Wi-Fi & 802.11 · Study deck

Wi-Fi Planning: Scenario Reviews and Failure Checks

Fixed sensors and moving tools stress a Wi-Fi design in different ways.

Radio Remi is your guide for this deck.

wifi-deploymentsite-surveywireless-design
Radio Remi, the module guide, in a scene from this chapter.
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After studying this chapter

Learning objectives

You will be able to:

  • Review Wi-Fi plans for fixed and mobile device cases.
  • Order failure checks by service impact and evidence.
  • Explain: Planning a Wi-Fi deployment means balancing two goals that pull apart.
  • Explain: The mathematical gist: With 20 dBm transmit power, 3 dBi gain gives 23 dBm EIRP and an idealised 315 m free-space distance to the chapter's −67 dBm target.
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Major section

Coverage and Capacity Are Different Goals

Planning a Wi-Fi deployment means balancing two goals that pull apart.

  • Coverage asks “is there enough signal everywhere devices live?” — a common target is RSSI around −67 dBm for reliable real-time traffic.
  • All can display “connected” while consuming airtime or missing deadlines in different ways.

Why it matters

Smaller cells, cleaner channel reuse, and scheduled telemetry usually beat stronger transmit power because they reduce contention instead of hiding it behind a larger signal footprint.

Deployment planning treats the access point as a shared airtime scheduler, not only a coverage source. Each client class brings a different rate, wake pattern, movement pattern, and tolerance for delay.
Deployment planning treats the access point as a shared airtime scheduler, not only a coverage source. Each client class brings a different rate, wake pattern, movement pattern, and tolerance for delay.
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Major section

Phoebe's Field Notes: Why Gain Cannot Buy Coverage, Only Trade It

The mathematical gist: With 20 dBm transmit power, 3 dBi gain gives 23 dBm EIRP and an idealised 315 m free-space distance to the chapter's −67 dBm target.

  • Raising gain to 8 dBi gives 28 dBm EIRP and 559 m, a 1.78× range ratio.

The same beamwidth approximation narrows a symmetric beam from about 144° to 81°: gain redirects power and trades angular coverage for range.

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Major section

Spatial Streams, MU-MIMO, and Beamforming

A practical evidence sheet should separate client capability from cell behavior.

  • The IoT reality check: most sensors are single-stream devices.
  • Beamforming still helps their link quality, but capacity planning must assume many slow single-stream clients, not a few fast laptops.
  • When those two records disagree, the lower one controls the deployment approval.

Why it matters

Vendor feature checklists are not enough because an IoT fleet often contains old radios, single-stream modules, sleepy firmware, and support phones on the same SSID.

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Major section

Spatial Streams, MU-MIMO, and Beamforming (continued)

Worked example: An AP advertising 4 spatial streams shares a channel with 30 single-stream sensors and 3 laptops.

  • MU-MIMO and multiple streams accelerate the laptops, but the sensors still transmit one slow stream each; if they all report on a schedule, their combined airtime, not the laptops', sets the ceiling.
  • The fix is OFDMA (pack the small sensor frames), band-steering laptops to 5/6 GHz, and staggering sensor reports — classic capacity engineering.
  • If the plan claims MU-MIMO capacity, confirm that the AP profile, client capabilities, and observed traffic actually use simultaneous downlink groups.
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Major section

Fast Roaming with 802.11k/v/r

Neither time is guaranteed: the control loop still needs a measured interruption budget, and clients may scan selectively or cache keys even without all three amendments.

  • Roaming quality, not raw coverage, is what makes mobile Wi-Fi IoT usable.
  • The hard part is compatibility.
  • Some clients ignore 802.11v steering requests, some embedded stacks support 802.11k neighbour reports but not 802.11r, and some security profiles make fast transition unavailable.

Why it matters

The best deployment evidence combines RF survey points with live movement traces, because the route tells you whether the design works while the device is doing its real job.

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Major section

Fast Roaming with 802.11k/v/r (continued)

The deployment plan should therefore name the exact client firmware, identity method, AP profile, and roam policy being approved.

