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Wi-Fi Fundamentals: A Guide to Key Concepts and Standards
- 1. Wi-Fi Fundamentals By Muhammad Talha Javaid (BTS-15-39)
- 2. Wi-Fi • Wi-Fi stands for Wireless-Fidelity • Wi-Fi is a technology for wireless local area networking with devices based on the IEEE 802.11 standards. • Wi-Fi is a trademark of the Wi-Fi Alliance • Devices communicate with each other via radio waves • Introduced in 1998
- 3. Wi-Fi modes
- 4. CSMA/CA
- 5. 802.11 Frame Format • 0x0 - Management frame • 0x1 – Control frame • 0x2 – Data frame
- 6. 802.11 Frame Format (cont.) • 0x00 Association Request Frame • 0x01 Association Response Frame • 0x02 Reassociation Request Frame • 0x03 Reassociation Response Frame • 0x04 Probe Request Frame • 0x05 Probe Response Frame • 0x08 Beacon Frame • 0x0A Disassociation Frame • 0x0B Authentication Frame • 0x0C Deauthentication Frame • 0x1B- RTS • 0x1C- CTS • 0x1D ACK
- 7. Non-overlapping Channels in 2.4 Ghz band for 802.11- 2.4 Ghz band provide 3 non- overlapping channels ( 1,6,11)
- 8. Non-overlapping Channels in 5 Ghz band for 802.11- 5Ghz band provide 24 non-overlapping channels
- 10. Wi-Fi Standards
- 11. Fact to know • Wi-Fi technology evolve by time to provide more and more data rates, low latencies and more range. • Data rates are directly proportional on the frequency and on the bit rate per symbol • So why not simply increase these factors? • Disadvantage of conveying many bits per symbol is that the receiver has to distinguish many signal levels or symbols; low SNR and more BER • Need sophisticated hardware Frequency increase Increasing Bit rate per symbol
- 12. 802.11 (legacy) • Released in 1997 • Spread spectrum – FHSS/DSSS • Speed 1-2 Mbps • Frequency – 2.4Ghz and 900Mhz 802.11 a & b • Both standards appeared at the same time – 1999 • 802.11 a • Introduces OFDM and takes speed up to 54 Mbps • Frequency band 5Ghz • Range 25m • 802.11 b • Bandwidth 11Mbps • Frequency band – 2.4Ghz • Up to 150 feet • Range 20 feet
- 13. 802.11 g • Standardized in 2003 • Best of both (a & b) • Frequency band – 2.4Ghz • Bandwidth 54 Mbps • Modulation – OFDM • Range – 150 feet • Used for a long time can still be found in networks
- 14. 802.11 n • Standardized on 29 October 2009 • Maximum speed – 600 Mbps (theoretical) • Frequency band - 5GHz & 2.4Ghz • 64-QAM • Backward compatible with 802.11 a/b/g • Support Packet aggregation • Channel bonding -> 20Mhz x2 = 40Mhz • MIMO-OFDM • Range – 175f+ • Available in 2x2 and 4x4 configurations.
- 15. MIMO ( Multiple-Input Multiple-output) • Technique for sending and receiving more than one data signal simultaneously over the same radio channel by exploiting multipath propagation. • Taking Advantage of the multipath effect. • SDM
- 16. 802.11n – Maximum Ratio Combining • The multipath effect = many waves carrying the same information are reflected differently from surfaces with varying clarity • In 802.11g, the DSP chose the wave with the best signal to noise ratio I will only select the signal with high SNR value and interpret it.
- 17. (cont.) • Problem : some weaker SNR waves are ignored even if there is the possibility that they contain relevant Information. • In 802.11n, MRC is implemented in the NIC’s DSP so that it takes all the waves and compose just one high-quality wave, thus increasing throughput • If you have an 802.11n board in a 802.11g network, you will have comparatively higher throughput. • Its like having a cat with multiple ears.
- 18. 802.11ac • Released in December 2013 • Frequency band : 5GHz • MU-MIMO • Channel width= 80MHz-160MHz • Up to 8 spatial streams • Up to 256-QAM (Some vendors offer a non-standard 1024-QAM mode) • Speed : 1300Mpbs-3.5Gbps • First time “Full duplex” communication
- 19. MU-MIMO • MU-MIMO adds multiple access (multi-user) capabilities to MIMO • Space division multiple access
- 20. 802.11ad • 60GHz (57-66Ghz) • Up to 7.2Gbps • Range : 30-40 feet • Better beamforming • Low powered • Very low penetration power • TP-link Talon AD7200 triband router • 4600Mbps • NETGEAR Nighthawk X10 AD7200 802.11ad • 7.2Gbps
- 21. END
Editor's Notes
- In 802.11n OFDM subcarriers = 48-52 (in 20Mhz channel)
- SISO => Intermittent reception ,fading, multiple path propagation MIMO can be sub-divided into three main categories: precoding, spatial multiplexing (SM), and diversity coding. Precoding is multi-stream beamforming, in the narrowest definition. In more general terms, it is considered to be all spatial processing that occurs at the transmitter. In (single-stream) beamforming, the same signal is emitted from each of the transmit antennas with appropriate phase and gain weighting such that the signal power is maximized at the receiver input. The benefits of beamforming are to increase the received signal gain – by making signals emitted from different antennas add up constructively – and to reduce the multipath fading effect. In line-of-sight propagation, beamforming results in a well-defined directional pattern. However, conventional beams are not a good analogy in cellular networks, which are mainly characterized by multipath propagation. When the receiver has multiple antennas, the transmit beamforming cannot simultaneously maximize the signal level at all of the receive antennas, and precoding with multiple streams is often beneficial. Note that precoding requires knowledge of channel state information (CSI) at the transmitter and the receiver. Spatial multiplexing requires MIMO antenna configuration. In spatial multiplexing,[33][34] a high-rate signal is split into multiple lower-rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures and the receiver has accurate CSI, it can separate these streams into (almost) parallel channels. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher signal-to-noise ratios (SNR). The maximum number of spatial streams is limited by the lesser of the number of antennas at the transmitter or receiver. Spatial multiplexing can be used without CSI at the transmitter, but can be combined with precoding if CSI is available. Spatial multiplexing can also be used for simultaneous transmission to multiple receivers, known as space-division multiple access or multi-user MIMO, in which case CSI is required at the transmitter.[35] The scheduling of receivers with different spatial signatures allows good separability. Diversity coding techniques are used when there is no channel knowledge at the transmitter. In diversity methods, a single stream (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called space-time coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beamforming or array gain from diversity coding. Diversity coding can be combined with spatial multiplexing when some channel knowledge is available at the transmitter.