## 6 VLC-IoT: Existing and Proposed Approaches
### Multiple Access Technique in VLC-IoT
#### 6.1.2 Proposed Approaches  
The following approaches have been proposed for VLC-IoT and a detailed account is presented in the subsection.  
In recent times, the deployment of MIMO to increase system capacity in VLC systems (MIMO-VLC) by using equipped LEDs has been widely implemented. By extension, the application of NOMA to MIMO-VLC networks has recently been proposed in the literature--albeit not explored extensively. Moreover, existing technologies utilized for NOMA-aided VLC networks would have to be upgraded while entirely new approaches need to be developed to implement NOMA for MIMO-VLC networks. Some power allocation techniques have, however, been proposed for MIMO-based networks [16; 33; 38]. Nonetheless, these techniques can so far only be implemented for NOMA-aided RF-MIMO systems. At the time of writing, these approaches are yet to be deployed for NOMA-aided MIMO-VLC networks. This is because of the special characteristics of light waves implemented in VLC systems as well as the high computational complexity of NOMA aided MIMO-VLC networks [42]. In addition, at this stage, the power allocation approaches deployed for single LED NOMA-aided MIMO-VLC cannot directly be applied in multiple LEDs NOMA-aided MIMO-VLC networks. Therefore, efficient low complexity power allocation techniques required for the deployment of the proposed NOMA aided MIMO-VLC networks for high-speed data communication are also a major concern [38; 41].  
Orthogonal frequency-division multiple access (OFDMA)-based VLCP  
Some IoT devices, e.g., robots require the integration of both high-speed transmission and high-accuracy positioning (VLCP) for indoor IoT setups [6; 41; 44]. For this reason, techniques such as the OFDMA-based VLCP which combines orthogonal frequency-division modulation (OFDM) with two-dimensional (2D) positioning algorithms for integrated VLCP systems have been proposed. However, OFDMA-based VLCP systems suffer from high out-of-bound interference (OOBI) of OFDM signals. As a result, an OFDMA-based VLCP system needs large guard bands to mitigate OOBI resulting in degraded communication and positioning performance as well as decreased bandwidth utilization efficiency. However, a different technique, the OFDMA-interleaving-based VLCP where idle positioning subcarriers are deployed to create frequency holes in the frequency domain can be deployed to mitigate this challenge. In such a case, positioning signals (blue color) that are immune to OOBI from OFDM signals are employed to fill the frequency holes in order to achieve higher positioning accuracy and bandwidth utilization performance.  
Filter bank multiple carrier (FBMC)-based VLCP  
Another technique proposed in the literature to mitigate OOBI for VLCP systems is the FBMC-based technique. This scheme uses the FBMC technique to filter interference leakage of each communication subcarrier to mitigate the negative effects of OOBI [12; 45]. In addition, FBMC-based VLCP improves spectral efficiency and the utilization ratio of subcarriers. Moreover, FBMC-based VLCP increases the positioning accuracy of VLCP systems. However, FBMC-based VLCP needs extra signal processing at the transmitter which results in high computational complexity [16].