Low Rate UWB for TG4a

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
TG4a Proposal for Low Rate DS-UWB
(DS-UWB-LR) Date Submitted January
2004 Source Matt Welborn Company
Freescale Semiconductor, Inc Address 8133
Leesburg Pike, Vienna VA 22182 Voice703-269-300
0, FAX , E-Mailmatt.welborn _at_
freescale.com Re Response to Call for
Proposals Abstract This document describes a
proposal for the TG4a baseline draft
standard. Purpose Proposal Presentation for
the IEEE802.15.4a standard. 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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UWB for Low Rate Communications

• UWB has great potential for low power
  communications
• Low fading margin can provide same range for
  lower transmit power
• Large (ultra-wide) bandwidth can provide fine
  time resolution provides potential for accurate
  ranging
• Drawbacks due to regulations
• Limited transmit power how much is enough?
• Operation at long ranges is highly dependent on
  NLOS path loss characteristics

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Proposal for TG4a Alternate PHY Layer
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Overview of DS-UWB-LR TG4a Proposal

• Based on higher rate DS-UWB proposal under
  consideration in TG3a, but modified for low power
  and lower complexity
• Variable-length code spreading with BPSK
  modulation of data
• Chip rates are 1/3 the rates used in DS-UWB (so
  about 450 MHz)
• Bandwidth is only 500 MHz (instead of 1500 M)
• Lower complexity FEC convolutional code
  (constraint length k4)
• Data rates of 30 kbps to 10 Mbps
• Use spreading codes of length 24 to 6144
• AWGN range of 15 to 75 meters (assuming n3.5 PL
  at gt 10m)
• Support for precise ranging
• Very straight forward solutions using RTT
  measurements with corrections for non-direct-path
  propagation effects
• Flexible pulse shaping
• Allows many pulse generation, antenna and
  receiver architectures
• Supports requirements for coexistence
  regulatory constraints
• Will enable interoperation between higher rate
  DS-UWB devices and low rate, low complexity TG4a
  devices
• Support wider range of asymmetric applications
• Enables active coexistence and coordination

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Benefits of Low Rate DS-UWB

• Bandwidth operating frequency
• Transmit power, ranging, complexity performance
• Pulse rate
• Effects on efficiency implementation
• Data Rate
• Interoperability Coexistence

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Operating Frequency

• Multiple operating channels with different center
  frequencies to provide FDM operation for
  different networks
• Three piconet bands at 3536, 4056, and 4576 MHz
• Different performance due to 20 Log10(Fc) term in
  path loss
• Also uses CDM for sharing of each band by
  different piconets
• Cost of generating the reference frequency
  depends on the specific frequency
• DS-UWB is based on low cost, high quality 26 MHz
  crystals (widely used in cell phones)
• Better frequency accuracy can relax other system
  constraints
• Acquisition at longer range requires longer
  integration and therefore more accurate reference
  frequency
• High accuracy clock can allow longer sleep time
  better power management
• Precise ranging using TOA methods requires high
  precision time measurements over relatively long
  intervals (RTT) to determine small differences in
  signal propagation times
• Simplified and improved with good reference clock

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Signal Operating Bands for Low Rate UWB
Relative PSD (dB)
Possible Lower Rate Signaling Bands (500 MHz
bandwidth)
High rate DS-UWB Low Band with RRC Pulse Shape
0
-3
FCC Mask
-20
4056
3536
4576
Frequency (MHz)
3100
5100

• Ultra-wideband 500 MHz bands for each piconet
• Code-division and Frequency-division multiplexing
  
• Multiple piconets in each band using different
  codes
• Operation in close proximity, interference
  avoidance or coexistence
• Three piconet bands at 3536, 4056, and 4576 MHz

