Mobile Communication

142
IT2402 MOBILE COMMUNICATION UNIT II Dr.A.Kathirvel, Professor and Head, Dept of IT Anand Institute of Higher Technology, Chennai

Transcript of Mobile Communication

Page 1: Mobile Communication

IT2402 MOBILE COMMUNICATION

UNIT – II

Dr.A.Kathirvel, Professor and Head, Dept of IT Anand Institute of Higher Technology, Chennai

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Unit - II

WIRELESS NETWORKS

Wireless LAN – IEEE 802.11 Standards – Architecture – Services – Mobile Ad hoc Networks- WiFi and WiMAX - Wireless Local Loop

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LAN/WLAN World

LANs provide connectivity for interconnecting computing resources at the local levels of an organization

Wired LANs

Limitations because of physical, hard-wired infrastructure

Wireless LANs provide

Flexibility

Portability

Mobility

Ease of Installation

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LAN Components

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Repeater

A repeater receives a signal, regenerates it, and passes it on.

It can regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media.

It operates at Physical Layer of OSI

The Four Repeater Rule for 10-Mbps Ethernet should be used as a standard when extending LAN segments.

This rule states that no more than four repeaters can be used between hosts on a LAN.

This rule is used to limit latency added to frame travel by each repeater.

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Hub

Hubs are used to connect multiple nodes to a single physical device, which connects to the network.

Hubs are actually multiport repeaters.

Using a hub changes the network

topology from a linear bus, to a

star.

With hubs, data arriving over the

cables to a hub port is electrically

repeated on all the other ports

connected to the same network

segment, except for the port on

which the data was sent.

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Bridge

Bridges are used to logically separate network segments within the same network.

They operate at the OSI data link layer (Layer 2) and are independent of higher-layer protocols.

The function of the bridge is to make intelligent decisions about whether or not to pass signals on to the next segment of a network.

When a bridge receives a frame on the

network, the destination MAC address is

looked up in the bridge table to determine

whether to filter, flood, or copy the frame onto

another segment

Broadcast Packets are forwarded

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Switch

Switches are Multiport Bridges.

Switches provide a unique network segment on each port, thereby separating collision domains.

Today, network designers are replacing hubs in their wiring closets with switches to increase their network performance and bandwidth while protecting their existing wiring investments.

Like bridges, switches learn certain information about the data

packets that are received from various computers on the

network.

Switches use this information to build forwarding tables to

determine the destination of data being sent by one computer to

another computer on the network.

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Switches: Dedicated Access

Hosts have direct connection to switch

Full Duplex: No collisions

Switching: A-to-A’ and B-to-B’ simultaneously, no collisions

Switches can be cascaded to expand the network

switch

A

A’

B

B’

C

C’

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Wireless networks

Wireless PANs (Bluetooth – IEEE 802.15) very low range

wireless connection to printers etc

Wireless LANs (WiFi – IEEE 802.11) infrastructure as well as ad-hoc

networks possible

home/office networking

Multihop Ad hoc Networks useful when infrastructure not

available, impractical, or expensive

military applications, emergencies

Wireless MANs (WiMAX-802.16)

Similar to cellular networks

traditional base station infrastructure systems

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802.11 Wireless LAN

Provides network connectivity over wireless media

An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network

The AP is connected to wired network and is equipped with antennae to provide wireless connectivity

Network

connectivity

to the

legacy

wired LAN

Desktop

with PCI 802.11 LAN card

Laptop

with PCMCIA 802.11 LAN card Access Point

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802.11 Wireless LAN Range ( Distance between Access Point and WLAN client)

depends on structural hindrances and RF gain of the antenna at the Access Point

To service larger areas, multiple APs may be installed with a 20-30% overlap

A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP (Hand-Off)

Three flavors:

802.11b

802.11a

802.11g

LAN Technologies

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Multiple Access with Collision Avoidance (MACA)

Before every data transmission Sender sends a Request to Send (RTS) frame containing

the length of the transmission Receiver respond with a Clear to Send (CTS) frame Sender sends data Receiver sends an ACK; now another sender can send data

When sender doesn’t get a CTS back, it assumes collision

sender receiver other node in

sender’s range RTS

CTS

ACK

data

other node in

receiver’s range

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WLAN : 802.11b

The most popular 802.11 standard currently in deployment.

Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band

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WLAN : 802.11a

Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band

Incompatible with devices operating in 2.4GHz

Supports Data rates up to 54 Mbps.

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WLAN : 802.11g

Supports data rates as high as 54 Mbps on the 2.4 GHz band

Provides backward compatibility with 802.11b equipment

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Medical Professionals

Education

Temporary Situations

Airlines

Security Staff

Emergency Centers

Wireless LAN Applications

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Wireless Local Area Networks

The proliferation of laptop computers and other mobile devices (PDAs and cell phones) created an obvious application level demand for wireless local area networking.

Companies jumped in, quickly developing incompatible wireless products in the 1990’s.

Industry decided to entrust standardization to IEEE committee that dealt with wired LANS – namely, the IEEE 802 committee!!

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In response to lacking standards, IEEE developed the first internationally recognized wireless LAN standard – IEEE 802.11

IEEE published 802.11 in 1997, after seven years of work

Most prominent specification for WLANs

Scope of IEEE 802.11 is limited to Physical and Data Link Layers.

IEEE 802.11 Wireless LAN Standard

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Appliance Interoperability

Fast Product Development

Stable Future Migration

Price Reductions

The 802.11 standard takes into account the following significant differences between wireless and wired LANs:

Power Management

Security

Bandwidth

Benefits of 802.11 Standard

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IEEE 802 Standards Working Groups

Figure 1-38. The important ones are marked with *. The ones marked with

are hibernating. The one marked with † gave up.

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Categories of Wireless Networks

Base Station :: all communication through an access point {note hub topology}. Other nodes can be fixed or mobile.

Infrastructure Wireless :: base station network is connected to the wired Internet.

Ad hoc Wireless :: wireless nodes communicate directly with one another.

MANETs (Mobile Ad Hoc Networks) :: ad hoc nodes are mobile.

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Wireless LANs

Figure 1-36.(a) Wireless networking with a base station. (b) Ad hoc networking.

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IEEE 802 LAN Standards Family

IEEE 802.3

Carrier

Sense

IEEE 802.4

Token

Bus

IEEE 802.5

Token

Ring

IEEE 802.11

Wireless

IEEE 802.2

Logical Link Control (LLC)

PHY OSI Layer 1

(Physical)

Mac

OSI Layer 2

(Data Link)

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The 802.11 Protocol Stack

Note – ordinary 802.11 products are no longer being manufactured.

Figure 4-25. Part of the 802.11 protocol stack.

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Wireless Physical Layer

Physical layer conforms to OSI (five options) 1997: 802.11 infrared, FHSS, DHSS 1999: 802.11a OFDM and 802.11b HR-DSSS 2001: 802.11g OFDM

802.11 Infrared Two capacities 1 Mbps or 2 Mbps. Range is 10 to 20 meters and cannot penetrate walls. Does not work outdoors.

802.11 FHSS (Frequence Hopping Spread Spectrum) The main issue is multipath fading. 79 non-overlapping channels, each 1 Mhz wide at low end of

2.4 GHz ISM band. Same pseudo-random number generator used by all stations. Dwell time: min. time on channel before hopping (400msec).

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Wireless Physical Layer

802.11 DSSS (Direct Sequence Spread Spectrum) Spreads signal over entire spectrum using pseudo-random sequence (similar

to CDMA see Tanenbaum sec. 2.6.2).

Each bit transmitted using an 11 chips Barker sequence, PSK at 1Mbaud.

1 or 2 Mbps.

802.11a OFDM (Orthogonal Frequency Divisional Multiplexing) Compatible with European HiperLan2.

54Mbps in wider 5.5 GHz band transmission range is limited.

Uses 52 FDM channels (48 for data; 4 for synchronization).

Encoding is complex ( PSM up to 18 Mbps and QAM above this capacity).

E.g., at 54Mbps 216 data bits encoded into into 288-bit symbols.

More difficulty penetrating walls.

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Wireless Physical Layer

802.11b HR-DSSS (High Rate Direct Sequence Spread Spectrum)

11a and 11b shows a split in the standards committee.

