and Mobile Computing MAP-I Manuel P. Ricardo Faculdade de - - PowerPoint PPT Presentation

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Wireless Communications and Mobile Computing

MAP-I Manuel P. Ricardo

Faculdade de Engenharia da Universidade do Porto

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Professors

Adriano Moreira

» Universidade do Minho

Manuel P. Ricardo (mricardo@fe.up.pt)

» Faculdade de Engenharia, Universidade do Porto » mricardo@fe.up.pt » http://www.fe.up.pt/~mricardo » Tel. 22 209 4200

Rui L. Aguiar

» Universidade de Aveiro

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Topics Scheduled for Today

New generation networks overview Mobile Devices platforms Communications networks technologies

» Fundamentals of communications » Wireless technologies (WLAN, WMAN) » Wireless technologies (GPRS, UMTS) » Broadcast and satellite technologies (DVB, DMB)

Services and applications in novel generation networks ... 3

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Mobile vs Fixed networks

Mobile communications systems characterised by

» wireless links » mobility of terminals

T switch

AP

T

AP 1 2 1 2

Terminal Mobility Computer Switch Computer AP Wireless link Wired link

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To Think About

How to obtain a low Bit Error Ratio (BER) in a wireless link?

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Reference Model

Physical Network Transport Data link Application Mobility Security Quality of Service

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Wireless Transmission

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Electromagnetic Waves – Generation and Propagation

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Frequencies for Radio Transmission

Frequency bands as defined by the ITU-R Radio Regulations

fc= 3 GHz  10 cm wavelength

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To Think About

How does the power of a received signal depend on the

» distance? » wavelength ( )?

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Signal Propagation and Wireless channels

Power of the signal received depends on 3 factors

– Path loss

Dissipation of radiated power; depends on the distance

– Shadowing

• caused by the obstacles between the transmitter and the receiver
• attenuates the signal  absorption, reflection, scattering, diffraction

– Multipath

constructive and destructive addition of multiple signal components

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Path Loss – Free Space Model

x b d G PG

l dB

20 ) log( . 20 4 log . 20

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Signal Propagation and Wireless Channels

PGdB

log(d)

Path loss Shadowing + Path loss Multipath + Shadowing + Path loss

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Carrier, Bandwidth

What is the difference betweeen B and fc?

f fc

B 2B

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Capacity of an Wireless Channel

Assuming Additive White Gaussion Noise (AWGN)

» Given by Shannon´s law N0 – power spectral density of the Noise

Capacity in a fading channel (shadowing + multipath)

 usually smaller than the capacity of an AWGN channel

(bit/s)

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Capacity of an Wireless Channel

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To Think About

How can we transmit bits using a continuous carrier?

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Digital Modulation

Digital modulation

» maps information bits into an analogue signal (carrier)

Receiver

» determines the original bit sequence based on the signal received

Two categories of digital modulation

» amplitude/phase modulation » frequency modulation

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Amplitude and Phase modulation

sent over a time symbol interval Amplitude/phase modulation can be:

» Pulse Amplitude Modulation (MPAM)

information coded in amplitude

» Phase Shift Keying (MPSK),

information coded in phase

» Quadrature Amplitude Modulation (MQAM)

information coded both in amplitude and phase

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Differential Modulation

Bits associated to a symbol

depend on the bits transmitted over prior symbol times

Differential BPSK (DPSK)

» 0  no change phase » 1  change phase by

Diferential 4PSK (DQPSK) the bit

» 00  change phase by 0 » 01  change phase by » 10  change phase by - » 11  change phase by

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Coding for Wireless Channels

Coding enables bit errors to be either

detected or corrected by receiver

Codes designed for AWGN channels

» do not work well on fading channels » cannot correct the long error bursts that occur in fading

Codes for fading channels are usually

» based on an AWGN channel code » combined with interleaving » objective  spread error bursts over multiple codewords

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Convolutional Code; Interleaving

Example: convolutional code Interleaving

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Adaptive Modulation/Coding

Adaptive transmission techniques

» aim at maintaining the quality  low/stable BER » works by varying: data rate, power transmitted, codes

