An Improved Performance of 2D ASCO-OFDM in Wireless Communication

This paper describes a novel modulation scheme of asymmetrically and symmetrically clipping optical (ASCO)-OFDM into two dimensional (2D) intensity modulation direct detection (IM/DD) optical wireless communications (OWC). The asymmetrically clipping optical (ACO)-OFDM symbols and the symmetrically clipping optical (SCO)-OFDM symbols are mapped into odd columns and even columns of transmitted matrices respectively. Due to an ASCO-OFDM signal consists of an ACOOFDM signal and a SCO-OFDM signal, the average data rate of ASCO-OFDM is higher than that of ACO-OFDM. An improved receiving technique for the asymmetrically and symmetrically clipping optical (ASCO)-OFDM is developed for wireless communication system. Analysis found that the interference caused by clipping only affects the symbols on the even subcarriers. At the receiver, the ACO-OFDM symbols can be easily obtained by detecting the data on the odd subcarriers; the SCO-OFDM symbols can be successfully recovered by subtracting the estimated ACOOFDM clipping noise and the SCO-OFDM clipping noise from the even subcarriers. The ACO-OFDM clipping noise is estimated from the received ACO-OFDM signals, and it can be reused to decrease the symbol error rate (SER) of ACO-OFDM signals. The SER of SCO-OFDM signals depend on the precision of ACO-OFDM signals. Thus, we apply an improved ACO-OFDM receiving technique in our current receiver to further improve the SER performance of SCOOFDM signals as well as that of the whole system. We show that the spectral efficiency of 2D ASCO-OFDM is twice as much as that of other OFDM modulation schemes. The major problem of OFDM high Peak-to-Average power ratio (PAPR) is reduced by 2dB. The channel capacity of ASCO-OFDM in AWGN channel is calculated. The symbol error rate (SER) performance of 2D ASCO-OFDM is simulated under the environment of additive white Gaussian noise (AWGN) and it exhibits better SER performance than 2D ACOOFDM and 2D ADO-OFDM in the same bit rate case