Broadcast of Transmission Timing Offset for Ranging in Femtocells Document Number: IEEE C802.16m-10/0500r1 Date Submitted: Source: Pei-Kai Liao, Yih-Shen Chen and Paul Cheng MediaTek Inc. Kuhn-Chang Lin, Yu T. Su NCTU Venue: IEEE Session #67, Bangalore, India Base Contribution: This is base contribution Re: Letter Ballot #31a on the Draft Amendment (IEEE P802.16m/D5) Purpose: For TGm members’ discussion and approval Notice: This document does not represent the agreed views of the IEEE 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 Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and. Further information is located at and.

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 2

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 3

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 4

Introduction (4/4) 5

Problem Statement (1/4) According to D5 Section , “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 are 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 uplink transmission timing adjustment 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 uplink transmission timing adjustment of the AMS  The adjustment value is equal to the round-trip time from the AMS to the overlapping macro-ABS 6

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 7

Problem Statement (3/4) Problem in initial ranging! 8

Problem Statement (4/4) Problem in handover ranging! 9

Proposed Solution S-RCH transmission timing offset broadcast in femtocells  S-RCH Transmission timing offset is broadcasted by femto- ABSs only  Transmission timing offset is applied to S-RCH transmission to fix timing alignment problem among different cell types No matter whether femto-ABS is synchronized to the overlay macro-ABS, it works well Specification modifications  S-SFH SP1 content modification for femtocell Use 3 bits for the broadcasting in femto-ABS only  It does not increase any bit to S-SFH SP1 10

Number of Bits Required for S-RCH Transmission Timing Offset Broadcast According to SRD, system performance has to be optimized for the cell coverage up to 5 km  Maximal round trip delay considered is 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 ± us timing error < ± 5.73 us Therefore, 3 bits are quite enough for the signaling 11

Why S-RCH Transmission Timing Offset 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 uplink 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  RCH_Tx_Timing_Offset = 2 × Propagation_Delay 12

Why S-RCH in Femtocells, Instead of NS-RCH? Since the time- domain structure of NS-RCH is different from other channels, the orthogonality can be destroyed When marco-AMS transmits data channel and femto- AMS transmits ranging channel, ranging performance in femtocell degrades significantly 13

Text Proposal 14