# A Comprehensive Worst Case Bounds Analysis of IEEE 802.15.7
## 3 Technical Overview
### Physical Layer  
Each PHY presented in this standard aims at targeting a specific application domain, as they support different data rates and modulation schemes. IEEE 802.15.7 supports 6 types of PHY layers, which are explained below:  
**PHY I:** This PHY type is used for supporting low data rate applications for outdoor usage. This PHY layer uses ON-OFF keying (OOK) (11-100 Kbps) and variable pulse position modulation (VPPM) (35-266 Kbps). The moderate data rates along with some light source interference mitigation characteristics make it interesting for outdoor monitoring applications. There are Automated Driving Assist Systems (ADAS) [21] that utilize the PHY I mode due its support for outdoor low rate applications.  
**PHY II:** This PHY type is used for moderate data rate applications in indoor usage. This mode uses ON-OFF keying (OOK) (6-96 Mbps) and variable pulse position modulation (VPPM) (1.25-5 Mbps). Transmission of bio-medical signals within a hospital setting using LED lighting has been done in the literature [22] and can be easily supported by this standard. One of the many advantages of using VLC in health care monitoring is that it can avoid interference from several electromagnetic fields such as Magnetic Resonance Imaging machines. This PHY complemented with GTS service at the MAC sub-layer can support efficient time critical communications within a single channeled VLC system. In a smart home/city setting, VLC can take retrofitting to the next notch [23; 24; 25] because every socket in a house can be turned into a VLC-enabled light source. For typical house hold appliances, a PHY such as PHY II that uses OOK modulation and provides up to 96 Mbps will be sufficient.  
**PHY III:** This PHY is used for applications using color-shift keying (CSK). This PHY is useful to support applications with multiple light sources and detectors, which need large data rates (12-96 Mbps), such as in a multimedia context. The CSK modulation of the IEEE 802.15.7 is power efficient and very reliable to support High Speed Wireless Visible Light Communications [26].  
**PHY IV:** This PHY is intended for usage with discrete light sources with data rates ranging from 10 to 18 Kbps using UFSOOK, Twinkle VPPM, S2-PSK, HS-PSK and VPWMmodulations. Vehicular application scenarios, which transmit the diagnostic information of the vehicle when idle, do not demand very large data rates. The usage of UFSOOK modulation can enable such applications with low cost [27].  
**PHY V:** This PHY is intended for use with diffused surface light sources with data rates ranging from 120 to 400 bps using RS-FSK, C-OOK, CM-FSK, MPM modulations. Modulations like MPM provide robust data transmission performance while considering the stringent lighting constraints [28].  
**PHY VI:** This PHY is intended for use with video displays (short-range OWC system utilizing screens). This PHY layer supports data rates up in the range of 5-256 Kbps, using A-QL, HA-QL, VTASC, SS2 DC, IDE-MPFSK Blend, IDE watermark modulations. This PHY layer is targeting VLC solutions such as Optical Camera Communication (OCC) [29] enabling a new set of data services embedded in displays.