BPI R4 WiFi range

[Betonmischer]

I’ve posted this on the OpenWrt forum, but this might be a better place. I noticed the SNR of 5 GHz clients one room away as seen on the router to be rather poor, which might be the root cause of coverage issues.

My old Archer C7 router shows the same signal strength for the clients, but noise level in the -100 dB range. Noise level on the BPI-R4 is -81 dB at best with Taoglas antennas and RG178 cables. I’d like to hear an expert opinion whether it’s normal to have such a high noise level and if this is something that can be improved by future drivers rather than a hardware flaw.

[kusmi (Michael Kussmaul)]

I see the very same thing with stock antenna (the ones bundled on AliExpress with BananaPi): On the BananaPi I have a reported noise level of around -80 dBm on both bands (5G, 6G), while on my client (MacBook) it is in the -95 dBm range. So it looks like the noise level is quite high on the BananaPi.

[SpectreDev]

Furthest room in my house and it’s the upper floor

[Thanks]

You can try with the official Banana Pi firmware that uses “proprietary” drivers to see if the same problem occurs:

• Banana Pi BPI-R4 | System Image

If the problem is solved when using Banana Pi firmware, it means that the culprit is MediaTek “open source” drivers, but if the problem occurs on both firmware (Banana Pi firmware with “proprietary” drivers and OpenWrt firmware with “open source” drivers), then the problem is in the Wifi 7 module design (BE14).

Remember that the BPI-R4 uses diplexer on the 2.4 GHz and 5 GHz bands (or radios), so both bands (or radios) use the same antennas, you can also try turning off the 2.4 GHz radio and only use the 5 GHz radio to see if this improves the SNR (Signal-to-Noise Ratio), this is the first time that Banana Pi uses diplexer and maybe it is poorly executed.

• Banana Pi BPI-R4-NIC-BE14 | BananaPi Docs
• Banana Pi BPI-R4 Wifi 7 Module design
• [BPI-R4] Which Wifi-Module version do you prefer?
  

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What is the Signal-to-Noise Ratio and Why You Need to Measure it

01. Understanding Signal-to-Noise Ratios

SNR isn’t a ratio, as in “there is 75% signal to 25% noise”, but is measured by taking the signal strength and subtracting the noise, not dividing it. Adding to the potential confusion is that the signal is measured in decibels. For those who work in audio, most people consider decibels a measure of sound as in how loud something is.

It gets worse. In WiFi, decibels are measured in negatives. If you remember old grade school math, negative numbers are the ones below 0. So if you have -15 dBm (deciBels per milliwatt), that is a stronger signal than -50 dBm. I know - it’s confusing, but once you get that the higher the number, the weaker the signal, the better off we’ll be.

Let’s take a look at two different rooms. In one, the average signal strength is -20, the noise is around -60. To get the signal to noise ratio, it’s the signal minus the noise, which means we have an average signal to noise of 40 in this case:

How about room 2, where the signal is also -20, but the noise is -25. Now our signal to noise is much lower — around 5:

Notice how difficult it is to tell the difference between the signal and noise lines on this chart compared to the first one? That’s the rule: the lower the signal to noise ratio, the worse communication will be. We want a nice, big number for our SNR or S/N ratio since that means there’s a lot of distance between our signal and our noise.

02. What is a Good Signal to Noise Ratio?

Remember that Signal to Noise ratio, sometimes referred to as S/N ratio, isn’t a “ratio” but the difference between the signal-to-noise. So the bigger the number, the better.

Most experts recommend that an SNR of 20 dB just for data — this is surfing the web, looking up charts and other related traffic. If you’re looking to stream high-quality videos or make good voice/video chats, then an SNR of 25 is going to be required. Here’s a list of what kind of Signal-to-Noise ratios to follow:

• 5dB to 10 dB: Just give it up now. Stop what you’re doing, and fix the problems. The noise is so high that its indistinguishable from the signal.

• 10 dB to 15 dB: Really slow, but at least there’s a signal. If all you’re doing is getting basic emails, then you can get by. Barely.

• 15 dB to 25 dB: This is average and competent for web browsing and file downloading. Just don’t expect to be watching 1080p videos off Netflix and Youtube at a good rate.

