P.A.M.-microwave transmission in coloured gaussian noise environment

In the current literature, the theoretical analyses which deal with the problem of additive coloured Gaussian noise (c.g.n.) assume that a pre-whitening filter is built into the receiver. This filter modifies the c.g.n. power spectrum density in such a way that, at the input of the threshold comparator, a bandlimited white Gaussian noise (w.g.n.) is obtained. The assumption of a pre-whitening filter is well justified for the purposes of theoretical analysis. Unfortunately, for practical systems, the design of a pre-whitening filter is not always feasible, as in the case of 1.544 Mbit/s data under voice (d.u.v.) hybrid microwave transmission. In this paper, the equations for the performance of a multilevel p.a.m. receiver (as is the case in d.u.v.) for a c.g.n. environment are presented and show that, without the insertion of the pre-whitening filter, the same results are obtained as in a w.g.n. environment. The validity of these results is demonstrated by using a number of noise filters to obtain c.g.n. for laboratory measurements and by practical field measurements on an eight-hop 6 GHz microwave system (RCA-MM-600) which employs 4-level p.a.m. transmission in a d.u.v. configuration.