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Packet Scheduling for Fairness and Performance Improvement in
OFDMA Wireless Networks
Nararat RUANGCHAIJATUPON and Yusheng JI
The Graduate University for Advanced StudiesNational Institute of Informatics (NII), Japan
The 26th Asia-Pacific Advanced Network MeetingAugust 4–8, 2008, Queenstown, New Zealand
August 4-8, 2008 26th APAN Meeting 2
Presentation Outline
OFDMA Scheduler and Resources Utility Matrix & Proportional Fairness Modified Simple Moving Average Utility Matrix-based Scheduling Simulation & Results Conclusion
August 4-8, 2008 26th APAN Meeting 3
OFDMA
Orthogonal Frequency Division Multiple Access
Reliability against fading channel Subchannelization (IEEE 802.16)
Distributed subcarrier permutation Adjacent subcarrier permutation
Adaptive Modulation Coding (AMC) Connectivity
August 4-8, 2008 26th APAN Meeting 4
System Model
- Centralized scheduler on BS- Uniform power allocation to each subchannel
August 4-8, 2008 26th APAN Meeting 5
Resources
August 4-8, 2008 26th APAN Meeting 6
Utility Matrix & Proportional Fairness
n
nmnm T
tRi
)(,,
Rm,n(t) – Achievable data rate of user n via
subchannel mTn – Average data rate
August 4-8, 2008 26th APAN Meeting 7
Modified Simple Moving Average
Tn – Average data rate in PF utility function)1(
)1()(
tV
tUtWT
n
nnn
0)1(
,00)1(
),1()(
)1()1(,
tqif
tqif
tRtU
tU
n
n
tmnmn
n
n
0)1(,1
0)1(,1)()1(
tqif
tqiftVtV
n
nnn
0)1(,
0)1(),()1(
tqifT
tqiftWtW
nn
nnn
Un(t) – keep sum of total instantaneous rates o
btained by user n during the non-empty-queue periodΩn(t) – the set of subchannels in which user n i
s scheduled at frame t
Vn(t) – records the number of frame
while user n has data in the queue
Wn(t) – to retain the average data rate whe
n user n’s queue is empty
August 4-8, 2008 26th APAN Meeting 8
Utility Matrix-based Scheduling
Find the maximum PF element
Allocate required time slots
Update average rate (and PF element)
Delete (column/row) from the utility matrix
August 4-8, 2008 26th APAN Meeting 9
Example A system of 3 MSs and 3 subchannels
MS1: Queue size 60 bits, average data rate 5 bps
MS2: Queue size 100 bits, average data rate 6 bps
MS3: Queue size 100 bits, average data rate 3 bps
Each subchannel has 8 time slots Each time slot is 1 second A packet has 1 bit
August 4-8, 2008 26th APAN Meeting 10
Example (cont.)
A utility matrix
310
65
57
35
69
58
37
68
510
Subchannel 1
Subchannel 2
Subchannel 3
MS 1 MS 2 MS 3
August 4-8, 2008 26th APAN Meeting 11
Example (cont.)
310
65
57
35
69
58
37
68
510
MS3
MS1
MS2
60 bits
100 bits
100 bits
Avg rate:
Avg rate:
Avg rate:
5 bps
6 bps
3 bps 6.5 bps
20 bits
5.610
65
57
5.65
69
58
5.67
68
510
0 bits
7.5 bps
August 4-8, 2008 26th APAN Meeting 12
Example (cont.)
5.610
65
5.77
5.65
69
5.78
5.67
68
5.710
MS3
MS1
MS2
60 bits
100 bits
100 bits
Avg rate:
Avg rate:
Avg rate:
5 bps
6 bps
3 bps 6.5 bps
20 bits
0 bits
7.5 bps
28 bits
7.5 bps
5.610
5.65
5.77
5.65
5.69
5.78
5.67
5.78
5.710
August 4-8, 2008 26th APAN Meeting 13
SimulationCell diameter 1 km
Number of MSs 48
Number of subcarriers/subchannel 48
Number of subchannels 4
Number of DL slots/subchannel 80
Frame duration 0.005 sec
User initial location Uniformly distributed
User speed Uniformly distributed [3,100] km/hr
Simulation time 20,000 frames
August 4-8, 2008 26th APAN Meeting 14
System Throughput
August 4-8, 2008 26th APAN Meeting 15
System Queue Size
August 4-8, 2008 26th APAN Meeting 16
Maximum Difference
Maximum difference ofthroughput per user
Maximum difference ofqueue size per user
August 4-8, 2008 26th APAN Meeting 17
Throughput Fairness Index
August 4-8, 2008 26th APAN Meeting 18
Computational Complexity
Scheduling scheme Complexity
MaxC/I O(M2N)
OFPF-MSMA O(M2N2)
OFPF O(M2N2)
PF O(M2N3)
Max-min O(M2N2)
August 4-8, 2008 26th APAN Meeting 19
Conclusion Centralized scheduler for OFDMA-TDD system To maximize system throughput and to provide
fairness with a consideration of queue status Utility function bases on proportional fairness
with modified simple moving averaging Utility matrix-based scheduling exploits multi-
user multi-channel diversity with a consideration of computational complexity
Simulation results show improvement in system throughput, queue length (queuing delay), and fairness (throughput difference, queue length difference
Thank you very much
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