1. Dedicated BR preamble and tile assignment in Femtocell (AWD-Femto) Document Number: IEEE C802.16m-09_1564r1 Date Submitted: 2009-07-09 Source: Kanchei(Ken) Loa, Tsung-Yu Tsai, Yi-Ting Lin, Jiun-Je Jian, Chun-Yen Hsu, Chiu-Wen Chen, Youn-Tai Lee, Yung-Lan Tseng E-mail: loa@iii.org.twloa@iii.org.tw Institute for Information Industry (III) Venue: Base Contribution: N/A Re : Call for Contribution on 80216m-09_0028r1 Purpose: Discussion and approval of the proposal into the IEEE 802.16m AWD 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 802.1 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. Introduction Bandwidth request channel (BR channel) is used in Femtocell –A BR channel occupies an LRU which is consist of 3 6X6 tiles separated in the physical band. –During BR, AMSs contend for bandwidth by transmitting in one of the tile in the BR channel.

3. Introduction In the Femtocell’s BR procedure in the quick access channel, an AMS transmits –If the quick access message is decoded successfully, the Femtocell BS grants the bandwidth for the following data according to the content in the quick access message. Thus the BW-REQ message can be omitted. If the quick access message is not decoded successfully (5-step BR procedure) If the quick access message is decoded successfully (3-step BR procedure)

4. Dedicated preambles Since the Femtocell BS serves only limited number of AMSs, it can assign a dedicated to each registered AMS for BR –Guarantee no preamble collision If two or more AMS send the same preamble in the same tile, it is difficult to early detect the potential error in either 3-step or 5-step procedure –Reduce the contention delay –Omit 12-bit STID in the quick access message The quick access message only contains about 12~16 bit information

5. Mechanism for dedicated assignment During each request, a predefined pseudo random assigning rule is used for the Femtocell BS and AMSs to obtain dedicated. –The predefined pseudo random assigning rule is synchronized among the Femtocell BS and AMSs. –Pseudo random assigning prevents some pairs of AMSs always suffer from message collision when they send the request in the same BR channel. –Pseudo random assigning could further minimize the average of message collision probabilities among all pairs of AMSs.

6. Pseudo random assignment Each is associated to a unique index between 1 and D D = (number of dedicated preambles) * (number of tiles in a quick access channel) During network entry, each AMS i is assigned to an unique integer, V i, which is between 1 and D. When an AMS transmits a request, the preamble and tile is determined as follows: 1. Generate a random integer R that is between 1 to D. R may be generated by a pseudo random function of frame and subframe number. 2. AMS i uses the associated with the element a Vi,R in the scramble matrix A to perform BR.

7. Definition of Scramble Matrix Scramble matrix A is a D*D matrix with following properties 1.Each entity of A are integers between 1 and D. 2.The elements of each column of A are different. 3.The elements of each row of A are different

8. Example of Scramble Matrix A simple and scalable D*D scramble matrix is generating a circular matrix with which the first row is [1 2 … D].

9. Performance Evaluation

10. Simulation Setup Number of preambles : 24 Number of tiles in an LRU : 3 D = 24 * 3 = 72 Number of requesting AMSs in an BR channel: 1~10 Evaluate the preamble collision probability –Preamble collision is the event that more than one AMS send the same preamble in the same tile

11. Simulation Result

12. Summary When the number of requested AMS in a BR channel is larger than four, the probability of preamble collision exceeds 8% for random access –Preamble collision is difficult for immediate detection and significantly degrade the efficiency and robustness of BR procedure in either 3- step or 5-step scenarios Dedicated preamble and tile guarantees no preamble collision –The efficiency of BR procedure is improved –Besides, dedicated preamble and tile could save the space of STID in the quick access message Allow the quick access message to carry more information and CRC which ensures the robustness of the quick access channel

13. Proposed Text 17.x Bandwidth request in Femtocell For bandwidth request in the BR channel, each AMS is assigned with a pair of dedicated preamble and tile. A pseudo-random assigning rule is used to assign each AMS’s dedicated preamble and tile in each request. The pseudo random assigning rule is synchronized among Femtocell BS and AMSs. A D*D circular matrix A, which has the first row vector [1 2 … D], could be used to facilitate the pseudo- random assignment.

14. where D is defined as N P * N t. Where N P is the number of dedicated preambles, and N t is the number of tiles in a BR channel. The value of N P is TBD. By the definition, the circular matrix A is

15. The mechanism of pseudo-random assignment is as follows: Each pair of preamble and tile is associated to a unique index between 1 and D. During network entry, each AMS i is assigned to an unique integer, V i, which is between 1 and D. When an AMS transmits a request, the steps of determining assigned dedicated preamble and tile is as follows: Step 1: Generate a random integer R by a pseudo random function of frame and subframe number taking value from 1~D Step 2: AMS i uses the associated with the element a Vi,R in the circular matrix A to perform bandwidth request.