Performance Comparison of OFDM Signal and CAP Signal Over High Capacity RGB-LED-Based WDM Visible Light Communication

Abstract

We experimentally demonstrate a visible light communication (VLC) system based on a single commercially available RGB-type LED. High spectrally efficient carrierless amplitude and phase (CAP) modulation and orthogonal frequency-division multiplexing (OFDM) are adopted in the intensity-modulation and direct-detection VLC system of limited bandwidth. In order to achieve higher capacity of the uneven-frequency-response LEDbased VLC system, OFDM signals are combined with the bit-and power-loading techniques, and CAP signals of various modulation are pre-emphasized to modulate one of the RGB chips. To reach the BER of less than 10 À3 , CAP and OFDM signals demonstrate the maximum data rates of 1.32 and 1.08 Gb/s, respectively, employing the blue chip. In addition to spectrally efficient formats, the wavelength-division-multiplexing (WDM) scheme is applied to further increase the capacity. After individually optimizing RGB chips, the maximum aggregate data rates of CAP and OFDM are 3.22 and 2.93 Gb/s, respectively, in our RGB-LED-based WDM VLC system. Hence, compared with OFDM, the CAP scheme shows competitive performance and provides an alternative spectrally efficient modulation for next generation optical wireless networks.

Multi-band carrier-less amplitude and phase modulation for bandlimited visible light communications systems

“…This technique is called adaptive bit-loading and is well known and widely reported in OFDM technologies [2]. To provide a brief overview, the same block diagram as proposed in Fig.…”

“…DVANCED modulation formats are becoming increasingly important in visible light communications (VLC) systems [1][2][3] using lightemitting diode (LED) infrastructure. One of the primary aims of VLC is to provide high capacity broadcasting networks to next generation smart homes and offices, whilst simultaneously providing full room illumination.…”

“…This enables an improvement in power and spectral usages over more traditional formats such as on-off keying (OOK), resulting in increased transmission speeds. For instance, transmission speeds in the region of 1 Gb/s/wavelength have been achieved in [2] by optimizing the OFDM modulation format using adaptive bit-and power-loading, while speeds in the order of hundreds of Mb/s have been achieved using OOK [4]. Adaptive loading techniques operate by adjusting the number of bits-per-symbol and power-per-subcarrier according to the measured error vector magnitude (EVM) at the receiver.…”

“…Currently, one of the most novel and popular modulation formats is carrier-less amplitude and phase modulation (CAP), which is simple to implement in available DSP hardware and has been experimentally shown to offer improved transmission speeds in comparison to OFDM when utilizing the same physical link [2]. This is significant, as CAP modulation is straightforward to implement in real time, with the most A computationally complex components being the single digitalto-analogue converter required, while the carrier frequencies are generated using finite impulse response (FIR) filters.…”

Position encoded asymmetrically clipped optical orthogonal frequency division multiplexing in visible light communications

“…Other VLC systems offering Gb/s data rates using OFDM were also reported in Refs. [15][16][17]. In IM/DD (Intensity Modulation and Direct Detection) based VLCs, the requirement for the light intensity to be positive and real implies that complex and bipolar signal formats such as the traditional OFDM cannot be used.…”