Multimedia Communications

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Multimedia Communications
QoS Support for Multimedia in IEEE 802.16
Networks A Survey of Scheduling Techniques
Aadil Zia KhanDepartment of Computer
ScienceLahore University of Management
SciencesEmail 06030004_at_lums.edu.pk
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IEEE 802.16 Networks (Introduction)

• One of the most promising solutions for wireless
  broadband access
• IEEE Project 802 working group 16 working towards
  building its standards
• Commercial forum Worldwide Interoperability for
  Microwave Access (WiMAX) was founded which
  includes more than 300 member companies
• WiMAX will provide the last mile internet access
  to residential users
• Especially useful in regions where wire lined
  infrastructure does not exist or can not be setup
• WiMAX will create an economical alternative to
  expensive leased line solutions for small and
  medium enterprises
• December 2004 Tsunami in Aceh, Indonesia - a
  success story

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IEEE 802.16 Networks (Evolution)

• Version 802.16
• Operated between 10-66 GHz
• Specified a single carrier
• Provided only Point-to-Multipoint (PMP)
  communication
• Version, 802.16a
• Extended the frequency band to below 11 GHz thus
  enabling non line of sight communication
• Two air interfaces 256-carrier Orthogonal
  Frequency Division Multiplex (OFDM) and
  2048-carrier Orthogonal Frequency Division
  Multiple Access (OFDMA) were provided
• Allowed mesh based topology in addition to the
  existing PMP communication
• Version 802.16d published in June 2004
• Incorporates all the previous versions to provide
  fixed BWA
• Version 802.16e accepted in 2005
• Supports full mobility at speed up to 70-80 m/s

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IEEE 802.16 Networks (Benefits)

• High Speed Access
• Wireless
• Broad Coverage
• Mobility

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IEEE 802.16 Networks (Operation Architecture)

• Operation
• Two types of nodes
• Tower / Base Station
• Receiver / Subscriber Station

• Network Architecture
• Two types of networks
• Point-to-Mulitpoint
• All the Subscriber Stations communicate only
  through the Base Station
• Mesh
• All the Subscriber Stations can communicate
  through the Base Station as well as directly with
  other Subscriber Stations

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IEEE 802.16 Networks (Phy. Layer Communication)

• Frequency Division Duplexing
• The uplink and downlink channels are on different
  frequencies
• Both the Half-Duplex and Full-Duplex modes are
  supported

• Time Division Duplexing
• The uplink and downlink channels are on same
  frequencies but occur at different time intervals
• TDD frame has a fixed duration and is divided
  into uplink and downlink subframes
• TDD framing is adaptive

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IEEE 802.16 Networks (MAC Layer Communication)

• Connection oriented architecture
• Each communication belongs to a particular
  connection and within that connection to a
  particular service flow class
• Channel access
• UL-MAP and DL-MAP transmitted at the start of
  each frame
• UL-MAP defines slots for uplink channel access as
  well as data burst profiles
• DL-MAP defines downlink data burst profiles

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IEEE 802.16 Networks (Bandwidth Allocation
Request)

• SS Bandwidth Request
• Use contention request opportunities when polled
  by the BS
• Send a bandwidth request in an allotted time slot
• Piggyback a bandwidth request on a data packet

• BS Bandwidth Allocation
• Grant per subscriber station
• Grant per connection
• Allocation decision based on available resources,
  bandwidth request and Quality of Service

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IEEE 802.16 Networks (What is Qos)

• Quality of Service, an architecture which treats
  packets differently
• One flow receives preferential treatment at the
  cost of other flows
• Guaranteed services are provided to the end users
• QoS guarantees can be for the following
• Delay
• Delay Jitter
• Reserved Bandwidth
• Error Rate

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IEEE 802.16 Networks (QoS Classes)

• For transmission, give preference to packets
  according to the service class they belong to
• WiMAX defines four services classes
• Unsolicited Grant Service
• For real time traffic with fixed packet size
• Provides fixed size unsolicited data grants
  periodically
• Real Time Polling Service
• For real time traffic with variable packet size
• BS offers unicast polls
• Contention isnt allowed but piggybacking is
  permissible
• Non Real Time Polling Service
• For non realtime flows requiring variable sized
  data grants
• BS offers unicast polls.
• Contention as well as piggybacking is allowed
• Best Effort
• BS doesnt offer unicast polls
• SS reserves bandwidth by contention and
  piggybacking

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IEEE 802.16 Networks (Scheduling Requirements)

• A good scheduling algorithm must catered to the
  following
• Bandwidth utilization must be efficient. For
  example, resources shouldnt be allocated to a
  bad link.
• The scheduler should be able to cater to
  different QoS requirements with a guarantee on
  the long term throughput for all connections.
• The scheduler should be fair in both the long run
  as well as the short run.
• The scheduler should have a low complexity so
  that the decision making is rapid.
• The system should be scalable.

