Time Reversed Impulse MIMO for Ultra-Wideband Communicationsultra.usc.edu/assets/002/39740.pdf ·...

Time Reversed Impulse MIMO for Ultra-Wideband Communications

Robert QiuRobert QiuWireless Networking System LaboratoryWireless Networking System Laboratory

Tennessee Technological UniversityTennessee Technological University

Presented at Workshop on Short Range UltraPresented at Workshop on Short Range Ultra--Wideband Radio SystemsWideband Radio Systems

Santa Monica, California, April 12, 2006Santa Monica, California, April 12, 2006

Robert Qiu Wireless Networking System Lab

ACKNOWLEDGMENTACKNOWLEDGMENT

In part funded by the Army Research Laboratory and In part funded by the Army Research Laboratory and the Army Research Office through a grant the Army Research Office through a grant (W911NF(W911NF--0505--11--0468) 0468)

and a Defense University Research Instrumentation and a Defense University Research Instrumentation Program (DURIP)Program (DURIP) grant (W911NFgrant (W911NF--0505--11--0111) 0111) ARL: Dr. B. M. Sadler, Dr. A. SwamiARL: Dr. B. M. Sadler, Dr. A. SwamiARO: Dr. R. UlmanARO: Dr. R. UlmanNRL: Dr. T. C. Yang NRL: Dr. T. C. Yang ONR: Dr. S. K. DasONR: Dr. S. K. Das


OutlineOutlineIntroductionIntroductionTutorial review of UWB Communications Tutorial review of UWB Communications –– ApplicationsApplications–– Receiver ChallengesReceiver Challenges

TimeTime--ReversalReversal——SpatioSpatio--Temporal FocusingTemporal FocusingTimeTime--Reversal SISO with MonoReversal SISO with Mono--bit A/Dbit A/DTimeTime--Reversal UWB MISO/MIMOReversal UWB MISO/MIMO–– Principles Principles –– ExperimentsExperiments

SummarySummary


Rich Multipath of a UWB ChannelRich Multipath of a UWB Channel

Source: R. Qiu, H. Liu, X. Shen, Comm. Mag., Feb. 2005.


Autocorrelation of CIRAutocorrelation of CIR

Source: Qiu, H. Liu, X. Shen, Comm. Mag., Feb. 2005.


UWB Receiver Design ChallengesUWB Receiver Design ChallengesEnergy collection versus complexity (cost)Energy collection versus complexity (cost)–– RAKE may be too costlyRAKE may be too costly–– OFDM (IEEE 802.15.3a) will be too expensiveOFDM (IEEE 802.15.3a) will be too expensive

Time synchronizationTime synchronization–– 10 10 psps timing accuracy for matched filtertiming accuracy for matched filter–– LeadingLeading--edge detectoredge detector

InterInter--symbol interference (ISI)symbol interference (ISI)–– 10 symbols overlapping for indoor (100 Mbps)10 symbols overlapping for indoor (100 Mbps)–– SymbolSymbol--level equalizer level equalizer

NonNon--coherent detectorcoherent detector–– Transmitted referenceTransmitted reference–– EnergyEnergy--detectordetector

UWB is ideal for moderate range (300UWB is ideal for moderate range (300--1000m) and data rate of a 1000m) and data rate of a few Mbps (IEEE 802.15.4a, started since Oct. 2003) few Mbps (IEEE 802.15.4a, started since Oct. 2003)


TimeTime--Reversal with Noncoherent Detection Reversal with Noncoherent Detection as an Alternative to Coherent Receptionas an Alternative to Coherent Reception

( ) ( ) ( ) ( )r t p t h t n t= ⊗ +

1

( ) ( ) ( )L

l l ll

h t a h t tδ τ=

= ⊗ −∑Time-Reversal uses the rich multipath channel as part of the matched filter.


