1. IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number:
Self-coordinated Femtocells to mitigate interference in IEEE m
IEEE Presentation Submission Template (Rev. 9)
Document Number:
IEEE C802.16m-08/1421
Date Submitted:
Source:
Mamadou Kone, Ming-Hung Tao, Ying-Chuan Hsiao, Richard Li
ITRI
Venue:
TGm call for contributions on IEEE m-08/040. Specific topic : “Support for Femtocells”
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N/A
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To be discussed and adopted by TGm.
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2. Background
Femto BS installation by customers in their own premises may result in significant interference between macro cell and femto cells, and also amongst femto cells, because of their arbitrary deployment.
Support for closed user group femto BSs(fBSs) has been specified in the SRD m-07/002r6 in Section 9.5.
Closed user group(CUG) fBSs can only be accessed by a pre-defined set of MSs, usually consisting of the customer’s own MSs.
Without unique spectrum for the femtocell network or very careful spectrum planning in the wider network, femtocells could suffer from severe interference problem.
Therefore, it is proposed to actively avoid the interference by introducing pre-configured profile in the DL/UL coupled with frequency selection in case of femto BSs deployments.

3. Approach There are two main ideas supporting this solution:
DL/UL sub frames in a super frame can be configured to support different profile.
The fBS can support less than 10 persons, therefore it makes no sense that the whole frequency be occupied by only one fBS. Different carrier frequency can be introduced.
The pre-configured profiles can be defined in the SCH and transmitted by the macro cell BS to the fBSs and this profile can be chosen by a fBS (depending on what it needs for the bandwidth).
The profile broadcast in the SCH and its number are set as FFS.
A new fBS can scan the neighbor fBS to have their measurement result and decide if it can use different profile at the same frequency or different frequency with any profile to avoid interference.
Several neighbor fBSs can share same frequency but they use different parts of "DL/UL sub frames"
Thus, a fBS can self-coordinate to avoid interference with other femto cell BSs and the macro cell BS.

4. Illustration of interference mitigation
SFH … A B C A B C
SFH
Macro cell A B C … A B C
fBS1 f2
MS1 f1
fBS2 f2
MS2
fBS4 f1
SFH …
Macro BS f3 A B C A B C f1
SFH f2
SFH … … A B C A B C
fBS3 A B C A B C
Different possible profile broadcast by macro BS
MS4
MS3
fBS1,fBS2 and fBS3 use the same frequency f2 with different profiles
fBS4 after measurement realizes there is no available profile for it to use, so it selects another frequency f3 and can choose the same profile as fBS1 without any interference.
A MS (as MS4) being in the macro cell will not interfere with any femto cell, because using different frequency, which is the macro cell frequency.

5. Femto cell interference mitigation
The procedure of interference mitigation can be described as follow:
A macro cell broadcasts certain profile in the SCH that a fBS can receive to configure itself according also to the measurement it obtained from the adjacent fBS profile.
Other way to receive the profile
When the adjacent fBS measurement result allow the fBS to use the same frequency but with different profile, then the fBS select one of the available profile at the same frequency as the adjacent fBS.
In case more fBS are in the dense areas overflowing the number of profile available, a fBS can select different frequency from its adjacent fBSs and choose a profile that could be the same or not as one of the adjacent fBS without creating any interference
Therefore adjacent fBS can be working in the same frequency but using different profile or use same profile with different frequencies.
The number of possible adjacent fBS is also increased in such a system without creating consequent interference.
For n frequencies and m profiles proposed by the macro cell BS, we can have in a dense area nxm adjacent femto BSs without creating interference.

6. Sub frames Profile in DL/UL
Possible profile for Sub frames in a super frame, these profile may be defined in the SCH
Super-frame A A A A A … …
SFH
Super-frame A B A A B A A B … …
SFH
Super-frame A C B A A C B A A C B … …
SFH

7. Proposed text -------------------------------------------------------
17.x.x Interference mitigation
A macro cell BS may communicate with femto BSs over the air and may broadcast in the SCH a number of profiles to be chosen by femto BSs. These profiles correspond to the use of different part of DL/UL scenarios.
A femto BS can scan the neighbor femto BSs and the macro cell BS to receive the defined and available profiles, their frequencies used and other information of measurement.
After receiving these information, the femto BS may decide either to use a different profile at the same frequency or choose a different frequency with any available profile to mitigate interference with adjacent femto BSs.
Therefore a femto BS can self-configure according to the information received from its neighbor femto BSs and the macro BS to mitigate interference in a dense area.
The profile defined in the SCH and its number are FFS.