IEEE 802.11n.ppt

IEEE 802. 802.1 11n  An overview

 Advantages of 802.11n 

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The new wireless LAN standard IEEE 802.11n —ratified as „WLAN Enhancements for Higher  Throughput“ in September  2009. Higher effective data throughput ◦

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WLAN based on 802.11a/g: 54MBPS WLAN based on 802.11n: 300mbps (theoretically) in reality (120-130 MBPS net) Standard defines upto 600MBPS with 4 data streams.

Improved & more reliable wireless: better signal coverage Greater Range: stronger wireless signal received by AP as compare to IEEE 802.11a/g

Compatibility with other  standards 

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In order to allow the co-existence of wireless LAN clients based on 802.11a/ b/g (called "legacy clients") 802.11n access points offer special modes for mixed operation: Greenfield mode: All Access points (AP’s) are IEEE802.11n. High performance HT Mixed mode: Device transmit a legacy format preamble followed by an HT format preamble.  An HT mixed mode device also send legacy format CTS to self or RTS/CTS frame before transmitting. But it reduces 802.11n WLAN throughput.

802.11 N vs 802.11a/b/g

Table: 802.11 network Standard Table

Technical Aspects 

Improved OFDM Modulation: ◦

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Like 802.11a/g, 802.11n uses the OFDM as its method of  modulation. This modulates the data signal not on just one carrier  signal but in parallel over several.

Number of carrier signals: Whereas 802.11a/g uses 48 carrier  signals, 802.11n can use a maximum of 52. Payload Data rate: 802.11a/g can operate at payload rates of 1/2 or  3/4 while 802.11n can use up to 5/6 of the theoretically available bandwidth for payload data.

 Figure : IEEE 802.11 Payload data rate 1 Gross bandwidth 2 Payload rate for 802.11a/b/g: ½ 3 Payload rate for 802.11a/b/g: ¾ 4 Maximum payload rate for 802.11n: 5/6 

MIMO Technology 

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MIMO (multiple input multiple output) is the most important new technology contained in 802.11n.

MIMO uses several transmitters and several receivers to transmit up to four parallel data streams on the same transmission channel The result is an increase in data throughput and improved wireless coverage. In MIMO, the AP’s splits the data into two groups which are then sent simultaneously via separate antenna to the WLAN client. Data throughput can be doubled by using 2 transmitter & 2 receiver antenna.

More Antenna = Higher Speed

Channel & Guard interval 

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40 MBPS channel It uses 2- 20MHz channel: Control Channel, Extension channel

Figure: Two channels in IEEE802.11n 

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IEEE802.11n transmits data over two contiguous channel. One assumes the task of control channel while other handles the administration of data transmission. The use of second channel remains optional .

Short guard interval 

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In order to avoid interference at the receiving end, a short break is made following the transmission period before the transmission of the next signal commences. Period: symbol length while break itself known as ‘guard band’

Figure : short guard band IEEE 802.11a/g uses a symbol length of 4 μs: the information transmitted on the carrier signal changes following transmission of 3.2 μs and a break of 0.8 μs. 802.11n reduces the break between transmissions to the socalled "short guard interval" of only 0.4 μs.