Adapting the data rate

» symbol rate is kept constant » modulation schemes / constellation sizes depend on  multiple data rates

Adapting the transmit power

» compensate Pr/N0B variation due to fading » maintain a constant received

Adapting the codes

» large  weaker or no codes » small  stronger code may be used

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Multicarrier Modulation

Multicarrier modulation (e.g. OFDM) consists

» dividing a bitstream into multiple low rate sub-streams » sending sub-streams simultaneously over sub-channels

Subchannel

» has bandwidth BN = B/N » provides a data rate RN R/N » For N large, BN = B/N << 1/Tm

 flat fading (narrowband like effects) on each sub-channel, no ISI

Orthogonal sub-carriers

» space between carriers  minimised » system capacity  maximised

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Wireless Data Link and Medium Access Control

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How to transmit signals in both directions simultaneously? How to enable multiple users to communicate simultaneously?

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Duplex Transmission

Duplex – transference of data in both directions

Uplink and Downlink channels required

Two methods for implementing duplexing

» Frequency-Division Duplexing (FDD)

– wireless link split into frequency bands – bands assigned to uplink or downlink directions – peers communicate in both directions using different bands

» Time-Division Duplexing (TDD)

– timeslots assigned to the transmitter of each direction – peers use the same frequency band but at different times

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To Think About

How to place several sender-receiver pairs communicating in the same physical space?

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Multi-Access Schemes

Multi-access schemes

» Identify radio resources » Assign resources to multiple users/terminals

Multi-access schemes

» Frequency-Division Multiple Access (FDMA)

resources divided in portions of spectrum (channels)

» Time-Division Multiple Access (TDMA)

resources divided in time slots

» Code-Division Multiple Access (CDMA)

resources divided in codes

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FDMA

» Signal space divided along the frequency axis

into non-overlapping channels

» Each user assigned a different frequency channel » The channels often have guard bands » Transmission is continuous over time

channel k channel 2 time code channel 1

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TDMA

» Signal space divided along the time axis

into non-overlapping channels

» Each user assigned a different cyclically-repeating timeslot » Transmission not continuous for any user » Major problem

synchronization among the users in the uplink channels users transmit over channels having different delays uplink transmitters must synchronize

time code … …

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CDMA

Each user assigned a code to spread his information signal

» Multi-user spread spectrum (Direct Sequence, Frequency Hopping) » The resulting spread signal

– occupy the same bandwidth – transmitted at the same time

Different bitrates to users

 control length of codes

Power control required in uplink

» to compensate near-far effect » If not, interference from close user swamps signal from far user

time code channel 1 channel 2 channel k …

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Combined Multi-access Techniques

Cellular planning Current technologies  combinations of multi-access techniques

» GSM: FDMA and then TDMA to assign slots to users

f1 f3 f3 f2 f2 f1 f3 f1 f3 f3 f2 f2 f1 f3 f1 f3 f3 f2 a) Group of 3 cells f4 f2 f6 f3 f5 f2 f1 f6 f3 f5 f7 f2 f3 f4 f5 f7 f2 f1 b) Group of 7 cells c) Group of 3 cells, each having 3 sectors f2 f3 f1 f2 f3 f1 f2 f3 f1 f5 f6 f4 f5 f6 f4 f8 f9 f7 f8 f9 f7 f8 f9 f7

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Wireless Medium Access Control Issues

Medium Access Control (MAC)

» Assign radio resources to terminals along the time

3 type of resource allocation methods

» dedicated assignment

resources assigned in a predetermined, fixed, mode

» random access

terminals contend for the channel

» demand-based

terminals ask for reservations using dedicated/random access channels

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Alhoa, S-Alhoa, CSMA

Alhoa  Efficiency of 18 %

if station has a packet to transmit

 transmits the packet  waits confirmation from receiver (ACK)  if confirmation does not arrive in round trip time, the station

computes random backofftime  retransmits packet

Slotted Alhoa  Efficiency of 37 %

stations transmit just at the beginning of each time slot

Carrier Sense Multiple Access (CSMA)  Efficiency of 54 %

– station listens the carrier before it sends the packet – If medium busy  station defers its transmission

ACK required for Alhoa, S-Alhoa and CSMA

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CSMA/CD – Not Used in Wireless

CDMA/Collision Detection  Efficiency < 80%

– station monitors de medium (carrier sense)

 medium free  transmits the packet  medium busy  waits until medium is free  transmits packet  if, during a round trip time, detects a collision

 station aborts transmission and stresses collision (no ACK packet)

Problems of CDMA/CD in wireless networks

Carrier sensing carrier sensing difficult for hidden terminal Collision detection near-end interference makes simultaneous transmission and reception difficult

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To think about?

