Abstract
In this paper, we propose a novel scheme of orthogonal frequency division multiplexing (OFDM) for intensity modulation direct detection (IM/DD) optical systems. By using this novel scheme of an OFDM optical system, not only odd subcarriers but also even subcarriers can be modulated to transmit a clipping optical signal. A conventional asymmetrically clipping optical (ACO)-OFDM is applied to modulate odd subcarriers while even subcarriers are modulated by a novel technique called a symmetrically clipping optical (SCO)-OFDM. Although both the asymmetrically clipping noise caused by ACO-OFDM and the symmetrically clipping noise caused by SCO-OFDM fall onto the even subcarriers, the former interference can be estimated and removed at the receiver. Thus, SCO-OFDM symbols carried on the even subcarriers can be recovered by subtracting the estimated ACO-OFDM clipping noise from the received signal. Then the SCO-OFDM clipping noise can be removed by subtraction due to its special transmission format. Note that no DC bias added on all subcarriers makes this novel scheme achieve better performance in terms of both power efficiency and symbol error rate (SER).
Highlights
Optical wireless systems with intensity modulation direct detection (IM/DD) have been extensively studied in recent decades [1,2,3]
The technique of Orthogonal frequency division multiplexing (OFDM) has been successfully applied in IM/DD optical wireless systems, such as a DC-biased optical OFDM (DCO-OFDM) [6] and an asymmetrically clipped optical OFDM (ACOOFDM) [7,8]
We propose a novel scheme, called an asymmetrically and symmetrically clipping optical (ASCO)-OFDM, to simultaneously transmit asymmetrically clipping optical (ACO)-OFDM symbols on the odd subcarriers and symmetrically clipping optical (SCO)-OFDM symbols on the even subcarriers
Summary
Optical wireless systems with intensity modulation direct detection (IM/DD) have been extensively studied in recent decades [1,2,3]. ACO-OFDM symbols can be recovered by detecting the data carried on the odd subcarriers. We propose a novel scheme, called an asymmetrically and symmetrically clipping optical (ASCO)-OFDM, to simultaneously transmit ACO-OFDM symbols on the odd subcarriers and symmetrically clipping optical (SCO)-OFDM symbols on the even subcarriers. The SCO-OFDM clipping noise does not affect ACO-OFDM symbols because it falls onto the even subcarriers. We prove this claim in Appendix 2. By using the same operation in ADO-OFDM, we can recover ACO-OFDM symbols by extracting the data on the odd subcarriers. Since no DC bias is added to all subcarriers, this novel scheme exhibits better performances in terms of optical power and symbol error rate (SER) than ADO-OFDM does.
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