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Uplink Timing Advance Broadcasting for Ranging in Femtocell for IEEE 802.16m Document Number: IEEE C802.16m-10/0220 Date Submitted: 2010-03-05 Source: Pei-Kai Liao, Yih-Shen Chen and Paul Cheng E-mail: firstname.lastname@example.org, email@example.com@firstname.lastname@example.org MediaTek Inc. Kuhn-Chang Lin, Yu T. Su NCTU Venue: IEEE 802.16 Session #66, Orlando, USA Base Contribution: This is base contribution Re: Letter Ballot #31 on the Draft Amendment (IEEE P802.16m/D4) Purpose: For TGm members 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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
Introduction (1/4) Network timing synchronization for a femto-BS can be categorized as the following two aspects Downlink network timing synchronization Can be achieved by backbone network signaling Uplink network timing synchronization Can be achieved by femto-BS ranging Due to downlink and uplink network timing synchronization requirement for a femto-BS, the TTG/RTG reserved to avoid the collision of downlink and uplink transmission may be different from that of macro- BS according to the deployment location of the femto-BS The reserved TTG is smaller if the femto-BS is farther away from the macro- BS The reserved RTG is larger if the femto-BS is farther away from the macro- BS
Introduction (2/4) In D4, the value of TTG/RTG is fixed, regardless of cell type Without TTG/RTG adjustment in femtocell, the uplink receiving of the femto-BS will be interfered by the uplink transmission of macro-MSs due to non-aligned uplink subframes if the time difference is not an integer number of OFDM symbols It is illustrated by two figures in the following slides Therefore, femto-BS may need to adjust its TTG/RTG so as to synchronize with the network signals over the air
Introduction (3/4) Distance A and Distance B are much larger than Distance C Distance A is approximately equal to Distance B Femto-BS1 is very close to Macro-BS
Problem Statement (1/4) According to D4 Section 16.4.6, A femto-ABS should be synchronized with the overlay ABS network, where the synchronization means the aligned frame boundary, and the aligned DL/UL split in TDD systems. Femto-ABS is not mandatory to synchronize with overlay ABS network It is mandatory only when Femto-ABS share the same frequency with Macro-ABS For AMSs which is turned on in the femtocell, there will be a large time difference between the ranging signal transmission by AMSs and the femto-ABS observation window if femto-ABS synchronizes with the overlay macro-ABS The time difference is the same as the TTG/RTG adjustment value of the femto-ABS The adjustment value is equal to the round-trip time from the femto-ABS to the overlapping macro-ABS For AMSs which handover from macrocell to femtocell, there is still problem if the femto-ABS does not synchronize with the overlay macro-ABS The time difference is the same as the TTG/RTG adjustment value of the AMS The adjustment value is equal to the round-trip time from the AMS to the overlapping macro-ABS
Problem Statement (2/4) Problem 1: The time difference results in incomplete receiving of ranging signal at the femto-ABS It is illustrated in the figure in the following slides Problem 2: The non-aligned transmission of ranging signal also introduces serious interference to the receiving of uplink data from other AMSs at the femto-ABS
Problem Statement (3/4) Problem in initial ranging!
Problem Statement (4/4) Problem in handover ranging!
Proposed Solutions TTG/RTG broadcasting TTG/RTG are configurable and may be different among different cell types TTG/RTG broadcasted by all BSs, including both macro- and femto-BSs Uplink timing advance broadcasting in femtocell Uplink timing advance is applied to uplink subframes to fix timing alignment problem among different cell types Uplink timing advance is broadcasted by femto-BSs only
TTG/RTG Broadcasting Flexible for the system TTG/RTG can be adjusted depending on the needs It requires the modification on TTG/RTG definition from fixed value to configurable one It may be confused with the definition in legacy systems Specification modifications TTG/RTG definition From fixed to configurable S-SFH SP1 content modification At least additional 3 bits are required for all ABS types Not preferred
Uplink Timing Advance Broadcasting in Femtocell No need to modify TTG definition Apply to femto-BS only No matter whether femto-BS is synchronized to the overlay macro-BS, it works Specification modifications S-SFH SP1 content modification for femtocell Use 3 used bits for the broadcasting in femto-ABS only It does not increase any bit to S-SFH SP1 Preferred!!!
Number of Bits Required for Uplink Timing Advance Broadcasting According to SRD, system performance has to be optimized for the cell coverage up to 5 km Maximal round trip delay considered is 33.33 us The maximal tolerable uplink timing error for synchronous ranging channel is < ± 5.73 us (1/8 CP) If 3 bits are used, the granularity is around 4.17 us, which introduces at most ± 2.085 us timing error < ± 5.73 us Therefore, 3 bits are quite enough for the signaling
Why UL Timing Advance is Round Trip Delay? Assume TTG is fixed, the expected UL start time for a macro-AMS with no adjustment is Start_Time_UL macro-AMS = End_Time_DL macro-ABS + Propagation_Delay + TTG = Start_Time_UL macro-ABS + Propagation_Delay To align with the UL subframes of macro-ABS, the UL timing advance should be applied Start_Time_UL macro-ABS = Start_Time_UL macro-AMS – UL_Timing_Advance + Propagation_Delay UL_Timing_Advance = Start_Time_UL macro-AMS + Propagation_Delay – Start_Time_UL macro-ABS = (Start_Time_UL macro-ABS + Propagation_Delay) + Propagation_Delay – Start_Time_UL macro-ABS = 2 × Propagation_Delay
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