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

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Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Mitsubishi-electrics-time-hopping-impulse-radio-st
andards-presentation Date Submitted November
15, 2004 Source Andreas F. Molisch et al.,
Mitsubishi Electric Research Laboratories Address
MERL, 201 Broadway Cambridge, MA, 02139, USA
Voice 1 617 621 7558, FAX [phone] ,
E-Mail Andreas.Molisch_at_ieee.org Re Response
to Call for Proposals Abstract Purpose Propos
ing a PHY-layer interface for standardization by
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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Ultra WideBand

• Mitsubishi Electric Proposal
• Impulse Radio
• A. F. Molisch, Z. Sahinoglu, P. Orlik, J. Zhang
• Mitsubishi Electric Research Lab
• M. Z. Win
• Massachusetts Institute of Technology
• S. Gezici
• Princeton University
• Y. G. Li
• Georgia Tech University

3
Contents

• Proposal overview
• Goals
• Impulse radio basics
• Proposed hybrid modulation
• Physical-layer details
• Simulation results
• Ranging
• Summary and conclusions

4
Goals

• Provide a system that can work with different
  modulation and detection methods
• Allows trade-offs among transmitter and receiver
  complexity/cost/performance
• Works with a variety of signaling (modulation)
  methods and pulse shapes
• Enables different receiver structures coherent,
  differential, incoherent
• Propose concrete system based on optimized
  technologies for impulse radio transceivers
• Share ideas with other 4a members in the hope of
  working together.

5
Impulse Radio Basics
6
Time Hopping Impulse Radio (TH-IR)
1
Tc
Tf
Ts
-1

• Each symbol represented by sequence of very
  short pulses
• Each user uses different sequence (Multiple
  access capability)
• Bandwidth mostly determined by pulse shape

7
TH-IR Coherent RAKE Receiver
Rake Receiver Finger 1
AGC
Rake Receiver Finger 2
Convolutional Decoder
Summer
Data Sink
Rake Receiver Finger Np
Optimum receiver for multipath channels
8
Transmitted Reference
data
Td
1
Tc
Tf
reference
Ts
-1

• First pulse serves as template for estimating
  channel distortions
• Second pulse carries information
• Drawback Waste of 3dB energy on reference pulses

9
Transmitted Reference Receiver Differentially
Coherent
Convolutional Decoder

Td
Advantage Simple receiver
10
Proposal Hybrid TR and TH-IR Modulation
11
Motivation

• Different applications require different
  performance
• Vendors want to differentiate themselves
• 802.15.4 already has different device types
• We provide proposal that allows trade-offs among
  complexity/capability/cost and performance
• Enables simple receivers without penalizing more
  complex ones

12
Heterogeneous Network Architectures
Modulation supports homogenous and heterogeneous
network architectures
Longer range when both transceivers are coherent
Coherent Rx
Differential Rx
13
Proposed Transmitter
Rake Receiver Finger 1
Rake Receiver Finger 2
Summer
BPSK symbol mapper
Delay

Pulse Gen. TH Seq
Multiplexer
Rake Receiver Finger Np
BPSK symbol mapper


Central Timing Control
One Transmitter Enables Multiple Receiver Types
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Proposed Transmitter Structure Sample Waveform
b0
b4
b2
b3
b1
b5
b-1
Tx Bits
0 0 1 1
0 0
1
Reference Polarity
-1 -1 1
1 -1
-1
1 -1 1
-1 1 -1
Data Pulse Polarity
Ts
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Physical Layer Details
16
Proposed Transmitted Reference Receiver
Differentially Coherent

• Addition of Matched Filter prior to delay and
  correlate operations improves output signal to
  noise ratio and reduces noise-noise cross terms

Matched Filter
Convolutional Decoder

Td
SNR of decision statistic
17
Proposed RAKE -- Coherent Receiver
Channel Estimation
Rake Receiver Finger 1
Rake Receiver Finger 2
Sequence Detector
Demultiplexer
Convolutional Decoder
Summer
Data Sink
Rake Receiver Finger Np

• Addition of Sequence Detector Proposed
  modulation may be viewed as having memory of
  length 2
• Main component of Rake finger pulse generator
• A/D converter 3-bit, operating at symbol rate
• No adjustable delay elements required

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Channel Estimation

• Swept delay correlator
• Principle estimating only one channel sample per
  symbol.
• Similar concept as STDCC channel sounder of Cox
  (1973).
• Sampler, AD converter operating at SYMBOL rate
  (1.2 MHz)
• Requires longer training sequence
• Two-step procedure for estimating coefficients
• With lower accuracy estimate at which taps
  energy is significant
• With higher accuracy determine tap weights
• Silence periods for estimation of interference

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Multiple Access

• Multiple access
• Combination of pulse-position-hopping and
  polarity hopping for multiple access
• More degrees of freedom for design of good
  hopping sequence than pure pulse-position-hopping
• Short or long hopping sequences possible
• Long hopping sequence period of sequence gt
  Number of frames in a symbol.

