An Efficient QoS Scheduling Architecture for IEEE 802.16Wireless MANs

8/14/2019 An Efficient QoS Scheduling Architecture for IEEE 802.16 Wireless MANs

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An Efficient QoS SchedulingArchitecture for IEEE 802.16Wireless MANs

Supriya Maheshwari

Under the guidance of

Prof. Sridhar Iyerand

Prof. Krishna Paul


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Broadband Wireless Access


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Broadband Wireless Access(Contd)

High demand for last-mile broadbandaccess.

Advantages of Broadband Wireless Access Fast deployment and high scalability.

High speed network access at low cost.

Broad geographic area. IEEE 802.16 WirelessMAN standard for

Broadband Wireless Access systems.


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Need for a QoS SchedulingArchitecture for IEEE 802.16

IEEE 802.16 has been designed to support QoSin both downlink and uplink directions.

IEEE 802.16 proposes uplink scheduling servicesand request-grant mechanisms to providedifferent levels of services for various classes ofuplink traffic.

Main component to accomplish this task i.e.packet scheduling mechanism is unspecified.


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Bandwidth Request-GrantProtocol

BS

SS1

SS2

1

2.1

2.2

1. BS allocates bandwidth to SSs for

transmitting bandwidth request.

2.1 SS1transmits bandwidth requests.2.2 SS2transmits bandwidth requests.

4. BS allocates bandwidth to SSs for

transmitting data based on their

bandwidth requests. Bandwidth is

also allocated for requesting more

bandwidth.

5.1 SS1transmits data and bandwidth

requests.

5.2 SS2transmits data and bandwidthrequests.

4

5.1

5.2


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Need for a QoS SchedulingArchitecture for IEEE 802.16

BS completely controls transmission in downlinkdirection.

Request-Grant protocol is used for uplink

bandwidth allocation which involves both BS andSS. Uplink Scheduling is complex as it needs to be in

accordance with uplink QoS provisions providedby IEEE 802.16.

Therefore, a single scheduling algorithm for thewhole system does not suffice.


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Problem Statement

Propose an efficient QoS schedulingarchitecture for IEEE 802.16 Wireless MANs.

Design Goals To provide delay and bandwidth guarantees for

various kinds of applications.

To maintain fairness among various flows based

on their priority. To achieve high bandwidth utilization.


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IEEE 802.16 Features

WirelessMAN air interface for fixed point to multi-point Broadband Wireless Access.

10-66 GHz frequency range.

Supports channel as wide as 28 MHz and datarate upto 134 Mbps.

Provides QoS support for various applications.

Bandwidth on demand.

Link adaptation.

High security.


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Contd

Downlink and Uplinkchannel.

Supports both TDD

and FDD. Downlink channel is a

broadcast channel.

Uplink is shared

among all SSsthrough DAMA-TDMA

The TDD Frame


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The Downlink SubframeThe Uplink Subframe


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Existing QoS Provisions of IEEE802.16

MAC Service Flows Uplink Scheduling Services

Unsolicited Grant Service (UGS) Support applications generating constant bit rate traffic periodically.

Provides fixed bandwidth at periodic intervals. Real-Time Polling Service (rtPS)

Supports real-time applications generating variable bit rate trafficperiodically.

Offers periodic opportunities to request bandwidth.

Non Real-Time Polling Service (nrtPS) Supports non-real-time applications generating variable bit rate traffic

regularly. Offers opportunities to request bandwidth regularly.

Best Effort (BE) Offers no guarantee.


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Bandwidth Requests and Grants

Ways

Bandwidth request packet.

Piggybacking bandwidth request with normal data

packet.

Request can be made during time slot assignedby base station for sending request or data.

Grant modes

Grant per Connection (GPC).

Grant per Subscriber Station (GPSS).


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Proposed QoS SchedulingArchitecture for IEEE 802.16

Design Goals

To provide bandwidth and delay guarantees to various

applications and maintain fairness among various flows while

still achieving high bandwidth utilization.

Uses GPSS mode. Scalable and efficient.

Smaller Uplink control information.

Suitable for real-time applications which require faster response. Enhances system performance.

Supports all types of service flows.


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Working of Components

BS/SS Data Classifier

Maps an IP packet to a particular connection.

BS/SS Traffic Shaper

Examines and shapes the incoming traffic.

BS Periodic Grant Generator

Grant at tk= t0+ k * Interval

Deadline = tk+ Jitter

BS Uplink Grant Classifier

Maps each grant to the corresponding SS.


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Working of Components (Contd)

BS Frame Partitioner Divides total frame bandwidth equally between downlink

and uplink subframe.

SS Request Generator For each connection, aggregate request based on current

queue length is generated.

