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Dedicated periodic/BR preamble assignment in Femtocell (AWD-Femto) Document Number: IEEE C802.16m-09_1564 Date Submitted: 2009-07-06 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

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Introduction Unified ranging channel is used in Femtocell. –An unified ranging channel occupies an LRU which is consist of 3 6X6 tiles separated in the physical band. –During initial/HO/periodic/BR ranging, AMSs contend for bandwidth by transmitting in one of the tile in the unified ranging channel.

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Introduction In the Femtocell’s ranging procedure, an AMS transmits –If the quick access message is decoded successfully, the Femtocell BS grants the bandwidth for the following RNG-REQ through RNG-RSP 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 ranging procedure) If the quick access message is decoded successfully (3-step ranging procedure)

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Dedicated preambles Since the Femtocell BS serves only limited number of AMSs, it can assign a dedicated to each registered AMS for periodic/BR ranging –guarantee no preamble collision between periodic/BR ranging –reduce the contention delay –omit 12-bit STID in the quick access message The quick access message only contains about 12~16 bit information. –obtain higher system performance

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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 unified ranging channel. –Pseudo random assigning could further minimize the average of message collision probabilities among all pairs of AMSs.

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Pseudo random assignment Each 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. D = (number of dedicated preambles) * (number of tiles in an unified ranging channel) 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 ranging.

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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

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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].

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Index Mapping of For assignment by the scramble matrix, each is associated to a unique index between 1 and D. However, the mapping of the integer to is related to the message collision probability between different pairs of AMSs. –Message collision is the event that two or more AMSs send request in the same tile. –Different AMS pairs (for example, AMS # 1 and AMS #20, AMS # 5 and AMS # 10, etc) may have different message collision probability. –For random access If there are two AMSs sending requests in a unified ranging channel, the message collision probability is 0.33. If there are three AMSs sending requesst in a unified ranging channel, the message collision probability is 0.78. If there are more than three AMSs sending requests in a unified ranging channel, the message collision probability must be 1.

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Index Mapping of The index mapping of has the following properties: –The average of message collision probability among all pairs of AMSs is as small as possible. For example, if D = 60, there are C(60,2) = 1950 pairs of AMSs –The highest collision probability among all pairs of AMSs is as small as possible.

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Recommended Index mapping for D = 60

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Average message collision probability among all pairs (1950) of AMSs is 0.322.

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Proposed Text 17.x ranging in Femtocell For periodic/BR ranging, 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.

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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 unified ranging channel. The value of N P is TBD. By the definition, the circular matrix A is

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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 ranging.

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Appendix: Simulation Result of Preamble Collision Probability

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Simulation Setup Number of preambles : 24 Number of tiles in an LRU : 3 D = 24 * 3 = 72 Number of requesting AMSs in an unified ranging channel: 1~10 –Number of initial/HO ranging AMS take range from 0~(number of requesting AMSs) Evaluate the preamble collision probability –Preamble collision is the event that more than one AMS send the same preamble in the same tile

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Simulation Result Preamble Collision Probability

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Summary The preamble collision probability of the quick ranging with dedicated preamble assignment is always smaller than or equal to that of random access quick ranging –The reduction in preamble collision probability is significant in the case that the number of initial/HO ranging requests is smaller than that of BR/periodic ranging requests –Since the situation that multiple initial/HO ranging requests appear in the same unified ranging channel (i.e. in the same subframe) is rarely occurred, in most case, dedicated preamble assignment has much lower preamble collision probability.

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