How to minimize collision in a wireless medium?

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CSMA with Collision Avoidance (CSMA/CA)

S2

DIFS

S3 S1

DATA DIFS S2-bo DIFS S3-bo S3-bo-e S3-bo-r DATA DIFS S3-bo-r DATA

• Packet arrival

DATA

• Transmission of DATA

DIFS

• Time interval DIFS

S2-bo

• Backoff time, station 2
• Elapsed backoff time, station 3

S3-bo-e S3-bo-r

• Remaining backoff time, station 3

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CSMA with Collision Avoidance (CSMA/CA)

Station with a packet to transmit monitors the channel activity until an idle period equal to a Distributed Inter-Frame Space (DIFS) has been observed If the medium is sensed busy a random backoff interval is

• selected. The backoff time counter is decremented as long as the

channel is sensed idle, stopped when a transmission is detected

• n the channel, and reactivated when the channel is sensed idle

again for more than a DIFS. The station transmits when the backoff time reaches 0 To avoid channel capture, a station must wait a random backoff time between two consecutive packet transmissions, even if the medium is sensed idle in the DIFS time

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CSMA/CA – ACK Required

AP

DIFS

S2 S1

SIFS DATA ACK DIFS S2-Backoff SIFS DATA ACK

• Packet arrival

DATA

• Transmission of DATA

DIFS

• Time interval DIFS

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CSMA/CA – ACK Required

CSMA/CA does not rely on the capability of the stations to detect a collision by hearing their own transmission A positive acknowledgement is transmitted by the destination station to signal the successful packet transmission In order to allow an immediate response, the acknowledgement is transmitted following the received packet, after a Short Inter-Frame Space (SIFS) If the transmitting station does not receive the acknowledge within a specified ACK timeout, or it detects the transmission of a different packet on the channel, it reschedules the packet transmission according to the previous backoff rules. Efficiency of CSMA/CA depends strongly of the number of competing

• stations. An efficiency of 60% is commonly found

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To Think About

How to enable hidden terminals to sense the carrier?

Hidden node  C is hidden to A

A C B D

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RTS-CTS Mechanism

AP

DIFS

S2 S1

SIFS DATA RTS DIFS S2-bo DATA

• Packet arrival

DATA

• Transmission of DATA

DIFS

• Time interval DIFS

CTS SIFS SIFS ACK

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RTS-CTS Mechanism

For some scenarios where long packets are used or the probability of hidden terminals is not irrelevant, the efficiency of CSMA/CA can be further improved with a Request To Send (RTS) - Clear to Send (CTS) mechanism The basic concept is that a sender station sends a short RTS message to the receiver

• station. When the receiver gets a RTS from the sender, it polls the sender by sending a

short CTS message. The sender then sends its packet to the receiver. After correctly receiving the packet, the receiver sends a positive acknowledgement (ACK) to the sender This mechanism is particularly useful to transmit large packets. The listening of the RTS or the CTS messages enable the stations in range respectively of the sender or receiver that a big packet is about to be transmitted. Usually both the RTS and the CTS contain information about the number of slots required to transmit the 4 packets. Using this information the other stations refrain themselves to transmit packets, thus avoiding collisions and increasing the system efficiency. SIFS are used before the transmission of CTS, Data, and ACK In optimum conditions the RTS-CTS mechanism may add an efficiency gain of about 15%

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Guaranteed Access Control

Polling

» AP manages stations access to the medium » Channel tested first using a control handshake

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Fundamental Networking

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Packet Switching

Technologies: Ethernet, IP Path defined by packet destination address

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To Think About

Suppose terminal a moves from port 2 to port 1

» What needs to be done so that terminal a can continue receiving packets?