BS Uplink Map Generator Allocates bandwidth to each SS for uplink transmission.

Uses two stage max-min fair allocation strategy.

Order of transmission among SSs is decided based ondeadline of UGS data.


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Example

Total Uplink Bytes = 100

2 SS and 1 BS

SS1 Demands:

UGS = 20

rtPS = 12

nrtPS = 15

BE = 30

SS2 Demands:

UGS = 10

rtPS = 10

nrtPS = 15

BE = 20

Total Demand Per Flow:

UGS = 30

rtPS = 22

nrtPS = 30

BE = 50

Flows: UGS rtPS nrtPS BE

1stRound 40 30 20 10

30 22 20 10

Excess Bytes = 18

2ndRound 30 22 20+12 10+6

30 22 32 16Excess Bytes = 2

3rdRound 30 22 30 16+2

30 22 30 18

SS1Allocation = 20 +12 + 15 + 9 = 56

SS2Allocation = 10 +10 + 15 + 9 = 44


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Working of Components (Contd)

BS Downlink Scheduler Reserved flows are served using WFQ scheduling

algorithm.

Remaining bandwidth is allocated to unreserved flows.

SS Uplink Scheduler Separate queue for each connection except for nrtPS

and BE flows with no reservation, divided into fourcategories.

UGS flows are served first.

rtPS and reserved nrtPS and BE flows are served usingWFQ scheduling.

Remaining bandwidth is allocated to unreserved flows.


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Implementation Details

Qualnet 3.6 Network Simulator is usedfor simulation.

IEEE 802.11b PHY as physical layer.


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BS State Transition Diagram


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SS State Transition Diagram


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Simulation Setup

Frame Duration=10ms

Bandwidth=11Mbps

Channel is assumed tobe error-free.

Performance Metrics

Effective BandwidthUtilization

Average Delay


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Effective Bandwidth Utilization VsOffered Load [Scenario 1]

Offered load by UGS > rtPS > nrtPS > BE

Maximum Effective Bandwidth Utilization ~ 93%


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Effective Bandwidth Utilization VsOffered Load [Scenario 2]

Offered load by UGS < rtPS < nrtPS < BE



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Effective Bandwidth Utilization VsNumber of SS [Scenario 1]




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Effective Bandwidth Utilization VsNumber of SS [Scenario 2]




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Average Delay Vs Number of SS

Maximum Subscriber Stations ~ 15

A D l V Ti


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Average Delay Vs Time[Scenario 1]


UGS and rtPS flows experience low delay.

A D l V Ti


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UGS and rtPS flows experience low delay.

A D l V Ti


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Fairness is maintained among flows across SSs

Three SSs with different type of uplink flows.

SS1- UGS and rtPS

SS2- UGS and nrtPS

SS3- UGS and BE


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Conclusion

An efficient QoS scheduling architecture for IEEE 802.16is necessary to provide required QoS guarantees tovarious applications.

Proposed an efficient QoS scheduling architecture forIEEE 802.16.

IEEE 802.16 MAC has been implemented in Qualnet 3.6along with the proposed architecture.

Simulation results are presented to show that ourarchitecture fulfills the stated design goals.


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Future Work

Contention slot allocation algorithm can be designed.

Admission control mechanism can be devised.

Performance Study of IEEE 802.16 MAC over IEEE

802.11b PHY.


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References

IEEE 802.16-2001. IEEE Standard for Local and Metropolitan Area Networks -Part 16: Air Interface for Fixed Broadband Wireless Access Systems. Apr. 8,2002.

GuoSong Chu, Deng Wang, and Shunliang Mei. A QoS architecture for the

MAC protocol of IEEE 802.16 BWA system.IEEE International Conferenceon Communications, Circuits and Systems and West Sino Expositions, 1:435439, June 2002.

Mohammed Hawa and David W. Petr. Quality of Service Scheduling in Cableand Broadband Wireless Access Systems. Tenth IEEE International Workshopon Quality of Service, pages 247255, May 2002.

Abhay K. Parekh and Robert G. Gallagher. A generalized processor sharingapproach to flow control in integrated services networks: the multiple node case.IEEE/ACM Trans. Netw., 2(2):137150, 1994. 21


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References

C. Eklund, R. B. Marks, K. L. Stanwood, and S. Wang, IEEE Standard802.16: A Technical Overview of the WirelessMANTM Air Interface forBroadband Wireless Access,IEEE Communications Magazine, 40(6):98-107, June 2002.

Andrew S. Tanenbaum, Computer Networks, Prentice-Hall India, Fourthedition, 2003.

S. Keshav. An Engineering Approach to Computer Networking. PearsonEducation, Sixth edition, 2003.

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An Efficient QoS Scheduling Architecture for IEEE 802.16Wireless MANs