Advances in Wireless Networks: IEEE 802.16(WiMAX)

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Advances in Wireless NetworksIEEE 802.16(WiMAX)

• Vinh Do
• Comp 529
• California State University of Northridge

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Outline

• Background
• IEEE 802.15 PAN
• IEEE 802.11 Wireless LANs
• 802.11 last-mile network
• Mesh network
• IEEE 802.16
• -Standards
• -Physical layer
• -MAC layer
• IEEE 802.20(proposed)

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Elements of a wireless network
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Elements of a wireless network
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Elements of a wireless network

• wireless link
• typically used to connect mobile(s) to base
  station
• also used as backbone link
• multiple access protocol coordinates link access
• various data rates, transmission distance

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Characteristics of selected wireless link
standards
54 Mbps
802.11a,g
5-11 Mbps
.11 p-to-p link
802.11b
1 Mbps
802.15
3G
384 Kbps
UMTS/WCDMA, CDMA2000
2G
56 Kbps
IS-95 CDMA, GSM
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Elements of a wireless network

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Elements of a wireless network

• Ad hoc mode
• no base stations
• nodes can only transmit to other nodes within
  link coverage
• nodes organize themselves into a network route
  among themselves

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Wireless Link Characteristics

• Differences from wired link .
• decreased signal strength radio signal
  attenuates as it propagates through matter (path
  loss)
• interference from other sources standardized
  wireless network frequencies (e.g., 2.4 GHz)
  shared by other devices (e.g., phone) devices
  (motors) interfere as well
• multipath propagation radio signal reflects off
  objects ground, arriving ad destination at
  slightly different times
• . make communication across (even a point to
  point) wireless link much more difficult

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Wireless network characteristics

• Multiple wireless senders and receivers create
  additional problems (beyond multiple access)

• Hidden terminal problem
• B, A hear each other
• B, C hear each other
• A, C can not hear each other
• means A, C unaware of their interference at B

• Signal fading
• B, A hear each other
• B, C hear each other
• A, C can not hear each other interferring at B

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802.15 personal area network(PAN)

• replacement for cables (mouse, keyboard,
  headphones)
• ad hoc no infrastructure
• master/slaves
• slaves request permission to send (to master)
• less than 10 m diameter
• master grants requests
• 802.15 evolved from Bluetooth specification
• 2.4-2.5 GHz radio band
• up to 721 kbps

radius of coverage
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IEEE 802.11 Wireless LAN

• 802.11b
• 2.4-5 GHz unlicensed radio spectrum
• up to 11 Mbps
• direct sequence spread spectrum (DSSS) in
  physical layer
• all hosts use the same chipping code
• widely deployed, using base stations

• 802.11a
• 5-6 GHz range
• up to 54 Mbps
• Orthogonal frequency division multiplexing(OFDM)
• 802.11g
• 2.4-5 GHz range
• up to 54 Mbps
• Orthogonal frequency division multiplexing(OFDM)
• All use CSMA/CA for multiple access
• All have base-station and ad-hoc network versions

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Wi-Fi with directional antennas
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Wi-Fi with directional antennas

• Increase range of 802.11
• Fixed access/ Last mile usage-802.11 with high
  speed antennas
• 802.11g is often selected
• -speed
• -ability to handle interference(OFDM)
• -interoperability with 802.11b-based devices
• Limitation
• -efficiency of the network decreases as the
  number of users on 802.11
• increases due to the overhead of managing
  additional subscriber
• -CSMA/CA contributed to network traffic

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802.11 Mesh network as MANs

• Interconnect 802.11x based nodes by wireless
  802.11 links
• 802.11a standard commonly used in AP to AP links
  (performance and non-chanel overlapped with
  802.11b/g)
• Properties
• 2.4GHz or 5 GHz unlicensed spectrum
• up to 54 Mbps
• Portable access
• Automatic learn and maintain dynamic path
  configuration
• Small nodes act as a simple router
• Connection is shared across nodes
• Based on propriety solutions
• May provide VoIP and QoS
• Coverage range can be over 10km
• Performance up to 100Mbps
• Better suited to blanket large areas with 802.11
  access

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Mesh network topology
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802.11 Mesh network(Cont.)

• Advantages over single hop and directional
  last-mile alternatives
• Robustness and resiliency
• The shorter transmission range limit interference
  allowing simultaneously, spatially separated data
  flows

• Benefits
• Lower costs to the operator due to product
  availability
• Balanced traffic
• Flexibility over wired installations can be
  achieved

• Limitations
• A large subscriber base is needed to cover large
  areas
• Using omni-directional antennas produces noise
  into network
• Shared bandwidth more users translate into less
  banwidth
• Latency latency increases with every hop
• Lack of standardization leads to unavailability
  of QoS.

