Statistical aspects of signal distortion in trunk-waveguide communication

The purpose of the paper is to develop a complete theory of signal distortion arising in waveguides due to modeconversion effects as caused by random waveguide irregularities. The general problem is approached by introducing the concept of a `travelling system function¿, which is a wave function travelling along the waveguide system in response to a unit impulse induced in the principal mode. In this way, the statistical variation of waveguide geometry is related to the statistical expectation of the system function. The results obtained are then applied, by way of illustration, to the solution of two particular problems: the expected waveguide attenuation, and the expected pulse distortion accompanying transmission of digital signals. The stability of statistical estimates obtained from measurements on experimental lengths of waveguide is examined. It is shown that, to reach reliable results, with close confidence limits, it is necessary to have substantial lengths of experimental waveguide available for tests.