Very High Density (vhd) 802.11ac Wireless Network Design and Deployment Basics

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Very High Density 802.11ac NetworksBasic Design & Deployment

March 8th, 2016 @ArubaNetworks |

Marcus Wehmeyer, ACMX #21

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Agenda

@ArubaNetworks |

–Very High Density VRDs –802.11ac vs. 802.11n in VHD networks–80-MHz vs. 40-MHz vs. 20-MHz Channels–DFS channel use–Collision Domains & RF Spatial Reuse–VHD Capacity Planning Methodology–Basic RF Design for Very High Density Coverage Areas–Example: Adjacent Large Auditoriums

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Very High Density VRD

100% 802.11acEnd-to-end system architecture & dimensioningNew capacity planning methodologyAddresses a wide range of customer use caseshttp://goo.gl/4epc9l

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Modular VRD Structure

Different guides for different audiences

IT LeadersCarrier StandardsAccount Managers

Customer EngineersPartner & Aruba SEsInstall Technicians

WLAN AchitectsCarrier RF Engineers

AllAudiences

VenueOwners

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802.11ac vs. 802.11n @VHD

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How Far We’ve Come

– “Coverage” WLANs came first

– These evolved into “Capacity” WLANs (with limited HD zones)

– 250m2 / 2500 ft2 = 25 devices per cell

– BYOD made every capacity WLAN a high-density network

– 3 devices/person = 75 per cell

– HD WLANs from 2011 are now very high-density (VHD)

– 100+ devices per “cell”. Devices may be associated to multiple BSS operators in same RF domain.

Waiting for the new Pope in St. Peter’s Square

NBC Today Show, February, 2013, http://instagram.com/p/W2BuMLQLRB/

http://instagram.com/p/W2BuMLQLRB/

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How Do 802.11ac Features Impact VHD Design?802.11ac Technology Promise VHD Impact

80-MHz & 160-MHz Channels Increase burst rates for individual STAs

None. Stay with 20-MHz channels for VHD areas

256-QAM New MCS rates up to 33% faster Minimal. Rates only usable within ~5m of AP

8 Spatial Streams Peak data rates up to 6.9Gbps None. In future, clients will be mostly capped at 2SS

DL MU-MIMO Transmit to 4 STAs at the “same” time TBD until Wave2 in 2016. Sounding overhead offsets gains

Frame Aggregation(A-MSDU & A-MPDU)

Enable the MAC to keep up with the 802.11ac PHY

Minimal. Majority of frames in VHD areas are bursty & small

802.11ac Technology Promise VHD Impact





DL MU-MIMO Transmit to 4 STAs at the “same” time Variable Sounding overhead offsets gains at density













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802.11ac Impact Promise VHD Impact

Broad-based DFS channel support

Open up 15 channels (FCC domains) Add up to 750Mbps of capacity

Faster AP CPUs Process small frames and collisions faster

Increase channel bandwidth closer to theoretical max

More AP memory Larger table sizes Better handle very high BSSID count environments

Clients converge to 2SS Increase per-STA burst rate even in narrow channels

Get clients off the air faster

Tx Beam Forming Improve SINRs both directions Robustness improvement; client-side CSI feedback







Clients converge to 2SS Increase per-STA burst rate even in narrow channels

Get clients off the air faster














Open up 16 channels (FCC domains) Add up to 800 Mbps of capacity @ 50Mbps/channel

Why 802.11ac Does Matter for VHD

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80-MHz vs. 40-MHz vs. 20-MHz Channel Widths

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12 x 40-MHzChannels Only 6 x 80-MHz

Channels (2 non-DFS)

Do not use ch. 144 until 802.11ac > 50%

Allowed Channels (FCC regulated countries)

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More channels = more distance between same-channel APs

Why 20-MHz Channels – Reuse Distance

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Why 20-MHz Channels – More RF Reasons

Reduced Retries – Bonded channels are more exposed to interference on sub-channels

Reduced Retries – Bonded channels are more exposed to interference on sub-channels

Using 20-MHz channels allows some channels to get through even if others are temporarily blocked

Higher SINRs – Bonded channels have higher noise floors (3dB for 40-MHz, 6dB for 80-MHz)

Higher SINRs – Bonded channels have higher noise floors (3dB for 40-MHz, 6dB for 80-MHz)

20-MHz channels experience more SINR for the same data rate, providing extra link margin in both directions

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Why 20-MHz Channels - Performance

Which Chariot test will deliver higher goodput?

