Cellular Cacophony

You can take a cellular telephone anywhere, but can you make it ring? Much of the world’s populated areas are covered by wireless systems that support cellular telephony. Hence the cellular telephony dream of from anywhere to anywhere at a low cost, should have already been a reality.

In reality, the “to anywhere” part works, made possible by the ubiquitous and interoperable POTS (Plain Old Telephone System). The POTS uses a standard signaling system that works around the globe. If you find an old rotary phone in an attic in Europe, and plug it into the modern POTS in the US and it will work. Take a new cell phone purchased in Taiwan and switch it on in India – and it will play dead.

Like the POTS, telecom engineers run cellular systems. Telecom people live and breathe standards. Standards are rules that are written and published. All telecom equipment have to adhere to standards, in order to work. Standards make it possible for equipment to interoperate and work harmoniously. The telecom mantra is “if it is not a standard, it does not exist”. Why then, is there not a cellular standard that makes it possible for a cell phone owner to make calls “from anywhere”? To understand this inconsistency, need to delve into a bit of cellular history.

Many years ago, even before the dot-com revolution, there were a handful of rich and powerful men (also known as fat cats), who cruised the crowded streets of New York in their stretched limousines, while sipping their favorite adult beverage and contemplating the next big move to make more big money. They all had the same problem – not being able to make phone calls while relaxing in traffic. So acute was the problem, that the FCC (an organization of bandwidth Nazi’s, who guard radio bandwidth with more zeal than a female grizzly guards her cubs) provided them with about 23 channels of radio space to make phone calls. Of course a standard was established and it was called IMTS for Improved Mobile Telephone Service. The fat cats were happy and made even more money, until the fat cat population grew to significantly higher than 25. In 1976 there were 545 IMTS subscribers in New York with a wait list of 3,700 people.

It is the ultimate misery is to have to step out of a car to make a phone call. It necessitates the use of a public phone, which the previous hobo has spit into. It even causes the distressing situation known as the Spilt Martini Syndrome. To the rescue came the then prestigious Bell Laboratories, who decided to use technology to reduce contact with spit and to conserve alcohol, and invented the cellular telephone. The telephone was 2 Kg gadget, mounted in a car. The FCC graciously provided 832 channels occupying 50MHz of bandwidth in the 800MHz band, and the first cellular standard was born. Each channel had a transmit and a receive carrier and occupied 30KHz each way using FM for voice encoding. The standard became known as the Advanced Mobile Phone Service or AMPS. This is how, in the mid-80’s, the cellular telephone was unleashed on to the unsuspecting American public as a expensive status symbol and a must-have toy for the rich.

Cell phones were invented for use in cars, and were commonly called car phones. Cars having car phones sported little antennas that resembled the tail of a pig. Car owners without car phones could dampen their car phone envy by gluing on fake antennas. After all which respectable BMW owner could risk being seen in his or her Yuppie-Mobile without a pigtail? The fake antennas of course proved to be big nuisance and caused loss of productivity for car phone thieves. For those few unfortunate people who did not own cars, a bag phone was available. A handheld model also became available, but it produced less transmit power. Of course, no red-blooded, “bigger is better”, American would want to be caught dead transmitting weakly and hence the handhelds were a failure in the US market. However the folks in Hong Kong had no such hang-ups.

While the car crazy Americans went forth and multiplied AMPS in their humongous land, the Europeans watched with suspicion. “Who needs car phones?” they said, “Civilized and ecologically responsible people like us, do not drive all the time, if ever”. So while Europe mused, the real cell phone revolution happened in Hong Kong. This little island of entrepreneurs with limited vehicle ownership suddenly was found to have the highest per-capita cell phone ownership in the world. Almost every person in the street had a handheld and used it as long as he or she was awake. It soon became quite difficult to order a meal in a restaurant without interrupting 10 conversations. Some Europeans, who lived in Hong Kong, went home on vacation and could not contain their stories of the mysterious Orient. They told a mystified audience how Confucius says a phone in the pocket spells happiness.

