1. –Self-coordinated Femtocells to mitigate interference in IEEE 802.16m IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: –IEEE C802.16m-08/1421r1 Date Submitted: –2008-11-06 Source: –Mamadou Kone, Ming-Hung Tao, Ying-Chuan Hsiao, Richard Li E-mail: makone@gmail.com, itri404759@itri.org.tw –ITRI Venue: –TGm call for contributions on IEEE 802.16m-08/040. Specific topic : “Support for Femtocells” Base Contribution: –N/A Purpose: –To be discussed and adopted by TGm. Notice: –This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release: –The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16. Patent Policy: –The contributor is familiar with the IEEE-SA Patent Policy and Procedures: – and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 –Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat

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 802.16m-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 mitigate the interference by introducing pre-configured profiles in the DL/UL sub frames coupled with frequency selection in case of femto BSs deployments.

3. Interference cases in Femtocells fBS1 fBS2 fBS3 Macro cell MS1 MS3 MS2 Interference between macro BS and femtocells –MS4 will have interference from fBS3 and cant receive macro BS DL/UL Interference between femtocells –There might be some overlapping zones between the different femtocells in dense area and that can be source of interference between fBSs in DL/UL Interference in transmission of DL/UL Normal transmission of DL/UL Interference zone Macro BS MS4 MS5

4. Approach There are two main ideas supporting this solution: DL/UL sub frames in a super frame can be configured to support different profiles. A fBS can support less than 10 MSs, therefore it makes no sense that the whole frequency be occupied by only one fBS. Different carrier frequency can be introduced. Any fBS should be able to scan Macro BS to retrieve information. The pre-configured profiles can be defined in the SFH 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). A new fBS should scan the neighbor fBS to have their measurement result and decide if it can use a different profile at the same frequency or use another frequency with any available profile. 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 femtocell BSs and the macro cell BS at the same time.

5. Illustration of interference mitigation fBS4 after measurement realizes there is no available profiles DL/UL for it to use, so it selects another frequency f3 and can choose the same profile as fBS1 without any interference. An MS being in the macro cell (outdoor) network will not interfere with any femtocell’s MS, because using different frequency. fBS3 fBS1 fBS2 Macrocell Frequency f1 used by Macro BS to serve outdoors MSs Frequency f2 used by fBS1, fBS2, fBS3 with different DL/UL profiles Mitigated Interference zone Macro BS SFH BA … CBAC BA … CBAC BA … CBAC BA … CBAC BA … CBAC fBS4 f1 f2 f3 Frequency f3, used by fBS4 to mitigate interference other fBSs Mitigated Interference by synchronizing every DL/UL transmission Different profiles and frequencies are broadcast by the macro BS

6. Interference mitigation in Femtocell The procedure of interference mitigation can be described as follow: A macro BS broadcasts certain profiles of DL/UL in the SFH and also includes information of frequency reuse that a fBS can receive to configure itself according also to the information it retrieved from scanning adjacent fBSs. When the adjacent fBSs information allows the fBS to use a same frequency but with different profile, then the fBS selects one of the available profile using same frequency as adjacent fBSs. In case of a dense area where more adjacent fBSs overflowed the number of profile available, a fBS can select a 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. Adjacent fBSs transmitting at the same frequency with different profiles should be synchronized in transmitting DL/UL. The number of possible adjacent fBSs is also increased in such a system without creating consequent interference. For n available frequencies and m profiles proposed by the macro cell BS, there are nxm possible adjacent femto BSs without interference.

7. Sub frames Profile in DL/UL An example of possible profiles of DL/UL in a super frame, these profiles may be defined in the SFH. DL Super-frame SFH … DL UL DL UL SFH DL … UL DL UL DL/UL of profile 1 DL/UL of profile 2DL/UL of profile 3 SFH DL … UL DL UL

8. Micro sleep in Femto cell The DL/UL profiles used to mitigate interference can be used to create a micro sleep for every MS in a femto cell. As the MS may just receive some specific DL/UL sub frames, there will be a number of sub frames without any traffic between MSs and the femto BS. Therefore, these sub frames time which are not used by the femto BS to transmit DL/UL with its MSs can be used for a micro sleep purpose. In case the MSs enter sleep mode, the power saving will be improved, because in a long listening window the MS can still use micro sleep to save power.

9. Micro sleep in DL/UL profiles DL Super-frame SFH … DL UL DL UL SFH … DL UL DL UL SFH … DL UL DL UL Micro sleep for profile 1 Micro sleep for profile 2 Micro sleep for profile 3 Micro sleep for profile 1 Micro sleep for profile 2 Micro sleep for profile 3

10. Proposed text ------------------------------------------------------- 17.x.x Interference mitigation A macrocell BS may communicate with femto BSs over the air and may broadcast in the SFH a number of profiles to be chosen by femto BSs. These profiles correspond to the use of different part of DL/UL scenarios. The broadcast information of the macro BS should also contain the number of available frequencies which can be used by femto BSs. A femto BS can scan the neighbor femto BSs and the macro cell BS to receive the available profiles, the 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 DL/UL profiles defined in the SFH and their number are FFS.