An Efficient QoS Scheduling Architecture for IEEE 802.16

Wireless MANs

Supriya Maheshwari

Under the guidance of

Prof. Sridhar Iyerand

Prof. Krishna Paul

Broadband Wireless Access

Broadband Wireless Access (Contd…)

High demand for “last-mile” broadband access.

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.

Need for a QoS Scheduling Architecture for IEEE 802.16

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

IEEE 802.16 proposes uplink scheduling services and request-grant mechanisms to provide different levels of services for various classes of uplink traffic.

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

Bandwidth Request-Grant Protocol

BS

SS1

SS2

1

2.1

2.2

1. BS allocates bandwidth to SSs for transmitting bandwidth request.

2.1 SS1 transmits bandwidth requests.2.2 SS2 transmits 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 SS1 transmits data and bandwidth requests.

5.2 SS2 transmits data and bandwidth requests.

4

5.1

5.2

Need for a QoS Scheduling Architecture for IEEE 802.16 BS completely controls transmission in

downlink direction. Request-Grant protocol is used for uplink

bandwidth allocation which involves both BS and SS.

Uplink Scheduling is complex as it needs to be in accordance with uplink QoS provisions provided by IEEE 802.16.

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

Problem Statement

Propose an efficient QoS scheduling architecture 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.

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 data

rate upto 134 Mbps. Provides QoS support for various applications. Bandwidth on demand. Link adaptation. High security.

Contd… Downlink and Uplink

channel. Supports both TDD

and FDD. Downlink channel is

a broadcast channel. Uplink is shared

among all SSs through DAMA-TDMA

The TDD Frame

The Downlink SubframeThe Uplink Subframe

Existing QoS Provisions of IEEE 802.16

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

traffic periodically. 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.

Bandwidth Requests and Grants Ways

Bandwidth request packet. Piggybacking bandwidth request with normal data

packet. Request can be made during time slot

assigned by base station for sending request or data.

Grant modes Grant per Connection (GPC). Grant per Subscriber Station (GPSS).

Proposed QoS Scheduling Architecture 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.

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.

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

on deadline of UGS data.

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 = 30rtPS = 22nrtPS = 30BE = 50

Flows: UGS rtPS nrtPS BE 1st Round 40 30 20 10

30 22 20 10Excess Bytes = 182nd Round 30 22 20+12 10+6

30 22 32 16 Excess Bytes = 23rd Round 30 22 30 16+2

30 22 30 18

SS1 Allocation = 20 +12 + 15 + 9 = 56

SS2 Allocation = 10 +10 + 15 + 9 = 44

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 four categories.

UGS flows are served first. rtPS and reserved nrtPS and BE flows are served

using WFQ scheduling. Remaining bandwidth is allocated to unreserved

flows.

Implementation Details

Qualnet 3.6 Network Simulator is used for simulation.

IEEE 802.11b PHY as physical layer.

BS State Transition Diagram

SS State Transition Diagram

Simulation Setup

Frame Duration=10ms

Bandwidth=11Mbps Channel is assumed

to be error-free. Performance Metrics

Effective Bandwidth Utilization

Average Delay

Effective Bandwidth Utilization Vs Offered Load [Scenario 1]

Offered load by UGS > rtPS > nrtPS > BE

Maximum Effective Bandwidth Utilization ~ 93%

Effective Bandwidth Utilization Vs Offered Load [Scenario 2]

Offered load by UGS < rtPS < nrtPS < BE

Maximum Effective Bandwidth Utilization ~ 93%

Effective Bandwidth Utilization Vs Number of SS [Scenario 1]

Offered load by UGS > rtPS > nrtPS > BE

Maximum Effective Bandwidth Utilization ~ 88%

Effective Bandwidth Utilization Vs Number of SS [Scenario 2]

Offered load by UGS < rtPS < nrtPS < BE

Maximum Effective Bandwidth Utilization ~ 88%

Average Delay Vs Number of SS

Maximum Subscriber Stations ~ 15

Average Delay Vs Time [Scenario 1]

Offered load by UGS > rtPS > nrtPS > BE

UGS and rtPS flows experience low delay.

Average Delay Vs Time [Scenario 2]

Offered load by UGS < rtPS < nrtPS < BE

UGS and rtPS flows experience low delay.

Average Delay Vs Time [Scenario 3]

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

Conclusion

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

Proposed an efficient QoS scheduling architecture for IEEE 802.16.

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

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

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.

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 Conference on Communications, Circuits and Systems and West Sino Expositions, 1:435–439, June 2002.

Mohammed Hawa and David W. Petr. “Quality of Service Scheduling in Cable and Broadband Wireless Access Systems”. Tenth IEEE International Workshop on Quality of Service, pages 247–255, May 2002.

Abhay K. Parekh and Robert G. Gallagher. A generalized processor sharing approach to flow control in integrated services networks: the multiple node case. IEEE/ACM Trans. Netw., 2(2):137–150, 1994. 21

References C. Eklund, R. B. Marks, K. L. Stanwood, and S. Wang, “IEEE Standard

802.16: A Technical Overview of the WirelessMANTM Air Interface for Broadband Wireless Access”, IEEE Communications Magazine, 40(6):98-107, June 2002.

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

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