Tuesday, December 30, 2008

Wireless Sensor Network

Network technologies are developing fastly with this improvements sensor has promoted.  

At first all sensor has one connection with host machine, but this method is occurs high cost, configuration management is difficult.

With wireless sensor network, sensors connected with each other and create a network this method is reduce costs and complexity.


They are autonomous devices and monitoring physical or environmental conditions such as:

  Temperature
Sound
Vibration 
Pressure
Motion

Sensor network is typically equipped with radio transceiver or other wireless communications device, a small microcontroller, an energy source, usually a battery.

The cost of sensor nodes is similarly variable, hundreds of dollars to a few cents, depending on the size, weight, energy consumption, sensitivity, speed and bandwidth.


The development of wireless sensor networks was originally for military applications such as battlefield surveillance.

However, wireless sensor networks are now used in many civilian application areas, including environment and habitat monitoring, healthcare applications, home automation, and traffic control.

Satellite-Related Terms

Earth Stations – antenna systems on or near earth
 Uplink – transmission from an earth station to a satellite
 Downlink – transmission from a satellite to an earth station
 Transponder – electronics in the satellite that convert uplink signals to downlink signals

Mobile Switching Center (MSC) Databases

Home location register (HLR) database – stores information about each subscriber that belongs to it
 Visitor location register (VLR) database – maintains information about subscribers currently physically in the region
 Authentication center database (AuC) – used for authentication activities, holds encryption keys
 Equipment identity register database (EIR) – keeps track of the type of equipment that exists at the mobile station

Cellular Systems Terms

 Base Station (BS) – includes an antenna, a controller, and a number of receivers
 Mobile telecommunications switching office (MTSO) – connects calls between mobile units
 Two types of channels available between mobile unit and BS

 -Control channels – used to exchange information having to do with setting up and maintaining calls
 -Traffic channels – carry voice or data connection between users

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)
 -Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-QAM
 IEEE 802.11b
 -Provides data rates of 5.5 and 11 Mbps
 -Complementary code keying (CCK) modulation scheme

IEEE 802.11 Architecture

 Distribution system (DS)
 Access point (AP)
 Basic service set (BSS)

 -Stations competing for access to shared wireless medium
 -Isolated or connected to backbone DS through AP
 Extended service set (ESS)
 -Two or more basic service sets interconnected by DS

Differences between LLC and HDLC

LLC uses asynchronous balanced mode of operation of HDLC (type 2 operation)
 LLC supports unacknowledged connectionless service (type 1 operation)
 LLC supports acknowledged connectionless service (type 3 operation)
 LLC permits multiplexing by the use of LLC service access points (LSAPs)

LLC Services

 Unacknowledged connectionless service
 No flow- and error-control mechanisms
 Data delivery not guaranteed
 Connection-mode service
 Logical connection set up between two users
 Flow- and error-control provided
 Acknowledged connectionless service
 Cross between previous two
 Datagrams acknowledged
 No prior logical setup

MAC Frame Format

MAC control
 Contains Mac protocol information
 Destination MAC address
 Destination physical attachment point
 Source MAC address
 Source physical attachment point
 CRC
 Cyclic redundancy check

Separation of LLC and MAC

The logic required to manage access to a shared-access medium not found in traditional layer 2 data link control
 For the same LLC, several MAC options may be provided

Internetworking Terms

Communication network – facility that provides a data transfer service among devices attached to the network
 Internet – collection of communication networks, interconnected by bridges/routers
 Intranet – internet used by an organization for internal purposes
 -Provides key Internet applications
 -Can exist as an isolated, self-contained internet

 End System (ES) – device used to support end-user applications or services
 Intermediate System (IS) – device used to connect two networks
 Bridge – an IS used to connect two LANs that use similar LAN protocols
 Router - an IS used to connect two networks that may or may not be similar

Layers of the OSI Model

 Application
 Presentation
 Session
 Transport
 Network
 Data link
 Physical



OSI Application Layer
 Provides access to the OSI environment for users
 Provides distributed information services


OSI Presentation Layer
 Provides independence to the application processes from differences in data representation (syntax)


OSI Session Layer
 Provides the control structure for communication between applications
 Establishes, manages, and terminates connections (sessions) between cooperating applications


