Broadband Access Networks and Services

1
Broadband Access Networks and Services
EE4541.759 Spring 2004

• Chapter 7
• IEEE 802.16 Standard
• Byeong Gi Lee
• Seoul National University

2
IEEE 802.16 Standard

• Overview
• Operation Modes
• Resource Allocation Mechanism
• Physical Layer
• Comparison to IEEE 802.20

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Overview

• Air Interface for Fixed Broadband Wireless Access
  -- The Last Mile
• Broad Bandwidth
• 1066 GHz with line-of-sight
• 211 GHz with non-line-of-sight
• QoS Support
• Multiple service classes
• TDM/TDMA/OFDMA

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Overview

• Air Interface Nomenclature
• WirelessMAN-SC Single carrier at 1066 GHz
• WirelessMAN-SCa Single carrier at 211 GHz
• WirelessMAN-OFDM OFDM at 211 GHz
• WirelessMAN-OFDMA OFDMA at 211 GHz
• WirelessHUMAN 211 GHz license-exempt bands
• Point-to-Multipoint Topology, with Mesh
  Extensions

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802.16 History

• Sponsors
• IEEE Computer Society
• IEEE Microwave Theory and Techniques Society
• Project Development Summer 1998
• WiMAX Forum
• 16 network companies Alvarion, Fujitsu, Intel,
  Nokia,
• Supports IEEE 802.16 Standard

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802.16 History

• 802.16 Standard
• 802.16 (2001) Air interface of MAC and 1066 GHz
  PHY
• 802.16a (2003) Amendment, 211 GHz
• 802.16c (2002) Detailed system profiles for
  1066 GHz
• 802.16d (under revision) Consolidation of
  802.16, 802.16a, and 802.16c
• 802.16e (under revision) Apply low mobility in
  licensed bands

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Frequency Bands

• 1066 GHz
• Severe attenuation
• Line-of-sight (LOS) is required
• Multipath is negligible
• 211 GHz
• LOS is not required
• Multipath is significant
• Additional functionality is required (power
  management, interference mitigation, ARQ, )

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Air Interface Nomenclature
9
Protocol Layering
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Protocol Layering

• Service Specific CS
• Classification of higher layer PDUs
• Payload header suppression
• ATM CS and packet CS
• MAC CPS
• System access, bandwidth allocation, connection
  management
• QoS provisioning

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Protocol Layering

• Privacy Sublayer
• Authentication, secure key exchange, encryption
• Physical Layer
• Four different physical layer specifications
• SC, SCa, OFDM, OFDMA

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Operation Mode

• Point-to-multipoint (PMP) Mode
• A central base station (BS) and multiple
  subscriber stations (SS)
• BS fully controls the downlink bandwidth
• SSs share the uplink bandwidth on a demand basis
  (bandwidth request, grant, polling)
• Four different scheduling service classes (UGS,
  rtPS, nrtPS, BE)

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Operation Mode

• Mesh Mode
• Optional operation mode in WirelessMAN-OFDM
• Traffic can be routed through SSs
• Centralized scheduling
• Mesh BS A system connected to backhaul services
• Mesh BS manages the uplink and downlink bandwidth
• Distributed scheduling
• Each node exchanges its schedule and bandwidth
  request/grant

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BW Request/Grant

• Requests
• SSs send requests when uplink bandwidth is
  required.
• Stand-alone message and piggyback
• Include required number of bytes
• Grants
• Bandwidth allocation by BS to an individual SS
• Connection-based request and SS-based grant

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Polling

• Unicast Polling
• BS allocates bandwidth to an SS
• The SS send bandwidth request using the allocated
  bandwidth
• The SS returns stuff bytes if the SS does not
  need bandwidth
• No individual polling for UGS connections

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Polling

• Multicast/Broadcast Polling
• When insufficient BW is available for unicast
  polling
• BS allocates bandwidth to a group of SSs
• Members of the group sends requests in the
  allocated bandwidth
• Each SS employs a contention resolution algorithm

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Uplink Scheduling Services

• Four Service Classes
• Unsolicited grant service (UGS)
• Real-time polling service (rtPS)
• Non-real-time service (nrtPS)
• Best effort (BE)

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Uplink Scheduling Service

• UGS
• For real-time services that generate fixed size
  packets periodically
• T1/E1, VoIP without silence suppression
• BS offers fixed size grants periodically
• Slip indicator set when additional bandwidth is
  required (due to clock rate mismatches, )
• Poll me bit request to be polled for a
  different, non-UGS connection

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Uplink Scheduling Service

• rtPS
• For real-time services that generate variable
  size data periodically
• MPEG video
• BS offers periodic unicast polling
• More request overhead but efficient data
  transport

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Uplink Scheduling Service

• nrtPS
• For non real-time services that generate variable
  size data regularly
• High bandwidth FTP
• BS typically polls on the order of one second
• Unicast or multicast/broadcast polling
• BE
• All forms of polling are allowed

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Scheduling in Mesh Mode

• Centralized Scheduling
• Mesh BS connected to backhaul services
• Each SS send request message to Mesh BS
• Mesh BS manages the uplink and downlink bandwidth
• No collision in schedule messaging

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Scheduling in Mesh Mode

• Distributed Scheduling
• Each node broadcasts its transmission schedule
  and available bandwidth
• Request/grant is exchanged cooperating with
  neighbors
• Coordinated and uncoordinated
• Schedule message may collide in uncoordinated
  mode

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Physical Sublayer

• PHY Characteristics
• MAP message states the slots at which
  transmission bursts begin
• Interval usage code describes the burst profile
  (modulation, coding rate, ) used on the interval
• Modulation QPSK, 16-QAM, 64-QAM, 256-QAM
• FEC RS convolutional code (mandatory),
  block/convolutional turbo code (optional)
• FDD/TDD (TDD only in license-exempt bands)

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Physical Sublayer

• Downlink Frame Structure

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Physical Sublayer

• Uplink Frame Structure

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Physical Sublayer

• Uplink Frame Structure
• The structure is described in UL-MAP
• Contention opportunities reserved for initial
  ranging
• Contention opportunities reserved for response to
  multicast and broadcast polls
• Intervals defined by data grant specifically
  allocated to individual SSs

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Physical Sublayer

• Frame Structure in Mesh Mode

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Physical Sublayer

• OFDM based PHY
• Subchannel set of active subcarriers, unit of
  resource allocation

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Physical Sublayer

• OFDMA Frame Structure

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Comparison to IEEE 802.20