Unified Ranging Structure for Femtocell BSs
Document Number: C80216m-0811
Date Submitted: 2009-04-24
Source:
Yih-Shen Chen, Peikai Liao and Paul Cheng
MediaTek
Chie-Ming Chou, Yung-Han Chen and Frank Ren
ITRI
E-mail: yihshen.chen@mediatek.com
E-mail: chieming@itri.org.tw, frank_ren@itri.org.tw
Venue: IEEE Session #61, Cairo, Egypt
Base Contribution: This is base contribution
Re: IEEE 802.16m-09/0021, “Call for Comments on Project 802.16m System Description Document (SDD)”
- CR to SDD: Chapter 15 Support of Femtocell
Purpose: For TGm members’ discussion and approval
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Ranging Channels in 802.16m
• In current SDD, there are three types of ranging channels:
– Non-synchronized ranging channel
• Initial ranging
– MS adjusts its frequency/timing/power with its potential
serving cell during initial network entry
• HO (handover) ranging
– MS adjusts its frequency/timing/power with its target cell
during handover
– Synchronized ranging channel
• Periodic ranging
– MS adjusts its frequency/timing/power with its potential
serving cell
– BR (bandwidth request) ranging
• MS sends out its transmission intention and requirements
2
Discussion on Synchronization Issue in
Femtocell
•
After DL synchronization with femtocell SCH, the maximal offset of
a MS is within synchronization requirement, given the cell
coverage is 30 meters at most
– RTD: (2*30)/(3*108)  0.2μs
• Synchronization requirement:
– For any duplexing, all SSs shall acquire and adjust their timing
so that all UL OFDMA symbols arrive time coincident at the BS
to a accuracy of ± 25% of the minimum guard-interval or better
(8.4.10.1.2, Rev2/D8)
– WiMAX profile requirement:
• Question: do we still need the differentiation, given shortrange?
3
Proposed Ranging Structure for Femtocell:
Unified Ranging Structure
• Single unified ranging channel configuration for all the
ranging purposes
– The PHY of the ranging channel consists of preamble and
message part (preamble+MSG PHY; i.e., BR PHY)
• Benefit:
– High spectral efficiency
» No guard channel is required
» Few subcarriers are required (ex: 18)
– High bandwidth efficiency
» BW request for RNG-REQ is sent along with preamble
» MS ID may be sent with preamble for UL ranging if a
specific femto-only ID is assigned (CSG scenario)
4
Example (Preamble+MSG PHY)
Time
0
1
34
35
Frequency
36
37
70
71
Contention-based
ranging code
72
73
106
107
Ranging message
5
Procedure of Initial Ranging in Femtocell
Initial ranging preamble +MSG
(ID, RNG-REQ size)
Initial ranging preamble +MSG
(ID, RNG-REQ size)
Acknowledgement of the initial ranging
Acknowledgement of the initial ranging
UL grant for sending RNG-REQ message
RNG-REQ
Figure out
the grant
size
UL grant for BW-REQ
BR header for RNG-REQ
UL grant for RNG-REQ message
RNG-RSP
RNG-REQ
...
RNG-RSP
...
(a) if the MSG part is correctly decoded
(b) if the MSG part is not correctly
decoded
6
HO Ranging to Femtocell
• Bandwidth request as well as HO preamble
sequence are sent to femtocell target at once
– Shorten handover interruption time
7
Performance Analysis of the Proposed
Unified Ranging Channel
• The timing offset of initial ranging can be absorbed by
CP
– Short coverage (≦30m)
• Low collision probability
– Small population number (≦10)
– ex: for 10 VoIP users, the arrival rate is 0.02/frame
• For OUG scenario, femto-BS can allocate more ranging
opportunities to reduce the collision probability
8
Performance Analysis of the Proposed Unified
Ranging Channel
~ spectral efficiency
• Assume PRBS code is reused for 16m initial
ranging
– The total occupancy resources will be 144x6
– The saving for unified ranging channel is 88.9% per subframe
• 1- [ (6*6*3)/(6*6*3+144*6)] = 88.9%
• There might be more than thousand femtoBS
installments
– FDM/TDM spectral utilization is required
• Spectral saving would be critical in femtocell
deployment
9
Implementation Impact
• No modification is required on ranging PHY structure
• No two analog filters are required
– In macrocell deployment, CP length is different for initial ranging
channel and BR ranging channel
• Re-define some parameters in the quick access
message
– One or few access-IDs
• Current only 12 out of 19 are defined for flow IDs
– BW-REQ ID may be ignored or apply a pre-configured common
ID
• ID may be pre-configured in CSG scenario
– 2-bit BW field can be re-defined as BW requirement for RNGREQ
10
Conclusion
• Unified ranging channel for femtocell can
provide
– Better spectral efficiency
– Easier deployment
– Shorter access latency
11
Text Proposal
[Adopt the following text modification into section 15.4.3 of P802.16m SDD]
BR ranging channel is configured as a unified ranging channel for
Femtocell BS to accommodate all types of ranging purposes. The PHY
structure of BR ranging channel is identical as macro BS. AMS can
send ranging preamble with associated flow ID inside the quick access
message to differentiate the ranging purposes. In order to optimize the
radio resource utilization and functional capability in Femtocell BS, the
Femtocell BS and other different kind of BSs should have different
attributes of ranging codes. The Femtocell BS ranging codes may be
assigned for different Femtocell BS operation, and some ranging codes
may be known only to the special group of MSs.
12
Appendix
13
Unsynchronized Ranging Channel for
Macrocells
14
UL Ranging Procedure for 802.16e
• RNG-REQ size mismatch problem [1]:
– Multiple TLVs are optional in RNG-REQ  BS has to figure out an
appropriate size by itself
– This is an IOT issue, identified by Samsung in WiMAX TWG
Initial ranging preamble
Figure out
the grant
size
UL grant for sending RNG-REQ message
RNG-REQ
RNG-RSP
...
[1]080717_TWG_Samsung_r4_allocation_of_RNG_REQ_size.doc
15