doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 1 The case for wideband sensing IEEE P Wireless RANs Date: Authors: Notice: This document has been prepared to assist IEEE 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 Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures 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 Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl R. Stevenson 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 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 2 Abstract This presentation builds the case for wideband sensing – in particular it proposes the use of shadowing correlation across frequencies to weed out unqualified users and enable cooperation between qualified users only. Such cooperation enables us to lower the system probability of harmful interference while also reducing the probability of missed opportunity.

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 3 Sensing architecture goals - Non-Interference constraint: Must not interfere with a primary receiver For this we want to be conservative and make minimal assumptions about the model - Opportunity maximization: If we won’t interfere we should allow transmission

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 4 Semi-ideal case: perfect location information Minimal No Talk Radius Primary System TV - Locations of TV transmitter and Cognitive radios are known. - Location of TV receivers is unknown Non-interference constraint translates into “Minimal No-talk” radius - Best possible spatial reuse Primary Receiver TV set

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 5 If we use SNR as a proxy for distance.. Minimal No Talk Radius LOS channel Primary System TV - With worst case shadowing/multipath assumptions - Detector sensitivity must be set as low as -116 dBm (-98 -> -116) Shadowing Detection Sensitivity = -116dBm - Un-shadowed radios are also forced to shut up Loss in Real estate ~ 100 km

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 6 How can we reclaim this lost real estate? Min No Talk Radius Primary System TV - Cooperation … can budget less for shadowing since the chance that all radios are shadowed may be very low No Talk radius with cooperation Detection Sensitivity = > -104 dBm When independence assumptions are not true we might cause interference

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 7 What if we knew our shadowing environment … Minimal No Talk Radius Primary System TV - Then we could dynamically change our sensitivity … and regain lost real estate Detection Sensitivity = -98dBm Detection Sensitivity = -116dBm Shadowing

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 8 Fremont Peak San Juan Battista 10 co-located transmitters Sutro Tower San Francisco 28 co-located transmitters

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 9 Frequency correlation of shadowing from collocated transmitters From indoor UWB channel experiments we see strong shadowing correlation between frequencies – even frequencies 1GHz apart

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 10 Basic idea behind wideband sensing Use information from sensing other frequencies to coarsely determine required sensitivity level

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 11 Summary of gains from wideband sensing Wideband sensing is a self calibration technique to determine a radio’s shadowing environment Gains from wideband sensing are universal. They can be used with any sensing technique. – Wideband sensing + Energy detection meets non-interference requirements! Wideband sensing enables a system to qualify radios. Hence the system can cooperate among ‘qualified’ users. – Such cooperation gives non-interference gains as well as improves on a system’s ability to use opportunities Non-Interference constraint is met with a single radio. – Do not require any assumptions about the joint spatial distribution of shadowing

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 12 Technical details - Preliminaries Probability of Harmful Interference (PHI): The probability that a cognitive radio system interferes with the primary user. – For a single radio with the primary signal at a given SNR, this P HI is the same as the P MD – This definition assumes that a radio that mis-detects the primary will always interfere with its receivers. γ is the received SNR of the primary signal and FΓ(γ) is its cumulative density function (CDF). Probability of Missed Opportunity (PMO): The probability that a cognitive radio system does not use a vacant channel. – For a single radio, this probability is the same as the probability of false alarm (PFA) in classical detection theory

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 13 Single radio performance characteristics N0 = -96 dBm SNR Mean = 3.2 dB SNR Std Dev = 5.5 dB

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 14 Noise + interference uncertainty Spurious Tones, filter shapes, Out of band interference, temperature changes – all impact our knowledge of noise. Calibration can reduce uncertainty but not eliminate it Cabric et al

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 15 Single radio performance with uncertainty N0 = -96 dBm SNR Mean = 3.2 dB SNR Std Dev = 5.5 dB Noise Uncertainty = 1dB For low P HI we suffer very high P MO

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 16 Wideband sensing algorithm Anchor band decisionDetected Not detectedNot Detected Primary band decisionDetectedNot detectedDetectedNot Detected Global DecisionPrimary PresentChannel FreeNot sure Fix number of time samples, M. Set energy detection thresholds for the primary ( P ) and anchor bands ( A ). Compute the empirical estimate of the energy in each band. T(Y A )  := test-statistic for anchor band T(Y P )  := test-statistic for primary band Let H P;1 denote the decision when T(Y P ) > P and H P;0 otherwise. Let H A;1 denote the decision when T(Y A ) > A and H A;0 otherwise. Anchor: A co-located transmitter that’s always ‘ON’

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 17 Wideband sensing algorithm performance P HI for Wideband radios: Probability that the radio detects the anchor but not the primary when the primary is ON P MO for Wideband radios: 1 - Probability that the radio does detect the anchors and does not falsely trigger for the primary when the primary is OFF

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 18 Wideband Sensing Performance Wideband sensing allows a single user to achieve the target probability of harmful interference

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 19 Scaling with frequency correlation asdadadadadada The more the correlation across frequencies, the more gains from wideband sensing

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 20 Qualifying users via ternary voting Anchor band decisionDetected Not detectedNot Detected Primary band decisionDetectedNot detectedDetectedNot Detected VotePrimary Present Channel Free Abstain Radios abstain if they don’t see the anchor - Radios which don’t see the anchor are dis-qualified from voting - This improves performance of cooperative sensing algorithms - Run cooperation algorithm among qualified users - For example, declare the primary is absent only if all the qualified users vote for the primary’s absence.

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 21 Performance of OR rule with ternary voting

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 22 Cooperation between wideband radios Cooperation between wideband radios improves on both P HI and P MO

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 23 Cooperation between wideband radios contd Can start with low P HI, large P MO point for a single radio.

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 24 Summary/Conclusions –Wideband detection can complement all detectors In the simulations we have used small number of samples (M) and an energy detector - if we had a more robust/powerful detector we could get better P HI –Idea is more to identify good radios coarsely rather than calibrate to a single known anchor. Want a simple rule like: If a radio sees ~5 TV channels, it is a qualified user. –Overall scheme would be to achieve target P HI with a single radio and then to count on cooperative gains to reduce P MO

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 25 References 1.R. Tandra and A. Sahai, ‘Fundamental limits on detection in low SNR under noise uncertainty’, In proceedings of the WirelessCom ‘05 Symposium on Signal Processing, G. Chouinard, D Cabric, M. Ghosh “Sensing Thresholds”, IEEE /0051r3, May Digital Telivision/HDTV channel list: San Francisco Bay Area. 4.J. Kunisch and J. Pamp, ‘Measurement results and modeling aspects for the UWB radio channel’, In Ultra Wideband Systems and Technologies, May Gerald Chouinard, ‘DTV signal stochastic behavior at the edge of the protected contour and resulting probability of detection from various sensing schemes’, IEEE Meeting Documents, March 2007

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 26 Backup

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 27 Wideband Sensing Performance Wideband sensing allows a single user to achieve the target probability of harmful interference

doc.: IEEE /0xxxr0 Submission July 2007 Mishra, Tandra, Sahai, UC BerkeleySlide 28 Cooperative Performance For low P HI we suffer very high P MO This is because there is no way to distinguish between good and base radios