TimeTime--Reversal UWBReversal UWB--MIMO MIMO Compensation for multipath propagation and array Compensation for multipath propagation and array imperfectionsimperfections–– Ideal for multipath energy captureIdeal for multipath energy capture–– Pulse wave shape distortion caused by channel and Pulse wave shape distortion caused by channel and

antennasantennas

Does not require knowledge of the detailed Does not require knowledge of the detailed properties of either the channel or the arrayproperties of either the channel or the array–– Environments adaptive to unknown channel/antennasEnvironments adaptive to unknown channel/antennas

Investigate noncoherent timeInvestigate noncoherent time--reversal as an reversal as an alternative to coherent receptionalternative to coherent reception




SummarySummary


TimeTime--ReversalReversal

Source: Fink, Scientific American, 1999.


Simultaneous Space and Time FocusingSimultaneous Space and Time Focusing

Source: Fink, Scientific American, 1999.Unique to time-reversed impulse signals.


Historical backgroundHistorical backgroundUltrasound and underwater soundUltrasound and underwater sound

Spatial focusing (w/o communications) in the last 15 years:Spatial focusing (w/o communications) in the last 15 years:–– ultrasound (Fink, Paris), ultrasound (Fink, Paris), –– underwater sound (underwater sound (KupermanKuperman, UCSD)., UCSD).

Theory for spatial focusing in TR in random media Theory for spatial focusing in TR in random media –– Jackson and Dowling (1990+), Jackson and Dowling (1990+), –– Fink (1995+), Fink (1995+), –– KupermanKuperman, , –– Stanford Math Group (2002).Stanford Math Group (2002).

TR communication schemes demonstrated by TR communication schemes demonstrated by –– KupermanKuperman (underwater sound, 2002), (underwater sound, 2002), –– Rouse. (passive underwater sound, 2001), Rouse. (passive underwater sound, 2001), –– Fink (ultrasound, 2003, and EM, 2004), Fink (ultrasound, 2003, and EM, 2004), –– LarazzaLarazza (underwater sound, 2002). (underwater sound, 2002). –– T. C. Yang (underwater acoustic communications, 2003)T. C. Yang (underwater acoustic communications, 2003)


Scheme of Time Reversal Mirror Scheme of Time Reversal Mirror Experiment in Underwater AcousticsExperiment in Underwater Acoustics

Source: Marine Physical Lab


Time Reversal: Time domainTime Reversal: Time domain

( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( )

*

1

*

1 1

TX

TX TX

N

n n eqn

N N

eq n n hhn k

y t h t h t x t h t x t

h t h t h t R t

=

= =

⎛ ⎞= ⊗ − ⊗ = ⊗⎜ ⎟⎝ ⎠

= ⊗ − =

∑

∑ ∑

( ) ( )*g t h t= −

Phase 1: The transmitter learns the channel impulse response

δ(t)

TX TX

Phase 2: Each transmitter applies a filter

and sends data (same data stream from all the elements)

Channel Assumptions:• Linear time-invariant• Reciprocal

Source: Persefoni Kyritsi, 2004


Autocorrelation of CIRAutocorrelation of CIR

Source: Qiu, H. Liu, X. Shen, Comm. Mag., Feb. 2005.


SpatioSpatio--Temporal FocusingTemporal Focusing——An Example in the Hall WayAn Example in the Hall Way

When the walls are lossless, the channel is reciprocalThe channel impulse response is identical if the locations of the

transceiver are switched.

UWB spectral band allocation allows time division duplexing (TDD)Source: C. Zhou, R. Qiu,Feb. 2006.


TimeTime--ReversalReversal------Exploiting MultipathExploiting Multipath

•Multipath increases the “effective” number of antenna elements•L paths of equal power enlarge the antennas elements by L times

Source: C. Zhou, R. Qiu,Feb. 2006.


TimeTime--Reversal: Spatial Focusing (Indoors)Reversal: Spatial Focusing (Indoors)

Ideal spatioIdeal spatio--temporal temporal focusingfocusing

( ( (h t h ' t 'δ δ∗r, - ) r , ) = r - r ) (t)

Source: S. E. Emami, J. Hansen, D. Kim, G. Papanicolaou, A.

