Performance Of The Radon Transform Method For Constellation Identification

The problem of identifying the type of signal constellation in use by a data modem without the active cooperation of the transmitting modulator is addressed in this paper. This prob- lem arises in so-called "multi-drop" networks in which nodes may independently enter and leave the network without ex- plicit initialization. A previous paper by the authors showed that Radon transform techniques can be used to recognize the type of rectangular or cross constellation in use, and to determine its orientation, even if the received signal-to-noise ratio is quite poor. This method is successful even when there is incomplete equalization and some residual carrier remains. With these estimates a decision-directed demodulator can be appropriately initialized. This paper develops an analytical structure which permits the performance of the identification method to be evaluated as a function of constellation size, noise levels and distributions, number of input samples, and the degree of angular quantization. /sup 1/