WiMAX for Broadband Wireless Access

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WiMAX for Broadband Wireless Access

• By
• Karim M. El Defrawy
• ICS
• UCI-2005

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Outline

• What is WiMAX
• 802.16 Introduction
• 802.16 MAC Highlights
• 802.16 Reference Model
• MAC Convergence Sub-Layer (CS)
• MAC Common Part Sub-Layer (CPS)
• MAC Privacy Sub-Layer (PS)
• Questions

3
What is WiMAX?

• Worldwide Interoperability for Microwave Access
  (WiMAX) is the common name associated to the IEEE
  802.16a/REVd/e standards.
• These standards are issued by the IEEE 802.16
  subgroup that originally covered the Wireless
  Local Loop technologies with radio spectrum from
  10 to 66 GHz.

4
IEEE 802.16 -- Introduction

• IEEE 802.16 (2001)
• Air Interface for Fixed Broadband Wireless Access
  System MAC and PHY Specifications for 10 66 GHZ
  (LoS)
• One PHY Single Carrier
• Connection-oriented, TDM/TDMA MAC, QoS, Privacy
• IEEE 802.16a (January 2003)
• Amendment to 802.16, MAC Modifications and
  Additional PHY Specifications for 2 11 GHz
  (NLoS)
• Three PHYs OFDM, OFDMA, Single Carrier
• Additional MAC functions OFDM and OFDMA PHY
  support, Mesh topology support, ARQ
• IEEE 802.16d (July 2004)
• Combines both IEEE 802.16 and 802.16a
• Some modifications to the MAC and PHY
• IEEE 802.16e (2005?)
• Amendment to 802.16-2004
• MAC Modifications for limited mobility

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IEEE 802.16 -- Introduction
Coverage range up to 50km and speeds up to
70Mbps(shared among users).
6
IEEE 802.16 -- Introduction
Source WiMAX, making ubiquitous high-speed data
services a reality, White Paper, Alcatel.
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IEEE 802.16 MAC -- Highlights

• WirelessMAN Point-to-Multipoint and optional
  mesh topology
• Connection-oriented
• Multiple Access DL TDM TDMA, UL TDMAUL OFDMA
  TDMA, DL OFDMA TDMA (Optional)
• PHY considerations that affect the MAC
• Duplex TDD, FDD, FDX FDD BS and SS, HDX FDD SS
• Adaptive burst profiles (Modulation and FEC) on
  both DL and UL
• Protocol-independent core (ATM, IP, Ethernet)
• Flexible QoS offering (CBR, rt-VBR, nrt-VBR, BE)
• Strong security support

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Reference Model
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Adaptive PHY
Source Understanding WiMAX and 3G for
Portable/Mobile Broadband Wireless, Technical
White Paper, Intel.
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Adaptive Burst Profiles

• Burst profile Modulation and FEC
• On DL, multiple SSs can associate the same DL
  burst
• On UL, SS transmits in an given time slot with a
  specific burst
• Dynamically assigned according to link conditions
• Burst by burst
• Trade-off capacity vs. robustness in real time

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Duplex Scheme Support

• The duplex scheme is Usually specified by
  regulatory bodies, e.g., FCC
• Time-Division Duplex (TDD)
• Downlink Uplink time share the same RF channel
• Dynamic asymmetry
• does not transmit receive simultaneously (low
  cost)
• Frequency-Division Duplex (FDD)
• Downlink Uplink on separate RF channels
• Full Duplexing (FDX) can Tx and Rx
  simultaneously
• Half-duplexing (HDX) SSs supported (low cost)

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IEEE 802.16 MAC OFDM PHY TDD Frame Structure
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IEEE 802.16 MAC OFDM PHY FDD Frame Structure
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FDD MAPs Time Relevance
DL MAP
UL MAP
DL MAP
UL MAP
DOWNLINK
UPLINK
frame
Broadcast
Half Duplex T
erminal 1
Full Duplex Capable User
Half Duplex T
erminal 2
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IEEE 802.16 MAC addressing and Identifiers

• SS has 48-bit IEEE MAC address
• BS has 48-bit base station ID
• Not a MAC address
• 24-bit operator indicator
• 16-bit connection ID (CID)
• 32-bit service flow ID (SFID)
• 16-bit security association ID (SAID)

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IEEE 802.16 MAC Convergence Sub-Layer (CS)

• ATM Convergence Sub-Layer
• Support for VP/VC switched connections
• Support for end-to-end signaling of dynamically
  created connections
• ATM header suppression
• Full QoS support
• Packet Convergence Sub-Layer
• Initial support for Ethernet, VLAN, IPv4, and
  IPv6
• Payload header suppression
• Full QoS support

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IEEE 802.16 MAC -- CS Packet Convergence
Sub-Layer

