We talk like WiFi is single carrier QAM, but in reality it is OFDM (802.11ac) or OFDMA (802.11ax) with 64 or 256 subcarriers per 20 MHz channel. Each subcarrier using QAM modulation. (But unlike ADSL, each subcarrier uses the same modulation level)
So in my mind’s simplified view, with single carrier QAM (like most licensed radios), there would be an automatic equalizer that would do much of the heavy lifting (along with a timing recovery mechanism). With OFDM, the multiple subcarriers do a lot of the work of the equalizer. I was involved in a more technical way with ADSL in my former life, and you could actually do a pretty good single carrier simulation by calculating the multicarrier throughput and assuming a good equalizer would achieve the same thing. But the ADSL twisted pair channel is quite different because it spans such a wide range of frequencies with drastically different attenuation and crosstalk, whereas microwave channels are fairly narrow and uniform. (although the “puncturing” feature of 802.11be seems to address non uniform channels) When we get into mitigating and even making constructive use of multipath propagation, I cannot wrap my head around how that works in a multicarrier system. Does it operate at the subcarrier level, or is there some kind of signal processing equalizer operating over the entire channel? And what does it use as a metric to drive its optimization? Even a younger me would struggle with the concept. Now I struggle with what to make for dinner, or remembering if I shut the garage door. It feels like when I look at the Differential Equations textbook on my bookshelf and realize I haven’t used any of that since the final exam for that class. Given that 802.11be supports up to 320 MHz channels (across non contiguous spectrum in different frequency bands), that would be what, 1920 subcarriers? (including pilot and guard tones). No idea if some of this is done on chip in dedicated hardware, but that’s an incredible amount of signal processing, especially at the symbol rates involved for multigigabit data. Even understanding how signal processing extracts V and H or +45 and -45 polarizations when the antenna is rotated is more than I can grasp. Although I probably have a digital communications textbook that would explain it. An amazing amount of microwave theory has been around since the 1950’s. But the processing power to handle stuff like 1920 or even 256 subcarrier OFDMA has obviously only existed recently. Amazing to be able to buy it for a couple hundred bucks and hold it in your hand. From: AF <[email protected]> On Behalf Of Chuck McCown Sent: Thursday, October 9, 2025 9:10 PM To: 'AnimalFarm Microwave Users Group' <[email protected]> Subject: Re: [AFMUG] 16 spatial streams how is that possible I can only presume that is referring to a particular pattern when phased in a certain way. I know the radars in fighter jets used to move the aim around with beamforming so the antenna didn’t have to move. Now a days I hear they have multiple main lobes that are independently steerable. No idea how the separate the signals coming from and going to the different beams. From: AF [mailto:[email protected]] On Behalf Of Adam Moffett Sent: Thursday, October 9, 2025 6:26 AM To: 'AnimalFarm Microwave Users Group' <[email protected] <mailto:[email protected]> > Subject: Re: [AFMUG] 16 spatial streams how is that possible Since you're the best expert we have: Is "spatial signature—gain phase pattern" a real thing or is there a blowhard editing Wikipedia? _____ From: AF <[email protected] <mailto:[email protected]> > on behalf of Chuck McCown <[email protected] <mailto:[email protected]> > Sent: Wednesday, October 8, 2025 10:06 PM To: 'AnimalFarm Microwave Users Group' <[email protected] <mailto:[email protected]> > Subject: Re: [AFMUG] 16 spatial streams how is that possible I used to do lots of RF, lots of microwave, waveguide stuff, antennas etc. Constantly heard folks refer to it as black magic. To me it was like anything else, once you get it digested it seems pretty simple. Smith charts scare people way I think, I think they are an aesthetically pleasing representation of the complex plane. I digress. Pulling multipath signal artifacts out of the ether and reconstructing them is truly black magic to me. From: AF [mailto:[email protected]] On