Converter for WiFi over alternative frequencies - Page 1
Forum section: electronics / projects

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 27, 2012, 04:57:34 am
content: In some places, the 2.4GHz band is too crowded for good performance, or for some other reason, it is necessary to run a network over something other than the 2.4GHz or 5GHz bands used by common WiFi hardware. And it does not have to be wireless. For example, 802.11n uses a pair of 20MHz wide channels (total of 40MHz bandwidth), so in principle, it could be possible to shift it down to 20-60MHz and send it over an otherwise unused phone line or even inject it onto the power lines in an existing building. At the remote end, another converter turns it back into 2.4GHz for reception by standard WiFi equipment.At one hotel I stayed at some time ago, they provided WiFi access by connecting a few special routers into the cable TV wiring and installing some active antenna box in every room. The box itself is about the size of sandwich and has a small wall wart power supply. (It also has a pass through for the TV.) I assume they just inject the 2.4GHz onto the coax and then just use amplifiers to get an acceptable signal levels, but they could have downconverted it to a frequency that travels through the coax easier.The main advantage of using WiFi equipment is that it's cheap and all of the communication details like CSMA, error correction, and security are already handled in a standardized manner. (In other words, it does not require a Tiffany Yep level of communication engineering and hundreds of dollars of FPGA boards...) Just buy some cheap routers, replace the antennas with converters, and then just send and receive the packets on whatever alternative medium you want.Maybe all it takes is a RF mixer and local oscillator, and perhaps a few amplifiers and RF switches.

author: T4P
author_rank: Super Contributor
timestamp: September 27, 2012, 05:55:16 am
content: Well, local regulations. 2.4GHz and 5GHz is the only two bandwidths that do not require royalty fees

author: AndyC_772
author_rank: Super Contributor
timestamp: September 27, 2012, 06:03:48 am
content: If you're broadcasting them over the air then sure, the signal has to stay within the licensed bands - but I think the OP is talking about ways to send the data through a cable.The reason it's not done that way is that it's pointless. There are already 1001 ways of sending digital data along a wire, and frequency shifting the wi-fi protocol isn't a good one. Why bother when there are already much better ways, like Ethernet and ADSL?

author: joelby
author_rank: Frequent Contributor
timestamp: September 27, 2012, 06:08:47 am
content: You could build a cross-band repeater - the main trick is that because your WiFi card probably uses a single antenna for transmit and receive, you'll need to detect which mode the radio is in and switch between receive and transmit yourself (unless perhaps you don't care about having an output power amplifier)I also can't really think of a great reason to do this for any sort of cabled medium when (cabled) Ethernet would be a lot easier to work with.

author: BravoV
author_rank: Super Contributor
timestamp: September 27, 2012, 06:25:30 am
content: Whats wrong with powerline ethernet ? 1st, it is dirt cheap, matured, low latency, relatively big bandwidth and has quite respectable distance over the power wire as long in single phase.Definitely beats (wifi + wire mod job) out of the water from price and performance point of view.

author: madires
author_rank: Super Contributor
timestamp: September 27, 2012, 03:02:16 pm
content: Quote from: BravoV on September 27, 2012, 06:25:30 am... and it drives HAMs and SWLs crazy :-(

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 28, 2012, 01:50:45 am
content: Quote from: AndyC_772 on September 27, 2012, 06:03:48 amEthernet expects a nearly perfect medium and will not run well at all over old phone wiring. (And it requires 2 pairs to work at all, frequency shifted WiFi can work on just 1 and would be highly robust to imperfections in the channel.) ADSL is slow compared to WiFi and moreover, I have yet to find a cheap way to emulate the ISP for standalone use. (Too bad, because used ADSL modems are easily found for free or almost free.)Someone has already done a DIY WiFi over coax, but that's without any frequency translation. (It's presumably similar to the hotel system I mentioned earlier.)http://wifiovercoax.mcleodnet.com/

author: amvakar
author_rank: Contributor
timestamp: September 28, 2012, 03:49:40 am
content: Quote from: NiHaoMike on September 28, 2012, 01:50:45 amI've seen Ethernet in use on single-pair phone wiring before. It was restricted to 10Mbps, though, and the hardware to do it isn't going to be common or cheap at this time.As far as phone lines and bringing down the frequency, satellite receivers have been doing such for years to use cheaper coax with the exact setup you described in the first post. Whether or not it will be cheaper than existing power line solutions depends entirely on how good the converters need to be to please the consumer interfaces, and on the wiring you're going to be using. Wifi can be quite picky about medium if you're aiming to get advertised speeds.

author: Monkeh
author_rank: Super Contributor
timestamp: September 28, 2012, 03:58:34 am
content: Quote from: NiHaoMike on September 28, 2012, 01:50:45 amPerhaps. VDSL2, however, can do 200Mbit (REALLY 200Mbit, not 200 marketing megabits like 802.11) over a couple hundred metres (WAY more than 802.11 can manage!) of plain old phone cable.And again: Power line networking. It already exists. You don't need to hack a wireless standard into working over a medium it's not designed for.

