Shanghai Breakout: 802.11ac Wi-Fi Fundamentals
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The document discusses 802.11ac Wi-Fi technology. It provides an overview of 802.11ac, including how it builds upon 802.11n with wider channels up to 160MHz, higher modulations up to 256-QAM, and more spatial streams up to 8. It then covers topics like understanding 802.11ac data rates in detail, discussing aspects like OFDM subcarriers, modulation, and error correction coding. Antenna technology is also summarized, including how antenna patterns and beamforming can improve coverage and throughput.
Shanghai Breakout: 802.11ac Wi-Fi Fundamentals
- 1. 802.11ac Wi-Fi Fundamentals Eric Johnson December 2014
- 2. CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved 2 #AirheadsConf Agenda 11ac Standards Physical Layer Overview 11ac Data Rates Antennas 11ac Beamforming Field Results
- 3. 3 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf 802.11ac Technology Overview Think of 11ac as an extension of 11n • 11n specification introduced/leveraged: • 2.4 and 5 GHz supported • Wider channels (40 MHz) • Better modulation (64- QAM) • Additional streams (up to 4 streams) • Beam forming (explicit and implicit) • Backwards compatibility with 11a/b/g 11ac introduces • 5 GHz supported • Even wider channels (80 MHz and 160 MHz) • Better modulation (256-QAM) • Additional streams (up to 8) • Beam forming (explicit) • Backwards compatibility with 11a/b/g/n • Refer to http://www.802- 11.ac.net for in-depth information
- 4. 4 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Wider Channels • 80 MHz channel widths supported in first generation – 80 MHz is 4.5x faster than 20 MHz – 80 MHz is contiguous – Per packet dynamic channel width decisions • Future releases will allow for 160 MHz channel widths – 160 MHz can be either contiguous or in two non-contiguous 80 MHz slices
- 5. 5 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Understanding 11ac Data Rates
- 6. -10MHz +10MHz 57 carriers 57 carriers f-20MHz c +10MHz -10MHz +20MHz 121 carriers 121 carriers f-40MHz -30MHz -20MHz -10MHz c +10MHz +20MHz +30MHz +40MHz 6 26 carriers 26 carriers -10MHz fc +10MHz CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Sub-carriers 52 subcarriers (48 usable) for a 20 MHz non-HT mode (legacy 802.11a/g) channel 28 carriers 28 carriers fc 56 subcarriers (52 usable) for a 20 MHz HT mode (802.11n) channel 114 subcarriers (108 usable) for a 40 MHz HT mode (802.11n) channel 242 subcarriers (234 usable) for a 80 MHz VHT mode (802.11ac) channel An 80+80MHz or 16MHz channel is exactly two 80MHz channels, for 484 subcarriers (468 usable) OFDM subcarriers used in 802.11a, 802.11n and 802.11ac Guard Tones
- 7. 7 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Terminology • Symbol: basic element containing 1 to 8 bits of information • Tone/Sub-Carriers: OFDM is made up of many tones. Each symbol is mapped to a tone. • Cyclic Extension: technique used in OFDM to protect against multipath interference – You need cyclic extension but it is dead air and consumes transmit time • Guard Band: Space between channels. In these regions tones have a constant value of zero amplitude • Pilot Tones: Used to train the receiver and estimate the channel • Radio Channel: For Wi-Fi 20, 40, 80, or 160 MHz of spectrum • Propagation Channel: everything that happens between the transmitter and receiver • FEC: Forward Error Correction. Redundant information that is sent to assist the receiver in decoding the bits.