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IEEE 802.16 Networks (Some Existing Scheduling
Techniques)

• WiMAX standard does not specify the type of
  scheduling algorithm to be used and instead
  leaves it to the discretion of the vendor
• Using Earliest Due Date for real time and
  Weighted Fair Queuing for non real time streams
• Token Bank Fair Queuing - Priority is the ratio
  of the number of tokens exchanged between the
  bank and that connection and the reserved rate. A
  negative ratio means that the connection has used
  more than the assigned number of tokens. The SSs
  are served based on their token generation rate
  to guarantee throughput and latency and the
  remaining bandwidth is distributed according to
  the priority ranking
• Frame Registry Tree Scheduler - This is a tree
  based approach. First level is taken to be the
  root. The second level represents time frames
  immediately after the current time frame. The
  third level represents the available modulation
  types. The fourth level organizes all the
  connections according to the SS each SS has one
  uplink node and one downlink node at this level.
  The fifth level organizes the connections
  according to their QoS. The last level consists
  of leaves for each active connection queue. The
  algorithm schedules each packet at the last time
  frame before its deadline. Changes in the
  connection characteristics like modulation type
  or service type of the channel can be easily
  updated

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IEEE 802.16 Networks (Contd.)

• Maximum Delay Utility - Marginal utility
  functions with respect to the average waiting
  time for the corresponding QoS requirements are
  used. The function used should be able to meet
  the deadline requirements for real time traffic,
  as well as control greediness in non real time
  traffic.
• Opportunistic Fair Scheduling - The scheduler
  firstly computes the fair share weights for each
  connection based on the knowledge it has of the
  average gains of the channels. The associated
  data rate of each SS is calculated by the
  adaptive modulation process in BS. The scheduler
  then sorts in descending order each SS based on
  its achievable rate. Transmissions follow this
  order.
• And many others which will be described in detail
  in the final paper.

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References
1 C. Cicconetti, L. Lenzini, and E. Mingozzi,
Quality of Service Support in IEEE 802.16
Networks 2 http//en.wikipedia.org/wiki/WiMAX
3 S. Ryu, B. Ryu, H. Seo, and M. Shin, Urgency
and Efficiency based Wireless Downlink Packet
Scheduling Algorithm in OFDMA System 4 W.
Park, S.Cho, and S. Bahk, Scheduler Design for
Multiple Traffic Classes in OFDMA Networks 5
K. Vinay, N. Sreenivasulul, D. Jayaraml, and D.
Das, Performance Evaluation of End-to-end Delay
by Hybrid Scheduling Algorithm for QoS in IEEE
802.16 Network 6 J. Sun, Y. Yao, and H. Zhu,
Quality of Service Scheduling for 802.16
Broadband Wireless Access Systems 7 W. K.
Wong, H. Tang, S. Guo, and V. C. M. Leung,
Scheduling Algorithm in a Point-to-Multipoint
Broadband Wireless Access Network 8 S. A.
Xergias, N. Passas, and L. Merakos, Flexible
Resource Allocation in IEEE 802.16 Wireless
Metropolitan Area Networks 9 H. S. Alavi, M.
Mojdeh, and N. Yazdani, A Quality of Service
Architecture for IEEE 802.16 Standards 10 J.
Chen, W. Jiao, and H. Wang A Service Flow
Management Strategy for IEEE 802.16 Broadband
Wireless Access Systems in TDD Mode 11 N.
Liu, X. Li, C. Pei, B. Yang, Delay Character of
a Novel Architecture for IEEE 802.16
Systems 12 M. Mehrjoo, M. Dianati, X. Shen, K.
Naik Opportunistic Fair Scheduling for the
Downlink of IEEE 802.16Wireless Metropolitan Area
Networks 13 G. Song, Y. Li, Utility-Based
Resource Allocation and Scheduling in OFDM-Based
Wireless Broadband Networks 14 F. De
Pellegrini, D. Miorandi, E. Salvadori and N.
Scalabrino. QoS Support in WiMAX Networks
Issues and Experimental Measurements 15
Christian Müller, Anja Klein, Frank Wegner,
Coverage Extension of WiMax Using Multihop in a
Low User Density Environment 16 D. Tarchi, R.
Fantacci, and M. Bardazzi, Quality of Service
Management in IEEE 802.16 Wireless Metropolitan
Area Networks 17 X. Meng, An Efficient
Scheduling For Diverse QoS Requirements in WiMAX
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