Extended CSM

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Extended Common Signaling Mode Date Submitted
July 15, 2004 Source Matt Welborn Company
Freescale Semi, Inc Address 8133 Leesburg
Pike Voice703-269-3000, FAX [phone]
Re Abstract This document provides an
overview some possible extensions for the
proposed Common Signaling Mode that would allow
the inter-operation or MB-OFDM and DS-UWB devices
at data rates as high as 110 Mbps. Purpose Prom
ote further discussion and compromise activities
to advance the development of the TG3a Higher
rate PHY 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.
2
Background

• Initial TG3a discussions on a Common Signaling
  Mode (CSM) began some months ago
• A few ad hoc meetings during January TG3a Interim
• Ad hoc meeting in February
• Several presentations in March Plenary
• Other attempts at compromise to allow forward
  progress in TG3a not successful
• 50/50 split in TG3a voter support for two PHY
  proposals
• Little support for two optional independent PHYs
• Can we re-examine some of the ideas for a single
  multi-mode UWB PHY as a path for progress?

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The CSM Vision

• A single PHY with multiple modes to provide a
  complete solution for TG3a
• Base mode that is required in all devices, used
  for control signaling CSM for beacons and
  control signaling
• Higher rate modes also required to support 110
  Mbps
• Compliant device can implement either DS-UWB or
  MB-OFDM (or both)
• Interoperability between all compliant devices at
  high rates
• All devices work through the same 802.15.3 MAC
• User/device only sees common MAC interface
• Hides the actual PHY waveform in use
• Effectively only one PHY with multiple modes

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Talking with each other Basic Requirements

• Each class of UWB devices (MB-OFDM or DS-UWB)
  needs a way to send control/data to the other
  type
• MB-OFDM ? DS-UWB
• DS-UWB ? MB-OFDM
• Goal Minimize additional complexity for each
  type of device while enabling this extra form of
  communications
• Use existing RF components DSP blocks to
  transmit message to other-class devices
• Also need to enable low-complexity receivers
• Data rates need to support full piconet operation
  without impacting throughput/capacity or
  robustness

5
UWB Consumer Electronics Applications
Home Entertainment
Computing
Mobile Devices
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Interoperation with a Common Signaling Mode
Images from camera to storage/network
Print from handheld
Exchange your music data
Stream DV or MPEG to display
Stream presentationfrom laptop/ PDA to
projector
MP3 titles to music player
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No Interoperation Tragedy of the Commons
Images from camera to storage/network
Print from handheld
Stream DV or MPEG to display
Stream presentationfrom laptop/ PDA to
projector
MP3 titles to music player
8
Interoperability Signal Generation

• One waveform possible for either class of device
  is a BPSK signal centered in the middle of the
  low band at 4GHz
• Such a signal could be generated by both MB-OFDM
  and DS-UWB devices using existing RF and digital
  blocks
• MB-OFDM device contains a DAC nominally operating
  at 528 MHz
• A 528 MHz BSPK (3 dB BW) signal is too wide for
  MB-OFDM band filters
• DAC an be driven at slightly lower clock rate to
  produce a BPSK signal that will fit the MB-OFDM
  Tx filter
• Result 500 MHz BPSK signal that DS-UWB device
  can receive demodulate
• DS-UWB device contains a pulse generator
• Use this to generate a 500 MHz BPSK signal at
  lower chip rate
• This signal would fit MB-OFDM baseband Rx filter
  and could be demodulated by the MB-OFDM receiver

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Issues Solutions for CSM

• Common frequency band
• Solution Use MB-OFDM Band 2
• Passed by MB-OFDM FE with hopping stopped
• Common FEC
• Solution Each receiver uses native FEC (e.g.
  k6/7 Viterbi)
• Every transmitter can encode for both codes low
  complexity
• Common clock frequency (chip rate)
• Close, but final resolution still TBD
• Initial CSM rates were too low for some
  applications
• Add extensions to higher rates (at slightly
  reduced ranges)
• As high as 110-220 Mbps for interoperability,
  depending on desired level of receiver complexity

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MB-OFDM DS-UWB Signal Spectrum with CSM
Compromise Solution
MB-OFDM (3-band) Theoretical Spectrum
Relative PSD (dB)
Proposed Common Signaling Mode Band (500 MHz
bandwidth)
DS-UWB Low Band Pulse Shape (RRC)
0
-3
-20
3960
3432
4488
Frequency (MHz)
3100
5100
FCC Mask
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Interoperability Signal Overview