  • A route test should record the starting BSSID, target BSSID, RSSI before roam, retry burst, service interruption, and recovery time so the approval is based on measured handoff behavior.
  • If the network waits too long to steer a client, the client may cling to a weak AP and consume excessive airtime with low-rate retries.
  • If the network steers too aggressively, the client can bounce between APs and create avoidable authentication and application pauses.
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Deck summary

Key takeaways

Planning a Wi-Fi deployment means balancing two goals that pull apart.

  • The mathematical gist: With 20 dBm transmit power, 3 dBi gain gives 23 dBm EIRP and an idealised 315 m free-space distance to the chapter's −67 dBm target.
  • A practical evidence sheet should separate client capability from cell behavior.
  • Worked example: An AP advertising 4 spatial streams shares a channel with 30 single-stream sensors and 3 laptops.
  • Neither time is guaranteed: the control loop still needs a measured interruption budget, and clients may scan selectively or cache keys even without all three amendments.
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Retrieval practice

Recall check 1 of 5

Radio Remi says: answer from memory, then check your reasoning.

Q1A team says a Wi-Fi sensor deployment is ready because every sensor joined the network on a bench beside one access point. How should reviewers decide whether the bench-tested Wi-Fi deployment is ready?

AApprove the deployment because joining once proves the radio works.
BAsk for an LPWAN replacement proposal first.
CAsk for installed-site evidence at final locations.
DApprove it from AP client capacity without installed-site tests.
Show answer

Answer: C Deployment approval needs installed evidence, not only a successful lab join.

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Retrieval practice

Recall check 2 of 5

Radio Remi says: answer from memory, then check your reasoning.

Q2A factory's Wi-Fi tools and sensors work overnight but lose service during shift changes. What should the deployment review investigate first?

ATrace ISP saturation during shift changes before measuring local AP behavior.
BTrace sensor firmware reconnect timing under busy-period load before checking AP capacity.
CRepeat the overnight channel survey and select the quietest channel before tracing shift-change client behavior.
DAssociation load, airtime, retries, AP resource limits, roaming or reconnect behavior.
Show answer

Answer: D Deployment plans should test the periods and routes where the service actually has to work.

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Retrieval practice

Recall check 3 of 5

Radio Remi says: answer from memory, then check your reasoning.

Q3Why is a single high-power AP often a poor choice for a dense IoT deployment?

AIt assigns 2.4 GHz to clients based on AP transmit power.
BIt always reduces received signal at the edge compared with several low-power APs.
CIt covers broadly yet crowds hundreds of clients into one airtime pool.
DIt violates a per-floor AP rule whenever more than one sensor type is installed.
Show answer

Answer: C Coverage is not capacity; dense deployments need smaller cells and channel reuse, not one loud AP.

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Retrieval practice

Recall check 4 of 5

Radio Remi says: answer from memory, then check your reasoning.

Q4How does downlink MU-MIMO increase a cell's capacity?

AIt queues clients in shorter turns by raising transmit power for the weakest client first.
BIt sends separate spatial streams to several clients on one channel.
CIt combines all clients into one shared stream so each frame has lower overhead.
DIt upgrades single-antenna sensors so they can receive several streams at once.
Show answer

Answer: B MU-MIMO multiplies capacity by transmitting to several clients simultaneously via spatial separation.

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Retrieval practice

Recall check 5 of 5

Radio Remi says: answer from memory, then check your reasoning.

Q5What does 802.11r (Fast BSS Transition) contribute to roaming?

AIt gives clients neighbour reports so they can skip scanning every channel.
BIt asks clients to move to a less busy AP before the link becomes weak.
CIt boosts transmit power briefly while a client moves between APs.
DIt caches transition keys for faster re-association.
Show answer

Answer: D 11r uses pre-derived transition keys to reduce authentication and key-transition delay at handoff; the installed route still needs a measured service-interruption test.

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Print reference

Answers 1 of 2

Answer key.

  1. C · Deployment approval needs installed evidence, not only a successful lab join.
  2. D · Deployment plans should test the periods and routes where the service actually has to work.
  3. C · Coverage is not capacity; dense deployments need smaller cells and channel reuse, not one loud AP.
  4. B · MU-MIMO multiplies capacity by transmitting to several clients simultaneously via spatial separation.
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Print reference

Answers 2 of 2

Answer key.

  1. D · 11r uses pre-derived transition keys to reduce authentication and key-transition delay at handoff; the installed route still needs a measured service-interruption test.
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