MAC Layer Part II TDMA and Polling

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MAC Layer Part II TDMA and Polling
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Cluster Network Architecture (UCLA-WAM
IS)

• Concept
• create a cluster based TDM infrastructure which
• (a) enables guaranteed bandwidth for voice/video
• (b) can support instant deployment and mobility
• Approach
• distributed clustering algorithm
• time division slotting within each cluster
• slot reservation for real time traffic
• virtual circuits for real traffic datagrams
  for data
• code separation across clusters
• slot synchronization
• Combines cellular radio and traditional packet
  radio features.

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Lowest-ID cluster-head election
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2
10
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1
6
9
3
4
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Distributed Cluster algorithm (lowest-ID)

• Each node is assigned a distinct ID.
• Periodically, the node broadcast the list of
  nodes that it can hear.
• ClusterHead hears only nodes with ID higher
  that itself (unless lower ID specifically gives
  up its role as CH) ? A,B,C
• Gateway hears two or more CHs ? G,H
• Ordinary node otherwise ?
• Properties
• No cluster heads are directly linked.
• In a cluster, any two nodes are at most two-hops
  away, since the CH is directly linked to any
  other node in the cluster.
• RE Emphremides, et al A Design Concept for
  Reliable Mobile Radio Networks with Frequency
  Hopping Signaling Proceedings of IEEE, Vol. 75,
  No.1, 1987

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Cluster network architecture

• Dynamic, distributed clustering alg. Partitions
  the system into cluster.
• Code separation among clusters.
• Local coordination provided within a cluster.
• Clusterheads act as local coordinator to
• resolve channel scheduling
• provide power measurement/control
• support virtual circuit setup for real time
  (voice and video) traffic
• maintain synchronization
• Dynamic adaptation (via periodic updates.)
• mobility
• failures
• Interference
• bandwidth requirements (B/W alloc.--TDMA slot
  assgn.)

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Channel Access
Within each cluster time-slotted frame

• Control Phase
• clustering algorithm
• routing
• power measurement and power
• code and slot assignment
• VC setup
• acknowledgments

• Data Phase
• voice/video (PRMA)
• data (Random Access)

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Virtual Circuit support in WAMIS

• Multimedia Traffic (eg, voice, video)
• connection oriented
• QoS based admission control
• VC based bandwidth allocation
• We need
• robust, QoS enabled routing
• elastic, reconfigurable VCs

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VC reconfiguration in Mobile Environment

• Conventional VC setup does not work (path breaks
  up too frequently)
• Proposed approach Fast Reservations, like in
  PRMA (Packet Reservation Multi Access)

• Packet follow shortest path
• First packet reserves the slot(s) along the path
• When path changes, first packet competes again
  for slots on new path (voice/video rate reduced
  by low priority pkt drop)
• If no path, packet is dropped
• reservation released if slot is unused

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Case study compare Random Access and TDMA in
Multimedia

• C. Richard Lin and Mario Gerla
• Computer Science Department
• University of California, Los Angeles

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CSMA DARPA PRNET (1970s)

• Single channel
• Spatial reuse
• CSMA
• Implicit ACK (echo ACK)
• Retransmission (for datagrams only)
• Duct routing (for voice traffic)
• Based on Bellman-Ford routing
• Alternate routing multiple paths used to carry
  multiple copies of a real-time packet to improve
  reliability
• Carrier sense will limit the fan-out

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• Limitation of PRNET
• no bandwidth reservations no access control (for
  voice)
• hidden terminal problem
• Enter Cluster TDMA (1994)
• different codes in each cluster
• TDMA type MAC access in each cluster
• QoS routing bdw reservation access control
• Fast VC set up (soft state)

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• Problems of CLUSTER TDMA cost and complexity
• global slot synchronization
• multiple codes
• initialization
• Enter MACA/PR (1996)
• (Multiple Access Collision Avoidance/Packet
  Reservations)
• no clustering single code easy initialization
• RTS/CTS dialog(to prevent hidden terminal
  problems)
• Packet Reservations (to support real time
  traffic)
• QoS routingp standby routs (for dynamic
  rerouting)

