Experimental Demonstration of Staggered CAP Modulation for Low Bandwidth Red-Emitting Polymer-LED Based Visible Light Communications

Abstract

In this paper we experimentally demonstrate, for the first time, staggered carrier-less amplitude and phase (sCAP) modulation for visible light communication systems based on polymer light-emitting diodes emitting at ∼639 nm. The key advantage offered by sCAP in comparison to conventional multiband CAP is its full use of the available spectrum. In this work, we compare sCAP, which utilises four orthogonal filters to generate the signal, with a conventional 4-band multi-CAP system and on-off keying (OOK). We transmit each modulation format with equal energy and present a record un-coded transmission speed of ∼6 Mb/s. This represents gains of 25% and 65% over the achievable rate using 4-CAP and OOK, respectively.

Visible light communication with efficient far-red/near-infrared polymer light-emitting diodes

“…This lifetime can be decreased to the sub-nanosecond range by engineering the MQW active layer volume, improving heat sinking, heavy doping, or using non-polar substrates [21][22][23][24] . As discussed in previous reports [9][10][11][12][13][14] , OLEDs' lower modulation bandwidths arise from their RC time constant, which strongly depends on charge mobilities of~10 −6 -10 −2 cm 2 /V s in OSs (at least three orders of magnitude lower than that in GaN) and the size of the photoactive area 13 . However, these mobilities are still suitable for a wide range of prospective connections, such as those expected for the implementation of the internet-of-things (IoT), which only require data rates of a few Mb/s (or less).…”

“…a Simplified block diagram of the real-time experimental VLC setup including pulse shaping p(n) and matched filtering p(−n) (where n is the current discrete time sample) using a square-root raised cosine, as defined in ref. 10 . Acronyms are defined as follows: USRP-RIO, Universal Software Radio Peripheral-(with) reconfigurable input/output, emulating data traffic in the on-off keying transmission mode at the transmitter (2953) and the receiver (2943); D s data source, N ss number of samples per symbol, LFTX/RX low-frequency transmitter/ receiver, DAC digital-to-analogue converter, PD ThorLabs PDA36A-2 silicon detector, ADC analogue-to-digital converter, Sync synchronisation, DOWN down-sampling, E s estimated data source, OLED organic light-emitting diode.…”

“…VLC links integrating OLEDs as optical transmitters have already been reported by our groups and others [9][10][11][12][13][14] , with data rates exceeding 10 Mb/s due to the leveraging of both equalisation algorithms and wavelength division multiplexing. Undoubtedly, such data rates are not as high as those afforded by "inorganic" VLC systems (up to 35 Gb/s) 20 based on multiple-quantum-well (MQW) LEDs and LDs, which are mainly limited by the intrinsic exciton decay lifetime [21][22][23][24] .…”

“…Approximately 98% of the EL signal decays in less than 1 μs, albeit at an~1000× slower rate than the PL dynamics. Such an apparent discrepancy, however, is due to the RC constant, which is the main limiting factor for high-frequency operation in OLEDs [9][10][11][12][13][14] . The effect of the parasitic RC is proved by the fact that we could measure some residual current (|J (t)|, black dotted lines in Fig.…”

“…These properties make inorganic LEDs 1,2 and LDs 7,8 suitable for integration into dualpurpose luminaires capable of simultaneously providing white lighting and data transmission. However, the use of organic light-emitting diodes (OLEDs) represents a valid alternative, which is gaining considerable attention for VLC [9][10][11][12][13][14] . The interest in OLEDs for communication is driven not only by their widespread use in display technologies but also by the very same advantages that have been driving the success of organic electronics.…”