Uplink Timing Advance Broadcasting for Ranging in Femtocell for IEEE 802.16m Document Number: IEEE...
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Transcript of Uplink Timing Advance Broadcasting for Ranging in Femtocell for IEEE 802.16m Document Number: IEEE...
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: [email protected], [email protected] Inc.
Kuhn-Chang Lin, Yu T. SuNCTU
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 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 >.
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-B
S
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)
Femto-BS2
Femto-BS1Macro-BS MS1
MS2
Served by Macro-BS
Served by Femto-BS2
Distance A
Distance B
Distance C
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
Introduction (4/4)
DL (Tx)Macro-BS1
Femto-BS1
MS2 synchronized to
Macro-BS1
DL (Tx)
UL (Rx)
UL (Rx)
DL (Tx)
DL (Tx)
UL (Rx)
UL (Rx)
DL (Tx) UL (Rx) DL (Tx) UL (Rx)
DL (Rx) UL (Tx) DL (Rx) UL (Tx)
TTG RTG
TTG RTG
DL Propagation Delay
Femto-BS2 with no TTG/RTG
adjustment
RTG
Interference Happens!!
Timing Difference
TTG
UL Timing Advance for MS2
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 overlappi
ng 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 ma
cro-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!Ranging PreambleRCP
Femto-BS with TTG/RTG adjustment
DL (Tx) DL (Tx)
UL (Tx)
DL (Tx)
UL (Rx)
MS not knowing TTG/RTG adjustment
Macro-BS DL (Tx)
UL (Tx)
UL (Rx)
UL (Rx)
DL (Rx) DL (Rx)
UL (Rx)
Femto-BS with TTG/RTG
adjustment (Rx)
MS not knowing TTG/RTG
adjustment (Tx)
Time Difference
Time Difference
Rx Observation Window
Incomplete Receiving!!Expected UL Start Time
TTG
TTG with Adjustment
RTG with Adjustment
RTG
TTG RTG
Expected Duration of RCP
Expected Duration of Ranging Preamble
Problem Statement (4/4)
Problem in handover ranging!
Ranging PreambleRCP
Femto-BS with no TTG/RTG
adjustment
DL (Rx) DL (Rx)
UL (Rx)
DL (Tx)
UL (Tx)MS with TTG/RTG adjustment
Macro-BS DL (Tx)
UL (Rx)
UL (Tx)
UL (Rx)
DL (Tx) DL (Tx)
UL (Rx)
Femto-BS with no TTG/RTG
adjustment (Rx)
MS with TTG/RTG
adjustment (Tx)
Time Difference
Time Difference
Rx Observation Window
Incomplete Receiving!!Expected UL Start Time
TTG
TTG with Adjustment
RTG with Adjustment
RTG
TTG RTG
Expected Duration for Ranging Preamble
Expected Duration for RCP
Proposed Solutions
TTG/RTG broadcasting TTG/RTG are configurable and may be different among dif
ferent cell types TTG/RTG broadcasted by all BSs, including both macro- a
nd 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 o
verlay 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 n
o adjustment is Start_Time_ULmacro-AMS = End_Time_DLmacro-ABS + Propagation_Delay + TTG = Start_Time_ULmacro-ABS + Propagation_Delay
To align with the UL subframes of macro-ABS, the UL timing advance should be applied Start_Time_ULmacro-ABS = Start_Time_ULmacro-AMS – UL_Timing_Advance + Propagation_Delay UL_Timing_Advance = Start_Time_ULmacro-AMS + Propagation_Delay – Start_Time_ULmacro-ABS
= (Start_Time_ULmacro-ABS + Propagation_Delay) + Propagation_Delay – Start_Time_ULmacro-ABS
= 2 × Propagation_Delay
Text Proposal
Text Proposal