Design of Farrow Structured Variable Fractional Delay Filter for Time-Varying LEO Communication Channel Emulator With SRRC Communication Waveforms

Low-Earth Orbit (LEO) satellite communication channel is characterized with time-varying delay, attenuation, and Doppler frequency shift. The development of communication transceivers for this channel requires a realistic channel emulator. In this paper we tackle the design problem of Farrow structured variable fractional delay filter which is the critical component in the LEO communication channel emulator for providing continuously time-varying delay effect. Instead of typical frequency or time domain design methods for general signals, we propose a new design method specific for squared-root raised-cosine (SRRC) waveforms which are commonly used for satellite communications such as those specified in the DVB-S2(X)/CCSDS standards. The proposed Farrow structured fractional delay filter is designed based on a least-square method specifically incorporating with the characteristics of the SRRC waveform. The performance of the resulted fractional delay filter is evaluated in terms of inter-symbol interference (ISI) versus fractional delay. For the most critical case, i.e., the over-sampling ratio (OVSR) being 2, the maximum ISI over fractional delay of the Proposed Farrow Structured Interpolators is equal to −36.47dB, which outperforms the well-known Cubic Farrow Structured Lagrange Interpolator and a published Polynomial FIR Interpolator with the same complexity by 7.88dB and 0.22dB, respectively.