Rosenberg gave a history of early cell phones — pic­tured here is an example of a phone that was used as part of the Improved Mobile Tele­phone Service (IMTS). | Wiki­Media Commons

Often taken for granted is the super­com­puter that rests in everyone’s pockets. Not many remember a day when a real map had to be used, when writing letters was the only way to contact a distant friend, or when real people had to perform any of the tasks that a smart­phone can com­plete at the touch of a finger.

One of the men respon­sible for making cell phones an achievable dream, Adam Rosenberg, Ph.D. – a Stanford and Princeton edu­cated expert in tele­phony – visited on Sep­tember 11 to talk to Hillsdale stu­dents about his expe­rience in the inno­v­ative field of early cell phones.

Rosenberg’s talk “did a good job of making the topic acces­sible for people at all levels of math,” according to Rose Schweizer, a senior studying math and Spanish.

He explained the nec­essary basics while still including the higher math that is more inter­esting to older stu­dents,” Schweizer said.

Rosenberg began his talk with an intro­duction to the dif­ference between analog and digital phone lines and the fight against inter­ference.

“If there was a radio station in Hartford Con­necticut, the nearest place they would reuse that station was in Bal­timore,” Rosenberg said. “Hun­dreds of miles away…the notion of inter­ference being some­thing we could manage was totally new.”

He went on to introduce two important figures who helped introduce the idea of cel­lular tele­phony. According to Rosenberg, cel­lular didn’t really become “real” until Dick Frenkiel and Phil Porter at Bell Lab­o­ra­tories wrote a memo in 1966 describing how this system would work.

The system this memo described con­sisted of radio antennae that would be placed atop large towers in major cities. Each of these antennae would be able to take 12 calls at a time on a sep­arate channel each. Anybody attempting to make a call within the city would have to wait for one of these channels to open up.

Engi­neers called this system Improved Mobile Tele­phone Service, although, as Rosenberg said, “Heaven knows what it was improved from.”

Obvi­ously, the IMTS system did not last long. Rosenberg went on to explain the decision to divide the world up into regions which they called cells, giving each cell its own site or bay station in the middle where they could manage inter­ference.

He explained that this emerging cel­lular tech­nology is called Advanced Mobile Phone Service, or AMPS for short.

Rosenberg himself helped create the system we use today — a grid made up of con­nected hexagons with a cell site within each. Making the grid out of hexagons ensures that there is always a sizable dis­tance between each cell to min­imize inter­ference.

“The further apart they are,” said Rosenberg, “the better.”

The initial tests of the AMPS system began in Chicago. When the engi­neers realized how well the cell system worked, they dis­covered that they could place smaller cells within the original grid and increase the ability of the system sub­stan­tially.

“Soon, we have added enough cells into the old grid that we have created a whole new grid,” Rosenberg added.

Com­bining these two grids, the engi­neers for AMPS were able to have lines available for more than 10,000 people, a remarkable feat for the time.

Rosenberg told some 20 stu­dents in atten­dance that he has always  been a “math geek” and that learning to program a com­puter and the idea of cre­ating a machine that could do a mathematician’s dirty work helped him make the decision to go into the field of tele­phony.

The talk drew many stu­dents seeking to learn about not only the history of cel­lular tele­phony but the science and math behind it as well. Jadon Lip­pincott, a senior studying math­e­matics, went into the talk with no pre­vious knowledge regarding cel­lular tele­phony.

I wanted to attend the talk because math is the most beau­tiful subject around, and math makes unex­pected appear­ances all the time,” Lip­pincott said.

Schweizer com­mended Rosenberg’s appli­cation of math to everyday func­tions.

It was nice to see how topics that seem com­pletely the­o­retical, like modular arith­metic or geometry, can be used in a real-world setting,” she said.

Rosenberg’s talk high­lighted some of the reasons such pow­erful machines now exist within arms reach whenever needed, or wanted, while addressing the sheer unpre­dictability of tech­nology.

 “Do I know what it’s going to look like in five years?” Rosenberg said. “I haven’t a clue.”