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Category Archives: Rants & Raves
Digital Radio
There are a few different technologies commonly used in two-way radio. One is digital voice, a la Motorola ASTRO / Project 25’s CAI (IMBE), which is a 9600bps (9.6kbps) digital stream. Another interesting technology is trunking: a city might have 12 talkgroups (think “virtual channels”), but only 4 frequencies. One frequency is designated as a “control channel,” which is a digital stream announcing system status. When you want to transmit, your radio will go out to the controller and get assigned one of the frequencies, and the system will then announce that you’re transmitting on one of them, and all radios in your group will switch over and listen. This allows much greater spectrum utilization: rather than needing a new frequency for every group that might want their own channel, you just need to license enough frequencies for however many simultaneous conversations you expect.
I’ve been thinking that it’d be interesting to merge the two technologies. Technologies like Speex will let you process audio at exceptionally low bitrates, seemingly as low as 3.4kbps. (And they have some neat technology, like variable bit-rate encoding and even further drops in data transfer in between words, dropping quite low for when it’s just background noise.) So I think it’d be neat to start a “data network” at 32 kbps, which could be done with relatively low bandwidth. You could keep one frequency, and yet fit as many as 7 or 8 simultaneous conversations on it. (And you can take its VBR support one step further, and have it scale to fit system capacity: on a system with minimal activity, allow 8-16 kbps, but when the system is starting to fill up, drop down to 4 kbps.) HE-AAC (also known as AACPlus) looks promising too, although it’s a proprietary technology.
And since it’s now a 100% data network, you can do what I’ve always thought mobile radio systems, especially those used by public safety agencies, ought to do: put a GPS unit in each radio, and have them embed GPS coordinates in each transmission, as well as periodically announcing their coordinates in the background.
The net result is insanely efficient (radio) bandwidth usage. For example, Boston PD has 16 frequencies licensed, but it’s rare for more than 2 or 3 to be in use at any given moment. They could get more efficient by switching to a trunking system, maybe with 5 frequencies (plus a control channel). Of course with an established system, there’s really no incentive to, but I digress. But if they could get entirely usable digital audio at 3-8 kbps, they could actually move to a single frequency and support multiple, simultaneous conversations.
Another neat side-effect is that linking the systems would get quite easy: the entire system, with multiple conversations, could even fit over a single dial-up modem link. And you can have better “emergency” support, although most trunking systems seem to do it anyway: public safety radios carry an “orange button,” which will signal an emergency to the radio system. Analog systems do this by basically making the radios “obnoxious”–they’ll just keep transmitting a distress signal over and over, increasing the odds that they get through. With an all-digital system, they can just send packets indicating an emergency, and have the network make way for them, going so far as to terminate existing conversations if needed.
Oh, and another novel benefit is power management. If I’m on a handheld radio and I’m standing twenty feet away from the tower, I can dial my power down as low as it goes and still make it in fine. But if I’m a few miles away, I need to be using the highest power I can to make sure I’m making it. Of course, no one in the field fiddles with power settings. (In fact, most radios don’t make this something the user can do.) But if you just exchange a bit of signal strength info in the data flowing between radios, you can make this automatic. As I talk to the tower, it’ll be periodically confirming that it’s hearing me. But when it does that, rather than just using a boolean, “Yup, got it,” it can send me signal strength data, and my radio can dial down power until it’s at a, “I’m still getting 100% of your packets but I wouldn’t go any lower in power…” point. The net result is longer battery life. (And potentially, less interference to distant users of the same frequency.) As a really obscure benefit, if you’re transmitting this information, and also embedding GPS coordinates in your transmissions, the system could silently log all of this and generate coverage maps, which would get more and more detailed over time.
Oh Dear
I’m shocked to report that the Westboro Baptist Church has apparently had a lien filed against its properties in an attempt to satisfy the $5 million judgment against them when they picketed the funeral of a (presumably straight) soldier killed in Iraq. These are also the people who have gone around with “Thank God for IEDs” (Improvised Explosive Devices, the roadside bombs that keep killing our troops in Iraq), “Thank God for Katrina” (referring to the hurricane that devastated New Orleans), and even the group that praised God for killing firefighters on 9/11. Why are they excited about all of these horrific events? Because they’re apparently God taking vengeance on America for its tolerance of homosexuals. (In other news, America is tolerant of homosexuals?)
By the way, I should disclaim that, although they’re the Westboro Baptist Church, the actual Baptist Church has been careful to distance itself from them.
I’m not familiar with the case, but I do have to admit that, on the surface, it seems as if the First Amendment ought to have protected them. But, well, this is one group I’m not too sad to see go under.
She Ate All the Gherkins
The UK’s Mark Steel has a particularly humorous piece on Hillary’s problems with accidentally mis-speaking and making strange claims, because she says so many words:
Her next round of soft-focus adverts will probably feature her soothingly saying, “My fellow Americans, I drank a pint of walrus milk once for a bet. I speak fluent Eskimo. I once ate all the gherkins in Belgium. My brother’s got a yak in his loft. I fell asleep on a night bus once and woke up in Munich, and had to get a lift back on a camel. I used to live on an iceberg. I’ve got a waffle-maker that works underwater.”