Each test uses the exact same 80-MHz bandwidth

Each test uses the exact same number of STAs

Both VHT40 BSS will victimize each other with ACI

All four VHT20 BSS will victimize each other

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5 10 25 50 75 100 0 Mbps

50 Mbps

100 Mbps

150 Mbps

200 Mbps

250 Mbps

300 Mbps

VHT20x4 UpVHT20x4 BidirectVHT40x2 UpVHT40x2 BidirectVHT80x1 UpVHT80x1 Bidirect Down Up Bidirect

Clients

VHT20 Beats VHT40 & VHT80 – 1SS Clients

VHT80 falls off at 25 STAs

VHT40 falls off at 75 STAs

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DFS Channels

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General Rule

Use DFS channels for VHD areas!!The number of collision domains is the primary constraint on VHD capacityThe number of STAs per collision domain is the second major constraint on capacityVHD networks are ultimately about tradeoffs

The benefit of employing DFS channels almost always* outweighs the cost.

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DFS Usage Exceptions

Client capabilitiesIf more than 15-20% of the expected clients are proven to be 5-GHz capable but

unable to use DFSProven, recurring radar events

A DFS survey with the actual APs to be deployed shows regular events on specific channels.Just because certain channels are impacted do not rule out the band

Survey should be done at multiple locations & elevationsAvoid channel 144 until >50% of STAs can see it

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Balancing the Risks & Rewards

Client capabilitiesSince 2015, the vast majority of mobile devices shipping in USA support DFS

channels Non-DFS clients will be able to connect due to stacking of multiple channels

(although perhaps at lower rates)It is easily worth it to provide a reduced connect speed to a an unpredictable

minority of clients, in exchange for higher connect speeds for everyone else all the time

Radar eventsIt is worth having a small number of clients occasionally interrupted in exchange

for more capacity for everyone all the time

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Collision Domains & RF Spectrum Reuse

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What Is A Collision Domain?

A physical area in which 802.11 devices attempting to send can decode one another’s frame preambles.A moment in time.

Two nearby stations on the same channel will not collide if they send at different times.

Dynamic regions that are constantly moving in space and time based on which devices are transmitting

A collision domain is therefore an independent block of capacity in an 802.11 system.

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How We Normally Draw Collision Domains

Typical cell diagram showing radius of cell edge

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How Collision Domains Actually Work

Standard rate vs. range curve (MCS rates)

Decode limit for high-rate control frames Preamble

interference range for all frames

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Preamble Interference Radius Is HUGE

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VHD Capacity Planning Methodology

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The Capacity Challenge

Supply vs Demand designsLimited number of timeslots / unique channels (supply)20k clients want 1Mbps+ of air time (demand)Rules of physics still apply, so…

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System vs. Channel vs. Device Throughput

Channel 1Throughput

Channel 2Throughput

Channel XThroughput

Per-DeviceThroughput

2.4 GHz 5 GHzTotalSystem Throughput

+

+

+

+

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The Capacity Challenge – Physics!

