Transmit power reduction through subcarrier selection for MC-CDMA-based indoor optical wireless communications with IM/DD

Abstract

This research addresses the issue of average transmit optical power reduction in multi-carrier code division multiple access (MC-CDMA)-based indoor optical wireless communications employing intensity modulation with direct detection. The problem is treated in a novel way by investigating pre-and post-equalization-based subcarrier selection for transmit power reduction in downlink transmissions. Analytical expressions are derived for upper bounds of the required fixed DC bias for both cases. The fixed DC bias is used to reduce the system complexity on one hand and to devise optimal subcarrier selection criteria on the other. Simulation results based on the proposed subcarrier selection reveal significant power reduction subject to the 10 −4 bit error rate (BER) requirement for 10-Mbps 64-subcarrier MC-CDMA-based indoor optical wireless communication systems. In addition, the BER performance obtained from pre-equalization is shown to be no higher than that obtained from post-equalization for the same transmit power.light. The key advantages of such optical wireless systems are usage of flexible unlicensed spectrum, high data rate support, energy efficiency, no electromagnetic interference, low-cost front ends, and inherent security. Major issues are eye and skin safety problems which can be dealt with by limiting the average transmit optical power.The contributions of this research, which are not reported previously to the best of the authors' knowledge, are highlighted as follows:1. Average transmit optical power reduction is accomplished by subcarrier selection for the first time in MC-CDMA-based indoor optical wireless communication systems employing intensity modulation with direct detection (IM/DD). Expressions for upper bounds of a fixed DC biasusing pre-and post-equalization-based subcarrier selection are analytically derived for MC-CDMA-based IM/DD system. 3. Optimal subcarrier selection algorithms that minimizes the bit error rate (BER) for a fixed transmit optical power are proposed for both pre-and post-equalization.

Multiple Access for Visible Light Communications: Research Challenges and Future Trends

“…Importantly, it is proved that the proposed system exhibits a 3-dB transmission gain for each user compared to on-off keying (OOK). In the same context, the contribution in [11] discusses a multi-carrier (MC) CDMA-based indoor optical wireless scheme that can be considered a hybrid between OFDM and CDMA techniques. In MC-CDMA, the data symbols in the frequency domain of each user are spread over OFDM subcarriers and the aggregate sum of the frequency domain symbols from the different users is subsequently represented in the time domain through OFDM modulation.…”

“…In MC-CDMA, the data symbols in the frequency domain of each user are spread over OFDM subcarriers and the aggregate sum of the frequency domain symbols from the different users is subsequently represented in the time domain through OFDM modulation. In addition, it was shown in [11] that sub-carrier selection can be utilized to reduce the average-transmit optical power in MC-CDMA along with sub-carrier selection criteria for both pre-and post-equalization. However, there is also a number of limitations in the O-CDMA scheme.…”

“…As a consequence, transmission angles tuning in this case degrades the overall system throughput. Finally, when comparing TDMA with NOMA, it was shown in [16] that the 11 latter is capable of increasing the system capacity by 125%, if LEDs with 30 • semi-angle (φ 1/2 ) are used. This is illustrated in Fig.…”

The Design of Wireless Communication Function of Traction Substation Electrical Signal Monitoring Device

“…Circuit module accomplish the adaptive variable precision signal acquisition, signal processing and analysis, digital signal transmission functions [9][10]. Adopts double CPU structure and CPLD technology and enhance the flexibility and expansibility of the system.…”

The design and performance analysis of optical wireless ACO-MC-CDMA system in the presence of clipping noise

“…The application of optical MC-CDMA in OWC is mainly motivated by the need to provide the MA capability, resist ambient light interference and combat ISI in highly hostile indoor optical channels. In [3,4], the baseband complex MC-CDMA signaling was employed in IM/DD. In [5], an MC-CDMA system based on polarity reversed optical OFDM was presented.…”