11b approved and hit the market before 11a.

Up to 11 Mbps in 2.4 GHz band using 11 million chips/sec.

Note in this bandwidth all these protocols have to deal with interference from microwave ovens, cordless phones and garage door openers.

Range is 7 times greater than 11a.

11b and 11a are incompatible!!

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Wireless Physical Layer

802.11g OFDM(Orthogonal Frequency Division Multiplexing)

An attempt to combine the best of both 802.11a and 802.11b.

Supports bandwidths up to 54 Mbps.

Uses 2.4 GHz frequency for greater range.

Is backward compatible with 802.11b.

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802.11 MAC Sublayer Protocol

In 802.11 wireless LANs, “seizing channel” does not exist as in 802.3 wired Ethernet.

Two additional problems: Hidden Terminal Problem

Exposed Station Problem

To deal with these two problems 802.11 supports two modes of operation DCF (Distributed Coordination Function) and PCF (Point Coordination Function).

All implementations must support DCF, but PCF is optional.

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Figure 4-26.(a)The hidden station problem. (b) The exposed station problem.

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The Hidden Terminal Problem

Wireless stations have transmission ranges and not all stations are within radio range of each other.

Simple CSMA will not work!

C transmits to B.

If A “senses” the channel, it will not hear C’s transmission and falsely conclude that A can begin a transmission to B.

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The Exposed Station Problem

This is the inverse problem.

B wants to send to C and listens to the channel.

When B hears A’s transmission, B falsely assumes that it cannot send to C.

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Distribute Coordination Function (DCF)

Uses CSMA/ CA (CSMA with Collision Avoidance).

Uses both physical and virtual carrier sensing.

Two methods are supported:

based on MACAW(Multiple Access with Collision Avoidance for Wireless) with virtual carrier sensing.

1-persistent physical carrier sensing.

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Access point (AP): A station that provides access to the DS.

Basic service set (BSS): A set of stations controlled by a single AP.

Distribution system (DS): A system used to interconnect a set of BSSs to create an ESS.

DS is implementation-independent. It can be a wired 802.3 Ethernet LAN, 802.4 token bus, 802.5 token ring or another 802.11 medium.

Extended service set (ESS):Two or more BSS interconnected by DS

Portal: Logical entity where 802.11 network integrates with a non 802.11 network.

IEEE 802.11 Terminology

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WLAN Topology: Ad-Hoc Network

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WLAN Topology: Ad-Hoc Network

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Distribution service (DS)

Used to exchange MAC frames from station in one BSS to station in another BSS

Integration service

Transfer of data between station on IEEE 802.11 LAN and station on integrated IEEE 802.x LAN

IEEE 802.11 Services: Distribution of Messages

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Association

Establishes initial association between station and AP

Re-association

Enables transfer of association from one AP to another, allowing station to move from one BSS to another

Disassociation

Association termination notice from station or AP

Association Related Services

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Re-Association

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Authentication

Establishes identity of stations to each other

De-authentication

Invoked when existing authentication is terminated

Privacy

Prevents message contents from being read by unintended recipient

Access and Privacy Services

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IEEE 802.11 Medium Access Control

MAC layer covers three functional areas:

Reliable data delivery

Access control

Security

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Reliable Data Delivery

Loss of frames due to noise, interference, and propagation effects

Frame exchange protocol Source station transmits data

Destination responds with acknowledgment (ACK)

If source doesn’t receive ACK, it retransmits frame

Four frame exchange for enhanced reliability Source issues request to send (RTS)

Destination responds with clear to send (CTS)

Source transmits data

Destination responds with ACK

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Distributed Coordination Function (DCF)

Distributed access protocol

Contention-Based

Makes use of CSMA/CA rather than CSMA/CD

Suited for ad hoc network and ordinary asynchronous traffic

Point Coordination Function (PCF)

Alternative access method on top of DCF

Centralized access protocol

Contention-Free

Works like polling

Suited for time bound services like voice or multimedia

Access Control

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CSMA/CD vs. CSMA/CA

CSMA/CD – CSMA/Collision detection

For wire communication

No control BEFORE transmission

Generates collisions

Collision Detection-How?