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MACA/PR (contd)
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Real Time Traffic Support Bandwidth Reservation

• 1st packet is treated as a datagram packet
• After successfully transmitting piggyback
  reservation is honored for subsequent packets
• Bounded delay and no collision
• Real -time Traffic and datagram traffic are
  interleaved (with datagram deferring to real-time
  traffic)

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Performance Comparison (parameters)

• A 100X100 feet area
• Number of radio station20
• Frame size 100ms
• Tx range 40 feet
• VC end-to-end hop distance3
• Maximum speed8 feet/sec
• Data rate800kbps
• Pkt size4kbits pkt acquisition500bits
• Multiple VCs,datagram background traffic
• Tx rate 1pkt/frame
• Call duration180 seconds.

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Performance Comparison of Various Schemes
Synchronous
Asynchronous
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Overall Performance Comparison

• PRNET
• No bandwidth reservation
• No acceptance control
• In heavy load duct routing generates excessive
  number of
• requests for alternate routes ( congestion)
• MACA/PR
• total VC throughput limited by lack of
  cluster/code separation
• Cluster TOKEN and TDMA
• high end to end delay due to token/TDMA latency

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Channel Propagation Models

• Radio channel propagation is characterized by
  three main parameters
• Attenuation free space loss, absorption by
  foliage, partitions
• Shadowing obstacles between transmitter and
  receiver
• Multipath due to the different phases on
  different paths

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Simulator MAISIE Channel Model

• Channel Fading Model in Maisie Simulator
• the Simulator utilizes the SIRCIM impulse
  response parameters to characterize the radio
  propagation model, i.e. multipath, shadowing
  effect, spatial correlation

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Radio Channel Simulation
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VC Performance free space vs fading model
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More MAC Layer protocols

• Bluetooth Piconet a polling/TDMA scheme
• HomeRF a hybrid random access and TDMA scheme
• Hiperlan2 a connection oriented, TDMA on demand
  scheme

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More TDM type MAC Layer protocols

• Bluetooth Piconet a polling/TDMA scheme
• HomeRF a hybrid random access and TDMA scheme
• Hiperlan2 a connection oriented, TDMA on demand
  scheme

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What does Bluetooth do for you?
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Example...
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Bluetooth Piconet

• Page - scan protocol
• to establish links with nodes in proximity

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Piconet MAC protocol Polling
FH/TDD
f1
f3
f4
f5
f2
f6
m
s1
s2
625 ?sec
1600 hops/sec
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Multi slot packets
FH/TDD
f1
f4
f5
f6
m
s1
s2
625 µsec
Data rate depends on type of packet
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Physical Link Types

• Synchronous Connection Oriented (SCO) Link
• slot reservation at fixed intervals

• Asynchronous Connection-less (ACL) Link
• Polling access method

m
s1
s2
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Home RF

• No new wires
• Simple to Install
• Easy to Use
• Low Cost 200 for 2 PCs
• Bandwidth To Support Common
• Home Applications
• Industry Standards

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HomeRF Working Group Mission Statement

• To enable the existence of a broad range of
  interoperable consumer devices, by establishing
  an open industry specification for unlicensed RF
  digital communications for PCs and consumer
  devices anywhere, in and around the home.

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Enabling the Vision
USB
Printer
Camera
Game Pad
1394
Stereo
Camcorder
VCR
TV
Multimedia (e.g. 1394)
HomePNA
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The SWAP Network
SWAP-CA Shared Wireless Access Protocol -
Cordless Access
Internet
USB
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HomeRF Origins
DECT Uses TDMA Good for Voice
802.11 Uses CSMA/CA Good for Data
SWAP TDMA CSMA/CA Good for Voice
Data Optimized for small networks (in
home) Simplified radio protocol to reduce cost
Both voice and data are important for home RF
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Device Types
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Hybrid MAC layer
SWAP Frame
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PHY Features