- 8. 8 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf QAM constellations Amplitude +1 Amplitude -1 Quadrature -1 Quadrature +1 Amplitude +1 Amplitude -1 Quadrature -1 Quadrature +1 Amplitude +1 Amplitude -1 Quadrature -1 Quadrature +1 16-QAM constellation 64-QAM constellation 256-QAM constellation Constellation diagrams for 16-, 64-, 256-QAM
- 9. 9 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf How do I get to the data rate for a given MCS? • Basic Symbol Rate – 312.5 KHz – 3.2 ms • Cyclic Extension – t/4 0.8 ms – t/8 0.4 ms • Bits Per Tone – BPSK 1 – QPSK 2 – 16 QAM 4 – 64 QAM 6 – 256 QAM 8 9
- 10. 10 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Raw Data Rates • #Tones * Bits per Tone * Symbol Rate – 16 QAM, 20 MHz – 52 * 4 * 0.3125 = 65 Mbps 10
- 11. 11 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Correct for Cyclic Extension 11
- 12. 12 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Apply FEC Coding 12
- 13. 13 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Receivers
- 14. 14 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Receiver Line Up 14 ADC Symbol Decode Down Convert LNA
- 15. 15 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Receiver Impairments • Analog Compression – Modern LNAs have very effective input power tolerance • Digital Compression – This is where a high power signal hits the Automatic Gain Control (AGC) Circuit. Gain drops and receiver sensitivity degrades – The radio can be totally blocked if the power hits the Analog to Digital Converter (ADC) and consumes all the bits • Intermodulation – Again, the effective linearity of modern LNAs reduces the impact of this 15
- 16. 16 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf DAS Interference: Example • Without filtering any signal that hits the receiver above -45 dBm will cause a reduction of sensitivity • The degradation continues until about -15 dBm at which point the signal is totally blocked • With a 100 mW (20 dBm) DAS system at 2100 MHz – Tx 20 dBm – Effective rx antenna gain 3 dBi – 1st meter at 2100 MHz -39 dB • Power at 1m -19 dBm – No impact distance 40 meters 16
- 17. 17 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Advanced Cellular Coexistence • Proliferation of DAS and new LTE bands at 2.6 GHz are creating issue for Wi-Fi solution • All new APs introduced by Aruba in the last 12 months and going forward have implemented significant filtering into the 2.4 GHz radio portion to combat this • Design solution – Use high-linear LNA followed with a high-rejection filter to achieve rejection target and little sensitivity degradation; – Design target: Minimal Sensitivity degradation with -10dBm interference from 3G/4G networks (theoretical analysis).
- 18. 18 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Antennas
- 19. 19 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Reading Antenna Pattern Plots - Omni 19 Azimuth Elevation Omnidirectional Antenna (Linear View) -3 dB Sidelobes
- 20. 20 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Reading Antenna Pattern Plots - Sector 20 Azimuth Elevation Sector Antenna (Logarithmic View) -3 dB -3 dB Backlobe Sidelobes Front Back Side
- 21. 21 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf 21 ANT-2x2-5010 Heat Maps
- 22. 22 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved 15 #AirheadsConf Ant-2x2-5010 Antenna Patterns 22 • Model 0 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 a a 5 dB per division • Measured
- 23. 0m 23 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved 200 m #AirheadsConf Ant-2x2-5010 Simple projection 23 15 0 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 a a 5 dB per division Assuming 20m install height 20m 50m 100 m
- 24. 24 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Analysis • The heatmaps are shown across 100m by 100m and 1000m by 1000m areas • These are flat earth models and the antenna is straight up above the plane • 2 ray propagation effects are not included 24
- 25. Heat Map: Antenna at 5 m height 25 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf C/I Contours CI dBm C/I Contours CI dBm 25 100 m 1000 m
- 26. Heat Map: Antenna at 10 m height 26 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf C/I Contours CI dBm C/I Contours CI dBm 26 100 m 1000 m
- 27. Heat Map: Antenna at 20 m height 27 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf C/I Contours CI dBm 27 C/I Contours 100 m 1000 m CI dBm
- 28. Heat Map: Antenna at 40 m height 28 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf C/I Contours CI dBm C/I Contours CI dBm 28 100 m 1000 m
