An Efficient QoS Scheduling Architecture for IEEE 802.16 Wireless MANs

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An Efficient QoS Scheduling Architecture for IEEE
802.16Wireless MANs

• Supriya Maheshwari
• Under the guidance of
• Prof. Sridhar Iyer
• and
• Prof. Krishna Paul

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Broadband Wireless Access
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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.

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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.

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Bandwidth Request-Grant Protocol
SS1
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.
1. BS allocates bandwidth to SSs for transmitting
bandwidth request. 2.1 SS1 transmits bandwidth
requests. 2.2 SS2 transmits bandwidth requests.
2.1
5.1
BS
1
4
SS2
2.2
5.2
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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.

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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.

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

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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
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The Downlink Subframe
The Uplink Subframe
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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.

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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 assigned by
  base station for sending request or data.
• Grant modes
• Grant per Connection (GPC).
• Grant per Subscriber Station (GPSS).

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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.

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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
  on deadline of UGS data.

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Example
Total Uplink Bytes 100 2 SS and 1 BS
Flows UGS rtPS nrtPS BE 1st Round 40
30 20 10 30 22 20
10 Excess Bytes 18 2nd Round 30 22
2012 106 30 22 32
16 Excess Bytes 2 3rd Round 30
22 30 162 30 22 30 18
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
SS1 Allocation 20 12 15 9 56 SS2
Allocation 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 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.

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Implementation Details

• Qualnet 3.6 Network Simulator is used for
  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 Duration10ms
• Bandwidth11Mbps
• Channel is assumed to be error-free.
• Performance Metrics
• Effective Bandwidth Utilization
• Average Delay

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Effective Bandwidth Utilization Vs Offered Load
Scenario 1
Offered load by UGS gt rtPS gt nrtPS gt BE
Maximum Effective Bandwidth Utilization 93
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Effective Bandwidth Utilization Vs Offered Load
Scenario 2
Offered load by UGS lt rtPS lt nrtPS lt BE
Maximum Effective Bandwidth Utilization 93
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Effective Bandwidth Utilization Vs Number of SS
Scenario 1
Offered load by UGS gt rtPS gt nrtPS gt BE
Maximum Effective Bandwidth Utilization 88
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Effective Bandwidth Utilization Vs Number of SS
Scenario 2
Offered load by UGS lt rtPS lt nrtPS lt BE
Maximum Effective Bandwidth Utilization 88
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Average Delay Vs Number of SS
Maximum Subscriber Stations 15
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Average Delay Vs Time Scenario 1
Offered load by UGS gt rtPS gt nrtPS gt BE
UGS and rtPS flows experience low delay.
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Average Delay Vs Time Scenario 2
Offered load by UGS lt rtPS lt nrtPS lt BE
UGS and rtPS flows experience low delay.
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Average Delay Vs Time Scenario 3
Three SSs with different type of uplink flows.
SS1 - UGS and rtPS SS2 - UGS and nrtPS SS3 - UGS
and BE
Fairness is maintained among flows across SSs
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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.

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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 Conference on
  Communications, Circuits and Systems and West
  Sino Expositions, 1435439, 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 247255, 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)137150, 1994. 21

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References

• C. Eklund, R. B. Marks, K. L. Stanwood, and S.
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