Wireless LANs are the hot new enterprise technology that every one is talking about and considering implementing in varying degrees for vertical markets like medical, education and manufacturing. Before delving straight into the details of wireless LAN standards let’s take a look at technologies that make it possible for a wireless LAN to operate. These technologies are
- Radio frequency systems
- Infrared systems
- Spread spectrum implementation
- Frequency Hopping Speed Spectrum
- Direct Sequence Speed Spectrum
How Blue Tooth came into existence ?
- WLANS (Wireless local area networks)
- WWANS (Wireless wide area networks)
Flexibility and mobility make wireless LANs an attractive alternative to wired networks. Wireless LANs provide all the functionality of wired LANs with out physical constraints of the wire itself. The above mentioned three types of networks differentiate in range, data rates, power consumption and cost. WLANS are 802.11b wireless Ethernet with higher speeds and longer ranges used in office buildings and homes.
WWANS such as cellular Networks, work over a large area but less lower data rates. WPANS such as Blue Tooth Piconets, provide short-range connectivity for devices such as laptops, PDAS, cellular phones and even PCs in a network with small geographical spread and support low data rates and limited ranges to achieve low cost and minimum power drain
Blue tooth uses the FHSS (Frequency Hopping Spread Spectrum) protocol as wireless LAN standard. Spread spectrum technology is a wide band radio frequency technique developed by the military for use in reliable, secure, mission-critical communication system. Spread-spectrum is designed to trade off bandwidth efficiency for reliability, integrity and security. Frequency Hopping spread spectrum (FHSS) uses a narrow band carrier that changes frequency in a pattern know to both transmitter and receiver. FHSS appears to be short-duration impulse noise radios in Blue tooth can be master or slave or be in simultaneous scenarios. Possible Bluetooth networks available
When we bring Blue tooth radios with in the range of each other they connect and form a piconet. one becomes master and other a slave .The master controls all the traffic in a piconet . Blue tooth radios in a piconet frequency hop together. Each piconet can have up to seven simultaneous or more than 200 active slaves. Radio in the piconet can be in one of five states
- Stand BY
Stand by is radio waiting to join a piconet. Inquire is a radio seeking other radio to connect. Page is a master radio asking to connect to a specific radio. Connect is a radio active on a piconet as a master slave or simultaneous. Park/Hold is a low power connected state.The master gives all the slaves in a piconet its clock-device ID and sets the unique hopping sequence based on the master device address.
Scatter nets occur when multiple masters exist in range of each other. A master radio may also be a slave radio on another piconet. Each piconet is hopping with a different sequence sharing the same as 2.4 GHz band. Because of the different hopping sequences, there is very little chance that any master will hit a channel at the same time as another master.