doc.: ieee 802.22-11/0080r0 submission july 2011 ivan reede, gerald chouinardslide 1 ofdm-based...

doc.: IEEE 802.22-11/0080r0

Submission

July 2011

Ivan Reede, Gerald ChouinardSlide 1

OFDM-based Terrestrial Geolocation

Name Company Address Phone email Gerald Chouinard

Communications Research Centre, Canada

3701 Carling Ave. Ottawa, Ontario Canada K2H 8S2

(613) 998-2500

[email protected]

Ivan Reede Amerisys Inc. Montreal, Canada (514) 620-8652 [email protected]

Authors:

Notice: This document has been prepared to assist IEEE 802.22. 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 grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11.

Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson <[email protected]> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <[email protected]>.

AbstractThis tutorial is to be presented during the IEEE 802 Plenary session on July 2011 in San Francisco. It gives an overview of the terrestrial geolocation technique jointly developed by Amerisys Inc. and the Communications Research Centre, Canada. This technique which relies on the PHY and MAC features required for operation of Wireless Regional Area Networks (WRAN) has been integrated into the IEEE Std 802.22-2011.

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Outline

1. Fine ranging using OFDMa. Fine ranging in OFDM systemsb. Sampling rate barrier paradigmc. Fine ranging operating principle

2. Fine ranging process between BS and CPE

3. The ‘Vernier’ processa. Construction of the “high-resolution” CIR functionb. Results of simulationsc. Results of measurementsd. Multipath excess delay time span

4. Geolocation process with one BS and two CPEs

5. Conclusions

doc.: IEEE 802.22-11/0080r0

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July 2011


Outline





5. Conclusions

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July 2011


• High accuracy ranging (+/-15 m) is required to geolocate terminals (Latitude and Longitude) within 50 m (FCC)

• OFDM systems inherently obtain channel impulse response information (CIR) for their operation

• Channel distortion characterized by such CIR information is usually– Annoying for communication systems– Need to be compensated to improving communication

performance

• Such information will now be shown to be valuable to carry out fine ranging

Fine ranging in OFDM Systems

doc.: IEEE 802.22-11/0080r0

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July 2011


• OFDM systems inherently transmit– A set of coherent pilot carriers (carriers are at slightly different

frequencies at RF, but are harmonically related at baseband, all transmitted simultaneously)

• The transmission channel– Introduces a complex warping in the signal

• Caused by multipath due to reflections and dispersion

• The sampling time shift at the receiver– Sampling time at the receiver, with respect to the sampling time used

to build the signal, can introduce a shift that results in an additional warping of the signal in the frequency domain

• OFDM receivers sample the complex warped signal


doc.: IEEE 802.22-11/0080r0

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July 2011


• Current receiver designs use preambles and pilot carriers to align the constellation demodulation process

• OFDM receivers demodulate with known phase resolutions

QPSK Constellation

16-QAM Constellation

To demodulate QPSKphase lock must be

much better than ±45°

To demodulate 16-QAMphase lock must be

much better than ±19°

To demodulate 64-QAMphase lock must be

much better than ±7.5°

64-QAM Constellation


doc.: IEEE 802.22-11/0080r0

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July 2011


OFDM Cyclic Prefix

2

1 .125

vp

10 p

sam ples

0 0 .063 0 .13 0 .19 0 .25 0 .31 0 .38 0 .44 0 .5 0 .56 0 .63 0 .69 0 .75 0 .81 0 .88 0 .94 12

1

0

1

2B a s e b a n d t im e d o m a in s ig n a l

D A C ou tpu t sam p le #

Starting discontinuity Tail end always aligns with the starting discontinuity

doc.: IEEE 802.22-11/0080r0

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July 2011


OFDM Cyclic Prefix

2

1 .125

vp

10 p

sam ples

0 0 .063 0 .13 0 .19 0 .25 0 .31 0 .38 0 .44 0 .5 0 .56 0 .63 0 .69 0 .75 0 .81 0 .88 0 .94 12

1

0

1



Starting discontinuity has been masked by copyingtail end and inserting itas a cyclic prefix

doc.: IEEE 802.22-11/0080r0

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July 2011


OFDM Cyclic Prefix

2

1 .125

vp

10 p

sam ples

0 0 .063 0 .13 0 .19 0 .25 0 .31 0 .38 0 .44 0 .5 0 .56 0 .63 0 .69 0 .75 0 .81 0 .88 0 .94 12

1

0

1



Initial filter ringing and inter-symbol interference has the time to decay before acquisition begins

doc.: IEEE 802.22-11/0080r0

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July 2011


OFDM Cyclic Prefix use

2

1 .125

vp

10 p

sam ples

0 0 .063 0 .13 0 .19 0 .25 0 .31 0 .38 0 .44 0 .5 0 .56 0 .63 0 .69 0 .75 0 .81 0 .88 0 .94 12

1

0

1


D A C ou tpu t sam p le #Signal acquisition interval does not have to be precisely aligned to get a valid orthogonal signal set

τ 1

doc.: IEEE 802.22-11/0080r0

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July 2011


Outline





5. Conclusions

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July 2011


• For 802.22, the sampling period is 146 nsec– (sampling frequency ≈ 8/7*6 MHz channel bandwidth)

• We will show that this is not the time resolution barrier– At first glance, it appears that

• One can't obtain information to a finer resolution than the sampling period

– This has proven to be a false impression

• Since channel bandwidth limitation provided by receiver analog filtering prevents aliasing– Nyquist criterion is met and information below this

sampling barrier is then recoverable.