20k clients want 1Mbps+ of air time (demand-based request)

Limited number of timeslots / unique channels (supply-based design)

1 6 11 36 40 44 48 52 56 60 64 100 104 108 112 116 132 136 140 149 153 157 161 165

1 6 11 36 40 44 48 149 153 157 161 165

50Mbps / 1Mbps = 50 users per channel

20,000 / 50 = 400 channels

400 / 24 = 16.6 times re-use required

100Mbps / 1Mbps = 100 users per channel

20,000 / 100 = 200 channels

200 / 24 = 8.3 times re-use required

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0

Total System Throughput Formula

Where:Channels = Number of channels in use by the VHD networkAverage Channel Throughput = Weighted average goodput achievable in one channel by the expected mix of devices for that specific facilityReuse Factor = Number of RF spatial reuses possible. For all but the most exotic VHD networks, this is equal to 1 (e.g. no reuse).

𝑻𝑺𝑻=𝑪𝒉𝒂𝒏𝒏𝒆𝒍𝒔∗ 𝑨𝒗𝒆𝒓𝒂𝒈𝒆𝑪𝒉𝒂𝒏𝒏𝒆𝒍 𝑻𝒉𝒓𝒐𝒖𝒈𝒉𝒑𝒖𝒕∗𝑹𝒆𝒖𝒔𝒆 𝑭𝒂𝒄𝒕𝒐𝒓

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Step 1 – Choose Channel Count

• US allows:• 9 non-DFS channels• 13-16 DFS channels*

• Deduct:•Channel 144•House channel(s)•Proven radar channels•AP-specific channel limitations

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Step 2 – Choose Unimpaired Channel Throughput

1 5 10 25 50 75 100 0 Mbps

50 Mbps

100 Mbps

150 Mbps

200 Mbps

250 Mbps

GS4 TCP UpGS4 TCP BidirectMBA TCP UpMBA TCP BidirectMBP TCP UpMBP TCP Bidirect

Simultaneously Transmitting Clients

Choose spatial stream mix that approximates expected device population

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Step 3 – Apply Impairment Factor

VHD Venue Type

Suggested 2.4-GHz

ImpairmentSuggested 5-

GHz Impairment** Rationale

Classroom /Lecture Hall

10% 5%

Above average duty cycles Little or no reuse of channels in the same room Structural isolation of same-channel BSS in adjacent rooms Minimal My-Fi usage

Convention Center 25% 10%

Moderate duty cycles Significant numbers of same-channel APs Large open areas with direct exposure to interference sources Non-Wi-Fi interferers Higher My-Fi usage in booth displays, presenters, attendees

Airport 25% 15% Minimal duty cycles (except for people streaming videos) Structural isolation of same-channel BSS in adjacent rooms Heavy My-Fi usage

Casino 25% 10% Low duty cycles on casino floor Low My-Fi usage

Stadium / Arena 50% 25%

Low-to-moderate duty cycles Significant numbers of same-channel APs Large open areas with direct exposure to interference sources Non-Wi-Fi interferers High My-Fi usage

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Step 4 – Choose Reuse Factor

RF spatial reuse must be assumed not to exist unless proven otherwise in VHD facilities of 10,000 seats or

less (RF = 1).

•Reuse factor is the number of devices that can use the same channel at exactly the same time•Reusing channel numbers is not the same as reusing RF spectrum

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Step 5 – Calculate TST By Band

VHD Venue TypeSuggested

5-GHz **Suggested

2.4-GHzLecture Hall 5% 10%Convention Center 10% 25%Airport 15% 25%Casino 10% 25%Stadium / Arena 25% 50%

Spatial Stream

Mix

50 Concurre

nt

75 Concurre

nt100

Concurrent1SS Device 50 Mbps 38 Mbps 31 Mbps2SS Device 100 Mbps 72 Mbps 51 Mbps3SS Device 158 Mbps 118 Mbps 78 Mbps