CSMA/CA – CSMA/Collision Avoidance

For wireless communication

Collision avoidance BEFORE transmission

Why avoidance on wireless?

Difference in energy/power for transmit & receive

Difficult to distinguish between incoming weak signals, noise, and effects of own transmission

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Interframe Space (IFS)

Defined length of time for control

SIFS - Short Inter Frame Spacing

Used for immediate response actions e.g ACK, CTS

PIFS - Point Inter Frame Spacing

Used by centralized controller in PCF scheme

DIFS - Distributed Inter Frame Spacing

Used for all ordinary asynchronous traffic

DIFS (MAX) > PIFS > SIFS (MIN)

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RTS-CTS-DATA-ACK

DIFS: Distributed IFS RTS: Request To Send SIFS: Short IFS CTS: Clear To Send ACK: Acknowledgement NAV: Network Allocation Vector DCF: Distributed Coordination Function

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MAC Frame Format

Frame

Control

Duration

ID Addr 1 Addr 2 Addr 3 Addr 4 Sequence

Control CRC

Frame

Body

2 2 6 6 6 6 2 0-2312 4

802.11 MAC Header

Protocol

Version Type SubType

To

DS Retry

Pwr

Mgt

More

Data WEP Order

Frame Control Field

Bits: 2 2 4 1 1 1 1 1 1 1 1

DS

From More

Frag

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MAC Layer Frames

Data Frames

Control Frames

RTS,CTS,ACK and PS-POLL

Management Frames

Authentication and De-Authentication

Association, Re-Association, and Disassociation

Beacon and Probe frames

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IEEE 802.11 Security

Authentication provided by open system or shared key authentication (Authentication is used instead of wired media physical connection)

Privacy provided by WEP (Privacy is used to provide the confidential aspects of closed wired media)

An Integrity check is performed using a 32-bit CRC

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Authentication

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WEP Encryption/Decryption

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Is WLAN Secure ?

The Parking Lot

attack

Man in the middle

attack

Freely available tools

like Air Snort, WEP

crack to snoop into a

WLAN

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Physical Media Defined by Original 802.11 Standard

Frequency-hopping spread spectrum

Operating in 2.4 GHz ISM band

Lower cost, power consumption

Most tolerant to signal interference

Direct-sequence spread spectrum

Operating in 2.4 GHz ISM band

Supports higher data rates

More range than FH or IR physical layers

Infrared

Lowest cost

Lowest range compared to spread spectrum

Doesn’t penetrate walls, so no eavesdropping

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Frequency Hopping Spread Spectrum

Signal is broadcast over seemingly random series of radio frequencies

Signal hops from frequency to frequency at fixed intervals

Receiver, hopping between frequencies in synchronization with transmitter, picks up message

Advantages

Efficient utilization of available bandwidth

Eavesdropper hear only unintelligible blips

Attempts to jam signal on one frequency succeed only at knocking out a few bits

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Direct Sequence Spread Spectrum

Each bit in original signal is represented by multiple bits in the transmitted signal

Spreading code spreads signal across a wider frequency band

DSSS is the only physical layer specified for the 802.11b specification

802.11a and 802.11b differ in use of chipping method

802.11a uses 11-bit barker chip

802.11b uses 8-bit complimentary code keying (CCK) algorithm

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IEEE 802.11a and IEEE 802.11b

IEEE 802.11a

Makes use of 5-GHz band

Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps

Uses orthogonal frequency division multiplexing (OFDM)

IEEE 802.11b

802.11b operates in 2.4 GHz band

Provides data rates of 5.5 and 11 Mbps

Complementary code keying (CCK) modulation scheme

For more information: http://home.no.net/coverage/rapport/80211.htm

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Other Standards

Japan has introduced Millimeter Wave Wireless LAN (MWWL).

