Chuck, wasn't that type of space diversity more vertical than horizontal for those long uW shots?
On Wed, Aug 26, 2015 at 11:10 AM, Ken Hohhof <[email protected]> wrote: > 3 dB is half power, so that is correct even assuming they are summed. > > *From:* Adam Moffett <[email protected]> > *Sent:* Wednesday, August 26, 2015 11:04 AM > *To:* [email protected] > *Subject:* Re: [AFMUG] Spacial Diversity - helps how much? > > On the tx power issue, I was also told that I only have to lower tx power > by 3 when using the 4x4. Apparently the time offset between the two pairs > of chains means their power is not summed. > > On 8/26/2015 11:51 AM, Ken Hohhof wrote: > > FWIW, Purewave sold us a 6x6 panel made by Mars that was essentially three > 2x2 sectors in one panel. They told us the WiMAX super sauce would work > better with three individual 2x2 antennas spaced a few feet apart. But a > lot of what PW told us was BS (and I don’t mean BaseStation). I never > tried the experiment, so can’t vouch for how much the increased spacing > would help. > > Also note the thing that always seems to get lost in MIMO discussions is > that you’re supposed to lower the xmt power on each chain to keep the total > EIRP within FCC limits, so the performance gain has to be more than the > per-chain xmt power penalty. No getting around the fact that signal, > noise, and channel width are the main factors determining channel > capacity. Anything is possible if you assume infinite signal, negligible > noise, or infinite channel width, but in the real world there are limits. > Channel coding does work, but typically there is a penalty and the coding > gain has to be greater than the penalty. > > A similar question I often ask is how much all those 802.11ac chains help > on the $300 routers where the antennas are spaced inches apart. > > > *From:* Cameron Crum <[email protected]> > *Sent:* Wednesday, August 26, 2015 10:38 AM > *To:* [email protected] > *Subject:* Re: [AFMUG] Spacial Diversity - helps how much? > > Spatial diversity is primarily used to combat multi-path. If you have > clear los, your chances of bad multi-path are fairly small and you probably > won't see a lot of benefit. If you have a lot of objects between you and > the tower that can cause reflections, then it will help more. Simple enough? > > On Wed, Aug 26, 2015 at 10:19 AM, Adam Moffett < <[email protected]> > [email protected]> wrote: > >> There are a couple of products out there selling 4x4 MIMO (Telrad is one, >> but there are others). >> >> In Telrad's case, two of the chains have a time offset from the other >> two, so you get two chains on each of two polarities. Their default >> antenna is a single sector antenna with 4 N-connectors on it, so there's no >> significant spacial diversity. In the past it's been suggested that we use >> two dual pol sector antennas and space them 3 feet apart to get spacial >> diversity. >> >> When I asked why they do the single antenna, a source at Telrad told me >> that spacial diversity "only helps a little". The party selling us the two >> panels considers it to add 6db when they run coverage projections. I >> suspect any gain from spacial diversity is going to depend on a lot of >> circumstances and I doubt it could be as simple as adding 6db. >> >> I'm wondering if anyone here has any opinions on the topic? Maybe even >> facts :) >> >> (I'm sort of eyeballing a certain guy in Utah who designs antennas and >> isn't trying to sell me anything.) >> > > > >
