Improved bit error rate estimationover experimental optical wireless channels

摘要

As a part of the EU-FP7 R&D programme, the OMEGA project (hOME Gigabit Access) aims at bridging the gap between wireless terminals and wired backbone network in homes, providing high bit rate connectivity to users. Beside radio frequencies, the wireless links will use Optical Wireless (OW) communications. To guarantee high performance and quality of service in real-time, our system needs techniques to approximate the Bit Error Probability (BEP) with a reasonable training sequence. Traditionally, the BEP is approximated by the Bit Error Rate (BER) measured by counting the number of errors within a given sequence of bits. For small BERs, required sequences are huge and may prevent real-time estimation. In this paper, methods to estimate BER using Probability Density Function (PDF) estimation are presented. Two a posteriori techniques based on Parzen estimator or constrained Gram-Charlier series expansion are adapted and applied to OW communications. Aided by simulations, comparison is done over experimental optical channels. We show that, for different scenarios, such as optical multipath distortion or a well designed Code Division Multiple Access (CDMA) system, this approach outperforms the counting method and yields to better results with a relatively small training sequence.