Frequency-dependent rejection, spectral separation coefficient, and interference analysis

Improving spectrum use to enable existing and upcoming modern communication and navigation services has increased the potential for interference. This potential is a critical issue that must be addressed carefully, to avoid degrading the performance of all the services utilizing a particular band of spectrum. Frequency allocation issues are addressed by agencies such as the National Telecommunications and Information Administration (NTIA) and the Federal Communications Commission (FCC) domestically, and the International Telecommunication Union (ITU) globally. When a new service is seeking to use a part of the spectrum already in use on a shared basis, the need for interference analysis cannot be overemphasized. Even when the spectrum allocation sought for a new system does not overlap the allocation of an existing, sensitive service, a comprehensive interference analysis must be done to establish acceptable operating parameters for their simultaneous operation. Otherwise, the existing service may be severely degraded. When it is critical to show that the new service seeking the spectrum will not harmfully interfere with the existing system, exhaustive testing may be necessary. Typically, effective signal-to-noise ratio (SNR), effective energy per bit-to-noise density ratio (E
_b
/N'
₀
) and effective carrier-to-noise density ratio (C/N'
₀
) are the parameters of interest. Frequency-Dependent Rejection (FDR) and Spectral Separation Coefficients (SSCs) are used as intermediate parameters for a quick assessment of the impact of interference on system performance. In this paper we discuss both FDR and SSC, show their relationship, and provide an interference calculation example to illustrate the use of FDR and SSC in interference analysis.