OSI Transport Layer
 Provides reliable, transparent transfer of data between end points
 Provides end-to-end error recovery and flow control


OSI Network Layer
 Provides upper layers with independence from the data transmission and switching technologies used to connect systems
 Responsible for establishing, maintaining, and terminating connections


OSI Data link Layer
 Provides for the reliable transfer of information across the physical link
 Sends blocks (frames) with the necessary synchronization, error control, and flow control


OSI Physical Layer
 Concerned with transmission of unstructured bit stream over physical medium
 Deals with accessing the physical medium
 Mechanical characteristics
 Electrical characteristics
 Functional characteristics
 Procedural characteristics

TCP/IP Layers

 Physical layer
 Network access layer
 Internet layer
 Host-to-host, or transport layer
 Application layer


TCP/IP Physical Layer
 Covers the physical interface between a data transmission device and a transmission medium or network
 Physical layer specifies:
 Characteristics of the transmission medium
 The nature of the signals
 The data rate
 Other related matters


TCP/IP Network Access Layer
 Concerned with the exchange of data between an end system and the network to which it's attached
 Software used depends on type of network
 Circuit switching
 Packet switching (e.g., X.25)
 LANs (e.g., Ethernet)
 Others


TCP/IP Internet Layer
 Uses internet protocol (IP)
 Provides routing functions to allow data to traverse multiple interconnected networks
 Implemented in end systems and routers


Transport Layer
 Commonly uses transmission control protocol (tcp)
 Provides reliability during data exchange
 Completeness
 Order


TCP/IP Application Layer
 Logic supports user applications
 Uses separate modules that are peculiar to each different type of application

Categories of Noise

Thermal Noise
 Intermodulation noise
 Crosstalk
 Impulse Noise

Thermal Noise

Thermal noise due to agitation of electrons
 Present in all electronic devices and transmission media
 Cannot be eliminated
 Function of temperature
 Particularly significant for satellite communication

Types of Antennas

Isotropic antenna (idealized)
 Radiates power equally in all directions
Dipole antennas
 Half-wave dipole antenna (or Hertz antenna)
 Quarter-wave vertical antenna (or Marconi antenna)
Parabolic Reflective Antenna

Differences between LANs and WANs

Scope of a LAN is smaller
 LAN interconnects devices within a single building or cluster of buildings
 LAN usually owned by organization that owns the attached devices
 For WANs, most of network assets are not owned by same organization
 Internal data rate of LAN is much greater

Characteristics of LANs

Like WAN, LAN interconnects a variety of devices and provides a means for information exchange among them
 Traditional LANs
 Provide data rates of 1 to 20 Mbps
 High-speed LANS
 Provide data rates of 100 Mbps to 1 Gbps

Characteristics of WANs

 Covers large geographical areas
 Circuits provided by a common carrier
 Consists of interconnected switching nodes
 Traditional WANs provide modest capacity
 64000 bps common
 Business subscribers using T-1 service – 1.544
Mbps common
 Higher-speed WANs use optical fiber and transmission technique known as asynchronous transfer mode (ATM)
 10s and 100s of Mbps common

Types of Communication Networks

 Traditional
 Traditional local area network (LAN)
 Traditional wide area network (WAN)
 Higher-speed
 High-speed local area network (LAN)
 Metropolitan area network (MAN)
 High-speed wide area network (WAN)

Time-Domain Concepts

- Analog signal - signal intensity varies in a smooth fashion over time
 No breaks or discontinuities in the signal
- Digital signal - signal intensity maintains a constant level for some period of time and then changes to another constant level
- Periodic signal - analog or digital signal pattern that repeats over time
 s(t +T ) = s(t ) -¥<>
 where T is the period of the signal
- Aperiodic signal - analog or digital signal pattern that doesn't repeat over time
- Peak amplitude (A) - maximum value or strength of the signal over time; typically measured in volts
- Frequency (f )
 Rate, in cycles per second, or Hertz (Hz) at which
the signal repeats
- Period (T ) - amount of time it takes for one repetition of the signal
 T = 1/f
- Phase (f) - measure of the relative position in time within a single period of a signal
- Wavelength (l) - distance occupied by a single cycle of the signal
 Or, the distance between two points of corresponding phase of two consecutive cycles

Transmission Fundamentals, Analog and Digital Data, Channel Capacity, Multiplexing

Transmission Fundamentals, Analog and Digital Data, Channel Capacity, Multiplexing

1         Transmission Fundamentals,

First thing we will examine is the description of radio signals or the electromagnetic signal.