So it was Europe’s turn. They decided that the American system of AMPS was too antiquated a system to use, and they were right. AMPS used one conversation per voice channel. Digital technology using speech compression can fit in three conversations per channel. AMPS phones were easy to “clone” and made cell phone fraud too easy. Digital encryption technology makes such fraud impossible. AMPS is not private, anyone with a rigged radio receiver could tune into cell phone conversations. Digital technology defeats such shenanigans.

Europe finally caved into the cell phone mania and chose a digital system called GSM (Global System for Mobile Communications) operating at the 900Mhz band. In GSM a person’s voice is first digitized, and then compressed yielding a bit stream of low bit rate (about 10Kb/sec, compared to 64Kb/sec for digital telephony used in the modern POTS). The bit stream is then transmitted with each bit occupying a specifically allocated spot in time, a spot reserved for each active cell phone. This technique is also called TDMA (Time Division Multiplexed Access). TDMA coupled with some particular methods for encryption, signaling, call setup and such, and a goofy phone numbering scheme became the GSM Standard.

GSM caught on overnight. Every country that set up cellular systems in the early 1990’s chose GSM. Since this was the heyday of new systems, GSM soon shone over all existing standards and was well set to become the panacea for “from anywhere”. However the first stumbling block was cost. When a subscriber of cellular company A, strays into the territory of cellular company of B, B uses the person as a blank check. Just a few dollars per minute sir! And it is quite hard to argue, after the bill has arrived, with someone with an attitude of “You have a problem with that?” in a language you have never known existed.

Roaming also never quite worked right. Suppose Joe who lives in London is visiting Mary who lives in Calcutta. While Joe was out sniffing the world-famous Calcutta smog, Mary called Joe on his cell phone. Between Joe and Mary they end up paying an exorbitant airtime charge along with the bill for two international calls. Yummy for the phone companies, yucchy for the customers.

As the GSM revolution spread across the globe, the sleeping technological giant (USA) woke up and saw its cell phone system was really the most antiquated in the world. “This cannot pass”, muttered the powers to be, “Oh, what can we do?” Adopting GSM would be expensive (all systems have to be replaced) and copying the Europeans is rather embarrassing too.

AT&T blinked first. They produced a hybrid system that used digitized voice glued on to the existing AMPS equipment, and called it, rather innovatively, TDMA and introduced it commercially around 1992. Soon, in 1994, a small company with a strange name, Qualcomm, patented a new cell phone system called CDMA. Soon a plethora of small and medium scale cellular companies deployed CDMA using 800 and 1900MHz bands. Sprint took CDMA nationwide (in the US) around 1996 and became the new cellular company to hate.

CDMA proved to be a US success story. It is amazingly cute technology. Unlike TDMA, which allocates a slice of time to each cell phone, CDMA uses the entire band for all telephones. They all talk simultaneously on the same channel. How each conversation is plucked out of this electronic cacophony is the magic of CDMA. TDMA has a fixed limit on the number of phones that can transmit simultaneously. CDMA has no such limit. There is a suggested limit, but this can be easily exceeded with some loss of quality. This little feature is greatly beneficial to the bottom line of cellular operators who embraced this technology with such gusto that Qualcomm stock rose from a $50 to $200 in 6 months.

So the US market got segmented into AMPS, TDMA, CDMA-800 and CDMA-1900. To make matters worse, GSM suddenly made an appearance too – running at 1900 Mhz. On the worldwide front, the GSM countries have split into two, those using the older GSM-900 and those using the newer GSM 1800 (not to be confused with the US GSM 1900).

The future is always brighter though it is not clear, for whom. A grab bag of so called G3 (third generation) technologies, which includes CDMA-2000 from Qualcomm, Wideband CDMA, GSM-CDMA and several others, are vying for attention. While all of these use some form of CDMA, its not the same form. The tragedy is that all of them are going to win a sizable slice of the pie, and we will be left with cacophony. Possibly forever.

Partha Dasgupta is on the faculty of the Computer Science and Engineering Department at Arizona State University in Tempe. His specializations are in the areas of Operating Systems, Cryptography and Networking. He carries a cell phone with him on his trips and often finds it hard to make it work right. This article was written while sipping a fake martini on the quiet stretched verandah of BNR Hotel in Puri while his borrowed GSM-900 phone, with a Calcutta number refused to make calls (there is GSM-900 service in Puri).

Partha Dasgupta