Alternate to wireless, or is WIFI the right solution?

there are some alternatives, designed to run "ethernet" over phone quality copper - 1 example (that i havent tried, so buyer beware)

speed / distance sounds like VHDL or similar - and it looks like it is designed for industrial use, so you are probably paying for the packaging to some extent.

But then, I'd sort of be

Linksys diversity means that if the signal comes in stronger on antenna A, then it goes out on A. If reception is better on B, then it goes out on B. The golf course study is checking out the idea of pointing each antenna in a different direction. Problem is, if it comes in direction A strong, then B direction is supposed to receive something, it's going out on A. In sum problem is not having one antenna disabled (or possibly just removed ) on a diversity system, it's having two antennas pointed in different directions with different clients competing for direction.

So my conclusion and advice I've seen in other places is: just remove the second antenna and use only one for a hi-gain antenna. If you can turn it off in the firmware, all the better. I have a linksys working that way right now. No problems at all.

I suppose if somebody came along in just the right place (single hi- gain antenna's dead spot) and connected to the router via the (weak but probably more omni/isometric) antenna-less side, it could screw things up, but I'm using mine like you would, as a bridge. It's only connected to one thing.

3) You can run ethernet 400 feet without a problem. Not that far out of bounds as the technical limit is 100 meters. It may or may not do full speed, but you'll be fine if it defaults to 10. I've got one at

4) Powerline is good option too. Well worth considering.

In sum, every solution will work. What's easiest (phone or powerline), cheapest (phone or powerline), most reliable (not wifi). You weigh it out.

Steve

PS. Where you on SAT before?

seaweedsteve hath wroth:

Sigh. Lots wrong.

Not Linksys, but varies with chipset and chipset manufactory. There are many different algorithms (most of them patented). There were some early models that would use diversity receive, but always transmit on the same "main" antenna. It's not a great way to do it, but there's not much benifit to "diversity transmit", especially if the wireless client has diversity receive capeabilities. Most PCMCIA cards have diversity. Most USB dongles don't have the space for two antennas and therefore do not.

Not exactly. Reception isn't a measure of anything useful. Many people assume that the selection is made by signal strength. It's not. It's by error rate. What the diversity switch is looking for are symptoms of frequency selective fading. That's usually in the form of totally trashed packets. The incident and reflected signals arrive 180 degrees out of phase and cancel. If they don't exactly cancel, they trash each other. Either way, the decoded packets show up as garbage. If enough corrupted packets arrive this manner, it's a fair assumption that the RF path is screwed up and that perhaps this would be a great time to try the other antenna.

Here's the part I'm not sure about. The diversity switch apparently does NOT stay on the "aux" antenna for very long. If the "aux" antenna works better than "main", it will continue to use the "aux" antenna until something convinces the diversity switch to go back to the "main" antenna. I haven't had time to figure out what that something is. My guess is that it's just a timeout. After so much time of no data, my guess(tm) is that it reverts back to the "main" antenna.

Yep. It's a common idea. I've even (wrongly) recommended such an arrangement. It doesn't work too well. The diversity switch cannot be used as a store and forward system. It will not switch between the "main" and "aux" antennas fast enough, or often enough (for each packet) to be usable. There's also a real possibility with two radically different antennas, that the diversity switch will settle on the worst antenna and stay there.

Exactly. If the switch could switch antennas for each packet, that will work. But it can't.

Yep, same here. I sometimes suggest terminating the unused antenna, but that's optional, especially if you can turn off the unused antenna in the configuration pages.

Yeah, it's possible, but improbable.

Incidentally, there are proprietary and non-standard systems that do spacial and frequency diversity available. See Mikrotic Nstreme2:

which uses two pairs of radios at each end, with seperate tx and rx antennas.

Ummmm... perhaps "phone line networking"?

That was me again. I haven't done much with extending 100BaseTX mostly because every time I try to go much over about 500ft, it screws up with lots of collisions. However, 10baseT-HDX is no problem up to at least 1000ft. I commonly attach RJ-45 plugs on the ends of a new roll of CAT5e cable for testing. Works fine. My longest installed run is 900ft.

I also use either RG-58a/u or RG-6/u (75 ohm) coax cable and 10base2 networking. I have one 1200ft link running CATV coax this way.

The price of fiber and fiber media converters is down to the point where using fiber optic cables are an option.

Power Line networking:

Phone line networking:

CATV coax sharing:

Ethernet extenders: (there are others)

Yep. Wireless has many advantages, but reliability is not one of them. One leaky microwave oven can take out the whole neighbhorhood.

Mass, not weight. You mass it out.

I came across this about a year ago, on the testing of multiple antenna devices. Part of the conclusion was "A concept as simple as diversity switching, which introduces the behavior of a software algorithm into what would normally be a simple RF problem, can result in unexpected and blatantly erroneous results".

kev hath wroth:

Nice article. The author is chair of the 802.11 group dealing with cellular and wi-fi conglomeration. That may actually happen, but not as long as cellular service providers continue to block the inclusion of wi-fi and other useful non-cellular features in their subsidized phones. In the US, something like 95% of the phones are purchased from the cellular providers. That's not the case in Europe, where I would expect to see more complicated conglomerations.

The author seems primarily concerned about polarization diversity. That's because antenna pattern switching diversity (spatial diversity) is near useless in a handset that's not large enough to provide adequate antenna separation. It's also not all that important with somewhat frequency selective fading immune multi-carrier OFDM systems (CDMA) as it is with TDMA systems (GSM). Polarization diversity antennas also take less spatial diversity.

The article also neglects the wi-fi related questions brought up in this thread, such as how important is receive diversity, and how duz it work? My opinion, based on substantial guesswork and limited access to internals, is that for OFDM, in a moveable environment, it's of marginal. For fixed PtP links, where the fade margin is inadequate, it's vital. For 802.11b modes, that lack multi-carrier modulation advantages for reducing frequency selective fading, diversity is very useful but not vital. My guess(tm) is that you could turn off diversity in most situations and never notice much difference, except perhaps in highly reflective environments.

As for implementation, I'm lost. What I read in the patents and what I see in my tinkering, often do not agree or make sense. I attached some wires to the diversity switch on my WRT54G (Broadcom) and ended up totally confused as to how it works. I had a difficult time intentionally getting the logic to switch from the "main" to the "aux" antenna, and could not reliably induce switching. Little wonder the designers haven't added flashing LED's on each antenna so the users can see the action. There was no action to see as it sat on the "main" antenna for most of my testing. More tinkering is required and I'm out of time (and bench space).

Diverse reading:

I have just been having a look at the HWB1151, that Frank was enquiring about drivers for, Data Sheet and it's yet another one depending on the algorithm written for it, although it only checks the signal during preamble.

"In the receive mode, the radio signal is received by one of the two external antennas. The antenna selected is optionally determined by an Antenna Diversity algorithm in the Baseband Processor which compares the quality of the received signal in each antenna during the Preamble and selects the better signal . This substantially improves the multipath performance of the assembly. Alternately, the antenna selection may be directly controlled by the software"

I get a blank page.

Says article no longer available.

Slowly looking.

kev hath wroth:

It doesn't explain how the built in diversity algorithm works. I suspect that I could dig through the various Harris/Intersil patents and probably find something.

Sigh. I always check the URL's before posting, but I cleverly tried to trim off the session ID and probably broke something. Trying again with the ID left intact:

If that doesn't work, punch the article ID into the search window. That works.

Note that the Communications Design search for "antenna diversity" yields 111 hits including quite a few on algorithms:

I skimmed the first few and found nothing that describes the antenna switching decision making process or algorithm.