• 25 dB to 40 dB: Fast speed. This is where you can do video conferences, stream high-speed videos, and download large files like gigabyte sized .iso files or movies.

• 40 dB and Up: You are in the Matrix, and have become the One.

Of course, this will be determined by your basic bandwidth strength. If your bandwidth strength is only -5 dB and your noise is 0, then your Signal to Noise is great but your signal strength is still trash. So first make sure the signal is strong, then focus on the signal to noise ratio.

03. How to Measure Signal vs Noise

One of the most useful tools that work as a signal to noise calculator comes from NetSpot.

The process is so easy, it’s just a few steps:

1. Launch Netspot.

2. Select Inspector.

3. Select the WiFi network in question.

4. Find the Signal and Noise levels.

5. Subtract Signal minus Noise to get to the SNR.

Take our sample network. Here we have a signal of -39, and a noise of -80. So running this through our signal to noise calculator and we get (-39) - (-80) = 41. Or to save time, just look at the Level setting. If it’s green, the signal is clean.

04. Fixing SNR Issues

Fixing Signal to Noise issues can take a multitude of approaches. First, get a WiFi signal analyzer. We’ve already mentioned NetSpot, and that’s a great place to start. It shows a list of all of the networks it identifies.

Once you see the list of WiFi signals, you can do a few things to increase the SNR ratio:

1. Remove Extra WiFi networks. This is especially true if this is a business environment. There are few reasons for someone to be running a separate WiFi network, whether it be from their cell phone and tethering or otherwise. With NetSpot, you can get an idea where it’s at as you trace it’s signal strength.

2. Check for “Noisy” devices. Take a look at the devices around the WiFi router. Is it next to a television, refrigerator, or other electronic devices? Try moving it away a bit. There was once a place with awful WiFi coverage until someone discovered that the WiFi router was next to the company’s fire alarm bell. Once it was moved away, the signal noise dropped.

3. Turn off unneeded signals. Some routers support multiple bands in the 2.4 GHz and 5 GHz range. Try turning off the 2.4 GHz signal if it’s not needed — it’s overcrowded compared to its 5 GHz sibling.

[Betonmischer]

Thanks for sharing your noise figures. I wonder if they could be improved by putting an RF shield on the BE board. It already has a line of solder pads around the ICs for that purpose. Plus, it would be nice if someone with the knowledge of RF circuit design took a look at the schematics to check if the noise is related to things like insufficient output filtering on voltage converters, etc.

[Thanks]

Here @simon mentions that the new WiFi 7 module models will use ePA (external power amplifier):

@simon

I will seriously consider whether to make a 10-antenna version, and maybe with ePA

@simon

ePA=External PA.

Many MTK chips have buildin PA/LNA inside, that’s iPA, but the power is not very high,

we can get higher power with an external PA.

[Betonmischer]

Thanks for sharing those tips. The stock firmware doesn’t report SNR and noise for clients, but I observed the same disproportional drop in transfer speed from the client to the router at distance. Turning off the 2.5 GHz radio didn’t help either. Even the proprietary driver likely isn’t perfect at this point to rule out a software issue, but I’m starting to suspect a hardware one.

It’d be nice if someone from the dev team took notice and shared the CAD for the RF shield so we could order one that would be a perfect fit. I’m sure they had it designed even though the shield didn’t make it to production. I’d like to try a makeshift shield made out of a piece of thin metal, but my BPI-R4 is buried inside its stock housing and already set up as a primary home router, which makes experimentation difficult.

[Betonmischer]

@simon Would you spare a minute to chime in to point out the likely source of high noise on the BE14 and whether there’s something we could do to reduce it?