Europe has introduced HIPERLAN (High Performance Radio Local Area Network)

Features, capabilities, and technology similar to those of IEEE 802.11 used in US

Developed by ETSI (European Telecommunications standards institute)

Provides high speed communications (20Mbps)

Has technical advantages such as inclusion of Quality of Service

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HIPERLAN-reference model

Medium Access Control

(MAC) Sublayer

Channel Access Control

(CAC) Sublayer

Physical (PHY) Layer

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

higher layer protocols

OSI

Reference Model

HIPERLAN

Reference Model

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Future of WLAN

WLANs move to maturity

Higher Speeds

Improved Security

Seamless end-to-end protocols

Better Error control

Long distances

New vendors

Better interoperability

Global networking

Anywhere, anytime, any-form connectivity…

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Mobile Ad Hoc Networks (MANETs)

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Why we need ad-hoc networks?

Ease & Speed of deployment.

Do not need backbone infrastructure support

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What is ad-hoc networks?

Decentralized multi-hop relaying network, where each node performs routing.

When we need ad-hoc networks?

In many scenarios where deployment of a wired network is impractical or impossible

4 W’s for Ad-hoc Networks

Where we need ad-hoc networks?

Military Applications

Emergency Operations

Meeting rooms

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Mobile Ad-hoc NETworks (MANET)

Self-configuring infrastructureless network of mobile devices.

Each device is free to move independently in any direction, and change its links to other devices frequently.

The primary challenge is equipping each device to continuously maintain the information required to properly route traffic.

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Single hop – Nodes communicate directly Multi hop – Traffic has to be forwarded

Ad-hoc networks - Classifications

a b

c

d

a

b

c

d

a b

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MANET

Two types of wireless networks:

Infrastructure network

base stations are the bridges

a mobile host will communicate with the nearest base station

handoff is taken when a host roams from one base to another

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MANET

Ad hoc network:

infrastructure less: no fixed base stations

without the assistance of base stations for

communication

Due to transmission range constraint,

two MHs need multi-hop routing for

communication

quickly and unpredictably changing topology

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Cell Phone Networks

Infrastructure

Network

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MANET

MANET = Mobile Ad Hoc Networks

a set of mobile hosts, each with a transceiver

no base stations; no fixed network infrastructure

multi-hop communication

needs a routing protocol which can handle changing topology

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MANET

Single-Hop Ad Hoc

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MANET

Multi-hop Ad Hoc

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MANET Single-hop Vs. Multi-hop systems

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Ad Hoc typical applications

Personal area networking

cell phone, laptop, ear phone, wrist watch

Military environments

soldiers, tanks, planes

Civilian environments

car network

meeting rooms

sports stadiums

boats, small aircraft

Emergency operations

search-and-rescue

policing and fire fighting

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Peer-to-Peer

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Multi-hop Peer-to-Peer

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Multi-hopping via Wireless Router

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Hopping on the Network

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Supports Mobility

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Supports Non Line-of-Sight

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Military applications

Situational Awareness (SA) and Command and Control (C2) for military.

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Nokia Roof Top Wireless Routing

A wireless broadband solution for residential markets, based on a multi hop Ad-Hoc (mesh) networking.

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Nokia Roof Top

Roof Top solution (Nokia, Finland)

Wireless router

a radio frequency (RF) modem

a digital Internet protocol (IP) router

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FHP

FHP Wireless, USA

ad hoc network in a campus

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FHP Wireless

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FHP Wireless

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Mesh Networks

Mesh Networks, USA

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System Architecture: Mesh Networks

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Networking Scenario: To Internet

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SkyPilot NeighborNet

• SkyPilot Network, USA

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WiFi

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What is the goal of 802.11 standard ?

To develop a Medium Access Control (MAC) and Physical Layer (PHY) specification for wireless connectivity for fixed, portable and moving stations

within a local area.

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802.11 sub-standards

802.11 MAC (Media Access Control) ratified 1999

802.11b PHY 2.4 GHz (max 11 Mbps) ratified 1999

802.11a PHY 5.0 GHz (max 54 Mbps) ratified 1999

802.11g PHY 2.0 GHz (max 54 Mbps) ratified 2003

802.11i Security draft number XXX

802.11e QoS, Multimedia draft number XXX

802.11h European regulations for 5GHz draft number XXX

802.11h Japan regulations for 5GHz draft number XXX

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Do I need any license to use 802.11 device ?

