IEEE 802.16

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IEEE 802.16
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Topics

• Introduction
• Physical Layer
• MAC Layer
• QoS

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• Introduction
• Physical Layer
• MAC Layer
• QoS

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• Goal Provide high-speed Internet access to home
  and business subscribers, without wires.
• Base stations (BS) can handle thousands of
  subscriber stations (SS)
• Access control prevents collisions.
• Supports
• Legacy voice systems
• Voice over IP
• TCP/IP-Applications with different QoS
  requirements.

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• 802.16 standards
• 802.16.1 (10-66 GHz, line-of-sight, up to
  134Mbit/s)
• 802.16.2 (minimizing interference
  between coexisting WMANs.)
• 802.16a (2-11 Ghz, Mesh, non-line-of-
  sigth)
• 802.16b (5-6 Ghz)
• 802.16c (detailed system profiles)
• P802.16e (Mobile Wireless MAN)

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• Introduction
• Physical Layer
• MAC Layer
• QoS

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• Adaptive Data Burst Profiles
• Transmission parameters (e.g. modulation and FEC
  settings) can be modified on a frame-by-frame
  basis for each SS.
• Profiles are identified by Interval Usage Code
  (Downlink Interval Usage Code (DIUC) and Uplink
  Interval Usage Code (UIUC).)

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• Using both
• TDM (Time Division Multiplexing) and
• TDMA (Time Division Multiple Access)
• What is the difference, you ask..
• TDM Time-Division Multiplexing (TDM) is a type
  of digital or (rarely) analog multiplexing in
  which two or more signals or bit streams are
  transferred apparently simultaneously as
  sub-channels in one communication channel, but
  physically are taking turns on the channel. The
  time domain is divided into several recurrent
  timeslots of fixed length, one for each
  sub-channel.
• TDMA Time division multiple access (TDMA) is a
  channel access method for shared medium (usually
  radio) networks. It allows several users to share
  the same frequency channel by dividing the signal
  into different timeslots. The users transmit in
  rapid succession, one after the other, each using
  his own timeslot. This allows multiple stations
  to share the same transmission medium (e.g. radio
  frequency channel) while using only the part of
  its bandwidth they require. TDMA is used in the
  digital 2G cellular systems such as Global System
  for Mobile Communications (GSM), IS-136, Personal
  Digital Cellular (PDC) and iDEN, and in the
  Digital Enhanced Cordless Telecommunications
  (DECT) standard for portable phones.

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• The main difference between tdm and tdma (also
  fdm/fdma, etc) is that with tdm (also fdm, etc.)
  the signals multiplexed (i.e. sharing a resource)
  come from the same node, whereas for tdma (also
  fdm, etc.) the signals multiplexed come from
  different sources/transmitters.

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Time Division Multiplexing (TDM) imply
partitioning the bandwidth of the channel
connecting two nodes into finite set of time
slots.
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Time Division multiple Access (TDMA) imply
partitioning the bandwidth of a channel shared by
many nodes, typically an infrastructure node and
several mobile nodes, where each node gets to
access its dedicated time slot.
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• Introduction
• Physical Layer
• MAC Layer
• QoS

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• Connection orienteded
• Connection ID (CID), Service Flows(FS)
• Channel access
• UL-MAP
• Defines uplink channel access
• Defines uplink data burst profiles
• DL-MAP
• Defines downlink data burst profiles
• UL-MAP and DL-MAP are both transmitted in the
  beginning of each downlink subframe (FDD and
  TDD).

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TDD Downlink subframe
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FDD Downlink subframe
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FDD burst framing
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Uplink subframe
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Upplink periods

• Initial Maintenance opportunities
• Ranging
• To determine network delay and to request power
  or profile changes.
• Collisions may occur in this interval
• Request opportunities
• SSs request bandwith in response to polling from
  BS.
• Collisions may occur in this interval aswell.
• Data grants period
• SSs transmit data bursts in the intervals granted
  by the BS.
• Transition gaps between data intervals for
  synchronization purposes.

