David J. Cohen

Abstract: The National Telecommunications and Information Administration (NTIA) and the Interdepartment Radio Advisory Committee (IRAC) require, for their management of the spectrum, technical guidance concerning the necessary bandwidth and spectral characteristics of digital modulation. The necessary bandwidth is the minimum emission bandwidth required for an acceptable quality of service. The NTIA Manual includes all guidance and criteria relating to necessary bandwidth in Annex J entitled "Determination of Necessary Bandwidth." In this report, the concept of necessary bandwidth is applied to digital modulation. The necessary bandwidths for several digital modulations are considered in detail. hese are phase shift keying (PSK), minimum shift keying (MSK), and frequency shift keying (FSK). The techniques used to determine necessary bandwidth are general and could be extended to other digital modulations. This report shows that for digital modulation systems, the necessary bandwidth, signal power, and bit error rate are all interrelated and trade-offs among these factors are possible.

Keywords: frequency shift keying (FSK); phase shift keying (PSK); digital modulation; bandwidth; minimum shift keying (MSK); necessary bandwidth

Disclaimer: Certain commercial equipment, components, and software may be identified in this report to specify adequately the technical aspects of the reported results. In no case does such identification imply recommendation or endorsement by the National Telecommunications and Information Administration, nor does it imply that the equipment or software identified is necessarily the best available for the particular application or uses.

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