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

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Frequency Shifted Reference UWB Physical
Layer Date Submitted January 12, 2008 Source
Dennis L. Goeckel, PhD Qu Zhang, PhD Robert
Jackson, PhD Zhiguo Lai, PhD, Department of
Electrical and Computer Engineering, University
of Massachusetts at Amherst, Amherst,
Massachusetts Contact Fanny Mlinarsky Voice
1 [phone], E-Mail Mlinarsky_at_ecs.umass.ed
u Abstract FSR-UWB based PHY layer for BAN
Networks Purpose Overview of the FSR-UWB
technology developed at University of
Massachusetts at Amherst 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 contributors reserve 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 in March08 it would be made
publicly available by P802.15.
Slide 1
Slide 1
2
Abstract

• Overview of existing UWB signaling techniques and
  introduction to Frequency-Shifted Reference (FSR)
  Ultra-WideBand (UWB)
• FSR-UWB represents a new alternative to
  transmitted reference (TR) UWB radio architecture
  3.
• FSR-UWB is implementationally simple compared to
  established UWB techniques and can meet the BAN
  requirements.

3
Approaches to UWB Signaling

• Coherent Impulse Radio (IR-UWB)
• Multi-Band (MB-UWB)
• WiMedia, aka wireless USB
• Transmitted Reference (TR-UWB)
• Frequency Shifted Reference (FSR-UWB)

4
IR-UWB Transmitter
Impulse Radio
x(t) is TX signal for the lth symbol
Ts symbol interval
Tf frame interval
0
Tf
2Tf
Ts
(Nf -1)Tf
b0 -1
b01
0
Tf
2Tf
Ts
(Nf -1)Tf
Ts Nf Tf where Nf is frames/symbol, Nf gtgt1
5
IR-UWB Rake Receiver
Impulse Radio

• Huge number of paths in a UWB fading channel
  makes the IR-UWB full rake receiver type
  architectures troublesome
• Large number of taps required for significant
  energy capture
• Channel estimation can be difficult 2
• These implementational issues have caused the
  industry to abandon impulsive UWB or
  direct-sequence UWB 13

6
MB-UWB OFDM
Multi-Band
OFDM 128 subcarriers QPSK / DCM signaling
528 MHz
10.56
3.168
4.752
6.336
7.920
9.504
GHz
Time-frequency Interleaving (TFI) or Fixed
Frequency Interleaving (FFI) is used to spread
the transmit power among the three sub-bands
thereby increasing the peak transmit power and
optimizing the range.
Existing products operate in Band Group 1
7
TR-UWB
Transmitted Reference

• TR-UWB was a strong candidate signaling scheme in
  the original effort of 802.15.4a (location and
  low data rate applications), but a major
  implementational issue delay line killed this
  approach
• Eventually the group adapted burst mode PPM
  (pulse position modulation)
• In the TR-UWB systems 3 each frame consists of
  two pulses
• The first is a reference pulse and has a fixed
  polarity
• The second is the data pulse and follows the
  reference pulse with some known delay, D
• The reference pulse provides a template to which
  to match the data pulse

8
TR-UWB Transmitter
Transmitted Reference
Reference pulse
b0-1
(Nf -1)Tf
0
Tf
2Tf
Ts
Data pulse
b01
(Nf -1)Tf
0
Tf
2Tf
Ts
D
9
TR-UWB Receiver
Transmitted Reference

• An example (b -1)

Multiple pulses are due to multipath in the
channel
r(t)
0
Tf
2Tf
Ts
(Nf -1)Tf

r(t-D)
0
Tf
2Tf
Ts
(Nf -1)Tf
D
10
TR-UWB Receiver
Transmitted Reference
11
TR-UWB vs. FSR-UWB
Frequency Shifted Reference
Delay line looks simple, but how do you build
it?
TR-UWB
4-6 outline challenges
LPF
rl
FSR-UWB
Delay line replaced by oscillator/mixer
7-8
12
Complexity of TR-UWB vs. Simplicity of FRS-UWB
Frequency Shifted Reference

