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:


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)