CCRI J. Bernardini1 High Throughput (HT) and n Module-10B Jerry Bernardini Community College of Rhode Island

Presentation Reference Material CWNA Certified Wireless Network Administration Official Study Guide (PWO-104), David Coleman, David Westcott, 2009, Chapter n Demystified Companion Guide, Xirrus Inc USING MIMO-OFDM TECHNOLOGY TO BOOST WIRELESS LAN PERFORMANCE TODAY - DATACOMM RESEARCH COMPANY 6/30/2015Wireless Networking J. Bernardini2

Summary Characteristics CCRI J. Bernardini3 ProtocolRelease Date Op. Frequency Throughput (Typ) Data Rate (Max) Modulation Technique Range (Radius Indoor) Depends, # and type of walls Range (Radius Outdoor) Loss includes one wall a19995 GHz23 Mbps54 MbpsOFDM~35 Meters~120 Meters b GHz4.3 Mbps11 MbpsDSSS -CCK~38 Meters~140 Meters g GHz19 Mbps54 MbpsOFDM & DSSS~38 Meters~140 Meters n June 2009 (est.) 2.4 GHz 5 GHz 74 Mbps248 MbpsOFDM MIMO~70 Meters~250 Meters CCK-Complementary Code Keying OFDM-Orthogonal Frequency Division Multiplexing DSSS-Direct Sequence Spread Spectrum MIMO-Multi-Input Multi-Output

802.11n Requirements Backward compatible with abg Higher throughput than abg Mixed mode operation CCRI J. Bernardini4

Review g Protection Before an g client can transmit to an g AP it must reserve the medium. Must transmit so b will understand. Two Protection Methods – CTS-to self at b modulation (slow Clear to Send) – RTS-CTS at b modulation CTS-to-self is more efficient but may not be seen by hidden-node RTS-CTS is more reliable but has more overhead Both Methods dramatically reduce the g throughput CCRI J. Bernardini5

802.11b/g Mixed Mode Operation CCRI J. Bernardini6 AP g Station g Station b 1-Slow CTS 2-Slow CTS 3-Fast Data 2-Slow CTS

Protection Throughput Effect Technology Transactions per second Mbps of TCP payload throughput Transactional speed relative to b 11b, 11 Mbps a, 54 Mbps2, g, 54 Mbps/no protection 2, g, 54 Mbps/CTS-to- self protection 1, g, 54 Mbps/RTS/CTS protection Based on Matthew Gast, Wireless Networks: The Definitive Guide CCRI J. Bernardini7

802.11g Conclusions g is significantly faster then b for all conditions b station associating with a g network drops throughput due to protection b station does not have to be active to reduce throughput (just associated ) Mixed b/g deployments are likely to be common for the foreseeable future Mixed b/a deployments will have higher throughput b/g/n will also have to provide protection CCRI J. Bernardini8

802.11n History In 2004 IEEE Group-n formed to improve standards n draft Main objectives – Increase data rates and throughput – Operate in 2.4 GHz and 5 GHz bands n Draft defines High Throughput (HT) – Defines PHY and MAC enhancements – Can provide data rates up to 600Mbps Wi-Fi Alliance Certification CCRI J. Bernardini9

802.11n Draft Amendment Defines HT Uses Multiple-input Multiple-output (MIMO) OFDM MAC layer enhancements Backward compatible to abg 6/30/2015Wireless Networking J. Bernardini10

Wi-Fi Alliance Certification802.11n Most vendors say draft 2.0 software can be upgraded to n final Two spatial stream support-mandatory Two spatial receive stream support-mandatory A-MPDU and A-MSDU support- mandatory Block ACK support-mandatory Dual Band support-optional 40 MHz band support-optional Greenfield support –optional Short guard interval-optional Concurrent 2.4 GHz and 5Ghz--optional 6/30/2015Wireless Networking J. Bernardini11

MIMO Multiple-input Multiple-output (MIMO) Takes advantage of multipath Multiple radios and antennas CCRI J. Bernardini12 Transmitter x Receiver MIMO Tx Rx MIMO 2 3 2x x x4

Antenna Beamforming and Diversity 6/30/2015Wireless Networking J. Bernardini13 Beamforming (beam steering) employs two transmit antennas to deliver the best multipath signal Diversity (receive combining) uses two receive antennas to capture the best multipath signal

Multi-Antenna Systems not the Same 6/30/2015Wireless Networking J. Bernardini14 Multi-antennas beam steering/diversity approach, only one signal is sent over the channel. MIMO uses multiple transmitters, receivers and antennas to send multiple signals over the same channel, multiplying spectral efficiency.