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L2 Networking – Ethernet Format

Ethernet

7x 10101010 10101011 Protocolo=IP

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L2 Networking - Bridges

Bridge builds forwarding tables automatically Address learning

» Source Address of received frame is associated to a bridge input port

 station reachable through that port

Frame forwarding

» When a frame is received, its Destination Address is analysed

– If address is associated to a port  frame forwarded to that port – If not  frame transmitted through all the ports but the input port

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L2 Networking - Single Tree Required

• Ethernet frame

– No hop-count – Could loop forever – Same for broadcast packet

• Layer 2 network

– Required to have tree topology – Single path between every pair of stations

• Spanning Tree Protocol (STP)

– Running in bridges – Helps building the spanning tree – Blocks ports

L2 Networking - Single Tree Required

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L3 Networking – Packet Formats IPv4 IPv6

Version HLen TOS Length Ident Flags Offset TTL Protocol Checksum SourceAddr DestinationAddr Options (variable) Pad (variable) 4 8 16 19 31 Data Version Traffic Class Flow Label Payload Lengtht Next Header Hop Limit SourceAddr (4 words) DestinationAddr (4 words) Options (variable number) 4 8 16 24 31 Data

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L3 Networking – Multiple Trees …

Every router

» finds the shortest path to the other routers and their attached networks » Calculates its Shortest Path Tree (SPT)

Routing protocol

» Run in routers » Helps routers build their SPT » RIP, OSPF, BGP

Destination Cost NextHop A 1 A C 1 C D 2 C E 2 A F 2 A G 3 A

B’s routing view

D G A F E B C

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Traditional TCP/IP Communications Stack

T1 IP TCP APP T1 | T2 T2 | T3 IP T3 | T4 IP T5 IP TCP APP

host bridge router router host

T4 | T5

bridge IEEE MAC address based switching IETF IP address based switching

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Tunnel IP-in-IP

T1 IP TCP APP T1 | T2 T2 | T3 IP T3 | T4 T5 IP TCP APP

H1 bridge R1 R2 Server

T4 | T5

bridge

IP IP IP

• uter IP header inner IP header

data

DA= red IP address of R2 SA= red IP address of H1 TTL IP identification IP-in-IP IP checksum flags fragment offset length TOS ver. IHL DA= Server SA=H1 TTL IP identification

• lay. 4 prot.

IP checksum flags fragment offset length TOS ver. IHL TCP/UDP/ ... payload

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Tunnel PPP over IP (E.g PPTP)

» GRE

– virtual point-to-point link – routers at remote points – over an IP network

» PPP adequate for

– Authentication – Transporting IP packets

T1 IP TCP APP T1 | T2 T2 | T3 IP T3 | T4 T5 IP TCP APP

H1 bridge R1 R2 Server

T4 | T5

bridge

IP IP IP PPP GRE GRE PPP

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IEEE 802.11

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Infrastructure Networks vs Ad-Hoc Networks

Infrastructure

AP AP AP wired network AP: Access Point

Ad-hoc

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IEEE 802.11 – Infrastructure Network

Station

» Terminal with radio access

Basic Service Set (BSS)

» Set of stations in the same band

Access Point (AP)

» Interconnects LAN to wired network » Provides access to stations

Stations communicate with AP

Portal  bridge to other networks Distribution System

» Interconnection network » Logical network

– EES, Extended Service Set – Based on BSSs

Distribution System Portal 802.x LAN Access Point 802.11 LAN BSS2 802.11 LAN BSS1 Access Point STA1 STA2 STA3 ESS

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IEEE 802.11 –Ad-Hoc Network

Direct communication between stations Independent Basic Service Set, IBSS

» Set of stations working the the same carrier (radio channel)

802.11 LAN IBSS2 802.11 LAN IBSS1 STA1 STA4 STA5 STA2 STA3

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IEEE 802.11 – Protocol Stack

mobile terminal access point fixed terminal application TCP 802.11 PHY 802.11 MAC IP 802.3 MAC 802.3 PHY application TCP 802.3 PHY 802.3 MAC IP 802.11 MAC 802.11 PHY LLC infrastructure network LLC LLC

