Understanding RF Fundamentals and the Radio Design for 11ac Wireless Networks Brandon Johnson Systems Engineer Agenda • Physics - RF Waves • Antenna Selection • Spectrum, Channels & Channel widths • MIMO & Spatial Streams • Cisco 802.11ac features • Beyond 802.11ac Electromagnetic Spectrum • Radio waves • Micro waves Colour Frequency Wavelength • Infrared Radiation Violet 668-789 THz 380-450nm Blue 606-668 THz 450-495nm • Visible Light Green 526-606 THz 495-570nm • Ultraviolet Radiation Yellow 508-526 THz 570-590nm • X-Rays Orange 484-508 THz 590-620nm • Gamma Rays Red 400-484 THz 620-750nm Radio Frequency Fundamentals λ1 λ • Frequency and Wavelength 2 • f = c / λ c = the speed of light in a vacuum • 2.45GHz = 12.3cm • 5.0GHz = 6cm • Amplitude • Phase * ϕ A1 A2 Radio Frequency Fundamentals • Signal Strength • Wave Propagation • Gain and Amplification – Attenuation and Free Space Loss • Loss and Attenuation – Reflection and Absorption – Wavelength Physics of Waves • In phase, reinforcement • Out of phase, cancellation RF Mathematics • dB is a logarithmic ratio of values (voltages, power, gain, losses) • We add gains • We subtract losses • dBm is a power measurement relative to 1mW • dBi is the forward gain of an antenna compared to isotropic antenna Now we know that …. How? CSMA / CA – “Listen before talk” • Carrier sense, multiple access / open spectrum • (open, low-power ISM bands) no barrier to entry • Energy detection must detect channel available – Clear Channel Assessment • On collision, random back off timer before trying again. • Clear channel is very important. Wireless Is Always A Two-Way Conversation Interference and Signal to Noise Ratio • Any RF signals other than what we want is interference • SNR is a ratio • The signal strength is a result of: • Transmit power • Receive sensitivity • Increase the signal, or decrease the noise Two way communication - Example Point Distance Point 20 A B 0 0 20 40 60 80 100 120 -20 -40 -60 -80 -100 -120 Antennas Antenna Fundamentals Omni-Directional Antennas Azimuth Elevation Omnidirectional Antenna Radiation Pattern 3D Not accurate or to scale; conceptual only Antenna Fundamentals Patch Antennas Azimuth Elevation Panel Azimuth and Elevation in 3D Not accurate or to scale; conceptual only Panel EM field in 3D (Hypothetically) Not accurate or to scale; conceptual only Antenna Fundamentals Internal Antennas Antenna Fundamentals High-Gain Antennas Azimuth Elevation Waveguide Azimuth and Elevation in 3D Not accurate or to scale; conceptual only Antenna Fundamentals High-Gain Antennas First Null is “Filled In” Second Null is not as deep Low signal regions occur close to tower to minimise the impact Low Signal Low Signal Antenna Design Cisco 2.4GHz Antenna Combined 2.4 and 5GHz Antenna Multipath Propagation Direct Channels 2.4GHz Channels – really only 3; not used -11ac Understanding 802.11ac • 80MHz Channel and 3 SS = 1.3Gbps • 5GHz only • 80MHz Channel and 2 SS = 866.6Mbps • Channel Bonding • 80MHz Channel and 1 SS = 433.3Mbps • 80 and 160MHz Channels • Modulation • 256-QAM • Spatial Streams • Support for up to 8 5GHz Channel Allocation Channel widths Resolution 20MHz – 1SS 80MHz – 1SS Resolution Modulation, SNR and Data Rates 4-QAM SNR=6SNR=10 Rate vs Range and the Laws of Physics 4-QAM 16-QAM 64-QAM Rate vs Range and the Laws of Physics 256-QAM Rate vs Range and the Laws of Physics Pop-Quiz Multi In – Multi Out MIMO Antenna Diversity Diversity Combining Multiple Input Multiple Output Maximal Ratio Combining Combined Effect (Adding all Rx Paths) 3 Antennas Rx Signals Multiple Input Multiple Output Implicit Transmit Beamforming Multiple Input Multiple Output Implicit Transmit Beamforming Multiple Input Multiple Output ClientLink 4.0 802.11a/g/n/ac 1SS 1SS 2SS 3SS Multiple Input Multiple Output Spatial Multiplexing Data Data The The The quick brown fox Data Data quick The quick The quick brown fox Multiple Input Multiple Output Spatial Multiplexing The Data Data The quick The quick brown fox quick brown Data Data The quick The quick brown fox brown fox fox 80MHz – 1SS 80MHz – 3SS Channel Bonding 20-MHz Gained Space 40-MHz Gained Space 20-MHz Gained Space 80-MHz 40-MHz Gained Space Channel Bonding 1SS 1SS 2SS 3SS 80-MHz 80-MHz Gained Space 160-MHz 80-MHz 160-MHz 80-MHz 5GHz Channel Allocation Engineer in a Can Features Enhanced HDX Turbo Performance Improves radio efficiency for higher throughput and client density Optimised Roaming Intelligently determines the optimum time to roam Cisco CleanAir® 80MHz Mitigates interference and improves channel capacity Cisco ClientLink 3.0 Improves legacy and 802.11ac Client performance Dynamic BW Selection Extends DCA to automatically select ideal channel widths AirTime Fairness Optimises medium access as allocation of airtime not bitrate Cross-AP Management* Directs Wireless Signal for Better Coverage