“ Non ideal behaviour of TXA equipment: Simulated BER performance”

Simulated BER curves of a satellite channel link with a X-Band Transmission Assembly (TXA) are presented in this paper. System under study models the TXA, an AWGN channel and an ideal receiver. TXA shall provide the appropriate signal amplification in order to perform the downlink at a given data rate ensuring a specified BER, in two different system configurations: with and without data coding (Reed Solomon). Hence TXA design is critical. The signal degradation due to the non idealities occurring in modulator and the use of nonlinear amplifiers shall be taken into account. An estimation of the effects of these non idealities on the BER performance is necessary in order to achieve the required performance with adequate design margins. Simulink offers a powerful mean to perform a detailed system simulation, allowing the comparison between the behaviour of a real system and an ideal system. Assuming as key parameters (phase/amplitude accuracy, phase noise and TWTA AM/AM and AM/PM characteristic) the typical measurements taken from the inherited hardware and using a RF filter foreseen in some TXA implementations, simulated BER curves show few differences with respect to measured BER curves during TXA test. Other BER curves have been obtained simulating a frequency reuse transmission scheme where two channels are allocated in the same transmission band and transmitted through two orthogonal polarizations (RHCP and LHCP).