3 ms·

Especially for cost--my group recently picked up a pair of 900 MHz Ethernet radio modems which acts basically like a 40km long line-of-sight Ethernet cable. Sup

by qchris 6y ago

Especially for cost--my group recently picked up a pair of 900 MHz Ethernet radio modems which acts basically like a 40km long line-of-sight Ethernet cable. Super useful for field research, but at US$900 per pair, they're above the "let's see what happens" budget for true experimentation. A $90 pair, on the other hand, even with a slightly lower range, would put them comfortably at about the price of a Raspberry Pi or other SBC, opening up a lot more possibilities.

morpheuskafka 6y ago
I looked at the same thing for a project a couple years ago. We wound up writing a simple script using the TUN interface to send the IP packets over Digi's XBee radios (there's a 900MHz edition). Of course, sending all the packets through a userspace Python script was by no means efficient and the radios had only a 100K RF data rate to begin with, so the data rate was like 800bytes/second or something like that IIRC. Probably would be enough to cause some applications to timeout or give up on the network, but it was good enough for SSH and simple REST APIs. There's no way 802.11ah will deliver 15Mbps, but if the standard is designed with that kind of data rate its gonna be a lot faster than what we were using (main reason is Wi-Fi is direct sequence spread spectrum while the XBees are frequency hopping, allowing a larger RF bandwidth). The one thing that is good about the XBees is they will support repeating messages for each other and they have a nice mesh functionality as opposed to Wi-Fi's client-AP model. Additionally, we were just using the small wire antenna on the XBee, which only outputs a fourth of the legal maximum power to begin with, limiting the range. The chipsets OP linked support the full 1 Watt output power. As an aside, I also saw a serial modem using MURS that you could theoretically run a dialup program over. Also ridiculously expensive.

by qchris 6y ago

morpheuskafka 6y ago

I looked at the same thing for a project a couple years ago. We wound up writing a simple script using the TUN interface to send the IP packets over Digi's XBee radios (there's a 900MHz edition). Of course, sending all the packets through a userspace Python script was by no means efficient and the radios had only a 100K RF data rate to begin with, so the data rate was like 800bytes/second or something like that IIRC. Probably would be enough to cause some applications to timeout or give up on the network, but it was good enough for SSH and simple REST APIs. There's no way 802.11ah will deliver 15Mbps, but if the standard is designed with that kind of data rate its gonna be a lot faster than what we were using (main reason is Wi-Fi is direct sequence spread spectrum while the XBees are frequency hopping, allowing a larger RF bandwidth). The one thing that is good about the XBees is they will support repeating messages for each other and they have a nice mesh functionality as opposed to Wi-Fi's client-AP model. Additionally, we were just using the small wire antenna on the XBee, which only outputs a fourth of the legal maximum power to begin with, limiting the range. The chipsets OP linked support the full 1 Watt output power. As an aside, I also saw a serial modem using MURS that you could theoretically run a dialup program over. Also ridiculously expensive.