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802.11 – Protocol Stack

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802.11 – Layers and Functionalities

Data plane

» MAC  medium access, fragmentation, encryption » PLCP - Physical Layer Convergence Protocol  carrier detection » PMD - Physical Medium Dependent  modulation, codification

Management plane

» PHY Management  channel selection, MIB » MAC Management  synchronisation, mobility, power, MIB » Station Management  coordenation management functions

PMD PLCP MAC LLC MAC Management PHY Management PHY DLC Station Management

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MAC Layer – Access Methods

MAC-DCF CSMA/CA

– Carrier sense, collision avoidance using back-off mechanism – ACK packet required for confirmations (except for broadcast packets) – mandadory

MAC-DCF with RTS+CTS

– Used to avoid hidden terminal problem – Optional

MAC- PCF

– Access Point asks stations to transmit – Optional

DCF – Distributed Coordination Function PCF - Point Coordination Function

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MAC Layer – Guard Time Intervals

» DIFS (DCF IFS)

– Lowest priority, used for asynchronous data

» PIFS (PCF IFS)

– Medium priority, used for real time traffic /QoS

» SIFS (Short Inter Frame Spacing)

– Maximum priority used for signalling: ACK, CTS, answers to polling t medium busy SIFS PIFS DIFS DIFS next frame contention direct access if medium is free DIFS

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MAC-DCF CSMA/CA

Sending a frame in unicast

» Station waits DIFS before sending the packet » If packet is correctly received (no errors in CRC)

 Receiver confirms reception immediatly, using ACK, after waiting SIFS

» In case of errors, frame is re-transmitted » In case of retransmission

 Maximum value for the contention window duplicates  Contetion window has minimum and maximum values (eg.: 7 and 255)

t SIFS DIFS data ACK waiting time

• ther

stations receiver sender data DIFS contention

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MAC- PCF

PIFS stations‘ NAV wireless stations point coordinator D1 U1 SIFS NAV SIFS D2 U2 SIFS SIFS SuperFrame t0 medium busy t1

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MAC-PCF II

t stations‘ NAV wireless stations point coordinator D3 NAV PIFS D4 U4 SIFS SIFS CFend contention period contention free period t2 t3 t4

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MAC – Frame Format

Frame types

» Data, control, management

Sequence number Addresses

» destination, source, BSS identifier, ...

Others

» Error control, frame control, data

Frame Control Duration/ ID Address 1 Address 2 Address 3 Sequence Control Address 4 Data CRC 2 2 6 6 6 6 2 4 0-2312 bytes Protocol version Type Subtype To DS More Frag Retry Power Mgmt More Data WEP 2 2 4 1 From DS 1 Order bits 1 1 1 1 1 1

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To Think About

STA1 needs to send a frame to STA2. In the Infrastructure mode, the frame is sent via the AP. What MAC addresses are required in the frame sent by STA1 to the AP?

Access Point 802.11 LAN BSS2 STA1 STA2

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Addresses in MAC

scenario to DS from DS address 1 address 2 address 3 address 4 ad-hoc network DA SA BSSID

• infrastructure

network, from AP 1 DA BSSID SA

• infrastructure

network, to AP 1 BSSID SA DA

• infrastructure

network, within DS 1 1 RA TA DA SA DS: Distribution System AP: Access Point DA: Destination Address SA: Source Address BSSID: Basic Service Set Identifier RA: Receiver Address TA: Transmitter Address

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Special Frames- ACK, RTS, CTS

Acknowledgement Request To Send Clear To Send

Frame Control Duration Receiver Address Transmitter Address CRC 2 2 6 6 4 bytes Frame Control Duration Receiver Address CRC 2 2 6 4 bytes Frame Control Duration Receiver Address CRC 2 2 6 4 bytes ACK RTS CTS (Fig. 7.17 do livro está errada)

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MAC Management

Synchronization

– Station discovers a LAN; station associates to an AP – stations synchronize clocks; Beacon is generated by AP

Power management

– Save terminal’s power  terminal enters sleep mode

 Periodically  No frame loss; frames are stored

Roaming

– Station looks for new access points – Station decides about best access point – Station (re-)associates to new AP

MIB - Management Information Base

PMD PLCP MAC LLC

MAC Management PHY Management PHY DLC

Station Management

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Synchronization by Beacon – Infrastructure Network

Stations must be synchronised. E.g.

