Proposal for a new ISO Ultra Wideband standard for RTLS

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• Proposal for a new ISO Ultra Wideband standard
  for RTLS
• Michael Mc Laughlin
• Ciaran Connell
• DecaWave Limited

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Three questions we need to answer

• Q1 Why use Ultra Wideband?
• Q2 What Physical Layer should we use?
• Q3 What application layer should we use

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Time of Arrival based systems

• Time of arrival based systems utilise information
  on the propagation time between systems

Time of Flight Trilateration
Time Difference of Arrival Multilateration
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UWB for Precision Locating
Reflection off wall through 2 partitions
Direct path through partition (Time of flight
for this 1st path gives distance)
Time
Reflection off wall
Reflection off wall (Receive Signal Strength is
dominated by this path which has been attenuated
by long flight path)

• Resolving Multipath Components, given that
• Resolution ? 1/BW
• d c.t
• thus
• 802.11 20MHz 1/BW 0.05µs 15m ?? low
  resolution
• 802.15.4a 1300MHz 1/BW 0.8ns 24cm ?? very
  high resolution

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IEEE 802.15.4a Standard

• "An international standard for an ultra-low
  complexity, ultra-low cost, ultra-low power
  consumption alternate PHY for IEEE Std 802.15.4.

802.15.4a Ratified Q1 07
Location, Communication, Control
Up to 27 Mbps, with location mobility
IEEE Standard
Capability
Utility
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UWB and IEEE802.15.4a

• IEEE 802.15.4a
• IEEE 802.15.4a is an IEEE personal area network
  standard.
• This is an alternative PHY developed for
  IEEE802.15.4
• Currently used by many standardised application
  layers including ZigBee and countless proprietary
  wireless sensor networks.
• This standard has a UWB PHY layer that provides
  communications with high precision
  ranging/location capability and ultra low power.
• Features of 802.15.4a- UWB
• Efficient spectral usage
• Modulation and coding combination close to ideal
• Perfect channel sounding
• Very high tag density
• Very long battery life
• Ultra low complexity implementations possible

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UWB and IEEE802.15.4a

• Efficient spectrum usage
• 802.15.4a uses pseudo random hopping for bursts
  of pulses. Among other advantages, this means
  that the spectrum has no spectral lines. This
  allows the mean spectrum to fill out the
  allowed spectrum. The overall effect is to allow
  up to 6dBs more power to be transmitted and
  still stay within the regulatory limits
• Modulation and coding combination close to ideal
• The concatenated codes used in 4a are extremely
  low complexity. For instance the Viterbi decoder
  uses lt3k gates. Despite this the performance is
  less than 2dBs shy of the Shannon limit for a
  system with one bit/symbol.
• Perfect channel sounding
• The 802.15.4a preamble uses an Ipatov sequence
  which is a ternary sequence with Perfect Periodic
  Autocorrelation Function. This allows the channel
  impulse response to be extracted without
  interference from side lobes of the
  autocorrelation function. This in turn allows the
  direct path to be extracted allowing the distance
  between transmitter and receiver to be
  calculated.

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UWB and IEEE802.15.4a

• Very high tag density
• High data rates allow the packet length to be
  very short (below 1ms). This allows compliant
  devices to transmit in very short bursts and
  hence, a very large number of assets can be
  tracked.
• Very long battery life
• 50 times less transmit power than an 802.15.4 or
  similar narrowband Transmitter
• Coherent 4a receiver takes 20 times less power
  than 802.15.4 or similar narrowband Receiver
• Non-coherent receiver is even more energy
  efficient.
• Ultra low complexity implementations possible
• Fully coherent tranceiver can be implemented in
  very small piece of silicon
• Non-coherent receiver option consists of little
  more than an energy detector
• Compliant transmitter can be implemented with a
  few off the shelf discrete components

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Summary of 802.15.4a- UWB

• Ultra-Wideband alternative PHY for 802.15.4
• Bitrates
• 110kbps, 850kbps, 6.8Mbps, 27Mbps
• Pulse Repetition Frequencies
• 4MHz, 15.6MHz, 62.4MHz
• Modulation scheme
• Burst position modulation with BPSK
• FEC Scheme
• Systematic Convolutional Code
• Reed Solomon code

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Summary of 802.15.4a- UWB cont.

• Ideal channel sounding preamble
• Periodic autocorrelation is an impulse or
  kronecker delta function
• Bandwidth
• 500MHz, 1100MHz or 1300MHz
• Channels
• 15 channels from 3GHz to 10GHz
• Designed to be usable for one-way or two way
  ranging
• Complexity choice for receiver
• coherent or non-coherent demodulation
• FEC can be ignored by receiver
• 802.15.4a convolutional code is very simple
• DecaWave Viterbi decoder is only 3k gates
• Complexity choice for transmitter. Either
• Pseudo Random Burst of Bipolar Pulses

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An Ultra Wideband Channel Model

