This paper describes and summarizes the characteristics of the modulation techniques most applicable to digital radio. The modulation techniques discussed are on-off-keying (OOK) with coherent and noncoherent detection, quadrature amplitude modulation (QAM), quadrature partial response (QPR), frequency-shift-keying (FSK) with noncoherent detection, continuous phase FSK (CP-FSK) with coherent and noncoherent detection, minimum-shift-keying (MSK), binary and quaternary phase-shift-keying (BPSK, QPSK) with coherent and differentially coherent detection, offset-keyed QPSK (OK-QPSK), M -ary PSK with coherent detection ( M = 8, 16 ), and 16-ary amplitude and phase-shift-keying (APK). Functional descriptions of these schemes are provided and their performance is compared in a series of tables summarizing the results of the literature of the past 20 years. The modulation schemes are compared with respect to ideal (white Gaussian noise) performance, spectral properties, signaling speed, complexity, and the effects on performance of interference, fading and delay distortion.

A Comparison of Modulation Techniques for Digital Radio

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.

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

Minimum shift keying (MSK)-type signals, while possessing all the advantages of MSK, allow input data pulse shaping in order to obtain more desirable spectral behavior. This paper presents a set of conditions on the pulse shape which enable an MSK-type signal to have a fast spectral rolloff. An M th order shaping function, resulting in an asymptotic spectral falloff as | f |^{-(4M + 4)} , is presented. Previously considered schemes such as MSK and sinusoidal frequency shift keying (SFSK) are shown to be special eases of this shaping function.

Spectral Shaping in Minimum Shift Keying (MSK)-Type Signals

A general method for numerical calculation of power spectra for digital FM signals is developed. Arbitrary baseband pulse shape, the modulation index and the number of levels of the data can be used. The probability density function of the statistically independent data symbols can also be chosen arbitrarily. With this method the autocorrelation function is first calculated and then numerically Fourier transformed, yielding the power spectrum. The time required to calculate a power spectrum on a digital computer is extremely small, and the calculations are simple and easy to use.

An easy way to calculate power spectra for digital FM

A new class of basic pulses is introduced into the MSK signaling format to gain improvements in the out-of-band power spectral density characteristic. Some loss in communications efficiency is incurred, but the loss may in certain cases be outweighed by the spectral improvements that are made available.

The Use of Quasi-Bandlimited Pulses in MSK Transmission

The spectral or band occupancy of an RF signal is often defined as the bandwidth that contains a specified fraction (usually 99 percent) of the modulated RF power. The band occupancy of binary and quaternary PSK signals with and without RF filtering and with modulation pulses of several shapes has been evaluated and the results presented in graphical and tabular form. For a binary FSK signal with phase deviation of ± π/2, sometimes called an FM-PSK signal, numerical values of the spectral occupancy with rectangular and raised-cosine signaling have been obtained and the results given in graphical form. For a binary PSK signal with signaling rate 1/T and with arbitrary baseband pulse shaping, we have derived a lower bound on the fraction of the continuous power contained outside any given band, but have not been able to get a bound on the total band occupancy. However, for an FM-PSK signal, a lower bound on the total band occupancy has been derived, and it is shown that the value of this lower bound for 99-percent power occupancy is 1.117/T. The 99-percent power occupancy bandwidth of an FM-PSK signal is 1.170/T with rectangular signaling and 2.20/T with raised-cosine signaling.

V. K. Prabhu

Papers

Spectral occupancy of digital angle-modulation signals