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Wireless LAN
Seong-Lyun Kim [email protected] Radio Resource Management & Optimization 1
Wireless LANS • • • • • •
Introduction Applications of wireless LANs Challenges of wireless LANs IEEE 802.11 HIPERLAN/2 Summary
SLKIM/ICU 2/48
1
Introduction • Evolution of computers and LANs • Evolution of wireless phones • Wireless LAN is a natural way of merging these two systems. – Introduce mobility of LANs – Introduce multi-media applications to cellular systems
SLKIM/ICU 3/48
Applications of Wireless LANs • • • • •
Office automation Finantial services Medical and hospital systems Education and training industrial automation
SLKIM/ICU 4/48
2
Applications of Wireless LANs • Ad-hoc networks – conference – education and training – project groups
• They do not replace wired solution – they complement them
SLKIM/ICU 5/48
Requirements of WLANs • • • • • •
Access to public networks Multiple networks and co-existance criteria Mobility Security Size and cost Spectrum and power requirements
SLKIM/ICU 6/48
3
Requirements of WLANS • Health hazards. • Licencing. • Roaming between different environments with the terminal.
SLKIM/ICU 7/48
Expected Features • High operating throuput • Delay. – important for time-bounded services.
• Ability to serve data, voice, and video. • Fairness of access – The MAC protocol should be able to resolve unfairness situations caused by fading, etc...
SLKIM/ICU 8/48
4
Challenges of WLANS • • • • •
Medium access. The hidden terminal problem. The exposed terminal scenario. Different received signal power from individual MTs. Higher error rates compared to wired medium.
SLKIM/ICU 9/48
Types of WLANS • Ad Hoc networks • Infrastructured networks
SLKIM/ICU 10/48
5
Ad Hoc Networks •
Group of mobile nodes get together and establish peer-to-peer communication among themselves.
•
Two possible aproaches
– No help from outside infrastructure – Brodcasting/flooding – Temporary infrastructure
SLKIM/ICU 11/48
Infrastructural Networks •
Similar to a cellular system – APs connected to a common architecture. – APs can be base stations or repeaters. – Allows users to move around while connected.
SLKIM/ICU 12/48
6
Structure of the Radio Interface •
The WLAN contains twp layers – The physical (PHY) layer – The data link layer (DDL)
SLKIM/ICU 13/48
IEEE 802.11 • • • •
1 and 2 Mbit/s. Supports both ad-hoc and infrstructure. Supports tim-bounded and data traffic. Three physical layers
SLKIM/ICU 14/48
7
IEEE 802.11 Archetecture • Distribution System (DS) – Basic Service Set (BSS) • Acess Point (AP) • Wireless Stations
SLKIM/ICU 15/48
IEEE 802.11 Archetecture • Ad-hoc networks – A set of independent wireless stations
SLKIM/ICU 16/48
8
Layers Description • The 802.11 protocol covers the MAC and Physical layer. – A single MAC which interacts with three PHYs (1 and 2 Mbit/s).
SLKIM/ICU 17/48
Physical Layers • Frequency Hopping SS in the 2.4 GHz band – 1 mbit/s using 2-level GFSK – 2 Mbit/s using 4-level GFSK
• Direct Sequence SS in the 2.4 GHz band – 1 Mbit/s using DBPSK – 2 Mbit/s using DQPSK – 11-chip barker code
• Infra Red – 1 Mbit/s uses 16-PPM – 2 Mbit/s uses 4-PPM
SLKIM/ICU 18/48
9
The Basic Acces Method: CSMA/CA •
The basic acces mechanism, called Distributed Coordination Function, is a Carrier Sense Multiple Access with Collision Avoidance mechanism. – A station desiring to transmit senses the medium • If the medium is busy the the station defer its transmission to a later time. • If the medium is sensed free then the station is allowed to transmit. – These protocols are effective when the medium is not heavily loaded. – More collisions at heavy loads and have to be accounted fo
SLKIM/ICU 19/48
The Basic Acces Method: CSMA/CA • •
The Ethernet uses Collision Detection (CD) to avoid collisions. Collision Detection is not possible in a wireless environment. – –
•
A full Duplex radio is needed which increases the price significantly. Not possible to assume that all stations hear each other.
Instead, the 802.11 uses a Collusion Avoidance (CA) mechanism together with a Positive Acknowledge scheme.