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Bandwidth request and allocation

• SubscribersStations may request bw in 3 ways
• Use the contention request opportunities
  interval upon being polled by the BS (multicast
  or broadcast poll).
• Send a standalone MAC message called BW request
  in an allready granted slot.
• Piggyback a BW request message on a data packet.

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• BS grants/allocates bandwidth in one of two
  modes
• Grant Per Subscriber Station (GPSS)
• Grant Per Connection (GPC)
• Decision based on requested bw and QoS
  requirements vs available resources.
• Grants are realized through the UL-MAP.

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Unicast Polling

• BS allocates space for the SS in the uplink
  subframe.
• SS uses the allocated space to send a bw request.
• BS allocates the requested space for the SS (if
  available).
• SS uses allocated space to send data.

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4 types of Scheduling Service

• Unsolicited Grant Service (UGS)
• Real-time, periodic fixed size packets (e.g. T1
  or VoIP)
• Restrictions on bw requests (Poll-Me bit)
• Slip Indicator (SI)
• Real-Time Polling Service (rtPS)
• Real-time, periodic variable sizes packets (e.g
  MPEG)
• BS issues periodic unicast polls.
• Cannot use contention requests, but piggybacking
  is ok.
• Non-Real-Time Polling Service (nrtPS)
• Variable sized packets with loose delay
  requirements (e.g. FTP)
• BS issues unicast polls regularly (not
  necessarily periodic).
• Can also use contention requests and
  piggybacking.
• Best Effort Service
• Never polled individually
• Can use contention requests and piggybacking

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Scheduling types
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• Introduction
• Physical Layer
• MAC Layer
• QoS

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• The 802.16 standard specifies two modes for
  sharing the wireless medium
• point-to-multipoint (PMP) and
• mesh(optional).

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• PMP With PMP, the BS serves a set of SSs within
  the same antenna sector in a broadcast manner,
  with all SSs receiving the same transmission from
  the BS. Transmissions from SSs are directed to
  and centrally coordinated by the BS.
• Mesh Traffic can be routed through other SSs and
  can occur directly among SSs. Access coordination
  is distributed among the SSs.

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PMP MODE

• uplink (from SS to BS) and downlink (fromBS to
  SS) data transmissions occur in separate time
  frames.
• In the downlink sub-frame, the BS transmits a
  burst of MAC protocol data units (PDUs).
• In the uplink sub-frame, on the other hand, any
  SS transmits a burst of MAC PDUs to the BS in a
  time-division multiple access (TDMA) manner.

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• Downlink and uplink sub-frames are duplexed using
  one of the following techniques, as shown in
  above figure
• Frequency-division duplex(FDD) is where downlink
  and uplink sub-frames occur simultaneously on
  separate frequencies, and time-division duplex
  (TDD) is where downlink and uplink sub-frames
  occur at different times and usually share the
  same frequency. SSs can be either full duplex
  (i.e., they can transmit and receive
  simultaneously)or half-duplex (i.e., they can
  transmit and receive at nonoverlapping time
  intervals).

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• The MAC protocol is connection-oriented all data
  communications, for both transport and control,
  are in the context of a unidirectional
  connection.
• At the start of each frame, the BS schedules the
  uplink and downlink grants in order to meet the
  negotiated QoS requirements.
• Each SS learns the boundaries of its allocation
  within the current uplink sub-frame by decoding
  the UL-MAP message.
• The DL-MAP message contains the timetable of the
  downlink grants in the forthcoming downlink
  sub-frame. More specifically, downlink grants
  directed to SSs with the same DIUC are advertised
  by the DL-MAP as a single burst. Both maps are
  transmitted by the BS at the beginning of each
  downlink sub-frame.
• Above Figure 2 shows the blueprint of the
  functional entities for QoS support, which
  logically reside within the MAC layer of the BS
  and SSs.
• Each downlink connection has a packet queue (or
  queue, for short) at the BS (represented with
  solid lines).
• In accordance with the set of QoS parameters and
  the status of the queues, the BS downlink
  scheduler selects from the downlink queues,on a
  frame basis, the next service data units (SDUs)
  to be transmitted to SSs.