Showing papers on "Continuous phase modulation published in 1984"

A Class of Reduced-Complexity Viterbi Detectors for Partial Response Continuous Phase Modulation

Abstract: Partial response continuous phase modulation (CPM) gives constant envelope digital modulation schemes with excellent power spectra. Both narrow main lobe and low spectral tails can be achieved. When these signals are detected in an optimum coherent maximum likelihood sequence detector (Viterbi detector), power efficient schemes can also be designed, sometimes at the expense of receiver complexity. This paper describes a general class of simple Viterbi detectors with reduced complexity compared to the optimum case. The key idea is that the approximate receiver is based on a less complex CPM scheme than the transmitted scheme. The asymptotically optimum reduced-complexity receiver is found for a variety of transmitted schemes and various complexity reduction factors, for a specific class of receivers and modulation indexes. A new distance measure is introduced for the performance analysis. Smooth schemes based on raised cosine pulses are analyzed and simulated for the case of simplified reception. A graceful performance degradation occurs with the reduction of complexity.

Optimum MSK-type receivers for CPM on Gaussian and Rayleigh fading channels

Abstract: Power efficient schemes with excellent power spectra are contained among the continuous phase modulation (CPM) schemes. This is a constant envelope digital modulation technique, which in general requires a maximum-likelihood sequence detector (Viterbi detector) for efficient detection. This optimum receiver is sometimes complex. In this paper a parallel MSK-type receiver is studied. It is useful for binary schemes with modulation index h = 1/2. We consider coherent detection of signals transmitted over an additive white Gaussian noise channel and also over a Rayleigh fading channel. The MSK-type receiver can be implemented with only two filters and simple decision logic. Error probability formulas are given both for the nonfading and the fading channel. A simple algorithm giving the optimum filter for the Gaussian channel for high signal/noise ratios is presented. The optimum filter for low signal/noise ratios is also derived. For intermediate signal/noise ratios numerical optimisations are presented, both for the Gaussian and the Rayleigh fading channels. We have also considered diversity schems with ideal two-branch maximal ratio combining and selection combining. The optimum receiver filters are given for some selected schemes. It is shown that also, for the more complex CPM schemes, the loss compared to the optimum receiver is moderate.

An improved algorithm for evaluating trellis phase codes (Corresp.)

Abstract: A method is described for evaluating the minimum distance parameters of trellis-phase codes, including continuous phase frequency shift keying (CPFSK), partial-response FM, and, more importantly, coded continuous-phase modulation (CPM) schemes. The algorithm provides dramatically faster execution times and smaller memory requirements than previous algorithms. Results of sample calculations and timing comparisons are included.

Minimum Euclidean distance for combinations of short rate 1/2 convolutional codes and CPFSK modulation

Abstract: Continuous phase frequency shift keying (CPFSK) is a constant amplitude modulation method with good spectral sidelobe properties. Good error probability properties can be obtained with coherent maximum-likelihood detection. In this paper we study the Euclidean distance properties of signals formed by a conventional rate 1/2 convolutional encoder followed by a binary or 4 -level CPFSK modulator. The minimum Euclidean distance is calculated for these signal sets as a function of the modulation index and the observation interval length. The optimum detector is discussed for rational modulation index values. The best obtainable codes are found for the case of short rate 1/2 codes with binary or 4 -level CPFSK modulation. Lists of the best codes are given. Among the results are that the noncatastrophic rate 1/2 convolutional codes with optimum free Hamming distance do not in general give the best Euclidean distance with CPFSK.

CPM - An efficient constant amplitude modulation scheme

Abstract: There is an increasing demand for digitial radio transmission. The cost of a channel is proportional to the bandwidth. For many applications power is limited. For satellite applications constant amplitude modulation is advantageous because of non-linear amplification. In this paper a class of power and bandwidth efficient constant amplitude continuous phase modulation (CPM) schemes is presented. The signals are analysed in great detail and the tools for both error probability analysis and power spectral calculations are presented. Numerical data for raised cosine (RC) pulse shaping is presented. This paper is basically an overview with new results on the trellis description of CPM. The transmission is assumed to be ideally coherent over the Gaussian channel. In a following paper we will deal with transmission imperfections such as bandlimitation and hard limiting and their effect on CPM1.

Simultaneous Adaptive Estimation of Carrier Phase, Symbol Timing, and Data for a 49-QPRS DFE Radio Receiver

Abstract: The use of adaptive decision feedback techniques in the joint estimation of data, carrier phase, and symbol timing is investigated for a 49-QPRS 90 Mbit/s digital radio. The performance of the carrier and timing recovery loops are analyzed, first in a multipathfree environment and then for the case of a multipath distorted signal and a fixed decision feedback equalizer. Finally, the joint problem of data recovery, estimation of carrier phase, and symbol timing for a

Demodulator for constant envelope and continuous phase signals which are angle modulated by a train of binary symbols

Abstract: The demodulator is for use with an angle modulated signal conveying a sequence of binary symbols. The signal is modulated at constant envelope and with continuous phase and may be treated as a sequence of elementary pulses that have been amplitude modulated using a principal function Fp (t) derived from the frequency pulse characteristic of the modulation. The demodulator comprises two filters matched to the principle function and connected to receive quadrature components constituting the complex envelope of the received signal. The filters are followed by samplers. A calculating circuit operating at the bit rate calculates metric increments on the basis of P stored complex samples and transmits the increments to a decision circuit which performs a dynamic programming algorithm to determine the values of the bits in the sequence recursively.