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IEEE 802.16 standards

• 802.16.1
• 10-66GHz unlicensed band
• LOS
• Up to 134Mbps
• 802.16.2 minimizing interference between
  coexisting WMANs
• 802.16-2004 (replace 802.16a/REVd)
• 2.5GHz, 3.5GHz licensed bands
• 5.8GHz licensed exempt band
• NLOS
• up to 75 Mbps
• Fixed end point
• 3 to 5 miles Maximum range 30 miles based on
  tower height, antenna gain and transmit power.

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IEEE 802.16 standards(Cont.)

• 802.16e
• 2-6 GHz license band
• NLOS
• up to 15 Mbps
• Mobility, regional roaming
• Support mobile user traveling at speeds up to 95
  miles/hr
• 1 to 3 miles
• Interoperability
• Built in QoS
• High performance
• Smart antennas
• Intelligent APs to monitor traffic

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Point to Multipoint Wireless MAN

• Base Station(BS) connected to public networks
• BS serves Subscriber Stations(SSs)
• SS typically serves a building(business or
  residence)
• Provide SS with first-mile access to public
  networks
• Multiple services with different QoS
• Compare to a wireless LAN
• Many more users
• Multimedia QoS
• Longer distance
• Higher data rate

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WIMAX network topology(fixed endpoints)
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WIMAX backhaul for a Wi-Fi mesh topology
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WIMAX as an intra mesh backhaul option
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WIMAX as a client connection option
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IEEE 802.16 standards
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Physical layer characteristics

• Line of sight(LOS)- because of 10-66GHz
• Broadband chanels
• Wide channels(20,25 or 28 MHz)
• High capacity(down and up links)
• Multiple Access
• TDM/TDMA
• High rate burst modems
• Adaptive burst profile on both uplink and
  downlink
• Multiple duplex schemes
• Time division Duplex (TDD)
• Frequency division duplex (FDD)-including burst
  FDD
• Support for half duplex terminals
• Adaptive modulation
• QPSK, QAM16, QAM64

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Adaptive Modulation

• Allow a wireless system to choose the higher
  modulation depending on the channel conditions
• Lower modulation(QPSK) for higher range
• Higher modulation(QAM) for lower range(increase
  throughput)

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Baud Rate and Channel Size(10-66 GHz)

• Flexible plan--allowing manufacturers to choose
  according to spectrum requirements

QPSK Bit Rate (Mbits/s) 32 40 44.8
16-QAM Bit Rate (Mbits/s) 64 80 89.6
64-QAM Bit Rate (Mbits/s) 96 120 134.4
Channel Width (MHz) 20 25 28
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Adaptive Burst profile

• Burst profile
• Modulation
• Reed Solomon FEC(forward error correction)
• to recover error frame lost due to frequency
  selective fading or burst error
• Automatic repeat request (ARQ) is used to correct
  errors that can not be corrected by FEC
• Dynamically assigned according to link conditions
• Burst by burst, per subscriber station
• Trade-off capacity vs robustness in real time
• Roughly double capacity for the same cell area
• Burst profile for downlink channel is well known
  and robust
• Up to 12 burst profiles can be defined
• The parameters of each are communicated to the
  SSs via MAC messages during the frame control
  section of the downlink frame

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Duplex scheme

• The downlink channel is time division
  multiplex(TDM)
• Information for each SS multiplexed onto a single
  stream of data and received by all SSs within the
  same sector
• The uplink is time division multiple access(TDMA)
• Channel is divided into a number of time slots
  which are assigned various uses(registration,
  user traffic)
• Frequency division duplex(FDD)
• DL and UL on the separate RF channel
• Support half-duplex SSs (SS does not
  transmit/receive simultaneously)
• Time division duplex(TDD)
• DL and UL time-shared the same RF channel
• SS does not transmit/receive simultaneously

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TDD Frame(10-66GHz)
Frame duration .5ms, 1ms, 2ms Physical slot(PS)
4 QAM symbols(1QAM symbol 4bits)
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TDD downlink subframe

• DIUC Downlink interval usage code
• Tr/Rx gap between the downlink burst and
  subsequent uplink bust
• Allows time for the BS to switch from transmit to
  receive mode and SSs to switch from receive to
  transmit mode

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FDD framing

• Example of FDD bandwidth allocation

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FDD downlink subframe

• TDMA portion transmit data to some half-duplex
  SSs(the ones scheduled to transmit earlier in the
  frame than they receive)
• -Need preamble to re-sync(carrier phase)

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Uplink subframe
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Uplink subframe descriptions

• Initial maintenance opportunities
• Ranging
• To determine network delay or to request power or
  profile change
• Collisions may occur in this interval
• Request contention opps
• SSs request bandwith in response to polling from
  BS.
• Collisions may occur in this interval
• Schedule data
• SSs transmit data bursts in the intervals granted
  by the BS
• Transition gaps between data intervals for
  synchronization purposes.

