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back to article Cambridge gets a white (space) wash

A consortium of Cambridge-based companies is to start testing white space radios in the UK, to see if they can coexist with each other, and everyone else. The trials are permitted under a multi-site test licence issued by Ofcom, and will allow the likes of Microsoft, BT, Nokia, Samsung, Spectrum Bridge and BSkyB to set up radio …

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Some evidence?

"But radios designed to find and use empty frequencies simply don't work, so white space proponents have been forced to use online databases of empty channels based on the location of the user"

A little technical reference available perforce? Or are you just going to spout ill considered opinion?

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Anonymous Coward

"spout ill considered opinion"

quote suggests you have techical reference for the contrary position. Care to share?

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Well

I have observed it work (as a commercial experiment) - external technical auditor for potential investor - and I think I understand how it does and also how it could be improved. The blanket "it dont work guv" is not good enuff.

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Anonymous Coward

@"spout ill considered opinion"

downvotes, for a request for info? hmmmm some brainiacs around today...

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Windows

Er, wouldn't it be simple??

When I was working at Nokia, for Type Approval, we took our kit to an Open Field test site.

One gentleman (Mr. Hubbard, from memory) used a Spectrum Analyser. (Rectum Tantalyser as we used to cal it). No, it was post-HP141T days...Oh, I'd give my eye-teeth to use one again, but I digress.

Piece of piss to find empty slots. If you were worried someone might use them occasionally, leave the thing on 'peak hold' measurement for a few days.

Never seen the film "White Noise"?

But this whole article seems in variance to the "Femtocell" article of a day or so ago...

Hey, what do I know? I'm old, and smell of pee/Tennants Extra.

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er ... won't work

Why not? Bluetooth frequency hops, why shouldn't other radio commuications do the same to avoid clashes? This doesn't imply it is simple, but it is certainly possible.

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won't work

The problem is that simply because you can't hear signals on a given frequency doesn't mean that you can use it without problems.

One such situation is the 'hidden transmitter" problem. Consider a transmitter "A" on one side of a hill, being received by someone on top of that hill, or off to one side of the hill. At a site "B" on the opposite side of the hill the frequency will seem to be clear, since the hill blocks the signal from "A", but anyone broadcasting on that frequency from site "B" will interfere with the signal being received from site A, since the receiver can 'see' both transmitters.

It is less of a problem for Bluetooth because it's very short range.

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Not only that ...

>> The problem is that simply because you can't hear signals on a given frequency doesn't mean that you can use it without problems.

Apart from the hidden transmitter problem, you also have the issue of widely differing signal strengths. Consider someone far from the TV transmitter and trying to get a signal on a portable set. The signal is lo win strength, and he is likely to be using an antenna that has poor directionality (or is even omnidirectional). Then you fire up a bit of wireless kit that can't detect the TV signal and starts spewing forth on the same channel - due to differences in distance, it's going to completely swamp the TV signal.

As an analogy, it would be like going to the Opera (or whatever your favoured entertainment is - but not the megawatt blast your eardrums out gigs) and finding yourself at the back where it can be hard to hear the quiet bits. Then someone sat next to you starts SHOUTING DOWN THEIR MOBILE - "YES, I'M AT THE OPERA, CAN'T HEAR A THING THOUGH".

And as for the comparison with WiFi and Bluetooth, words almost fail me ! Both WiFi and Bluetooth are designed on the basis that the space is crowded and all parties can hop around and/or delay their transmissions so that everyone get get a word (or packet) in edgeways. TV isn't. You fire up something else on the same frequency and the TV transmitter doesn't suddenly hop to another channel - no, the receiver just stops getting a usable signal.

And for the first poster asking for evidence that "it doesn't work". IIRC it was reported here by TheReg that trials in the states were quite spectacular in their demonstration of that.

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Joke

flat earth

That's why they're doing the trial in Cambridge - no hills!

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Also what about weather patterns...

I hold an amateur radio licence and am well aware of various implications these transmissions could cause, not just for local people but even for people on the other side of the globe.

Wi-Fi and Bluetooth isn't too bad as the devices that use them barely pump out enough power or have a large enough antenna to make that kind of difference, and also use not very good frequencies, although radio is a very strange medium and even when you think everything is perfect something strange and unexpected can happen.

Radio can easily escape out of it's boundaries depending on atmospheric conditions such as weather and cause problems not just in and around the area the transmission is designed to be in, but also for many miles outside the area, and even on the other side of the world if it happens to bounce on the ionosphere.

