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Wireless LANs June – September 2005. Physical Layer. ผศ. ดร . อนันต์ ผลเพิ่ม Asst. Prof. Anan Phonphoem, Ph.D. anan@cpe.ku.ac.th http://www.cpe.ku.ac.th/~anan Computer Engineering Department Kasetsart University, Bangkok, Thailand. Outline. Physical Layer Architecture

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physical layer

Wireless LANsJune – September 2005

Physical Layer

ผศ. ดร. อนันต์ผลเพิ่ม

Asst. Prof. Anan Phonphoem, Ph.D.

anan@cpe.ku.ac.th

http://www.cpe.ku.ac.th/~anan

Computer Engineering Department

Kasetsart University, Bangkok, Thailand

outline
Outline
  • Physical Layer Architecture
  • Physical Layer Operations
  • IEEE 802.11 Physical Layer
    • FHSS
    • DSSS
    • IR
physical layer architecture
Physical Layer Architecture

MAC Layer

PHY SAP

Physical Layer

PLCP Sublayer

PMD SAP

PMD Sublayer

plcp sublayer
PLCP Sublayer
  • Physical Layer Convergence Procedure
  • Communicate to MAC via primitives through Physical Layer Service Access Point (SAP)
  • Prepare PLCP protocol data unit (PPDU) (append fields to MPDU)
  • PPDU provides for asynchronous transfer of MPDU between stations
pmd sublayer
PMD Sublayer
  • Physical Medium Dependent
  • Provide actual transmission and reception of Physical Layer entities via wireless medium
  • Interface directly to the medium
  • Provides modulation and demodulation of the transmission frame
physical layer operations
Physical Layer Operations
  • 3 State machines
    • Carrier Senses: determine the state of the medium
    • Transmit: send the data frame
    • Receive: receive the data frame
carrier sense function

MAC

PMD

PLCP

Carrier Sense Function
  • Station is not in Tx
  • or Rx mode
  • Clear channel
  • assessment

Check medium

Carrier Sense info

  • Medium Idle

PHY-CCA.indicate

  • Clear channel
  • assessment

Check medium

Carrier Sense info

  • Medium Busy

PHY-CCA.indicate

  • Check preamble
  • monitor header

Carrier Sense info

  • Try to synchronize
transmit function

MAC

PLCP

PMD

PHY-DATA.request

Pass Data

PHY-DATA.confirm

Transmit Function

PHY-TXSTART.request

Switch to TX mode

PHY-TXSTART.confirm

  • Switch to TX mode
  • Sending preamble & header to antenna @ 1 Mbps

PHY-DATA.request

Pass Data

PHY-DATA.confirm

  • Transmit data @ specified rate

PHY-TXEND.request

Switch to RX mode

PHY-TXEND.confirm

  • Switch to RX mode
receive function

MAC

PMD

PLCP

PHY-DATA.indication

DATA

PHY-DATA.indication

DATA

Receive Function
  • Clear channel
  • assessment found
  • media busy

Carrier Sense info

  • Check preamble
  • monitor header
  • Check Power level
  • > 85 dBm

PHY-RXSTART.indication

  • Check CRC
  • Set octet counter

  • Final Octet

PHY-RXEND.indication

multiple antenna diversities
Multiple Antenna Diversities
  • Receive function will operate with
    • Single Antenna
    • Multiple Antennas
  • Signal Degradation Factors
    • Distance
    • Atmosphere
    • Barrier
  • Multiple-path propagation
    • Decrease the signal strength
    • Use multiple antennas (diversity) to improve the received signal
ieee 802 11 phy layer
IEEE 802.11 PHY Layer
  • FHSS Physical Layer
  • DSSS Physical Layer
  • Infrared (IR) Physical Layer
fhss physical layer
FHSS Physical Layer
  • Low cost
  • Low power consumption
  • Most tolerant to noise
  • Low potential data rate
  • Medium range (< DSSS)
fhss architecture
FHSS Architecture
  • FHSS PLCP Sublayer
  • FHSS PMD Sublayer
  • Primitives
fhss plcp frame

PLCP Preamble

PLCP Header

80 bits

16 bits

12 bits

4 bits

16 bits

0-4095 Octets

SYNC

Start Frame

Delimiter

PLW

PSF

Header

Error

Check

Whitened PSDU

Payload (MPDU)

Reduce DC bias, scramble

PLCP Signaling Field: data rate (1- 4.5 Mbps)

16-bit CRC

0000110010111101: define the beginning of a frame

PSDU Length word

0 & 1 alternating : synchronization purpose

FHSS PLCP frame

PSDU=PLCP Service Data Unit

fhss pmd
FHSS PMD
  • Perform actual Tx/Rx of PPDU by hopping between channel (hopping sequence)
  • Provides FHSS modulation/demodulation
dsss physical layer
DSSS Physical Layer
  • High cost
  • High power consumption
  • High potential data rate
  • More range
dsss architecture
DSSS Architecture
  • DSSS PLCP Sublayer
  • DSSS PMD Sublayer
  • Primitives
dsss plcp frame

PLCP Preamble

PLCP Header

8 bits

128 bits

16 bits

8 bits

8 bits

16 bits

SYNC

Start Frame

Delimiter

Signal

Service

Length

Frame

Check

Sequence

MPDU

16-bit CRC

Reserved

#microsec. To transmit the MPDU

1111001110100000: define the beginning of a frame

Modulation type: data rate

0 & 1 alternating : synchronization purpose

DSSS PLCP frame
dsss pmd
DSSS PMD
  • Perform actual Tx/Rx of PPDU
  • Provides DSSS modulation/demodulation
ir physical layer
IR Physical Layer
  • Lowest cost
  • Highest tolerant to RF noise
  • Lowest range
  • Need ceiling
  • More secure
  • No frequency regulating
  • No product ?
  • IrDA: Infrared Data Association Standard
ir architecture
IR Architecture
  • IR PLCP Sublayer
  • IR PMD Sublayer
ir plcp frame

PLCP Preamble

PLCP Header

57-73 slots

4 slots

3 slots

32 slots

16 slots

16 slots

0-2500 octets

SYNC

Start Frame

Delimiter

Data

Rate

DC Level

Adjust.

Length

Frame

Check

Sequence

MPDU

16-bit CRC

Specified for 1 and 2 Mbps

#microsec. To transmit the MPDU

1001: define the beginning of a frame

Data rate

Pulse alternating : synchronization purpose

IR PLCP frame
ir pmd
IR PMD
  • Mostly use diffused infrared
  • Perform actual Tx/Rx of PPDU, translate binary to infrared light
  • Provides IR modulation/demodulation
ir pmd27
IR PMD
  • Noise affects amplitude (not phase)

 Pulse position reduces interference

  • Pulse position modulation :PPM
    • Vary position of pulse
  • For 1 Mbps  16 PPM
  • For 2 Mbps  4 PPM