Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: Message sequences for ranging. Date Submitted: March 9, 2006 Source: Vern Brethour, Time Domain Corp Contact: Vern Brethour, Time Domain Corp Voice: +1 256.536.9663; E-Mail: vern.brethour@timedomain.com; Re: TG4a Abstract: Overview of the traffic flow for Standard and Private Ranging with 15.4a Purpose: To establish the algorithmic flow of ranging in preparation for letter ballot re-circulation. Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Vern Brethour

Ranging still needs some work • The good news is that we got LB33 out on time. • The bad news is that the ranging material was pretty ragged. • This presentation is to set us up to edit the draft for the re-circulation. Vern Brethour

Ranging Material ragged? • For example….. This looks pretty good. • Except that these sections do not actually exist in Clause 6.8! Writing these sections fixes comment 520. Vern Brethour

What’s missing? • We need a switch to turn on ( & off ) channel sounding in the PHY. • When channel sounding is turned on, then the PHY will commence a channel sounding and leading edge search after every acquisition. • When not actually doing ranging, the application would be wise to turn this switch off to save the power that would be consumed by the channel sounding engine. Vern Brethour

Okay, we’ll have a way to “arm” the devices for ranging activity. Then what? • Let’s run through the message sequence for a ranging exchange and do an inventory. • The festivities begin with a ranging request primitive. Vern Brethour

Standard Ranging Originator MAC Originator PHY Target PHY Target MAC Range request Range packet Range initiation Range response Long Preamble ACK Range confirm Timestamp indication No encryption, just send it out in a different message. Timestamp response Timestamp reply Timestamp report ACK response Ack Timestamp confirm Vern Brethour

The range request primitive. • It is talked about in clause 7.5.7a.4 and 7.5.7a.5, but not is not defined anywhere. • It needs to be in Clause 6.2 • The information it contains: • Preamble length for initiation • Preamble length for response • Standard or Private protocol • If Private, the preamble code for response. Vern Brethour

The Range request primitive causes transmission of a Range packet • This is a standard message on the air. It will generally use a long preamble. • The receiver will do a channel sounding with the preamble because it was already armed to do so. Vern Brethour

The Range Packet • The Range Packet is referred to extensively in clause 7.5 but is not defined anywhere. • The information it contains: • Preamble length for response • Standard or Private protocol • If Private, the preamble code for response. Vern Brethour

Upon receipt, the PHY does a range initiation primitive. • This isn’t defined either. • The PHY passes to the MAC, • Preamble length for response • Standard or Private protocol • If Private, the preamble code for response. • The PHY keeps the FOM information to itself for now. A counter is running in the PHY which started at the delimiter of the range packet. Vern Brethour

Upon receipt, of the Range initiation primitive, the MAC must (quickly) issue a range response primitive • The Range response is talked about in clause 7.5.7a.5, but not is not defined anywhere. • It needs to happen fast: There is a PHY counter running and crystals are drifting. • It contains: • Preamble length for response • Standard or Private protocol • If Private, the preamble code for response. Vern Brethour

The range response is almost a normal ACK • It just (potentially) has a long preamble. • If it is private, the preamble code will be the one specified by the MAC. • If it is Private, the start time of the response is dithered. The dithering is purely the vendor’s choice. Anything reasonable will be fine and interoperability is not affected. Vern Brethour

After the Range response goes out; the target PHY sends the target MAC a timestamp indication primitive. • The primitive is not discussed in the LB33 draft, although it’s data elements are. • The timestamp indication contains 5 things: • The turnaround time (32 bits); • The tracking time(32 bits); • The tracking offset (24 bits) • The Ranging Figure of Merit (8 bits) • Potentially more future things, because the top bit of the FOM is an expansion bit. Vern Brethour

Upon receipt of the Ranging response packet, the originator PHY sends the originator MAC a range confirm primitive. • You guessed it: It’s not in the draft yet. • It contains: • The turnaround time measured by the originator PHY (32 bits); • The tracking time measured by the originator PHY (32 bits); • The tracking offset measured by the originator PHY (24 bits) • The Ranging Figure of Merit measured by the originator PHY (8 bits) • Potentially more future things, because the top bit of the FOM is an expansion bit. Vern Brethour

