doc.: ieee 802.19-04/0018r0 submission may 2004 steve shellhammer, intel corporationslide 1 ieee...

May 2004

Steve Shellhammer, Intel CorporationSlide 1

doc.: IEEE 802.19-04/0018r0

Submission

IEEE 802.19Wireless Coexistence TAG

Steve Shellhammer

[email protected]

An Analytic Coexistence Assurance Model

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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.

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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 PT

fc fc + B/2fc - B/2

PT

B

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

Model of Interferer

• Pulse TP duration is a random variable

• Space TS between pulses is a random variable.

TP TS TP TPTS

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

Path Loss Model

• Some standard path loss model will be recommended, like the one used in 802.15.2.

• 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.

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

Topology of Wireless Devices

• One possible topology

Transmitter

ReceiverSystem ANetwork Under Test

System BInterferer

d

Does not interfere dueto distance from NUT

PrimaryInterferer

Is not interfered with due todistance from interferers

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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.

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

Receiver Model

Interferer PSDat Receiver

Receiver Filter

NI

1

NI

• Noise after the receiver filter is the same height as before the filter, but possibly a smaller bandwidth

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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

– During a portion of the received packet when there is no interference during the packet

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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.

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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.

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

Bit Error Rate

Receiver Filter1

NI

BF

BAF

NI

BAF

BAF

BF( )

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

Effective AWGN• Power after receiver is NI BAF

• To get the same power after filter we have to have,

Neff BF = NI BAF

• 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

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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 N0

• With interference use Neff

• Can also add N0 to Neff

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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.

TD

T

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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,TD)

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

Probability Density of T

• An example of a PDF for T

fT(t)½

0 TD

1/(2T)

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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,

TD, assuming it is variable

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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

May 2004


doc.: IEEE 802.19-04/0018r0

Submission

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.

doc.: ieee 802.19-04/0018r0 submission may 2004 steve shellhammer, intel corporationslide 1 ieee...

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