No , 2.4 GHz and 5.0 GHz are public available frequency !!!

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Context with OSI layers

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Logical Link Control Services

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Standard 802.11 frame format

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Frames types and subtypes

Three types of frames:

Control

(ACK,RTS,CTS ,Power Save …)

Management

(Beacon,Probe Request ,Probe Response,

Association request , Association response …)

Data

(Data, Null Data, Data_CF_Ack , ….)

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Infrastructure Model includes:

Stations (STA) any wireless device

Access Point (AP) connects BSS to DS controls access by STA’s

Basic Service Set (BSS) a region controlled by an AP mobility is supported within a single

BSS

Extended Service Set (ESS) a set of BSS’s forming a virtual BSS mobility is supported between BSS’s

in an ESS

Distribution Service (DS) connection between BSS’s

802.11 MAC –Infrastructure model

DS

BSS1

BSS2

BSS3 STA1

STA2

STA3

ESS1

AP1

AP2

AP3

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802.11 MAC supports infrastructure and ad hoc network models

Ad Hoc Model includes:

Stations (STA) any wireless device act as distributed AP

Independent Basic Service Set (IBSS) BSS forming a self

contained network no AP and no connection

to the DS

IBSS

STA1

STA2

STA3

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Two types of access to air

DCF (distributed coordination function ) means everybody can speak and try

to get air : 100% on the market

PCF (point coordination function) means ONE point coordinator (BOSS)

who will allowed you to speak

(like in bluetooth)

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Summary of required features and difficulties vs 802.11 features

Features High speed operation (PHY only) Fair access (DCF, PCF) Time-bounded access (PCF) Flexible configuration (BSS, IBSS) Security (WEP) Mobility support (ESS) Low power (PS)

Difficulties Hidden terminals (RTS/CTS) Capture (CSMA/CA, ACK) Noise and interference (ACK, frag) Limited spectrum (licencing, PHYs)

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WiMax

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WiMAX

Goal: Provide high-speed Internet access to home and business subscribers, without wires.

Base stations (BS) and subscriber stations (SS)

Centralized access control to prevents collisions

Supports applications with different QoS requirements

WiMAX is a subset of IEEE 802.16 standard

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IEEE 802.16 standards

802.16.1 (10-66 GHz, line-of-sight, up to 134Mbit/s)

802.16.2 (minimizing interference between coexisting WMANs)

802.16a (2-11 Ghz, Mesh, non-line-of-sight)

802.16b (5-6 Ghz)

802.16c (detailed system profiles)

P802.16e (Mobile Wireless MAN)

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Physical layer

Allows use of directional antennas

Allows use of two different duplexing schemes:

Frequency Division Duplexing (FDD)

Time Division Duplexing (TDD)

Support for both full and half duplex stations

Adaptive Data Burst profiles

Transmission parameters (e.g. Modulation, FEC) can be modified on a frame-by-frame basis for each SS

Profiles are identified by ”Interval Usage Code”

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Time Division Duplexing (TDD)

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Media Acces Control (MAC)

Connection oriented

Connection ID (CID), Service Flows

Channel access: decided by BS

UL-MAP

Defines uplink channel access

Defines uplink data burst profiles

DL-MAP

Defines downlink data burst profiles

UL-MAP and DL-MAP are both transmitted in the beginning of each downlink subframe

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TDD Downlink subframe

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Uplink subframe

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Uplink periods

Initial Maintenance opportunities Ranging - to determine network delay and to request power or

profile changes Collisions may occur in this interval

Request opportunities SSs request bandwith in response to polling from BS Collisions may occur in this interval

Data grants period SSs transmit data bursts in the intervals granted by the BS Transition gaps between data intervals for synchronization

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Bandwidth request

SSs may request bandwidth in 3 ways:

Use the ”contention request opportunities” interval upon being polled by the BS

Send a standalone MAC message called ”BW request” in an allready granted slot

Piggyback a BW request message on a data packet

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Bandwidth allocation

BS grants/allocates bandwidth in one of two modes: Grant Per Subscriber Station (GPSS) Grant Per Connection (GPC)

Decision based on requested bandwidth and QoS requirements vs available resources

Grants are notified through the UL-MAP

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Bandwidth Request-Grant Protocol

BS

SS1

SS2

1

2.1

2.2

1. BS allocates bandwidth to SSs for transmitting bandwidth request.

2.1 SS1 transmits bandwidth requests. 2.2 SS2 transmits bandwidth requests.

4. BS allocates bandwidth to SSs for transmitting data based on their bandwidth requests. Bandwidth is also allocated for requesting more bandwidth.