Sampling Rate Barrier Paradigm

doc.: IEEE 802.22-11/0080r0

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July 2011


• IFFT processing usually preserves– The real values of CIR output components


• Discarding the imaginary component of CIR– Causes the apparent sampling rate timing barrier

• The imaginary component of the CIR– Embeds precious timing information

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• Combining both real and imaginary components allows for very fine correlation and interpolation


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July 2011


OFDM receivers sample at regular discrete intervals in time

Sampling instants Time

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Sampling decimates timing information thereby creating an ambiguity window

Timeambiguitywindow


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July 2011


Impulse signal and its frequency representation

Timeambiguitywindow


I

Q

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Delayed signal and its frequency representation

I

Q

Timeambiguitywindow


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Sampling time and phase of multiple carriers

-1

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

-90 -60 -30 0 30 60 90 120 150 180 210 240 270 300 330 360

Time in angular units (degrees)

Am

pli

tud

e

Sin(x)

Sin(2x)

Zero-ref

-1

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

-90 -60 -30 0 30 60 90 120 150 180 210 240 270 300 330 360

Time in angular units (degrees)

Am

pli

tud

e

Sin(x)

Sin(2x)

Zero-ref

Cyclic prefix Cyclic prefix

a) zero phase reference carriers at transmission b) phase of carriers at receiver sampling time

f1 f2 f1 f2

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Fractional sampling time echo shift and its phase information

Shift= -0.5 sampling period

146 nsStimulus

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146 nsStimulus


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July 2011



146 nsStimulus

Shift= +0.0 sampling period

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July 2011



146 nsStimulus


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July 2011


• Sampling rate is not the ‘time of arrival’ resolution limit– Determination of the time of arrival of each specular or discrete

echo is not limited by the sampling rate and can be precisely determined

– The precise time of arrival of an echo within the sampling period can be deduced from it phase.

– Only limited by the A/D and FFT/IFFT resolution (bits/sample)

• Signal bandwidth limits the dispersion resolution– Nyquist limit determines how close echoes can be before they will

appear as clumped together and cannot be discriminated:

Nyquist limit = 1/BW = 1/5.63 MHz = 178 ns = 59 m(More practical limits= 68 m between 2 equal amplitude echoes

76 m between echoes with 7 dB difference)

The Barrier is Broken !

doc.: IEEE 802.22-11/0080r0

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July 2011


Outline





5. Conclusions

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July 2011


• Uses the normal OFDM encoding and decoding process on specific ranging symbols

• Uses PN-sequence known at both terminals to modulate the carriers

Fine ranging operating principle

Y/X

Frequency domain response of aDirac pulse distorted by channel

Frequency

...

Carrier phase reversalbased on the PN-sequence

QI

QI

2048 carriers

IDFT

Time

QI

Time

Cyclic prefix

Convolution with thechannel impulse response

Time

QI

QI

2048 samples

QI

QI

QI

OFDM carrier setdistorted by channel

Frequency

...

QI

QI

τ 1

Y

2048 carriers BPSKmodulated by PN-sequence

2048 time domain samples

2048 carriers

DFT

Signal transmittedto terminal 2

Frequency

...X

PN

-seq

uen

ce

Signal receivedby terminal 2

OFDM carrier set

doc.: IEEE 802.22-11/0080r0

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July 2011


• OFDM can generate bandwidth limited repetitive classic Dirac-like RADARpulse if PN = 1 + j0 (with DC carrier removed)


OFDM bandwidth limited Dirac pulse train with DC carrier removed

Y/X


Frequency

...


QI

QI

2048 carriers

IDFT

Time

QI

Time

Cyclic prefix


Time

QI

QI

2048 samples

QI

QI

QI


Frequency

...

QI

QI

τ 1

Y



2048 carriers

DFT


Frequency

...X

PN

-seq

uen

ce


OFDM carrier set

doc.: IEEE 802.22-11/0080r0

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July 2011


• OFDM can generate all possible bandwidth limited repetitive signals with other known complex PN sequences


6 .411

6 .411

vp

10 p

sam ples

0 0 .063 0 .13 0 .19 0 .25 0 .31 0 .38 0 .44 0 .5 0 .56 0 .63 0 .69 0 .75 0 .81 0 .88 0 .94 110

5

0

5


D A C ou tpu t sam ple #

Am

plit

ude

Normalized time samples

Am

plit

ude

Normalized time samples

Y/X


Frequency

...


QI

QI

2048 carriers

IDFT

Time

QI

Time

Cyclic prefix


Time

QI

QI

2048 samples

QI

QI

QI


Frequency

...

