Sinusoidal Frequency Shift Keying Research Articles

Two New Pulse Shapes

This paper presents two pulse shapes. One pulse, obtained by amplitude modulating the Gaussian pulse by a modified sine pulse, offers much less intersymbol interference (ISI) than that offered by the Gaussian pulse modulated in amplitude by a sinc pulse. The other pulse, obtained by convolving the modified sinusoidal frequency shift keying (MSFSK) pulse with a square pulse, requires lesser bandwidth than that required by the pulse, obtained by convolving the sinusoidal frequency shift keying (SFSK) pulse with a square pulse. The power density spectra of the proposed pulses are much narrower than those offered by the aforesaid pulses.

Two New Pulse Shapes

This paper presents two pulse shapes. One pulse, obtained by amplitude modulating the Gaussian pulse by a modified sinc pulse, offers much less intersymbol interference (ISI) than that offered by the Gaussian pulse modulated in amplitude by a sinc pulse. The other pulse, obtained by convolving the modified sinusoidal frequency shift keying (MSFSK) pulse with a square pulse, requires lesser bandwidth than that required by the pulse, obtained by convolving the sinusoidal frequency shift keying (SFSK) pulse with a square pulse. The power density spectra of the proposed pulses are much narrower than those offered by the aforesaid pulses.

The effects of filtering and nonlinear amplification on the performance of DS-CDMA with OQPSK-type modulations

This paper investigates the effects of channel filtering and nonlinear amplification on the signal-to-noise ratio (SNR) performance of direct-sequence code-division multiple-access systems employing offset quadrature modulation formats with various chip waveforms. An average SNR analysis is developed and followed by numerical examples to illustrate relative performance merits among modulation formats, including offset quaternary phase-shift keying (OQPSK), minimum shift keying (MSK), sinusoidal frequency shift keying (SFSK), and time-domain raised-cosine shaped QPSK (TDRC). The channel filtering considered is based on Butterworth-type filters with varying 3-dB cutoff bandwidth, and the nonlinear amplification is modeled by amplitude hard limiting. The results obtained show little SNR performance differences between the cases of filtering alone and combined filtering and hard limiting. It is also found that for tighter filtering (one-sided 3-dB bandwidth on the order of half the chip rate), all modulations have comparable performance, but that for wider filter bandwidth values, differences become more noticeable, with SFSK and TDRC slightly better than MSK (on the order of 0.5 dB) and clearly outperforming OQPSK (by up to 1.5 dB). On the other hand, examples with strictly bandlimited signals employing frequency-domain Nyquist raised cosine (FDRC) filtering with a rolloff factor varying from zero to one showed a clear degradation in performance (by about 1 dB) due to the introduction of hard limiting. These schemes were also outperformed by all of OQPSK, MSK, SFSK, and TDRC modulations when combined with strict brick wall filtering, with SNR differences ranging from 1 to 2 dB.

DS-CDMA chip waveform design for minimal interference under bandwidth, phase, and envelope constraints

This paper investigates the effect of chip waveform shaping on the error performance, bandwidth confinement, phase continuity, and envelope uniformity in direct-sequence code-division multiple-access communication systems employing offset quadrature modulation formats. An optimal design methodology is developed for the problem of minimizing the multiple-access interference power under various desirable signal constraints, including limited 99% and 99.9% power bandwidth occupancies, continuous signal phase, and near-constant envelope. The methodology is based on the use of prolate spheroidal wave functions to obtain a reduced-dimension discrete constrained optimization problem formulation. Numerous design examples are discussed to compare the performance achieved by the optimally-designed chip waveforms with other conventional schemes, such as offset quadrature phase-shift keying, minimum-shift keying (MSK), sinusoidal frequency-shift keying (SFSK), and time-domain raised-cosine pulses. In general, it is found that while the optimized chip pulses achieved substantial gains when no envelope constraints were imposed, these gains vanish when a low envelope fluctuation constraint was introduced. In particular, it is also shown that MSK is quasi-optimal with regard to the 99% bandwidth measure, while the raised-cosine pulse is equally good with both the 99% and 99.9% measures, but at the expense of some envelope variation. On the other hand, SFSK is quasi-optimal with regard to the 99.9% bandwidth occupancy, among the class of constant-to-low envelope variation pulses.

New bandwidth efficient overlapped pulse shape

A new pulse shape of duration twice the symbol interval is proposed for bandwidth efficient modulation. The proposed pulse shape is obtained by convolving a square pulse shape with a sinusoidal frequency shift keying (SFSK) pulse shape. The power spectral density (PSD) of a signal with the proposed pulse shape shows less power in spectral sidelobes than that of a signal with overlapped raised-cosine pulse shape.

