Doc.: 15-05-0005-00-004a Submission January 2005 Molisch et al., Preliminary Proposal Project: IEEE...

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January 2005

Molisch et al., Preliminary Proposal

doc.: 15-05-0005-00-004a

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: Andreas.Molisch@ieee.org

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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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. LiPrinceton University

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Contents

– Proposal overview – Goals

– Impulse radio basics

– Proposed hybrid modulation

– Physical-layer details

– Ranging

– Simulation results

– 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

• Specific proposal built on novel 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)

• 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

Rake ReceiverFinger 2

SummerConvolutional Decoder Data

Optimum receiver for multipath channels

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Transmitted Reference

•First pulse serves as template for estimating channel distortions

•Second pulse carries information

•Drawback: Waste of 3dB energy on reference pulses

reference

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Transmitted Reference Receiver – Differentially Coherent

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

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Proposed Transmitter

Pulse Gen.TH Seq

BPSK symbol mapper

Central Timing Control

Multiplexe

Summer

One Transmitter Enables Multiple Receiver Types

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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

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

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

• 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

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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-

• 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

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

– Depends on

• Solution: adaptive frame duration– Feed back delay spread and interference to transmitter

– Depending on those parameters, TX chooses frame duration

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PER Performance Coherent Reception

608 Kbps, Td = 20ns, 20 Frames per symbol

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PER Performance Differential Reception

608 Kbps, Td = 20ns, 20 Frames per symbol

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P a r a m e t e r V a l u e ( T R -I R R e c e i v e r )

V a l u e ( T H -I R R e c e i v e r )

T h r o u g h p u t ( R b ) 6 0 8 K b / s 6 0 8 K b / s

A v e r a g e T x p o w e r ( TP ) - 4 . 3 d B m - 4 . 3 d B m

T x a n t e n n a g a i n ( TG ) 0 d B i 0 d B i

maxmin' fff c : g e o m e t r i c c e n t e r f r e q u e n c y o f

w a v e f o r m ( minf a n d maxf a r e t h e - 1 0 d B e d g e s

o f t h e w a v e f o r m s p e c t r u m )

5 . 7 3 G H z 5 . 7 3 G H z

P a t h l o s s a t 1 m e t e r ( )/4(lo g2 0 '1 01 cfL c )

81 03 c m / s

4 7 . 6 d B 4 7 . 6 d B

P a t h l o s s a t d m ( )(lo g2 0 1 02 dL ) 2 9 . 5 4 d B a t d = 3 0 m e t e r s

2 9 . 5 4 d B a t d = 3 0 m e t e r s

R x a n t e n n a g a i n ( RG ) 0 d B i 0 d B i

R x p o w e r (21 LLGGPP RTTR ( d B ) ) - 8 1 . 4 d B m - 8 1 . 4 d B m

A v e r a g e n o i s e p o w e r p e r b i t ( )(lo g*1 01 7 4 1 0 bRN )

- 1 1 6 . 2 d B m - 1 1 6 . 2 d B m

R x N o i s e F i g u r e R e f e r r e d t o t h e A n t e n n a T e r m i n a l (

FN ) 1 7 d B 7 d B

A v e r a g e n o i s e p o w e r p e r b i t ( FN NNP ) - 1 0 9 . 2 d B m - 1 0 9 . 2 d B m

M i n i m u m E b / N 0 ( S ) 1 2 d B 6 d B

I m p l e m e n t a t i o n L o s s 2 ( I ) 3 d B 3 d B

L i n k M a r g i n ( ISPPM NR ) 1 2 . 8 d B 1 8 . 8 d B

P r o p o s e d M i n . R x S e n s i t i v i t y L e v e l 3 - 9 4 . 2 d B m - 1 0 0 . 2 d B m

Link Budget

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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)

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Step-I: Energy Detection

TRF TRB

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 decisionStep-II

i = Ranging Block index

j = Ranging Frame index

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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 N2 frames to have sufficient SNR

– Solution of first arriving path found by hypothesis testing methods on zi

r(t), received signal

s(t-TC), shifted template signal

(.) zi

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Ranging System Settings

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Ranging Results

• Residential LOS

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Ranging Results

• AWGN

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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

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 the second step of the acquisition, a conventional serial search algorithm, or the hypothesis testing based approach can be applied, depending on the complexity and performance constraints

• If ranging is performed no separate acquisition step is necessary

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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

Doc.: 15-05-0005-00-004a Submission January 2005 Molisch et al., Preliminary Proposal Project: IEEE...

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