– To preview PCF cycles – To change state: sleep  wake

Infrastructure networks

– Access Point sends (almost) periodically a Beacon with timestamp e BSSid sometimes medium is busy – Timestamp sent is the correct – Other stations adjust their clocks

beacon interval t medium access point busy B busy busy busy B B B value of the timestamp B beacon frame

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Power Management

Objective

» If transceiver not in use sleep mode

Station in 2 states: sleep, wake Infrastructure network

» Stations wake periodically and simultaneously » They listen beacon to know if there are packets to receive » If a station has packets to receive  remains awake until it receives them

– If not, go sleep; after sending its packets!

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Power Management – Infrastructure Network

Infrastructure network  traffic information sent in the beacon

» Traffic Indication Map – TIM: list of unicast receivers » Delivery Traffic Indication Map - DTIM: list broadcast/multicast receivers

TIM interval t medium access point busy D busy busy busy T T D T TIM D DTIM DTIM interval B B B broadcast/multicast station awake P PS poll P D D D data transmission to/from the station

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802.11 – Physical Layer

3 versões: 2 rádio, 1 IR

– Bitrates: 1, 2 Mbit/s

FHSS (Frequency Hopping Spread Spectrum)

– Spreading, despreading – 79 sequências de salto pseudo aleatórias. Para 1 Mbit/s, modulação de 2 níveis GFSK

DSSS (Direct Sequence Spread Spectrum)

– 1 Mbit/s  Modulation DBPSK (Differential Binary Phase Shift Keying) – 2 Mbit/s  Modulation DQPSK (Differential Quadrature PSK) – Preamble and header of frame transmitted at 1 Mbit/s (DBPSK)

 Remainning transmitted at 1 (DBPSK) ou 2 Mbit/s (DQPSK)

– Maximum radiated power  1 W (EUA), 100 mW (UE), min. 1mW

Infravermelho

– 850-950 nm, distância de 10 m – Detecção de portadora, detecção de energia, sincronização

All versions provide Clear Channel Assessment (CCA)

– Used by MAC to detect if medium is free

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Frame FHSS PHY

» Sincronization  010101... » SFD (Start Frame Delimiter  0000110010111101 » PLW (PLCP_PDU Length Word)

– Payload length in bytes, including 2 CRC bytes. PLW < 4096

» PSF (PLCP Signaling Field)

– Transmission bitrate of payload (1, 2 Mbit/s)

 PLCP (preâmbulo and header) sent at 1 Mbit/s  Payload sent at 1 ou 2 Mbit/s

» HEC (Header Error Check)

– CRC with x16+x12+x5+1

» Data MAC  scrambled with z7+z4+1

synchronization SFD PLW PSF HEC payload PLCP preamble PLCP header 80 16 12 4 16 variable bits

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Frame DSSS PHY

– Barker sequence of 11 chips  +1,-1,+1,+1,-1,+1,+1,+1,-1,-1,-1 – Sincronization

 Sincronization  Gain control, Clear Channel Assessement, compensate frequency deviation

– SFD (Start Frame Delimiter  1111001110100000 – Signal

 Payload bitrate (0A: 1 Mbit/s DBPSK; 14: 2 Mbit/s DQPSK)

– Service  utilização futura, 00 = conforme 802.11 – Length  Payload length in us – HEC (Header Error Check)

 Protection of sinal, service and length, using x16+x12+x5+1

– Data (payload) MAC  scrambled with z7+z4+1 synchronization SFD signal service HEC payload PLCP preamble PLCP header 128 16 8 8 16 variable bits length 16

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IEEE 802.11b

Bitrate (Mbit/s)