M-ary continuous phase frequency shift keying with modulation index 1/M

Abstract: In the paper, two techniques for the detection of multilevel continuous phase frequency shift keyed signals with modulation index equal to the inverse of the number of levels (M-ary CPFSK) are described. The first technique is a noncoherent technique which is similar to the conventional differentially coherent detection method of DPSK and the error rate of this detector is equal to the error-rate in DPSK. The second technique is a coherent technique which utilises a coherent carrier, and the detection method is similar to the coherent detection and differential decoding of differentially encoded PSK. The error rate in this case is equal to the error rate in coherent-detection/differential-decoding of PSK. Finally, expressions are derived for the autocorrelation functions and the power spectral density functions of M-ary CPFSK. By numerical computation, it is shown that M-ary CPFSK have approximately the same autocorrelation function and approximately the same power spectral density function regardless of the number levels when M ≥ 4. The power spectral characteristics of M-ary CPFSK are compared with those of M-ary PSK.

Frequency shift keyed demodulation system

Abstract: A demodulator for continuous phase frequency shift keyed signals is implemented through the medium of computer software and processes incoming signals which are initially passed through an interference reduction filter. The disclosed demodulation algorithm makes use of the fact that the phase is continuous between adjacent symbols, as well as other symbol to symbol correlations, to reduce the error rate by processing a string of symbols utilizing a two step symbol decision process, instead of merely demodulating a symbol from a time slice of the received signal. The two step symbol decision process consists of a forward and reverse pass, wherein a candidate symbol predecessor is recursively chosen for each symbol, according to a maximum likelihood decision criterion, on the forward pass. Once a singular candidate predecessor is encountered, a reverse pass is initiated, so that a unique sequence of symbols is chosen back to a previously encountered singular predecessor.

Modulation Transfer Noise Effects from a Continuous Digital Carrier to FDM/FM Carriers in Memoryless Nonlinear Devices

Abstract: An analysis of the modulation transfer noise effects from a continuous (nonbursty) digital carrier to multiple FDM/FM carriers in a common memoryless nonlinear amplifier (e.g., satellite transponder TWTA) is presented. It is shown that the modulation transfer noise, which is caused by the random envelope variations of the digital carrier due to the random data patterns and filtering of the PSK pulses, consists of both discrete and continuous spectral components in the baseband of the FDM/FM carriers. Numerical examples in terms of the noise power ratio as well as a comparison between measured and computed results are given. In general, the discrete or tonal interference component at the symbol rate of the digital carrier is quite significant. Results of this paper should be useful in the planning of FDMA satellite transponders employing the mixed PSK-FM mode of operation.

Method for digital quadrature amplitude modulation

Abstract: Spectrum-converting digital filters are employed for quadrature amplitude modulation. Given the method of the invention, the frequency of the two carrier oscillations residing at 90° relative to one another amounts to one-fourth the sampling frequency and, in addition, their phase positions relative to the sampling times is selected such that every second sample of both carrier oscillations is alternately zero.

CPM - The effect of filtering and hard limiting

Abstract: The attractive properties of the digital constant amplitude modulation scheme CPM (continuous phase modulation) have been demonstrated in a previous paper in this journal.1 This concerned both the power and spectral efficiency of the large family of CPM schemes over the Gaussian channel. In this paper the considered channel can be both bandlimited or band- and amplitude-limited at the same time. Analytical results as well as simulations are presented for a number of selected CPM schemes. In today's increasing demand for bandwidth, CPM is an attractive candidate for future satellite applications because of its spectral efficiency. In addition to this comes the fact that the transmitted signal has a constant amplitude and good detection performance when optimal coherent detection is performed.

Demodulator for continuous phase fsk signal

Abstract: PURPOSE:To regenerate a binary signal directly from a signal after continuous phase FSK modulation without generating a ternary signal temporarily and to simplify the hardware of a demodulator by using a delay cosine detector which has one-bit time delay to an input signal and sends out an output signal with a cosine function to the phase of the input signal, and identifies the binary signal directly from the output of this delay cosine detector. CONSTITUTION:The binary signal is modulated by a modulating circuit 2 into a duobinary code. The output signal of this modulating circuit 2 is converted by a continuous phase FSK modulating circuit 3 into a continuous phase FSK signal, which is transmitted from an antenna 5 through a transmitting circuit. A receiver converts the signal received by an antenna 6 into a base-band signal by a receiving circuit 7 and the signal is inputted to the delay cosine detector 8. The output of this detector 8 is supplied to a binary identifying circuit 9 to be regenerated into a binary code, which is outputted. The detector 8 includes a delay circuit 12 which delays the input signal by one-bit time, mixing circuit 13 which multiplies the output signal of the circuit 12 by said input signal, and low-pass filter which extracts a basic frequency component from the output signal of the circuit 13.