Error rate estimation in a multi-channel active phased array

The symbol error rate (SER) degradation due to intermodulation and sidelobe (or co-channel) interference in a multi-channel active phased array satellite communication system is investigated. The intermodulation products are generated by the RF power amplifier nonlinearity, and the sidelobe interferences are introduced when multiple channels use the same carrier frequency. Traditionally, the far field power of the intermodulation and sidelobe signals are combined non-coherently with the thermal noise power at the receiver to form the total system noise (N+I). The SER is then estimated based on the carrier to total noise ratio, C/(N+I), by assuming the total noise to be white Gaussian and uncorrelated with the desired signal. The coherency effects of the interferences are therefore ignored. In this paper, we test the accuracy of this method. We develop expressions to calculate the intermodulation and sidelobe far-field powers, and we analytically estimate the symbol error rate (SER/sub est/). We also compute the symbol error rate (SER/sub c/) with a Monte Carlo simulation that includes filtered QPSK channels, the active phased array, and a coherent receiver with thermal noise. When we compared the results of the two methods, we observed a discrepancy in bit error rate that is caused by ignoring the coherent effects of the interferences in the analytical method. This discrepancy was larger when the interference consisted of only sidelobe signals than when the interference contained both sidelobe and intermodulation signals.