The curves below represent the mean and worst 10
attenuation plotted as a function of
distance. The red curves are for a signal with
20MHz bandwidth The green curves are for a signal
with 500MHz bandwidth It can be seen that the
wider bandwidth has much lower worst 10
attenuation
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Coherent Link Margin and Range Tag to Reader
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Coherent Link Margin and Range Reader to Tag
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802.15.4a Receive Signal Buried In Thermal Noise
15.4a Receive Signal _at_ 110kps and noise at -31dB
SNR. This corresponds to a distance of 450 meters
outdoors, 40 meters indoors
15.4a Receive Signal _at_ 6.8Mbps and noise at -11dB
SNR. This corresponds to a distance of 60 meters
outdoors, 17 meters indoors
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Bandplan Facilitating Worldwide Deployment
Double-ended arrows show allowed UWB
frequency bands in various regions. LDC low
duty cycle i.e. infrequent TX
Pink and purple lines show the .4a
defined frequency channels and bandwidths
Japan _at_ gt50Mbps Japan until end 2010 Korea Korea
with LDC China
North America USA indoors and out Europe Europe
with LDC
.4a 500MHz .4a gt1GHz 802.15.4
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FEC and Symbol Structure
Determines which half of symbol contains burst
Determines whether or not entire burst is inverted
Single burst of pulses with pseudo-random
individual polarity
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15.4a UWB Packet Structure
Preamble
SFD
PHR
Payload
16 4096 symbols
8 or 64 symbols
19 bits
0 127 bytes
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AWGN PER of 802.15.4a Convolutional code
This figure shows the performance of the
convolutional code used in 802.15.4a. A PER of
10-2 is achievable at an EbNo of about 5dB
This improves to about 3.5dB if a RS decoder is
also used in the receiver
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Channel Sounding Preamble

• Example preamble sequence
• -1 1 0 1 1 0 0 0 -1 1 -1 1 1 0
  0 1 1 0 1 0 0 -1 0 0 0 0 -1 0 1 0 -1
• This has Perfect periodic auto correlation
  thus
• Now, a non-coherent receiver only sees if there
  is energy there or not i.e. this
• 1 1 0 1 1 0 0 0 1 1 1 1 1 0
  0 1 1 0 1 0 0 1 0 0 0 0 1 0 1 0 1

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Non-coherent channel sounding
This show the cross correlation of 1 1 0 1 1
0 0 0 1 1 1 1 1 0 0 1 1 0 1 0 0
1 0 0 0 0 1 0 1 0 1 With 1 1 -1 1
1 -1 -1 -1 1 1 1 1 1 -1 -1 1 1 -1 1 -1
-1 1 -1 -1 -1 -1 1 -1 1 -1 1 i.e. 0 replaced
by -1
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IEEE 802.15.4a-UWB Ranging Options

• Two way ranging option

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IEEE 802.15.4a-UWB Ranging Options

• IEEE 802.15.4a-UWB has the option of being
  transmit only
• The capabilities required to accomplish one-way
  ranging are sufficiently similar that this
  standard allows operation in that mode as well

4a Tag
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COOK Transmitter option

• Many of the original companies who worked on
  802.15.4a wanted a way to do a simple OOK
  transmitter and receiver.
• A joint contribution was submitted by a group of
  these companies, including Samsung and ETRI. The
  full contribution can be downloaded from the IEEE
  website
• 15-05-0132-03-004a-merged-proposal-chaotic-uwb-sy
  stem-802-15-4a.pdf
• The task group listened to their concerns and the
  result was Annex-H of 802.15.4a.
• This defines an optional OOK type modulation

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802.15.4a Annex H COOK option

• Extract from 802.15.4a

Another noncoherent optional pulse shape that
may be used is a chaotic waveform. This optional
pulse shape shall be used only when all other
devices within the PAN are using a chaotic pulse.
This mode can be used for low-power applications
where long battery life is critically important.
Since chaotic on-off keying (COOK) is
noncoherent modulation, the receiver does not
need to generate a corresponding chaotic signal
for demodulation. For that reason, the technique
chosen for generating a chaotic waveform can be
freely determined by implementers.
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Benefits of COOK

• The UWB transmitter can be implemented with a few
  discrete components
• Instead of a coherent burst of pseudo ransom
  pulses with a predictable pattern that the
  receiver can compare with, in Annex H, the
  transmitter just sends a burst of energy in the
  band of interest. 
• The beauty of Annex H from a non-coherent OOK
  point of view is that it doesn't matter what type
  of energy you send. The receiver is not expecting
  a coherent signal. Although it is referred to as
  a chaotic signal, it can be anything at all. The
  implementer decides what to generate and how to
  generate it.
• This allows a conventional 4a transmitter to
  transmit a coherent train of pseudo random
  pulses, but also allows, for example, a COOK
  transmitter, which works directly in the band of
  interest, to just send a spurge of energy.
• This system has precisely the same performance as
  conventional OOK for the same average transmit
  power
• Because regulations limit the power of the worst
  case data packet, COOK has a 3dB advantage over
  OOK in practice

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802.15.4a Prototypes

• Prototype Demonstration HW
• 2 such boards in Demo System, each connected to
  individual PCs

Prototype Demonstration Application SW -SW runs
on each PC to control boards and Implement comms
ranging functionality

• Achieved 104m LOS
• at 850Kbits/s
• across atrium of Hyatt Regency SFO (at 8th
  floor)
• limited by size of atrium

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What should the RTLS application layer be?

• ISO 24730-5 is an existing ISO RTLS standard
• The PHY layer in this standard uses the CSS
  option in 802.15.4a
• ISO 24730-5 has a comprehensive RTLS application
  layer which was design and approved by SC31/WG5
  i.e. this WG
• For ISO 24730-uwb, we should take this
  application layer and swap in the UWB 4a PHY

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In brief

• IEEE802.15.4a-UWB is an extremely low complexity
  ultra wideband communications and RTLS Standard
• Many companies and individuals with wide-ranging
  expertise worked on 4a
• It has been scrutinised by many pairs of eyes
• Non-coherent option enables ultra-low cost
  receiver implementations
• Transmitter is very simple to implement
• COOK option can be assembled from readily
  available components
• Coherent receiver option allows much larger
  range
• Complexity of RFID reader is usually less
  critical than tag

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ISO-24730-uwb Proposal Summary

• Use UWB PHY from 802.15.4a as the PHY layer for
  24730-uwb
• Use the Application layer from the existing
  24730-5 ISO standard as the new application layer
  for 24730-uwb