UL CQI Channel Allocation
Document Number:
IEEE C80216m-08/288r2
Date Submitted:
2008-05-09
Source:
Xiaoyi Wang, Yousuf Saifullah, Shashikant Maheshwari
Nokia Siemens Networks
Heping Li Dongjie, No.11
Beijing, China
IEEE C80216m-08/288r2
Voice:
+8613511021252
E-mail: xiaoyi.wang@nsn.com
Venue:
IEEE 802.16m-08/016r1: Call for Contributions on Project 802.16m System Description Document (SDD).
Target topic:
“Uplink Control Structures”.
Base Contribution:
N/A
Purpose:
Discussion and approval by TGm for the 802.16m SDD
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IEEE C80216m-08/288r2
Motivations
• Current 16e UL control channel allocation
is lack of flexibility and have a lot of
overhead.
• The SRD requirements (IEEE 802.16m08/002r4) necessitate efficient control
channel signaling design with capability of
accommodating a large numbers of users
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IEEE C80216m-08/288r2
Current fast-feedback allocation in 16e
•
A “semi-dynamic” way of fast-feedback channel allocation is adopted in
current .16 systems.
–
–
–
–
•
•
First, BS sends an index and an interval number to users (e.g. CQICH_alloc_IE).
BS dynamically allocates a fast-feedback region at every frame.
With the region information, SS locates its own fast-feedback channel by index.
SS uses fast-feedback at a certain interval (interval number) so that multi-user may
reuse one fast-feedback channel.
The index allocation is static since related signalling messages are designed to
be transmitted once and the fast-feedback region is allocated dynamically.
The 802.16e method is a simple way to allocate fast-feedback channels to
users. However, it wastes some fast-feedback channels in the following cases:
1. When some CQICH indexes are de-allocated,
• Either messages like CQICH_alloc_IE are needed to re-adjust the index of some other users
• or there will be some empty gaps in fast-feedback region (some channels are not used).
2. Since some users may not need feedback at every frame, CQICH control IE also
assign an periodicity to users which could be 1,2,4,8. However, this couldn’t
guarantee a full occupation of the fast-feedback region. E.g. there are 5 users with
interval of 8. Some feedback channels are wasted
•
Besides, 802.16e method only provides a fixed density of fast-feedback usage
to every user. It requires new allocation message whenever MS changes fastfeedback usage density
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IEEE C80216m-08/288r2
Fast-feedback Channel Vacancy Problem
1
2
3
4
5
6
Frame number
1
SS1
SS1
SS1
SS1
SS1
2
7
8
SS1
SS1
SS1
SS2
SS3
SS2
SS3
SS2
SS3
SS2
SS3
Fast-feedback
Channel Index
3
SS4
SS5
SS4
SS6
SS4
SS5
SS4
SS6
4
SS8
SS9
SS7
For semi-dynamic Fast-feedback allocation method,
since the index are assigned semi-statically. There
might be some vacancy if some user stop using fastfeedback channel. In that case, BS might assign new
index to other users to occupy that vacancy :
“rearrange”. But such allocation requires signaling
messages in DL.
SS7
Frame #n
CQI Channel #4
CQI Channel #3
CQI Channel #2
CQI Channel #1
SS7
Frame #n
#4
SS8 SS9
SS4
SS5
SS2
SS6
SS3
SS1
SS2&4&6
stop and
SS10 start
using CQI
channel
#3
SS7
Frame #n+1
#4
SS8 SS9
Vacancy
SS4
SS5
Vacancy
#3
SS7
SS8 SS9
#2
SS5
SS10
Rearrange
#2
#1
Vacancy
SS10
SS3
SS1
#1
SS3
SS1
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IEEE C80216m-08/288r2
Simulation results
A simulation has been done to estimate the overhead of
using semi-dynamic allocation for UL feedback channels.
Whenever the fast-feedback channel vacancy is more than
threshold, BS will send index allocation messages to users
to adjust fast-feedback channel occupation. Simulation
results shows that for the best threshold value, there will be
more than 4 slots wasted resource in every frame (DL
singling overhead +UL fast-feedback vacancy).
Considering UL resource is more valuable, the total
overhead is more than that.
Outputs
Description
1
Idle CQI channel
num
Average idle CQI channel num per frame
2
Idle Ration
Ration of idle CQI channel num to total
utilized CQI channel num
3
Adjust Times
4
Total Overhead
Simulation Assumptions
1
Ideal Wireless Channel
2
Enough CQI Channels
3
Enough signaling resource
4
Each SS in network has occupied no more than 1 CQI
channel
5
There are average 100 SSs using CQI channels
6
On every CQI index change, signaling overhead is 2 slots
7
Ration of different intervals(1:2:4:8): 1:3:3:3
Average fast-feedback index allocatioin
message num per frame
Adjust times * 2 + Idle CQI channel Num
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IEEE C80216m-08/288r2
Dynamic UL control channel allocation
•
•
A dynamic method is developed for fast-feedback channel allocations.
When BS detects sufficient gaps in the fast-feedback region because of de-allocation
of some CQICH channels for some MSs.
–
•
•
•
•
BS transmits the bitmap in the UL-MAP to perform the shifting of CQICH channel used by
active MS scheduled to transmit fast-feedback information in scheduled fast-feedback region.
a compact fast-feedback occupation can be achieved. E.g. if the bit map is #1010,
Where user 1 and user 3 are active while fast-feedback channel of user 2 and user 3
are de-allocated.
In this case BS shall schedule a fast-feedback region with 2 channels.
user with “bitmap index=1” should use fast-feedback channel 1 and user3 (index=3)
should occupy fast-feedback channel=2, since user=2 has been de-allocated
Since bitmap is multicast, users know which fast-feedback channel it should use.
User
Index:
1 2 3 4 5 6 7 8 9
1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7
Bitmap
1 0 1 0 1 1 1 0 1 0 1 0 1 1 1 0 0
Index:
1 3 5 6 7 9
1 1 1 1
1 3 4 5
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IEEE C80216m-08/288r2
Advantages
• Proposed compact method of remapping the
CQICH channel for MSs.
• No waste of any fast-feedback channels if some
MS’s CQICH channels are de-allocated.
• Proposal can be dynamically used by BS to
maximize the benefits.
• Proposed method is flexible to adjust the density
of fast-feedback channel usage of every user
whenever needed.
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IEEE C80216m-08/288r2
Proposed Text to be included in SDD
Insert the following text into section 10.
• 10.x Fast-feedback channel allocations
– Each user are assigned with an index.
– BS may broadcast the “CQICH Channel Remapping
bitmap” to perform the shifting of CQICH channel
used by MS scheduled to transmit fast-feedback
information in the scheduled fast-feedback region. MS
determines its current CQICH channel index by
subtracting the number of Zero’s in the “CQICH
Channel Remapping bitmap” before its allocated
CQICH channel index.
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