J. Paulraj, D. Cheung, and C. Prettie, IEEE Comm. Letts., 2002.




SummarySummary


TimeTime--Reversed Transmitted Reference Reversed Transmitted Reference ((TiRTiR--TR) SchemeTR) Scheme

Source: TTU, Dec. 2004.


TimeTime--Reversal UWB MISO + NonReversal UWB MISO + Non--Coherent Receiver:Coherent Receiver:

Extreme Simple System StructureExtreme Simple System Structure

TimeReversalMirror Energy

DetectorAmp Threshold

Decision…

MultipathChannel

Multipathscattering

Pulse distortion

h1(T-t)

h2(T-t)

hN(T-t)

All antennaelementsreachmaximum at t=T

SNR grows linearly with N


MultipathChannel

TimeReversalMirror LNA Compare

Decision …

L equal paths

Pulse distortion

All antenna elements reach maximum at t=0

Total Capture Energy grows linearly with LMN

2dt∫BMP Sampler

γ

zk 1

0

k

k

H if zH if z

γγ

≥<

11

( )N

nn

h t=

−∑

21

( )N

nn

h t=

−∑

1

( )N

Mnn

h t=

−∑

…

( ) tt (-t)* (t)=MIMOH H H

M elements N elements

Time-Reversed UWB-MIMO

Time Reversal

( ( (h t h ' t 'δ δ∗r, - ) r , ) = r - r ) (t)Ideal spatio-temporal focusing


Experimental SpatioExperimental Spatio--Temporal FocusingTemporal Focusing

( ( (h t h ' t 'δ δ∗r, - ) r , ) = r - r ) (t)

At the intended user location ( (h t h t∗

r : r, - ) r, )

At an intended user location ( (

' :h t h ' t∗

rr, - ) r , )

Ideal spatio-temporal focusing


Coherent Sum of Signals Received from Coherent Sum of Signals Received from Multiple AntennasMultiple Antennas

When M transmitter antennas (MISO) are used,the SNR will increase proportionally to M.

1

1

( ) ( ) * ( ) * ( ) ( )

( ) ( ) ( )m m

M

m mm

M

xx m h hm

y t x t c t h t n t

R t A R t n t

=

=

= +

⎛ ⎞= ∗ +⎜ ⎟

⎝ ⎠

∑

∑

*( ) ( )* ( )m mh h m mR t h t h t= − 2 2exp( ) *exp( ) ( ).j t j t tα α δ=


TimeTime--Reversed Impulse MIMOReversed Impulse MIMO

( ) tt (-t)* (t)=MIMOH H H

Transmitter

Receiver

1 1 1

1 1 1 1, 1,

(a sum of MISO signals)

( ) ( ) ( )

( ) ( ) ( ) ( )

M M N

MIMO mn mln m l

N M M N N

mn mn mn mln m m n n l l l n

Signal Interfere

h t A h t h t

A h t h t A h t h t

= = =

= = = = ≠ = ≠

⎧ ⎫⎡ ⎤ ⎡ ⎤= − ∗⎨ ⎬⎢ ⎥ ⎢ ⎥

⎣ ⎦ ⎣ ⎦⎩ ⎭⎧ ⎫⎡ ⎤ ⎡ ⎤⎡ ⎤ ⎪ ⎪= − ∗ + − ∗⎨ ⎬⎢ ⎥ ⎢ ⎥⎢ ⎥

⎣ ⎦ ⎪ ⎪⎣ ⎦ ⎣ ⎦⎩ ⎭

∑ ∑ ∑

∑ ∑ ∑ ∑ ∑nce

( ) InterferencetMIMOh t trace (-t)* (t)⎡ ⎤= +⎣ ⎦H H



TimeTime--ReversalReversal——SpatioSpatio--Temporal FocusingTemporal FocusingTimeTime--Reversal SISO with MonoReversal SISO with Mono--bit A/Dbit A/DTimeTime--Reversal UWB MISOReversal UWB MISO–– Principles Principles –– ExperimentsExperiments

SummarySummary


Experimental SetupExperimental Setup


TimeTime--Domain Channel SounderDomain Channel Sounder


TimeTime--Reversal UWBReversal UWB--MISO: MISO: ExperimentsExperiments

Source: Qiu et al, IEEE Antenna and Wireless Prop. Letters, to appear, 2006.


