Thanks for this explanation. Now I understand there is some sophistication to how a MANET is deployed, not just brute force. I'm sure TDM can be used to <div><br></div><div>My goal is to eventually make the existing phone carriers optional (e.g. in areas that don't have coverage thru MANET) because at $80-$100/mo for the basic plan a lot of people would be willing to switch to MANET in no time once the tech matures because MANET can potentially cost users $0. </div>
<div><br></div><div>Making money is not the motivator for a project like this. Saving people from having to pay for using "air" is a great motivator! :)</div><div><br></div><div>Is there an introductory article or book that covers MANET general principles? a la How Stuff Works?</div>
<div><br></div><div>Is there an introductory article or book that covers RF considerations in the context of MANET network design (if a book, then one that dedicates at least one chapter to RF considerations in MANET) and not just RF engineering principles in general? </div>
<div><br></div><div>Any pointers would be greatly appreciated!</div><div><br></div><div>Thanks,</div><div><br></div><div>Marc</div><div><br><div class="gmail_quote">On Sun, Jan 17, 2010 at 9:04 AM, L. Aaron Kaplan <span dir="ltr"><<a href="mailto:aaron@lo-res.org">aaron@lo-res.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div style="word-wrap:break-word"><br><div><div class="im"><div>On Jan 16, 2010, at 10:15 PM, marc fawzi wrote:</div><br>
<blockquote type="cite"><div>Thanks Aaron,</div><div><br></div>Does that mean that OLSR is optimized to work best when having a lot of nodes in the network each with a small radius of 2-way coverage...? and that increasing the radius of 2-way coverage per node (for all nodes) degrades performance?<div>
<div><br></div></div></blockquote></div><div>Roughly you are on the right track, yes. But let's take a look first at layer 1 and 2 (OLSR is on OSI layer 3)...</div><div><br></div><div>If you look at physics then the signal decreases with the square root of the distance.</div>
<div> </div><div> S(x) = 1/(x^2) ... x = distance in meters. (equation 1)</div><div><br></div><div>Now you need to know the noise in your area. Let's call this "N". If you now look at the encoding techniques of Wi-Fi you will see that certain encodings require a minimum "SNR" (or signal to noise ratio). </div>
<div>Or mathematically speaking:</div><div><br></div><div> SNR = S/N (at location x). (see: <a href="http://en.wikipedia.org/wiki/Signal-to-noise_ratio" target="_blank">http://en.wikipedia.org/wiki/Signal-to-noise_ratio</a>) (equation 2)</div>
<div><br></div><div>Based on my own experience, you can still establish a link with SNR > 10 dB. But it will be a bit crappy. You can achieve pretty good links with an SNR > 30 dB. </div><div>So, to increase the SNR you can now either use a "booster" ( stronger signal) or a better antenna (more directional antenna), or you can reduce the noise. But what happens when everybody in your neighborhood (that includes your own nodes) increases S? Right, the stronger S becomes N for somebody else :)</div>
<div><br></div><div>So the very best for building good Wi-Fi links is a) to use directional antennas (don't pick up noise from other directions) b) to send softly (in order to keep the overall noise low).</div><div>But what happens when you send softly? Well, in order to have good SNR (and not disturb others), you can take a look at equation 1 and see that you need to place the next Wi-Fi hop close to you. Then it will have a good SNR from your signal, but still your node won't disturb others so much. </div>
<div><br></div><div>q.e.d </div><div><br></div><div>I hope it helped a bit.</div><div><br></div><div>In general, getting a few folks together and building an initial Wi-Fi mesh network can be a very rewarding experience.</div>
<div>You do something good for the community, you learn each day and who knows - maybe you might be after some time the only (community-) ISP who will offer decent broadband connectivity in some areas :))</div><div><br></div>
