packet scheduling for fairness and performance improvement in ofdma wireless networks nararat...
TRANSCRIPT
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
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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
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System Model
- Centralized scheduler on BS- Uniform power allocation to each subchannel
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Resources
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Utility Matrix & Proportional Fairness
n
nmnm T
tRi
)(,,
Rm,n(t) – Achievable data rate of user n via
subchannel mTn – Average data rate
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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
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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
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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
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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
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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
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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
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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
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System Throughput
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System Queue Size
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Maximum Difference
Maximum difference ofthroughput per user
Maximum difference ofqueue size per user
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Throughput Fairness Index
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Computational Complexity
Scheduling scheme Complexity
MaxC/I O(M2N)
OFPF-MSMA O(M2N2)
OFPF O(M2N2)
PF O(M2N3)
Max-min O(M2N2)
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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
Questions and Answers