• The General Electric team developed a testbed for
  the standard TR-UWB that required a 20-foot
  coaxial cable in the receiver because of the need
  for a 20ns wideband analog delay element 11.
• The proposed FSR-UWB system is simple enough to
  have been implemented by University of
  Massachusetts at Amherst undergraduates.
• The prototype operates with at up to10 kbps in
  the 600 MHz-7 GHz range
• Our simulations based on the latest BAN channel
  models demonstrate feasibility of 10 Mbps
  operation

13
FSR-UWB Principle
Frequency Shifted Reference

• FSR-UWB system uses a reference that is a
  slightly frequency-shifted version of the
  data-bearing signal.
• The reference signal and data signal are
  orthogonal over a symbol interval.
• For low data rates, the frequency shift between
  the reference signal and data signal is small
  compared to the channel coherence bandwidth.
• The reference goes through approximately the same
  channel as the data signal.

14
Nf Frames per Symbol for FSR-UWB vs. TR-UWB

• A symbol interval Ts Nf Tf Nf frames, each
  of duration Tf
• Nf can be increased until either
• The gains from the increased average energy are
  offset by the degradation due to interframe
  interference (IFI), or
• The FCC spectral limit is reached
• FSR-UWB requires only 1 pulse per frame, vs.
  TR-UWB that requires 2 pulses per frame, which
  means that Nf can be higher for FSR-UWB,
  improving signal integrity
• FSR-UWB is also more tolerant of IFI and, thus,
  can employ a higher Nf to improve average energy
  aggregation
• With the FCC constraint Nf,FSR5.83Nf,TR
• Over a wide range of error probabilities and
  constraints, FSR-UWB offers a 1.0 to 1.5 dB gain
  over TR-UWB

15
FSR-UWB makes Practical Implementations Possible
Small (TX fits on a 1.5 x 3.25 PCB), Low
cost, Efficient (120 mW quiescent power)
Tag transceiver including a Vivaldi antenna 10,
UWB chipset and battery
FSR-UWB Based RFID Tag UMass project
Developing silicon at the IBM 180 um foundry in
Burlington, MA SBIR Phase II, funded by US Army
RTP, NC ready for commercialization
16
FSR-UW Low Power Consumption
1 Mbps operation
17
Power Consumption Assumptions

• Operational life of FSR-UWB system 5 years
  (43,800 hours)
• Minimum operating voltage 1.5V

18
FSR-UWB Benefits

• Robust in the presence of interference, multipath
  and electromagnetic obstructions, including metal
  and water content
• Extremely low power - 120 mW continuous power,
  yielding 5 years of battery powered operation
• Low cost NewLANs estimates 2.64/tag production
  cost

19
FSR-UWB System Considerations

• In the FSR-UWB, a frequency offset between the
  reference impulse train and data impulse train is
  the inverse of the symbol period.
• Pulse shaping waveform is half the frequency of
  the data rate and this frequency, f0 1/(2TS),
  must be below the frequency coherence of the
  channel
• Frequency coherence of the channel the
  bandwidth over which the channel is roughly
  constant is described by the channel models
• Symbol timing, d, must also be synchronized
  symbol clock
• This can be achieved using adaptive algorithms to
  minimize ??2(d) versus d

