All About 802.11N
802.11n is one among the family of standards IEEE 802.11 which is mainly framed for wireless LANs. This standard is basically designed to develop the throughput of the network far better than its previous versions 802.11g and 802.11b. It also increases the data rate of the OSI physical layer from 54 Mbps to 600 Mbps. The throughput may be translated up to 110 Mbps depending on the environment.
The interoperability of the “draft N” products which are defined by Wi-Fi alliance is fully based on this 802.11n standard. On assuming with this standard, excellent compatibility and affordability are ensured with the products. The compatibility tests of the alliance are upgraded so as to coincide with the publication of the amendment. The major feature of the standard is the MIMO (Multiple Input Multiple Output) option. This MIMO involves a number of antennas to resolve the incoming information instead of using a single antenna.
As a result, spatial multiplexing and antenna diversity are achieved. SDM or spatial division multiplexing is the involvement of independent multiple data streams by making use of single spectral channel of bandwidth. Since there is increase in the number of spatial data streams, naturally the throughput is also increased. The basic requirement for this SDM is that the discrete antenna should be located at both the transmitter and the receiver ends. Another feature is the frame aggregation which is amended with the MAC layer.
Frame aggregation is a process of sending two or more data frames in a single transmission in order to deploy the overall throughput of the network. There are two types of aggregations which are found as MSDUs (MAC service data units) at the top of MAC layer and MPDUs (MAC protocol data units) at the bottom of the MAC layer. By packing these multiple MSDUs and MPDUs, the overheads like inter frame spacing, process of contention, acknowledgment of frames and headers of PHY. With an increased channel width of 40 MHZ, the PHY data rate is 450 Mbps which is comparatively greater than the previous versions.
The channel width was actually 20 MHz in the previous versions of 802.11. With the help of four spatial data streams and 40 MHz channel width, 600 Mbps data rate is achieved. The more the number of antennas, the more the data streams are transmitted and received. A usual notation is a x b: c. ‘a’ indicates the number of transmit antennas, ‘b’ indicates the number of receive antennas and finally ‘c’ indicates the number of data streams. The coexistence management is extended by this 802.11n which is basically designed to protect the devices.
Maximum throughput is achieved by using a pure 802.11n standard of 5 GHz. This higher throughput can be achieved only if the overlapping of signals is avoided and radio interference is minimized. So, because of its higher throughput, major manufacturers are releasing the products based on the terminologies ‘draft N’, MIMO and ‘pre draft’. With this 802.11n, an improved stability is also assured. The ratification of the standard is under progress in order to make the users free from the existing problems which would be amended with the upcoming releases.
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