Doc.: IEEE 802.19-05/0034r0 Submission September 2005 Jim Lansford, AlereonSlide 1 Detect and Avoid for MB-OFDM Notice: This document has been prepared

September 2005

Jim Lansford, Alereon

Slide 1

doc.: IEEE 802.19-05/0034r0

Submission

Detect and Avoid for MB-OFDM

Notice: This document has been prepared to assist IEEE 802.19. 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.

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Date: 2005-09-20

Name Company Address Phone email Jim Lansford Alereon 7600C N. Capital of

Texas Hwy Suite 200 Austin, TX 78731

+1 512 345 4200 x2166

[email protected]

Authors:

September 2005


Slide 2

doc.: IEEE 802.19-05/0034r0

Submission

Abstract

Detect and Avoid (DAA) is under discussion by both Japanese and European regulatory agencies as a non-collaborative coexistence technique. DAA requires the receiver to detect the presence of interference and suppress energy in that portion of the band. MB-OFDM is particularly well suited to implement DAA, because the FFT can be used as a channelized radiometer, and the IFFT can be used to sculpt the transmit spectrum.

September 2005


Slide 3

doc.: IEEE 802.19-05/0034r0

Submission

Background

• UWB was developed as an “underlay”– FCC bought into the concept– Most of the rest of the world has been sceptical– It’s a coexistence problem

• What are the issues?– Detecting the presence of an “incumbent” signal (FWA)– Dropping emissions in the shared band so that interference on the

“incumbent” is minimized

• This is a form of cognitive radio– Similar to “waterfilling”

• TBD: Detection level/confidence and suppression level

September 2005


Slide 4

doc.: IEEE 802.19-05/0034r0

Submission

How does MB-OFDM implement DAA?• Detect: Channelized radiometer

– 128 channel FFT inherent in the design

– Integrate spectra to achieve desired Pd

• Avoid: Bandstop filter (frequency domain)– 128 point IFFT– Additional signal processing techniques can increase notch depth, subject to RF linearity

ADC

DAC

FFT/IFFT

Filter/Decimate

Interp./Filter

AGC

Detect

DespreadDemapDeinterleaveDepuncture

Viterbi

SpreadingMappingInterleavePuncture

Convo-lutionalCoder

MA

C/P

HY

Interface

Chan EstCFO

Equalize

ADC

DAC

FFT/IFFT

Filter/Decimate

Interp./Filter

AGC

Detect

DespreadDemapDeinterleaveDepuncture

Viterbi

SpreadingMappingInterleavePuncture

Convo-lutionalCoder

MA

C/P

HY

Interface

Chan EstCFO

Equalize

Mixer & Filter

Mixer & Filter

90°

September 2005


Slide 5

doc.: IEEE 802.19-05/0034r0

Submission

Detect (1)• Channelized radiometers have been used for decades

– Narrowband detection in a wideband channel– Used in Radar and communication intercept receivers– Theory well developed

• If FFT bins contain noise alone, distribution is Rayleigh

• If narrowband signal + noise, distribution is Rician

FF

T

(●)2 ∫ <>

P(N) P(S+N)

September 2005


Slide 6

doc.: IEEE 802.19-05/0034r0

Submission

Detect (2)• Averaging spectra reduces the

variance of the distribution• For ensemble average of N

spectra, variance within a bin decreases by 1/N, standard deviation by 1/sqrt(N)

• Thus, detection probability can be made arbitrarily close to 1 but integration time can become large

• There is a considerable body of research for fluctuating signals (such as pulsed beacons)

September 2005


Slide 7

doc.: IEEE 802.19-05/0034r0

Submission

Detect (3)

• For MB-OFDM system, FFT resolution is 528/128=4.125MHz

• kTB for a single tone is -174+66= -108dBm• Assume 6.6dB NF in RF => N0= -101dBm• FWA characteristics

– 5 or 10MHz BW– 4W uplink, Downlink power <-90dBm at UWB system

• For FWA downlink, detection probability at -90dBm should be more than adequate – unless DL is in a fade– Uplink can always be easily detected– Uplink confirms local activity after downlink detected

September 2005


Slide 8

doc.: IEEE 802.19-05/0034r0

Submission

Detect (4)

