Hybrid Super-Nyquist CAP Modulation based VLC with Low Bandwidth Polymer LEDs

Abstract

Visible light communication systems often suffer from high frequency attenuation when transmitting outof-band. This effect has been ameliorated by multi-band modulations such as multi-band carrier-less amplitude and phase (m-CAP), which minimises the effect of decreased high frequency magnitude and maximises signal-to-noise ratio-per-sub-band. On the other hand, in the pass-band region, super-Nyquist CAP (SCAP) can offer throughput improvements with no additional complexity at the receiver, at the cost of bit error rate. We propose, for the first time, a new hybrid SCAP modulation format that takes advantageous of both SCAP (i.e. overlapped sub-bands within the modulation bandwidth) and conventional m-CAP (orthogonally spaced bands outside the modulation bandwidth) while maintaining isolation between noise sources. We show higher baud rates within the passband region whilst supporting out-of-band transmission at lower error vector magnitudes.

Carrierless amplitude and phase modulation in wireless visible light communication systems

“…In this variant, typically referred to as super-Nyquist (SN-CAP), the spacing between the CAP subbands is reduced in order to increase the spectral efficiency of the scheme [96,[124][125][126]. However, this results in spectral overlap (band interference) between adjacent bands which destroys the orthogonality of the respective pulse shaping filters and in the distortion of the transmitted waveforms.…”

“…Additionally in [96], it has been demonstrated that the induced IBI can be modelled as a MIMO system and therefore appropriate equalizers can be deployed to mitigate IBI and enable the successful symbol recovery on each subband. Hybrid super-Nyquist multi-band CAP schemes have also been proposed where some of the subbands are overlapped and some are kept orthogonal as in conventional m-CAP [126], achieving a balance between induced IBI and channel crosstalk (non-orthogonality) due to the non-flat frequency response of the channel. The scheme has been shown to achieve better performance than the respective conventional m-CAP and pure SN-CAP in an OLED-based VLC link [126].…”

“…Hybrid super-Nyquist multi-band CAP schemes have also been proposed where some of the subbands are overlapped and some are kept orthogonal as in conventional m-CAP [126], achieving a balance between induced IBI and channel crosstalk (non-orthogonality) due to the non-flat frequency response of the channel. The scheme has been shown to achieve better performance than the respective conventional m-CAP and pure SN-CAP in an OLED-based VLC link [126]. Similarly, hybrid schemes where CAP channels have been combined with PAM signals have also been proposed and demonstrated achieving better performance than the respective conventional m-CAP scheme [127].…”