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Spectral Shaping Interference Suppression
(Optional)

• Basis pulse use simple pulse shape gaussian,
  raised cosine, chaotic, etc.
• Drawbacks
• Possible loss of power compared to FCC-allowed
  power
• Strong radiation at 2.45 and 5.2 GHz

Monocycle, 5th derivative of gaussian pulse
Power spectral density of the monocycle
10log10P(f)2 dB
frequency (Hz)
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Linear Pulse Combination

• Solution linear combination of delayed, weighted
  pulses
• Adaptive determination of weight and delay
• Number of pulses and delay range restricted
• Can adjust to interferers at different distances
• (required nulldepth) and frequencies
• Weight/delay adaptation in two-step procedure
• Initialization as solution to quadratic
  optimization problem (closed-form)
• Refinement by back-propagating neural network
• Matched filter at receiver ?good spectrum helps
  coexistence and interference suppression

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Spectral Shaping Polarity Scrambling
Td 10 ns
Td 20 ns
W/ Polarity Scrambling
W/O Polarity Scrambling
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Adaptive frame duration

• Advantage of large number of pulses per symbol
• Smaller peak-to-average ratio
• Increased possible number of SOPs
• Disadvantage
• Increased interframe interference
• In TR also increased interference from reference
  pulse to data pulse
• Solution adaptive frame duration
• Feed back delay spread and interference to
  transmitter
• Depending on those parameters, TX chooses frame
  duration

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Parameters

• Modulation coding
• Hybrid-impulse radio (slides 12-13)
• Pulse shape 5th derivative gaussian (0.5 ns
  pulse width)
• Symbol rate 1.21 Msym/sec
• Td 20nsec 20 frames/symbol
• Rate ½ convolutional code
• Constraint length 7
• polynomial 117, 115octal
• Receivers
• Matched filter differential receiver (slide 16)
• Filter matched to reference pulse sequence
• Coherent RAKE (slide 17)
• 10 fingers with MR combining
• Length 2 sequence detector
• Channel model version 7 was used for all results
  ? will update with version 8 at march meeting

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PER Performance Coherent Reception (CM1 AWGN)
608 Kbps, Td 20ns, 20 Frames per symbol, 10
RAKE fingers
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PER Performance Differential Reception (CM1
AWGN)
608 Kbps, Td 20ns, 20 Frames per
symbol Modified Match Filter Differential Receiver
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SOP PER Performance Coherent Reception (CM1)
7 meter separation distance
608 Kbps, Td 20ns, 20 Frames per symbol,
Reference distance 58 meters 10 RAKE fingers
used in receiver
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SOP PER Performance Differential Reception (CM1)
8 meter separation distance
608 Kbps, Td 20ns, 20 Frames per symbol,
reference distance 23 meters Modified Match
Filter Differential Receiver
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Link Budget
30
Narrowband Interference
DUT is operating in CM1
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Ranging
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Two Step Ranging Algorithm

• Step-I
• Estimate rough TOA of the incoming signal in a
  time window by detecting received signal energy
• Step-II
• Determine the arrival time of the first signal
  path by using hypothesis testing (change
  detection)

Low rate sampling is sufficient
3.6MHz
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Step-I Energy Detection
j
1
2
N1
i
TRF 531.14ns
TRB 26.56ns
Y2,2
Y2,1
Y2,N1
i Ranging Block index
Y1
Y2
YNB
j Ranging Frame index
Block Decision Mechanism
Step-II
Block decision
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Step-II Chip Detection

• TOA is estimated at chip resolution
• Once a ranging block is detected, the chips in
  that block plus M1 extra chips prior to the
  ranging block (to prevent errors due to
  multipath) are searched
• Correlations of the received signal with time
  delayed versions of a template signal are
  considered
• Correlation output is obtained over multiple
  symbol duration to have a sufficient SNR
• Solution of first arriving path found by
  hypothesis testing methods on zi

r(t), received signal
zi
s(t-TC), shifted template signal
35
Ranging System Settings
36
Ranging Results

• AWGN

• Round Trip ranging error
• (with no drift compensation)
• 16cm (0.088ms), no clock drift
• 19cm (1ppm)
• 27cm (4ppm)
• 42cm (10ppm)
• 121cm (40ppm)

