OFDM-Based Optical Spatial Modulation

Abstract

Spatial modulation (SM) has proven to be a promising multiple-input-multiple-output (MIMO) technique which provides high energy efficiency and reduces system complexity. In SM, only one transmitter is active at any given time while the rest of them remain silent. The index of the active transmitter carries information. This spatial information is in addition to the data carried by the constellation symbols in the signal domain. Therefore, SM increases the transmission rate of the communication system compared to single-input-single-output and space-time block coding (STBC)-MIMO. For signal domain data encoding, orthogonal frequency division multiplexing (OFDM) has been widely adopted. The key benefits in multi-carrier intensity-modulation and direct-detection (IM/DD) systems are: i) the capability to achieve high spectral efficiency and ii) the ability to effectively mitigate direct-current (DC) wander effects and the impact of ambient light. However, current off-theshelf light emitting diodes (LEDs) which are used as transmit entities are primarily bandwidth limited. Thus, there are benefits of combining SM and OFDM to enhance transmission speeds while maintaining low complexity. In this paper, the two most common OFDM-based SM types, namely frequency domain SM (FD-SM) and time domain SM (TD-SM), are investigated for optical wireless communications (OWC). Moreover, proof-ofconcept experimental results are presented to showcase practical feasibility of both techniques. The obtained results are also compared with Monte Carlo simulations. The results show that TD-SM with an optimal maximum-a-posteriori-probability (MAP) detector significantly outperforms FD-SM. It can be inferred from the results that TD-SM is a strong candidate among OFDMbased optical SM systems for future optical IM/DD wireless communication systems.

Hybrid Adaptive Bias OFDM-Based IM/DD Visible Light Communication System

“…The combination of QAM and PAM achieves the advantage of high spectral efficiency. However, the hybrid optical OFDM signal of w n is a bipolar signal, and it is necessary to ensure the non-negativity of the signal in the optical OFDM scheme [19]. In order to guarantee the non-negativity of w n , we design the adaptive bias according to the characteristics of the superimposed signal.…”

Improvement of Multipath Channel Performance for Optical MIMO-OFDM in LED Modulation with Fully Generalized Spatial-Frequency

“…The OFDM definition provides the best data rate coverage where the pace is found to be drop [1]. The MIMO idea has increased frequency, but the data coverage has been found to be low [2].…”

Review of advanced techniques for multi‐gigabit visible light communication

“…Moreover, dimming conditions are used to completely eliminate the flicker effect on human eye using MGSM [126]. To improve the spectral efficiency of the O‐OFDM signal for time/frequency domain, a fully generalised index‐spatial LED modulation scheme has been proposed in [127] and for 16 × 16 MIMO‐OFDM in [22]. In addition, improvement of spectral efficiency by SM combined with space shift keying and spatial pulse position modulation was investigated by Olanrewaju et al [128].…”

“…Oxford University has comprehensive research background on multi‐Gbps VLC system including hybrid equalisation method for modulated optical sources, LD based white‐light communications link, VLC receiver design for Internet of Things (IoT) applications, and GaN‐based micro‐LED (µLED) fabrication [18, 19]. Prof. Harald Haas (PureLiFi's CSO) established a LiFi centre at the University of Edinburgh and is working on high‐speed bi‐directional VLC link [20], LiFi mobility [21], spatial modulation (SM) [22], µLEDs [23], and improvement for optical wireless networks. Furthermore, North Umbria University is working on the application of polymer LEDs for 5G networks.…”