Minimum shift keying and offset QPSK are two well-known modulations which can be interpreted as a set of time/phase-shifted AM pulses. We show in this paper that any constant amplitude binary phase modulation can also be expressed as a sum of a finite number of time limited amplitude modulated pulses (AMP decomposition). New methods for computing autocorrelation and power frequency spectrum are derived, which give very simple results for half-integer index modulations. We also show that the signal can be built with good accuracy using only one optimized pulse ("main pulse"). This synthesis is particularly satisfactory for modulations that have good spectral characteristics and/ or low index.

Exact and Approximate Construction of Digital Phase Modulations by Superposition of Amplitude Modulated Pulses (AMP)

M inimum Shift Keying (MSK) [ 11 or Fast Frequency Shift Keying (FFSK) is a digital modulation technique with constant amplitude which has been studied extensively during recent years. The properties of MSK are now understood [2-51. In this article, we report on methods to improve on MSK while maintaining a constant amplitude. By improvement we mean a narrower power spectrum, lower spectral sidelobes, better error probability, or all of the above. The cost of signal processing and the speed and complexity with which it can be performed has steadily been improved over recent years. Further improvements are to be expected. Therefore, it is reasonable to study what can be accomplished with methods that might be too complex for cost effective realization today, but perhaps may be easily achievable tomorrow. In this paper, we consider a number of methods for constructing constant amplitude signals which significantly outperform MSK [5-1031. We also discuss at what level of complexity these improvements are obtained and realized.

Continuous phase modulation

A new modulation technique, cross-correlated phase-shift keying ( XPSK ), is introduced. XPSK is a band-limited offset QPSK modulation technique which has an almost constant envelope. In XPSK modulators, a controlled amount of cross correlation between the in-phase ( I ) and quadrature ( Q ) channels is introduced. I and Q cross correlation reduce the envelope fluctuation Of the intersymbol-interference and jitter-free OQPSK (IJF-OQPSK) modulation scheme, introduced by Feher et al. [1], [2], from 3 dB to approximately 0 dB, thus further improving the performance of IJF-OQPSK systems in nonlinear radio systems [7], [14]. It is shown that the baseband signal of the modulator, the P_{e} = f(E_{b}/N_{0}) performance, and the spectral characteristics of nonlinearly amplified (hard-limited or saturated) radio systems of XPSK and tamed frequency modems (TFM) are practically the same. The XPSK demodulator is a conventional OQPSK demodulator, the TFM demodulator requires a somewhat more complex signal processor. For this reason, the XPSK approach may lead to significant demodulator hardware cost savings, particularly in point-to-multipoint distribution systems such as broadcast systems. Simulation results for linear and nonlinear (saturated amplifier) systems operated in an adjacent-channel interference environment (in addition to thermal noise) are presented. Measurement results performed on a 128 kbit/s rate hardware-prototype modem are also reported. Experimental eye diagram and power spectrum density measurement results are in close agreement with the computer simulation results.