Spectrum Intelligence CleanAir and iBeacon • iBeacons use Bluetooth Low-Energy to send advertising signals • Smart phone applications using simple RSSI information figure out micro- location & apps then fetch relevant advertising content • BLE /iBeacons can be used to improve the way finding experience Radio Resource Management . Dynamic Channel Assignment / Dynamic Bandwidth Selection . Transmit Power Control . Coverage Hole Detection and Mitigation … and more • What It Does • What It Does NOT Do • Dynamically balances • Substitute for a site survey infrastructure and mitigate changes • Correct a poor design • Monitor and maintain • Manufacture spectrum or coverage for all clients otherwise counteract the laws • Provide the optimal of physics… throughput under changing conditions Optimised Roaming DCA and 802.11ac – Channel Width • Selection of 20 MHz – all AP’s set to 20 Mhz • Selection of 40 MHz – All 40 MHz capable AP’s set to 40 MHz • 20 MHz only AP’s will be left on 20 Mhz • Selection to 80 MHz – all 80 MHz capable AP’s set to 80 MHz • Others – 802.11n will be at 40 Mhz, and 802.11a at 20 Mhz Wireless=>802.11a/b=>RRM=>DCA 802.11AC and the OBSS and Coexistence • Using the example of an 80 MHz OBSS – (Overlapping BSS) • AP-AC wins contention on my primary channel and will send data on that channel and 3 other bonded channels. • The VHT header tells all 802.11AC stations that I’m using an 80 MHz OBSS and even tells what 20 MHz sub channels it’s using • But What of the lowly 802.11a station, or the 802.11n (HT) station who don’t speak 802.11ac and it’s fancy VHT language? 802.11AC and the OBSS (Overlapping BSS) Protocol Primary Secondary 20 MHz Secondary 40 MHz 802.11a -82 dBm 802.11n -82 dBm -62 dBm (20 dB liberty) 802.11ac -82 dBm -72 dBm (10 dB liberty) -76 to -79 (3-6 dB liberty) • Never Fear – LBT (Listen before Talk) to the rescue – CCA! (Clear Carrier Assessment) • CCA thresholds where adjusted in the 802.11ac specification to allow Overlapping BSS and IBSS stations coexist by adjusting the contention requirements for Sub Channels • In the table above – you can see that all 3 protocols have equal contention on the primary. • Any primary operating within a secondary 20 or 40 will loose contention • Any secondary 20 operating in a secondary 40 will win contention over other secondary's! Awesome, so what? 600 TCP Down MBA • More co-channel interference models to 500 worry about 400 • So What? It’s still fast – right? 300 • TCP downlink testing using 80 MHz channel width on channel 36. 200 Interference AP set on channel 44 20 100 MHz – in the secondary 40 Mhz 0 MBA MBA Interfereing MBA Without With If you had set an 802.11ac radio to 80 MHz, that radio will wait until all 80 MHz is free before it will transmit It will not roll back and use 40 MHz or 20 MHz Enter Cisco Dynamic Bandwidth Selection Before After Complex configuration and inefficient use of spectrum Automatic and intelligent use of spectrum 56 60 64 80 MHz Channel 52 52/56/60/64 Primary Secondary Secondary 20 20 40 56 60 64 Interference impacts 52 80 MHz…what can 52 56 60 64 I use? • 80-MHz channel 52/56/60/64 • Interference is impacting only channel 60 • 3x20 MHz channels still available or 1x40 MHz and 1x20 MHz Radio Resource Automatic detection Difficult to find non- RRM selects channel Management (RRM) of non-overlapping overlapping channels and channel width selects channel only channels Cisco Features (802.11ac) Cisco Dynamic Bandwidth Selection Before After Complex configuration and inefficient use of spectrum Automatic and intelligent use of spectrum 56 60 64 80 MHz Channel 52 52/56/60/64 Primary Secondary Secondary 20 20 40 56 60 64 Interference impacts 52 80 MHz…what can 52 56 60 64 I use? • 80-MHz channel 52/56/60/64 • Interference is impacting only channel 60 • 3x20 MHz channels still available or 1x40 MHz and 1x20 MHz Radio Resource Automatic detection Difficult to find non- RRM selects channel Management (RRM) of non-overlapping overlapping channels and channel width selects channel only channels Cisco CleanAir Before After Rogue Wi-Fi interference decreases reliability and performance Mitigated RF interference for improved until next dynamic channel assignment (DCA) cycle reliability and performance Improved Client Performance Air Quality Performance Air Quality Performance Granular Non-Wi-Fi Wi-Fi and Dynamic Rogues seen as spectrum interference non-Wi-Fi mitigation security threat only visibility and aware ED-RRM prioritized control Complete Automatic Interference Mitigation Solution for Rogues and Non-Wi-Fi Interference Cisco Air Time Fairness Before After Rate limiting can only specify a bit rate (throughput) limit. Air time is allocated per SSID, per realm, per client. There is no way to limit the duration that the bit rate will use. There is now better control over how air time is shared.