Electrifying career

How many times a day do you text your loved ones, look something up, scroll through social media or use your favorite apps? For many of us, the answer is probably at least in the hundreds; cell phones have become an integral part of our lives. However, for all the time we spend on our phones and despite all of the helpful services they provide, many of us also don't understand how it became possible for us to carry a computer in our pocket.

Throughout a career that spans decades, Professor Emeritus Leonard "Len" Cimini has charted the course of cellular technology through groundbreaking research while encouraging generations of students to continue pushing the boundaries of electrical and computer engineering.

From Scholar to Caller

After graduating from high school in South Philadelphia, Cimini attended the University of Pennsylvania where he majored in electrical engineering, a decision that was motivated by his desire to use his talents and interests in math and physics. He continued at Penn for a master's degree followed by a Ph.D. in electrical engineering with a dissertation focused on signal processing. Throughout his studies, Cimini would interview for different jobs, but none matched his ambitions. Once he earned his doctorate, he landed a job at his dream company: Bell Labs.

Bell Labs, the former research and development arm of AT&T, revolutionized telecommunications throughout the 20th century with inventions including the transistor, the solar cell, the Unix operating system and several programming languages. When Cimini joined Bell Labs in 1982, he began working on the development of the first cellular phone system in the United States. Today, we know this as wireless, and it's the reason why our phones aren't tethered by a cord.

Cimini worked with colleagues in the Forward Looking Radio group on what would become 2G, or the second generation cellular network, to both digitize the network and enable higher bit rates over a wireless or radio channel. Cimini specifically was looking into how to make the data services feasible, and it was during this time that he discovered how orthogonal frequency-division multiplexing (OFDM) could be applied to digital cellular technology.

High-Speed Foundations

OFDM is a method of data transmission where the bits of data being sent to the receiver are transmitted over multiple closely spaced subchannel frequencies. The subchannel frequencies are spaced in such a way so they can be separated at the receiver. By using many narrow subchannels, OFDM overcomes the bit rate limit set by the channel. It also simplifies the design of the data transmitter and receiver, in contrast to a traditional single channel data transmission where only one bit of information is transmitted at a time.

"If you wanted a cable to your house and you wanted a bit rate to your house of 20 megabits per second and the cable you have only gives you one, what would you do?" explained Cimini. "You'd go to the cable company and say, 'Can I have 20 cables?'…OFDM is the same way. It's saying that if I transmit a signal, and I'm limited to five megabits per second, if I want 100 megabits per second, I just buy myself 20 channels."

Cimini was the first person to theoretically apply the OFDM method for digital mobile channels, publishing his landmark paper, Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing, in IEEE Transactions on Communications in 1985. As of publication, this research paper has been cited over 3,800 times, but in 1985 Cimini's finding flew under the radar at the time because engineers did not have the technology available to implement OFDM in existing mobile devices. Although Cimini's goal was application in second generation cellular networks, OFDM would not be implemented until fourth generation cellular networks were created.

"The adoption of OFDM has had a transformative impact on wireless communications, evident in several key areas: enhancing data rates, improving robustness to fading (signal fluctuation), ensuring efficient bandwidth usage and serving as a foundation for modern wireless communication standards," Charles Black Evans Professor of Electrical Engineering Ken Barner said.