QI

QI

τ 1

Y



2048 carriers

DFT


Frequency

...X

PN

-seq

uen

ce


OFDM carrier set

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Y/X


Frequency

...


QI

QI

2048 carriers

IDFT

Time

QI

Time

Cyclic prefix


Time

QI

QI

2048 samples

QI

QI

QI


Frequency

...

QI

QI

τ 1

Y



2048 carriers

DFT


Frequency

...X

PN

-seq

uen

ce


OFDM carrier set

• Cyclic prefix is added to absord echoes and eliminate ISI

• The channel generally alters the signal waveform due to echoes, reflections and dispersion

• Propagation delays distorts and attenuates the signal


doc.: IEEE 802.22-11/0080r0

Submission

July 2011


• The OFDM receiver amplifies and samples the received waveform– Normally uses a synch advance into the

cyclic prefix:(to avoid ISI due to pre-echoes)


τ 1

Y/X


Frequency

...


QI

QI

2048 carriers

IDFT

Time

QI

Time

Cyclic prefix


Time

QI

QI

2048 samples

QI

QI

QI


Frequency

...

QI

QI

τ 1

Y



2048 carriers

DFT


Frequency

...X

PN

-seq

uen

ce


OFDM carrier set

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


• The OFDM receiver performs an FFT on the received samples


Y/X


Frequency

...


QI

QI

2048 carriers

IDFT

Time

QI

Time

Cyclic prefix


Time

QI

QI

2048 samples

QI

QI

QI


Frequency

...

QI

QI

τ 1

Y



2048 carriers

DFT


Frequency

...X

PN

-seq

uen

ce


OFDM carrier set

doc.: IEEE 802.22-11/0080r0

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July 2011


• The known complex PN sequence is removed: Y/X

• The result is:– A mathematical representation of the

complex channel impulse response in the frequency domain

– Normally used to correct the carrier constellation for proper data decoding


Y/X


Frequency

...


QI

QI

2048 carriers

IDFT

Time

QI

Time

Cyclic prefix


Time

QI

QI

2048 samples

QI

QI

QI


Frequency

...

QI

QI

τ 1

Y



2048 carriers

DFT


Frequency

...X

PN

-seq

uen

ce


OFDM carrier set

Up to this point, normal OFDM receiver operation

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Y/X


Frequency

...


QI

QI

2048 carriers

IDFT

Time

QI

Time

Cyclic prefix


Time

QI

QI

2048 samples

QI

QI

QI


Frequency

...

QI

QI

τ 1

Y



2048 carriers

DFT


Frequency

...X

PN

-seq

uen

ce


OFDM carrier set

• This channel impulse response is practically identical to that of a classic Dirac Pulse RADAR in the frequency domain

• This channel impulse response will be used for fine ranging calculations

• These calculations can all be done by an off-line processor (e.g., at the NOC)

• Practically no hardware costs !– No wiring– No additional antenna– No additional installation– Guaranteed co-location– Tamper resistant


doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Outline





5. Conclusions

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Propagation time between Base Station and CPE(Coarse Time Difference of Arrival: TDOA)

Downstream

Upstream

1. CPE synchronizes with BS and is in phase-lock with the RF carrier.The sampling frequency (≈ 8/7*BW) is derived from the same clock

2. BS and CPE carry out normal association and ranging and adjust the advance A1 so that all CPE upstream bursts arrive at the BS at the same time independently of their distance, within ±25% of the smallest cyclic prefix (±2.33 sec)A1 is regularly updated by the ranging process, in sampling clock units,

TU≈1/(8/7*BW) (e.g., 145.8576 ns for 6 MHz)

A1 roughly corresponds to double the BS-CPE distance:BS-CPE distance = 1/2 * A1*145.8*0.3 (m)

< RNG-REQ

RNG-RSP >A1

BS CPE

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Propagation time between Base Station and CPE(Fine Time Difference of Arrival: TDOA)

T1

Downstream

Upstream

1. BS transmits a RNG-RSP to the specific CPE and initiates its counter T1 (in sampling intervals: TU’s) at the moment where the downstream burst leaves the BS (at the start of the frame preamble).

2. The BS knows exactly the symbols on which the solicited Ranging burst will be transmitted by the CPE on the upstream since it is registered in the US-MAP. The BS keeps this value T2 in memory

3. The BS knows the size of the TTG in TU’s (e.g., 1439 TU for 6 MHz),

4. The precise residual CPE time delay DCPE is sent to the BS at initialization (measured with an accuracy of at least +/-30 ns in a test setup corresponding to the CPE being co-located with the BS and A1 set to zero).

Note: A1, the advance obtained through coarse ranging, is known at the BS.