• Nominal 100 mW transmit power
• Minimum receiver sensitivity of -76 dBm (2FSK)
• range gt50 m in typical homes/yards
• -85 dBm sensitivity typical
• Cost effective filter requirements
• Use MAC to reduce PHY cost
• Makes single-chip integration simpler

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MAC Features

• MAC provides good support for voice and data
• Leverages existing DECT technology for voice
• Excellent integration with TCP/IP networking
  protocols
• easy integration with Ethernet
• Supports broadcast, multicast and fragmenting
• Data security - Basic/Enhanced levels of
  encryption
• Basic 24-bit Network ID and Frequency Hopping
• Enhanced Basic LFSR algorithm
• Extensive power management for ultra-portable
  devices

Optimizes existing technology for home use
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Voice Robust clarity
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Data transmission
Service Slot
B
D3
D4
D4
D2
D3
D1
Contention period
D2
D3
D1
Hop
Hop
CSMA/CA access mechanism
U4
U3
U2
U1
U3
U4
U3
U2
U1
Superframe - 20ms
CFP 2
CFP 1
Contention free periods

• CSMA/CA during the contention period
• Efficient for small networks
• Tolerant of interference
• Data for entire frame if no voice

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Hiperlan2

• 5 GHz technology, up to 54 Mbit/s
• Generic architecture supportingEthernet, IEEE
  1394, ATM, 3G etc
• Connection-oriented with QoS per conn.
• Security - authentication encryption
• Plug-and-play radio network using DFS
• Optimal throughput scheme

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H2GF - The vision
Local Area WLAN Datacom
Airport
Home
Hotel Conference
Roaming
Train station
Public space
Wide area Cellular Datacom
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HiperLAN2 Global Forum

• A consortium of 50 companies
• Launched September 1999
• Marketing and education
• Interoperability on system level
• Protect and harmonize spectrum worldwide
• http//www.hiperlan2.com

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H2GF - The Mission

• Drive the adoption of HiperLAN2 as the global
  broadband wireless technology in 5 GHz band,
  providing untethered connectivity for mobile
  devices in corporate, public and home environments

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When?

• Commercial products on market late 2001/early
  2002
• Interoperable products mid 2002
• Enterprise market first, soon followed by
  operator, and the home

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Key Goals

• H/2 will support all existing and planned
  applications in enterprise, public, and homegt
  address the combined WLAN market!
• Smooth interworking with 3G
• Affordable technology

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HiperLAN2 Technologies

• MAC scheduler at AP
• Centralised control
• Supports uniform traffic load
• Inter Intra system interference mitigation
• Dynamic Frequency Selection (DFS)
• Link Adaptation
• Transmit Power Control (TPC)
• Support of smart (sectored) AP antennas

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H/2 MAC Layer

• Access Point centralized control
• Time Division Duplex - TDMA
• Up and Down link slots allocated dynamically
  based on need
• Data (up/down) transmitted in dedicated slots
• Contention allowed in random access slots

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MAC Layer

MAC frame fixed duration 2ms BCH broadcast ch
(info on pwr levels, FCH RCH lengths, etc) FCH
Frame ctr ch (describes resource allocations in
this MAC frame) DL/UL user data trains (dn/up)
of multiple 54 byte payloads ACH access
feedback channel feedback on previous RCH
attempts RCH random access ch to request MAC
resources (high priority Res Requests for UL/DL
allocation, low pr RRs to initiate handover)
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MAC Layer (cont)

• Logical channels built on top of MAC channels
• SBCH slow broad ch, dwnlk only, coveys contr
  signals (eg MAC-ID assign, encrypt seed)
• DCCH Dedicated cntr ch, signaling between AP
  and MT(Mobile Terminal)
• UDCH User data channel ARQ optional
• Connection uniquely identified by MAC and DLC IDs
• Connection set up does not imply immediate
  resource assignment
• Capacity requested by MT on demand via RR packets

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Spectrum Allocation in 5 Ghz