<div>You can get a very good intro to RF engineering from this book:</div><div>"The Electronics of Radio", David B. Rutledge, Cambridge University Press 1999.</div><div>I personally love that book.</div><div><br>
</div><font color="#888888"><div>a.</div><div><br></div><div><br></div></font></div><div class="im"><div><br><blockquote type="cite"><div><div><br><br><div class="gmail_quote">On Sat, Jan 16, 2010 at 12:54 PM, L. Aaron Kaplan <span dir="ltr"><<a href="mailto:aaron@lo-res.org" target="_blank">aaron@lo-res.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0.8ex;border-left-width:1px;border-left-color:rgb(204, 204, 204);border-left-style:solid;padding-left:1ex">
<div style="word-wrap:break-word"><br><div><div><div>On Jan 16, 2010, at 9:25 PM, marc fawzi wrote:</div><br><blockquote type="cite"><div><br></div><div>I just found this list of supported OpenWrt hardware:</div>
<div><br></div><div><a href="http://nuwiki.openwrt.org/toh/start" target="_blank">http://nuwiki.openwrt.org/toh/start</a> <div><br></div><div>But what is the problem with wanting to enhance the reception by using an amplifier like this one? <span style="font-family:arial, sans-serif;font-size:13px;border-collapse:collapse"><a href="http://www.danets.com/turbotenna/turbotenna%20009xt.php" style="color:rgb(0, 0, 204)" target="_blank">http://www.danets.com/turbotenna/turbotenna%20009xt.php</a></span></div>
<div><br></div></div></blockquote><div><br></div></div>The problem is that you disturb everyone else. And that is against the idea of a mesh. At the end you start a race who sends "louder" and then at some point all stations "scream" at each other. This results in high noise for everybody but no bandwidth.</div>
<div><br></div><div><div><br><blockquote type="cite"><div><div>I assume the higher the reception s/n the wider the coverage area per node (assuming you pick hardware that has sufficiently high Tx power)</div><div>
<font face="arial, sans-serif"><span style="border-collapse:collapse"><br></span></font></div></div></blockquote></div>Think: many small mesh nodes which whisper. Much more effective re-use of shared spectrum.</div><div>
<br>
</div><div><br><blockquote type="cite"><div><div><div><font face="arial, sans-serif"><span style="border-collapse:collapse">
</span></font></div><div><a href="http://www.danets.com/turbotenna/turbotenna%20009xt.php" style="color:rgb(0, 0, 204)" target="_blank"></a><font face="arial, sans-serif"><span style="border-collapse:collapse">In other words, what is wrong with wanting to boost both transmit and receive signals (above and beyond what the hardware is capable of)?</span></font></div>
<div><font face="arial, sans-serif"><span style="border-collapse:collapse"><br></span></font></div><div><font face="arial, sans-serif"><span style="border-collapse:collapse"><br>
</span></font></div><div><font face="arial, sans-serif"><span style="border-collapse:collapse"><br></span></font></div><div><font face="arial, sans-serif"><span style="border-collapse:collapse"><br>
</span></font><div><br></div><div><br><br><div class="gmail_quote">On Sat, Jan 16, 2010 at 12:08 PM, Henning Rogge <span dir="ltr"><<a href="mailto:hrogge@googlemail.com" target="_blank">hrogge@googlemail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Am Samstag 16 Januar 2010 21:05:54 schrieb Mitar:<br>
<div><div></div><div>> Hi!<br>
><br>
> On Sat, Jan 16, 2010 at 8:54 PM, marc fawzi <<a href="mailto:marc.fawzi@gmail.com" target="_blank">marc.fawzi@gmail.com</a>> wrote:<br>
> > I'm limited to the WRT54-GL because I thought that's the only model that<br>
> > OLSR has been ported to .... ?<br>
><br>
> Where you got this? If it runs (more or less standard) Linux it runs<br>
> OLSR. So for example wherever you can put OpenWrt you can have OLSR.<br>
> (Limited by CPU and memory of course and other similar limitations.)<br>
</div></div>Let's not forget that OLSRd runs on BSD, Win32 and OSx.<br>
<font color="#888888"><br>
Henning Rogge<br>
</font></blockquote></div><br></div></div></div></div>
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