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Low Rate DS-UWB Pulse Rate

• Impulse radio (IR) originally meant low pulse
  rate (10s of M pulse/sec) using time hopping
  for multiple access and pulse position modulation
  (PPM)
• More generally, IR is just pulse-based spread
  spectrum with data modulation
• Many choices for modulation (BPSK, PPM, OOK,
  etc.)
• One or more pulses per data symbol
• Low rate DS-UWB uses a chip rate that is designed
  to meet minimum 500 MHz bandwidth for simple BSK
  modulation
• Center frequency is always a multiple of 26 MHz
• Chip rate is equal to center frequency divided by
  9 (e.g. 4052 / 9 450.66MHz)
• Spreading codes are based on 24-chip code
• Longer spreading codes are derived from the basic
  code by further sreading with PN sequence (e.g.
  length 192 code is a length 24 code spread by a
  length 8 PN code)
• Pulse rate does not fundamentally affect transmit
  power, signal bandwidth or system performance
• Pulse rate does affect energy per pulse and
  therefore peak power (and voltage)

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Higher Pulse Rate Lower Peak Power
Higher peak power voltage for same average
power

• Lower pulse rate requires higher energy per
  pulse and therefore higher peak power (and
  voltage) for same transmit power
• Process technology can limit available peak
  voltage that can be achieved without an external
  power amplifier ___
• If pulse rate is 100x slower, then peak voltage
  is ?100 10x higher

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Data Rate Considerations

• Lowest PHY data rate does not necessarily mean
  lowest energy consumption
• In fact, a fast radio can potentially be more
  energy efficient than a slow radio. Example
• Compare a 1 Mbps radio at 100 mW versus 10 kbps
  radio at 10 mW
• 32 kB _at_ 10 kbps 0.256 mWseconds
• 32 kB _at_ 1 Mbps 0.0256 mWseconds 1/10 of the
  energy per bit!
• Assumptions
• Both radios achieve minimum range requirement for
  application
• Minimum acquisition time is a function of SNR
  (range) not data rate
• Requires fast wake-up and shut down of radio with
  aggressive power management
• Relative energy usage depends on packet size
• Fast radio advantage is higher for longer packets
  
• Notice transmit power is a small fraction of the
  total power (lt1)
• The largest power use is turning on the radio and
  processing signal

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Data Rate Considerations
Lower radio power, but longer transmission time
for data payload
Power
Preamble
Time
Higher peak power but shorter transmission time
for same payload
Power
Preamble
Time

• Total energy use from battery is the area under
  the power vs. time curves shown above
• Relative efficiency depends on power duration
  (payload size)

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Low Rate DS-UWB Data Rates

• LR-DS-UWB data rates are designed to support
  relatively high rate operation at relatively
  small duty cycle

Spreading code Length Symbol Rate FEC Rate PHY Bit Rate
192 2.35 MHz 0.5 1.17 Mbps
768 587 kHz 0.5 293 kbps
6144 73 kHz 0.5 37 kbps
24 18.778 MHz 0.5 9.4 Mbps
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Link Budget
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Link Budget Notes

• Assumptions
• Chipping rate 450.66 MHz
• Includes 1.9 dB Tx power reduction for spectral
  ripple in certification testing
• Assumes 3.8e-5 BEr to achieve 1 Per with 32
  octet data packet

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Interoperability Coexistence

• All of the specific co-existing systems in the
  Slection Requirements are out-of-band to
  LR-DS-UWB
• Robustness against in-band interference is
  provided by the UWB bandwidth of the LR-DS-UWB
  system (large processing gain)
• Many types of other UWB systems and waveforms
  will share the UWB bands
• Interoperability between TG4a higher rate
  systems could enable improved coexistence
• Interoperation with higher rate systems could
  increase the utility of the TG4a standard
• Interoperability of low cost sensor/RFID devices
  with nearby UWB CE devices
• Interoperability with DS-UWB could be quite
  simple if correct parameters are chose for TG4a
• Common reference frequency, codes operating
  bands

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Technical Feasibility

• The Low rate DS-UWB solution for TG3a has a high
  level of manufacturability
• Based on existing DS-UWB technology
• Can be implemented in low-cost CMOS technology
• Time to Market
• Time to market is quite reasonable. Compliant PHY
  implementations could be available for
  integration in 2005.
• Regulatory Impact
• DS-UWB technology is know to be compliant with
  FCC UWB rules
• Other regulatory administrations are using FCC
  rules as a basis for initial discussions
• Many mechanisms exist to ensure compliance for
  other regions that adopt other regulations

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System Performance

• System and SOP simulations are underway results
  TBD