Channel Reciprocity Channel Reciprocity

The correlation between these two waveforms is as high as about 0.98.In supersonic waves, the correlation of 0.96 was reported by Fink et al.



Received Waveform for each virtual Received Waveform for each virtual antennas antennas



A comparison of equivalent impulse A comparison of equivalent impulse responsesresponses

The SNR grows linearly with M



TimeTime--Reversed MIMO: ExperimentsReversed MIMO: Experiments

-150 -100 -50 0 50 100 150-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Time(ns)

Equ

ivel

ent I

mpu

lse

Res

pons

e: M

ISO

-150 -100 -50 0 50 100 150-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Time(ns)

Equ

ivel

ent I

mpu

lse

Res

pons

e: M

ISO

-150 -100 -50 0 50 100 150-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Time(ns)

Equ

ivel

ent I

mpu

lse

Res

pons

e: M

ISO

-150 -100 -50 0 50 100 150-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Time(ns)

Equ

ivel

ent I

mpu

lse

Res

pons

e: M

ISO

-150 -100 -50 0 50 100 150-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time(ns)

Equi

vele

nt Im

puls

e R

espo

nse:

MIM

O

The energy captured by the MIMO grows linearly with MN.

The energy captured by the MISO grows linearly with M.




SummarySummary


Sounding Pulse and Its AutoSounding Pulse and Its Auto--CorrelationCorrelation


Conceptual Diagram of Time-Reversal Equipped Transmitter

Source: Guo, Qiu, and Sadler, IEEE Trans. Wireless Comm., Submitted, April 2006.

Mono-Bit A/D is assumed.


Temporal Focusing of TimeTemporal Focusing of Time--ReversalReversal



Performance ComparisonPerformance Comparison

30 nsbT =



Performance of a Three-user system

50 nsbT =

Mono-bit A/D



Demonstration of ChannelDemonstration of Channel--Based Security Based Security



A General Purpose UWB A General Purpose UWB TransceiverTransceiver------Transmitter FPGATransmitter FPGA


SUMMARYSUMMARYTimeTime--Reversal UWBReversal UWB--MIMO is a paradigm shiftMIMO is a paradigm shift–– CostCost--effective, noncoherent energyeffective, noncoherent energy--detection is made detection is made passiblepassible–– SNR grows SNR grows linearly linearly with LMN, # of paths and antenna elementswith LMN, # of paths and antenna elements–– Range extension Range extension –– Parallel independent Gaussian channels increases the channel Parallel independent Gaussian channels increases the channel

MonoMono--bit A/D sampling is sufficient for practical usebit A/D sampling is sufficient for practical useExperiments verified the basic assumptions of the theoryExperiments verified the basic assumptions of the theory–– An indoor UWB channel with rich multipath is reciprocal An indoor UWB channel with rich multipath is reciprocal –– Theory is valid for all waves with multiple scatteringTheory is valid for all waves with multiple scattering–– Theory is valid for other radio bandsTheory is valid for other radio bands–– It is easier to do experiments indoors, compared with HF (over tIt is easier to do experiments indoors, compared with HF (over the sea)he sea)

Future workFuture work–– Robustness of temporalRobustness of temporal--spatial focusingspatial focusing–– Signaling, protocols and network Signaling, protocols and network –– Hardware testbed validationHardware testbed validation–– Extension to other radio bands such as HFExtension to other radio bands such as HF

Thank You !Thank You !

Robert Qiu [email protected]

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