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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 1 IEEE Wireless Coexistence TAG Steve Shellhammer An Analytic Coexistence Assurance Model

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 2 An Analytic CA Model Make reasonable approximations of PHY and MAC layers. Provide a method of predicting the impact of interference in a timely manner. Not a detailed model intended to predict absolute performance of either system. Is intended to predict relative impact of interference. Only considering non-hoppers at this point Intended as a first-order approximation.

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 3 Model of Interferer Interferer sends pulses When transmitting a pulse the interferer is models in the frequency domain as band-limited white noise of power P T fcfc f c + B/2 f c - B/2 PTPT B

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 4 Model of Interferer Based on our knowledge of the interferer traffic the temporal model of the interferer is a stochastic process of pulses. Need to consider various models. –Distribution of pulse durations –Distribution of spacing between pulses

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 5 Model of Interferer Pulse T P duration is a random variable Space T S between pulses is a random variable. TPTP TSTS TPTP TPTP TSTS

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 6 Example of Pulse Model The interferer is sending TCP IP packets. There is an AP far away sending ACK packets. So we don’t consider this an interferer. Throughput is about half the data rate. TP = 1.0 ms TS is a uniform RV –TS = U(30, 1300) us

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 7 Path Loss Model Some standard path loss model will be recommended, like the one used in Other path loss models could be used. Give a topology of devices you can determine the interference power at the receiver based on path loss model. pl(d) = path loss in dB, with d in meters.

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 8 Topology of Wireless Devices One possible topology Transmitter Receiver System A Network Under Test System B Interferer d Does not interfere due to distance from NUT Primary Interferer Is not interfered with due to distance from interferers

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 9 Receiver Model Model receiver filter as an ideal brick wall filter, as far as interference goes. The portion of the interfering signal that is within the passband of the receiver filter is pass though undisturbed Any portion of the interfering signal outside the filter passband is eliminated entirely.

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 10 Receiver Model Interferer PSD at Receiver Receiver Filter NINI 1 NINI Noise after the receiver filter is the same height as before the filter, but possibly a smaller bandwidth

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 11 Bit Error Rate It is assumed that there is formula for BER for the receiver in AWGN. ber( ) = BER versus SNR for AWGN. There are two periods of stationarity when we want to calculate the BER (which will help us get PER) –During a portion of the received packet when there is no interference during the packet

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 12 Bit Error Rate BER when there is no interference is based on thermal noise. Since this is not very high we can –Assume it is very low –Or set up realistic topology and calculate BER Since absolute performance is not a primary concern method one is recommended.

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 13 Bit Error Rate BER when interference is present is based on equivalent AWGN. Pick AWGN level that would give equivalent power after the receiver filter.

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 14 Bit Error Rate Receiver Filter 1 NINI BFBF B AF NINI BFBF ( )

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 15 Effective AWGN Power after receiver is N I B AF To get the same power after filter we have to have, N eff B F = N I B AF The issue is that the interfere may not be as wide as filter. So we are dropping the PSD and widening the bandwidth This is another approximation

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 16 Bit Error Rate Summary We now have a method to calculate the BER when there is no interference and when there is interference. Calculate Eb from path-loss With no interference use N 0 With interference use N eff Can also add N 0 to N eff

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 17 Packet Error Rate A packet in the network under test (NUT) is sent from transmitter to the receiver. There is a (possible) overlap between that packet and an interfering pulse. TDTD T

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 18 Probability Analysis Calculate probability density function for the random variable T. (Work still to be done). T is a mixed random variable. There will be a finite probability that T is zero, and some density function over the interval (0,T D )

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 19 Probability Density of T An example of a PDF for T f T (t) ½ 0TDTD 1/(2T)

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 20 Packet Error Rate Step 1 –Calculate PER for a fixed value of T Step 2 –Average over all values of T using the previously calculated PDF for T Step 3 –If necessary, average over packet duration, T D, assuming it is variable

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 21 Other Metrics Calculate other metrics based on PER and necessary approximations (e.g. independence) –Throughput –Latency –Packet Loss Rate (assuming a fixed time to complete transmission) –Other

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doc.: IEEE /0018r0 Submission May 2004 Steve Shellhammer, Intel CorporationSlide 22 Conclusions Outlined an approach to analytic solution. Next steps –Work out technique for determining PDF of collision time. –Write up document giving details. –Apply to an example and use for comparison with other techniques.

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