• MB-OFDM band 2 center frequency for common
  signaling band
• Centered at 3960 MHz with approximately 500 MHz
  bandwidth
• BPSK chip rate easily derived from carrier chip
  carrier frequency / 9
• Frequency synthesis circuitry already present in
  MB-OFDM radio
• 500 MHz BPSK is similar to original
  pulsed-multiband signals
• Proposed by several companies in response to TG3a
  CFP
• Better energy collection (fewer rake fingers)
  than wideband DS-UWB
• More moderate fading effects than for MB-OFDM
  (needs less margin)
• Relatively long symbol intervals (10-55 ns)
  avoids/minimizes ISI
• Equalization is relatively simple in multipath
  channels
• Not necessary for lowest (default) CSM
  control/beacon rates
• Use different CSM spreading codes for each
  piconet
• Each DEV can differentiate beacons of different
  piconets
• Provides processing gain for robust performance
  signal BW is much greater than data rate

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Packets For Two-FEC Support
CSM PHY Preamble
Headers
FEC 1 Payload
FEC 2 Payload

• FEC used in CSM modes to increase robustness
• Each device can use native FEC decoder (e.g k7
  or 6)
• For multi-recipient packets (beacons, command
  frames)
• Packets are short, duplicate payload for two FEC
  types adds little overhead to piconet
• For directed packets (capabilities of other DEV
  known)
• Packets only contain single payload with
  appropriate FEC
• FEC type(s) data rate for each field indicated
  in header fields

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Overhead of a Slower Beacon for Superframe

• Assume a heavily loaded piconet 100 information
  elements in beacon
• Fast 15.3a beacon overhead with 100 IEs (e.g.
  CTAs) _at_ 55 Mbps
• (15 us preamble 107 us payload 10 us SIFS) /
  65 ms 0.2
• CSM beacon overhead, assume 100 IEs (e.g. CTAs) _at_
  9.2 Mbps
• (50 us preamble 643 us payload 10 us SIFS) /
  65 ms 1.1
• Overhead (as a percent) would be higher for
  shorter superframe duration
• Conclusion Slower beacon data rates can lead to
  acceptable increase in beacon overhead (Too slow?
  at 1 Mbps, overhead grows to 10)

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Data Rates Possible for CSM
CSM Mode Data Rate FEC Rate Code Length Symbol Time Link Margin
MB-OFDM to DS-UWB 9.2 Mbps ½ 24 55 ns 9.3 dB at 10 m
MB-OFDM to DS-UWB 27 Mbps ½ 8 18 ns 6.5 dB at 10 m
MB-OFDM to DS-UWB 55 Mbps ½ 4 9 ns 3.5 dB at 10 m
MB-OFDM to DS-UWB 110 Mbps ½ 2 5 ns 0.4 dB at 10 m
MB-OFDM to DS-UWB 220 Mbps 1 2 5 ns 0.8 dB at 4 m
DS-UWB to MB-OFDM 6.3 Mbps 11/32 24 55 ns 12 dB at 10 m
DS-UWB to MB-OFDM 19 Mbps 11/32 8 18 ns 9.1 dB at 10 m
DS-UWB to MB-OFDM 68 Mbps 5/8 4 9 ns 2.8 dB at 10 m
DS-UWB to MB-OFDM 137 Mbps 5/8 2 5 ns -0.2 dB at 10 m
DS-UWB to MB-OFDM 220 Mbps 1 2 5 ns 0.8 dB at 4 m
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Implementation

• Mandatory/optional modes determined by TG to meet
  performance complexity goals for applications
• Implementations do not need optimal receivers
• Sufficient margins for moderate range
  interoperability
• Shorter codes for higher rates can be based on
  sparse codes (e.g. 1-0-0-0)
• Eliminate need for transmit power back-off
• Peak-to-average still supports low-voltage
  implementation
• Equalizers desirable at higher CSM rates (gt20
  Mbps?)
• Complexity is very low (a few K-gates), and works
  great
• Other transceiver blocks (Analog FE, ADC/DAC,
  Viterbi decoder, digital correlators, etc.)
  already in radio

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CSM Link Budgets with DS-UWB FEC
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CSM Link Budgets with MB-OFDM FEC
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Concerns

• A two PHY solution will confuse the market
• PHY waveform is transparent to application
• This multi-mode PHY solution allows
  interoperability with high functionality and
  prevents interference/QoS breakdown
• Even a single PHY solution will have multiple
  modes allows devices with different capability
  levels
• CSM interoperability data rates can be high
  enough to meet PAR (110 Mbps) -- even between
  dissimilar device classes
• Complexity CSM additional complexity can be very
  low and doesnt require optimal receivers
• Higher rates benefit from simple equalizers
  and/or digital rake
• I would really like to continue attending TG3a
  meetings indefinitely!
• Are you crazy?