On the Capacity of Intensity-Modulated Direct-Detection Systems and the Information Rate of ACO-OFDM for Indoor Optical Wireless Applications

• Published in: IEEE transactions on communications 2012-03, Vol.60 (3), p.799-809
• Main Authors: Xia Li, Vucic, J., Jungnickel, V., Armstrong, J.
• Format: Article
• Language: English
• Subjects: ACO-OFDM; Applied sciences; Asymmetry; Bandwidth; Channel capacity; Channels; Electric power generation; Exact sciences and technology; Fiber optic communications; Fiber optic networks; Frequency modulation; Indoor; information rate; Information rates; Information theory; Information, signal and communications theory; intensity modulated direct detection; Line of sight; Modulation; Multiplexing; OFDM; Optical modulation; Optical receivers; Optical telecommunications; Optical transmitters; optical wireless; Orthogonal Frequency Division Multiplexing; Signal and communications theory; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Transmission and modulation (techniques and equipments); Wireless communication; Wireless optical communications
• ISSN: 0090-6778; 1558-0857
• DOI: 10.1109/TCOMM.2012.020612.090300

In this paper we derive information theoretic results for asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) in an intensity modulated direct detection (IM/DD) optical communication system subject to a range of constraints. ACO-OFDM is a form of OFDM designed for IM/DD systems. It is an effective solution to intersymbol interference (ISI) caused by a dispersive channel and also requires less optical power than conventional optical modulation formats. Although the classical Shannon capacity formula cannot be applied directly to an IM/DD system, we show that when ACO-OFDM is used in an IM/DD system, it can be adapted to calculate the information rate of the data-carrying odd frequency subcarriers. As a result conventional water filling techniques can be used for a frequency selective channel. These results are applied to indoor wireless systems using realistic parameters for the transmitter, receiver and channel. The maximum rate at which data can be transmitted depends on the channel, the electrical bandwidth and the transmitted optical power. Even when there is no line of sight (LOS) path, when the electrical bandwidth is limited to 50 MHz and the average optical power is limited to 0.4 W, data rates of approximately 80 Mbit/s can theoretically be achieved.