wireless bridge, transmit power

[squigish]

I'm trying to share an internet connection between two cabins ("bungalow" and "dive") using a wireless bridge. The current setup is a motorola surfboard cable modem/router/802.11g access point/ethernet switch in the dive, with the internet connection, and a Linksys WAP54G v3 with DD-WRT firmware acting as a repeater bridge in the bungalow. Both devices are in the corners of the two houses that are closest to each other. I am running separate SSIDs on each device, so that I can tell what I'm connected to.

The performance in general is very unsatisfactory. I can sometimes get a connection using the "bungalow" network (from the repeater), but it often seems less reliable than the faint traces of the "dive" network I can get while some parts of the bungalow.

My plan is to add two more wireless devices to the setup, in the hope of increasing performance. I plan on putting a Linksys WRT54G running DD-WRT in the dive, connected to the existing cable modem via ethernet. I will add a Linksys WRT210 to the setup in the bungalow. The setup would then be a "dive" network on channel 6, that serves only the dive, a hidden "bridge" network on channel 1 that connects the WRT54G in the dive to the WAP54G in the bungalow, and a "bungalow" network on channel 11 broadcast by the WRT210. My thinking is that because the only devices on the "bridge" network are access points running DD-WRT, I can crank up the transmit power and actually get results, because the extra power will be on both ends.

How high can I safely set the transmit power on my hardware? DD-WRT lets me set it as high 251 mW, and the default is 70 mW.

Will I be better off using directional antennas (both devices in the bridge network have removeable antennas)? If so, where can I buy them, and how fussy is the process of aiming them? The router in the dive will be up high and out of reach, but the router in the bungalow is on a dresser where it is likely to be bumped occasionally.

I'd like to avoid running an ethernet cable between the two houses if at all possible, even though I know that would be the most stable solution.

I'd love your thoughts and advice on this plan, which I plan on starting to implement next week.

 

[thetoad30]

I wouldn't mess with the transmit power in DD-WRT. I used DD-WRT for over 6 years, and for the past year or two found it to be going downhill, if not complete crap.

You'll be lucky if changing the setting at most does nothing (since it isn't "hooked-up"), or at most doesn't fry your router.

High-gain amplifying antennas are the way to go. Hawking makes nice directional antennas.

One thing you need to be aware of is that just because you can make multiple wireless networks on DD-WRT, doesn't mean they don't use the same radios. If you really wanted to make this work better, you'd get dedicated APs for the wireless bridge, and dedicated APs for serving the wireless. As it is, you're cutting your network speed by four times, and probably more since the link between bridges is more than likely at a low rate.

On top of that, if you use directional antennas without separate radios for each wireless portion, you'll be pretty much dedicating the "interior" wireless onto the directional wireless link since the radios are the same. Even if you only use one "antenna" port, you'll be losing your antenna diversity as well. It would be like using one TV antenna to run two TVs on different channels - if you tune the antenna so that TV 1 gets CBS in clear, TV 2 on NBC might be nothing but snow. Retuning the antenna for TV 2 on NBC would then result in TV 1 losing signal on CBS.

Just something to think about if you're gonna go with directional antennas.


Try doing a Google search for hawking antennas; I believe they had outdoor antennas as well that would probably be good for your install. But I still warn that you should really be using four different router/aps for this.

 

[stevech]

"How high can I safely set the transmit power on my hardware? DD-WRT lets me set it as high 251 mW, and the default is 70 mW. "

That high power setting in DD-WRT is just not true. Though you may request high power in the web GUI, the low level firmware in the WiFi product is programmed to use no more power than it is able to do while also meeting the WiFi alliance's mandatory signal quality standards, i.e., do not transmit a distorted signal that cause bit errors at the receiving end. This is called the waveform Rho and there are tight specs on it if you honor WiFi's rules.

They could just as well have put a 10 Watt choice in the GUI.

Also, the weaker signal FROM the client device TO the router/AP is the range constraint. A megawatt router/AP won't change this fact.

Instead of fighting WiFi range issues...
1. Is there TV coax that goes out there and is connected to the house system? If so, see the MoCA section here.
2. Is the AC wiring out there derived from a breaker box for the house? If so, see the HomePlug section here.
3. A pair of outdoor $60 bridges from Engenius or some such (see Newegg) will do fine, and cost same/less than the above.
5. Run the cat 5 overhead or buried (with proper type of cable).

 

[squigish]

One thing you need to be aware of is that just because you can make multiple wireless networks on DD-WRT, doesn't mean they don't use the same radios. If you really wanted to make this work better, you'd get dedicated APs for the wireless bridge, and dedicated APs for serving the wireless. As it is, you're cutting your network speed by four times, and probably more since the link between bridges is more than likely at a low rate.

