INTERFERENCE EFFECTS ON SPACE STATION FREEDOM AND SPACE-SHUTTLE ORBITER KU-BAND DOWNLINKS

The space shuttle orbiter (SSO) Ku-band single access return (KSAR) li nk and the space station freedom (SSF) KSAR link1 via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. T he interference between spacecraft is minimized by opposite antenna po larizations 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 [1], [2] simulated the mutual i nterference effects, using a practical nonlinear bandlimited channel. The purpose of this paper is to demonstrate that a simplified (i.e., l inear band-limited channel) analytical approach will yield adequate ac curacy for the expected range of operating conditions. Relative degrad ation in bit energy-to-thermal noise power spectral density ratio to a chieve a 10(-5) coded bit-error-probability is determined to be 4 dB f or the Kuband SSO-to-TDRS I-channel return link with a 4.5 dB effectiv e signal-to-interference total power ratio (S/I) when the Ku-band SSF- to-TDRS return link interferes, whereas Su's simulation yields approxi mately 5 dB degradation. For the Ku-band SSF-to-TDRS return link, both analysis and simulation results yield a relative signal degradation o f 0.4 dB at the effective S/I = 21.6 dB. In conclusion, interference o n the Ku-band SSO-to-TDRS I-channel return link is significant, but on the Ku-band SSF-to-TDRS return link it is negligible.