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MAC Layer

• Designed for Point-to-multipoint broadband
  wireless access apps
• Support difficult user environments
• High bandwidth, hundreds of user per channel
• Continuous and burst traffic
• Very efficient use of spectrum
• Protocol independent core
• ATM, IP, Ethernet,
• Flexible QoS offerings
• Best Effort(BF), rt-VBR,nrt-VBR, ATM CBR
• Security
• Support PHY alternatives
• Adaptive mod, TDD/FDD, single-carrier, OFDM/OFDMA

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Service-specific convergence sublayers

• ATM convergent sublayer defined for ATM services
• Packet convergent sublayer
• Defined for mapping services such as IPv4, IPv6,
  Ethernet
• Preserve or enable QoS
• Enable bandwidth allocation
• Classify service data units(SDUs) to the proper
  MAC connection

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MAC addressing

• SS has 48bits IEEE MAC address
• Use mainly as equipment id
• 16-bit Connection ID(CID)
• Used in MAC PDUs

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MAC PDU format

• The Generic MAC header has fixed format
• One or more MAC sub-headers may be part of the
  payload
• The presence of sub-headers is indicated by a
  Type field in the Generic MAC header

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Generic MAC header

• LEN PDU length in bytes(2048 max) HT header
  Type Type subheader,
• CID Connection ID
  EC Encryption Control HCS Header
  Check
• EKS Encryption Key Sequence CI CRC
  indicator Sequence

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MAC PDU Transmission

• MAC PDUs are transmitted in PHY burst
• A single burst can contain multiple Concatenated
  MAC PDUs
• The PHY burst can contain multiple FEC blocks
• MAC PDUs may span FEC block boundaries
• The TC(Transmission convergence) layer between
  the MAC and PHY allows for capturing the start of
  the next MAC PDU in case of erroneous FEC blocks

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Downlink Transmissions

• Two kinds of bursts TDM and TDMA
• TDMA bursts have resync preamble
• Each terminal listens to all bursts at its
  operational IUC or a more robust one
• Each burst may contain data for several terminals
• SS must recognize the PDUs with known CIDs
• DL-MAP message signals downlink usage

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Burst profiles

• Each burst profile has mandatory exit threshold
  and minimum entry threshold
• SS allowed to request a less robust DIUC once
  above the minimum entry level
• SS must request fall back to more robust DIUC
  once at mandatory exit threshold
• Requests to change DIUC done with Downlink burst
  profile change REQ(DBPC-REQ) or RNG-REG messages

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Transition to more robust burst profile
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Transition to less robust burst profile
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Uplink Transmissions

• Transmissions in contention slots
• Bandwidth requests
• Contention resolved using truncated exponential
  backoff
• Transmissions in initial ranging slots
• Ranging requests(RNG-REQ)
• Contention resolved using truncated exponential
  backoff
• Bursts defined by UIUCs
• Transmissions allocated by the UL-MAP message
• All transmissions have synchronization preamble

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Uplink Services

• Unsolicited Grant Services (UGS)
• Used for constant-bit-rate (CBR) service flows
  (SFs)
• Best Effort (BE)
• For best-effort traffic
• Real time Polling Services (rtPS)
• For rt-VBR SFs such as MEPEG video
• None Real time Polling Services (nrtPS)
• For nrt SFs with better than BE service such as
  bandwidth-intensive file transfer

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Request/Grant scheme

• Bandwidth Requests are always per Connection
• Self Correcting
• No acknowledgement
• Grants are either per Connection (GPC) or per SS
  (GPSS)
• Grants (given as durations) are carried in the
  UL-MAP messages
• SS needs to convert the time(durations) to amount
  of data using information about the UIUC
• Bandwidth Grant per Subscriber Station (GPSS)
• BS grants bandwidth to the SS
• SS may re-distribute bandwidth among its
  connections
• Suitable for many connections per terminal
• Low overhead but requires intelligent SS
• Bandwidth Grant per Connection (GPC)
• BS grants bandwidth to a connection
• Mostly suitable for few users per SS
• High overhead, but allows simpler SS