Some examples of strange radio anomalies I've encountered which show the problem are -

When I lived in Preston I used to be able to receive Wire FM from Warrington, they're signal was so strong it used to wipe out Tower FM which was nearer to me in Bolton, and Wire FM was only supposed to have an area of Warrington, Widnes and Runcorn. My only thought on that one is that it could have been using one of the Tower FM repeaters to re-broadcast itself.

In Manchester Key 103 and Galaxy 102 (Capital 102) regularly interfere with each other, despite Key 103 being on 103Mhz and Galaxy being 1Mhz lower than Key 103, you actually can't listen to either one in Manchester as you get 5 seconds of one and then 5 seconds of another, and back to 5 seconds of one. This is caused due to the way the bandwidth of FM works, Key 103 probably have a bandwidth of over 500Khz and the same for Capital and so the two are crossing each others bandwidth and causing major interference.

In some parts of North Wales, especially Anglesey, but even on the coast near Rhyl and Towyn you can receive RTE 2FM crystal clear, and in some places on the A55 it even blocks out other local stations.

So you have to be very careful of all these problems radio can cause, even on frequencies where it sounds to your equipment that there is nothing, sometimes there can be something else there that you can't hear that someone else is trying to receive in a different location to you and you could block it out.

In addition to this you also have harmonics to think about, something that might be transmitting on the third harmonic of the frequency you are using could have it's communication interfered with, even though it sounds like the frequency you are using is empty, this includes some things like emergency services. Most people don't seem to realise that if you send something out on say for example 90Mhz you also create major interference on 270Mhz which even though you might think well that's not a problem that is outside my radio's scope as my radio only goes from 88Mhz to 108Mhz, that frequency may be being used by someone else (for example an emergency frequency) and they don't want your broadcast wandering all over it. This used to happen in Warrington a lot when a local bus company used to have their PMR for the buses on a harmonic of 97.4 so anyone listening to Rock FM used to regularly get interrupted by some bus driver reporting back to base, thankfully now they have a digital radio system so it's not as problematic, but to them they were just transmitting on what appeared to be an unused PMR frequency without realising the problems they were causing further on up the dial.

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WTF?

No Hills in Cambridge? lol

Then you don't know Cambridge. Castle Hill, Lime Kiln, the Gogs immediately come to mind.

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but also....

I'm no expert, but another problem is presumably that various systems spread signals such that they appear to be below the noise floor. A slot may appear to be clear, but adding more energy in it may swamp out these signals.

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Hills in Cambridge...

The gogs aren't Cambridge. The others are pretty much irrelevant - I can't imagine Castle "Hill" blocking transmissions between any two interesting points.

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Stop

Propagation

Castle Hill was so good at blocking transmissions from the lower part of the city that the emergency services at Parkside had to locate their antennae on Shire Hall and Madingley Hill rather than on their own buildings.

The point being that Cambridge has its own propagation characteristics, and to get good coverage, hills outside the city have been used for years to overcome the problems.

Just how the triallists are going to communicate from the city with one of their "partners" in Melbourn will be interesting

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Hmmm...Industry led testing

So if I read the article correctly, the people who stand to make money out of this are going to independantly test the premise and report every possible problem which stands between them and making money.....

anyone else see a small credibility gap here?

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"But radios designed to find and use empty frequencies simply don't work"

Tell that to Spektrum.

My various model flying things now work by hunting about the 2.4ghz band and picking two out of 80 available channels. TX and RX are bound together in a similar manner to Bluetooth. If one channel gets futzed with, the other acts as a redundant spare until some blank space can be located for both channels to fire up again. This all happens fast enough that I don't even notice it. Given how twitchy some aerobatic frames can be, you want a reaction time of under some 1/50th of a second or that daisy-strimming low pass just turned into a splat. The technology makes the old 35Mhz FM method with matched crystal pairs positively ancient and vastly more dangerous in comparison.

Go and research Spektrum's DSM2 technology, then come back and say that radios can't find empty frequencies with a straight face.

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Er...

All well and good as an anecdote - but what OTHER equipment did you interfere with in the process? How do you know? What if 41 of you guys get together and try to use the devices all in range, all at the same time? What if your radios have powers capable of reaching across km rather than 100's of m? What makes you think something running in 2.4GHz cares about what it stomps over compared to something that could, potentially, be sitting right next to an emergency frequency and not have to interfere with it? What if some device comes online and stomps over BOTH channels simultaneously?

