Design Considerations for UL Ranging Channels in 802.16m
Document Number: S80216m-08/321
Date Submitted: 2008-05-08
Source:
Yih-Shen Chen, Kelvin Chou, I-Kang Fu,
and Paul Cheng
Voice: +886-3-5670766
E-mail: yihshen.chen@mediatek.com, IK.Fu@mediatek.com,
Paul.Cheng@mediatek.com
MediaTek Inc.
Venue:
IEEE session #55, Macau
Base Contribution:
C80216m-08/321.
Purpose:
To be discussed and adopted by TGm for the P802.16m SDD.
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Introduction & Motivation
• Uplink (UL) ranging channel is a region where
MSs maintain link quality or perform accessing
to network
• Issues on contention-based ranging channel
– Code contention and collision
– BW negotiation
• Purpose and Summary
–
–
–
–
Flexible UL ranging channel configuration
Fast response mechanism for UL ranging channels
Efficient BR ranging procedure
Parameters for ranging request
2
UL Ranging Channel Configuration
• In current 802.16e:
– Four kinds of ranging requests:
• Initial ranging, HO ranging, BR ranging, Periodic
ranging
– Two kinds of ranging channels:
• Initial ranging/HO ranging, BR ranging/Periodic
ranging
– Four code sets:
• Each code set is used exclusive for a specific
ranging purpose
3
Comparison of Possible Partition
Methods
Advantage
Overlapping partition
Non-overlapping partition
- High bandwidth efficiency
-No collision between high and
low priority rangings
- Larger code pools for each
ranging
Disadvantage -High-priority ranging may
- Low bandwidth efficiency
collide with low-priority
ranging
- Smaller code pools for each
ranging
• The tradeoff criterion is network loading
4
Proposed Partition for UL Ranging
Channels
• G-RCH (General-purpose ranging channel)
– applied for all ranging purposes
• S-RCH (Specific-purpose ranging channel)
– applied for a specific set of ranging purpose
• D-RCH (Dedicated ranging channel)
– applied upon the assignment from MAC management
message for quick ranging.
• The ranging codes for the G-RCH and S-RCH
are partitioned accordingly
5
Example
• If the network wants to reduce the forced
termination rate for handover MSs,
– HO ranging requests can be applied in S-RCH, and
– the others are applied in G-RCH
Initial ranging codes
Total number of
Ranging codes
BR ranging codes
Total number of
Ranging codes
HO ranging codes
Periodic ranging
codes
G-RCH
S-RCH
An example of ranging code partition
6
Contention Resolution for UL Ranging
•
When an 802.16e MS sends
a ranging code for initial
ranging, it starts a T3 timer to
wait the response from BS.
• The overall delay causes by
ranging collision can be
calculated by
Delay = (T3+backoff_time)*R,
where T3 is the timer value
ranging from 60ms to 200ms
and R is the number of retry.
MS
BS
Ranging code
(collided)
T3
Collision
detected
Backoff
Ranging code
CDMA Allocation IE
7
Discussion on Code Collision
• Three possible scenarios for ranging code
collision:
1. The ranging codes are not detected due to low SINR
or multi-user collision
2. The ranging codes actually are detected, but no
enough bandwidth can be allocated for the MS
3. At least two MSs have selected identical ranging
code and ranging slot
• For case 1and 2, the MS waits for T3 and gets
no response, which results in undesirable long
ranging latency
– a fast response mechanism is required
8
Example: Ranging Status Indicator
• A bitmap is used to indicate the receiving status
of each RO within the ranging channel in the
previous frame
DL i
UL i
1110
DL-MAP
Preamble
Ranging slots
UL-MAP
FCH
DL-MAP
Preamble
FCH
UL-MAP
– 1: the ranging codes are correctly decoded
– 0: the codes are not detectable or insufficient BW for
future operation
Collided slot
1101
Ranging status
indicator
DL i+1
UL i+1
9
BR Ranging Procedure
• Typical BR ranging procedure consists of
contention resolution phase and bandwidth
negotiation phase
– 5-step message transaction is required
MS
BS
BR_RNG_CODE (1)
Contention resolution
phase
CDMA_ALLOC_IE (2)
BR header (3)
Resource grant (4)
Bandwidth negotiation
phase
UL data (5)
10
BR Ranging Procedure
• Problems are:
– Long transmission latency for real-time services or
time-critical MAC management messages
– Inefficient transmission for some short-burst services
• ex: short message services, instant messages
• Therefore, we suggest that the BR ranging
codes may be further classified into two
categories:
– Variable-size BR ranging codes
• Typical BR ranging procedure
– Fixed-size BR ranging codes
• Simplified BR ranging procedure
11
Simplified BR Ranging Procedure
• The simplified BR ranging procedure takes only
3-step message transaction
– bandwidth negotiation phase is skipped
MS
BS
BR_RNG_CODE (1)
Contention resolution
phase
CDMA_ALLOC_IE (2)
UL data (5)
• The UL bandwidth allocation may be
– pre-defined and broadcasted by BS via broadcasting
messages, or
– negotiated during connection establishment
12
Parameters in the BR Ranging Procedure
• During the bandwidth negotiation procedure, BS
determines
– the UL bandwidth allocation, and
– the corresponding transmission format, UIUC
• In some cases, BS may has no knowledge of absolute
transmission power of MS
– Power is updated by adjustment
• To facilitate the allocation, we suggest the UL channel
condition parameter may be also included into the BR
header
– the UL channel condition parameters may be
• UL Tx power,
• received CINR, or
• recommended UIUC
13
Text Proposal
•
•
•
•
11.x Uplink Control Structures
11.x.y UL ranging channel
11.x.y.1 Configuration of UL ranging channel
11. x.y.2 Fast response message for UL ranging
channel
• 11.x.y.3 BR ranging procedure
• 11.x.y.3.1 negotiation procedure
• 11.x.y.3.2 Parameters in the BR ranging
procedure
14