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Kirim PertanyaanHow many channels does 5 GHz actually give you to plan with?
Count channels before you count access points. In the US, 5 GHz splits into UNII-1 (36–48), UNII-2 and UNII-2e (52–144, shared with radar) and UNII-3 (149–165). Without DFS that leaves nine 20MHz channels to reuse — four at 40MHz, two at 80MHz and a single one at 160MHz.
Doubling the width is a trade, not an upgrade. Each step from 20 to 40 to 80MHz doubles the airtime one transmission occupies and halves the number of cells that can transmit at the same time; it also adds roughly 3dB of noise, so a wider channel buys raw rate at the same signal-to-noise ratio, never a better one.
- 20MHz: four non-overlapping channels in UNII-3, and that number decides reuse on the whole floor
- 40MHz: only two, so neighbouring APs on the same channel are hard to avoid
- 80MHz: only one, which is a single-cell radio and only works where nobody else hears it
Why does the AP datasheet have to come first?
Read the frequency line of the exact model before drawing any plan. Most ceiling units in our catalog are listed as 2.4/5.8GHz, eight list the full 5.180–5.825GHz range and a few add 6GHz. If your bill of materials only covers 5.8GHz, planning around DFS channels is wasted work.
That 5.8GHz line matters more than it looks: UNII-3 sits above 5.725GHz, no radar shares it, and it offers four clean 20MHz channels (149, 153, 157, 161) plus 165, which stays at 20MHz because there is no spectrum above it to bond. Four channels is the entire reuse budget on that band, and every width increase divides it.
Ask which channel widths the firmware actually exposes before you order. That is a datasheet question, not a marketing one: the spec sheet of the exact model is the only answer that survives an audit, and anything the sheet does not state is not something we will invent for it.
Which channel width fits which space?
Choose the width from the room, not from the headline number on the box. A high-density hall wants narrow channels and many cells; a six-user hotel floor can take width. Set one width per band for the whole floor and keep it there — mixed widths degrade everyone.
| Space | Width | Reusable on 5.8GHz | What you give up |
|---|---|---|---|
| High-density office, classroom, auditorium | 20MHz | 4, plus 165 at 20MHz only | Per-client peak rate, bought back with more cells |
| Hotel floors, standard office, retail | 40MHz | 2 | Half the reuse, so cells must be spaced further apart |
| Single-AP rooms, small plant offices, point-to-point backhaul | 80MHz | 1 | No reuse at all; acceptable only where nothing else hears it |
| 2.4GHz, any space | 20MHz | 3 (1, 6 and 11) | Bonding 40MHz in 2.4GHz is never worth it |
How do you lay four channels across one floor?
Lay the channels on a grid and keep the same channel at least three cells apart, so two different channels sit between any two APs that share one. Adjacent APs never share a channel; that single rule removes most co-channel damage before anyone picks up a survey tool.
Spacing comes from the cell radius you intend to hold, not from the ceiling grid. For a 20MHz 5GHz radio mounted at three metres, design a cell of roughly 10 to 15 metres for voice-grade signal at the edge, then place APs at about 1.2 to 1.5 times that radius so cells overlap enough for roaming but not enough to hear each other strongly.
Write the plan as a table before the install crew arrives: AP ID, floor, channel, width and transmit power. If two neighbouring rows share a channel, move one now — it is free at this stage and expensive on a ladder. A staggered example: row one on 149/153/157/161, row two offset to 153/157/161/149 so vertical neighbours differ as well.
Where does 2.4GHz fit in the same plan?
Treat 2.4GHz as a service band, not a capacity band. Use 20MHz and only channels 1, 6 and 11; every other setting drags in adjacent-channel interference from networks you do not control, and 40MHz bonding at 2.4GHz costs three channels to gain something nobody can measure.
Put scanners, sensors, cameras and legacy handhelds there and keep phones and laptops on 5GHz. As 5GHz cells get denser, disable the 2.4GHz radio on a share of the APs — the same three channels are being asked to cover a floor that now carries eight radios.
What breaks the plan after handover?
Most channel plans die quietly: the controller re-optimises overnight, a neighbour turns on a wide AP, someone adds a point in a meeting room, or a DFS radio meets radar and hops. None of that shows up as an outage — only as retries and slow afternoons.
Keep the plan as a document, freeze channels on critical floors, and read channel utilisation and retry counters in the hour the complaints happen. If signal is strong while utilisation is high, the fix is a narrower channel or a moved point — not a wider one.
How does the plan decide which AP to buy?
The plan tells you how many radios you need and where they go; the model follows from power and uplink, not from the rate number on the box. A four-channel 20MHz grid usually needs more units than people expect, and needs less headroom from each one.
Check three lines on the datasheet against your grid: PoE draw (our ceiling units range from under 8W to under 24W by tier), uplink speed, and antenna gain, because a 3dBi internal antenna does not cover like a 5dBi one at the same transmit power. Then confirm the access switch can power the whole row at once.
If the site has never been surveyed, start there: a plan drawn on a floor plan is a hypothesis until somebody walks the aisles with a meter.
Pertanyaan yang Sering Diajukan
Is 80MHz always faster than 40MHz?
For one client on a clean channel, yes, the peak rate is higher. On a floor with several APs, 80MHz collapses the pool to one channel, neighbouring cells fall into co-channel contention, and real throughput often ends up below a four-channel 20MHz grid. Judge by how many APs can hear each other, not by the peak figure.
Should we enable DFS channels?
Only when every AP supports the DFS range, the local regulator allows it, and you can live with the channel hop that radar detection forces. In the US it lifts the 20MHz reuse pool from 9 channels to 25, the largest single gain available to a dense floor — but if the bill of materials only covers 5.8GHz, that spectrum does not exist for you.
Can some APs run 20MHz while others run 40MHz on the same floor?
Not advisable. A wide channel occupies the spectrum a narrow neighbour is using, which triggers protection overhead and degrades both sides. Use one width per band per floor; if you must split, do it building-wide or zone-wide, never AP by AP.
With 5.8GHz-only APs, how many units does a 1,000 m2 floor need?
Work it out on the four-channel grid rather than picking a number: fix the cell radius first (about 10 to 15 metres at three-metre mounting for voice-grade edge signal), space points at 1.2 to 1.5 times that radius, then stagger 149/153/157/161 across them. A 1,000 m2 open office usually lands between four and eight units; partitions, rack heights and client density decide the rest, and the survey settles it.
Can we plan straight from a floor plan without a survey?
Use the floor plan for a quote and a point schedule, but not as an acceptance basis. Load-bearing walls, racking, glass partitions and metal ceilings change the real coverage shape, most of all in warehouses and plants. Draft first, correct with a survey, then lock channels and power.