That's exactly what I'm planning on doing. I realize that each "box" only has one radio. The plan I described involved using a total of four boxes: the motorola surfboard cable modem/wifi router, the WRT54G, the WAP54G, and the WRT210.

On top of that, if you use directional antennas without separate radios for each wireless portion, you'll be pretty much dedicating the "interior" wireless onto the directional wireless link since the radios are the same. Even if you only use one "antenna" port, you'll be losing your antenna diversity as well.

I don't totally understand you here. The plan is for the surfboard to cover the interior wireless, and the WRT54G to cover the link. If I get something like this indoor antenna or this outdoor one, and hook it up to one of the two antenna ports on the back of the WRT54G, will that be a good solution? I can tell the DD-WRT firmware which antenna port to use for transmitting, and which for receiving, so I'm assuming I'd just set them both to the external antenna, and not use the other port.

Also, the weaker signal FROM the client device TO the router/AP is the range constraint. A megawatt router/AP won't change this fact.

Yes, I understand this. I was only planning on jacking up the power on the "bridge" network, where the only client is another access point. Thus I could jack up the power level on both devices, so that I wouldn't have the TX power constraint. Is there any way to increase transmit power using software?

Instead of fighting WiFi range issues...
1. Is there TV coax that goes out there and is connected to the house system? If so, see the MoCA section here.
2. Is the AC wiring out there derived from a breaker box for the house? If so, see the HomePlug section here.
3. A pair of outdoor $60 bridges from Engenius or some such (see Newegg) will do fine, and cost same/less than the above.
5. Run the cat 5 overhead or buried (with proper type of cable).

1. and 2. There is no wiring of any kind between the two houses, coax, AC, or phone.

3. This would be a pair of devices that are combination directional antennas and access points, to be mounted outdoors? Is that right?

4. What happened to number 4?

5. Overhead wiring hadn't occurred to me. Is there a particular type of cat5/6 wiring that is better suited for overhead stringing? I'm assuming I'd want something designed to hold more tension.

Also, if I just got a directional antenna for the WRT54G in the house with the network connection, and pointed it at the other house, would another access point configured as a repeater in the second house possibly be sufficient?

Thanks a bunch to both of you (and anyone else) for your help!

 

[thetoad30]

My apologies. I don't think I saw that you were using four different devices - I had figured on only two.

As for the antenna diversity - yes, you will lose antenna diversity on the bridge routers if you only hook up one antenna. As long as you make sure there is a directional antenna and a regular antenna, you should be okay though. Whatever you do, do not leave an antenna port open. It will eventually fry the radio (SWR will shoot up, and the radio will over-exert itself).

If you're able to, the outdoor antenna will be much better. The window will reduce/reflect/refract the signal beam, resulting in worse signal.

Other than that, as long as you have four separate radios as you stated you did, you should be okay.

An overhead/underground cat5 is still the best bet for solid signal, and as long as you use outdoor rated (usually shielded as well) cat5 or 5e, you should have no problem. I think the outdoor stuff is usually UV hardened and as I stated shielded to prevent external interference.

 

[squigish]

As for the antenna diversity - yes, you will lose antenna diversity on the bridge routers if you only hook up one antenna. As long as you make sure there is a directional antenna and a regular antenna, you should be okay though. Whatever you do, do not leave an antenna port open. It will eventually fry the radio (SWR will shoot up, and the radio will over-exert itself).

So if I attach a directional antenna to the left port, and a regular antenna to the right port, which should I tell the software to use for TX, and which for RX? Should I set both to the left port?

 

[thetoad30]

So if I attach a directional antenna to the left port, and a regular antenna to the right port, which should I tell the software to use for TX, and which for RX? Should I set both to the left port?

It depends. I know, crap answer. But it depends because of the way that "left" and "right" is set.

Some radios/routers, left is left when looking from the back to the front. Some routers, left is left when looking from front to back. Some routers don't care and will lose signal if you set to "left".

I haven't kept up with DD-WRT, so I am not sure what has changed lately with diversity. Your best bet, I think, is to "leave it alone" and connect up the antennas, and then play with it a bit. Usually leaving it alone will make it "auto", and the signal will be strongest on the directional link, so it will use that. Plus, if there is any "overage" on the signal and it decides to pick it up on the internal antenna (the stub), it will still receive/transmit.

Wireless is always tricky when you're adding additional elements that a router was not really designed for.

