IEEE standard – PHY frame format for CM-FSK and C-OOK

This post reviews the design of the Physical-layer Packet Data Unit (PPDU) for CM-FSK  and C-OOK operating modes within PHY V of IEEE 802.15.7m.

For a detailed explanation of how these modes operate, please visit the previous CM-FSM post and the previous C-OOK post. The comparison between these modulation schemes for rolling shutter OCC was discussed in this previous post.

Here are some demo videos for CM-FSK, C-OOK Manchester code, and C-OOK 4B6B code.

General PPDU

Given the general structure of PPDU for all OCC Operating modes as illustrated in Figure 1.

• SHR: Synchronization Header
• PHR: Physical-Layer Header
• HCS: Header Check Sequence
• PSDU: PHY service data unit

“Use of over-the-air PHY frame configuration is forbidden for PHY types IV, V and VI. It is mandatory that PHY frame configuration be done via the PHY PIB. This is due to the fact that unlike traditional wireless LAN/PAN, the data rates associated with OCC are such that the configuration overhead cannot be tolerated.” -IEEE 802.15.7m

The details on the format of PHY V operating mode, particularly for CM-FSK are reviewed as follows.

CM-FSK PPDU

CM-FSK Preamble Field

The preamble field for CM-FSK is two symbol times long that carries two different frequencies, f_SF and f’_SF (table 1) which are defined by a corresponding PHY PIB attribute.

Table 1- CM-FSK preamble

CM-FSK PHY Header

There is no need for CM-PSK PHY header to reduce transmission overhead. The entire information related to CM-FSK PPDU format is readable from PHY PIB attributes.

CM-FSK PSDU

The PHY data service packet unit can be transmitted right after the preamble. Thus, the transmission overhead is only caused by the preamble.

The length of CM-FSK PSDU is variable, and its range is also readable from one of the PHY PIB attributes. So once again, no overhead is wasted.

C-OOK PPDU

C-OOK Preamble Field

The preamble field for C-OOK is an OOK signal that operates at an out-of-band frequency

C-OOK PHY Header

There is no need for C-OOK PHY header to reduce transmission overhead. The entire information related to C-OOK PPDU format is readable from PHY PIB attributes.

C-OOK PSDU

The C-OOK PSDU consists of multiple data sub-packets (denoted as DS). Each sub-packet DS consists of its preamble (DS preamble) and its payload carrying asynchronous bits (front Ab and rear Ab) and data bits.

The configuration of PSDU length is implemented via the PHY PIB phyCookPsduLength.

Table 2 -PSDU frame format

Table 3 – C-OOK Subpacket format

The preamble field for C-OOK subpacket has a variable length based upon the choice of RLL coding used in the payload. The selection of the preamble is readable from one of the PHY PIB attributes.

Table 4 – C-OOK Preamble Choice for subpacket

That means, C-OOK follows the packed-mode transmission.

Summary

PHY frame formats for rolling shutter OCC modes (CM-FSK and C-OOK) are reviewed.