SLKIM/ICU 20/48
10
CSMA/CA and the Backoff Algorithm • Backoff is a method to solve contention between different stations willing to access the medium. • The Exponential Backoff Algorithm must be be excuted in the following case – MS senses the medium before the first transmission of a packet and the medium is busy. – After each retransmission. – After a successful transmission.
• This meachanism is not used when the MS decides to transmitt a new packet and the medium has been free for more than DIFS.
SLKIM/ICU 21/48
CSMA/CA and the Backoff Algorithm •
Each MS chooses a random number between 0 and CW. CWmax=255
SLKIM/ICU 22/48
11
Hidden Terminal Problem •
MS3 cannot hear MS1 – –
•
It may start transmitting while MS1 is also transmitting. MS1 and MS3 cannot detect collision.
only the receiver can help avoid these collisions.
SLKIM/ICU 23/48
4-Way Handshake
SLKIM/ICU 24/48
12
Virtual Carrier Sense •
Each station adujsts its Network Allocation Vector (NAV) for the duration.
SLKIM/ICU 25/48
Frame Types Three main types of frames: – Data Frames: for data transmission – Control frames: to control access to the medium (e.g., RTS, CTS, and ACK), and – Management Frames
SLKIM/ICU 26/48
13
Frame Formats All 802.11 frames are composed as follows: Preample
PLCP Header
MAC Data
CRC
MAC Data
Frame Control Field
SLKIM/ICU 27/48
Frame Formats RTS Frame Format
CTS Frame Format
ACK Frame Format
SLKIM/ICU 28/48
14
Synchronization in 802.11 • Timing Synchronization Function (TSF) • Used for power management – Beacons sent at well known intervals – All stations timers in BSS are synchronized
• Used for Point Coordination Timing – TSF timer used to predict start of contention free burst
• Used for Hop timing for FH PHY – TSF timer used to time Dwell interval – All Stations are synchronized, so they hop at the same time.
SLKIM/ICU 29/48
Synchronization Approach • All stations maintain a local timer. • Timing Synchronization Function – keeps timers from all stations in synch – AP controls timing in infrastructure networks – distributed function in independent BSS (ad-hoc)
• Timing conveyed by periodic Beacon transmissions – Beacons contain Timestamp for the entire BSS – Timestamp from Beacons used to calibrate local clocks – not required to hear all Beacons to stay in synch
SLKIM/ICU 30/48
15
Power Management •
Allow idle stations to go to sleep.
•
Aps buffer packets for sleeping stations.
– – –
station’s power save mode stored in AP. AP announces which stations have frames buffered. Traffic Indication Map (TIM) sent with every Beacon.
•
Power Saving stations wake up periodically.
•
TSF assures AP and Power Save stations are synchronized.
– – –
•
listen to Beacons. stations will wake up to hear a Beacon. TSF timer keeps running when stations are sleeping.
Independent BSS has similar power management but distributed.
SLKIM/ICU 31/48
Roaming • •
Stations decides that link to its current AP is poor Station uses scanning function to find another AP
• •
Station sends Reassociation Request to nw AP If Reassociation Response is successful
–
– –
•
or uses information from previous scans
then station has roamed to the new AP else stations scans for another AP
if AP accepts Reassociation Requiest – – –
AP indicates Reassociation to the Distribution System Distribution System information is updated normally old AP is notified through Distribution System
SLKIM/ICU 32/48
16
Scanning •
Scanning required for many functions – – –
•
finding and joining a network finding a new AP while roaming initializing an Independent BSS (ad-hoc) network
802.11 MAC uses a common mechanism for all PHY. – –
single or multi channel passive or active scanning
•
Passive scanning
•
Active Scanning
– –
Find networks simply by listening for Beacons On each channel •
Send a Probe, Wait for a Probe Response.
SLKIM/ICU 33/48
Active Scanning Example
SLKIM/ICU 34/48
17
HIPERLAN/2 • A short range mobile system under development by ETSI BRAN (Broadband Radio Access Networks). – 30 m indoor, 150 m outdoor. • Full coverage cellular system possible. • Minimum peak data rate 25 Mbps to the PHY layer. • Throughput of at least 20 Mbps in single cell environment. • At least 4 Mbps should be provided by the MS to the PHY layer in 95% of the area.
SLKIM/ICU 35/48
HIPERLAN/2 • Designed for use in hot spot areas • Designed to operate in several scenarios – Private LAN – Public access – Public access in combination with cellular systems.