• Detection test setup– This is a demo

– Fading channel tests will be done later

UWBtransmitter

UWBReceiver

FWA signalGenerator

Rhode & SchwartzSpectrum Analyzer

+

September 2005


Slide 9

doc.: IEEE 802.19-05/0034r0

Submission

Detect (5)

Att 0 dB

A

*Ref -80 dBm

*1 RM

AVG

20 MHz/Center 3.31 GHz Span 200 MHz

*

*

RBW 1 MHz

VBW 3 MHz

SWT 10 ms*

PA

-110

-105

-100

-95

-90

-85

-80

Date: 12.SEP.2005 01:04:29

Att 0 dB

A

*Ref -80 dBm

*1 RM

AVG


*

*

RBW 1 MHz

VBW 3 MHz

SWT 10 ms*

PA

-110

-105

-100

-95

-90

-85

-80

Date: 12.SEP.2005 01:04:46

Spectrum analyzerNoise floor

MB-OFDM signal(zoomed: 200MHz)

September 2005


Slide 10

doc.: IEEE 802.19-05/0034r0

Submission

Detect (6)

Att 0 dB

A

*Ref -80 dBm

*1 RM

AVG


*

*

RBW 1 MHz

VBW 3 MHz

SWT 10 ms*

PA

-110

-105

-100

-95

-90

-85

-80

Date: 12.SEP.2005 01:05:05

Att 0 dB

A

*Ref -80 dBm

*1 RM

AVG


*

*

RBW 1 MHz

VBW 3 MHz

SWT 10 ms*

PA

-110

-105

-100

-95

-90

-85

-80

Date: 12.SEP.2005 01:05:25

“FWA” Signal@ -90dBm

“FWA” Signal + OFDM Signal(10ms averaging, MB-OFDM @ -81dBm)

September 2005


Slide 11

doc.: IEEE 802.19-05/0034r0

Submission

Avoid (1)

• Spectral “notches” have been discussed widely in 802.15.3a in reference to MB-OFDM

• Generally, can be considered frequency domain bandstop filters (FIR)– Like any FIR filter, intentional ISI can be introduced to control

notch depth and width

– EVM of RF chain must be consistent with desired depth

• Typically, these notches can be 15-20dB in depth

• More advanced techniques are under evaluation to achieve deeper notches

September 2005


Slide 12

doc.: IEEE 802.19-05/0034r0

Submission

Avoid (2)Att 0 dB

A

*Ref -80 dBm

*1 RM

AVG


*

*

RBW 1 MHz

VBW 3 MHz

SWT 10 ms*

PA

-110

-105

-100

-95

-90

-85

-80

Date: 12.SEP.2005 01:06:05

Att 0 dB

A

*Ref -80 dBm

*1 RM

AVG


*

*

RBW 1 MHz

VBW 3 MHz

SWT 10 ms*

PA

-110

-105

-100

-95

-90

-85

-80

Date: 12.SEP.2005 01:05:44

MB-OFDM signal with20MHz notch (5 tones)

MB-OFDM signal plus “FWA”inside 20MHz notch

20MHz

September 2005


Slide 13

doc.: IEEE 802.19-05/0034r0

Submission

Summary

• These measurements were made on an actual MB-OFDM system

• BER/PER increase from removal of five tones is insignificant– Erasure performance has been well documented

• Detection algorithm works, but needs further study– Fluctuating FWA signal– Strategies for downlink+uplink detection

• Collaborative coexistence (in a laptop, for example) would work even better

• Spectral sculpting really works…

September 2005


Slide 14

doc.: IEEE 802.19-05/0034r0

Submission

References

• M.Skolnik, Introduction to Radar Systems, McGraw Hill, 1980

• Johanna Vartiainen, “Concentrated Signal Extraction using Consecutive Mean Excision Algorithms,” Proceedings of the 2005 Finnish Signal Processing Symposium - FINSIG'05, August, 2005, Kuopio, Finland, pp. 87-90.

• S. M. Kay, Fundamentals of Statistical Signal Processing: Detection Theory., Prentice Hall, 1998.

Documents

Doc.: IEEE 802.19-05/0034r0 Submission September 2005 Jim Lansford, AlereonSlide 1 Detect and Avoid for MB-OFDM Notice: This document has been prepared