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Since the Second World War or World War II, the wireless communication is been attached great importance, there is lack of wireless communication standard although it keeps developing.
802.11 is a set of Wireless LAN standards that created and maintained by Institute of Electrical and Electronics Engineers (IEEE).
Many people are confused with IEEE 802.11 and Wi-Fi, but actually they are different. Wi-Fi is a trademark under Wi-Fi Alliance. Data can be exchanged wirelessly by using Wi-Fi through a computer network. Wi-Fi Alliance is an independent association that carries out product certification based on IEEE 802.11 standard for interoperability and backward compatibility. They also help to promote Wireless LAN (Local Area Network) technology.
List of 802.11 Protocol
IEEE 802.11 (legacy mode)/ IEEE 802.11-1997/ IEEE 802.11-1999
It is the original version of IEEE 802.11 Wireless LAN standard that was released in 1997 and clarified in 1999. It is mainly used for data access, the maximum data rate per stream is 1 or 2 megabits per second (Mbit/s) with forward error correction code. Forward error correction (FEC) also known as channel coding is a method to control error in data transmission over communication channel which is unreliable and full of noise. The message sending is encoded using an error-correcting code (ECC) in redundant way. It operates in the 2.4GHz band.
In order to have better communication quality in different communication environment, CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol that operates under Data Link Layer (Layer 2) of the OSI model is used. The fundamental principle for CSMA/CA is that it will listen to the network first so that collision is not happened and avoided. This will help to prevent collision before it is happened. Nodes are transmitting certain data only when specific channel is said to be in â€œIdleâ€.
Three alternative physical layer technologies are specified:
Diffuse infrared operating at 1Mbit/s
Frequency hopping spread spectrum (FHSS) operating at 1Mbit/s or 2 Mbit/s (Frequency hopping is a method that switch a carrier quickly among many frequency channels when transferring radio signals by using a pseudorandom sequence)
Direct-sequence spread spectrum (DSSS) operating at 1Mbit/s or 2Mbit (DSSS method makes the intended bit sent by the sender is combined with higher data rate bit sequence or known as chip code)
IEEE 802.11a is the revised standard version of the original standard. The maximum raw data transfer rate of IEEE 802.11a is 54Mbps. It operates in the 5GHz band with error correction code. It uses 52 subcarriers orthogonal frequency-division multiplexing (OFDM) which is a frequency division multiplexing (FDM) technique.
The advantages of using unused 5Hz band compared to heavily used 2.4GHz band is the interference occurs might be small and this results to better throughput. As high carrier frequency leads to smaller wavelength, so 802.11 a signal cannot penetrate as far as 802.11b signal. Besides that, 802.11a signals are also easily absorbed by walls or solid materials in their path.
The maximum raw data transfer rate of IEEE 802.11b is 11Mbps which is 5 times faster than the IEEE 802.11 standard that was clarified in 1999. It operates in 2.4GHz band. Interference is happened within IEEE 802.11b devices from other devices operating in the 2.4GHz band such as cordless telephone, Bluetooth devices, microwave ovens, baby monitors and some amateur radio equipment.
The operation principle of IEEE 802.11b is similar with IEEE 802.3, both are using Carrier Sense Multiple Access (CSMA) method to control the information transmitting in the network. The only difference is Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) method but IEEE 802.11b uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) media access method. IEEE 802.11b utilizes Complementary Code Keying (CCK) as its modulation.
IEEE 802.11g is the third modulation standard that was ratified in June 2003. Compare to previous IEEE 802.11 protocol standard, IEEE 802.11g has two characteristics: It operates in the 2.4GHz band but uses orthogonal frequency-division multiplexing (OFDM) modulation technique same as IEEE 802.11a which makes the maximum raw data transfer rate increases up to 54Mbit/s plus forward error correction codes or about 19Mbit/s net throughput; It is fully backward compatible with IEEE 802.11b hardware.
IEEE 802.11g devices also suffer with interference from the devices operating in 2.4GHz band such as wireless keyboard and wireless mouse
IEEE 802.11n operates on both 2.4GHz and 5GHz frequency band. IEEE 802.11n standard is improved by adding multiple-input multiple-output (MIMO) feature that supports up to 4 spatial streams. MIMO improves wireless communication performance by using multiple antennas at both transmitter and receiver. Other features for IEEE 802.11n are frame aggregation and security improvements. IEEE 802.11n also uses orthogonal frequency-division multiplexing (OFDM) modulation technique. It has maximum raw data rate from 54Mbit/s up to 600Mbit/s. The frequency width is increased from 10MHz (IEEE 802.11g) to 40MHz. The higher of the frequency width, the higher of the theoretically data rate speed but the hardware must support the frequency width too.
802.11ac is drafted by The Institute of Electrical and Electronics Engineers (IEEE) on September 2008. The first three drafts was passed on November 2011, February 2012 and June 2012, the approval time for IEEE 802.11ac is approximately on December 2013. It operates in the 5GHz frequency band with very high throughput.
It supports up to 8 spatial streams with MIMO feature compared to IEEE802.11n that is 4 spatial streams only. IEEE 802.11ac also supports up to 80MHz frequency width with maximum 1300Mbps theoretically raw data rate. Beamforming, MAC modification are the features added to IEEE 802.11ac standard.