satellite modem research in rfic technologies
model and simulate the performance of a digital phase shift keyed satellite modem. The probability of bit error (P sub b) at different levels of energy per bit to noise power ratio (E sub b/N sub o) was the performance measure. The channel was assumed to contribute only additive white Gaussian noise. A second order Costas loop performs demodulation in the modem and was the key part of the simulation. The Costas loop with second order Butterworth arm filters was tested by finding the response to a phase or frequency step. The Costas loop response was found to be in agreement with theoretical predictions in the absence of noise. Finally, the effect on P sub b of a rate 1/2 constraint length 7 convolutional code with eight level soft Viterbi decoding was demonstrated by the simulation. The simulation results were within 0.7 dB of theoretical. All computer simulations were done at baseband to reduce simulation times. The Monte Carlo error counting technique was used to estimate P sub b. The effect of increasing the samples per bit in the simulation was demonstrated by the 0.4 dB improvement in P sub b caused by doubling the number of samples…. Modem, Computerized simulation, Convolution, Encoding, Costas loop, Coding, Phase modulation.