The Target Mac now sends the target PHY a timestamp response primitive. • There is no hurry for this. • The timestamp response contains 5 things: • The turnaround time (32 bits); • The tracking time(32 bits); • The tracking offset (24 bits) • The Ranging Figure of Merit (8 bits) • Potentially more future things, because the top bit of the FOM is an expansion bit. Vern Brethour

The Target PHY then sends a Timestamp reply message • Nothing special here. The preambles are normal length. There is no urgency. • The contents are the same 5 items: • The turnaround time (32 bits); • The tracking time(32 bits); • The tracking offset (24 bits) • The Ranging Figure of Merit (8 bits) • Potentially more future things, because the top bit of the FOM is an expansion bit. Vern Brethour

Upon receipt of the timestamp reply by the originator PHY, a timestamp report primitive is sent to the originator MAC. • The timestamp report contains our now familiar set of 5 items: • The turnaround time (32 bits); • The tracking time(32 bits); • The tracking offset (24 bits) • The Ranging Figure of Merit (8 bits) • Potentially more future things, because the top bit of the FOM is an expansion bit. Vern Brethour

The Receipt of the timestamp report causes a completely normal acknowledge sequence. • There is nothing special about this sequence. • The eventual receipt of the timestamp confirm by the target MAC is the end of the festivities. Vern Brethour

The Originator MAC ends up with lots of “Stuff” • The originator MAC has 2 FOMS and 2 sets of tracking information. • Each set was measuring the same thing (relative oscillator drift) by each of the two PHYs. • What to do with 2 sets? Vern Brethour

What to do with 2 sets? • Whatever the application wants to do! • A simple application can pick the set with the best FOM and throw the other one away. • A fancier application could average the 2 sets. • An even fancier application could do a FOM weighted average of the 2 sets. • At the 15.4a level, we don’t care. Vern Brethour

Okay! So we know what we have to do for standard ranging. • It’s not that bad….. • So… What about Private Ranging? • Not to worry: It’s mostly the same stuff: Vern Brethour

Private Ranging Originator MAC Originator PHY Target PHY Target MAC Private Range setup request Private Range setup request Private Range setup ACK response Ack Setup confirm Range request Range packet Range initiation Range response This is all the same as for standard ranging Long Preamble ACK Range confirm Timestamp indication Regular 15.4b data encryption Timestamp response Timestamp reply Timestamp report ACK response Ack Timestamp confirm Vern Brethour

Well, ALMOST the same! Originator MAC Originator PHY Target PHY Target MAC Private Range setup request Private Range setup request Private Range setup ACK response Ack Setup confirm Range request Range packet Range initiation Range response Long Preamble ACK Range confirm Timestamp indication Regular 15.4b data encryption Timestamp response Timestamp reply Timestamp report ACK response Ack Timestamp confirm Vern Brethour

What’s different with Private Ranging is an up-front set-up sequence. • The set-up sequence serves to pre-warn the target PHY what preamble code to expect on the Ranging Packet. • The actual data calling out the preamble is encrypted and decrypted by the application. The 15.4a layer just passes it through. Vern Brethour

Private Ranging Originator MAC Originator PHY Target PHY Target MAC Private Range setup request Private Range setup request Private Range setup ACK response Ack Setup confirm The set-up sequence Range request Range packet Range initiation Range response Long Preamble ACK Range confirm Timestamp indication Regular 15.4b data encryption Timestamp response Timestamp reply Timestamp report ACK response Ack Timestamp confirm Vern Brethour

What’s the target Mac do? • Upon receipt of the Private Range Set-up primitive, the Target MAC passes the encrypted preamble designator to the application and forgets about it. • The application will be responsible for switching the target PHY to listen for the expected new preamble. Vern Brethour

How are we doing with the inventory? • Not that bad: • We have 4 messages over the air to define. • We have 9 primitives to define. • Finishing this will resolve all 18 comments in the “timestamp” cluster, and many of the comments in the “Private Ranging” cluster. Vern Brethour

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)