Wireless and Mobile Computing
802.11b is a wireless LAN (WI-FI) standard that belongs to a group of wireless networking standards that are commonly referred to as the 802.x.The 802.x standard is divided into several series that cover both physical and data-link aspects of networking. Examples of networking standards under the 802.x series include 802.1, 802.2, 802.5, 802.3, 802.4, 802.6, 802.11c 802.11n. 802.11b wireless standard is used for wireless internet purpose mainly to connect to the internet or a network wirelessly. These networking standards have been used in personal computers or home networks and internet “hotspots” found in various locations such as restaurants, coffee shops, shopping malls and public parks. Various devices use the 802.11b standard to facilitate wireless networking or communication. Some of these devices include personal computers via the 802.1b card, wireless routers which use the standard to establish or set up access points and other hand held devices.
Coding in the 802.11b is done through system that is referred to as binary convolution coding. This coding system uses a 64-state Binary Convolution Code (BCC) and a cover sequence. The coding process involves encoding the output of the Binary Convolution Code (BCC) jointly into I and Q channel. The incoming data is first encoded with a Binary Convolution Code, after which application of a cover code is done to the encoded data. The encoded data is only transmitted to the channel after a cover code has been applied (Kurose & Ross, 2010). Modulation in 802.11b standard is done through a scheme known as the PBCC Modulator Scheme. In this scheme, information is first fed into an encoder that uses error control coding method. This error control coding then sends two bits for every one bit of data or information. The coded information is then fed or directed into a cover map. The cover map used in the 802.11b is known as Quadrature Phase Shift Key (QPSK).The QPSK cover map subsequently sends the appropriate bits to the I and Q channels (Gast ,2005).
In 802.11b standard, the position of the bits on the real/imaginary planes is determined by the cover sequence. Four different modulations are supported by the 802.11b standard. Basic access rates characterized by 1mbit/s use DQPSK modulation, in enhanced access rates with 2mbit/s, DQPSK CCK modulation is normally embraced. Finally high access rates use DQPSK CCK modulation (Gast, 2005).
802.11b supports a maximum data rate of 11mbps.This is a rate better than that of the traditionally used Ethernet that had a maximum data rate of 10mbps.However, comparing the 802.11b to newer networking standards reveals that it performs slower than the new standards such as the 802.11g standard and even the Fast Ethernet. The 802.11b is also prone to wireless interference. This results from the transmission of unregulated 2.4GHz frequency. This standard is mainly affected by radio interference from devices such as codeless telephones, garage door openers and microwave ovens (Gast, 2005).
The 802.11b standard divides the spectrum into channels so that multiple access points can each be set to different channels and are able to work closely without interference. Though the 802.11b data rate of 11mbps is higher than that of the traditional Ethernet and the 802.11a, this rate is distant dependent. As the distance increases, the data rates also decrease. It therefore requires access points at every 300 feet in each direction making it inferior to newer networking technologies such as the 802.11g standard whose graph data rate falls to 6mbps as the distance increases to 180 feet. The 802.11b standard is asymmetrical .The up linking and down linking operations is handled differently and independently in order to achieve high data rates.
The IEEE 802.11b standard is therefore capable of handling more users and this makes it able to serve in more demanding applications such as wireless multimedia video transmission as well as in broadcast MPEG.
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