Coding for uncoordinated multiple access in visible light positioning systems

To avoid interference among the signals from different transmitters in a visible light positioning (VLP) system, central unit is usually used. This resists us to simply deploy a VLP system on the existing lighting infrastructure. This paper proposes an uncoordinated multiple access scheme for VLP systems without the need for central unit. A unique codeword is allocated to each transmitter equipped with a light emitting diodes (LED). The transmitters send the code words in an asynchronous manner. A receiver can eliminate the interference among the LEDs by using Fast Fourier Transform (FFT) to estimate the average received powers from each LED. Then the estimated power is used for position estimation. The required FFT size and the scheme delay, i.e., the minimum received signal duration needed by the receiver to estimate the average received powers from the LEDs, grow linearly with the number of LEDs. The proposed scheme is compared with the existing schemes in literature. Simulation results show that the proposed scheme outperforms the existing schemes in terms of receiver complexity, scheme delay and system performance. The average 3-dimensional position error of 3 cm is achievable for average transmitting optical flux of 500 lm. Our proposed scheme can be applied to a system with a large number of LEDs. The potential of the proposed scheme for data communication is discussed.