• Functions
• Classification mapping the higher layer PDUs
  (Protocol Data Units) into appropriate MAC
  connections
• Payload header suppression (optional)
• MAC SDU (Service Data Unit), i.e, CS PDU,
  formatting

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IEEE 802.16 MAC -- CPS MAC PDU Format
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IEEE 802.16 MAC -- CPS-- Three Types of MAC PDUs

• Data MAC PDUs
• HT 0
• Payloads are MAC SDUs/segments, i.e., data from
  upper layer (CS PDUs)
• Transmitted on data connections
• Management MAC PDUs
• HT 0
• Payloads are MAC management messages or IP
  packets encapsulated in MAC CS PDUs
• Transmitted on management connections
• BW Req. MAC PDUs
• HT 1 and no payload, i.e., just a Header

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IEEE 802.16 MAC -- CPS Data Packet
Encapsulations
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IEEE 802.16 MAC CPS-- MAC Management
Connections

• Each SS has 3 management connections in each
  direction
• Basic Connection
• short and time-urgent MAC management messages
• MAC mgmt messages as MAC PDU payloads
• Primary Management connection
• longer and more delay tolerant MAC mgmt messages
• MAC mgmt messages as MAC PDU payloads
• Secondary Management Connection
• Standard based mgmt messages, e.g., DHCP, SNMP,
  etc
• IP packets based CS PDU as MAC PDU payload

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IEEE 802.16 MAC CPS MAC Management Messages

• MAC mgmt message format

• MAC mgmt msg can be sent on Basic connections
  Primary mgmt connection Broadcast connection
  and initial ranging connections
• 41 MAC mgmt msgs specified in 802.16
• The TLV (type/length/value) encoding scheme is
  used in MAC mgmt msg, e.g., in UCD msg for UL
  burst profiles,
• (type1, length1, value1) ? QPSK modulation
• (type1, length1, value2) ? 16QAM modulation
• (type1, length1, value3) ? 64QAM modulation

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IEEE 802.16 MAC CPS MAC PDU Transmission

• MAC PDUs are transmitted in PHY Bursts
• The PHY burst can contain multiple FEC blocks
• MAC PDUs may span FEC block boundaries
• Concatenation
• Packing
• Segmentation
• Sub-headers

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IEEE 802.16 MAC CPS MAC PDU Concatenation
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IEEE 802.16 MAC CPS MAC PDU Fragmentation
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IEEE 802.16 MAC CPS MAC PDU Packing
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IEEE 802.16 MAC CPS QoS

• Three components of 802.16 QoS
• Service flow QoS scheduling
• Dynamic service establishment
• Two-phase activation model (admit first, then
  activate)
• Service Flow
• A unidirectional MAC-layer transport service
  characterized by a set of QoS parameters, e.g.,
  latency, jitter, and throughput assurances
• Identified by a 32-bit SFID (Service Flow ID)
• Three types of service flows
• Provisioned controlled by network management
  system
• Admitted the required resources reserved by BS,
  but not active
• Active the required resources committed by the
  BS

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IEEE 802.16 MAC CPS Uplink Service Classes

• UGS Unsolicited Grant Services
• rtPS Real-time Polling Services
• nrtPS Non-real-time Polling Services
• BE Best Effort

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IEEE 802.16 MAC CPS Uplink Services UGS

• UGS Unsolicited Grant Services
• For CBR or CBR-like services, e.g., T1/E1.
• The BS scheduler offers fixed size UL BW grants
  on a real-time periodic basis.
• The SS does not need to send any explicit UL BW
  req.

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IEEE 802.16 MAC CPS Uplink Services rtPS

• rtPS Real-time Polling Services
• For rt-VBR-like services, e.g., MPEG video.
• The BS scheduler offers real-time, periodic, UL
  BW request opportunities.
• The SS uses the offered UL BW req. opportunity to
  specify the desired UL BW grant.
• The SS cannot use contention-based BW req.

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IEEE 802.16 MAC CPS Uplink Services nrtPS

• nrtPS non-real-time polling services
• For nrt-VBR-like services, such as,
  bandwidth-intensive file transfer.
• The BS scheduler shall provide timely (on a order
  of a second or less) UL BW request opportunities.
• The SS can use contention-based BW req.
  opportunities to send BW req.

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IEEE 802.16 MAC CPS Uplink Services BE

• BE Best Effort
• For best-effort traffic, e.g., HTTP, SMTP.
• The SS uses the contention-based BW request
  opportunities.