Channel Type

USA 5-GHz

CountNon-DFS 9DFS 11Total 20

Step 1 - Channels Step 2 – Unimpaired Throughput Step 3 – Impairment

# DescriptionChannel

s

Unimpaired

Throughput

Impaired 5-GHz TP

Impaired 2.4-GHz

TPReus

e 5-GHz TST 2.4-GHz TST

1 Non-DFS Lecture Hall 9 + 3 100Mbps 95Mbps 90Mbps 1 9 * 95Mbps = 855

Mbps3 * 90Mbps = 270

Mbps

2 DFS Arena 20 + 3 40 Mbps 30 Mbps 20 Mbps 1 20 * 40Mbps = 800 Mbps

3 * 20 Mbps = 60 Mbps

3 DFS Stadium 20 + 3 40 Mbps 30 Mbps 20 Mbps 4 3.2 Gbps 240 Mbps

Step 5 – Calculate TST By Band


s

Unimpaired

Throughput

Impaired 5-GHz TP

Impaired 2.4-GHz

TPReus




Mbps

2 DFS Arena 20 + 3 40 Mbps 30 Mbps 20 Mbps 1 20 * 40Mbps = 800 Mbps

3 * 20 Mbps = 60 Mbps


s

Unimpaired

Throughput

Impaired 5-GHz TP

Impaired 2.4-GHz

TPReus




Mbps

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Close to 3Gbps is about right…

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Per-Device Throughput Formula

Where:Associated Device Capacity (ADC) = Percentage of seating capacity with an active Wi-Fi device * average number of Wi-Fi devices per person. Typically computed per band.Device Duty Cycle = Average percent of time that any given user device attempts to transmit

𝑨𝑷𝑫𝑻=𝑻𝒐𝒕𝒂𝒍𝑺𝒚𝒔𝒕𝒆𝒎𝑻𝒉𝒓𝒐𝒖𝒈𝒉𝒑𝒖𝒕

𝑨𝒔𝒔𝒐𝒄𝒊𝒂𝒕𝒆𝒅 𝑫𝒆𝒗𝒊𝒄𝒆𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒚∗𝑫𝒆𝒗𝒊𝒄𝒆 𝑫𝒖𝒕𝒚 𝑪𝒚𝒄𝒍𝒆

It is generally impossible to guarantee a specific per-device value in a VHD system.

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Step 1 – Estimate ADC

Start with the seating / standing capacity of the VHD area to be coveredThen estimate the take rate (50% is a common minimum) Choose the number of devices expected per person. This varies by venue type. It might be lower in a stadium and higher in a university lecture hall or convention center salon.

For example, 50% of a 70,000 seat stadium would be 35,000 devices assuming each user has a single device100% of a 1,000 seat lecture hall where every student has an average of 2.5 devices would have an ADC equal to 2,500

More users should be on 5-GHz than 2.4-GHz. ADC should be computed by frequency band. In general you should target a ratio of 75% / 25%. Association demand is assumed to be evenly distributed throughout the coverage space.

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Step 2 – Choose a Device Duty Cycle

•Subjective decision made by the network architect, based on expected user applications

•This duty cycle is %Time the user or device wants to perform this activity. •It is not the same as the application duty cycle!

Category Duty Cycle User & Device Behavior ExamplesBackground 5% Network keepalive / App phonehome

Checking In 10% Web browsing / Checking email / Social updates

Semi-Focused 25% Streaming scores / Online exam

Working 50% Virtual desktop

Active 100% Video streaming / Voice streaming / Gaming

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Examples

#Descriptio

nSeat

sTake Rate

Devices/

Person ADC

3 DFS Stadium 60K 50% 1 30K

#Descriptio

nSeat

sTake Rate

Devices/

Person ADC

1 Lecture Hall 500 75% 2.5 938

#Descriptio

nSeat

sTake Rate

Devices/

Person ADC

2 DFS Arena 20K 50% 1 10K

5-GHz Per-Device Goodput

2.4-GHz Per-Device Goodput





Band Split

Duty Cycle

5-GHz TST

2.4-GHz TST

50/50 20% 855 Mbps

270 Mbps

Band Split

Duty Cycle

5-GHz TST

2.4-GHz TST

75/25 10% 800 Mbps 60 Mbps

Band Split

Duty Cycle

5-GHz TST

2.4-GHz TST

75/25 10% 3.2 Gbps

240 Mbps

500 * 75% * 2.5 = 938 938 / 2 = 469

20,000 * 50% * 1 = 10,000

60,000 * 50% * 1 = 30,000

10K * 75% = 7,500

30K * 75% = 22,500

If only 1 or 2 reuses is actually achieved, drops by 50-75%

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Basic RF Design for Very High Density Coverage Areas