5.1 SS1 transmits data and bandwidth requests.

5.2 SS2 transmits data and bandwidth requests.

4

5.1

5.2

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Scheduling services

Unsolicited Grant Service (UGS) Real-time, periodic fixed size packets (e.g. VoIP) No periodic bandwith requests required

Real-Time Polling Service (rtPS) Real-time, periodic variable sizes packets (e.g MPEG) BS issues periodic unicast polls

Non-Real-Time Polling Service (nrtPS) Variable sized packets with loose delay requirements (FTP) BS issues unicast polls regularly (not necessarily periodic) Can also use contention requests and piggybacking

Best Effort Service Never polled individually Can use contention requests and piggybacking

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Example

Total Uplink Bytes = 100

2 SS and 1 BS

SS1

Demands:

UGS = 20

rtPS = 12

nrtPS = 15

BE = 30

SS2

Demands:

UGS = 10

rtPS = 10

nrtPS = 15

BE = 20

Total Demand Per

Flow:

UGS = 30

rtPS = 22

nrtPS = 30

BE = 50

Flows: UGS rtPS nrtPS BE

1st Round 40 30 20 10

30 22 20 10

Excess Bytes = 18

2nd Round 30 22 20+12 10+6

30 22 32 16

Excess Bytes = 2

3rd Round 30 22 30 16+2

30 22 30 18

SS1 Allocation = 20 +12 + 15 + 9 = 56

SS2 Allocation = 10 +10 + 15 + 9 = 44

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116

802.11/802.16

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117

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118

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Wireless Local Loop (WLL)

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Definition

What is WLL?

WLL is a system that connects subscribers to the local telephone station wirelessly.

Systems WLL is based on:

Cellular

Satellite (specific and adjunct)

Microcellular

Other names

Radio In The Loop (RITL)

Fixed-Radio Access (FRA).

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A general WLL setup

Page 122: Mobile Communication

WLL services

Desirable:

Wireless feature should be transparent

Wireline Custom features

Other:

Business related

Hunt groups,

Call transfers

Conference calling

Calling cards, coin phones

V.29 (9600bps)

ISDN (64kbps)

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WLL should provide…

Toll-quality service

Expand from a central office to about 5 miles

Low license cost

Subscriber costs equivalent or better than copper

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Ideas for U.S. market

Supplement Copper Lines

Easier third telephone line

Data service

Fixed Mobile Users

Take phone wherever you want / charged on 2 levels

“home” could mean neighborhood

Charged regular mobile rate if you’re on the road

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Cost Considerations

Wireless cost is constant over distance for WLL

Wireline depends on distance AND terrain

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Situations “made” for WLL

Environments where 3rd line is degraded might be cheaper to go wireless

Where it’s impossible to lay copper (3rd world, small islands)

Business parks, industrial areas

Speedy deployment, stop gap application till wireline is in

90-120 days for activation

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Developed vs Developing

Developed: Wireline service

Firmly established, cellular penetration is relatively high

Incumbent operator would use it to install 2nd, 3rd lines, coverage to rural areas

2nd or 3rd competitive operator deploy it for fast & cost effective deployment

Quick way to establish market presence

cellular complement to their offerings

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Developed vs Developing

Developing

Quick & easy to deploy in countries with little copper line service, so as to accommodate people on enormous waiting lists for basic service

Low maintenance costs

Allows more competition in provider market

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Examples

UK

150 PTOs have licenses for wireless

Focus on regional networks

WLL Commercial services

Ionica, Atlantic Telecom, Scottish Telecom

Poland

Most exciting market in eastern Europe

Local loop is the bottleneck

150,000 WLL lines since 1996 (15% of new)

