Cupo (S'76-M'78-SM'9 1 ) received the Ph.D. degree in electrical engineering from Cornell University in 1982
- L. Robert
- IEEE TRANSACTIONS Or-; COMMUNICATIONS. VOL. 43. r…
Abstroct-Volterra functional expansions are power series with memory that explicitly characterize the input/output relationship of a finite-memory single-valued nonlinear black box whenever the latter is time-invariant and stable. The purpose of this paper is to iutroduce and report on the streugths and weaknesses of two distinct Volterra-series-type classes of adaptive nonlinear techniques for the Iluantitative measuremeut of secondand third-order harmonic distortion present in the communications channel of a, possibly signal space coded, QAM data communi cation system. Our investigation was originated as part of a re quest for new nondisruptive impairment measurement algorithms that would reliably characterize in real-time the performance of voiceband modems over both Dl conditioned private lines and the Direct-Distance-Dialing (DDD) Public Switched Network. Though, contrary to earlier studies, we do not contemplate nonlinear distortion compensator design, experimental evidence obtained by implementing the simplest of our nondisruptive al gorithms on a Digital Signal Processor chip verifies that over a certain range of signal-to-secondand third-order intermod ulation distortion ratios our measurements are consistent with those obtained via the disruptive digital four tone test under a variety of voiceband telephone channel impairment conditions. Unrortunately, our experiments also indicate that neither the digital four-tone test nor any of our nondisruptive techniques have chances to prove useful for greater than 5% of the existing voiceband channels. However, this is entirely due to the special nature of the telephone channel environment and is not likely to dilute the importance of our proposal for other types of nonlinear environments such as radio channels or sateUite links.