What is radio signal?

It is a function of time and frequency

This means there is a signal and this signal changes with frequency and time.

 

There is analog and digital signal.

 

Analog signal: no break or discontinuity, signal varies in a smooth fashion

Digital signal: signal intensity maintains a constant level for some period, and then changes to another constant level. Imagine 1 and 0 s.

 

Periodic signal: analog or digital signal pattern that repeats over time.

Aperiodic signal: doesn’t repeat over time

 

Peak amplitude: maximum value or strength of the signal

Frequency: rate, cycles per second, Hertz (Hz)

 

Period: amount of time it takes for one repetition of the signal

T=1/f

 

Phase: measure of the relative position in time within a single period of a signal.

 

Wavelength: distance occupied by a single cycle of the signal.

 

Drawings and mathlab examples:

 

t=0:0.01:1;

x=2*pi*t+0;

plot(t,sin(x)), grid on

>>  t=0:0.01:1;

x=2*pi*t+0;

plot(t,2*sin(x)), grid on

>>  t=0:0.01:1;

x=2*pi*2*t+0;

plot(t,2*sin(x)), grid on

>>   t=0:0.01:1;

x=2*pi*0.5*t+0;

plot(t,2*sin(x)), grid on

>>   t=0:0.01:4;

x=2*pi*0.25*t+0;

plot(t,sin(x)), grid on

>> t=0:0.01:4;

x=2*pi*0.25*t+90;

plot(t,sin(x)), grid on

 

 

 

 

1.2         Analog and Digital Data,

Analog: video, audio

Digital: text, integers

 

Analog signal: coninuously varying electromgnetic wave, can propogate analog and digital data

 

Digital signal: a sequence of voltage pulses, cheaper than analog signaling, less susceptiple to noise, suffer from attenuation..

 

Digital signals can propagate analog and digital data

 

Analog transmission---attenuation limits length of transmission link, amplifiers increase ranges..analog data can tolerate distortion, but digital data intruduces errors...

 

Digital transmission---attenuation endangers integrity of data, repeaters achieve greater distance, repeaters recover the signal and transmit

 

1.3         Channel Capacity,

the maximum data rate transmitted over a communication path, or channel.

 

Concepts:

Data rate: rate (bits per second)

Bandwidth: bandwidth of the transmitted signal constrained by the transmitter and the nature of the transmission medium. (hertz)

Noise:

Error rate:

 

1.4         Transmission media

Guided: wired—copper, fiber, coaxiel cables

unguided media---wireless transmission, antennas, directional, omnidirectional

 

 

 

 

 

 

 

 

 

1.5         Multiplexing

Carrying multiple signals on a single medium.

More efficient use of transmission medium


FDM –frequency-division multiplexing

TDM—time-division multiplexing

Protocols and the TCP/IP Protocol Suite

Protocol architecture
Overview of TCP/IP
Open systems interconnection (OSI) reference model
Internetworking

Communication Networks

Comparison of basic communication network technologies
 - Circuit switching
 - Packet switching
 - Frame relay
 - ATM

Transmission Fundamentals

Basic overview of transmission topics
 Data communications concepts
 - Includes techniques of analog and digital data transmission
 Channel capacity
 Transmission media
 Multiplexing

Limitations and Difficulties of Wireless Technologies

 Wireless is convenient and less expensive
 Limitations and political and technical difficulties inhibit wireless technologies
 Lack of an industry-wide standard
 Device limitations
 E.g., small LCD on a mobile telephone can only
displaying a few lines of text
 E.g., browsers of most mobile wireless devices use
wireless markup language (WML) instead of HTML

Background
 Provides preview and context for rest of
book
 Covers basic topics
 Data Communications
 TCP/IP

Broadband Wireless Technology

 Higher data rates obtainable with broadband wireless technology
 - Graphics, video, audio
 Shares same advantages of all wireless services: convenience and reduced cost
-  Service can be deployed faster than fixed service
-  No cost of cable plant
-  Service is mobile, deployed almost anywhere

