Orthogonal Frequency Division Multiplexing Quadrature Index Modulation on Visible Light using a Discreet Fourier Transform Spread
Piece written by Gavin J Howell and consulted on by Telejett Consulting(March 2023):
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Innovative multi-carrier techniques are rapidly being investigated and developed in industry and academic institutions [1,2] to maximize the data throughput efficiency of carrier technologies like radio and now most recently, the visible light part of the electromagnetic spectrum, for use without optic fiber. This is in response to the demand on modern communication systems to produce ever increasing data throughput rates for high security applications, which has become intense over the last decade with the standardization of 5G and the inception of 6G protocols facilitating IOT(internet of things) connections [3-5] across the largest global mobile networks.
Electromagnetic data carrier spectral efficiency has become paramount in determining whether networks can deliver the high data throughput rates required. Using visible light as a data carrier has some advantages over using radio, for example, an enhanced physical layer security with little or no electromagnetic interference and no license requirements for the use of spectrum resources. There are also some challenges to using visible light as a carrier but these challenges need not be a barrier to the effective use and enhancement of existing data maximizing technologies across the visible light spectrum, like Orthogonal Frequency Division Multiplexing with Quadrature Index Modulation (OFDM-QIM). More specifically, a Discreet Fourier Transform Spread, DFT-S-OFDM-QIM, has successfully been investigated as a high-speed data throughput enhancing technology that is robust against LED non-linearity which is one of the challenges when using visible light as a carrier [1,2].
(OFDM-QIM) is a fairly novel technique[6-7], that evolved from a knowledge of spatial modulation[8-12] and involves multiplexing the extra data bits that are carried on both the in-phase and quadrature components of the sub-carrier indices of the VLC transmitter/carrier [13,14]. The data throughput before multiplexing is maximized by using innovative high-order amplitude constellations to carry data on the Quadrature and Index spatial components. By using a Discreet Fourier Transform (DFT) spread (S) across the simulated and experimental mechanism of OFDM-QIM, it is possible to suppress the Bit Error Rate (BER) of the transceiver sent data versus the receiver received data. The Peak to Average Power ratio (PAPR) of OFDM-QIM can also be optimized by using DFT spreading. This technique guards against the non-linearity of the LED transmitters. Using these methods of carrier manipulation, a data throughput rate of between 172.5 and 225 Mb/s has been achieved on a blue LED VLC carrier under experimental conditions [1,2].
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