Interference effects on Space Station Freedom and Space Shuttle orbiter Ku-band downlinks

AbstructThe space shuttle orbiter (SSO) Ku-band single access return (KSAR) link and the space station freedom (SSF) KSAR link' via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. The interference between spacecraft is minimized by opposite antenna polarizations and by TDRSS antenna beam pointing, but if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. Recently, Tsang and Su [l], [2] simulated the mutual interference effects, using a practical nonlinear bandlimited channel. The purpose of this paper is to demonstrate that a simplified (Le., linear band-limited channel) analytical approach will yield adequate accuracy for the expected range of operating conditions. Relative degradation in bit energy-tothermal noise power spectral density ratio to achieve a lop5 coded bit-error-probability is determined to be 4 dB for the Kuband SSO-to-TDRS I-channel return link with a 4.5 dB effective signal-to-interference total power ratio ( S / I ) when the Ku-band SSF-to-TDRS return link interferes, whereas Su's simulation yields approximately 5 dB degradation. For the Ku-band SSFto-TDRS return link, both analysis and simulation results yield a relative signal degradation of 0.4 dB at the effective S/I = 21.6 dB. In conclusion, interference on the Ku-band SSO-toTDRS I-channel return link is significant, but on the Ku-band SSF-to-TDRS return link it is negligible.