Slide Informasi IEE 802

8/12/2019 Slide Informasi IEE 802

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Informasi IEE 802.11n

Rincian teknis tentang standar WLAN baru


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Agenda IEEE 802.11n

Tujuan Desain IEEE 802.11n

Perbaikan Physical Layer IEEE 802.11n

Perbaikan MAC Layer IEEE 802.11n

Bagaimana Menganalisis IEEE 802. 11n

Pengukuran Throughput

Gambaran Standard WLAN & Tipe Frame

Kompabilitas dengan IEEE 802.11a/b/g

Masa Depan IEEE 802.11n


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Tujuan Desain IEEE 802.11n

IEEE 802.11n merupakan amandemen standard jaringannirkabel dari IEEE 802.11-2007

Meningkatkan kecepatan transfer lapisan MAC hingga minimumthroughput Data 100 Mbps

Kompatibel dengan IEEE WLAN seperti 802.11a/b/gMeningkatkan tingkat transmisi lapisan PHY diatas standardsebelumnya, seperti 802.11a /b/g dengan High Througput (HT)pilihan.


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How the goals are achieved

A combination of technical functions at PHY and MAC layers are

added to the existing 802.11 standard:

Increasing the physical transfer rate with new modulationscheme and timing up to 600Mpbs

New multi-streaming modulation technique using MIMO(Multiple input, multiple output antennas)

Joining two adjacent channels with channel bonding

Support for frame aggregation A-MPDU & A-MSDUNew Block Acknowledgments


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PHY layer improvements

Modified OFDM

The number of OFDM data sub-carries is increased from 48 to52 which improves the maximum throughput from 54 to 58.5Mbps

Improved forward Error Correction

FEC is a system of error control whereby the sender addsredundant data to allow the receiver to detect and correcterrors. coding rate is improved with 5/6 boosting the link ratefrom 58.5 to 65 Mbps.


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PHY layer improvments (cont.)

Shorter Guard interval (GI)

The GI between OFDM symbols is reduced from 800ns to 400ns

and increases throughput from 65 to 72.2 Mbps

Channel Bonding

Doubling channel bandwidth from 20 to 40 MHz slightly morethan doubles rate from 72.2 to 150 Mbps

Spatial MultiplexingSupport of up to four spatial streams (MIMO) increasesthroughput up to 4 times 150 to 600 Mbps


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Short Guard Interval (GI)

OFDM carries the bits in so called symbols, the gap between thesymbols in the Guard Interval.

Short Guard Interval can be used, if the multipath delay is lowand symbols from streams do not interfere.


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Channel Bonding

802.11n supports bundling of two 20 MHz channels

Select a control channel # and the channel offset Both channels

must fit inside allowed frequency range A-Band does not allowto select channel # manually


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Channel Bonding 2.4 GHz Band


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Channel Bonding 5 GHz Band


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Channel Allocation 5 GHz Band

Some channels only allowed for inhouse use

New stricter FCC DFS2 rule valid off July 20, 2007


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Multiple-Input, Multiple-Output (MIMO)

802.11n Supports Multi-Streaming Modulation

MIMO is the most difficult aspect of 802.11n to understand.

In MIMO, the transmitting and receiving stations each havemultiple RF chains with multiple antennas. The 802.11nstandard mandates at least two and up to four spatial streams.

Multipath (RF signal reflection between transmitter andreceiver) is normally the enemy of perfomance, but with MIMOit is used constructively.


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Spatial Multiplexing

A signal stream Is broken down into multiple signal streams,each is transmitted from a different antenna. Each of these

spatial streams arrives at the receiver with differentamplitude (signal strength) and phase.


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MIMO Combinations


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Modulation Coding Scheme (MCS)

802.11n Introduces a new MCS

802.11 b/g adapts to channel conditions by selecting the highest

of 12 possible rates from 1 to 54 Mbps.

The 802.11n standard will allow some 77 possible MCS somecompulsory, some optional.

MCS selects, based on RF channel conditions, the bestcombination of 8 data rates, bonded channels, multiple spatialstreams, different guard intervals and modulation types.


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MCS Rate Chart


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How to analyze 802.11n


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HT Capability Announcement in Beacons


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MAC layer improvements

Frame Aggreation Mechanisms

Aggregate-MAC Service Data Unit (A-MSDU) wraps multiple

Ethernet frames in a 802.11 frame up to 8Kb

Aggregate-MAC Protocol Data Unit (A-MPDU) allows bursting802.11 frames up to 64Kb

A-MPDU is performed in the software where as A MSDU isperformed in the hardware

Block Acknowledgment

Block ACK effectively eliminates the need to initiate a newtransfer for every MPDU


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MSDU Aggregation

Multiple Ethernet frames for a common destination arewrapped in a single 802.11 frame

More efficient than A-MPDU as only one radio-and 802.11 MACheader is applied

Whole frame must be retransmitted if no acknowledge


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A-MSDU Analysis


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MPDU Aggregation

Multiple Ethernet frames for a common destination aretranslated to 802.11 format and set as burst

Elements of an A-MPDUs burst can be acknowledge individuallywith one single Block-Aknowledge

Only not-acknowledged A-MPDUs are retransmitted


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A-MPDU Analysis


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Block-Acknowledge Mechanism

Rather than sending an individual acknowledge following eachdata frame, 802.11 introduces the technique of confirming a

burst of up to 64 frames with a single Block ACK (BA) frame.

The Block ACK even contains a bitmap to selectivelyacknowledge individual frames of a burst (comparable toselective acknowledges to TCP)

The use of combined acknowledges can be requested bysending a Block ACK Request (BAR)


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Block-Ack Mechanism (cont.)

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