- 29. 29 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Antenna Basic Physics • When the charges oscillate the waves go up and down with the charges and radiate away • With a single element the energy leaves uniformly. • Also known as omni-directionally 29
- 30. 30 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Building Arrays: 2 Elements • By introducing additional antenna elements we can control the way that the energy radiates • 2 elements excited in phase 30 l/2 0 30 60 90 120 150 180 210 240 270 300 330 Linear Plot 15 0 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 dB Plot
- 31. 31 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf 15 0 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 Building Arrays: 4 Elements • By introducing additional antenna elements we can control the way that the energy radiates • 4 elements excited in phase – Equal amplitude 31 Linear Plot dB Plot 0 30 60 90 120 150 180 210 240 270 300 330
- 32. 32 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf 15 0 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 0 30 60 90 120 150 180 210 240 270 300 330 Building Arrays: 4 Elements • By shaping the amplitude we can control sidelobes • 4 elements excited in phase – Amplitude 1, 3, 3, 1 32 Linear Plot dB Plot
- 33. 33 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf 15 0 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300 315 330 345 0 30 60 90 120 150 180 210 240 270 300 330 Building Arrays: 4 Elements Phase • By altering phase we can alter the direction that the energy travels • 4 elements excited with phase slope – Even amplitude 33 Linear Plot dB Plot
- 34. 34 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf 802.11ac Beamforming
- 35. 35 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Beamforming: Notes • AP 22x series has 11ac beamforming support in 2.4 and 5 GHz bands • Works with clients that support 11ac beamforming function – This is at a minimum all 11ac client devices using Broadcom chipsets – Support will have to come to all devices to compete with Broadcom offering • 11ac beamforming is standards based – first standard that is doing this the “right” way – 11ac beamforming represents the consensus view of the 1000’s of contributors to the standards process • 11ac beamforming is implemented in baseband. – It works with all antenna subsystems – The total number of beamforming combinations is effectively infinite • 11ac actively tracks users so has a recent channel estimate between the AP and client that is updated frequently 35
- 36. Beamformer Beamformee sounding frames feedback from sounding Beamformed frames 36 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Channel state information, implicit and explicit beamforming estimation 36 Explicit feedback for beamforming (802.11n and 802.11ac) 1 (Beamformer) Here’s a sounding frame 2 (Beamformee) Here’s how I heard the sounding frame 3 Now I will pre-code to match how you heard me Explicit feedback for beamforming Actual CSI
- 37. - 5 - 4 - 3 - 2 - 1 0 1 2 3 4 5 37 1 10 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf 1 10 - 4 - 3 0.01 Antenna 1 Antenna 2 Antenna 3 Wavelengths E Field Amplitude Client Antennas h11 h21 h31
- 38. 38 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Practical Example: Beam forming
- 39. 39 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved 20 10 350 330 #AirheadsConf Line of Sight • 3 stream AP • Smartphone – 1 Antenna/1 Stream Client AP 0 30 40 50 60 70 100 90 80 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 340
- 40. 40 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved 350 330 #AirheadsConf Simple Reflection • Let’s introduce two reflection surfaces and look at the impact of one bounce on each side Client AP 20 10 0 30 40 50 60 70 100 90 80 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 340 Virtual Antenna Pattern
- 41. 41 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved 20 10 350 330 20 10 350 330 #AirheadsConf Multi Stream Client • The reflections allow beamforming to send different streams with different antenna pattern through the system Client AP 20 10 0 30 40 50 60 70 100 90 80 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 350 330 320 340 0 30 40 50 60 70 100 90 80 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 340 0 30 40 50 60 70 100 90 80 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 340 Stream 1 Stream 3 Stream 2
- 42. 42 10 1 0.1 - 3 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Beamforming • Stream 3 now appears on all three antenna – Here is how each transmitted component shows up at the client 42 - 5 - 4 - 3 - 2 - 1 0 1 2 3 4 5 1 10 0.01 Antenna 1 Wavelengths E Field Amplitude Now add them!
