project: ieee p802.15 working group for wireless personal area networks (wpans)

Molisch et al., Preliminary ProposalSlide 1

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Submission

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

Submission Title: Mitsubishi-electrics-time-hopping-impulse-radio-standards-presentation Date Submitted: November 15, 2004Source: Andreas F. Molisch et al., Mitsubishi Electric Research LaboratoriesAddress MERL, 201 Broadway Cambridge, MA, 02139, USA Voice: +1 617 621 7558, FAX: +1 617 621 7550 , E-Mail: [email protected]

Re: [Response to Call for Proposals]

Abstract:

Purpose: [Proposing 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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Submission

Ultra WideBand

Mitsubishi Electric Proposal

Impulse Radio

A. F. Molisch, Z. Sahinoglu, P. Orlik, J. ZhangMitsubishi Electric Research Lab

M. Z. WinMassachusetts Institute of Technology

S. GeziciPrinceton University

Y. G. LiGeorgia Tech University


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Contents

– Proposal overview – Goals

– Impulse radio basics

– Proposed hybrid modulation

– Physical-layer details

– Simulation results

– Ranging

– Summary and conclusions


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Goals• Provide a system that can work with different

modulation and detection methodsAllows trade-offs among transmitter and receiver

complexity/cost/performance Works with a variety of signaling (modulation) methods

and pulse shapesEnables 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.


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Impulse Radio Basics


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Time Hopping Impulse Radio (TH-IR)

Ts

Tc

Tf

+1

-1

• Each symbol represented by sequence of very short pulses

• Each user uses different sequence (Multiple access capability)

•Bandwidth mostly determined by pulse shape


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TH-IR Coherent RAKE Receiver

Rake ReceiverFinger Np

AGC

Rake ReceiverFinger 2


SummerConvolutional Decoder Data

Sink

Optimum receiver for multipath channels


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Transmitted Reference

Ts

TcTf

Td

+1

-1

•First pulse serves as template for estimating channel distortions

•Second pulse carries information

•Drawback: Waste of 3dB energy on reference pulses

reference

data


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Transmitted Reference Receiver – Differentially Coherent

Td

0

Convolutional Decoder

Advantage: Simple receiver


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Proposal – Hybrid TR and TH-IR Modulation


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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


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Heterogeneous Network Architectures

Coherent Rx

Differential Rx

Modulation supports homogenous and

heterogeneous network architectures

Longer range when both transceivers are coherent


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Proposed Transmitter

Pulse Gen.TH Seq

BPSK symbol mapper

BPSK symbol mapper

Delay

Central Timing Control

Multiplexe

r

Td

0




Summer

One Transmitter Enables Multiple Receiver Types


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Ts

Proposed Transmitter Structure – Sample Waveform

+1 -1 +1 -1 +1 -1

-1 -1 +1 +1 -1 -1

0 0 1 1 0 0 1

b0 b4b3b2b1 b5b-1

Tx Bits

Reference Polarity

Data Pulse Polarity


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Physical Layer Details


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Proposed Transmitted Reference Receiver – Differentially Coherent

Td

0

MatchedFilter

Convolutional Decoder

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

SNR of decision statistic


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Proposed RAKE -- Coherent Receiver


Demultiplexer Rake ReceiverFinger 2


Summer

Channel Estimation

Convolutional Decoder Data

Sink

Sequence Detector

• 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 > 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

frequency (Hz)

Monocycle, 5th derivative of gaussian pulse

Power spectral density of the monocycle

10

log

10|P

(f)|

2 d

B


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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

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 1010

-220

-210

-200

-190

-180

-170

-160

-150

-140

-130

-120

W/ Polarity ScramblingW/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, 115]octal

• 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)

608 Kbps, Td = 20ns, 20 Frames per symbol, Reference distance = 58 meters

10 RAKE fingers used in receiver

7 meter separation distance


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SOP PER Performance Differential Reception (CM1)

608 Kbps, Td = 20ns, 20 Frames per symbol, reference distance = 23 meters

Modified Match Filter Differential Receiver

8 meter separation distance


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Link BudgetParameter

Differential Rx Coherent Rx

Throughput (Rb) 608 K b/s 608 Kb /s

Average Tx power ( TP ) -4.3 dBm -4.3 dBm

Tx antenna gain ( TG ) 0 dBi 0 dBi

maxmin' fff c : geometric center frequency of

waveform ( minf and maxf are the -10 dB edges

of the waveform spectrum)

5.73GHz 5.73GHz

Path loss at 1 meter ( )/4(log20 '101 cfL c

)

8103c m/s

47.6 dB 47.6 dB

Path loss at d m ( )(log20 102 dL ) 29.54 dB at d=30 meters

29. 54 dB at d=30 meters

Rx antenna gain ( RG ) 0 dBi 0 dBi

Rx power ( 21 LLGGPP RTTR (dB)) -81.4 dBm -81 .4 dBm

Average noise power per bit ( )(log*10174 10 bRN )

-11 6.2 dBm -116 .2 dBm

Rx Noise Figure Referred to the Antenna Terminal ( FN )1

7 dB 7 dB

Average noise power per bit ( FN NNP ) -109 .2 dBm -109.2 dBm

Minimum E b/N 0 (S) 12 dB 6 dB

Implementation Loss 2 (I) 3 dB 3 dB

Link Margin ( ISPPM NR ) 12.8 dB 18 .8 dB

Proposed Min. Rx Sensitivity Level 3 -94 .2 dBm - 100 .2 dBm


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Narrowband Interference

802.11a In-Band Tone

In-Band Modulated Tone

Coherent <1m <1m <1m

Differential <1m <1m <1m

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)

3.6MHz


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Step-I: Energy Detection

TRF =531.14ns TRB = 26.56ns

1 2 … NB 1 2 … NB 1 2 … NBi =

1 2 N1j =

Y2,1 Y2,2 Y2,N1

2|)(| tr 2|)(| tr 2|)(| tr

Y2Y1 YNB

Block Decision Mechanism

Block decision

Step-II

i = Ranging Block index

j = Ranging Frame index

k

bk̂


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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

s(t-TC), shifted template signal

FC

C

TNiT

iT

2

(.) zi


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Ranging System Settings

Notations and Terms Definition Value in Simulations

Tf Pulse repetition interval, frame 531.135 ns

Nb Number of blocks within a Tf 20

Nc Number of chips within a Tf 1000

TH{} Time hopping sequence in chips {h1, ...., h5}

POL{} Polarity codes {p1, ..., p5}

N1 Number of frames in the 1st-step 50

N2 Number of frames in the 2nd-step

30

winshift search back interval in #of chips 5

BW Bandwidth 7.5GHz

Chip duration Duration of a chip in samples 11 samples

Sample Period Sampling interval 4.8285e-11

Wave propagation speed Speed of radio wave 3e8

C Number of correlators 10


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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 LOSTrue Distance (m) One-way ranging

error (confidence)

25m 8cm (97%)

30m 8cm (~90%)

39m 8cm (73%) 136cm(80%)

55m 8cm (60%) 136cm(%78)


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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

TOA estimation error

TOA estimation error

T

Second transmission may help filter out clock drifts, if the Tx has a more reliable clock


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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


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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

project: ieee p802.15 working group for wireless personal area networks (wpans)

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