Behalf Of Bill Prince Sent: Wednesday, October 8, 2025 6:57 PM To: [email protected] <mailto:[email protected]> Subject: Re: [AFMUG] 16 spatial streams how is that possible I have seen signal tests with a local operator deploying Tarana getting some remarkable throughput even in NLOS situations. The main feature is using multipath in time and polarization to enable signal reconstruction. bp <part15sbs{at}gmail{dot}com> On 10/8/2025 4:04 PM, castarritt wrote: The 450M did beam steering with phase delay that allowed it to shape the pattern, but only in a sort of sawtooth like preset pattern that it could scan left and right. Tarana can dynamically beamform to shape the pattern towards and away from specific azimuths as needed, and perhaps most importantly, the Tarana client radios can do the same. On Wed, Oct 8, 2025 at 5:34 PM Ken Hohhof <[email protected] <mailto:[email protected]> > wrote: Over the years I’ve become suspicious of the term beamforming. In the hands of marketing people, having multiple antennas and choosing the one with the strongest signal, becomes “beamforming”. Even a Cambium 450m I don’t think does beamforming (in the sense of feeding multiple array elements with different phase delays to shape the antenna beam), it just has 14 narrow sectors inside. But that allows it to talk to multiple SMs at the same time. I think cellular antennas may use actual beamforming, I don’t know. Tarana talks like they use active beamforming, but it could just be the usual marketing hype, again I don’t know. From: AF <[email protected] <mailto:[email protected]> > On Behalf Of Adam Moffett Sent: Wednesday, October 8, 2025 5:11 PM To: 'AnimalFarm Microwave Users Group' <[email protected] <mailto:[email protected]> > Subject: Re: [AFMUG] 16 spatial streams how is that possible I suppose there's electronic beam forming, but could that really work with an array of 16 little dipoles in a circle? Since all the clients are 2x2, and the DSP magic to differentiate all those other chains has to come with a monetary and electrical cost that most consumers aren't going to pay, I'm guessing that a16x16 router would just be a bicycle with 14 extra wheels. _____ From: Adam Moffett <[email protected] <mailto:[email protected]> > Sent: Wednesday, October 8, 2025 5:51 PM To: 'AnimalFarm Microwave Users Group' <[email protected] <mailto:[email protected]> > Subject: Re: [AFMUG] 16 spatial streams how is that possible What could you theoretically subtract from the raw received signal to leave you with one desired transmission distinct from the others? It's the 21st century, so we don't need to worry about how computationally intensive it would be; we only need to worry about whether you could do it. For instance, if I have 16 different QAM constellations on top of each other, but I knew they each had a certain phase offset, then could I separate them? What about a time offset? And oh boy, what if there's one 802.11n client on the WLAN? He's 2x2 and doesn't have the magic to handle 8 or 16 chains. Whenever the AP sends a frame to that guy does it have to temporarily stop transmitting on all the other chains? I bet it does. -Adam _____ From: AF <[email protected] <mailto:[email protected]> > on behalf of Ken Hohhof <[email protected] <mailto:[email protected]> > Sent: Wednesday, October 8, 2025 3:07 PM To: 'AnimalFarm Microwave Users Group' <[email protected] <mailto:[email protected]> > Subject: [AFMUG] 16 spatial streams how is that possible In the list of supposed advantages of WiFi7 over WiFi6, I see 16 spatial streams vs 8. Can someone explain to me the mechanism for using 16 spatial streams in a typical WiFi environment? I have a hard time wrapping my head around anything more than 2 using V/H or dual slant polarization. I was willing to believe that maybe you could get more (like maybe 4 spatial streams) due to reflections off furniture and stuff, and that somehow signal processing could magically separate out the streams (even though I don’t understand how it does that). But 8 or 16 just sounds like crazy talk. Maybe it’s like the rich people houses with 16 car garages, if I were rich people I would understand? -- AF mailing list [email protected] <mailto:[email protected]> http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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