– 1, 2, 5.5, 11 (depends on SNR) – Useful bitrate  6

Transmission range

– 300m outdoor, 30m indoor

Frequencies  open, ISM 2.4 GHz band Only physical layer is redefined

» MAC and MAC management are the same

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IEEE 802.11b – Trama PHY

synchronization SFD signal service HEC payload PLCP preamble PLCP header 128 16 8 8 16 variable bits length 16 192 µs at 1 Mbit/s DBPSK 1, 2, 5.5 or11 Mbit/s short synch. SFD signal service HEC payload PLCP preamble (1 Mbit/s, DBPSK) PLCP header (2 Mbit/s, DQPSK) 56 16 8 8 16 variable bits length 16 96 µs 2, 5.5 or 11 Mbit/s Long PLCP PPDU format Short PLCP PPDU format (optional) Payload bitrate

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Channel Selection

2400 [MHz] 2412 2483.5 2442 2472 channel 1 channel 7 channel 13 Europe (ETSI) US (FCC)/Canada (IC) 2400 [MHz] 2412 2483.5 2437 2462 channel 1 channel 6 channel 11 22 MHz 22 MHz channel i = 2412MHz + (i-1)*5MHz There are 14 channels of 5MHz In 801.11b only 3 non-overlap channels can be used

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IEEE 802.11a

Bitrate (Mbit/s)

» 6, 9, 12, 18, 24, 36, 48, 54 (depends on SNR) » Mandatory  6, 12, 24

Useful bit rate (frames 1500 bytes, Mbit/s)

» 5.3 (6), 18 (24), 24 (36), 32 (54)

Transmission range

» 100m outdoor, 10 m indoor

– 54 Mbit/s até 5 m, 48 até 12 m, 36 até 25 m, 24 até 30m, 18 até 40 m, 12 até 60 m

Frequencies

» Free, band ISM » 5.15-5.35, 5.47-5.725 GHz (Europa)

Only the physical layer changes

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Operating channels for 802.11a / US U-NII

5150 [MHz] 5180 5350 5200 36 44 16.6 MHz center frequency = 5000 + 5*channel number [MHz] channel 40 48 52 56 60 64 149 153 157 161 5220 5240 5260 5280 5300 5320 5725 [MHz] 5745 5825 5765 16.6 MHz channel 5785 5805

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OFDM in IEEE 802.11a

OFDM with 52 used subcarriers (64 in total) 48 data + 4 pilot (plus 12 virtual subcarriers) 312.5 kHz spacing

subcarrier number 1 7 21 26

• 26 -21
• 7 -1

channel center frequency 312.5 kHz pilot

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802.11a – Rate Dependent Parameters

250 kSymbol/s

% of useful information

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IEEE 802.16

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IEEE 802.16 - Commonly used terms

BS – Base Station SS – Subscriber Station, (i.e., CPE) DL – Downlink, i.e. from BS to SS UL – Uplink, i.e. from SS to BS FDD – Frequency Division Duplex TDD – Time Division Duplex TDMA – Time Division Multiple Access TDM – Time Division Multiplexing OFDM – Orthogonal Frequency Division Multiplexing OFDMA - Orthogonal Frequency Division Multiple Access QoS – Quality of Service

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IEEE 802.16 - Introduction

Source: WiMAX, making ubiquitous high-speed data services a reality, White Paper, Alcatel.

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Reference Model

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Adaptive PHY

Source: Understanding WiMAX and 3G for Portable/Mobile Broadband Wireless, Technical White Paper, Intel.

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Adaptive Burst Profiles

Burst profile - Modulation and FEC On DL

» multiple SSs can associate the same DL burst

On UL

» SS transmits in an given time slot with a specific burst

Dynamically assigned according to link conditions

» Burst by burst » Trade-off capacity vs. robustness in real time

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OFDM PHY TDD Frame Structure

DL Subframe

Frame n-1 pre. Time Adaptive Frame n Frame n+1

UL subframe

FCH DL burst 1 DL burst n

UL MAP

Broadcast Conrol msgs

...

UL burst 1 UL burst m

DL MAP DCD

• pt.

UCD

• pt.

...

DL burst 2 UL TDMA DL TDM

pre. pre.

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OFDM PHY FDD Frame Structure

DL Subframe

Frame n-1 pre. Time

Broadcast Control Msgs

Frame n Frame n+1

UL subframe

FCH DL burst 1 DL burst k

...

