC, (India) and UTC (PTB, Germany) of (7.0 + or - 0.1) x 10 to the -13 power agrees well with that obtained in a satellite experiment.