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.