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Comment: Re:too much multi pathing at that frequency (Score 1) 52

by petermgreen (#48204795) Attached to: Gigabit Cellular Networks Could Happen, With 24GHz Spectrum

... or you could rely on that interference at the point of reception to form unique signals for every recevier by synthesizing waveforms from an array of transmitters, dynamically calculated based on the location of each transmitter + receiver + interference pattern. This would effectively give an unlimited number of signals within the same spectrum with no additional bandwidth (constrained only by the number of transmitters).>

MIMO techniques can be useful but they aren't as magic as you seem to think (and a nieve analysis would suggest)

In reality a couple of things limit your performance.

1: the channel estimation is nessacerally imperfect
2: the calculations needed to seperate out the virtual channels also tend to amplify the noise.

This is especially true if the antennas are close together.

This is what Artemis is now testing with their pCell tech, using a data-center of waveform-calculating servers + cheap low-power transmitters about the size and cost of a off-the-shelf wireless router:

Yeah distributed mimo has the potential for significant gains. It also has a significant cost as it needs very high bandwidth fixed line connections from the "waveform calculating servers" to the transcivers.

Be careful not to take marketing material too literally.

Comment: Packet data is low priority. (Score 1) 105

by petermgreen (#48185807) Attached to: Ask Slashdot: LTE Hotspot As Sole Cellular Connection?

Traditionally mobile phone networks worked as follows

SMS (at least with GSM) goes on the control channel, so if the phone can associate with the network it can almost certainly get a SMS through.
Voice calls need data channels but those data channels are circuit switched and have priority over packet data. So provided you are outdoors (indoors multipath can screw stuff up) you can usually get an intelligable voice call through..
Packet data gets the capacity left over after circuit switched stuff (mostly voice, circuit switched data also exists in theory but is rarely used in practice) has taken the slots it needs. If a cell has capacity problems then it is packet data service that will bear the brunt of the problem. On the plus side web browsing, email etc are much more tolerant of jitter/loss than voice calls are so they sometimes work acceptablly indoors when voice call quality becomes unacceptablly poor.

By trying to run VOIP over packet data services you are giving yourself the worst of both worlds, the low priority of packet data services with the jitter/loss intolerance of voice communication.

Now with LTE they are moving away from circuit switching but I would still expect voice calls to have priority over generic packet data service. Also many areas don't have LTE coverage.

Your proposal may work if you live your whole life in an area with good uncongested LTE coverage. If you want to remain in communication in areas that don't have those things then forget about it.

Comment: Re:Some Sense Restored? (Score 3, Interesting) 519

by petermgreen (#48169943) Attached to: Debian Talks About Systemd Once Again

Debian's offering of Gnome 3 and Systemd are not comparable. Gnome 3 is only the default desktop for people who just want to click through the installer.

It's also what everyone previously using gnome2 on squeeze would get on upgrade to wheezy or above.

A fork of gnome 2 did eventually make it back into debian but it wasn't in wheezy and you still have to manually remove all the gnome bits and replace them with their forks.

Even if one hangs on to sysvinit as one's init system, programs like Gimp on Debian now end up pulling in systemd libs.

Pulling in libs related to things you don't use isn't really anything new.

The bigger question IMO is to what extent will systems that don't use systemd as init be supported going forward? Will users of other init systems be treated as second-class citizens. When the technical comitee chose the default init system they refused to rule on this issue and it looks like the current GR is what this is about.

Comment: Re:A lease on a CPO might be interesting... (Score 1) 126

by petermgreen (#48088023) Attached to: Tesla Is Starting a Certified Preowned Program

While an electric vehicle won't be zero vibration it will likely be much better than a vehicle based around a reciprocating internal combustion engine for serveral reasons.

1: IC engine vehicles need to "idle". That is run the engine with no load as part of the startup process and during short stops. Mechanisms running unloaded are much worse from a vibration point of view than the same ones running under load. Electric cars can simply turn the main motors off when stopped (accessories can use their own motors which are sized to be appropriate to the load in question).
2: a reciprocating engine by it's very nature has objects of substantial mass changing position (rather than simply rotating). They try to balance this of course but said balancing is often of limited effectiveness. An electric motor (or a gas turbine but those didn't catch on in cars for other reasons) by contrast only has rotating parts.
3: while it's true that electric motors do have an optimal speed they have a much wider band of usable performance than an internal combustion engine. This means that it is practical for electric cars to use a fixed-ratio transmission.

Comment: Re:Surprisingly (Score 1) 142

by petermgreen (#48044235) Attached to: Boeing Told To Replace Cockpit Screens Affected By Wi-Fi

How do you know they are using "crap lead free solder". Doesn't ROHS have exemptions for this sort of stuff.

Also even if they are using lead free solder I don't think the situation is anywhere near as bad as you imply. I have plenty of stuff that still works which is 5-10 years old. Capacitor failure still seems to be a bigger problem than solder failure.

Comment: Re:Question from the lawn (Score 3, Informative) 35

by petermgreen (#48044095) Attached to: DARPA Technology Could Uncover Counterfeit Microchips

The problem is testing "every possible op code" is insufficiant, you would have to test every possible opcode/operand/register state combination since the condition for "evil behviour" may test on a tight combination of those. Doing so is compututationally infeasible.

Comment: Re:Define "counterfeit" (Score 1) 35

by petermgreen (#48044059) Attached to: DARPA Technology Could Uncover Counterfeit Microchips

Often manufacturers seem to do a really shitty job of marking their chips requiring you to hold them to the light in just the right way to read the bloody things.

I suspect you wouldn't even need to erase the markings to relabel those, just print the new markings in a way that was actually visible under normal conditions.

Comment: Re:No warning? (Score 1) 54

by petermgreen (#48020131) Attached to: Update: At Least 31 People Feared Dead After Japan Volcano Erupts

The scientists were well aware of the small quakes. The prosecution alledged that they should have known that this meant an elevated risk of a big quake and that their downplaying of said risks was sufficiently negligent to ammount to manslauter. The court agreed with the prosecution and convicted them but the sentances were apparently suspended until appeal.

Did the court convict because they took a detatched view and found the people truely negligent or was their verdict colord by rage and the need to find a scapegoat. That is why we have appeals.

Unfortunately I can't seem to find any information on whether the appeal was successful, a failure or still in-progress.

Comment: Re:OLEDs not generic LEDs (Score 1) 182

by petermgreen (#48007775) Attached to: Breakthrough In LED Construction Increases Efficiency By 57 Percent

I don't mind paying $20 for a light bulb I'll probably never have to replace again.

With CFLs we were promised 10 times the life of incandescents, some live up to that but many don't even from supposedly reputable brands. Fully enclosed fitings with the lampholder above the bulb seem to be particular death to CFLs.

Yes in theory an LED bulb can last even longer than a CFL but i'd be very reluctant to pay such high bulb prices on a relatively unproven and easy to screw up (AIUI high power LEDS need careful cooling design and drive circuit failure is also an issue as it is with CFLs) tech.

Things are not as simple as they seems at first. - Edward Thorp