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RF Coverage Strategies

Overhead Coverage: APs are placed on a ceiling, catwalk, roof, or other mounting surface directly above the users to be served.

Side Coverage: APs are mounted to walls, beams, columns, or other structural supports that exist in the space to be covered.

Floor Coverage: This design creates picocells using APs mounted in, under, or just above the floor of the coverage area.

Radio coverage can be done in three ways, regardless of the type of area to be served

APs with integrated antennas are used for any VHD area of under 5,000 seats (very few exceptions)

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Overhead Coverage

•Overhead coverage is a good choice when uniform signal is desired everywhere in the room. •No RF spatial reuse is possible because of the wide antenna pattern and multipath reflections. •Integrated antenna APs should always be used for ceilings of 10 m (33 ft) or less.•Note the 20-MHz channel width, and that no channel number is used more than once. •This is an example of a static, non-repeating channel plan intentionally chosen by the wireless architect. •Requires access the ceiling with minimal difficulty or expense to pull cable and install equipment.

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Examples – Overhead Coverage #1

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Examples – Overhead Coverage #2

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Side Coverage

•Wall, beam, and column installations with side-facing coverage are very common in VHD areas. •Some ceilings are too difficult to reach, others have costly finishing that cannot be touched, or there may be no ceiling such as open-air atriums.•No RF spatial reuse in indoor environments is possible when mounting to walls or pillars. •50% of the wall-mounted AP signals are lost to the next room (and 75% of the signal in the corners). •Note that adjacent APs on the same wall always skip at least one channel number.

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What Does No RF Spatial Reuse Mean?

-55dBm Filter -60dBm Filter -65dBm Filter

Every AP can be heard everywhere in the room

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Examples – Side Coverage

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Floor Coverage

•Venues <= 10K seats should always use overhead or side coverage. •Above > 10K seats, a more exotic option called “picocell” has been proven to deliver significant capacity increases.•Density of picocell can be much higher than overhead or side coverage. •Picocell design leverages absorption that occurs to RF signals as they pass through a crowd (known as “crowd loss”).•Cost and complexity of picocells may not always justify the extra capacity generated.

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Examples - Picocell

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Aruba 802.11ac Indoor APs•Buy the highest performance AP that you can afford for VHD areas.•The rest of your deployment may use a more economical model. •Use the right tool for the job.

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Choosing an AP Model for VHD Areas

AP-225 is faster with 3SS clients

3SS Laptop – VHT80 2SS Laptop – VHT80

AP-205 works well up to 25 concurrent clients

AP-225 is best beyond 50 clients

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AP Placement for Adjacent VHD Areas

Place APs all facing same direction. Stagger horizontal placements.

Same rules apply to wall deployments. Use rear lobe to your advantage.

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Back-to-Back APs on Same Wall

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Example:Adjacent Large Auditoriums

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Typical Multi-Auditorium Scenario• Hotel conference center or

university building with multiple adjacent auditoriums

• Dimensioning metrics:

Physical Layout

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Understanding Offered Load in Auditoriums

• Common apps are web browsing, email, and office collaboration.

• Class presentation and exam software, are bursty with high concurrent usage.

• Cloud service latency is not visible to users.

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Step 2/3 - Estimate Associated Device CapacityStart with seating capacity

Use per-user device to estimate ADC

Break out by frequency band.

