Abstract
When the characteristics of a digitally modulated signal are not known, the estimation of its modulation parameters is crucial for many emitter interception applications. This paper presents the Modified Cramer-Rao Lower Bound (M-CRLB) on the modulation parameters of a QAM signal embedded in AWGN. The modulation parameters considered are the carrier frequency, carrier phase, signal amplitude and symbol time. The M-CRLB results indicate that the carrier frequency has the highest estimation accuracy, followed by the symbol time, the signal amplitude and the carrier phase. The M-CRLBs of the four parameters are affected by the modulation level and the pulse shaping function. When the modulation level increases, the estimation accuracy decreases. When a raised cosine pulse shaping filter is used, the M-CRLBs on the four parameters all increase as the raised cosine roll-off factor increases. For lowpass pulse shaping filter, the M-CRLB on the symbol time decreases as the filter bandwidth increases. However, the M-CRLBs on the other three parameters increase.
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