Citation
Abstract
Traditional methods for carrier synchronization of uncoded binary phase-shiftkeyed (BPSK) signals, e.g, conventional and polarity-type Costas loops, data-aided loops, demodulation-remodulation loops, etc., are obtained from approximations made to a closed-loop structure motivated by the maximum a posteriori (MAP) estimation of carrier phase. Inherent in all of these loops is the fact that their input data are assumed to be equiprobable (balanced) independent identically distributed (i.i.d.) binary sequences, and the MAP estimation loop from which these various structures are derived is predicated on this fact. The tracking performance limitation of such loops is the so-called squaring loss associated with the mean-squared phase error, which is the result of signal and noise products created by the necessity to remove the data modulation from the loop error signal. By reducing the amount of randomness (information) in the data that are input to the carrier synchronizer (hence the term information-reduced carrier synchronization), yet maintaining their i.i.d (but not necessarily balanced) property and also their independence of the additive noise, and then suitably modifying the synchronizer structure in accordance with this data reduction, one can obtain a significant squaring-loss improvement relative to what is achievable with the above-mentioned structures. One method for accomplishing this reduction in data randomness is through the use of decision feedback at the input of the loop structure, which should be contrasted with conventional structures such as the data-aided or polarity-type Costas loops that use decision feedback within the loop structure itself, and hence do not modify the structure based on the amount of information reduction achieved. While applying such a method to uncoded modulations will not satisfy the noise independence constraint on the modiffed data sequence (for reasons explained in the article), for coded modulations, we show that it is indeed possible to approximately satisfy both the i.i.d and noise independence conditions and, thus, to achieve the above-mentioned gains. Although the article focuses on binary modulation, the concepts and results are easily extended to multiple phase-shift-keyed (M-PSK) modulations with M ‚ 4.
Details
- Volume
- 42-130
- Published
- August 15, 1997
- Pages
- 1–21
- File Size
- 494.4 KB