IEEE 802'15 subject

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Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Objectives of Signaling for Ranging Date
Submitted 24 April, 2005 Source Vern
Brethour Company Time Domain Corp. Address
7057 Old Madison Pike Suite 250 Huntsville,
Alabama 35806 USA Voice(256) 428-6331, FAX
[phone], E-Mail vern.brethour_at_timedomai
n.com Re 802.15 4a. Abstract A
discussion of the purpose of a ranging header in
a proposed 802.15.4a message. Purpose To
establish a common notion of ranging signal
processing for 802.15.4a. 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.
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Signaling for ranging for 802.15.4a

• Emphasis on the why of the a ranging header.

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UWB Ranging is all about determining time of
flight of our UWB signal.

• The start time is a time stamp embedded in the
  message.
• The stop time is when the message arrives at
  the receiver.
• Sounds simple enough, but lets look closer.

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The question today is WHEN exactly do we click
these stopwatches?
This picture is from 04-0581r5
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Artists concept of a UWB message
Data (to include the time stamp of when the
delimiter was at the antenna of the transmitter.
Channel sounding
Acquisition
The Delimiter is a unique signal event that
defines the end of the acquisition header.
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So we have the answer to the first question When
did the clock start (the first time stamp)?
Data (to include the time stamp of when the
delimiter was at the antenna of the transmitter.
Channel sounding
Acquisition
It was when this event was at the transmit antenna
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It might seem like there is a simple answer to
the second question When did the clock stop (the
second time stamp)?
Data (to include the time stamp of when the
delimiter was at the antenna of the transmitter.
Channel sounding
Acquisition
It was when this event was at the receive
antenna, but lets look closer When, really, was
that?
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Artists concept of a single pulse at the receive
antenna after it has gone through (a really
benign) channel
Other reflections of the pulse in the environment
corresponding to other paths.
Leading edge of the pulse energy corresponding
to the line of sight path
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A hallway in the Time Domain office
This ceiling is fake
UWB Radio on a cart
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What is above the fake ceiling?
Very reflective steel underlayment of the real
roof
This is Time Domain Shipping/Receiving area where
we dont have the fake ceiling.
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In Time Domains office, (typical commercial
construction) there will often be a return off of
the roof underlayment that is bigger that the
line of sight path.
Signal off the roof (for example).
Leading edge of the pulse energy corresponding
to the line of sight path
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If acquisition picks up the receive waveform here
Do we call that the receive time? We better
not The receive time is here.
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Actual channel sounding in Time Domains office
hallway.
The actual line of sight energy is arriving here
Our UWB radio acquisition algorithm picked up the
waveform here. (Thats why it says zero on the
display!)
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So thats what channel sounding is about!
Data
Acquisition At the end of this time we only know
we have a signal, but we are here
Channel sounding During this time we are
building the rest of the picture, so we can find
the leading edge of our arriving pulse energy.
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Lets go back to our artists concept signal.
Other reflections of the pulse in the environment
corresponding to other paths.
Its not even enough to find which of the
arriving pulses was the first one. In addition,
the start of that pulse must be resolved to under
a nanosecond. (Our target error budget of 15 cm
is half a nano-second.)
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So thats why the channel sounding part is
relatively long.
Acquisition
Data (to include the time stamp of when the
delimiter was at the antenna of the transmitter.
Channel sounding During this time we are
suppressing the noise so that we can resolve this
event to half a nano-second.
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Summary

• When Ranging, it is not enough to acquire a UWB
  signal.
• Following acquisition, we must do a channel
  sounding to find the offset from our acquisition
  point to the first arriving energy of our
  acquisition pattern.
• During channel sounding, we must do significant
  signal integration to suppress the noise in the
  earliest pulse such that the pulses leading edge
  can be resolved to half a nano-second.