SLKIM/ICU 36/48
18
HYPERLAN/2 • H/2 is core network independent. • A network convergence sublayer is needed.
Core network
Core network
Core network
Network convergence sublayer HIPERLAN/2 DLC HIPERLAN/2 PHY SLKIM/ICU 37/48
Description of H/2 • A typical H/2 system consists of a number of APs connected to a backbone network. – AP can use omni antenna, multi beam antenna, or a number of distributed antenna elements. – Each AP serves a number of MTs associated to it. – mobility between APs is supported on the same backbone network, i.e., handover between APs.
SLKIM/ICU 38/48
19
H/2 Archecture • HIPERLAN/2 supports two modes of operations – Centralised mode (infrastructure based). • Central controller connected to a core netwrork. • All traffic must pass by the AP. • A mendatory feature for all MTs and APs.
– Direct mode • Central contoller does not need to be connected to a core network. • Direct exchange of data between MTs possible. • Optional feature.
SLKIM/ICU 39/48
HYPERLAN/2 Functions
•
Convergence layer – offers a service to the higher layers – Mapping between HL and DLC connections.
•
Physical layer – Synchronization – FEC + Modulation – RF
•
Data Link Layer – Error Control Coding (EC) – Medium Access Control function (MAC) – Radio Link Control function (RLC)
SLKIM/ICU 40/48
20
H/2 - Physical Layer Overview • Coded OFDM – – – – – – – –
64 subcarriers: 48 for data, 4 pilots OFDM symbol duration of 4 microsec Guard interval of 800 ns 20 MHz carrier spacing 20 MHz samplig rate coherent modulation BPSK, QPSK, 16QAM (64QAM, optional) convolutional codes: 1/2, 3/4, (+9/16)
– Bite rates: 6, 9, 12, 18, 27, 36, (54 optional) Mbps.
• 5 GHz physical layer common with IEEE 802.11
SLKIM/ICU 41/48
PHY Block Diagram
PDU train from DLC (transmit)
scrambling
OFDM
FEC coding
PHY burst
interleaving
mapping
transmitter
information bits (receive)
antenna receiver
SLKIM/ICU 42/48
21
H/2 OFDM Characteristics • Sampling rate: 20 MHz • Symbol duration: 4 micro seconds • ofdm symbol with cyclic prefix – 64/(20 MHz) + 0.8 micro cyclic prefix
• Carrier spacing: 312.5 kHz
SLKIM/ICU 43/48
DLC Layer •
The Data Link Control (DLC) layer comprises – – –
•
Medium Access Control (MAC) Error Control (EC), based on Automatic Repeat Request (ARQ) Radio Control Protocol (RCP).
Load adaptive TDMA/TDD – – –
2 ms fixed frame duration with ressource allocation on a frame by frame basis. Built in support for sector antennas. QoS and flexibility with resonable complexity.
SLKIM/ICU 44/48
22
DLC Function Entities • The RCP defines all DLC control information – – –
Association Control Functions (ACF) Radio Resource Control (RRC) DLC User Connection (DCC)
• The EC is responsible for detection and recovery of transmission errors not corrected by PHY layer (PHY). • The MAC is responsible for – – –
mapping control and user PDU (Protocol Data Units) into MAC frames (TDMA/TDD) MAC controlled by the AP (a central controller) MAC of MT set the uplink PDUs to be transmitted into granted part to the MAC frame.
SLKIM/ICU 45/48
The MAC Frame Structure • •
Two modes: centralised and direct (DM) Random Access (uplink): contention based
MAC frame splitted into phases Broadcast phase
Downlink phase
Uplink phase
Random access phase
MAC frame splitted into phases with DM Broadcast phase
Downlink phase
Direct Mode phase
Uplink phase
Random access phase
SLKIM/ICU 46/48
23
PHY Burst Structure
Preamble
Payload
• The Preamble is a number of fixed (short) OFDM symbols •AGC setiing, time (frame and clock) synchronization
• Broacast Channel (BCH) • 4 symbols for preamble, 4 symbols of pauload (always BPSK) • Frame Control Channel (FCC) • 2 symbols preamble, pauloads depends on length of FCH
SLKIM/ICU 47/48
Summary • Wireless LAN offers very interesting solutions and possiblities • Design of wireless LAN equipments is very challenging. • Still a lot of work going on in this area.
