1. IEEE 802.16m Fast and Efficiently Identifying Femtocells Subscriber Groups Document Number: IEEE C80216m-09_1232 Date Submitted: 2009-07-03 Source: Ying Li, Zhouyue Pi, Baowei Ji, Email: yli2@sta.samsung.com Phone: +1-972-761-7903yli2@sta.samsung.com Farooq Khan, Jaehee Cho, Jung Je Son, Anshuman Nigam Samsung Electronics Venue:IEEE Session #62 Base Contributions: Re: Change Request for IEEE 802.16m SDD, Section 15 Purpose: Discussion and Approval 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. Use cases to support Use cases will direct and shape our specific design The possibilities of use cases could be, for example, – 1. Home E.g., a home owner can buy a femto and open it up only to family members and friends – 2. Enterprise E.g., a company can buy tens/hundreds femtocells to enhance the connectivity, then such femtos can be open only to the company employees – 3. Membership E.g., a use can buy a membership of Starbucks, which means all the femtocells owned by Starbucks should be open to the user – 4. Operator E.g., the operator uses femtocells to fix coverage holes, then such femtocells should be open to subscribers of this operator – And so on. 2

3. 3 Motivation (1/3) IEEE 802.16m System Requirements – Shall support CSG (Closed Subscriber Group) – Shall allow dense deployment of large number of Femtocells – Shall support preferred access and handover of MS’s to their designated Femtocell BSs Some operations (such as Cell Selection, Network RE-/Entry) could be different for Femtocells and macro cells, and for CSG and OSG (Open Subscriber Group) Femtocells. Therefore, an MS may need to differentiate Femtocells from macro cells, CSG from OSG, or one CSG from the other CSG.

4. 4 Motivation (2/3) Accessibility of a BS – Macro BS: accessible to all MSs – OSG Femtocell BS: accessible to all MSs – CSG Femtocell BS: only accessible to its authorized MSs, though open to all MSs for emergency access. An MS needs to determine whether it is allowed to access a CSG Femtocell – CSG BS may not be accessible to many MSs, the chance that an MS cannot access to a CSG BS is large, so the accessibility should be checked early. – The number of SCH symbols for cell IDs may not be large enough to differentiate a potential large number of CSG Femtocells. – PBCH can be a good place to offer information for MS to check accessibility. – Consider methods avoiding using expensive PBCH payload.

5. 5 Motivation (3/3) CSG ID – to ease the management – Several Femtocell BSs could belong to a same CSG entity, which have the same group of authorized MSs. – Benefits of using a common CSG ID for this set of BSs  Shorten the list of allowable femtocells stored in MS  To ease the management at the paging controller, and avoid location update when the MS is moving inside the CSG.  To ease the management of subscriber groups. E.g., an MS subscribes a membership of Starbucks, which has stores throughout country. Consider Starbucks installs a new femto BS,  Without CSG ID, Starbucks has to ask the operator to update it by adding this new femtocell to the white list of all its membership subscribers  With CSG ID, such update is not needed.

6. 6 Challenges Given potential large number of subscriber groups, CSG ID may need quite a few bits. CSG ID needs to be broadcast by femtocells. The additional bits in SFH to identify femtocells may consume the expensive SFH payload. – Consider approaches to avoid/reduce the payload consumption, such as by using the CRC scrambling with different masks on SFH.

7. 7 Subscriber Group ID Differentiated by SFH CRC Scrambling (1/3) Illustration of femto BS operation (an example) – OSG Femtocell BS and specific CSG Femtocell BS are differentiated by scrambling the CRC of a SFH burst with different masks (called s-code herein). – Send: M + (CRC Xor s-code), where M is the SFH message, CRC is produced from M, s-code is a scrambling code.  Each CSG Femtocell BS uses the s-code corresponding to its assigned CSG ID

8. 8 Illustration of MS operation (an example) MS decodes SFH by Step 1. decode the message (M^) Step 2. calculate the CRC^ Step 3. calculate s-code^ = CRC^ Xor (CRC Xor s-code) – If s-code^ = any CSG-ID in MS’ list, it is a CSG Femto BS with CSG-ID s-code^ – Otherwise, CRC fails and MS keeps searching/measurement. Subscriber Group ID Differentiated by SFH CRC Scrambling (2/3)

9. 9 Rationale: – An MS may only subscribe a few CSGs. In information thoery prospective, this gives the chance of reducing the overhead by scrambling CRC. Subscriber Group ID Differentiated by SFH CRC Scrambling (3/3)

10. 10 In current AWD 80216m-09_0010r2, – S-SFH SPs have fixed size. – 16-bit CRC is used for S-SFH. – In S-SFH SP1, there is a 16bit field for BS_EIRP What we propose is – Femtocell uses 8bit for BS_EIRP, instead of 16bit, in SP1 – Femtocell uses 24bit CRC, instead of 16bit – Femtocell 24bit CSGID scrambles 24bit CRC Rationale: – SP1 for femtocells different from macrocells, which is logically possible since femto and macro are differentiated by preamble partitions. Proposed Detailed Solution Based on SFH Design in AWD 80216m-09_0010r2

11. Advantages – Fast: Both femto BSID and CSGID (separately) can be carried in SP1. – Reliable: If an MS subscribes less than 2^8=256 groups (which may be in most cases), the CRC is enhanced compared to 16bit CRC. – Efficient: 24bit femto CSGID is carried within a fixed size SFH SP. No need to enlarge the size of the current SP1 for macro/femto. 11

12. Summary CSG ID of femtocells is carried by using CSG ID as the mask to scramble CRC The operation is for femtocell only. No change for macrocell. The approach reduces overhead, and enhances CRC capability. 12

13. 13 Proposed text Insert the following text to the end of 15.3.2. Subscriber groups of femtocells may be differentiated by scrambling the CRC of an SFH burst with different masks. Each CSG femtocell BS uses the mask corresponding to the CSG ID.