Uplink Scheduling with Quality of Service
in IEEE 802.16 NetworksJuliana Freitag and Nelson L. S. da Fonsec
aState University of Campinas, Sao Paulo, Brazil
IEEE Global Telecommunications Conference, 2007.
GLOBECOM '07.
Mei-Jhen ChenMei-Jhen Chen
OutlineOutline
IntroductionIntroduction A scheduling MechanismA scheduling Mechanism Simulation ExperimentsSimulation Experiments ConclusionsConclusions
IntroductionIntroduction
To support a wide variety of multimedia applications, the IEEE 802.16 standard defines four types of service flows, each with different QoS requirements.
Each connection between the SS and the BS is associated to one service flow. UGS (Unsolicited Grant Service) rtPS (real time Polling Service) nrtPS (non-real time Polling Service) BE (Best Effort)
Introduction Introduction (cont.)(cont.)
A signaling mechanism for information exchange between the base station (BS) and subscriber stations (SSs) was defined. allow the SSs to request bandwidth to the BS Bandwidth allocation is provided on demand When an SS has backlogged data, it sends a band
width request to the BS. The BS allocates time slots to the SS.
Each frame is divided in two parts the downlink subframe and the uplink subframe
Introduction Introduction (cont.)(cont.)
different scheduling mechanisms have been proposed not all of them comply with the IEEE 802.16 standard
Authors introduce a BS uplink scheduling algorithm which allocates bandwidth to the SSs based on the QoS requirements of the connections.
The proposed policy is fully standard-compliant and it can be easily implemented in the BSs.
A Scheduling MechanismA Scheduling Mechanism
According to the IEEE 802.16 standard the BS uplink scheduler provides grants (time slots)
at periodic intervals to the UGS flows to send data. Periodic grants are also given to rtPS and to nrtPS fl
ows to request bandwidth. the uplink scheduler must guarantee that the delay
and the bandwidth requirements of rtPS and nrtPS flows are met.
The BS executes the uplink scheduler during each frame, and it broadcasts the schedule in the UL-MAP message in the downlink subframe.
A Scheduling MechanismA Scheduling Mechanism
low priority queue
intermediate queue
high priority queue
A Scheduling MechanismA Scheduling Mechanism
A Scheduling Mechanism A Scheduling Mechanism -CheckDeadline-CheckDeadline
low priority queue
intermediate queue
high priority queue
current_time = 8ms
Frame_duration = 5ms
13 2123
UGS request
rtPS request
nrtPS request
BE request
ServerUL-MAP
deadline = 18ms 13ms 20msframe[i] : 2 1 2
A Scheduling Mechanism A Scheduling Mechanism -CheckMinimumBandwidth-CheckMinimumBandwidth
low priority queue
intermediate queue
high priority queue
current_time = 8ms
Frame_duration = 5ms
13
2
123
UGS request
rtPS request
nrtPS request
BE request
ServerUL-MAP
BWmin : 10 13 11 20 24granted_BW_tmp : 15 8 10 15 14backlogged_tmp : 16 17 13 12 15Priority[i] = backlogged_tmp[CID] – (granted_BW_tmp[CID]-BWmin[CID])
0 12 18 17 25
Simulation Experiments Simulation Experiments --assumptionassumption
NS-2 250x250 meter area
a BS : located at the center the SSs : uniformly distributed
The frame duration : 5 ms the capacity of the channel : 40 Mbps
Simulation Experiments Simulation Experiments --assumptionassumption
Each SS has only one traffic flow. four types of traffic
Voice “on/off” : a mean of 1.2 s and 1.8 s During “on” periods, packets of 66 bytes are generated
every 20 ms Video
real MPEG traces FTP
a hybrid Lognormal/Pareto distribution an area of 0.88 with a mean of 7247 bytes the tail is modeled with a mean of 10558 bytes
WEB exponential distribution with a mean of 512 KBytes.
Simulation Experiments Simulation Experiments --assumptionassumption
UGS The interval between data grants is 20 ms since t
he BS rtPS
The interval is 20 ms the delay requirement is 100 ms
nrtPS the interval of the nrtPS service 1 s. minimum bandwidth requirement of 200Kbps
BE not have any QoS requirement
Simulation Experiments -Simulation Experiments -experiment 1experiment 1
Whether the BS is able to allocate bandwidth to connections in the same service level in a fair way, regardless the number of connections in the network.
one BS the number of SSs varies between 10 and 30
Each SS has one nrtPS connection that generates FTP traffic with rate of 600 Kbps.
Simulation Experiments -Simulation Experiments -experiment 1experiment 1
Fig. 2. Throughput of each SS
Simulation Experiments -Simulation Experiments -experiment 2experiment 2
whether or not the increase of the UGS traffic load degrades the QoS level of services with lower priority.
one BS and 81 SSs 6 rtPS connections 20 nrtPS connections 20 BE connections the number of active UGS connections varies fro
m 15 to 35.
Simulation Experiments -Simulation Experiments -experiment 2experiment 2
Fig. 3. Delay of UGS and rtPS connections
Simulation Experiments -Simulation Experiments -experiment 2experiment 2
Fig. 4. Throughput of nrtPS and BE connections
Simulation Experiments -Simulation Experiments -experiment 3experiment 3
the impact of the load increase of the rtPS service on the performance of other service classes.
one BS and 62 SSs 15 UGS connections 20 nrtPS connections 20 BE connections the number of active rtPS connections varies fro
m 1 to 7
Simulation Experiments -Simulation Experiments -experiment 3experiment 3
Fig. 5. Delay of UGS and rtPS connections
Simulation Experiments -Simulation Experiments -experiment 3experiment 3
Fig. 6. Throughput of nrtPS and BE connections
Simulation Experiments -Simulation Experiments -experiment 4experiment 4
whether the increase of the BE traffic load influences or not the QoS level of services which has higher priority.
one BS and 70 SSs. 15 UGS connections 5 rtPS connections 15 nrtPS connections the number of active BE connections varies from
10 to 35.
Simulation Experiments -Simulation Experiments -experiment 4experiment 4
Fig. 7. Delay of UGS and rtPS connections
Simulation Experiments -Simulation Experiments -experiment 4experiment 4
Fig. 8. Throughput of nrtPS and BE connections
ConclusionsConclusions
An uplink scheduling mechanism for IEEE 802.16 networks was introduced.
The proposed solution supports the four service levels specified by the standard and considers their QoS requirements for scheduling decisions.
The complexity of the proposed mechanism is
O(k + rlogr)k : number of slots in the uplink subframer : the number of rtPS and nrtPS bandwidth requests in the intermediate queue
Thank You!Thank You!