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Imagine an endless tiling of 10' x 10' x 10' rooms each with 10 WiFi clients. Walls are two sheets of dry wall for a total 4 cm. Floors and ceilings are one sheet of dry wall at 2cm and one layer of wood at 2cm. Is it possible to run a WiFi 6e router at the center of the ceiling of each room without interfering with the WiFi signal of any other room if the WiFi signal is restricted to 6.525 - 7.125 GHz?

I'm basically wondering whether tenants can host their own APs without interfering with their neighbors.

My thoughts, which may be completely incorrect:

According to the FCC, the maximum indoor signal strength is 30dbm [2]. Expect 12 db of attenuation for the walls [1] and 9db attenuation for floor and ceiling [2] (is wood really only 1.5db/cm?). The signal detect for 802.11 is 4db above the noise floor. No adjacent room must be able to detect a signal of this strength. This does not consider attenuation from the 2x4 beams between walls nor any furniture or people within the rooms. This also ignores any noise from signal multipathing (or whatever problems multipathing presents).

Working backwards, the maximum SNR at the source cannot exceed 13db - perhaps 10db for safety. Assume all adjacent routers contribute to the noise floor. Assume that I have a clue what I'm saying. So:

  1. Can you tell a 6e router to transmit at no more than 10db above the noise floor?
  2. Can a 10db signal fulfill the theoretical capabilities of WiFi 6e for a single room with many clients?

Am I wrong?

Sources:

  1. MULTI-FREQUENCIES PENETRATION LOSS AND MODELING AT 6.5 GHZ TO 38 GHZ FOR 5G COMMUNICATIONS SYSTEM EVALUATION

  2. FCC FACT SHEET* Unlicensed Use of the 6 GHz Band

  3. Building Materials and Propagation, Final Report, Ofcom

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  • Several years ago, FCC and other international agencies forced router firmware teams to limit the channels only allowed within their region. The solution to this problem was hardware that was locked down so only allowed channels in a specific could be enabled. The point of this statement is to say, you are going to be hard-pressed to find the hardware you can manipulate the way you describe. At the very least you will be limited by the channels allowed in your region, and any limitations that go with that, and these limitations cannot be bypassed by code.
    – Ramhound
    Commented Oct 17, 2021 at 2:32
  • "Can tenants host their own AP's without interfering with neighbours". No. To the extent this might be possible with appropriate hardware and careful design as soon as tenants get their own AP's - or start fiddling with yours - the robustness of the network goes out the window.
    – davidgo
    Commented Oct 17, 2021 at 6:27

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There are settings in most routers to lower the signal strengths. Lowering is generally a bad idea. 6e may use any combination of 2.4, 5 and 6 Ghz, with upwards of 10 Gb/second data throughput. The technique is CSMA/CA. The Carrier Senses With Multiple Access and Collision Avoid to avoid stepping on the other transmitters. There are also multiple methods used to avoid interference. Frequency hopping, Direct Spread, an advanced transmission technique called Orthogonal Frequency Division Multiplexing, OFDM.

The signal out of a Wifi radio is a maximum of -30 dBm. If noise was zero, or close to it, such as in a shielded room or microwave oven with power off, you would have a very high or theoretically infinite S/N. S/N is a ratio of signal to noise. If noise was at -100 dbm, and the received signal -30dbm, then the S/N would be extremely good, at 70 dbm. A radio that picks up a -90 dbm signal is so close to that -100 dbm noise floor (just 10dbm) that it is unlikely it would pick up any signal at all.

Secondly, many routers will also automatically seek to find a unused channel. There are 11 channels in the USA and 13 in Europe. Full-powered Access Points and client systems in the same area and all on the same frequency will still work securely and at high speed due to the design of WiFi. The design prevents eavesdropping which seems to be your concern here. This is based on the remark "I'm basically wondering whether tenants can host their own APs without interfering with their neighbors." The answer to that is generally Yes, but with some tloss of throughput due to shared channels.

It would be better to have "collisions" at high power instead of operating near the noise floor. A given Wifi channel consists of many spread-out frequencies and each client or Access Point will negotiate a pseudo-random hopping sequence, such as 1,2,3,4,5 and for a second Client or AP, a different sequence such as 5,4,3,2,1. These radio "hops" overlap periodically, but the data is redundant and data will almost always get through in spite of interference.

In addition, Wi-Fi channels always overlap. It can be shown that for the 11-channel 2.4 Ghz standard, there are no more than 3 non-overlapping channels. Yet hundreds of people can use Wifi at the same time in any given area.

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