XPSK: A New Cross-Correlated Phase-Shift Keying Modulation Technique

Foreword. Preface. Chapter 1: Introduction. Chapter 2: Constant Envelope Modulations. 2.1 The Need for Constant Envelope. 2.2 Quadriphase-Shift-Keying and Offset (Staggered) Quadriphase-Shift-Keying. 2.3 Differentially Encoded QPSK and Offset (Staggered) QPSK. 2.4 /4-QPSK: A Variation of Differentially Encoded QPSK with Instantaneous Amplitude Fluctuation Halfway between That of QPSK and OQPSK. 2.5 Power Spectral Density Considerations. 2.6 Ideal Receiver Performance. 2.7 Performance in the Presence of Nonideal Transmitters. 2.7.1 Modulator Imbalance and Amplifier Nonlinearity. 2.7.2 Data Imbalance. 2.8 Continuous Phase Modulation. 2.8.1 Full Response-MSK and SFSK. 2.8.2 Partial Response-Gaussian MSK. 2.9 Simulation Performance. References. Chapter 3: Quasi-Constant Envelope Modulations. 3.1 Brief Review of IJF-QPSK and SQORC and their Relation to FQPSK. 3.2 A Symbol-by-Symbol Cross-Correlator Mapping for FQPSK. 3.3 Enhanced FQPSK. 3.4 Interpretation of FQPSK as a Trellis-Coded Modulation. 3.5 Optimum Detection. 3.6 Suboptimum Detection. 3.6.1 Symbol-by-Symbol Detection. 3.6.2 Average Bit-Error Probability Performance. 3.6.3 Further Receiver Simplifications and FQPSK-B Performance. 3.7 Cross-Correlated Trellis-Coded Quadrature Modulation. 3.7.1 Description of the Transmitter. 3.7.2 Specific Embodiments. 3.8 Other Techniques. 3.8.1 Shaped Offset QPSK. References. Chapter 4: Bandwidth-Efficient Modulations with More Envelope Fluctuation. 4.1 Bandwidth-Efficient TCM with Prescribed Decoding Delay-Equal Signal Energie. 4.1.1 ISI-Based Transmitter Implementation. 4.1.2 Evaluation of the Power Spectral Density. 4.1.3 Optimizing the Bandwidth Efficiency. 4.2 Bandwidth-Efficient TCM with Prescribed Decoding Delay-Unequal Signal Energies. References. Chapter 5: Strictly Bandlimited Modulations with Large Envelope Fluctuation (Nyquist Signaling). 5.1 Binary Nyquist Signaling. 5.2 Multilevel and Quadrature Nyquist Signaling. References. Chapter 6: Summary. 6.1 Throughput Performance Comparisons. References.

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Bandwidth-Efficient Digital Modulation with Application to Deep Space Communications

In portable wireless communication systems, power consumption is of major concern. Traditional modulation and coding schemes have been designed from the standpoint of minimizing average power. However, for linear power amplifiers needed for spectrally efficient modulation formats, amplifier efficiency and hence power consumption are determined by the peak power of the transmitted signal. This paper looks into modulation formats which minimize peak power and retain high spectral efficiency. Peak power is broken into a sum (in terms of decibels) of average power and a peak-to-average power ratio, and a variety of modulation formats are evaluated in terms of peak power efficiency in both a Gaussian noise and Rayleigh fading channel. A generalized phase shift keying (PSK) modulation format is developed and shown to offer superior peak power efficiency relative to that of commonly used linear modulation formats. Two schemes are presented for reducing the peak-to-average power ratio of various modulation formats. First, data translation codes are used to avoid data sequences which cause large peaks in the transmitted signal. This approach was found to be most productive in quadrature amplitude modulation (QAM) formats. Finally, an adaptive peak suppression algorithm is presented which further reduces the peak-to-average power ratios of the PSK and generalized PSK formats. The peak suppression algorithm is also applicable to /spl pi//4-QPSK and was found to improve peak power efficiency of that format by about 1.25 dB over a Rayleigh fading channel.

Peak power and bandwidth efficient linear modulation

A variation of an old but neglected pulse shaping technique, raised-cosine, is investigated. By overlapping raised-cosine pulses in each of two data streams and then by quadrature combining them, a simple QPSK/MSK type modulation results. This quadrature overlapped raised-cosine (QORC) modulation exhibits a hybrid structure of QPSK and MSK modulations. The power spectral density of QORC is shown to take on the form of the product of the power spectral densities of MSK and QPSK. The obvious consequences are that the power spectral density main lobe retains the width of the spectral density main lobe of QPSK, but the sidelobes drop off much faster (1/f^{6}) . A simple QORC modulator can be implemented similar to an MSK modulator. Several correlation type receivers are investigated and their performances calculated. Computer simulation results are used to compare end-to-end system performance of QORC and staggered QORC (SQORC) with MSK, QPSK, and staggered QPSK (SQPSK) for both linear and nonlinear satellite channels. The performance of QORC and SQORC compares very favorably with QPSK, SQPSK, and MSK. QORC performs particularly well in the presence of a nonlinear channel. The effect of phase equalization of the channel filter was investigated with outstanding performance improvement. The simulation results show that sidelobe regeneration caused by the channel nonlinearity is much less for SQORC than it is for the other modulation formats considered.

Ming Chang

Papers

Quadrature Overlapped Raised-Cosine Modulation