author: T4P
author_rank: Super Contributor
timestamp: September 28, 2012, 05:43:24 am
content: Of course, until you get to the fact that running 200MBPS no matter what topology on a copper wire 60 years old is not exactly brilliant.The ping times will be quite bad not to mention that above 1.6km it's no different from ADSL2+ which is dead and done for, a local ISP has used ADSL2+ for all this while and it's the stuff of nightmaresWell of course, everyone's switching to Fiber networking now due to the government funding nationwide fibernet rollout

author: ejeffrey
author_rank: Super Contributor
timestamp: September 28, 2012, 08:03:01 am
content: Quote from: NiHaoMike on September 28, 2012, 01:50:45 amAnd you think you can do better with some crazy idea to pipe 802.11n over phone lines? For short runs you can use HomePNA, for longer runs ADSL. Those technologies are specifically designed to work over phone lines and are going to give better performance than anything resembling wifi over phone lines.

author: ptricks
author_rank: Frequent Contributor
timestamp: September 28, 2012, 12:35:48 pm
content: Here in North Carolina we are doing trials of non licensed usage of the tv channel spectrum for the frequencies that are not in use by local stations. When you think about it there is a whole lot of bandwidth not being used in most places. The frequencies are lower which means that a really low power radio can reach for miles through trees, walls, just like a tv signal . Licensing right now is not required and really the only cost is the radio . Unfortunately there are not a lot of radio manufacturers right now and so the cost is rather high. The downside of using this tech is that since the signals do travel further it is very easy for two people to use the same frequencies and so it requires some careful planning not to interfere with everyone else.I have wanted to build a radio myself but just haven't found the time.Anyone wanting to read what the FCC decided and the rules can get it here:http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-12-36A1.pdf

author: Monkeh
author_rank: Super Contributor
timestamp: September 28, 2012, 12:36:49 pm
content: Quote from: T4P on September 28, 2012, 05:43:24 am200Mbps is a lot better than wifi will get you, and who said anything about 60 year old wire?Quote... no worse than wifi for short distances.QuoteWe are not talking about long distances, and ADSL2+ is not dead.QuoteBlablabla NO RELEVANCE.

author: T4P
author_rank: Super Contributor
timestamp: September 28, 2012, 02:30:21 pm
content: Don't you go and read? VDSL2 will fade out very quickly! Hell when unblocked WiFi is better! And even for short distances the thereotical can drop very heavilyWell i'm about 40m in front of my weak router with a wall in between, what speeds am i getting? 50MBPS. For a 150MBPS connectionWithout interference i'm getting 100mbps on a 300mbps connectionThis one is better and easierhttp://en.wikipedia.org/wiki/Hybrid_fibre-coaxialActually scratch that.FIBER NETWORK!

author: Monkeh
author_rank: Super Contributor
timestamp: September 28, 2012, 02:50:08 pm
content: Quote from: T4P on September 28, 2012, 02:30:21 pmAnd it'll still do 100Mbps up to about 500m with modern cable. With older installations, you'll still get 50Mbps out there easily. And we're talking 200m or less, not kilometres of public phone system.QuoteWhich is 'good' for wifi, but pathetic in real terms. VDSL2 beats that. Copper always will.QuoteRelevance. Look up the term.

author: T4P
author_rank: Super Contributor
timestamp: September 28, 2012, 02:53:55 pm
content: Yes? Fiber-optic communication? Isn't that relevant?

author: Monkeh
author_rank: Super Contributor
timestamp: September 28, 2012, 02:56:26 pm
content: Quote from: T4P on September 28, 2012, 02:53:55 pmNot to this topic, which is about alternatives to 2.4/5GHz wifi without installing new cabling.

author: T4P
author_rank: Super Contributor
timestamp: September 28, 2012, 03:07:08 pm
content: Quote from: Monkeh on September 28, 2012, 02:56:26 pmBut do you want to bother with having to dialup on any DSL?

author: Monkeh
author_rank: Super Contributor
timestamp: September 28, 2012, 03:09:51 pm
content: Quote from: T4P on September 28, 2012, 03:07:08 pmDialup? It's DSL. There's no dialing. You can easily use DSL within an existing building to get high-speed networking (again, real 200Mbps throughput IS possible with VDSL2 at shorter ranges, unlike wifi which literally never meets the published figures in any situation) over existing phone infrastructure.

author: T4P
author_rank: Super Contributor
timestamp: September 28, 2012, 03:16:58 pm
content: DSL, no dialing? Really? My nation's ADSL2+ requires dialing on bootup that is done by the modem

author: Monkeh
author_rank: Super Contributor
timestamp: September 28, 2012, 03:45:48 pm
content: Quote from: T4P on September 28, 2012, 03:16:58 pmYes, really. Please look up how DSL actually works.

author: nctnico
author_rank: Super Contributor
timestamp: September 28, 2012, 03:46:18 pm
content: Quote from: NiHaoMike on September 27, 2012, 04:57:34 amIn a hotel I either choose a cable or use a 3G modem.

author: baljemmett
author_rank: Unknown
timestamp: September 28, 2012, 03:55:00 pm
content: Quote from: T4P on September 28, 2012, 03:16:58 pmYou're confusing the communications system with the data you're pushing over it.

author: grumpydoc
author_rank: Super Contributor
timestamp: September 28, 2012, 06:30:20 pm
content: QuoteI presume that you mean mega-bitsper second, not bytes (i.e 50Mbps).Well, I'm about600m from my VDSL cabinet and can get the same.I'd be quite pleased with 50Mbps at 40m though from 802.11, I've never seen anything like the theoretical max distances that WiFi is supposed to cover.