Yes, but any direction helps some. Depends on the nature of the reflection.
From: Cameron Crum Sent: Wednesday, August 26, 2015 10:18 AM To: [email protected] Subject: Re: [AFMUG] Spacial Diversity - helps how much? 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 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 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]> 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.)
