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IMANET+ Project Closing Seminar Interference control and model in contention-based network

Presenter: Byungjin Cho / Aalto

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Contents

Controlling

co-channel Interference from contention based networks to

primary system by tuning carrier sensing threshold

Modeling

mean self-interference at a user in contention based network

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Motivation and Goals

Background (Hardcore point process)

Primary-secondary system model

How to set hardcore distance (HCD) for interference control

How to set CS threshold given HCD

Results

Conclusion

Controlling the co-channel interference from

contention based networks to primary system

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Interference control is required for accessing the primary system spectrum

With a fixed transmission power allocation rule for all secondary transmitters,

different types of secondary(SU) networks can control their generated

interference to the primary(PU) system by adjusting different parameters

• Cellular systems Reuse distance

• Random access (ALOHA) networks Activity factor

• Systems with contention-based MAC Minimum separation between

concurrent transmitters

Motivation & Goal

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In practice, CS range is controlled by tuning CS threshold

• The lower the threshold the lower the density of transmitters

We propose to control the density of transmitters in secondary network

by tuning CS threshold

Our method consists of two steps

• Upper bound the density of secondary transmitters to protect PU system

• Map the density to a CS threshold

Motivation & Goal

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System illustration

WLAN is deployed outside the primary(PU) protection area

PU SINR target must be satisfied for PU QoS

Mean interference should be kept under interference margin

A snapshot of PPP (no contention control) and MPP (contention control)

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Background (Hardcore point process )

Matern hardcore point process (MPP) models the set of active nodes in

networks with contention control

• Hardcore distance (HCD) of MPP models the CS range

MPP results from a dependent thinning of a PPP

MPP type II and type III

• In MPP type II a point is discarded only if there is another point within the

HCD with smaller random mark.

• Suffers from underestimation problem, since all points are involved in

selection process

• MPP type III solves the underestimation problem of MPP type II but there is

no closed-form for the active node density.

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Step1: How to set HCD (upper bound)

Mean interference from a MPP II at an arbitrary

point in the plane is equal to the mean

interference due to an equi-dense PPP

Problem due to border effects

• Underestimating active node density close to border

• Equi-dense PPP gives a lower bound for the HCD PU violation

Proposed solution for upper-bounding HCD (2 densities & 2 sub-steps)

• Equi-dense PPP at distances larger than the HCD from the borders (area S1)

• Higher density than equi-dense PPP up to HCD from the borders (area S2)

• Express the mean interference using the two-tier PPP and increment HCD until

mean interference constraint is satisfied

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Step1: How to set HCD(Result)

Equi-dense PPP results in smaller HCD than the minimum required

Violation of PU protection

Proposed method results in a tight upper bound for the HCD protecting PU service

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Step2: How to set CS threshold(lower)

Realization with existing method

• Mean self-interference from MPP type II at each SU can be used as CS thresh.

Problem

• Different interference in different nodes Heavy computation time

• Underestimation problem of MPP type II Violating TV protection limits

• Second moment measure No closed form expression

Solution

• Common CS threshold calculated at the border

Lower bound to CS thresh.

• Doubling HCD for MPP type III

Upper bound to HCD

• Equi-dense PPP in full area

Closed form / Lower bound to CS threshold

S

X

nr

TVR

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Blue (Simulation): node can transmit only if mean interference is below CS thresh.

Sustaining maximum density .

Black (Method for MPP type II): results in lower CS threshold & active density

due to several approximations

Red (Method for MPP type III): results in very low CS threshold & active density

due to doubled HCD

Result: CS threshold & Active density

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Result: SINR distribution at PU

By the simulated threshold value,

the outage probability is same as

target value 10%

Figure: CS threshold based on MPP II

results in lower outage probability due

to the conservative approximations

adopted by our proposal

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CS threshold can be used as a common parameter

to control the generated secondary interference and protect primary system

Proposed method

• guarantees the primary system protection

• allows computing the CS threshold in real-time due to its low complexity,

thereby adapting to frequent changes in SU density.

Further work

• Need to reduce approximation errors allowing higher active node density

This result is published in IEEE CrownCom 2013

B.Cho, K. Koufos, and R. Jäntti, “Interference control in cognitive wireless networks by

tunning the carrier sensing threshold”, in IEEE CrownCom, 2013

Conclusion

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Motivation and Goals

Proposed bounds on PCF

Proposed bounds on Mean interference

Results

Conclusion

Modeling the mean self-interference

at a user in contention based network

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Motivation

Matern type II captures the spatial distribution of transmitters in wireless

network with contention control

For the calculation of the mean interference at an arbitrary location,

density of effective points (first order moment measure) in MPP type II

is a sufficient parameter

For the calculation of the mean interference at a specific location,

correlation(second order moment measure) between pairs of points

should be taken into account due to dependent property in MPP type II.

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Calculating mean interference at a specific location involves integral of

the pair correlation function(PCF)

• However, it is not straightforward to compute the mean

interference due to the complicated PCF

Characterizing the properties of the PCF for MPP type II is needed for

bounding the mean interference.

We derive simple and more accurate lower and upper bounds for the

mean interference in MPP type II network

Goal

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Proposed and existing bounds on PCF

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• Using bounds on the PCF, we can obtain tighter bounds than existing

bounds on the mean interference

Proposed bounds on mean interference

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Gap between the proposed bounds

• In asymptotic case, difference between the proposed bounds on

the mean interference never exceeds 0.2dB

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Conclusion

We propose low-complex upper and lower bounds on the mean

interference at a node in wireless network with contention control

• The convexity property makes it possible to obtain tighter bounds than

existing bounds for the mean interference in MPP type II networks

We derive simple and more accurate lower and upper bounds for the

mean interference in MPP type II network

• Lower bound at a transmitter can be useful when controlling the

interference generated to another system through CS threshold

• Upper bound at a receiver can be used to ensure satisfying target

outage probability

This result is published in IEEE Wireless Communications Letters

B.Cho, K. Koufos, and R. Jäntti, “Bounding the mean interference in Matern Type II

Hard-Core Wireless Networks”, in IEEE Wireless Communications Letters, vol.PP,

no.99, pp.1-4, 2013

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Thanks

Byungjin.cho@aalto.fi