Wireless LAN & 802.11ac Wi-Fi Fundamentals #AirheadsConf Italy
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Transcript of Wireless LAN & 802.11ac Wi-Fi Fundamentals #AirheadsConf Italy
802.11ac Wi-Fi Fundamentals
Eric Johnson
June 2014
CONFIDENTIAL
© Copyright 2014. Aruba Networks, Inc.
All rights reserved2 #AirheadsConf
Agenda
11ac Standards Physical Layer Overview
11ac Data Rates
Radio Realities
Receivers
Antennas
11ac Beamforming
11ac Products
3CONFIDENTIAL
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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
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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
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Channel Allocations
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802.11ac Channels (ETSI)
Channel
Freq (MHz)
UNII I and UNII II
2x 80 MHz
4x 40 MHz
8x 20 MHz
Channel
Freq (MHz)
UNII II extended
2x 80 MHz
5x 40 MHz
11x 20 MHz
36 4844 5240 56 6460 Band
Edge
5180 5200 5220 5240 5260 5280 5300 5320 5350
Band
Edge
5150
100 112108 116104 120 128124
5500 5520 5540 5560 5580 5600 5620 5640
Band
Edge
5470
136 140 Band
Edge
5680 5700 5725
132
5660
7CONFIDENTIAL
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802.11ac Channels (FCC)
Channel
Freq (MHz)
UNII I and UNII II
2x 80 MHz
4x 40 MHz
8x 20 MHz
Band
EdgeChannel
Freq (MHz) 5850
US UNII III
1x 80 MHz
2x 40 MHz
5x 20 MHz
Channel
Freq (MHz)
UNII II extended
3x 80 MHz
6x 40 MHz
12x 20 MHz
36 4844 5240 56 6460 Band
Edge
5180 5200 5220 5240 5260 5280 5300 5320 5350
Band
Edge
5150
149 161157153
5745 5765 5785 5805
Band
Edge
5725
165
5825
100 112108 116104 120 128124
5500 5520 5540 5560 5580 5600 5620 5640
Band
Edge
5470
136 140 Band
Edge
5680 5700 5725
132
5660
144
5720
Weather
Radar
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Dynamic Bandwidth Management:Channel Usage with Two APs
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Wave 2
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Wave 2 of 11ac
• What will wave 2 802.11ac deliver?• MU-MIMO
• Use AP MIMO resources more effectively
• Transmit data to multiple devices simultaneously: for example 4SS AP streaming data to four 1SS clients simultaneously
• 4x4:4SS
• Benefit of additional stream mostly for MU-MIMO
• Not anticipating any 4x4:4SS client devices
• Adds 33% to max datarate
• VHT160
• Doubles max datarate
• Practical problem: only 2 VHT160 channels available in entire 5GHz band
• Max 5GHz radio throughput triples again!• 450 (11n 3x3 HT40), 1,300 (11ac 3x3 VHT80), 3,467 (11ac 4x4 VHT160)
• When will it be available?• Radio chipsets available late 2014
• Products in 2015
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Reasons not to wait for Wave 2
• Unlikely to see any 4x4:4SS client devices
• Use of VHT160 not practical for typical enterprise deployment
• MU-MIMO is a nice-to-have optimization.• How well it will work and what the real benefits are is still not entirely
clear
• Requires new client devices (Wave 1 clients also not FW upgradeable)
• Wave 1 is here now (technology, products, market momentum), offering huge advantages over 11n. Wave 2 is the expected next step in the evolution of the technology.
• In general: the next wave in technology is always around the corner, something better is always coming Once Wave 2 is available, we’ll for sure be talking about Wave 3.
• No different from when 11n 2x2 products were introduced and it was clear that 3x3 products would be available within 18 months.
14CONFIDENTIAL
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11ad and what it means
• 60GHz band, three channels in most countries (each 2.16GHz wide), each providing up to 6.8Gbps PHY datarate
• No MIMO
• Challenges: Non-Line of Sight (NLOS) connections, range, penetrating obstacles (and people)
• Targeted to clean up a cluttered desk or TV cabinet
• Likely not appropriate for traditional AP use. But can be interesting for related applications like wireless docking, high-capacity WLAN hotspots, AP backhaul/aggregation, etc.
• It is being investigated (but no product plans as of yet)
• Standard is available, certification program in place
• Wi-Fi Alliance WiGig Alliance
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Understanding 11ac Data Rates
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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.