T2 < RNG-REQ

RNG-RSP >

TTG

DCPE

A1

BS CPE

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


802.22 Frame structure

DS sub-frame

TT

G

RT

G

US sub-frame(smal l est US burst por t ion on a given subchannel= 7 symbol s)

26 to 42 symbols cor responding t o bandw idths f rom 6 MHz t o 8 MHz and cycl ic prefi xes f rom 1/ 4 t o 1/ 32

Fram

e Pr

eam

ble

FCH

DS-

MA

P

Burs

t 1DC

D

Burs

t 2 ti

me

buff

er

tim

e bu

ffer

Self

-coe

xist

ence

win

dow

(4 o

r 5

sym

bols

wh

en s

ched

ule

d)

Burst 1

60 s

ubch

anne

ls

Burst 2

Burst 3more than 7 OFDMA symbols

Burst

Burst n

Burst

Burs

t m

Ranging/ BW request / UCS not ifi cat ion

Burst

Burst

Burst s

Burs

ts

fram e n-1 fram e n fram e n+1... Tim e...

10 m s

US-

MA

P

US-

MA

PU

CD

Reference start time for T1 counter

TTG+T2

DS-MAP for the RNG-RSP MAC message

RNG-RSP MAC

message

US-MAP for the CDMA

Ranging burst

Solicited CDMA

Ranging burst

An example of a RNG-RSP and RNG-REQ exchange between BS and CPE.

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



Vernier-1 Downstream

Upstream

5. Vernier-1 uses the information on the frequency domain equalization process done at the CPE to precisely calculate the arrival of the first multipath relative to the synchronization time at the CPE recovered by the receiver synchronization: (Note that an advance of a few TU’s will normally be inserted by the CPE synchronization scheme to avoid ISI due to pre-echoes.)

6. The CPE responds by sending a ranging burst during the frame specified in the RNG-CMD message and at the specified symbol offset T2.

7. BS receives the ranging burst and stops the T1 counter at the arrival of the ranging burst, precisely at the time of the first sampling period belonging to the burst. (T1 counter is in sampling periods, TU’s, at the BS.)

< RNG-REQ

RNG-RSP >

T1

T2

TTG

DCPE

BS CPE

τ 1

doc.: IEEE 802.22-11/0080r0

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July 2011


Vernier time reference

Time reference for the FFT window during symbol generation at the transmitter where the residual phases calculated by the Vernier are zero.

Synchronized 2k FFT sampling window

Reference 2k FFT sampling window

Time reference for the FFT window at the receiver resulting from the synchronization scheme using the preamble plus an advance of a number of samples to avoid pre-echo leakage)

Typical Vernier value (ns) (including all received multipaths)

Channel impulse response

Cyclic prefix

Symbol period

τ 1

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



Vernier-1

Vernier-2

Downstream

Upstream

8. BS acquires the I&Q values of the ranging burst carriers at the output of the FFT (Vernier-2) and removes the PN-sequence.

9. Off-line signal processing can be applied onto the received 168 reference upstream subcarriers to resolve the precise time of arrival (ns) of the first multipath relative to the reference sampling time at the BS (V2).

10. The values of the frequency domain vector of Vernier-1 that were acquired during the downstream burst is queried later by the BS

11. The CPE sends these values (1680 I&Q values coded in 8 bits) to the BS.12. Once the Vernier-1 vector is acquired by the BS, signal processing can be

performed off-line. The precise delay (ns) of the first channel echo relative to the synchronization reference at the CPE can be extracted: V1.

< RNG-REQ

RNG-RSP >

T1

T2

TTG

DCPE

BS CPE

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



Vernier-1

Vernier-2

Upstream

13. BS knows:TTG in sampling periods TU’s (e.g., 1439 TU for 6 MHz),T2 in symbols from the scheduling of the ranging burst,DCPE representing the precise delay inherent to the CPE,T1 from the stopped counter in sampling periods,V1 from the processing of the acquired Vernier-1 vector in ns,V2 from the processing of the acquired Vernier-2 vector in ns.

14. All the information necessary to calculate the propagation time between the BS and CPE is known down to a nanosecond accuracy:Ptime = T1 - (T2 + TTG) - DCPE + V1 + V2 (ns)

Distance = c * Ptime/2 (m)

T1

T2

TTG

DCPE

BS CPE

Downstream

< RNG-REQ

RNG-RSP >

doc.: IEEE 802.22-11/0080r0

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July 2011


Outline





5. Conclusions

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Submission

July 2011


The ‘Vernier’ process

Syncadvance IQ Vector

LTS

Frequency

...

IDFT

Time

QI

Time

Cyclic prefix

QI

QI

QI

Time

2048 samples

QI

DFT

LTS distortedby channel

Frequency

...

QI

QI

τ1

Dirac distortedby channel

Frequency

...

Carrier phase reversalbased on the LTS coding

QI

QI

QI

Convolution with channelimpulse response

QI

IDFT

Complex channel impulse response relativeto the receiver synchronization time

QI

Sampling time

Imaginary

Re

al

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


The ‘Vernier’ process (cont’d)

Complexcorrelation

Channel impulse responserelative to the sampling time

τ 1

τ 2τ 3

Amplitude1 Delay1Amplitude2 Delay2Amplitude3 Delay3Amplitude4 Delay4 etc...

