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LiFi Physical Layer basics | LiFi PHY-I,II,III types

This page describes LiFi physical layer basics with block diagram. It mentions different types of LiFi physical layer versions viz. PHY-I, PHY-II and PHY-III with supported features and modulation code rates.

Following are the functions of LiFi Physical layer:
• Provide services to upper layer.
• Used to provide error correction at the receiver by using FEC techniques such as Convolution encoding and RS encoding.
• Used to activate and de-activate VLC transceiver.
• Provides WQI for all the received frames.
• Helps in synchronization at the receiver using preamble incorporated in the frame structure.
• Inserts header (PHR) at transmit end. This is decoded at receive end to determine length field of the PSDU.
• It is used for channel selection as per requirement.
• RLL (Run Length Limited) Encoding helps in correcting DC balance, clock recovery and flicker mitigation.

There are different LiFi physical layers based on different data rate and application of use such as indoor or outdoor.


LiFi PHY-I version is developed to meet low data rate requirement from 12 to 267 Kbps. It is ideally used for outdoor application.

LiFi Physical-Layer PHY-I Type
Fig-1: LiFi Physical Layer Transmitter (version: PHY-I)

Modulation RLL Code Optical
Clock rate
FEC(RS outer code) FEC(CC inner code) data rate
OOK Manchester 200 KHz (15,7) 1/4 11.67 Kbps
(15,11) 1/3 24.44 Kbps
(15,11) 2/3 48.89 Kbps
(15,11) None 73.3 Kbps
None None 100Kbps
VPPM 4B6B 400 KHz (15,2) None 35.56 Kbps
(15,4) None 71.11 kbps
(15,7) None 124.4 Kbps
None None 266.6 Kbps

Table-1: LiFi PHY-I Operating Modes (Modulation, Code rates)


LiFi PHY-II version is developed to meet moderate data rate requirement from 1.25Mbps to 96 Mbps. It is ideally used for indoor application.

LiFi Physical Layer PHY-II Type
Fig-2: LiFi Physical Layer Transmitter (version: PHY-II)

Modulation RLL Code Optical
Clock rate
FEC data rate
VPPM 4B6B 3.75 MHz RS(64,32) 1.25 Mbps
RS(160,128) 2 Mbps
7.5 MHz RS(64,32) 2.5 Mbps
RS(160,128) 4 Mbps
None 5 Mbps
OOK 8B10B 15MHz RS(64,32) 6 Mbps
RS(160,128) 9.6 Mbps
30 MHz RS(64,32) 12 Mbps
RS(160,128) 19.2 Mbps
60 MHz RS(64,32) 24 Mbps
RS(160,128) 38.4 Mbps
120 MHz RS(64,32) 48 Mbps
RS(160,128) 76.8 Mbps
None 96 Mbps

Table-2: LiFi PHY-II Operating Modes (Modulation, Code rates)


LiFi PHY-III version is developed to meet data rate requirement of 12 Mbps to 96 Mbps. It is used in the systems where color source based on RGB and detectors are widely employed.

LiFi Physical Layer PHY-III Type
Fig-3: LiFi Physical Layer Transmitter (version: PHY-III)

Modulation Clock rate FEC Data rate
4-CSK 12MHz RS(64,32) 12 Mbps
8-CSK 12MHz RS(64,32) 18 Mbps
4-CSK 24MHz RS(64,32) 24 Mbps
8-CSK 24MHz RS(64,32) 36 Mbps
16-CSK 24MHz RS(64,32) 48 Mbps
8-CSK 24MHz NONE 72 Mbps
16-CSK 24MHz NONE 96 Mbps

Table-2: LiFi PHY-III Operating Modes

Note: Information provided on this page is derived from IEEE 802.15.7-2011 draft version. Pls. refer latest standard specifications published time to time by IEEE for any updates.

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