USS Clueless - GSM 3G

Stardate 20021005.2128

(On Screen): As I think many of my readers know, I used to work for Qualcomm designing cell phones. Qualcomm is the company which invented CDMA, and made it practical, and made it into a market success, and it now dominates the American market, where Verizon and Sprint both use it. There are two other nationwide cellular systems: AT&T currently uses IS-136 TDMA, which is obsolete and has no upgrade path. Cingular uses GSM, a more sophisticated form of TDMA from Europe.

And right now I'm basking in the evil glow of a major case of schadenfreude.

The original cell phones were analog, using fairly straightforward FM for voice communication. When your phone was in a call, it was granted a frequency by the cell and used it exclusively for the entire duration of the call. FM encoding is extremely inefficient in use of bandwidth, and spectrum was scarce and expensive, and it rapidly became clear that FM wasn't able to handle the traffic which was expected and which was really needed to make cellular telephony a profitable business. One obvious approach was to use digital communications, and to take advantage of advances in microprocessor and digital IC technology to compress the voice traffic going both directions, and thus you saw deployment of the first Time Division Multiple Access (TDMA) digital systems. What they do is to take a single channel and timeshare it among several phones, who digitize and compress their voice traffic and transceive it during their timeslice. With IS-136, a 30 KHz channel which had carried only one voice call with AMPS could now carry three digitized calls.

GSM went further than that, and abandoned the old channel size entirely. It allocated 200 KHz channels and divided them into 8 slices, giving each phone somewhat less than 25 KHz effective bandwidth. (There are some losses due to time guardbands and protocol overhead.)

GSM also included a very powerful set of features above that, and included some interesting features not directly associated with the RF link, such as a personality module which contained a customer's phone number and billing information that could be moved to another phone any time the customer wished to. (That particular featured turned out to be a decidedly mixed blessing. While that ability was very convenient for legitimate customers, it was also a magnet for thieves and frauds.)

GSM was clearly superior to IS-136 or such abortions as IDEN (a Motorola design which never became an industry standard because Moto was never willing to license it, which meant that systems which adopted it could only get infrastructure and handsets from Motorola).

In Europe, various governments decided that they (the Europeans) had designed the ultimate digital cellular system, and they passed laws making it illegal to deploy anything except GSM, whose primary supporters/suppliers were Nokia, Ericsson, Siemens and Alcatel.

Meanwhile, the FCC decided that it would not mandate any industry standard. It granted licenses for spectrum but permitted the licensee to choose whatever equipment and standard it wanted. (Within limits. There were certain certification standards required by the FCC to guarantee safety and to avoid interference between neighboring systems.)

And all through the 90's, me and everyone else in the US cell phone industry put up with constant ragging from Europeans about the evident virtues of GSM and the equally evident virtues of a government mandated standard. While in the US you had what seemed at the time to be utter chaos, with a huge number of small companies using a bewildering array of different standards, in Europe anyone could carry their phone almost anywhere in the continent, and if they couldn't use it they could move their personality module into a local phone and use that.

Of course, that apparent chaos in the US was only a temporary phenomenon, and I think maybe the FCC and the rest of the government knew it would be. There's always shakeout, but in the meantime this kind of government policy of keeping hands off meant that the industry was given broad ability to experiment. And within that environment, early in the 1990's, the founders of my former employer Qualcomm began to work on a radically different way to handle cell phones called Code Division Multiple Access, or CDMA. It's radical in many, many ways but by far the most obvious is that all the phones in the system and all the cells in the system operate simultaneously on the same carrier frequency. They don't "take turns" because they don't need to.

In the computer industry we talk about the "ISO seven layer model", where the process of communication is modularized and each layer uses the one below it without worrying how the lower layer actually works. TCP works whether the physical layer is 802.11b or ethernet or something else entirely, and TCP itself doesn't change based on that. TCP uses IP, and IP uses the datalink layer, and the problems of the physical layer are dealt with by the datalink layer. But if the physical layer is a 56 KBaud modem, then there are things which won't be possible, which might be possible with 100 megabit ethernet. No amount of work at higher levels can compensate for the fundamental superiority of ethernet over a telephone modem.

Cell phone protocols do the same kind of thing. There's an RF layer and protocols above that, some of which can be very high level and quite abstract, such as the one which controls sending of text messages. However, t

Captured by MemoWeb from on 9/16/2004