2048 I&Q samples at samplingperiod (i.e., every 145.86 ns)

High resolution bandlimited impulse response

(e.g., every 0.81 ns)

QI

2048 x 180 I&Q samplesat every 0.81 nsQI

-1

01

Precise time sampleImaginary

Rea

l

-1

0

1

I

Q


Sampling times

ImaginaryR

eal

doc.: IEEE 802.22-11/0080r0

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Outline





5. Conclusions

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July 2011


802.22 OFDM Subcarrier Set

0-1-840 +840+1Subcarrier index

Am

pli

tud

e

doc.: IEEE 802.22-11/0080r0

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July 2011


Construction of the “high-resolution” CIR function

6000 6500 7000 7500 8000 8500 9000 9500 10000-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1LTS prototype function

Precise time sample

Rea

l

=146/180= 0.8 ns


Am

plitu

de

IDFT [ ]

doc.: IEEE 802.22-11/0080r0

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July 2011



6000

7000

80009000

10000

-1

-0.5

0

0.5

1-1

-0.5

0

0.5

1

Precise time sample

LTS prototype function

Imaginary

Rea

l

145.8 ns

Stimulus

=145.86/180= 0.81 ns


Am

plitu

de

IDFT [ ]

doc.: IEEE 802.22-11/0080r0

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July 2011



6000

7000

80009000

10000

-1

-0.5

0

0.5

1-1

-0.5

0

0.5

1

Precise time sample


Imaginary

Rea

l

145.8 ns

Stimulus

=146/180= 0.8 ns


Am

plitu

de

IDFT [ *e-jwt]

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



60007000

80009000

10000

-1

-0.5

0

0.5

1-1

-0.5

0

0.5

1

Precise time sample


Imaginary

Rea

l

145.8 ns

Stimuli

=146/180= 0.8 ns


Am

plitu

de

IDFT [ *e-jwt]

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



60007000

80009000

10000

-1

-0.5

0

0.5

1-1

-0.5

0

0.5

1

Precise time sample


Imaginary

Rea

l

=146/180= 0.8 ns

145.8 ns

Stimuli


Am

plitu

de

IDFT [ *e-jwt]

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



60007000

80009000

10000

-1

-0.5

0

0.5

1-1

-0.5

0

0.5

1

Precise time sample


Imaginary

Rea

l

=146/180= 0.8 ns

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



6000 6500 7000 7500 8000 8500 9000 9500 10000-1

0

1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8



Rea

l

=146/180= 0.8 ns

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



6000 6500 7000 7500 8000 8500 9000 9500 10000-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8


Precise time sample

Rea

l

=146/180= 0.8 ns

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Validation of the Vernier concept

Complexcorrelation


τ 1

τ 2τ 3





QI


-1

01


Rea

l

-1

0

1

I

Q


Sampling times

ImaginaryR

eal

High resolution channel

deconvolution

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Outline





5. Conclusions

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


IEEE 802.22 Channel Model B

Delay (microseconds)

Rel

ativ

e am

plitu

de

-6 dB

0 dB

-7 dB

-22 dB

-16 dB

-20 dB

16141210864200

0.2

0.4

0.6

0.8

1

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Typical LTS generated multipath response

20 40 60 80 100 120 140 160 180 200-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time samples

Am

plit

ud

e

RealAbs

(1 sample = 145.86 ns)

SNR= 0 dB

τ 1

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Validation of the Vernier concept

Complexcorrelation


τ 1

τ 2τ 3





QI


-1

01


Rea

l

-1

0

1

I

Q


Sampling times

ImaginaryR

eal

High resolution channel

deconvolution

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Typical correlation output waveform

Precise time samples

Co

rrel

atio

n O

utp

ut A

mp

litu

de

0.5 1 1.5 2 2.5 3 3.5x 10

4-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

RealSamples

(1 sample = 0.81 ns)τ 1

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


Co

rrre

lati

on

Ou

tpu

t Am

plit

ud

e

RealSamples

(1 sample = 0.81 ns)τ 1

High resolution Samples

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Typical LTS generated multipath response

5 10 15 20 25 30 35 40 45 50 55 60-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Time samples

Am

pli

tud

e

RealAbs

(1 sample = 145.86 ns)

SNR= 0 dB

τ 1

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


Co

rrre

lati

on

Ou

tpu

t Am

plit

ud

e

RealSamples

(1 sample = 0.81 ns)τ 1

High resolution Samples

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


7500 8000 8500 9000 9500

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Correlation Response


Rea

l and

Im

agin

ary

Am

plitu

des

Imag Real Samples


(1 sample = 0.81 ns)

High resolution Low resolution (Abs) Samples

+ a fraction of a sampling period

τ 1N sampling periods from

τ 1X high resolution sampling periods from

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


8763 8764 8765 8766 8767 8768 8769 8770 8771

0.3932

0.3934

0.3936

0.3938

0.394

0.3942

0.3944

0.3946

0.3948

0.395

Correlation Response


Rea

l and

Im

agin

ary

Am

plitu

des

Imag Real Samples



(48 sampling periods + 127/180)*180 = 8767 micro samples

High resolution (Real)

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Multipath results summarySNR (dB) = (dB) 60 20 10 6 3 0 -3 -6 -10Micro-shift (1/10 sampling period) (ns) -72.93 -72.93 -72.93 -72.93 -72.93 -72.93 -72.93 -72.93 -72.93

