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Hi Eric,
Definitely a good call out for the reasonings behind the additional settings modifications. I will try my best:
1. Transmit power at 0db – currently the distance between my access point and the 902AC is 60cm and I use a 10db gain external antenna on the the 902AC and while trying all the options I found out that even this 10db gain is almost too much power when the distance is so small. This means that I do not need any additional amplification from the 902AC. While negotiating interference in my place I found out that the antenna power setup on both, the access point and the 902AC, plays a significant role when it comes to retries. If too strong, or too weak, the retries will increase. If anybody is interested how a rough setup guide, continue reading… I found a way to quickly find this relatively „optimal“ strength. Basically, keep increasing the power on the access point (Tx) until you reach a plato value where the receiving unit (902AC) does not register extra signal (Rx) in db no matter how much you increase the transmit power. Set the the transmit power at the lowest setting that gives this max db reading in the 902AC (or even 1dbm less). Repeat the same exercise, but this time increasing the transmit signal (Tx) of the 902AC and monitoring the signal receiving strength (Rx) on the access point. Note that the amplification of both units should be in the similar range or the unit with a much stronger signal will choke the transmission of the other unit, again having a significant impact on retries. For example, currently antenna power settings I run are 12dbm on the access point and 10dbm on the 902AC (the strength of the external antenna alone). Finally, I found out that access point to client distance should not be too short. I had significantly lower retries at 1,5m distance than at 50cm. Yesterday I increased to 60cm and this helped much more then I hoped for, but due to my living room limitations this is the max distance I can have right now. Definitely, keep the distance 60cm or more. One final note, once the signal is stronger than -30db to -28db, it is too powerful and retries start increasing again.
2. NTP settings – this is something I had an experience many years ago in a completely non audio networking situation where I had encountered background processes when NTP settings were not synchronised. I can’t say I experienced or noticed any issues in the current setup, but since the 902AC with openwrt is still a router communicating between two IP subnets, I like it to have the least variables to try and sort out. Still not sure how to best implement this. Maybe the most efficient is to have it set to use the DHCP communicated values. This way it is automatic and will have the same setting as the main router and that is ideal.
3. Long vs short preamble – it is an error redundancy check and only recommended to use the long preamble in higher interference, low signal environments as it is more robust, but it is slower and makes the client work more as it relies on a larger and a slower header overhead. Ideally, both the access point and the client should have the same preamble enabled. In other words, if there is no interreference it is better to keep the short preamble.
4. Rx LDPC – it is a decoding „algorithm“ which is used to maximise the wifi network at full bandwidth usage by detecting and correcting errors in data transmission. In layman’s terms, it is created so that it reduces retries by fixing the received data and sending it downstream. It sounds good, but it involves many iterations to „fix“ the data and in turn requires significantly higher compute power to perform. If this option is disabled then is is a simple yes/no situation where good data gets send downstream and the corrupted data is requested again. Other than the processing power it also impacts latency due to time it takes to fix these errors. Bottom line, it is meant to enable high quality throughput in full bandwidth usage wifi scenarios. Streaming uncompressed audio is only using 1% bandwidth for 16/44 files and approximately 10% for 24/192 files on a 5ghz channel with 20mhz width. This is not even close to full bandwidth scenarios. I suggest to try disabling this one, it was some time ago I did it, but the impact was noticeable.
Through a bunch of tests I realised that the speed of wifi has nothing to do with audio streaming quality. The stability of the signal has everything to do with quality of audio streaming as impacts retries which impact the workload on the client (or even stream drops). Most of these tweaks are all geared towards this wifi stability and/or reduction of any kinds of processes in the 902 AC.
Hope I didn’t over complicate it:)
Cheers,
B.
PS. This is potentially a Pandora’s box, but if you are running two 902ACs, one as AP and one as client, I would love to se what happens if WDS or 802.11s protocols are used. Basically, they are supposed to create a completely transparent connection making the client act like a wireless switch where all the IPs are in the same IP subnet. I tried enabling it between the Aruba and the 902AC, but no luck (Even changed my main router’s (Fritzbox) IP to the openwrt range)
<p style=“text-align: left;“>Hi Stefan,</p>
In my case, openwrt has much more flexibility to fine tune the WiFi connection to the router or access point. Compared to openwrt the stock to link OS is very limited, especially in channels and power settings. In my, high WiFi interference environment I could never get a good enough signal to stream without drops. With openwrt I can get an almost perfect, interference free signal. Which I found has a very obvious impact on sound as it reduces all the work done by the 902ac to sort out all the retries. I did some tests yesterday and even a small amount of extra retries takes the 902ac load from under 10% up to 50% (this is seen within the overview section of the openwrt web interface).These are my reasons for the openwrt direction. Others might have different reasons.
Cheers,
B.
Hi Eric,
I did it again and it worked with the modified IP address to avoid IP conflict. Though, this time I used Putty to SSH into the 902AC and it worked like a charm. Thank you ! The idea of a headless setup is really making a lot of sense! Now I have to figure out how to tweak your script so that I can:
1. Set transmit power to a specific value (0dbm in my case)
2. Set up NTP connection
3. disable short preamble
4. disable Rx LDPC
The chase for the ultimate setup never ends:)
Cheers,
B.
