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DoD Dreams of Efficient Spectrum Usage
Unstrung writes "US Military research agency DARPA is sick of all those static-filled cellphone calls and dropped connections too. The shadowy eggheads are working on a way of using the bandwidth available today more efficiently."
They're the one's that implemented TCP/IP, and that's still in use today.
I wonder if that's what'll happen with cell phones: people running their own Cell providers, just like TCP/IP services today.
Pi
this link seems to actually work: http://www.ntia.doc.gov/osmhome/allochrt.html
Click here or here.
Next generation GSM uses CDMA. Period.
CDMA proved itself technologically superior to TDMA. It allows more users in the same piece of space/bandwidth than TDMA does.
"Better Range" is not an advantage of CDMA. The advantage is better spectral efficiency. I think it may also be more resistant to multipath, but I am not sure. Certainly WCDMA will be.
Market forces and regulation, of course, distort how this affects what people actually have. Compatibility is in fact very important, which is why GSM provides, today, superior service in *that* particular regard. I am not sure why GSM is expanding so fast in the US, but I would bet it is to take advantage of the vast variety of GSM phones due to its superior compatibility. Also, due to the spectacular collapse of share values in telecom companies (partly caused by their grossly overbidding for bandwidth sold by greedy governments), the next generation (3 G wireless) has been delayed... perhaps for a long time.
Today, the US has in inferior system due to its lack of compatibility and resultant duplication of resources. You might say that US users are suffering from the regulatory decision that allowed mankind to realize the benefits of CDMA in the future!
The multiple standards had nothing to do with the us "protecting its native manufacturers." You may have noticed that if that was the goal, it failed! The multiple standardsd were due to a regulatory philosophy of reducing the standardization ordered by the government. The FCC decided to regulate based on spectral efficiency, rather than specific technical specifications. Both TDMA and CDMA met the initial requiremens, and the US thus has two kinds of TDMA (GSM and US) and CDMA. The choice was made completely by the providers. A provider could choose whatever standard he desired, as long as it met the FCC's spectral efficiency standards (and related things such as tolerance of out of band interference, etc). The result is this very frustrating hodge podge of systems. In the short run, it certainly provides on benefit to US telecom providers: it reduces churn - it makes it harder for a consumer to change providers. In the long run, I think it will hurt them, because various applications (such as instant messaging, etc) will not appear as quickly or be as ubiquitous as they are in GSM countries.
BTW... the US is not the only country with multiple standards. Japan also has at least two.
Frankly, I wish the French or some other country had done the experiment so we in the US could have a single standard... but that's not how it worked out. We are the guinea pigs.
CDMA, btw, was invented by the president of Qualcomm, and would never have made it as a standard without this competitive build-out. In general, the "established" carriers took the proven approach - TDMA. Others took the gamble of the unproven technology (CDMA). CDMA is so bizarre that it was not really possible to predict it's bandwidth efficiency without large scale builds.
BTW... from a technical standpoint, CDMA is a very elegant way to do things. Basically, one takes a high rate pseudo-random bit sequence and multiplies the data stream (at a slower bit rate) by it. One transmits the result, perhaps after shifting the frequency.
The receiver has a synchronized pseudo-random bit sequence, and inverts the transform by multiplying the received RF signal (mixing) by it, and out of a loss pass filter appears the original data (audio) stream.It is a form of Direct Sequence Spread Spectrum technology.
Pretty cool - nice an isomorphic - with pseudorandom. I love it! I've loved DSS for years.
Interfering signals in the same bandwidth are multiplied, of course, by the same bit stream. But since it is pseudorandom, and the interfering signals are not correlated to it, they appear as broadband noise to the receiver. With techniques like this, you can also hide a signal so it is not detectable except by a receiver with the synchronized code. This stuff was first used for military secure and LPD (Low Probability of Detection) systems. The original inventor was the 1940's actress Heddy Lamar, who invented a system which multiplied music from a phonograph by audio (and recovered it by the same process). This was used to allow Roosevelt and Churchill to communicate over short wave radio without being deciphered.
The only good weather is bad weather.
GSM does not make very efficient use of spectrum - while it is very handy to be able to use my GSM phone almost everywhere in the world, most GSM operators are having to upgrade to the CDMA-based UMTS (aka W-CDMA) in order to use spectrum more efficiently.
GSM works well, but suggesting it as a solution for spectrum efficiency is quite bizarre, particularly when cdmaOne (used by Sprint PCS and Verizon in the US) is more spectrum-efficient.
GSM is not going to go away! Those GSM operators who have a 3G license (about 100 of them, out of hundreds of GSM operators) will deploy overlay UMTS/W-CDMA networks, but an absolutely critical feature of these networks and any 3G phones will be seamless roaming to GSM.
GSM has over 70% of the world market, and UMTS (or CDMA2000 1x etc) will not have anything like universal coverage for a long time... CDMA is more spectrum-efficient than GSM, but GSM is going to stay around particularly in rural areas where large cells are important and 3G won't have that sort of coverage. CDMA2000 1x is an easy upgrade from cdmaOne, but going to 1xEV-DO/DV (the true 3G versions) will be a similarly expensive operation.
GSM was decreed by the European standards bodies, but it has been an incredible success - you can use GSM phones in almost every country in the world, on over 400 networks. Call quality is great, coverage is good wherever I've been (including parts of India), and you have universal services such as short message service (text messaging).