DL TDMA UL burst 1 UL burst m DL burst 2 DL burst n DL burst k+1

...

DL TDM

...

UL TDMA

DL MAP UL MAP DCD

• pt.

UCD

• pt.

pre. pre.

UL MAP for next MAC frame UL bursts

pre. pre.

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FDD MAPs Time Relevance

frame Broadcast Full Duplex Capable User Half Duplex T erminal #1 Half Duplex T erminal #2 UPLINK DOWNLINK

DL MAP UL MAP DL MAP UL MAP

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OFDMA

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OFDMA

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OFDMA, TDD

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IEEE 802.16 MAC Addressing and Identifiers

SS has 48-bit IEEE MAC address BS has 48-bit base station ID

» Not a MAC address; 24-bit operator indicator

16-bit connection ID (CID) 32-bit service flow ID (SFID) 16-bit security association ID (SAID)

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Convergence Sub-Layer (CS)

ATM Convergence Sub- Layer

» Support for VP/VC connections » Support for end-to-end signaling of dynamically created connections » ATM header suppression » Full QoS support

Packet Convergence Sub- Layer

» Initial support for Ethernet, VLAN, IPv4, and IPv6 » Payload header suppression » Full QoS support

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MAC – CPS – Data Packet Encapsulations

P H SI

MAC PDU

Ethernet Packet

Ethernet Packet

Packet PDU (e.g., Ethernet) CS PDU (i.e., MAC SDU)

HT FEC block 1 CRC MAC PDU Payload OFDM symbol 1

PHY Burst

(e.g., TDMA burst)

Preamble OFDM symbol 2 OFDM symbol n

...... FEC

FEC Block 2 FEC block m

......

FEC Block 3

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MAC – CPS – MAC PDU Transmission

MAC PDUs are transmitted in PHY Bursts The PHY burst can contain multiple FEC blocks MAC PDUs may span FEC block boundaries Concatenation Packing Segmentation Sub-headers

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MAC – CPS – MAC PDU Concatenation

MAC PDU 2

HT FEC block 1 CRC MAC PDU Payload OFDM symbol 1

PHY Burst

(e.g., TDMA burst)

Preamble OFDM symbol 2 OFDM symbol n

...... FEC

FEC Block 2 FEC block m

......

FEC Block 3

MAC PDU 1

HT CRC MAC PDU Payload

...... MAC PDU k

HT CRC MAC PDU Payload

Multiple MAC PDUs are concatenated into the same PHY burst

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MAC – CPS – MAC PDU Fragmentation

FEC block 1 OFDM symbol 1

PHY Burst

Pre.

MAC SDU

OFDM symbol n1

...... FEC

FEC Block m1

......

MAC SDU seg-1

HT CRC MAC PDU Payload HT CRC MAC PDU Payload

A MAC SDU can be fragmented into multiple segments, each segment is encapsulated into one MAC PDU

FEC block 1 OFDM symbol 1

PHY Burst

Pre. OFDM symbol n2

......

FEC Block m2

......

HT CRC MAC PDU Payload

MAC SDU seg-2 MAC SDU seg-3

F S H F S H Fragmentation Sub-Header (8 bits) F S H

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MAC – CPS QoS

Three components of 802.16 QoS

» Service flow QoS scheduling » Dynamic service establishment » Two-phase activation model (admit first, then activate)

Service Flow

» A unidirectional MAC-layer transport service characterized by a set of QoS parameters (latency, jitter, throughput) » Identified by a 32-bit SFID (Service Flow ID)

Three types of service flows

» Provisioned: controlled by network management system » Admitted: the required resources reserved by BS, but not active » Active: the required resources committed by the BS

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MAC – CPS – Uplink Service Classes

UGS: Unsolicited Grant Services rtPS: Real-time Polling Services nrtPS: Non-real-time Polling Services BE: Best Effort

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MAC – CPS – Automatic Repeat reQuest (ARQ)

A Layer-2 sliding-window based flow control mechanism Per connection basis Only effective to non-real-time applications Uses a 11-bit sequence number field Uses CRC-32 checksum of MAC PDU to check data errors Maintain the same fragmentation structure for Retransmission Optional