High Speed Chemical Vapor Communication Using Photoionization Detectors in Turbulent Flow

Abstract

We consider data transfer between a chemical vapor emitter and photoionization detectors (PIDs) in a constrained airstream (flow tube). Owing to flow unsteadiness, the system is stochastic so that Karhunen–Loeve (K–L) channel characterization is useful. We project sensor traces onto a K–L-derived signal space, formulate likelihood ratios and obtain high bit rates (≥10 bps) at low probability of error ( $\ll ~0.01$ ) over meter-scale emitter-sensor separations. At higher data rates (30 and 40 bps) inter-symbol interference (ISI) requires we enlarge the K–L characterization window to include earlier bit intervals. By taking prior bits into account we achieve error rates on the order of ≈ 0.01 at 40 bps. We consider the effects of flow rate and timing jitter on performance. Within the limits of our experimental apparatus, the probability of error decreases with increasing wind speed, owing to decreased ISI at higher wind velocity, but perhaps also as a result of previously derived fundamental bounds related to jitter.