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IEEE 802.16 MAC CPS Bandwidth Grant

• BW grants are per Subscriber Station
• Allows real-time reaction to QoS need, i.e., SS
  may re-distribute bandwidth among its
  connections, maintaining QoS and service-level
  agreements
• Lower overhead, i.e., less UL-MAP entries compare
  to grant per connection
• Off- loading base stations work
• Requires intelligent subscriber station to
  redistribute the allocated BW among connections

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IEEE 802.16 MAC CPS BW Request/Grant
Mechanisms

• Implicit requests (UGS) No actual requests
• BW request messages, i.e., BW req. header
• Sends in either a contention-based BW req. slot
  or a regular UL allocation for the SShe special
  B
• Requests up to 32 KB with a single message
  Request
• Incremental or aggregate, as indicated by MAC
  header
• Piggybacked request (for non-UGS services only)
• Presented in Grant Management (GM) sub-header in
  a data MAC PDU of the same UL connection
• is always incremental
• Up to 32 KB per request for the CID
• Poll-Me bit
• Presented in the GM sub-header on a UGS
  connection
• request a bandwidth req. opportunity for non-UGS
  services

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IEEE 802.16 MAC CPS -- Contention UL Access

• Two types of Contention based UL slots
• Initial Ranging
• Used for new SS to join the system
• Requires a long preamble
• BW Request
• Used for sending BW req
• Short preamble
• Collision Detection and Resolution
• Detection SS does not get the expected response
  in a given time
• Resolution a truncated binary exponential
  backoff window

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IEEE 802.16 MAC CPS UL Sub-Frame Structure
Source http//www.cygnuscom.com/pdf/WP_PN_Article
.pdf
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IEEE 802.16 MAC CPS Ranging

• Ranging is a process of acquiring the correct
  timing offset, and PHY parameters, such as, Tx
  power level, frequency offset, etc. so that the
  SS can communicate with the BS correctly.
• BS performs measurements and feedback.
• SS performs necessary adjustments.
• Two types of Ranging
• Initial ranging for a new SS to join the system
• Periodic ranging (also called maintenance
  ranging) dynamically maintain a good RF link.

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IEEE 802.16 MAC CPS Automatic Repeat reQuest
(ARQ)

• A Layer-2 sliding-window based flow control
  mechanism.
• Per connection basis.
• Only effective to non-real-time applications.
• Uses a 11-bit sequence number field.
• Uses CRC-32 checksum of MAC PDU to check data
  errors.
• Maintain the same fragmentation structure for
  Retransmission.
• Optional.

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IEEE 802.16 MAC Privacy Sub-layer (PS)

• Two Major Functions
• Secures over-the-air transmissions
• Protects from theft of service
• Two component protocols
• Data encryption protocol
• A client/server model based Key management
  protocol (Privacy Key Management, or PKM)

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IEEE 802.16 MAC PS -- Security Associations

• A set of privacy information, e.g., encryption
  keys, used encryption algorithm
• Three types of Security Associations (SAs)
• Primary SA established during initial
  registration
• Static SA provisioned within the BS
• Dynamic SA dynamically created on the fly
• Identified by a 16-bit SAID
• Connections are mapped to SAs

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IEEE 802.16 MAC PS -- Multi-level Keys and
Their Usage

• Public Key
• Contained in X.509 digital certificate
• Issued by SS manufacturers
• Used to encrypt AK
• Authorization Key (AK)
• Provided by BS to SS at authorization
• Used to derive KEK
• Key Encryption Key (KEK)
• Derived from AK
• Used to encrypt TEK
• Traffic Encryption Key (TEK)
• Provided by BS to SS at key exchange
• Used to encrypt traffic data payload

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IEEE 802.16 MAC PS -- Data Encryption

• Use DES (Data Encryption Standard) in CBC (Cipher
  Block Chaining) mode with IV (Initialization
  Vector).
• CBC IV is calculated from
• IV parameter in TEK keying info and
• PHY synchronization field in DL-MAP.
• Only MAC PDU payload (including sub-headers) is
  encrypted.
• MAC PDU headers are unencrypted.
• Management messages are unencrypted.

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IEEE 802.16 MAC one big item is out of scope

• Scheduler

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• Questions ??

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References

• IEEE802.16-2004
• Alcatel White Paper WiMAX, making ubiquitous
  high-speed data services a reality
• Intel White Paper Understanding WiMAX and 3G for
  Portable/Mobile Broadband Wireless
• WiMAX Forum www.wimaxforum.com
• http//en.wikipedia.org/wiki/WiMax

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IEEE 802.16 MAC commonly used terms

• BS Base Station
• SS Subscriber Station, (i.e., CPE)
• DL Downlink, i.e. from BS to SS
• UL Uplink, i.e. from SS to BS
• FDD Frequency Division Duplex
• TDD Time Division Duplex
• TDMA Time Division Multiple Access
• TDM Time Division Multiplexing
• OFDM Orthogonal Frequency Division Multiplexing
• OFDMA - Orthogonal Frequency Division Multiple
  Access
• QoS Quality of Service