Maximum number of hops for centralized scheduling mode IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE 802.16j-08/050 Date Submitted: 2008-01-23 Source: Yuefeng Zhou Voice: +44 20 87523460 NEC E-mail: yuefeng.zhou@ieee.org IEEE 802.16 Session #53, Levi, Finland Base Contribution: None Purpose: For the discussion of the Maximum number of hops for centralized scheduling mode 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: <http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and <http://standards.ieee.org/guides/opman/sect6.html#6.3>. Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >.２

Maximum number of hops for centralized scheduling mode As defined in the standard draft, P802.16j/D2, the centralized scheduling is the mode of operation applicable to multihop relay where an MR-BS determines the bandwidth allocations and generates the corresponding MAPs (or dictates the information used by RSs to generate their MAPs) for all access and relay links in the MR-cell. When increasing the number of hops, the MR-BS will have very heavy MAP overhead, since it has to generates the MAPs for each hop.

Maximum number of hops for centralized scheduling mode Figure 1 shows the estimated MAP and FCH overhead for legacy one-hop 16e system, when normal map is used. (FFT size = 1024; DL:UL = 32:15; Assume one burst for one connection; assume UL and DL subframe has same number of connections; 3 segmentation is used) Fig. 1. FCH & MAP overhead (percentage within DL subframe) vs. Number of connections (CIDs) used.

Maximum number of hops for centralized scheduling mode From the estimated results in Fig. 1, when number of connections is 10, by using repetition rate of 4 and normal MAPs, the overhead of FCH and MAPs will use about 70% of the whole DL subframe! In 16j with centralized scheduler mode, when number of hops is bigger, the MR-BS will consume much bigger FCH&MAP overhead. For example, when number of hops is 3, averagely, only two connections could be supported by each RS and MR-BS to make sure the MR-BS has enough resource to allocate all FCH and MAPs. Obviously, it is not efficient to use centralized scheduling mode when number of hops is big, e.g. > 2.