SLKIM/ICU 48/48
24
Seong-Lyun Kim [email protected] Radio Resource Management & Optimization 1
Wireless LANS • • • • • •
Introduction Applications of wireless LANs Challenges of wireless LANs IEEE 802.11 HIPERLAN/2 Summary
SLKIM/ICU 2/48
1
Introduction • Evolution of computers and LANs • Evolution of wireless phones • Wireless LAN is a natural way of merging these two systems. – Introduce mobility of LANs – Introduce multi-media applications to cellular systems
SLKIM/ICU 3/48
Applications of Wireless LANs • • • • •
Office automation Finantial services Medical and hospital systems Education and training industrial automation
SLKIM/ICU 4/48
2
Applications of Wireless LANs • Ad-hoc networks – conference – education and training – project groups
• They do not replace wired solution – they complement them
SLKIM/ICU 5/48
Requirements of WLANs • • • • • •
Access to public networks Multiple networks and co-existance criteria Mobility Security Size and cost Spectrum and power requirements
SLKIM/ICU 6/48
3
Requirements of WLANS • Health hazards. • Licencing. • Roaming between different environments with the terminal.
SLKIM/ICU 7/48
Expected Features • High operating throuput • Delay. – important for time-bounded services.
• Ability to serve data, voice, and video. • Fairness of access – The MAC protocol should be able to resolve unfairness situations caused by fading, etc...
SLKIM/ICU 8/48
4
Challenges of WLANS • • • • •
Medium access. The hidden terminal problem. The exposed terminal scenario. Different received signal power from individual MTs. Higher error rates compared to wired medium.
SLKIM/ICU 9/48
Types of WLANS • Ad Hoc networks • Infrastructured networks
SLKIM/ICU 10/48
5
Ad Hoc Networks •
Group of mobile nodes get together and establish peer-to-peer communication among themselves.
•
Two possible aproaches
– No help from outside infrastructure – Brodcasting/flooding – Temporary infrastructure
SLKIM/ICU 11/48
Infrastructural Networks •
Similar to a cellular system – APs connected to a common architecture. – APs can be base stations or repeaters. – Allows users to move around while connected.
SLKIM/ICU 12/48
6
Structure of the Radio Interface •
The WLAN contains twp layers – The physical (PHY) layer – The data link layer (DDL)
SLKIM/ICU 13/48
IEEE 802.11 • • • •
1 and 2 Mbit/s. Supports both ad-hoc and infrstructure. Supports tim-bounded and data traffic. Three physical layers
SLKIM/ICU 14/48
7
IEEE 802.11 Archetecture • Distribution System (DS) – Basic Service Set (BSS) • Acess Point (AP) • Wireless Stations
SLKIM/ICU 15/48
IEEE 802.11 Archetecture • Ad-hoc networks – A set of independent wireless stations
SLKIM/ICU 16/48
8
Layers Description • The 802.11 protocol covers the MAC and Physical layer. – A single MAC which interacts with three PHYs (1 and 2 Mbit/s).
SLKIM/ICU 17/48
Physical Layers • Frequency Hopping SS in the 2.4 GHz band – 1 mbit/s using 2-level GFSK – 2 Mbit/s using 4-level GFSK
• Direct Sequence SS in the 2.4 GHz band – 1 Mbit/s using DBPSK – 2 Mbit/s using DQPSK – 11-chip barker code
• Infra Red – 1 Mbit/s uses 16-PPM – 2 Mbit/s uses 4-PPM
SLKIM/ICU 18/48
9
The Basic Acces Method: CSMA/CA •
The basic acces mechanism, called Distributed Coordination Function, is a Carrier Sense Multiple Access with Collision Avoidance mechanism. – A station desiring to transmit senses the medium • If the medium is busy the the station defer its transmission to a later time. • If the medium is sensed free then the station is allowed to transmit. – These protocols are effective when the medium is not heavily loaded. – More collisions at heavy loads and have to be accounted fo
SLKIM/ICU 19/48
The Basic Acces Method: CSMA/CA • •
The Ethernet uses Collision Detection (CD) to avoid collisions. Collision Detection is not possible in a wireless environment. – –
•
A full Duplex radio is needed which increases the price significantly. Not possible to assume that all stations hear each other.
Instead, the 802.11 uses a Collusion Avoidance (CA) mechanism together with a Positive Acknowledge scheme.
