wireless lan overview
DESCRIPTION
Wireless LAN Overview. Sunggeun Jin 2005-10-17. Outline. IEEE802.16 MAC IEEE802.11 MAC. IEEE802.16 (a, e, Wibro). Original goal alternative to cabled access network to provide network access to buildings it came from DOCSIS spec. Amendments IEEE802.16a for fixed service subscribers - PowerPoint PPT PresentationTRANSCRIPT
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Wireless LAN OverviewWireless LAN Overview
Sunggeun Jin2005-10-17
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OutlineOutline
IEEE802.16 MAC IEEE802.11 MAC
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IEEE802.16 (a, e, Wibro)IEEE802.16 (a, e, Wibro)
Original goal alternative to cabled access network to provide network access to buildings it came from DOCSIS spec.
Amendments IEEE802.16a
for fixed service subscribers IEEE802.16e
for movable service subscribers Feature
FDD or TDD TDD as to Wibro
TDM, TDMA, OFDM, OFDMA OFDM/OFDMA for Wibro
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Protocol Layers of IEEE802.16Protocol Layers of IEEE802.16
-System Access-Bandwidth Allocation-Connection set-up -Connection maintenance- QoS
-Authentication-Secure key exchange-Encryption
-Transformation ofexternal network datainto MAC SDUs;
-Payload header suppression
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System operationsSystem operations
BS
SS trying to access to BS
SS performing periodic ranging
CD
Transmit Initial Ranging Code
Transmit Periodic Ranging Code
Transmit BW-Req. Code
Data transmission service
Requesting BW allocation
MAP
UL Data
DL Data
CD/MAP
• BS access inf.• Burst Profile• Power Control • BW allocations
• Frame Information
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Initial RangingInitial Ranging
BS
SS
Get sync.
SS
BS BS
SS
BS
SS
BS
SS
MAP
BS
SS
MAP
RNG-REQ(MAC_Address)
Adjustment of timing and frequency offset
CD/MAP
Transmit “Initial Ranging Code”
RNG-REQ (Code)
RNG-RSP(Success)
SS
BS
SS
BS BS
SS
RNG-RSP(Management CIDs)
RNG-REQ (Code)
Binary-exponential Random Backoff
Transmit RNG-REQ message with MAC Addr.
RNG-RSP (Management CIDs)
RNG-REQ (Code)
RNG-RSP(Continue)
timing and frequency offset adjustments obtaining management CID
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CIDsCIDs
Basic CID
Primary Management CID
Secondary Management CID
Transport CID1
Transport CID2
Management Connection Basic CID
Short, Urgent MAC Messages Primary Management CID
Longer, More Delay Tolerant MAC Messages
Secondary Management CID Delay Tolerant, Standard-Based
Management Messages E.g., : DHCP, TFTP, SNMP
Transport Connection Multiple CIDs exist BS assigns them to SS Data transmission
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MAP and frame structureMAP and frame structure
Preamble
MAP_Bursts#(N-1)**
Traffic Bursts #1
Traffic Bursts #5
Traffic Bursts #(M-1)
Traffic Bursts #3
L_0*
Traffic Bursts #4
SICH
Traffic Bursts #2
.
.
.
MAP_Bursts#1**
MAP_Bursts#0**
.
.
.
Traffic Bursts #1
Traffic Bursts #5
Traffic Bursts #(M-1)
Traffic Bursts
#3Traffic Bursts #4
Traffic Bursts #2
.
.
.
Ranging slot#0
.
.
.
Ranging slot#1
Ranging slot
#(N-1)
TTG
L_1*
L_(N-1)*
.
.
.
Frame in case of TDD
Frames in case of FDD
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IEEE802.11IEEE802.11
Application overview Wireless Ethernet with compatible speed Enable (indoor) wireless and mobile high-speed
networking Functional overview
Runs at unlicensed bands at 2.4GHz and 5GHz Connectionless MAC and multiple PHYs Supports up to 11 and/or 54 Mbps within >100
m range
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802.11 Reference Model802.11 Reference Model
MAC Sublayer
MAC Management Sublayer Entity
(MLME)
PHY Management Sublayer Entity
(PLME)
PLCP Sublayer
PMD Sublayer
Station Management
Entity(SME)
MAC SAP
PHY SAP
PMD SAP
MLME_PLME SAP
MLME SAP
PLME SAP
MAC
PHY
IEEE 802.2Logical Link Control
(LLC)
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Two ModesTwo Modes
Infrastructure mode Infrastructure Basic Service Set BSS An access point (AP) and multiple stations (STAs) Every transmission is with AP; no peer-to-peer communica
tion
Station 3
Access Point (AP)
Station 1
Station 2
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Two Modes cont.Two Modes cont.
Ad hoc mode Independent Basic Service Set IBSS Multiple stations (STAs), and no AP Peer-to-peer communication only
Station 3Station 1
Station 2
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Two Coordination FunctionsTwo Coordination Functions
Mandatory Distributed Coordination Function (DCF) For distributed contention-based channel access
Optional Point Coordination Function (PCF) For centralized contention-free channel access
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Distributed Coordination Function (DCF)Distributed Coordination Function (DCF)
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) similar to IEEE 802.3 Ethernet CSMA/CD
BusyMedium
SIFS
PIFS
DIFS
BackoffWindow
Slot Time
Defer Access Select Slot and decrement backoffas long as medium stays idle
DIFS
Contention WindowImmediate access whenmedium is idle >= DIFS
Next Frame
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Carrier-Sense MechanismsCarrier-Sense Mechanisms
Physical carrier-sense Provided by PHY, and depends on PHY Clear Channel Assessment (CCA) by PHY
Virtual carrier-sense Provided by MAC via Network Allocation Vector (NAV)
counter Each frame carries Duration value in the header Any correctly received frame updates NAV if the new
NAV is larger Assumes busy channel if non-zero NAV irrespective of
CCA!
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Stop-and-Wait ARQStop-and-Wait ARQ
Receiver of a directed frame returns an ACK If ACK not received, sender retransmits after another back-off
DATA
SIFS
DIFS
Backoff
DIFS
Next Frame
ACK
Source
Destination
Others
Defer Access Backoff after Defer
NAV
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ReferencesReferences
Carl Eklund and et al, “IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access,” IEEE Comm. Mag. Jun. 2002
IEEE802.11 tutorial material presented by Sunghyun Choi, Seoul Natl. Univ. IEEE802.16 tutorial material presented by Samsung IEEE802.16 tutorial material presented by ETRI