¶ … Bluetooth
Wireless technology has developed a large way from its infancy and is fast becoming the latest trend in communication. Wireless LANs have added an entirely new dimension to the communication sector. The advent of cellular technology, infrared and spread spectrum radio services have bought about a huge change to our world of communication and wireless technology has materialized our dream of a mobile workforce. Today there is no single standard in the industry and there are different wireless technologies available. Let us have a brief outlook of the 'IEEE 802.11' and 'Bluetooth', two of the important wireless LAN technologies.
IEEE 802.11 Protocol
The IEEE 802.11 (First adapted in 1997) is primarily a standard developed to provide time bound and asynchronous wireless services. The MAC layer is meant to handle different physical layers with distinct medium and transmission characteristics. The standard uses 2.4 GHz ISM band and a minimum data transfer rate of 1 Mbits / s. IEEE 802.11 specifies the physical and the medium access layer standards in particular to the wireless LAN's. IEEE 802.11 has seamless integration with other standards for wired networks. The Data link layer and the Logical Link layer control other aspects pertaining to different forms of the media. The MAC layer is concerned with three main tasks namely medium access, data fragmentation and encryption while the Physical layer takes care of the modulation, encoding and decoding of the signals. Let us study these two layers in a little detail.
Physical Layer
The protocol supports three types of physical layers based on two kinds of radio and one infrared transmission. The protocol includes channel detection provision, which (CCA) is used for medium control.
Frequency Hopping Spread Spectrum
IEEE 802.11 includes Frequency hopping spread spectrum technique whereby communication on one channel of radio spectrum is transferred to another channel as data is transferred through the network. [Raymond P. Wenig, 57] Currently for a 1 Mbit data transfer a 2 level FSK (Frequency Shift Keying) is used as the standard. Each data frame in the physical layer consists of two main parts namely the physical layer convergence protocol (preamble and the header) and the payload. The PLCP is always transmitted at a standard speed of 1 Mbits/s while data part can vary from 1 Mbit/s to 2 Mbit/s. An 80-bit Synchronization pattern is used to synchronize the receivers with the transmitter once the receiver gets a line clear signal from the CCA. (Clear channel assessment signal). This is followed by a start frame delimiter (16 bits), which helps to synchronize the individual frames of data. The next part PLW (PLCP_PDU length word) contains information regarding the size of the payload. Next part of the frame is the PSF field (PCLP signaling Field), which indicates the actual data speed of the payload. (Either 1 or 2 Mbit/s). Furthermore data is scrambled using the polynomial equation s (z) = z^7 +Z^4+1. The field immediately before the actual payload is the HEC (Header Error Check) [Jochen Schiller, 171]
Direct Sequence Spread Spectrum
This is another form of spectrum wherein modulation is achieved by codes and not by frequency. Instead of the frequency shift keying the DSSS system uses the binary phase shift keying system for 1 Mbit/s data transfer and differential quadrature phase shift keying for 2 Mbit/s data transfer. Each data frame consists of seven parts with the first part being a 128 bit-synchronizing pattern followed by a 16-bit frame delimiter and an 8-bit stream indicating the data rate. (1 Mbit/s or 2 Mbit/s). The other fields are the Service, Length (length of the data or payload) and the HEC. [Jochen Schiller, 172]
Infrared
The third type of transmission based on infrared light uses visible light in the range of 850 to 950 nm. The infrared transmission is of very short-range (10 m) and is primarily used for transmission within a confined area.
MAC Layer of IEEE 802.11
The MAC layer is responsible not only for medium access but also for managing power control, roaming and authentication services. In 802.11 there are three main types of medium access methods namely the CSMA/CA, a modified form of CDMA/CA with RTS and CTS, and a contention free polling method. In the CSMA / CA method if the medium is sensed busy the nodes have to wait for the longest waiting time (DIFS) before entering the contention phase. Each of the nodes wait for a random backoff time within its contention window. If a node does not have access to the medium during a particular cycle it stops its backoff timer and waits for the channel to be idle once gain. Once the channel is sensed to be...
Wireless Local Area Networks The establishment of home and business networks desirous of upgrading to Wireless Local Area Network- WLAN confront with the problems of choosing from available alternatives. The vendors offer several products for sale that hovers around different wireless standards like 802.11a, 802.11b, 802.11g and Bluetooth. During the year 1997, the Institute of Electrical and Electronics Engineers -- IEEE developed the first WLAN standard. They termed it 802.11 in
Bluetooth devices use encryption security and this makes the requirement of a "unique key session key to derive per-packet keys thus avoiding frequent key reuse." (Kennedy and Hunt, 2008, p.4) Kennedy and Hunt report that ZigBee is a reasonably priced low energy consumption two-way CDMA/BA-based wireless communications standard which is based on IEEE 802.15.4 which is referred to commonly as a 'Low Rate Wireless Personal Area Networks (LR-WPANs) and which
These aspects should be considered while designing and implementing a network to gain maximum efficiency. (Trulove, 19-20) The standard that defines the application of a WLAN is IEEE 802.11 WLAN standard. Though this is the basic standard amended ones define the additional prescriptions added to it like 802.11a or 802.11b. The capacity of a WLAN is defined by its basic compatibility. WLAN of the latest version comes with an 11
Wireless Broadband Technology Overview of Wireless technology Presently it is quite evident to come across functioning of a sort of wireless technology in the form of mobile phone, a Palm pilot, a smart phone etc. With the inception of fast connectivity in the sphere of commerce it is customary and useful to operate from central locations communicating with the remote branches, conducting conferences in remote places, discussing with every body at every
BluetoothTM is a low cost, low power, short-range radio technology- originally perceived as cable replacement alternative for the cable / wire connected devices such as mobile phone hand, headsets, and portable computers. The BluetoothTM's goals expanded to include standardized wireless communications between any electrical devices and created a notion of Personal Area Network. The write-up traces history of BluetoothTM starting with its unusual name to formation of Special Interest Group,
(Gutierrez, Jose a; Callaway, 7) Another benefit of WSN is the minimum damage or repair. A wiring may be lost or disconnected or might break due to various reasons. This is called last meter connectivity problem. Such problems are reduced by WSN. In a WAN, it is usually called the last mile connectivity problem. Finally, WSN enables collection of recurring information from a manufacturing environment to upgrade the quality of
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