Wireless Comes of Age

 Guglielmo Marconi invented the wireless telegraph in 1896
 Communication by encoding alphanumeric characters in analog signal
 Sent telegraphic signals across the Atlantic Ocean
 Communications satellites launched in 1960s
 Advances in wireless technology
 Radio, television, mobile telephone,communication satellites
 More recently
 Satellite communications, wireless networking,cellular technology

Breaking down the issues in Mobile Computing

• Technical Challenges of Mobile Computing
portability,
mobility,
wireless communications
system issues


Traveling people and their needs with respect to applications and technologies
application perspective: which applications are of benefit?
Which applications can be implemented and used effectively regarding the often narrow bandwidth, limited computing power, small memory and battery capacity and other resources of the terminals?


•Wireless Networks
to main types: terrestrial cellular and satellite networks – determine to a large extent application architectures and usable protocols
communication autonomy is an important feature of the terminals in these networks: thus the terminals are not always reachable for variety of reasons

•Data Management issues
where to keep the data, when to transmit it, whether to use caching and where in the network, how to optimize data placement, pull/push approach, transactional services, location-dependent queries etc
these questions are closely related with the
networking issues and properties of the terminals

Nomadic or Mobile Computing

Nomadic computing is concerned with the connection of portable (mobile) computers, and with the migration of software, from a home platform to a remote one;

– It is now recognized that access to computing and communications is necessary not only from one's "home base," but also while one is in transit and when one reaches one's destination.

– The goal of "transparent virtual networking" or "nomadic" computing is precisely to permit users and programs to be as effective as possible in this environment of uncertain connectivity, without changes to the manner in which they operate.

– Using diverse phones from everywhere in the world is not activity that could be called nomadic computing (because there is no computing (data processing) involved)

– Dragging around a laptop and working with it without being able to set up a connection to the “home base” through a computer network is neither nomadic
computing in a strong sense; one must be able to communicate with “home base” and people in other organizations

– Does nomadic computing require some devices to be dragged around by the people?
(not necessarily, an infrastructure with suitable access devices could be offered to traveling people - in the same manner as telephones are offered in hotels, airports, etc.)

– Another important development are the advances in computer networking infrastructure that make global connectivity possible.

– One notable development is the Internet as a global networking infrastructure, but in this context especially the wireless technologies are very important.

• The role of wireless technologies in mobile computing:

– wired portable devices can be connected to the network infrastructure only in certain locations for a certain period of time => communication activity of a
nomad is spatially and temporally restricted – wireless portable devices, especially those operating with radio transmitter/receiver avoid the above problem to a great extent


nomadic or mobile computing consists of: traveling people using
portable wireless computing and communication devices connected to
computer network infrastructure supporting global connectivity and remote computing

First & Second Generation Mobile Phones

Mobile phones were born when a number of mobile radio users decided to make mobile phone technology more popular. Mobile telephones were firstly installed in vehicles on a permanent basis, later some versions appeared which were named transportables, could also be carried. Motorola developed a two way radio in a rucksack, the walkie-talkie, and this was widely regarded as one of the first mobiles.

First Generation Phones

First mobile phones are called as first generation (1G) mobile phones. Mobile phones started to gain popularity with the introduction of cellphones that were based on cellular networks.

Mobile phones were originally much bigger than current ones, they were designed for installation in vehicles only, which is called the car phone. These big phones were later converted for use as transportable phones the size of a small.
This system used a single large transmitter on top of a tall building and had a single channel, used for both sending and receiving. To talk, the user had to push a button that enabled the transmitter and disabled the receiver. This system is known as push – to - talk systems.

Second Generation Phones

Second generation, is also called 2G. Second generation telephone systems were different because of their use of digital circuit switched transmission. 2G is the introduction of advanced & quick telephone to network signals. The introduction of 2-G systems saw telephones move from historic 1G telephones to small hand held items, which were much more portable. This change was made useful improvements in technology for example more advanced batteries and energy efficient electronics.

The second generation mobile telephones had several advantages over 1G items. These included SMS messaging, which initially became possible on GSM networks & eventually on all digital networks. SMS text messaging soon became the communication method of choice & the general public now prefer sending messages to placing voice calls.
The first generation of mobile phones was analog; the second generation was digital. The voice signal picked up by the microphone is digitized and compressed.