SLKIM/ICU 20/48
10
CSMA/CA and the Backoff Algorithm • Backoff is a method to solve contention between different stations willing to access the medium. • The Exponential Backoff Algorithm must be be excuted in the following case – MS senses the medium before the first transmission of a packet and the medium is busy. – After each retransmission. – After a successful transmission.
• This meachanism is not used when the MS decides to transmitt a new packet and the medium has been free for more than DIFS.
SLKIM/ICU 21/48
CSMA/CA and the Backoff Algorithm •
Each MS chooses a random number between 0 and CW. CWmax=255
SLKIM/ICU 22/48
11
Hidden Terminal Problem •
MS3 cannot hear MS1 – –
•
It may start transmitting while MS1 is also transmitting. MS1 and MS3 cannot detect collision.
only the receiver can help avoid these collisions.
SLKIM/ICU 23/48
4-Way Handshake
SLKIM/ICU 24/48
12
Virtual Carrier Sense •
Each station adujsts its Network Allocation Vector (NAV) for the duration.
SLKIM/ICU 25/48
Frame Types Three main types of frames: – Data Frames: for data transmission – Control frames: to control access to the medium (e.g., RTS, CTS, and ACK), and – Management Frames
SLKIM/ICU 26/48
13
Frame Formats All 802.11 frames are composed as follows: Preample
PLCP Header
MAC Data
CRC
MAC Data
Frame Control Field
SLKIM/ICU 27/48
Frame Formats RTS Frame Format
CTS Frame Format
ACK Frame Format
SLKIM/ICU 28/48
14
Synchronization in 802.11 • Timing Synchronization Function (TSF) • Used for power management – Beacons sent at well known intervals – All stations timers in BSS are synchronized
• Used for Point Coordination Timing – TSF timer used to predict start of contention free burst
• Used for Hop timing for FH PHY – TSF timer used to time Dwell interval – All Stations are synchronized, so they hop at the same time.
SLKIM/ICU 29/48
Synchronization Approach • All stations maintain a local timer. • Timing Synchronization Function – keeps timers from all stations in synch – AP controls timing in infrastructure networks – distributed function in independent BSS (ad-hoc)
• Timing conveyed by periodic Beacon transmissions – Beacons contain Timestamp for the entire BSS – Timestamp from Beacons used to calibrate local clocks – not required to hear all Beacons to stay in synch
SLKIM/ICU 30/48
15
Power Management •
Allow idle stations to go to sleep.
•
Aps buffer packets for sleeping stations.
– – –
station’s power save mode stored in AP. AP announces which stations have frames buffered. Traffic Indication Map (TIM) sent with every Beacon.
•
Power Saving stations wake up periodically.
•
TSF assures AP and Power Save stations are synchronized.
– – –
•
listen to Beacons. stations will wake up to hear a Beacon. TSF timer keeps running when stations are sleeping.
Independent BSS has similar power management but distributed.
SLKIM/ICU 31/48
Roaming • •
Stations decides that link to its current AP is poor Station uses scanning function to find another AP
• •
Station sends Reassociation Request to nw AP If Reassociation Response is successful
–
– –
•
or uses information from previous scans
then station has roamed to the new AP else stations scans for another AP
if AP accepts Reassociation Requiest – – –
AP indicates Reassociation to the Distribution System Distribution System information is updated normally old AP is notified through Distribution System
SLKIM/ICU 32/48
16
Scanning •
Scanning required for many functions – – –
•
finding and joining a network finding a new AP while roaming initializing an Independent BSS (ad-hoc) network
802.11 MAC uses a common mechanism for all PHY. – –
single or multi channel passive or active scanning
•
Passive scanning
•
Active Scanning
– –
Find networks simply by listening for Beacons On each channel •
Send a Probe, Wait for a Probe Response.
SLKIM/ICU 33/48
Active Scanning Example
SLKIM/ICU 34/48
17
HIPERLAN/2 • A short range mobile system under development by ETSI BRAN (Broadband Radio Access Networks). – 30 m indoor, 150 m outdoor. • Full coverage cellular system possible. • Minimum peak data rate 25 Mbps to the PHY layer. • Throughput of at least 20 Mbps in single cell environment. • At least 4 Mbps should be provided by the MS to the PHY layer in 95% of the area.
SLKIM/ICU 35/48
HIPERLAN/2 • Designed for use in hot spot areas • Designed to operate in several scenarios – Private LAN – Public access – Public access in combination with cellular systems.
