Dongsun Seo

White LED-based optical wireless link with improved transmission capacity using nonorthogonal multiamplitude phase frequency modulation

Abstract. A nonorthogonal amplitude, phase, and frequency modulation (APFM) technique that can increase the transmission capacity of an optical wireless link based on white light-emitting diode (LED) is proposed. It is implemented by the simultaneous use of nonorthogonal frequency shift keying (FSK) and quadrature amplitude modulation (QAM). A white LED-based wireless link using a 64-APFM scheme is constructed to experimentally verify the proposed technique, where the 64-APFM scheme is implemented by the combination of nonorthogonal 4-FSK and 16-QAM. Two more bits per symbol are transmitted using the proposed scheme with the same bandwidth of QAM. No intercarrier interference effect is observed at the 0.02-% frequency spacing (0.001 MHz) for the used RF carrier (5 MHz) because the correlation between the received 64-APFM signal and only one carrier at a time is accomplished with the help of digital signal processing. 6-Mbit/s (1-Msymbol/s) data are successfully transmitted through an optical wireless channel with a limited bandwidth of 1 MHz. This indicates that six bits per symbol can be transmitted using the proposed APFM technique at the same physical bandwidth as 16-QAM.

Non-orthogonal frequency shift keying for optical wireless link based on visible light emitting diode

A non-orthogonal frequency shift keying (NOFSK) modulation technique, which improves the transmission capacity of an optical wireless link based on a visible light emitting diode (LED), is proposed in this paper. A NOFSK signal with the modulation order of 4 is generated and then is transmitted using an optical wireless link based on the white LED in order to verify experimentally the proposed technique. One more bit per symbol are transmitted successfully showing the only 3% increase of 2-MHz physical bandwidth at the bit error rate (BER) below 10-5.

Three dimensional modulation for improved transmission capacity in white LED based optical wireless link

A three dimensional modulation, which can improve the channel capacity of visible optical wireless transmission, is proposed, where it is implemented by the use of the simultaneous modulation of amplitude, phase, and frequency without the request of additional physical bandwidth compared with two dimensional modulation such as quadrature amplitude modulation (QAM). Using the proposed technique, a 64-ary amplitude, phase, and frequency modulation (APFM) is accomplished by combining 4-frequency shift keying (FSK) and 16-QAM. Using an experimental optical wireless link based on white light emitting diode (LED), the 64-ary APFM signal with 1-MHz channel bandwidth is transmitted wirelessly at 106 symbols/s and then only two errors are observed. This means that 6 bits/symbol can be transmitted using the proposed technique.

White light-emitting diode based wireless orthogonal frequency division multiplexing link with improved transmission capacity using Bayesian compressive sensing

Abstract. We propose a technique that improves the channel capacity of an optical wireless orthogonal frequency division multiplexing (OFDM) transmission, which employs a visible light-emitting diode. An OFDM waveform encoded by quadrature phase shift keying (QPSK) or 16-quadrature amplitude modulation is compressed and then transformed into a sparse waveform using a proposed advanced systematic sampling. At the optical wireless receiver, the original waveform is recovered by L1-minimization based on a Bayesian compressive sensing. Our experimental results show the significant increase in the channel capacity from 31.12 to 51.87  Mbit/s at forward error correction limit (i.e., error vector magnitude of 32%) in case of QPSK symbols.