IMANET+ Project Closing Seminar - ee.oulu.fiatolli/IMANET+_technical_seminar/IMANET_Closing... ·...
Transcript of IMANET+ Project Closing Seminar - ee.oulu.fiatolli/IMANET+_technical_seminar/IMANET_Closing... ·...
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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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• 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