With the increase in the number of mobile users as well, wireless networks are now far from being an innovation and a luxury and have become one
of the indispensable components of Internet access. Since they do not have a fixed physically limiting connection to the network, thus bringing ease
of use, use of wireless networks are not only faced with intense demand at hotels, cafes, airports, shopping malls, but also at offices and homes. The
wireless access that was initially provided by WLAN cards which used to support 802.11b standard, and were produced for the PCMICA interface has later
become to support 802.11a/g standard as well with the introduction of chipsets embedded within the motherboard and has become the indispensable
hardware of almost all laptop computers. This fact has brought forward the increase in the number of users and the need and the demand for being able
to make use of all sorts of applications, more bandwidth, more access, more security, and wider coverage area. In order to meet the demand, work on a
new standard was started in 2003 by the IEEE and the task group 802.11TGn (TG = Task Group) was set up. The pace of the progress on the standard may
be observed at the http://www.ieee802.org/11/Reports/tgn_update.htm address. It is
expected for standard to be published in November 2009 in its final state.
Its compatibility with the previous technology, its feature of enabling higher speeds of data transfer, providing access to more distant areas and
higher security are the fascinating aspects of 802.11n wireless network technology. The current instrumentation available can reach speeds up to
300 Mbps per receiver. This value was 54 Mbps for 802.11a/g networks and 11 Mbps for 802.11b networks. While 802.11b and g technologies are using
the 2.4 GHz frequency band and the 802.11a technology is using the 5 GHz frequency band, the 802.11n wireless network connection can use both the
2.4 GHz and the 5 GHz frequency bands that has been assigned, simultaneously.
Let's now have a look at what types of new technologies this standard makes use of, in order to provide the above mentioned superior
MIMO (Multiple Input / Multiple Output)
While wireless network devices that incorporate 802.11a/b/g standard transmit via a single antenna, the wireless devices that incorporate 802.11n
standard have two or more antennas for transmission at the transmitter side and they use more than one antenna at the receiver side and with their
improved signal processing technique they defragment more than one broadcast, transmitted / received. MIMO technology enables the information to
broadcast to be separated into fragments and be transmitted across making use of different antennas. The transmitted data reaches the receiver
antenna following different routes, at different times and more than once due to reflections from walls, doors and other surfaces. This unavoidable
situation hinders the defragmentation of the signal and reduces the Wi-Fi performance when 802.11a/b/g standards are used. However, the MIMO
technology used by the 802.11n takes advantage of this situation and enables the signal to be strengthened and reach more distant areas. Thanks to
this, the number of numb areas and the packets to be retransmitted can be reduced.
When MIMO is active on both the transmitter side and the receiver side, the performance reaches the maximum. Even if the transmitter is a MIMO
supported wireless network device and the receiver side has the classical 802.11a/b/g standard, the MIMO technology may be able to provide a 30%
performance increase in such a case. With all the plus points of MIMO the disadvantages are not null; more power consumption and high costs. Since
the increased power need of 802.11n reaches the limit of 15.4 watt, defined as the maximum limit for existing Power over Ethernet (PoE) standard,
an extra power supply becomes necessary especially when dual radio channel is broadcast. The figure below shows how MIMO increases the
The figure has been obtained from http://www.ecnasiamag.com/ address.
The most basic way to increase the capacity of a network is to increase the working bandwidth. With the 802.11b/g standard which uses 2.4 GHz
band, there are 13 channels each of which is 20 MHz. However, channels 1. , 6. and 11. do not coincide with each other. With the 802.11n standard
the two 20 MHz channels that do not overlap can be joined and the bandwidth can be doubled. Thanks to this, the amount of information transmitted
per unit time is increased greatly. Because of the fact that the number of channels that do not coincide in the 2.4 GHz band is low, it is
recommended that "Channel Bonding" technique be applied with the at the 5GHz channel where 802.11a standard is being used. Using the "Channel
Bonding" at 2.4 GHz band leaves fewer channels to be used by other devices.
For the 802.11a/b/g standards each packet starts with fixed length header information and this decreases the efficiency as the data transfer ratio
increases. The 802.11n standard enables combining more than one data packet under a single header information added for all, and this results in
the reduction of number of headers thus increasing the amount of data transfer per unit time. The technique is especially more beneficial for some
specific packet types like the FTP (file transfer protocol). For real time products such as sound and image applications packet aggregation can
cause unwanted delays.
Instrumentation operating under the 802.11n standard do support 802.11a/b/g standard wireless network device users. Any 802.11n wireless network
device can provide service to 802.11n supporting and 802.11a/b/g supporting device users simultaneously. Nevertheless, the existence of an 802.11
a/b/g device user reduces the performance of the network and the overall amount of data transfer. Specifically, when an 802.11b standard device
user accesses an 802.11n standard network there appears a considerable drop in the overall performance of the network. For this reason, in order
to make out the most of the performance of an 802.11n standard network, one might even consider permitting 802.11n, 802.11a/g standard device
users in, and excluding 802.11b standard network cards.
Even though the standard is at the stage of development, there are network access devices and client interfaces already on the market and
applications are conducted in accordance with the drafted standard. At this point, the manufacturing companies presume that when the 802.11n
standard reaches its final state the devices would be updated by changes on their software and they expect that there would be no hardware changes
To sum up, although the 802.11n is an incomplete standard it is possible to observe some of its applications. This standard, with its promising
data speed and dependability, will be at a scale to answer the quest of band width necessary for Internet phone, music and video broadcast,
backup, IPTV applications.
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