On the representation of CPM signals by linear superposition of impulses in the bandpass domain

A novel signal generation concept for continuous phase modulations (CPMs) with modulation index 1/2 based on real impulses is presented. With this concept, bandpass CPM signals can be generated directly in one step instead of the two consecutive steps, namely, the generation of the complex envelope and the modulation of the carrier by the complex envelope, which are necessary in conventional signal generators. Mathematical expressions for both the real impulses and the bandpass CPM signals are derived and a simple modulator structure is discussed. Examples for the real impulses are given. Among these are the well-known CPM schemes of minimum shift keying (MSK), sinusoidal frequency shift keying (SFSK), and Gaussian minimum shift keying (GMSK). As an example, the validity of the novel signal generation concept is shown for the latter CPM scheme. >

Frequency selective fading and adjacent channel interference performance of MSK and SFSK

The performance of minimum-shift keying (MSK) and sinusoidal frequency-shift keying (SFSK) in adjacent-channel interference and frequency-selective fading is investigated analytically. The receiver system considered uses a sampling detector and hence is suboptimum. In addition to the above impairments, the system model incorporates other disturbances, namely stationary white Gaussian noise, quadrature channel interference, random timing misalignment, and random carrier phases of interfering signals. Results and comparisons are presented for both coupled effects and individual effects of frequency-selective fading, adjacent-channel interference, and quadrature-channel interference. >

Required Transmit Filter Bandwidths in Digital Radio Systems

Widely used digital radio modulations such as quaternary phase shift keying (QPSK), minimum shift keying (MSK), and sinusoidal frequency shift keying (SFSK) usually require some form of transmit filtering to ensure compliance with spectrum emission rules. Typically, radio transmit filters are of a specified type, such as fourthorder Butterworth, where the bandwidth parameter (\beta) is a design variable. We specify β to be optimal for a particular filter when it has the largest value for which the transmitted signal satisfies the emission rules, and we present numerical solutions for β over a wide range of conditions. These data can be used in design studies that compare contending modulation/transmit filter combinations. The solutions given are for systems subject to the spectral limits of FCC Docket 19311. The types of modulation considered are generalizations of those cited above; the types of transmit filters considered are Butterworth and Chebyshev filters of various orders; and β is tabulated as a function of channel width-to-symbol rate ratio for numerous modulation/filter combinations. While computed specifically, for the 6 GHz common carrier band, the results are also valid, to within a few percent, for the 4 and 11 GHz bands.

Close Packing PCSFSK Signals--Model and Simulation Results

In many signal processing satellite applications, it is necessary to pack as many bit-time unsynchronized, power imbalanced digital FDM users as possible into the available bandwidth. In certain important cases the on-board demodulator (which simultaneously detects each user bit-stream individually) is not able to maintain phase reference. Phase comparison sinusoidal frequency shift keying (PCSFSK), a phase incoherent demodulation method with low adjacent-channel crosstalk properties, has been proposed as one way of meeting the requirements mentioned above. This paper describes a mathematical model and computer simulation which have been used to analyze the effects of adjacent-channel crosstalk on bit-error rates for a PCSFSK demodulator. Both the model and the simulation are flexible enough to incorporate many users of various strengths and center frequency separations and may be modified to yield results for any phase comparison MSK-type modulation. The results of this work show very close agreement between the model's prediction and the simulation. User scenarios of interest involve from two to eight users both with and without additive white Gaussian channel noise. Of particular interest is the performance of one weak user among many stronger users. A typical example involves eight users, seven of which are 20-dB stronger in power than the user whose probability of error was monitored. In this case, a bit-error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> requires that adjacent users be separated in frequency by two times the data rate. If, however, all users are of equal strength, the minimum frequency separation need only be equal to the data rate. The above results indicate that close packing of signals is possible when incoherent detection (PCSFSK) is used, and that optimum user spacings can be determined if the relative power ratio between users is known.

Efficient Pulse Shaping Using MSK or PSK Modulation

The increasing requirement for high data rate, bandwidth efficient digital radio systems has led to the development of MSK-type modulation methods designed to achieve a compact signal spectrum. These modulation methods include sinusoidal frequency shift keying (SFSK), special MSK-type pulse shapes, and multiamplitude minimum shift keying (MAMSK). When more compact signal spectra are required, bandlimited filtering must be introduced. This note considers the use of conventional MSK or PSK modulators followed by newly developed bandlimited pulse shaping filters. With this approach, it is shown that MSK and offset QPSK modulators yield identical signals on the channel when filtered by properly designed bandlimited pulse shaping networks.

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

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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> th order shaping function, resulting in an asymptotic spectral falloff as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">| f |^{-(4M + 4)}</tex> , is presented. Previously considered schemes such as MSK and sinusoidal frequency shift keying (SFSK) are shown to be special eases of this shaping function.