- 43. 43 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Similarly Stream 1 and 2 43 Stream 1 Stream 2
- 44. 11ac Beamforming across an 80 MHz channel • The standards based algorithm actually works out patterns for each sub carrier • Below is the pattern for stream 1 at 5460, 5500, 5540 MHz 44 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved 350 330 #AirheadsConf 20 10 0 30 40 50 60 70 100 90 80 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 340 20 10 0 30 40 50 60 70 100 90 80 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 350 330 320 340 20 10 0 30 40 50 60 70 100 90 80 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 350 330 320 340
- 45. 45 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Aruba 11ac Solutions
- 46. 46 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf AP-224/225 802.11ac 3x3 AP • Enterprise class 3x3 802.11ac • Aggregate TCP platform throughput performance >1Gbps • Two platform models: – AP-224: external antennas (3x, dual band) – AP-225: integrated antennas – “Advanced Cellular Coexistence” support • Dual radio: – 802.11n 3x3:3 HT40 2.4GHz(450Mbps), support for “TurboQAM” – 802.11ac 3x3:3 HT80 5GHz (1.3Gbps) – 11ac beamforming supported in both bands • Wired interfaces – Network: 2x 10/100/1000Base-T Ethernet, with MACSec support – USB 2.0 host interface, console port, DC power • Will require 802.3at PoE (or DC power) for full functional operation – Functional, but capabilities reduced when powered from 802.3af POE • Enterprise temperature range, plenum rated, TPM
- 47. 47 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Indoor 802.11ac Needs an Outdoor Complement • Fully ruggedized for extreme environments • Gigabit performance • Simplified installation • Inconspicuous design • Designed for indoor-use • Gigabit performance
- 48. 48 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf AP-270 Series – Detailed Overview Antenna Gain: 5 dBi 2G: 3x3:3 11ac (2.4 GHz) 5G: 3x3:3 11ac (5.15 to 5.875 GHz) 11ac Beamforming Conducted Tx Power 2G: 23 dBm per branch (28 aggregate) MAX EIRP = 36 dBm 5G: 23 dBm per branch (28 aggregate) MAX EIRP = 36 dBm Power Interface: AC and 802.3at (PoE+) Power Consumption: 25 W Gigabit Ethernet WAN + LAN Port Advanced Cellular Coexistence Designed to Both IP66 and IP67 -40 to +65°C No Heater. Start and operate.
- 49. 49 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf What 11ac can Deliver
- 50. 50 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Performance: 3 Stream 11ac outdoors! 850 Mbps TCP!
- 51. 51 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf Performance: Samsung GS4
- 52. 52 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved #AirheadsConf
- 53. Thank You 53 #AirheadsConf CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
Editor's Notes
- #4: 11ac is an extension of 11n. Those of you who were around for the 11n roll out will notice a lot of déjà vu. The big difference with 11ac is that end users care about wireless speeds now. Client devices are differentiating themselves with 11ac support (HTC One, Samsung GS4, MacBook Air)
- #5: More on channel widths later. The important thing to know right now is that you get more than a 1 for 1 improvement in throughput. And we think must customers can deploy 80 mhz channels without significant problems now that the standard does a better job of detecting channel width. The AP will automatically fall back to 20 or 40 mhz channels.
- #18: 50 cm from das 1-2 from directional base station
- #20: This is the pattern plot for a high gain omnidirectional antenna. The azimuth (top view) shows almost equal signal in all directions. The elevation (side view) shows a narrow beamwidth to each side. It is important to realize that the polar pattern plot is showing the pattern of the antenna in decibels. Remember that for every 6 dB decrease, the signal travels half the distance. If you convert the pattern plot to a scaled or linear representation of the signal, it would look somewhat like the linear view at the bottom center of the slide.
- #21: This antenna is a directional sector antenna. The polar pattern plots shows a horizontal beamwidth of about 90 degrees and a vertical beamwidth of about 16 degrees. Notice that the 3 dimensional view at the bottom of the slide is a logarithmic view and not a linear view, therefore it is displaying the antenna pattern based upon the decibel measurements.
- #47: TurboQAM: proprietary solution to support 11ac 256-QAM modulation in 2.4GHz, potentially offering 33% throughput increase 802.3af POE: No USB No second Ethernet port 1x3:1ss 2.4GHz radio