Path #Relative

power (dB)Nominal

delay (us)Samples Delay (us) Delta (ns) Delta (ns) Delta (ns) Delta (ns) Delta (ns) Delta (ns) Delta (ns) Delta (ns) Delta (ns)

2 0 0 0 5.104 0.810 0.000 0.000 0.000 0.810 0.810 1.620 2.431 1.6201 -6 -3 -21 2.042 -0.810 -0.810 -0.810 -0.810 -1.620 -1.620 -0.810 0.000 5.6713 -7 2 14 7.146 -0.810 -0.810 0.000 -1.620 0.000 -0.810 2.431 0.810 -6.4815 -16 7 48 12.104 0.810 0.810 -1.620 0.810 -1.620 -1.620 -5.671 36.458 6.4816 -20 11 75 16.042 -1.620 -1.620 -4.051 0.810 -4.051 -4.051 -2.431 -8.912 -1.620

Wrong echoes: 1 1 2 5 2 8 94 -22 4 27 9.042 -4.861 -4.861 -0.810 -8.912 -20.255 15.394 -682.986 18035.532 -638.426

SNR (dB) = (dB) 60 20 10 6 3 0 -3 -6 -10Micro-shift (1/10 sampling period) (ns) 0 0 0 0 0 0 0 0 0

Path #Relative

power (dB)Nominal


2 0 0 0 5.104 0.810 0.810 0.810 0.810 0.000 0.810 -0.810 2.431 -0.8101 -6 -3 -21 2.042 -0.810 -0.810 -0.810 0.000 -3.241 -2.431 2.431 -2.431 4.0513 -7 2 14 7.146 -0.810 0.000 -0.810 -0.810 -1.620 0.000 2.431 4.861 7.2925 -16 7 48 12.104 0.810 1.620 1.620 3.241 -3.241 -3.241 -3.241 -181.481 20.2556 -20 11 75 16.042 -1.620 -3.241 0.000 -3.241 8.912 -1.620 -29.977 8.102 -330.556

Wrong echoes: 1 1 1 1 7 84 -22 4 27 9.042 -4.861 -3.241 -0.810 -8.102 1.620 -4.051 -9547.222 9583.681 -5045.023

SNR (dB) = (dB) 60 20 10 6 3 0 -3 -6 -10Micro-shift (1/10 sampling period) (ns) 72.93 72.93 72.93 72.93 72.93 72.93 72.93 72.93 72.93

Path #Relative

power (dB)Nominal


2 0 0 0 5.104 0.000 0.000 0.000 1.620 0.810 1.620 0.810 0.000 0.0001 -6 -3 -21 2.042 -0.810 -0.810 -0.810 -2.431 -1.620 -4.051 0.810 0.000 1.6203 -7 2 14 7.146 -0.810 0.000 -0.810 0.000 -0.810 0.000 -2.431 3.241 -1.6205 -16 7 48 12.104 0.810 0.810 1.620 2.431 -1.620 3.241 -0.810 -12.153 -12.9636 -20 11 75 16.042 -0.810 0.000 -8.102 -2.431 -5.671 -2.431 4.861 21.065 8708.681

Wrong echoes: 1 1 1 2 2 5 2 54 -22 4 27 9.042 -4.861 -4.051 -3.241 12.963 -0.810 -5.671 1088.079 448.843 -6167.940

doc.: IEEE 802.22-11/0080r0

Submission

July 2011



1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1


Co

rrre

lati

on

Ou

tpu

t A

mp

litu

de

RealSamples


Wrong echo

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Multipath results summarySNR (dB) = (dB) 60 20 10 6 3 0 -3 -6 -10Micro-shift (1/10 sampling period) (ns) -72.93 -72.93 -72.93 -72.93 -72.93 -72.93 -72.93 -72.93 -72.93

Path #Relative

power (dB)Nominal


2 0 0 0 5.104 0.810 0.000 0.000 0.000 0.810 0.810 1.620 2.431 1.6201 -6 -3 -21 2.042 -0.810 -0.810 -0.810 -0.810 -1.620 -1.620 -0.810 0.000 5.6713 -7 2 14 7.146 -0.810 -0.810 0.000 -1.620 0.000 -0.810 2.431 0.810 -6.4815 -16 7 48 12.104 0.810 0.810 -1.620 0.810 -1.620 -1.620 -5.671 36.458 6.4816 -20 11 75 16.042 -1.620 -1.620 -4.051 0.810 -4.051 -4.051 -2.431 -8.912 -1.620

Wrong echoes: 1 1 2 5 2 8 94 -22 4 27 9.042 -4.861 -4.861 -0.810 -8.912 -20.255 15.394 -682.986 18035.532 -638.426

SNR (dB) = (dB) 60 20 10 6 3 0 -3 -6 -10Micro-shift (1/10 sampling period) (ns) 0 0 0 0 0 0 0 0 0

