Uplink Scheduler and Admission
Control for the IEEE 802.16 standard
Juliana Freitag Borin and Nelson L. S. da Fonseca
Institute of Computing, University of Campinas
IEEE GLOBECOM 2009 proceedings
報告者：李宗穎
Outline
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Introduction and Related Work
Admission Control Algorithm
Scheduling Mechanism
Simulation and Numerical Result
Conclusion
2
Introduction
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In 802.16 wireless network QoS guarantee,
the major challenges are scheduling in the
uplink direction at the BS
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downlink direction and at the SSs are less
complex since information about the queues
status is locally available
3
Standard-compliant uplink scheduler
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admission control mechanism should work jointly
with the uplink scheduler
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BS should distribute the uplink bandwidth such that
QoS requirements of each connection are satisfied
the BS should allocate bandwidth not only for data
transmission but also for bandwidth requests
transmission
the uplink scheduler should support all QoS parameters
defined by the standard
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QoS Parameter
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the admission of new connections
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the scheduler allocates grants with size
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maximum latency
UGS and ertPS
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maximum traffic burst
real time connections
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minimum reserved traffic rate
unsolicited grant interval
tolerated jitter
rtPS and nrtPS
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unsolicited polling interval
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Related Work (1/3)
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Many solutions proposed for the IEEE 802.16
uplink scheduler combine classic scheduling
policies developed for wired networks, such as
Strict Priority, Weighted Fair Queuing (WFQ), and
Earliest Deadline First (EDF)
[5] D. Tarchi, R. Fantacci, and M. Bardazzi, Quality or Service management in IEEE 802.16 wireless
metropolitan area networks. In Proceedings of the IEEE International Conference on Communications,
pg. 1789-1794.
[8] J. Chen, W. Jiao, and H. Wang, A Service Flow Management Strategy for IEEE 802.16 Broadband
Wireless Access Systems in TDD Mode. In Proceedings of the IEEE ICC, pp. 3422-3426, 2005.
[12] K. Wongthavarawat and A. Ganz, IEEE 802.16 based last mile broadband wireless military
networks with Quality of Service support. In Proceedings of the IEEE MILCOM’03, pp. 779-784, 2003.
6
Related Work (2/3)
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The admission control scheme proposed in
this paper as well as other solutions
available in the literature [7], [8] use only
the minimum rate requirement in the
decision process
[7] H. Wang, B. He, and D. P. Agrawal, Above packet layer level admission control and bandwidth
allocation for IEEE 802.16 wireless MAN. Simulation Modeling Practice and Theory, vol. 15, no. 14,
pg. 266-382.
[8] J. Chen, W. Jiao, and H. Wang, A Service Flow Management Strategy for IEEE 802.16 Broadband
Wireless Access Systems in TDD Mode. In Proceedings of the IEEE ICC, pp. 3422-3426, 2005.
7
Related Work (3/3)
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Chandra and Sahoo [16] considered the overhead
of different type of services, however, the ertPS
service is not included in the mechanism.
Additionally, the authors do not detail the
algorithm used by the search routine, which is an
important part of the proposed mechanism
[16] S. Chandra, and A. Sahoo, An efficient call admission control for IEEE 802.16 networks. In
Proceedings of the 15th IEEE Workshop on Local & Metropolitan Area Networks, pg. 188-193.
8
Admission Control Algorithm
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TRiservice : the traffic rate that should be guaranteed to the
new connection i of service type service (includes an
estimate of the overhead)
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Creserved : the capacity reserved to the connections already
admitted in the system
C : the capacity available for the uplink scheduler
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UGS and ertPS connections
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The grant size is fixed, based on the
maximum sustained traffic rate (minimum
reserved traffic rate) of the service
unsolicited grant interval
tolerated jitter
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rtPS and nrtPS connections
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Besides the minimum reserved traffic rate,
rtPS and nrtPS connections also need
periodic grants to request bandwidth
upSlots : the number of slots used by the unicast polling
Upii : the value provided by the unsolicited polling interval parameter
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Scheduling Mechanism (1/2)
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The proposed uplink scheduler uses three
queues :
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Low priority queues
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Intermediate priority queues
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BE bandwidth requests
bandwidth requests sent by both rtPS and nrtPS
connections
These requests can migrate to the high priority
queue
High priority queues
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periodic grants and unicast request opportunities
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Scheduling Mechanism (2/2)
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for UGS and ertPS, the scheduler generates
periodic grants and inserts them into the
high priority queue
for rtPS and nrtPS, the BS assigns a
deadline for each bandwidth request in the
intermediate queue
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move to high priority queue
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deadlines expiring two frames (rtPS)
not received the minimum reserved traffic rate in a
window with duration T (nrtPS, rtPS)
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Dual leaky bucket
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the bandwidth allocated to a
single connection is less than or
equal to the maximum traffic
burst requirement
the scheduler does not allocate
bandwidth for a connection if it
results in violation of the
maximum sustained traffic rate
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Scheduling Algorithm
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Check Deadline procedure
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the scheduler tries to migrate the rtPS
requests from the intermediate queue to the
high priority queue
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there is available bandwidth
the deadline of a rtPS request expires during the
frame following the next one
the corresponding connection has not received
the minimum reserved traffic rate
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MigrateBWRequest procedure
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checks whether or not the amount of
bandwidth solicited by the migrating
request (BR[i]) is available in the uplink
subframe
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Avoid violation of the maximum traffic burst
value, a new request j is created with BR[j]
equals to BR[i] − grantSize and it is inserted at
the end of the intermediate queue
traffic
maximum traffic burst
BR[j]
intermediate queue
high priority queue
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CheckMinimumBandwidth procedure
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Calculates and sort a priority value for each
request in the intermediate queue
the scheduler tries to migrate requests to the
high priority queue using the
MigrateBWRequest procedure
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DistributeFreeResources procedure
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distributes the available bandwidth among
the BE requests by migrating some of them
from the low priority queue to the high
priority queue
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Simulation Experiments (1/2)
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The simulated network consists of a BS, with the SSs
uniformly distributed around it (using ns2 with WiMAX
module)
QoS
traffic
Distribution
UGS
voice
constant (66bytes-20ms)
ertPS
voice (on-off)
exponential on/off (1.2s/1.8s) (66bytes-20ms)
rtPS
video
real-MPEG trace
nrtPS
FTP
exponential (mean 512KB)
BE
Web
lognormal/pareto (mean 7274B/10558B)
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Simulation Experiments (2/2)
Lifetimes : exponentially distributed mean 600s (rtPS), 300s (UGS, ertPS, and
nrtPS)
Arrival rates : exponential distribution mean varying 2s to 60s for each type
BE connections : equal to 20 in all the simulated situations
maximum latency requirement : 100ms (rtPS)
minimum reserved traffic rate : 200Kbps (nrtPS), X-Kbps (each rtPS)
maximum sustained traffic rate requirement : 300Knps (nrtPS), Y-Kbps (each rtPS)
unsolicited grant interval : 20ms (UGS, ertPS)
unsolicited polling interval : 20ms (rtPS) , 1s (nrtPS)
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Blocking probability
UGS : 26 Kbps
ertPS : 80Kbps
nrtPS : 200Kbps
rtPS : 200 ~ 900Kbps
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Average latency of UGS, ertPS
and rtPS services
rtPS
ertPS
UGS
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average throughput of rtPS connections
with minimum rate requirement 500 Kbps
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Average throughput of nrtPS
connections
MAC header overhead
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Conclusion
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The proposed scheduler provides maximum
latency and minimum rate guarantees
without violating the maximum sustained
traffic rate and the maximum traffic burst
values
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