Synchronization in Visible Light Communication for Smart Cities

• Published in: IEEE sensors journal Vol. 18; no. 5; pp. 1877 - 1886
• Main Authors: Vappangi, Suseela, Vakamulla, Venkata Mani
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Amalgamation; carrier frequency offset; Communication; CRLB; DCO-OFDM; Illumination; Light emitting diodes; Lighting; Lower bounds; Mathematical analysis; OFDM; Optical communication; Optical modulation; Organic light emitting diodes; Orthogonal Frequency Division Multiplexing; Orthogonality; Parameter estimation; Radio frequency; Smart cities; symbol time offset; Synchronism; Synchronization; VLC
• DOI: 10.1109/JSEN.2017.2777998
• ISSN: 1530-437X

The rapid deployment of light emitting diodes and the prominence of facilitating simultaneous illumination and communication have driven Visible Light Communication (VLC) to gain enormous prevalence in the recent times. This expedited VLC to become amalgamated with many smart city applications in particular, with the lighting infrastructure to enable seamless connectivity. The underlying challenge of this technology is to assure high data rate communication while fulfilling illumination requirements in smart cities. In this regard, optical orthogonal frequency division multiplexing (OOFDM) compatible with intensity modulated/direct detection (IM/DD) system can be exploited for VLC. Where, IM and DD is one approach of envisioning VLC. DC biased Optical OFDM (DCO-OFDM), the earliest variant of OFDM for VLC is employed in this paper. It is apparent that, the advantages of OOFDM cannot be utilized if its orthogonality is destroyed by any means. The striking difference between RF-based OFDM and OOFDM is that, OOFDM necessitates the transmitted time-domain signal to be both real and unipolar. Hence, the synchronization techniques existing for RF cannot be directly applied for VLC and consequently must be revisited. This paper analyzes the effects of carrier frequency offset (CFO) and symbol time offset (STO) in DCO-OFDM over VLC channel. Here, mathematical analysis is performed showing the effects of CFO and STO in OOFDM. Synchronization algorithms, such as Moose, Classen and Training Symbol assisted are revisited. Detailed analysis of Cramer Rao lower bound is carried out considering the joint parameter estimation of both CFO and channel estimation error.