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In this paper the two Optical Wireless orthogonal frequency division multiplexing (OFDM) techniques in intensity modulated/direct detection (IM/DD) optical systems are compared. These are asymmetrically clipped optical OFDM (ACO-OFDM) and DC biased optical OFDM (DCO-OFDM). The comparison is done by the analysis of BER versus SNR of ACO-OFDM and DCO...
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... graph of bit error rate (BER) versus SNR is used for the performance analysis. Bit error rate (BER) of a communication system is defined as the ratio of number of error bits and total number of bits transmitted during a specific period. It is the likelihood that a single error bit will occur within received bits, independent of rate of transmission. The bit error rate or bit error ratio (BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. BER has been measured by comparing the transmitted signal with the received signal and computing the error count over the total number of bits. For any given modulation, the BER is normally expressed in terms of signal to noise ratio (SNR). SNR is defined as the ratio between signal power to noise power and it is normally expressed in decibel (dB). The figure 3 shows the BER versus SNR graph for ACO- OFDM and DCO-OFDM. From the figure it can be observed that there is a clear difference between two OFDMs in terms of BER and SNR. In the initial stage BER for ACO-OFDM is higher than DCO-OFDM. As SNR value increases the BER will decrease suddenly for ACO-OFDM and in DCO-OFDM when SNR value increases the BER will be constant up to 30dB and then it will decrease. But for larger SNR the value of BER for DCO-OFDM is less. Because a larger DC-bias is used in DCO-OFDM, the nonlinear distortion is mitigated, but more power is sacrificed. Since there is no DC-bias for ACO- OFDM, it has significant advantages in terms of power efficiency. i.e. DCO-OFDM is less efficient in terms of average optical power in lower SNR values but for larger values it is power efficient. This is because the DC bias used in DCO-OFDM is inefficient in terms of optical power, while the use of only half of the subcarriers to carry data in ACO- OFDM is inefficient in terms of bandwidth. In this paper two forms of orthogonal frequency division multiplexing (OFDM) in intensity modulated/direct detection (IM/DD) optical systems are compared. They are asymmetrically clipped optical OFDM (ACO-OFDM), DC biased optical OFDM (DCO-OFDM). The comparison is done by the analysis of BER versus SNR of ACO-OFDM and DCO- OFDM for intensity-modulated direct-detection systems DCO -OFDM is less efficient in terms of optical power than ACO- OFDM for lower SNR value. But for higher SNR values it is power efficient. I would like to thank all my classmates for their support and positive responses. My teachers who supported me at every stage of my research work. My parents for their unending love and support. And God, Almighty for helping me to fight all the challenges that came on my ...
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![Fig 1. Subcarrier of the OFDM signal [3]](profile/Othman-S-Al-Heety/publication/328824433/figure/fig1/AS:694328192143363@1542552149598/Subcarrier-of-the-OFDM-signal-3_Q320.jpg)
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Citations
Visible Light Communication (VLC) concurrently affords illumination and communication. VLC emerged to overcome the demerits of Radio Frequency communication and the congestion of spectrum. The incorporation of dimming in Light Emitting Diodes (LEDs) endows energy saving and increases the alluring value of the spot. While dimming the LEDs the problem faced is flickering. The flickering can be mitigated using Variable Delta Sigma Modulation (vDSM). The Non Return to Zero (NRZ) encoded data and Optical-Orthogonal Frequency Division Multiplexing (O-OFDM) symbols are transmitted over vDSM digital dimming signals. The transmission of O-OFDM signal, Enhanced Reverse Polarity Optical OFDM (ERPO-OFDM) assures enhanced bit rate, better spectral and optical power efficiency than the transmitted NRZ encoded data through the dimming signal. The paper makes us to look onto the performance analysis of data transmission over various digital dimming modulation techniques. The ERPO-OFDM technique supports high speed communication with efficient energy saving capability in indoors under flicker avoidance while data transmission through dimmed LEDs.
An orthogonal frequency division multiplexing (OFDM) scheme is used to achieve high data rate and good performance under various channel conditions. The negative peaks in the OFDM signal are clipped based on the DC bias applied to the system which proportionally increases the peak‐to‐average power ratio (PAPR). The PAPR can be optimized by modulating the signal using a direct‐current optical orthogonal frequency division multiplexing (DCO‐OFDM) scheme. In the proposed model, the negative peak of the transmitting signal is accurately clipped off, thereby improving the performance of the modulating scheme. The optical characteristics of the LED and the photodiode are demonstrated in the transmitter and receiver respectively. The results of the system show that the DCO‐OFDM enhances the visible light communication in various channels with the increasing number of users.
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