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!