20
Proposed synchronization metric
??2(d) versus d in normalized symbol periods
for a system with parameters given in 8. The
system can be synchronized by finding the d that
results in the maximum receiver output energy.
21
Receiver for the proposed FSR-UWB system
The delay element of the standard TR-UWB scheme
has been replaced by a mixer in (a). Since
multiplication is commutative, the receiver in
(a) can be drawn in the more convenient form
given in (b).
22
FSR-UWB receiver diagram showing the unknown time
synchronization parameter, d 8
Clock recovery and phase synching of the shaping
oscillator are both tied to d, which is fed back
from the signal processing block in the RX
23
BER probability vs. peak pulse energy to noise
ratio ?b/No on a BAN channel per IEEE
P802.15-08-0780-04-0006 document
Data rate 5 Mbps Pulse 2nd derivative Gaussian
pulse of width 0.5 ns (roughly 10 GHz of
bandwidth) Frames per bit 20 Frame length 10
ns The bold red line is the average of 1000 runs
and the bold green line is the average of 980
runs excluding the worst 20.
24
BER probability vs. peak pulse energy to noise
ratio ?p/No on an AWGN channel for FSR-UWB
Tf 40 ns and Rb 1/(Nf Tf ) Zero-to-zero
pulse width 0.25 ns Solid lines represent
simulation results dashed-lines represent
analytical results from 8 equation (10).
25
BER probability vs. ?p/No for FSR-UWB
Fast fading multipath channel the multipath
fading channel changes independently from frame
to frame.
26
FSR-UWB Demo
FSR-UWB prototype

• 2006 UWB Workshop in California sponsored by the
  army research office
• Published papers can be found at
  http//www-unix.ecs.umass.edu/goeckel/uwb.html

27
References (1 of 3)

• 1 IEEE 802.15 WPAN Low Rate Alternative PHY
  Task Group 4a (TG4a), http//www.ieee802.org/15/p
  ub/TG4a.html.
• 2 M. Z. Win and R. A. Scholtz, On the energy
  capture of ultra-wide bandwidth signals in dense
  multipath environments,IEEE Commun. Lett., vol.
  2, pp. 245247, Sept. 1998.
• 3 R. Hoctor and H. Tomlinson, An overview of
  delay-hopped, transmittedreference RF
  communications, General Electric Technical Report
  2001CRD198, Jan. 2002.
• 4 M. Casu and G. Durisi, Implementation
  aspects of a transmittedreference UWB receiver,
  Wireless Communications and Mobile Computing,
  Vol. 5 pp. 537-549, May 2005.
• 5 L. Feng and W. Namgoong, An oversampled
  channelized UWB receiver with transmitted
  reference modulation, to appear in the IEEE
  Transactions on Wireless Communications.
• 6 S. Bagga, S. Haddad, W. Serdijn, J. Long and
  E. Busking, A delay filter for an IR-UWB
  front-end, Proceedings of the IEEE International
  Conference on Ultra-wideband, pp. 323-327, Sept.,
  2005.

28
References (2 of 3)

• 7 D. Goeckel and Q. Zhang, Slightly
  frequency-shifted reference ultrawideband (UWB)
  radio TR-UWB without the delay element,
  Proceedings of the Military Communication
  Conference, Oct., 2005.
• 8 D. Goeckel and Q. Zhang, Slightly
  frequency-shifted reference ultrawideband (UWB)
  radio, revision submitted to the IEEE
  Transactions on Communications.
• 9 Q. Zhang and D. Goeckel, Multi-Differential
  Slightly Frequency-Shifted Reference
  Ultra-Wideband (UWB) Radio, Proceedings of the
  Conference on Information Sciences and Systems,
  March 2006.

29
References (3 of 3)

• 10 A. Stigliari, Design and characterization
  of a planar ultra-wide band antenna, MS
  dissertation, Electrical and Computer
  Engineering, University of Massachusetts Amherst,
  Feb., 2005.
• 11 N. van Stralen, A. Dentinger, K. Welles II,
  R. Gaus Jr., R. Hoctor, and H. Tomlinson, Delay
  hopped transmitted reference experiemental
  results, Proceedings of UWBST, pp. 93-98, May
  2002.
• 12 J. Proakis and D. Manolokis, Digital signal
  processing, Prentice-Hall, third edition, 1996.
• 13 A. Batra, J. Balakrishnan, G. Aiello, J.
  Foerster, and A. Dabak, Design of a Multiband
  OFDM System for Realistic UWB Channel
  Environments, IEEE Transactions on Microwave
  Theory and Techniques, Vol. 52 pp. 2123-2138,
  September 2004.