MIMO Codes for Uniform Illumination Across Space and Time in VLC With Dimming Control

Abstract

Indoor visible light communications (VLC) require simultaneous illumination and communication. Hence, uniformity in the illumination is a key consideration for user comfort and data transfer in the VLC systems. Several run-length-limited codes have been proposed in the literature that mitigate flicker for single-input and single-output VLC systems. Recently, codes have been proposed for multiple-input multiple-output (MIMO) VLC systems. However, uniform illumination along with dimming control has not been considered for MIMO VLC systems. Hence, in this paper, we propose codes with generalized algorithms for encoding and decoding that maintain consistency in the illumination across space and time and achieve the desired dimming level. We present the expressions for code rate, run-length, and Hamming distance for the proposed codes. Through Monte Carlo simulations, we compare the code matrix error rate (CER) performance of the proposed codes with zero-forcing, minimum mean square error, and maximum likelihood based detectors for various number of transmit and receive antennas. We also compare the mutual information of the proposed codes for various number of transmit and receive antennas. The numerical results show that the proposed codes exhibit good performance while satisfying the design criteria.

Constant Weight Space-Time Codes for Dimmable MIMO-VLC Systems

“…The code matrix of the UISTC scheme strictly guarantees the same number of bit '1' in every time slot while ensuring the dimming control constraint. The position of bit '1' in each row of the UISTC code matrix can be achieved by iterative computations provided in [18]. Compared with the CWSTC scheme we proposed, the UISTC scheme focuses more on the uniformity of illumination in each time slot and has higher encoding/decoding complexity.…”

“…Therefore, in this paper, we first define the number of transmitters is N and introduce the CWSTC scheme applied to N × N MIMO-VLC systems and then present a supplementary explanation for the scheme applied to N t × N r MIMO-VLC systems. The proposed scheme has better spectral efficiency and BER performance than the UISTC scheme introduced in paper [18].…”

“…We can regard a space-time code as a N × N square matrix. The dimming factor γ of the schemes IEEE Photonics Journal CWSTC for Dimmable MIMO-VLC Systems based on space-time codes can be defined as [18].…”

“…Paper [22] proposed a run-length limited code that can decrease error, achieve the dimming target, and avoid flicker. Many dimming control schemes take into consideration run-length limitation such as [18], [23] and [24]. Thus run-length limitation is essential for dimmable VLC systems.…”

“…Paper [17] proposed a scheme for uniform illumination, but the illumination consistency for every LED is not taken into account. Uniform illumination space-time codes (UISTC) scheme [18] is a dimming control scheme for MIMO systems. It can realize high data rate communication and achieve dimming targets, but the error performance and spectral efficiency are still likely to be improved.…”