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Ranging Results

• Residential LOS

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Two-way Ranging Protocol

• Developed for transceivers that can first detect
  the coarse TOA of a signal and then determine the
  offset (error) of the coarse estimation
• No need to transmit extra information to correct
  the timing offset or the processing delay
• Each node switches between receive and transmit
  mode every T seconds until the ranging is complete

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Conventional Two-way Ranging Protocol
Enhanced Two-way Ranging Protocol
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Acquisition

• The first step of the TOA estimation algorithm is
  also suitable for acquisition
• For block level acquisition, select the highest
  energy block index
• For refining to the chip level, select the
  highest correlator output index

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Summary and Conclusions

• Impulse radio based standards proposal
• UWB signaling achieves accurate ranging.
• Innovative modulation technique
• Admits multiple transmit waveforms
• Provides framework for multiple receiver types
• Offers trade-off of cost/complexity/performance
• Coherent and differentially coherent receivers
  suppress interference
• More users
• Innovative ways to manage spectrum
• Meet FCC requirements
• Improve performance in interference environment
• Decrease interference to other systems
• Allows cheap implementation
• All digital operations at symbol rate, not chip
  rate

42
References

• Proposal content has been reviewed and published
  in various technical journals and conferences
• S. Gezici, F. Tufvesson, and A. F. Molisch, On
  the performance of transmitted-reference impulse
  radio, Proc. Globecom 2004,
• F. Tufvesson and A. F. Molisch, Ultra-Wideband
  Communication using Hybrid Matched Filter
  Correlation Receivers, Proc. VTC 2004 spring
• A. F. Molisch, Y. G. Li, Y. P. Nakache, P. Orlik,
  M. Miyake, Y. Wu, S. Gezici, H. Sheng, S. Y.
  Kung, H. Kobayashi, H.V. Poor, A. Haimovich,and
  J. Zhang, A low-cost time-hopping impulse radio
  system for high data rate transmission, Eurasip
  J. Applied Signal Processing, special issue on
  UWB
• S. Gezici, Z. Tian, G. B. Giannakis, H.
  Kobayashi, A. F. Molisch, H. Vincent Poor and Z.
  Sahinoglu, "Localization via Ultra-Wideband
  Radios," IEEE Signal Processing Magazine, invited
  paper (special issue)
• S. Gezici, E. Fishler, H. Kobayashi, H. V. Poor,
  and A. F. Molisch, Performance Evaluation of
  Impulse Radio UWB Systems with Pulse-Based
  Polarity Randomization in Asynchronous Multiuser
  Environments, Proc. WCNC 2004,
• S. Gezici, E. Fishler, H. Kobayashi, H. V. Poor,
  and A. F. Molisch, Effect of timing jitter on
  the tradeoff between processing gains, Proc. ICC
  2004, in press. F. Tufvesson and A. F. Molisch,
  Ultra-Wideband Communication using Hybrid
  Matched Filter Correlation Receivers, Proc. VTC
  2004 spring

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References (Cont)

• Z. Sahinoglu, A. Catovic, "A Hybrid Location
  Estimation Scheme for Wireless Sensor Networks,
  IEEE ICC'04, June 2004, Paris
• S. Gezici, Z. Sahinoglu, H. Kobayashi, H. Vincent
  Poor, Book Chapter Ultra Wideband Geolocation,
  Ultra Wideband Wireless Communications by H.
  Arslan and Z. N. Chen, John Wiley Sons, Inc. ,
  February 2005.
• S. Gezici, Z. Sahinoglu, H. Kobayashi, H. Vincent
  Poor, "Impulse Radio Systems with Multiple Types
  of UWB Pulses," submitted to ICASSP'05.
• A. Catovic, Z. Sahinoglu, "The Cramer-Rao Bounds
  of TOA/RSS and TDOA/RSS Location Estimation
  Schemes", IEEE Comm. Letters, October 2004
• H. Sheng, A. Haimovich, A. F. Molisch, and J.
  Zhang, Optimum combining for time-hopping
  impulse radio UWB Rake receivers, Proc. UWBST
  2003, in press
• Li, Y.G. Molisch, A.F. Zhang, J., "Channel
  Estimation and Signal Detection for UWB",
  International Symposium on Wireless Personal
  Multimedia Communications (WPMC), October 2003
• Nakache, Y-P Molisch, A.F., "Spectral Shape of
  UWB Signals - Influence of Modulation Format,
  Multiple Access Scheme and Pulse Shape", IEEE
  Vehicular Technology Conference (VTC), April 2003