Ericsson, Motorola contracts

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Connection Setup

PSTN Switch

function

WLL

Controller

AM

HLR

Transceiver WASU

Trunk Air Interface

UWLL

TWLL

Wireless Access Network Unit(WANU)

Interface between underlying telephone network and wireless link

consists of

Base Station Transceivers (BTS)

Radio Controller(RPCU)

Access Manager(AM)

Home Location Register(HLR)

WANU

Wireless Access Subscriber Unit (WASU)

located at the subscriber

translates wireless link into a traditional telephone connection

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Important Results of Fixed to Fixed Propagation in WLLs

Signal channel is not a Rayleigh fading channel:

Power control algorithms are simpler and can be utilized more effectively

Channel Randomness is lost:

Makes analysis difficult

Pathloss exponent is considerably smaller (Why?):

20dB/dec compared to 40dB/dec

Decreases cell capacity

Allows for larger coverage area

Page 132: Mobile Communication

Fixed to Fixed Propagation(cont’d)

No handoffs necessary:

Decreases hardware costs and system complexity

Increases quality of service through accurate traffic predictions

Allows usage of directional antennas:

Can greatly reduce interference and increase cell capacity

-30dB

30dB

0o 60o -40dB

10dB

0o 120o 180o

BS antenna Subscriber antenna

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In-Cell Interference (CDMA)

I = (Nh – 1)aS NhaS a = voice activity factor

Nh = total # of houses

S = power received at cell site from every house

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Out-of-Cell Interference

Pathloss: 20dB/dec as opposed to 40dB/dec

need to take in account more tiers

Only from houses whose antennas are directed at the center cell base station

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Interference from Another Cell

• Blue area is region of interferers for C

• It is Not a perfect pie shape

• If w = (1/2)*(antenna width)

(in radians)

• W = w+2sin-1((R/D)sin(w/2))

• If w<<1 and R<<D:

W = w (1+(R/D))

is the “pie” arc length

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Per-Tier Interference

Integration over W and all the cells at tier n yields:

In = [aNhSw/(3sqrt(3))][1/n] for n>4

Interference is proportional to antenna width w and inversely proportional to the tier number.

Decreasing the antenna width can greatly reduce interference.

As the number of tiers approaches infinity, so does the total interference. Therefore, system capacity is a function of the total number of tiers in the system.

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Capacity comparison for 5 MHz spectrum allocation

Detail IS-95 CDMA IS-136 TDMA ETSI (GSM)

Mobile WLL Mobile WLL Mobile WLL

Chan. BW

(kHz)

1250 1250 30 30 200 200

# channels 4 4 167 167 25 25

Eb/N0 7 dB 6dB 18dB 14dB 12dB 12dB

Freq. Reuse 1 1 7 4 3 3

Effective Chan.

Per sect.

4 4 7.95 13.92 2.78 2.78

Erlangs per cell

Per MHz

38.3 48.7 9.84 19.6 9.12 9.12

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Comparison

WLL Mobile Wireless Wireline

Good LOS component Mainly diffuse components No diffuse components

Rician fading Rayleigh fading No fading

Narrowbeam directed

antennas

Omnidirectional antennas Expensive wires

High Channel reuse Less Channel reuse Reuse Limited by wiring

Simple design, constant

channel

Expensive DSPs, power

control

Expensive to build and

maintain

Low in-premises mobility

only, easy access

High mobility allowed,

easy access

Low in-premises mobility,

wiring of distant areas

cumbersome

Weather conditions effects Not very reliable Very reliable

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Examples of services provided

Marconi WipLL (wireless IP local loop)

Based on Frequency hopping CDMA

Internet Protocol 64kbps to 2.4Mbps rates Committed Information Rate or best effort service

Lucent WSS (wireless subscriber system)

800 to 5000 subscribers per switch

Uses FDMA/FDD 12 Km to 40Km coverage

GoodWin WLL

DECT standards

9.6 kbps rate

Specified conditions -5°С...+55°С, 20...75% humidity

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WLL

Basie station

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Future of WLL

Depends on

economic development

existing infrastructure of a region

Offers

market competition

quick deployment

relatively reliable service at low costs

Page 142: Mobile Communication

Questions ?