Path #Relative

power (dB)Nominal


2 0 0 0 5.104 0.810 0.810 0.810 0.810 0.000 0.810 -0.810 2.431 -0.8101 -6 -3 -21 2.042 -0.810 -0.810 -0.810 0.000 -3.241 -2.431 2.431 -2.431 4.0513 -7 2 14 7.146 -0.810 0.000 -0.810 -0.810 -1.620 0.000 2.431 4.861 7.2925 -16 7 48 12.104 0.810 1.620 1.620 3.241 -3.241 -3.241 -3.241 -181.481 20.2556 -20 11 75 16.042 -1.620 -3.241 0.000 -3.241 8.912 -1.620 -29.977 8.102 -330.556

Wrong echoes: 1 1 1 1 7 84 -22 4 27 9.042 -4.861 -3.241 -0.810 -8.102 1.620 -4.051 -9547.222 9583.681 -5045.023

SNR (dB) = (dB) 60 20 10 6 3 0 -3 -6 -10Micro-shift (1/10 sampling period) (ns) 72.93 72.93 72.93 72.93 72.93 72.93 72.93 72.93 72.93

Path #Relative

power (dB)Nominal


2 0 0 0 5.104 0.000 0.000 0.000 1.620 0.810 1.620 0.810 0.000 0.0001 -6 -3 -21 2.042 -0.810 -0.810 -0.810 -2.431 -1.620 -4.051 0.810 0.000 1.6203 -7 2 14 7.146 -0.810 0.000 -0.810 0.000 -0.810 0.000 -2.431 3.241 -1.6205 -16 7 48 12.104 0.810 0.810 1.620 2.431 -1.620 3.241 -0.810 -12.153 -12.9636 -20 11 75 16.042 -0.810 0.000 -8.102 -2.431 -5.671 -2.431 4.861 21.065 8708.681

Wrong echoes: 1 1 1 2 2 5 2 54 -22 4 27 9.042 -4.861 -4.051 -3.241 12.963 -0.810 -5.671 1088.079 448.843 -6167.940

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Outline





5. Conclusions

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Lab measurement setup

PN-sequencegenerator

LTSsequence

construction

2048-point

ifft

512-pointCyclicPrefix

addition

AgilentESG4438C

signal generator

AgilentN9020A MXAVector Signal

Analyzer

Samplingfrequencyconverter

Ethernetinterface

MATLAB

I&Q Channel impulseresponse estimate

LTSSignatureremoval

CyclicPrefix

RemovalCorrelator

MATLAB

Ethernetinterface

Signal generationand modulation

AgilentReferenceOscillator

Calibratedmultipathand noise

HP 11759CChannel

Simulator

UHF TVchannel

ifft fft

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


LTS-H I&Q Vector for analysis

Samples

Vec

tor

Am

pli

tud

e (A

BS

)

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Precise channel impulse after correlation with prototype function

enlever

Co

rre

lati

on

re

sp

on

se

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Precise time samples (1 sample= 0.81 ns)

Correlation output

Impulse response samples

4.950231 usec sync advance

2.997847 usec

Error= 2.15 ns

Pre-echo= 3 usec

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Outline





5. Conclusions

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Multipath excess delay time span

802.22 Downstream: full multiplex from the BS• Fine ranging uses LTS frame preamble

Long training sequence: 840 subcarriers (one every two subcarriers)– Total extent of time quantified without aliasing:

½ symbol period= 150 sec (Can easily absord all multipaths)

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Downstream channel impulse response(840 subcarriers)

200 400 600 800 1000 1200 1400 1600 1800 2000-70

-60

-50

-40

-30

-20

-10

0CIR for 840 subcarriers distributed every 2 subcarrier over the 5.625 MHz bandwidth

Time samples (1 sample = 145.83 ns, Entire span = 298.655 usec)

Rela

tive A

mplit

ude (

dB

)

Sub-sampled function

Entire function

300 µs

150 µs

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Multipath excess delay time span

802.22 Downstream: full multiplex from the BS• Fine ranging uses LTS frame preamble

Long training sequence: 840 subcarriers (one every two subcarriers)– Total extent of time quantified without aliasing:

½ symbol period= 150 sec (Can easily absord all multipaths)

802.22 Upstream: multiplex shared among CPEs• Fine ranging uses a CDMA ranging burst

Fine ranging burst uses 6 sub-channels out of 60:1/10 of the upstream

multiplex– 168 subcarriers evenly spread (one every 10 subcarriers)– Total extent of time quantified without aliasing:

1/10 symbol period= 30 sec (Can absord all practical multipaths)

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


200 400 600 800 1000 1200 1400 1600 1800 2000-70

-60

-50

-40

-30

-20

-10

0CIR for 168 subcarriers distributed every 10 subcarriers over the 5.625 MHz bandwidth

Time samples (1 sample = 145.83 ns, Entire span = 298.655 usec)

Rel

ative A

mplit

ude (

dB)

Sub-sampled function

Entire function

Upstream channel impulse response(168 subcarriers)

300 µs

30 µs

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Outline





5. Conclusions

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Propagation time between BS and CPE1

(Fine Time Difference of Arrival: TDOA)

Vernier-1

Vernier-2

Downstream

Upstream

1. The terrestrial geolocation process requires one BS for which the geolocationis known and at least 2 CPEs, one of which is a reference CPE (waypoint) for which the geolocation is known.