Determine address space

Estimate staff / facility devices separately

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Step 4 - Estimate the AP Count

Take 5-GHz ADC

Divide by per-radio metric

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Calculate System Throughput (Excluding CCI)

Take AP count Multiply by estimated channel capacity

Convert to channels Total maximum load if zero CCI

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Total System Throughput Formula

Where:•Channels = Number of channels in use by the VHD network•Average Channel Throughput = Weighted average goodput achievable in one channel by the expected mix of devices for that specific facility•Reuse Factor = Number of RF spatial reuses possible. For all but the most exotic VHD networks, this is equal to 1 (e.g. no reuse).

𝑻𝑺𝑻=𝑪𝒉𝒂𝒏𝒏𝒆𝒍𝒔∗ 𝑨𝒗𝒆𝒓𝒂𝒈𝒆𝑪𝒉𝒂𝒏𝒏𝒆𝒍𝑻𝒉𝒓𝒐𝒖𝒈𝒉𝒑𝒖𝒕∗𝑹𝒆𝒖𝒔𝒆 𝑭𝒂𝒄𝒕𝒐𝒓

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Estimating Unimpaired Channel Throughput

Choose spatial stream mix that approximates expected device population

Choose estimated number of simultaneously transmitting clients

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Understanding CCI & Estimating Reuse Factor

DFS channels minimize reuse

Same-channel APs are widely spaced

Avoiding DFS channels means greatly increased CCI

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Calculate Total System Throughput (Including CCI)

Model different reuse factors

Revised capacity for DFS scenario

Revised capacity for non-DFS scenario

Most likely outcomes

The TST directly dimensions the required WAN uplink.

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Effect of Beacon Rates in High-BSSID Facilities

1 2 31 0.44% 0.89% 1.33%

5 2.22% 4.44% 6.67%

10 4.44% 8.89% 13.33%

15 6.67% 13.33% 20.00%

20 8.89% 17.77% 26.66%

25 11.11% 22.22% 33.33%

30 13.33% 26.66% 39.99%

35 15.55% 31.10% 46.66%

40 17.77% 35.55% 53.32%

45 20.00% 39.99% 59.99%

50 22.22% 44.43% 66.65%

APs per Channel

Number of SSIDs1 2 3

1 0.19% 0.38% 0.57%

5 0.95% 1.90% 2.86%

10 1.90% 3.81% 5.71%

15 2.86% 5.71% 8.57%

20 3.81% 7.62% 11.43%

25 4.76% 9.52% 14.28%

30 5.71% 11.43% 17.14%

35 6.67% 13.33% 20.00%

40 7.62% 15.23% 22.85%

45 8.57% 17.14% 25.71%

50 9.52% 19.04% 28.56%

APs per Channel


1 0.16% 0.32% 0.48%

5 0.80% 1.59% 2.39%

10 1.59% 3.18% 4.78%

15 2.39% 4.78% 7.16%

20 3.18% 6.37% 9.55%

25 3.98% 7.96% 11.94%

30 4.78% 9.55% 14.33%

35 5.57% 11.14% 16.71%

40 6.37% 12.73% 19.10%

45 7.16% 14.33% 21.49%

50 7.96% 15.92% 23.88%

APs per Channel


1 0.13% 0.26% 0.38%

5 0.64% 1.28% 1.92%

10 1.28% 2.56% 3.84%

15 1.92% 3.84% 5.76%

20 2.56% 5.12% 7.68%

25 3.20% 6.40% 9.59%

30 3.84% 7.68% 11.51%

35 4.48% 8.96% 13.43%

40 5.12% 10.23% 15.35%

45 5.76% 11.51% 17.27%

50 6.40% 12.79% 19.19%

APs per Channel

Number of SSIDs

Revolution Wi-Fi Capacity Planner, http://www.revolutionwifi.net/capacity-planner. Reprinted with permission.

6 Mbps Beacon Rate 18 Mbps Beacon Rate 24 Mbps Beacon Rate 36 Mbps Beacon Rate

http://www.revolutionwifi.net/capacity-planner

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Questions?

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