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Bandwidth Requests

• Come from the Connection
• Implicit requests (UGS)
• No actual messages, negotiated at connection
  setup
• BW request messages
• Uses special BW request header
• Requests up to 32 KB with a single message

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Maintaining QoS in GPSS

• BS sees the requests for each connection based
  on this, grants bandwidth to the SSs (maintaining
  QoS and fairness)
• SS scheduler maintains QoS among its connections
  and is responsible to share the BW among the
  connections (maintaining QoS and fairness)
• Algorithm in BS and SS can be very different

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SS Initialization

• Channel Acquisition
• Scan frequency list to find an operation channel
• Establish synchronization with the BS
• Obtains the modulation and FEC schemes used on
  the carrier via Uplink Channel Description (UDC)
• Perform ranging and Capabilities Negotiation
• SS send a RNG_REQ in the ranging window
• BS measures arrival time and signal power
  calculates timing advance and power adjustment
• BS send adjustment in RNG-RSP
• SS adjusts timing advance and power sends new
  RNG-REQ
• Continue until power and timing is ok
• Authorize SS and perform key exchange

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SS Initialization(Cont.)

• Perform registration
• SS send a list of capabilities and parts of the
  configuration file to the BS in the REG-REG
  message
• BS replies with the REG-RSP message(indicates
  with capabilities are supported/allowed
• SS acknowledges the REG-RSP with REG-ACK message
• Establish ID connectivity (via DHCP)
• Set up connections
• BS passes Service Flow Encodings to the SS in
  multiple Dynamic Service Addition Request
  (DSA-REQ) messages
• SS replies with DSA-RSP messages
• Service Flow Encodings contain either
• Full definition of service attributes
• Service class name (ASCII string which is known
  at the BS and which indirectly specifies a set of
  QoS parameters such as jitter and latency)

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SS Authentication and Registration

• Trust relation assumed between equipment
  manufacturer and network operator
• Each SS contains both the manufacturers X.509
  certificate and the the manufacturers
  certificate.
• SS sent both certificates to the BS in the
  Authorization Request and Authentication
  Information messages
• BS verifies the identity of the SS by checking
  the certificates and level of authentication of
  the SS
• BS response with an Authorization Reply
  containing the Authorization key (AK) encrypted
  with the SSs public key if the SS is authorized
  to join the network
• The SS registers with the network upon successful
  authorization

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Privacy and Encryption

• Secures over-the-air transmissions
• Protocol based on Privacy Key Management (PKM)
  from DOCSIS(Data over Cable Service Interface
  Specification)
• Designed to allow new/multiple encryption
  algorithms
• Data encryption
• Currently 56-DES (Data Encryption Standards) in
  CBC (cipher block chaining) mode
• Initialization Vector (IV) based on frame number
• Authentication
• X.509 certificates with RSA public key encryption
• Strong authentication of SSs (prevents theft of
  service)
• Prevents cloning
• Message authentication
• Most important MAC management messages
  authenticated with one-way hashing using Hashed
  Message Authentication Code(HMAC) with SHA-1

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Security Associations

• A set of privacy information
• Shared by a BS and one or more of its client SSs
  in order to support secured communications
• Includes Traffic Encryption Keys (TEKs) and CBC
  IVs
• Security Association Establishment
• Primary SA established during initial
  registration
• Other SAs may be provisioned or dynamically
  created within the BS

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IEEE 802.20 Wireless WANs( proposed)

• Similar to 802.16e, 3G
• Mobility, regional roaming
• Differences
• lt 3.5 GHz
• Cell ranges up to 8 miles
• Support mobile user traveling at speeds up to
  155miles/hr

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References

1. IEEE Standard 802.16 A Technical Overview of the
   WirelessMAN Air Interface for Broadband Wireless
   Access
2. IEEE 802.16-2001, IEEE Standard for local and
   Metropolitan Area NetworksPart 16 Air Interface
   for Fixed Broadband Wireless Access Systems
3. WiMAX The Critical Wireless Standard, Carolyn
   Gabriel
4. Understanding Wi-Fi and WiMAX as Metro-Access
   Solutions,
5. 802.16 A Look Under the Hood by Beth Cohen and
   Debbie Deutsch (www.wi-fiplanet.com)
6. WiMAX Anticlimax by Andy Dornan
   (www.networkmagazine.com)