MIMO and Multi-path – Normally when a signal is transmitted from A to B the signal will reach the receiving antenna via multiple paths, causing interference. – MIMO uses this multipath propagation to increase the data rate by using a technique known as spatial division multiplexing. – The data is split into a number of spatial streams and these are transmitted through separate antennas to corresponding antennas at the receiver. – Doubling the number of spatial streams doubles the raw data rate, enabling a far greater utilization of the available bandwidth. – The current n standard allows for up to four spatial streams. 6/30/2015Wireless Networking J. Bernardini15

Spatial Multiplexing (SM or SDM) MIMO employs multiple independent radio transmitter-receiver pairs Radio pairs send independent signals Transmitter antennas spaced by half-wave length or more – insuring different paths Each independent signal is a spatial stream Spatial streams are combined at the access point Referred to as: – Spatial Multiplexing (SM) or – Spatial Diversity Multiplexing (SDM) 6/30/2015Wireless Networking J. Bernardini16

MIMO Diversity Increasing the number of receiving antennas can improve overall signal to noise Pre n used switched diversity to select best multipath signal Increasing antennas (3 or 4) increases the receiver choice for a “good” signal MIMO maximal ratio combining (MRC) allows for additive effective of multipath signals – increasing signal to noise ratio 6/30/2015Wireless Networking J. Bernardini17

Transmit Beamforming (TxBF) n optional feature Multiple transmitter antennas “focus” the signal to a receiver Used by radar; phased-array antenna systems Transmitter is the beamformer Receiver is the beamformee Feedback from the beamformee allows the beamformer to adjust the antennas and signal to improve SNR 6/30/2015Wireless Networking J. Bernardini18

802.11n HT Channel Technology n uses OFDM (just as ag) n has option to use 20 MHz and 40 MHz channels n can use can combine channels for Channel Bonding n can use variable Guard Interval (GI) n can use various Modulation and Coding Schemes (MCS) CCRI J. Bernardini19

Non-HT and HT Channels (clause 20) ag use 20 MHz OFDM channels Each channel are made of 52 subcarriers – 48-subcarriers transmit data – 4-subcarriers transmit pilot tones for transmitter-receiver calibrations n can use either 20 MHz or 40 MHz channels Each HT 20 MHz channel has 56 subcarriers – 52-subcarriers transmit data – 4-subcarriers transmit pilot tones for transmitter-receiver calibrations Each HT 40 MHz channel has 114 subcarriers – 108-subcarriers transmit data – 6-subcarriers transmit pilot tones for transmitter-receiver calibrations 6/30/2015Wireless Networking J. Bernardini20

Channel Bonding 40 MHz channels are formed by bonding two 20MHz channels When bonding two channels there no need for a guard band 5 GHz UNNI band allows twenty three 20 MHz channels to be bonded 2.4 GHz ISM band allows only one bonding of two 20 MHz channels (only 3 non-overlapping channels) 6/30/2015Wireless Networking J. Bernardini21

Channel Bonding 6/30/2015Wireless Networking J. Bernardini22

Guard Interval (GI) Digital Symbol is a collection of bits If the bits overlap Inter-symbol Interference (ISI) is experienced ag uses a 800 ns guard interval between symbols n can use a 800 ns or 400 ns guard interval between symbols 400 ns GI improves throughput by 10% The 400 ns GI should only be used in a “good” RF environment 6/30/2015Wireless Networking J. Bernardini23

Modulation and Coding Schemes (MCS) n defines data rates as Modulation and Coding Schemes (MCS) MCS are based upon – Modulation technique (BPSK, QPSK, 16-QAM, 64-QAM) – Spatial streams (1, 4) – Channel size (20 MHz, 40 MHz) – Guard Interval (400 ns, 800 ns) n requires Eight mandatory 20 MHz MCSs Total of 78 MCSs Data rates vary from 6.5 Mbps to 600 Mbps 6/30/2015Wireless Networking J. Bernardini24

HT PHY and MPDU frame is a MAC Protocol Data Unit (MPDU) The payload is the MAC service Unit (MSDU) (layer 7- 3 data) MPDU is made up of the header and body At the PHY layer is the Physical Layer Protocol Data Unit (PPDU) PPDU = MPDU + PHY preamble-header n defines three PHY preamble-headers Legacy format, HT Mixed, HT Greenfield CCRI J. Bernardini25

HT PPDU Formats Non-HT Legacy – Mandatory for n – Only 20 MHz channels – Same format as ag HT Mixed – Two part preamble – First part can be decoded by ag – Second part can not be decoded by ag HT Greenfield – Preamble can not be decoded by ag – Can use both 20 MHz and 40 MHz channels 6/30/2015Wireless Networking J. Bernardini26

HT MAC CCRI J. Bernardini27

HT Operation 20/40 Channel Operation – Legacy communication using 20 MHz only – n can use 20MHz or 40 MHz HT protection Modes – Four modes – Mode 0, 1, 2, 3 Dual-CTS protection – Send both legacy and HT RTS/CTS combinations Phased Coexistence Operation (PCO) – Time slices between 20MHz or 40 MHz channel usage CCRI J. Bernardini28

Through Put Comparison 6/30/2015Wireless Networking J. Bernardini29