Estimating the Characteristics of the Aeronautical Telemetry Channel during Bit Error Events

Abstract

This paper presents estimated aeronautical telemetry channel characteristics during bit error events. A T-39 aircraft was flown around various test corridors while transmitting a filtered 10 Mb/s pseudo-noise (PN) sequence binary phase shift keying (BPSK) signal. The received signal was down converted to 70 MHz, digitized when trigger criteria were met, and stored for later analysis. Received signal strength was also recorded. The first step in data analysis consisted of dividing the fast Fourier transform (FFT) of the recorded signal by the FFT of the expected signal. The received signal strength data was then used to correct for flat fade effects. The resulting signal is the difference (dB) between the expected signal at the receiver intermediate frequency (IF) output and the measured receiver IF output during the error event. This difference is the aeronautical telemetry channel characteristic. The characteristics of this difference signal were then matched against a 2-ray and 3-ray multipath fading model with reflected signal amplitude and path delay as the variables.