2. BS sends a RNG-RSP message to one of the CPEs involved to carry out thefine ranging as described before.

3. Upon arrival of the RNG-RSP request, the CPE will start its Vernier-1 and capture the I&Q values of the reference carriers from the frame preamble and respond with the RNG-REQ burst in the slot allocated.

4. BS will use the values of all variables T1, T2, TTG, DCPE, V1 and V2 to calculate the propagation time (Ptime1) and the corresponding distance to CPE1 .

T1

T2

TTG

DCPE

BS

CPE1

CPE2

< RNG-REQ

RNG-RSP >

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Propagation time between BS and CPE2


Vernier-1

Vernier-2

5. BS sends a RNG-RSP message to the second CPE involved to carry out the fine ranging as described before.

6. Upon arrival of the RNG-RSP request, CPE2 will start its Vernier-1 and capture the I&Q values of the reference carriers from the frame preamble and respond with the RNG-REQ burst in the slot allocated.

7. BS will use the values of all variables T1, T2, TTG, DCPE, V1 and V2 to calculate the propagation time (Ptime2) and the corresponding distance to CPE2 .

T1

T2

TTG

DCPE

BS

CPE1

CPE2

< RNG-REQ

RNG-RSP >

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Propagation time between CPE1 and CPE2


Downstream

8. BS will request CPE1 to transmit a CBP burst during the SCW scheduled at the end of the frame with a T3 timing advance in TU’s and a specified EIRP depending on the expected distance between CPE1 and CPE2

9. BS will request CPE2 to receive and sample this CBP burst for its FFT using its synchronization locked to the BS.

10. Upon arrival of the CBP burst from CPE1, the CPE2 will start its Vernier-3 and capture the I&Q values of the reference carriers from the CBP preamble.

11. CPE2 will respond to the query from the BS with the acquired values: V3.

Vernier-3

CBP burst

BS

CPE1

CPE2

UpstreamDCPET3

SCW: Self-coexistence window CBP: Coexistence beacon protocol

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Propagation time between CPE1 and CPE2


Downstream

12. BS will use the values of all variables: Ptime1, Ptime2, DCPE, T3, and V3 to calculate the propagation time between CPE1 and CPE2 down to a nanosecond accuracy (Ptime3) and the corresponding distance:Ptime3= -Ptime1 + T3 + (Ptime2-DCPE) +V3 (ns)Distance= c * Ptime3/2 (m)

13. Once the three distances between the BS and the two CPEs and between these two CPEs are known and that the geolocation of two devices is known (e.g., BS and CPE1), the geolocation of the third device (CPE2) can be found by normal triangulation.

Note: These 3 steps of fine ranging can be done concurrently during the same frame or over closely spaced frames to minimize any drift in the timing references.

Vernier-3

CBP burst

BS

CPE1

CPE2

UpstreamDCPET3

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Outline





5. Conclusions

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


Conclusions• This terrestrial geolocation technique does not require any additional

hardware and uses features already existing in the 802.22 Standard.• The fine ranging process is typically 6 dB more robust to SNR than the

most robust data transmission of the 802.22 systems.• The fine ranging process requires minimal transmission capacity:

– For each BS-to-CPE fine ranging:• one tenth of a symbol (0.4% of a frame) for the upstream ranging burst• 3.36 kbyte packet for the Vernier transmission from the CPE

– For each CPE-to-CPE fine ranging:• one SCW (5 symbols) which corresponds to about 20% of a frame to carry

the CBP burst (the CBP burst can also be shared for other CBP functions)• 3.36 kbyte packet for the Vernier transmission from the CPE

– Some small capacity for the RNG-RSP and RNG-REQ MAC messages.• Distances can be found down to a few meters accuracy outdoors and

indoors as long as distinct signals and echoes can be received:– Needs distinct (specular) echoes to work reliably– Resolution between close-in echoes is limited by Nyquist:

Resolution= 1/BW= 1/5.63 MHz = 178 ns = 59 m– Diffused echoes will not result in successful fine ranging

• Redundancy amongst CPEs that can be used for geolocation can compensate for unreliable fine ranging cases.

doc.: IEEE 802.22-11/0080r0

Submission

July 2011


References

1. IEEE Std 802.22-2011TM, Standard for Wireless Regional Area Networks—

Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Policies and procedures for operation in the TV Bands, July 2011

2. 22-06-0206-00-0000 Ranging with OFDM Systems.ppt

3. 22-10-0054-02-0000_OFDM-based Terrestrial Geolocation.ppt

4. 22-10-0055-0000 Multicarrier ranging.ppt

5. 22-11-0076-00-0000 Echo resolution simulation results

6. 22-11-0077-00-0000 Impact of bandwidth on echo resolution.ppt

doc.: ieee 802.22-11/0080r0 submission july 2011 ivan reede, gerald chouinardslide 1 ofdm-based...

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