Okay, so maybe it’s overly critical of her. But I can’t help but chuckle as I read it.
Lightning
A cool map of lightning frequency over time across the globe. And a live version for the U.S. Heck, a zoomed-in version on the Northeast for the past 60 minutes. It turns out that you can even buy a small Lightning Detector to map local lightning strikes on your PC. It listens for the signature static crashes from lightning, sometimes called sferics (short for atmospheric noise), much like you can hear on an AM radio during a storm. You can even listen to streaming audio from NASA‘s (Alabama) VLF receiver.
Argh!
All of a sudden my Treo 650 locks up hard when I try to enable Bluetooth. You have to do a hard reset (wiping all data) to get the phone feature to work again. I was able to back it up before doing this, but… What gives? I can live without Bluetooth, but I kind of like it, when, you know, all of the phone’s features work.
Sit in the Corner
I started a blog post about this, but it talked about terabytes NASs, HDTV DVRs, VoIP / SIP, LDAP, DNS caches, NTP strata, and a bunch of acronyms.
So instead I’ll be incredibly precise. This PC, seemingly sold only at Walmart, is really cool. It’s not that fast. Its specs are bad any way you look at them. Unless you look at power consumption. 20 Watts peak power, 2 Watts average. By comparison, my desktop machine has a 300 Watt power supply. For someone who wants to set up an always-on Linux server, this thing is screaming your name. I’m strongly attracted to the idea of setting this thing up with handful of 500 GB drives, to build a network fileserver with a terabyte or two of capacity. And doing software RAID across them. (I’m fairly certain that the hard drives would draw more power than the whole system… Although you could set up power-saving features, since a home fileserver could surely power down the drives periodically.)
There’s also a cheaper one that seems to be the same, except it comes with 512 MB RAM instead of a gig, and comes with gOS instead of Vista. I’m dying to play with OpenFiler, a Linux-based “appliance” software package for some superb fileserver tools.
Sheesh
Now that Comcast has vowed to quit arbitrarily blocking services on their Internet service, they’ve decided to shift the degraded quality to their HD offerings. This article talks a bit about how Comcast is running some heavy compression to fit more HD channels into finite bandwidth, but it has lots of words. So check out some pictures of screen captures of identical footage from FiOS versus Comcast. Slashdot has the story here.
ShotSpotter
Are you familiar with the Shotspotter system? I’d seen it on a National Geographic TV show, and remembered in the back of my head reading about it being deployed in parts of Boston. It’s actually very cool how it works — it essentially has a big array of microphones, and when it “hears” a gunshot, it’ll compare the exact time of arrival of the sound at each location to triangulate a position, which then pops up on a dispatcher’s screen.
So I’m listening to Boston PD on the radio, and maybe five minutes ago the dispatcher called out for a reading on the ShotSpotter system. “Five, six, seven, looks like eight shots fired.” She figured out the location from the map (apparently, an alley), and started a couple cars. In maybe 60 seconds an officer was on the scene, reported a car leaving, and had confirmed that shots were fired with a witness.
About a minute later, the dispatcher said that they had received a 911 call for shots fired from the same location. (Which means that they had an officer arriving on scene by the time the call came in!) They’ve just pulled over a possible suspect, and another officer found the shell casings. Detectives are en route now for forensics processing.
I’ve got to say, this seems like a pretty impressive system.
Write It Out
I’ve seen this suggested before, but only half-believed it.
When you’re stumped by a question, write it out. We’re hosting a video game tournament tomorrow, and I was thinking about scoring. I got stumped by some technical problems with the way the bracket would work.
So I decided to burn my weekly Ask MetaFilter question. Except, three-quarters of the way through writing out the question (in great detail), I realized exactly how you solve the problem.
The thing is, if I sat here and tried sketching out how the bracketing would work, I never would gotten it. For some reason, writing it as a question caused me to be able to answer my own question, in a way that starting at it didn’t.
Seriously, try it next time you come across a tough question. It obviously doesn’t work 100% of the time (“How many escalators are in Wyoming?”) But something about writing it out causes the mind to look at it differently. And sometimes that’ll solve your problem!
Also, an Excel hint… How do you do “Best 2 out of 3?” in Excel? There’s no native function to do it. And if you asked me to write code, I’d overthink it and write some contrived thing that would take the best x of y items. But let’s say that cells A3, A4, and A5 (thus A3:A5) contain the three scores, and you want the best (highest) two of the three. =SUM(A3:A5) - MIN(A3:A5) does it. Best two out of three is the same as “All of them, discarding the lowest.” This doesn’t scale: if you wanted the best six out of eight, it’d be much harder to compute. But here, you’re just dropping the lowest.