And let's be honest - a model flying area is going to be pretty empty in terms of radio frequencies - unlikely to have microwaves (i.e. something not DESIGNED to be a radio but emitting anyway), wifi, bluetooth etc. abound in large SNR's. Hell, I can't pick up my own wifi at the end of my garden - the local park must be relatively dead in comparison.

You're talking two entirely different concepts - picking up a pair of relatively empty frequencies from a range deliberately reserved for hobbyist use, so that you can communicate with a low power device that's nearby (and sod everyone else trying to use that frequencies) in a way that interference causes less than 1/50ths of a second renegotiation on a channel that can theoretically communicate in the order of 10^9th's of a second - versus - a wideband, hole-spotting, "unlicensed" carrier that could be pushing MW or mw, over kms or metres, right up against working, reserved frequencies and that *can't* just stomp over anything at all (because even a silent channel, or one displaying static, is pretty indistinguishable from one that is idle and/or encrypted properly), and that *everyone* has the same device in a small area and tries to use it.

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From field to street.

"unlikely to have microwaves (i.e. something not DESIGNED to be a radio but emitting anyway), wifi, bluetooth etc. abound in large SNR's."

Okay let's put it this way: I'm flying single-channel foam and micro variants up and down a very wirelessly connected street and it's not having a problem. The 2.4ghz band is not reserved for hobbyist use, it's using the same standard ISM frequencies that your wifi, bluetooth and microwave oven uses. The only difference is where your wifi is using great fat bands that split 2.4ghz into 16 channels or so, these things have 80 tiny little channels available. By the way, you can run 41 aircraft without a problem. It's just that one of you is going to have no redundancy.

I'm not saying it's simple to achieve over very long range, but just dismissing whitespace radio as impossible when there's a range of technologies from DSM2 to 802.11n that work by finding and exploiting blank frequencies is disingenious.

And aren't emergency frequencies reserved? So you make your kit to say "these are the areas you can't stomp on. Have fun with the rest."

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Meh

working example

Wireless microphones are another case, and the problem when of someone's fridge is broadcasting on your frequency was a problem that had to be solved. Of course, when everybodies printer is singing, there will be more overlap risk, but perhaps delays are more acceptable?

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Do we /need/ more radio channels?

There are hundreds of unlistened-to stations out there, what's going to transmit on these new channels?

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Facepalm

GPS? Open sky?

But... surely... it’s a radio, so it could receive a radio signal on a fixed frequency. You know, one that would tell it what other frequencies to use? eg DAB text on a local radio station?

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Facepalm

rtfa

and how would that allow it to know where in the country it is?

Your geographical location determines which frequencies are available. So that's why GPS is needed, and GPS is why visibility of the sky is needed.

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Mushroom

title

Forget the Technicial details:

Ofcom will fuck it up. No ifs, no buts. That's what Ofcom do.

still waiting for the ConDems to point their gun at the one fucking quango that deserves it.

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Of course....

Of course Ofcom will fcuk it up. They know nothing about radio propagation/frequency planning any more

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Anonymous Coward

KISS

"That means every white space access point will have to have GPS or similar built in, and be able to see the sky too; they'll also have to periodically check back with the database to see if things have changed."

Why so complicated?

Base stations can be told where they are (either with a postcode or grid reference) when they are installed. They won't be much use if they are not connected to the internet so getting database updates won't be a problem.

Mobile devices will have to use whatever frequency the local base station is using so they can ignore the problem of permitted frequencies.

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The Anonymous Mr. W...?

Hi Mr. W, is that you, or just someone aping your style?

Bottom line is that before these things are allowed to be released 'into the wild', we should all be 110%, no 150%, no 200% certain that they are not going to interfere with existing licensed users of TV white space...who wants their £75 U2 (insert band of preference here) live experience screwed over by interference from unlicensed, free loading white space devices? Spectrum efficiency vs. entertainment delivery?

Before we all tumble headlong into a brave new white space device future, let's take some time to consider what the unintended (or otherwise) consequences might be to both those that receive DTT, as well as those that are responsible for the production of the content that is carried on whatever network.

Caution, that's the way...the sharing of TV whitespace with new services has never been attempted before...should we be screwing up our ability to make and deliver TV content just so we can all upload our pictures to facebook that little bit quicker...?

Think about it....

http://www.theregister.co.uk/Design/graphics/icons/comment/alert_32.png

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Anonymous Coward

What in the who now?

Whether base stations locate themselves with an expensive GPS-based solution or a postcode, the interference problems (or not) will be exactly the same. So I'm not sure why you're addressing your interference worries to me.

Anyway, who is Mr W? My poor writing style is entirely my own.

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