SLKIM/ICU 36/48
18
HYPERLAN/2 • H/2 is core network independent. • A network convergence sublayer is needed.
Core network
Core network
Core network
Network convergence sublayer HIPERLAN/2 DLC HIPERLAN/2 PHY SLKIM/ICU 37/48
Description of H/2 • A typical H/2 system consists of a number of APs connected to a backbone network. – AP can use omni antenna, multi beam antenna, or a number of distributed antenna elements. – Each AP serves a number of MTs associated to it. – mobility between APs is supported on the same backbone network, i.e., handover between APs.
SLKIM/ICU 38/48
19
H/2 Archecture • HIPERLAN/2 supports two modes of operations – Centralised mode (infrastructure based). • Central controller connected to a core netwrork. • All traffic must pass by the AP. • A mendatory feature for all MTs and APs.
– Direct mode • Central contoller does not need to be connected to a core network. • Direct exchange of data between MTs possible. • Optional feature.
SLKIM/ICU 39/48
HYPERLAN/2 Functions
•
Convergence layer – offers a service to the higher layers – Mapping between HL and DLC connections.
•
Physical layer – Synchronization – FEC + Modulation – RF
•
Data Link Layer – Error Control Coding (EC) – Medium Access Control function (MAC) – Radio Link Control function (RLC)
SLKIM/ICU 40/48
20
H/2 - Physical Layer Overview • Coded OFDM – – – – – – – –
64 subcarriers: 48 for data, 4 pilots OFDM symbol duration of 4 microsec Guard interval of 800 ns 20 MHz carrier spacing 20 MHz samplig rate coherent modulation BPSK, QPSK, 16QAM (64QAM, optional) convolutional codes: 1/2, 3/4, (+9/16)
– Bite rates: 6, 9, 12, 18, 27, 36, (54 optional) Mbps.
• 5 GHz physical layer common with IEEE 802.11
SLKIM/ICU 41/48
PHY Block Diagram
PDU train from DLC (transmit)
scrambling
OFDM
FEC coding
PHY burst
interleaving
mapping
transmitter
information bits (receive)
antenna receiver
SLKIM/ICU 42/48
21
H/2 OFDM Characteristics • Sampling rate: 20 MHz • Symbol duration: 4 micro seconds • ofdm symbol with cyclic prefix – 64/(20 MHz) + 0.8 micro cyclic prefix
• Carrier spacing: 312.5 kHz
SLKIM/ICU 43/48
DLC Layer •
The Data Link Control (DLC) layer comprises – – –
•
Medium Access Control (MAC) Error Control (EC), based on Automatic Repeat Request (ARQ) Radio Control Protocol (RCP).
Load adaptive TDMA/TDD – – –
2 ms fixed frame duration with ressource allocation on a frame by frame basis. Built in support for sector antennas. QoS and flexibility with resonable complexity.
SLKIM/ICU 44/48
22
DLC Function Entities • The RCP defines all DLC control information – – –
Association Control Functions (ACF) Radio Resource Control (RRC) DLC User Connection (DCC)
• The EC is responsible for detection and recovery of transmission errors not corrected by PHY layer (PHY). • The MAC is responsible for – – –
mapping control and user PDU (Protocol Data Units) into MAC frames (TDMA/TDD) MAC controlled by the AP (a central controller) MAC of MT set the uplink PDUs to be transmitted into granted part to the MAC frame.
SLKIM/ICU 45/48
The MAC Frame Structure • •
Two modes: centralised and direct (DM) Random Access (uplink): contention based
MAC frame splitted into phases Broadcast phase
Downlink phase
Uplink phase
Random access phase
MAC frame splitted into phases with DM Broadcast phase
Downlink phase
Direct Mode phase
Uplink phase
Random access phase
SLKIM/ICU 46/48
23
PHY Burst Structure
Preamble
Payload
• The Preamble is a number of fixed (short) OFDM symbols •AGC setiing, time (frame and clock) synchronization
• Broacast Channel (BCH) • 4 symbols for preamble, 4 symbols of pauload (always BPSK) • Frame Control Channel (FCC) • 2 symbols preamble, pauloads depends on length of FCH
SLKIM/ICU 47/48
Summary • Wireless LAN offers very interesting solutions and possiblities • Design of wireless LAN equipments is very challenging. • Still a lot of work going on in this area.
SLKIM/ICU 48/48
24
