IEEE 802.16m DL Interference Mitigation
Document Number:
IEEE C802.16m-08/626
Date Submitted:
2008-06-07
Source:
Shirish Nagaraj, Phil Fleming, Fan Wang
E-mail:
[email protected]
Motorola
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Venue:
TGm – Call for contributions on Project 802.16m System Description Document – IEEE 802.16m-08/024
(interference mitigation)
Base Contribution:
IEEE C802.16m-08/626
Abstract:
Proposal for 16m downlink interference mitigation.
Purpose:
Adoption of proposed text/content for 802.16m System Description Document
Notice:
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contained herein.
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DL Interference Mitigation
 Background
& Problem
 Latency-sensitive traffic (VoIP, video etc) capacity is determined by the
air-interface delay outage.
 Coverage improvements even for other classes of traffic are highly
desirable, especially to allow dynamic fractional frequency reuse
• Loading conditions in real deployments not known a-priori
 Objective
is to improve coverage and reduce outage with
minimal impact to system capacity:
 Interference Overload Feedback: feedback from MS to interfering cells
to indicate interference overload
• Enables slow but dynamic adaptation of Fractional Frequency Reuse (FFR)
patterns using feedback from all users
• Adapts to actual cell and traffic distributions as opposed to static
power/bandwidth partitioning
2
Adaptive Interference Mitigation

Interference mitigation by fractional frequency reuse (FFR)



Partition total bandwidth into sub-bands
Reduce power spectral density (PSD) on specific sub-bands to achieve
interference relief to users in other cells
Allocate different cells a priority ordering of sub-band usage –
• high priority indicates that the PSD will not be reduced, and low priority indicated PSD
can be reduced on that sub-band


A cell will schedule its bad geometry users to a high priority (Priority I)
sub-band, and good users on the lowest priority (low PSD) sub-band
Power distribution on sub-bands is not fixed a-priori




Users have a periodic (slow) signaling opportunity to indicate
interference overload on their sub-band
Signal is sent over the air through the UL Interference Overload
Feedback information
Cells respond to the composite Interference Overload Feedback signal
and reduce their PSD on specific sub-bands according to received
power of received signal
Achieves adaptation in FFR patterns autonomously, without having to fix
power distributions
3
Adaptive FFR using Interference
Overload Feedback
• Users in Priority I sub-band
in all cells transmit
Interference Overload
Feedback indicating subband used
• In response to received
Interference Overload
Feedback indicating subband 2, Cell A will reduce
PSD by a larger value
compared to Cell C
• Default power configuration
is equal PSD for all subbands
• Cells re-adjust their PSD
levels after the reception of
every Interference Overload
Feedback signaling interval4
Interference Relief using Interference
Overload Feedback

Slow adaptation of fractional frequency reuse patterns



Depending on an aggregate metric of Interference Overload Feedback signal, a BS
can decide how much power to reduce on a given sub-band to allow for “soft FFR”
Signaling is fed back at a slow basis, and allows FFR to adapt to network-specific
loading conditions
Other cells know the sub-band request by the position/modulation of the
Interference Overload Feedback
•


Requires a pool of common resources allocated for Interference Overload
Feedback signaling
Users can send the Interference Overload Feedback in a CDM or FDM fashion
•

All the Interference Overload Feedback signals corresponding to the same sub-band request will
incoherently combine at each base-station receiver
Cells will mute or reduce transmit PSD on those requested sub-channels for the a
duration following the request till the next Interference Overload Feedback
opportunity
•

Users will automatically reach their dominant interfering cells (immediate neighbors)
How much power to reduce depends on the total power of the received (composite) Interference Overload
Feedback signal, and the sub-band priority for that cell
Power of Interference Overload Feedback signal can be boosted to reach strongest
interfering cell
5
Standards Support Required for
Adaptive Interference Mitigation

Ability for MS to transmit an Interference Overload Feedback signal
on UL




Can use a system-wide common pool of bandwidth for such signaling
(UL common control channel)
Signaling opportunities in time also defined system-wide, with a given
periodicity
Same Interference Overload Feedback signal is transmitted by all users
corresponding to a given sub-band given incoherent combining gains at
the cell site
Signaling can be a CDM waveform modulated with on-off keying, with a
specific signature sequence for each sub-band
• Users not experiencing outage (or lower than expected data rates), will not transmit any
energy on Interference Overload Feedback signal


Sub-bands defined can be logical (no need to be physically contiguous)
See C80216m-08_275 on UL Interference Overload Feedback
6