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Sub-carriers
52 subcarriers (48 usable) for a 20 MHz non-HT
mode (legacy 802.11a/g) channel
fc +10MHz-10MHz
26 carriers 26 carriers
56 subcarriers (52 usable) for a 20 MHz HT
mode (802.11n) channel
fc
28 carriers 28 carriers
114 subcarriers (108 usable) for a 40 MHz HT mode (802.11n) channel
fc +10MHz-20MHz
57 carriers 57 carriers
+20MHz-10MHz
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)
121 carriers 121 carriers
fc +10MHz-20MHz +20MHz-10MHz-40MHz -30MHz +30MHz +40MHz
OFDM subcarriers used in 802.11a, 802.11n and 802.11ac
+10MHz-10MHz
Guard Tones
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QAM constellations
Amplitude +1
Amplitude -1
Quadra
ture
-1
Quadra
ture
+1
Amplitude +1
Amplitude -1Q
uadra
ture
-1
Quadra
ture
+1
Amplitude +1
Amplitude -1
Quadra
ture
-1
Quadra
ture
+1
16-QAM constellation 64-QAM constellation 256-QAM constellation
Constellation diagrams for 16-, 64-, 256-QAM
19CONFIDENTIAL
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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
19
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Raw Data Rates
• #Tones * Bits per Tone * Symbol Rate
– 16 QAM, 20 MHz
– 52 * 4 * 0.3125 = 65 Mbps
20
21CONFIDENTIAL
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Correct for Cyclic Extension
21
22CONFIDENTIAL
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Apply FEC Coding
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Receivers
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Receiver Line Up
32
ADCSymbol
DecodeDown
ConvertLNA
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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
33
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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
34
35CONFIDENTIAL
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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).
41CONFIDENTIAL
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Antennas
42CONFIDENTIAL
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Reading Antenna Pattern Plots -Omni
42
Azimuth Elevation
Omnidirectional Antenna (Linear View)
-3 dB
Sidelobes
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Reading Antenna Pattern Plots -Sector
43
Azimuth Elevation
Sector Antenna (Logarithmic View)
-3 dB
-3 dB
SidelobesBacklobe
Front
Back
Side
44CONFIDENTIAL
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44
ANT-2x2-5010
Heat Maps
45CONFIDENTIAL
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Ant-2x2-5010 Antenna Patterns
45
• Model
0
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a
a 5 dB per division
• Measured
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Ant-2x2-5010 Simple projection
46
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a
a 5 dB per division
Assuming 20m install height
0m20m
50m100 m200 m
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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
47
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C/I Contours
CI dBm
C/I Contours
CI dBm
Heat Map: Antenna at 5 m height
48
100 m 1000 m
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C/I Contours
CI dBm
C/I Contours
CI dBm
Heat Map: Antenna at 10 m height
49
100 m 1000 m
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C/I Contours
CI dBm
Heat Map: Antenna at 20 m height
50
100 m 1000 m
C/I Contours
CI dBm
51CONFIDENTIAL
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C/I Contours
CI dBm
C/I Contours
CI dBm
Heat Map: Antenna at 40 m height
51
100 m 1000 m
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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
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53CONFIDENTIAL
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Building Arrays: 2 Elements
• By introducing additional antenna elements we
can control the way that the energy radiates
• 2 elements excited in phase
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l/2
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Linear Plot
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dB Plot
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0
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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
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Linear Plot
dB Plot
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55CONFIDENTIAL
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Building Arrays: 4 Elements
• By shaping the amplitude we can control
sidelobes
• 4 elements excited in phase
– Amplitude 1, 3, 3, 1
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Linear Plot
dB Plot
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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
56
Linear Plot
dB Plot
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802.11ac Beamforming
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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
58
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Channel state information, implicit and explicit beamforming estimation
59
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
sounding frames
Beamformed frames
feedback from sounding
Explicit feedback for beamforming
Beamformer Beamformee
Actual
CSI
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5- 4- 3- 2- 1- 0 1 2 3 4 51 10
4-
1 103-
0.01Antenna 1
Antenna 2
Antenna 3
Wavelengths
E F
ield
Am
plitu
de
Client Antennas
h11
h21
h31
#airheadsconf61
Practical Example: Beamforming
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Line of Sight
• 3 stream AP
• Smartphone
– 1 Antenna/1 Stream
Client
AP
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Simple Reflection
• Let’s introduce two
reflection surfaces
and look at the
impact of one bounce
on each side
Client
AP
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Virtual
Antenna Pattern
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Multi Stream Client
• The reflections allow
beamforming to send
different streams
with different
antenna pattern
through the system
Client
AP
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Str
eam
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ea
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eam
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Beamforming
• Stream 3 now appears on all three antenna
– Here is how each transmitted component shows up at the
client
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5- 4- 3- 2- 1- 0 1 2 3 4 51 10
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0.01
0.1
1
10Antenna 1
Wavelengths
E F
ield
Am
plitu
de
Now add them!
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Similarly Stream 1 and 2
66
Stream 1
Stream 2
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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
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Aruba 11ac Solutions
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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
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Indoor 802.11ac Needs an Outdoor Complement
• Fully ruggedized for extreme environments
• Gigabit performance
• Simplified installation
• Inconspicuous design
• Designed for indoor-use
• Gigabit performance
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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°CNo Heater. Start and operate.
72 @arubanetworks
What 11ac can Deliver
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Performance: 3 Stream 11ac outdoors!
850 Mbps
TCP!
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Performance: Samsung GS4
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76
Thank You
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