IEEE 802. 16 m Identifying Subscriber Groups of Femtocells Document Number: IEEE C 80216 m-09_0451 Date Submitted: 2009 -02 -27 Source: Ying Li, Zhouyue Pi, Baowei Ji, Farooq Khan, Jaehee Cho, Jung Je Son, Anshuman Nigam Email: yli 2@sta. samsung. com Phone: +1 -972 -761 -7903 Samsung Electronics Venue: IEEE Session #60 Base Contributions: Re: Change Request for IEEE 802. 16 m SDD, Section 17 Purpose: Notice: Discussion and Approval 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: <http: //standards. ieee. org/guides/bylaws/sect 6 -7. html#6> and <http: //standards. ieee. org/guides/opman/sect 6. html#6. 3>. Further information is located at <http: //standards. ieee. org/board/pat-material. html> and <http: //standards. ieee. org/board/pat >.
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
Motivation (1/3) • IEEE 802. 16 m 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. 3
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. 4
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 Ø Shorten the list of allowable femtocells stored in MS Ø To ease the management at the paging controller, and avoid location update when the MS is moving inside the CSG. Ø 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, Ø Without CSG ID, Café C has to ask the operator to update it by adding this new femtocell to the white list of all its membership subscribers Ø With CSG ID, such update is not needed. 5
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. 6
Subscriber Group ID Differentiated by SFH CRC Scrambling (1/2) • 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. Ø All OSG Femtocell BS uses a special s-code (e. g. 0 x 0001) Ø Each CSG Femtocell BS uses the s-code corresponding to its assigned CSG ID 7
Subscriber Group ID Differentiated by SFH CRC Scrambling (2/2) • Illustration of MS operation (an example) having acquired SCH, the MS starts decoding a 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^ = 0 x 0001 (e. g. ), it is an OSG Femtocell BS – 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. 8
Advantages(1/2) • The operation is for femtocell only • Advantage via an example: Scramble 24 bit CSG ID with 24 bit CRC. • Compare with: 24 bit CSG ID as payload in SFH, plus 16 bit CRC • Advantages – Less overhead, 24 vs 40, save 40% – Mostly enhanced CRC capability • If an MS subscribes 2^a (a<=8) CSGs, the CRC capability is roughly enhanced by (8 -a) bits. – E. g. , MS subscribes 2^8=256 CSGs, CRC same capability – E. g. , MS subscribes 2^7=128 CSGs, CRC enhanced by 1 bit. – E. g. , MS subscribes 2 CSGs, CRC enhanced by 7 bits. • Typically, MS may subscribe to its femto at home, in office, and tens of memberships such as café, airport, etc. • Most likely, MS only subscribes less than 2^8=256 CSGs [note that multiple femtocells can share one CSG ID). 9
Advantages (2/2) • • Advantage via more examples Given CSG ID x bits (x>=16) Scramble x-bit CSG ID with x-bit CRC. Compare with: x-bit CSG ID as payload in SFH, plus 16 bit CRC The example is only meant to show the advantage of the approach. Specific approach can be FFS for stage-3 text. 16 bit CSG ID 20 bit CSG ID 24 bit CSG ID Overhead 16: 32, save 50% 20: 36, save 44% 24: 40, save 40% Maximum CSGs MS subscribes without hurting CRC 0 2^4=16 2^8=256 Enhancement Use 20 bit CRC, overhead 20: 32, save 37. 5% CSGs without hurting CRC 2^4=16 10
Proposed text 17. X Femtocell BS Identification Subscriber groups of femtocells may be differentiated by scrambling the CRC of a SFH burst with different masks. Each CSG femtocell BS uses the mask corresponding to the CSG ID. 11
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