I'm really thinking that with the cost you're incurring using two directional antennas at around $100 a piece, plus now the aiming/using a third-party firmware to get everything right (which is not bad, just not exactly easy), you might be better off going with the dedicated outdoor AP products from EnGenius as stevech said. Really, you'd be getting much better/newer products with radios that are meant for this and designed as such, plus you'd be getting wireless N which is a much better technology for wireless links in my opinion.

And again the ultimate would be a cat5 connection. But I understand that's sometimes hard to do. That's why I think the EnGenius is a much better option for ease of installation depending on distance and how high/what kind of terrain you have. Sometimes a direct LOS is easier with wireless than it is to string up a wire.

So, really, with your situation, for cheaper, you get better wireless with the EnGenius products. For about the same money or cheaper, depending on distance, the cat5 is the ultimate solution.

EDIT: Here's a 2.4GHz N product: http://www.newegg.com/Product/Product.aspx?Item=N82E16833168093

And here's a 5GHz product that would all but eliminate wireless interference (remember there are only three channels that are not overlapping in the 2.4GHz band - you'd use channel 1 or 6 for the bridge link, and then 1 or 6 for one room depending on the one you picked for the link, and then 11 for the other room). This product would allow you to have both rooms on channel 1 or 6 for best coverage in the rooms, and then use the 5GHz band for the link which will mean that wireless clients will never interfere since 5GHz clients have non-overlapping channels: http://www.newegg.com/Product/Product.aspx?Item=N82E16833168092&Tpk=ENH500

 

[stevech]

So if I attach a directional antenna to the left port, and a regular antenna to the right port, which should I tell the software to use for TX, and which for RX? Should I set both to the left port?

Unlikely the product user interface and low level firmware will allow you to make that choice.

Some WiFi has additional internal antennas. Let's assume yours does not.

So the two antennas are used for "switched diversity". With this, the low level firmware chooses, for each arriving data frame (hundreds per second), which antenna has the best received signal. It uses that for the rest of the frame, and subsequent transmissions, until another frame arrives.

Expensive multi-stream MIMO works differently, and usually with 3+ antennas.

 

[sfx2000]

Instead of fighting WiFi range issues...
1. Is there TV coax that goes out there and is connected to the house system? If so, see the MoCA section here.
2. Is the AC wiring out there derived from a breaker box for the house? If so, see the HomePlug section here.
3. A pair of outdoor $60 bridges from Engenius or some such (see Newegg) will do fine, and cost same/less than the above.
5. Run the cat 5 overhead or buried (with proper type of cable).

Best advice on this entire thread...

DD-WRT allow one to "increase" power, but it doesn't consider that the PA's, when pushed that hard, start to distort... (layman's terms)

It's kind of like of Scotty from StarTrek - the Di-Lithium Crystal's, they just kinna handle it

stevech's recommendations are on the mark, and I firmly agree with him...

 

[stevech]

Best advice on this entire thread...

DD-WRT allow one to "increase" power, but it doesn't consider that the PA's, when pushed that hard, start to distort... (layman's terms)

The power amps (PAs) don't actually get pushed hard and distort. The vendor's firmware IGNORES attempts from the user/GUI to set it higher than viable for some bit rate. And the bit rate varies fast between clients and according to conditions. So DD-WRT et al really deceive users with that GUI. As said above, DD-WRT et al should have put a 10W choice on the UI to stir up discussion.

And BTW, the PAs in WiFi are a huge portion of the hardware cost. Keeping the PAs highly linear for the high OFDM bit rates costs too much if one wants more than 40mW or so AND the product has to be cost competitive.

 

[sfx2000]

Depending on the chipset and driver, you can drive the PA so hard that it goes non-linear, and you'll see Adjacent Channel Power Ratio go out of spec, along with intermod spurs out of band. It can get pretty ugly if I recall...

But you're also right, with many chipsets, once you max the bits, that's the end of it, no matter how hard you twist the knob from there

Been a long time since I've been involved with the RF front end, going on 4 years now... feel free to correct me

 

[StratmanX]

But you're also right, with many chipsets, once you max the bits, that's the end of it, no matter how hard you twist the knob from there

Reminds of the amps that go to 11 in Spinal Tap.

 

[stevech]

Reminds of the amps that go to 11 in Spinal Tap.

That's hilarious!

 

[tipstir]

Depending on the chipset and driver, you can drive the PA so hard that it goes non-linear, and you'll see Adjacent Channel Power Ratio go out of spec, along with intermod spurs out of band. It can get pretty ugly if I recall...

But you're also right, with many chipsets, once you max the bits, that's the end of it, no matter how hard you twist the knob from there

Been a long time since I've been involved with the RF front end, going on 4 years now... feel free to correct me

Your corrected! Just joking.. But your right on this subject. That's why I had quit using DD-WRT would burn out the routers I had used quicker.