[kusmi (Michael Kussmaul)]

I could help, my BananaPi is still in “experimental” state - I’m more the software guy and don’t have that much experience in RF-tech, so perhaps some stupid questions:

• client/server noise level difference: Do we need to measure the noise level on the bpi r4 itself, as each device has his own noise on the receiver side? Because if I open a tool like NetSpot an my Mac, the noise is fine (in the -95 dBm region), but I assume, this is just the noise as measured on my client. The bpi r4 has its own noise level for its receiving end.
• noise level reported correctly?: Can we be sure the reported noise level on bpi r4 is “correct”? I assume, as you experience drops in bandwidth as you move farther away, this is a sign of problematic signal detection. So transfer from bpi r4 → client are still ok, and you only see drops client → bpi r4? I try to measure the behavior on mine.
• foil around module: Perhaps my most stupid question: should I try to shield the parts of the module DIY as an experiment - was thinking of placing some aluminium foil in a plastic bag (so foil is insulated and will not produce a short). And what parts should be covered - I guess it does not help to wrap the whole module. But it might change RF characteristics: foil+plastic might in fact act like a capacitor?

Edit: As a follow-up: I see the same behavior in drops of bandwidth as I move farther away from the bpi-r4 wifi: While the throughput (measured with iperf3 in reverse more) bpi-r4 → client only drops slightly, I see very large drops from client → bpi-r4. Additionally OpenWRT GUI reports a sharply dropping RX rate as I move farther away, while TX rate has much less drop, stayed almost the same.

[Betonmischer]

Awesome! I’m glad you’re willing to help.

• Yes, you’ll have to look for the signal and noise levels displayed on the BPI-R4 for clients. Noise level is specific to the receiving device, the router in this case.
• I don’t know if it it’s possible for the router to be overestimating the noise, but the outcome is the same and we could still try to offset that by shielding. Low SNR makes the transmitter switch over to lower MCS Index, thus restricting the throughput.
• I suggest to first find the channel that would provide the lowest noise level and better throughput. In my case, switching from channel 36 to 132 on the 5 GHz band alone dropped the noise by ~10 dB and improved speed. Channel 100 was even better, but it’s not allowed in my country and some clients won’t even search for networks on that frequency if they have their geolocation turned on.
• The area is outlined by the unused solder pads for RF shielding, that’s pretty much the whole module. I’d simply form a tight (the tighter, the better) box-like cover over the BE14 board with well-insulated foil. It should then be connected to any ground point in the system to act as a shield, no meaningful capacitance added. The only issue would be cooling the three ICs, but they should be fine for quick noise measurement.
  

Edit. For better insulation I’d cover the foil in two layers of plastic tape rather than using a bag and put some tape on the mainboard around the Wi-Fi module to be extra safe. Foil could also serve to transfer heat from the wireless ICs if small cut-outs are made in the tape to put thermal pads between the ICs and the foil.

[kusmi (Michael Kussmaul)]

I guess I would also need to cover the back of the board (at least on pictures I also see those traces for omitted RF shielding).

[Betonmischer]

Good catch. I’ve rarely seen backside shielding on PCBs, but those pads were put there for a reason.

[Thanks]

Here you can see internal photos of several WiFi routers and ALL have RF shielding:

• ASUS RT-AX89X
• Acer Predator W6
• ASUS TUF-AX6000
• Ubiquiti UniFi 6 Plus
• GL.iNet GL-MT6000 (Flint 2)
• Linksys E8450 (aka. Belkin RT3200)

@sinovoip and @simon, why didn’t you put RF shielding on all the chips? This is the most basic of the basics. I don’t understand how you decided to save a few cents on something that is very important in a WiFi router and @dangowrt, as a developer and beta tester, why didn’t you inform them that this is important?.

[SpectreDev]

Oh man I don’t wanna buy another WiFi card, they’re already expensive as it is

[SpectreDev]

I have an idea for this one, maybe we can find a shield that fits the board and put tape on and put thermal pads between shields and chips and one big thermal pad outside between shield and case

[kusmi (Michael Kussmaul)]

A potential problem is: the shield can‘t be rectangular, as it would then cover the screw holes and you can‘t screw it on the mainboard anymore. Perhaps we could drill a hole into the shield and later cover it with some spare metal…

In the meantime I bought some copper foil from my local hardware store - but they only had 0.5 mm thick ones, that‘s not that easy to bend…

[SpectreDev]

Hmm what thickness would you recommend, also let us know if it makes a difference

[SpectreDev]

From my kitchen and the router is in my living room

[gabriwinter]

Did you make any change to get -89dBm noise level? I’m getting far worse (-75dBm)

[SpectreDev]

I’m not using BPI antenna, I’m using the Taoglas antennas