Hi Eric,
Thank you for the detailed instructions, unfortunately I can’t get your image and script to work (yet). I only changed the LAN interface IP and inserted my wireless credential info. I’m stuck somewhere and don’t know where yet:(
Will try later again.
Cheers,
B.
Hi Eric,
Thank you for sharing. I am actually trying to install your image file, but my home router is set to the same ip as the LAN interface in the scrip (198.168.1.1). Am I correct to assume that this LAN interface IP address needs to be on a different IP subset? So if I was to change it to 198.168.2.1 it should work?
Thank you,
Bosko
Hi Eric,
Thank you for uploading the files and very detailed instructions! As I use a few other tweaks to the 902ac, can I ask you to share which final list of packages did you use? Ideally, I would like to try a similar build but with Luci interface so I can still modify some of the settings and be able to see signal strength and the load on the system. For example antenna strength, Rx ldpc, short preamble…
Thank you!
Cheers,
B.
Hi Eric,
For package selection/ removal, I followed the guidelines on this link: https://openwrt.org/docs/guide-user/additional-software/saving_space
Then started building images on this image builder page: https://firmware-selector.openwrt.org/
Then under INSTALLED PACKAGES i made it work with the following selection/ removal of packages:
base-files ca-bundle dnsmasq dropbear firewall4 fstools kmod-gpio-button-hotplug kmod-leds-gpio kmod-mt7603 kmod-nft-offload libc libgcc libustream-mbedtls logd mtd netifd nftables odhcp6c odhcpd-ipv6only opkg ppp ppp-mod-pppoe swconfig uci uclient-fetch urandom-seed urngd wpad-basic-mbedtls kmod-mt7615e kmod-mt7663-firmware-ap kmod-usb2 kmod-usb-ohci kmod-usb-ledtrig-usbport -ppp -ppp-mod-pppoe -ip6tables -odhcp6c -kmod-ipv6 -kmod-ip6tables -odhcpd-ipv6only -odhcpd -iptables uhttpd uhttpd-mod-ubus libiwinfo-lua luci-base luci-app-firewall luci-mod-admin-full luci-theme-bootstrap luci-proto-relay -opkg
The above can be copied directly into the image builder and should work with both, 902AC V3 or 902AC V4 as the first thing one selects is the model of the router/ AP. The rest is the same.
This removes the all IPV6 related packages, DHCP server, opkg, adds basic luci interface and the relayd packages.
<p style=“text-align: left;“>Hi Eric,</p>
This is unbelievable, I was away from the forum for 2 days and it turns out we have been working on the same thing! I just managed to make an optimised openwrt image for the 902as V4. I used the online image builder and it took me 7 or 8 retries until it worked. Best part is that it uses less resources and has the relayd package integrated. It’s been working for 6 hours straight without a glitch! If there is a way to share slightly larger files on the forum I’d be more than happy to upload it. About to go and listen to it!Cheers,
B.
Hi Eric,
I’m jealous that you can get those results with the Fritz alone. And fully agree, I also do not believe the access point improves sound (other then maybe radiation onto the equipment). It only helps setting up a clean channel in a space with lots of interference. Actually, now that I know a bit better how it works, I think two 902ac units (one as access point and one as a client) with openwrt and external antennas set on a narrow 5ghz channel could most probably be a great lower cost solution to areas with lots of interference.
Cheers,
Bosko
Hi everyone,
Here are the printscreens of my Aruba setup. It could be a good starting point.
Cheers,
Bosko
Hi Eric,
Your post for the external antenna was also the inspiration for my setup. I’m using the same setup but with a different antenna.
Kr,
B.
Hi Rghanbari,
Here are some photos of the antenna connector on the 902ac. Looking at the back of the 902ac, the centre of the antenna connector is exactly 15mm from the top and 30mm from the left outer edges. The hole does not have to be more than 4mm in diameter. Just beware that the hirose connector sticks out more than a centimeter.
Hi Rghanbari,
Congratulations on the Aruba! I’m a bit busy today, but will share the exact location of the hirose connector and some printscreens of my Aruba setup over the next few days.
Cheers,
B.
Hi Basillus,
The link works for me. Thank you for sharing. I will probably get one of these later. Please be aware that when using a directional antenna on the 902ac a change of a few degrees can change the signal up to 10 dB, or make the orientation such that the antenna becomes sensitive to room activity. For example, if someone walks through the room, you might get a change in signal reflections and this can impact the retries big time. It is exactly for this reason I’m using my daughter’s old Lego, so I can build the base where I can change the angle of the Aruba as well as of the directional antenna to get the most stable signal between the two. I tried wall mounting, but I always get better results when the Aruba is not parallel to walls. Keep in mind that Aruba has the strongest signal at 30 degrees down from horizontal and my test proved this angle does work the best….in my case it is tilted around 30 degrees down and around 3 to 5 degrees in the horizontal plane. For me, setting up the directional antenna and getting good results was a very long and a frustrating process. I never tried it, but getting an omnidirectional antenna could also work and might be easier to dial in. I did a setup with two directional antennas using their t-adapter. It did make the signal stronger by about 3db but it was also less stable. On the other hand, this same dual antenna setup could work when using 2 omnidirectional antennas. Here is the link to this duomax adapter where you basically connect two identical antennas to a single pigtail cable. https://frixtender.de/shop/frixtender-duomax-sets/
Cheers,
B.
