3 ms·

Does Wi-Fi use the same frequency for a transmitter and receiver? In general, this statement is not true: "Relatedly, even if there is no explicit beamforming

Does Wi-Fi use the same frequency for a transmitter and receiver? In general, this statement is not true: "Relatedly, even if there is no explicit beamforming feedback, in theory you can calculate the phase differences by listening to the signals from the remote end on each of your router's antennas. Because the signals should be following exactly the same path in both directions, you can guess what phase difference your signal arrived with by seeing which difference his signal came back with, and compensate accordingly." But maybe the frequencies are close enough such that the channel matches.

ralph84 7y ago
> Does Wi-Fi use the same frequency for a transmitter and receiver? Yes
grahamburger 7y ago
Yes, WiFi uses the same channel for xmit/recv and is half-duplex at the MAC layer.
hinkley 7y ago
I think it helps to think about the problem from a multiparty standpoint. On wired ethernet the simplest case is one wire going between two machines. In coax everyone shares one channel and so RX and TX have to interlace instead of overlap. You go to twisted pair and it’s unambiguous that full duplex is available and desirable. But, now you cant just wire three machines together, because everyone’s TX has to connect to your RX and vice versa and how would that work? How about with fifty machines. You’d need some sort of star arrangement, or a little box in the middle to juggle every outbound to every inbound. With wireless there is no box in the middle (except, very loosely, in two-tier mesh networks where infrastructure nodes talk on two channels and leaf nodes on one), so it’s really like wireless coax with the occasional router. If you want more bandwidth you could run several channels everywhere, or segment fewer machines into separate channels and connect them with more routers.
- madengr 7y ago
  You actually can overlap RX and TX bandwidth on coax, though you need magic-tees and very good impedance matching in either end, and of course constant impedance cable. That limits it to about 100 Mbps, but you can buy the (magnetic) magic tees to do it. These are specifically for replacing analog video cameras with IP over the existing coax.

ralph84 7y ago

> Does Wi-Fi use the same frequency for a transmitter and receiver? Yes

grahamburger 7y ago

Yes, WiFi uses the same channel for xmit/recv and is half-duplex at the MAC layer.

hinkley 7y ago

I think it helps to think about the problem from a multiparty standpoint. On wired ethernet the simplest case is one wire going between two machines. In coax everyone shares one channel and so RX and TX have to interlace instead of overlap. You go to twisted pair and it’s unambiguous that full duplex is available and desirable. But, now you cant just wire three machines together, because everyone’s TX has to connect to your RX and vice versa and how would that work? How about with fifty machines. You’d need some sort of star arrangement, or a little box in the middle to juggle every outbound to every inbound. With wireless there is no box in the middle (except, very loosely, in two-tier mesh networks where infrastructure nodes talk on two channels and leaf nodes on one), so it’s really like wireless coax with the occasional router. If you want more bandwidth you could run several channels everywhere, or segment fewer machines into separate channels and connect them with more routers.

madengr 7y ago
You actually can overlap RX and TX bandwidth on coax, though you need magic-tees and very good impedance matching in either end, and of course constant impedance cable. That limits it to about 100 Mbps, but you can buy the (magnetic) magic tees to do it. These are specifically for replacing analog video cameras with IP over the existing coax.