Image courtesy of Rex Boggs Creative Commons

(Image courtesy of Rex Boggs, Creative Commons).

Start-Up Takes Aim at 5G Air Interface

Seven years ago, Shlomo Rakib attended a lecture about an unusual branch of algebra known as representation math. He became intrigued with the idea of applying the subject to wireless technology and signal processing, which had seldom been done before. “It just clicked," he said in a recent interview.

"It completely turned upside down everything we knew about wireless at the time,” Rakib said. He was so convinced that he founded a start-up with the mathematician who gave the lecture, Ronny Hadani, an associate professor of mathematics at the University of Texas at Austin. The company, Cohere Technologies, is now pushing to get its technology included in 5G standards.

Cohere, which has quietly worked in Silicon Valley for years, says it has developed a more efficient way for backhauling data. Their new modulation scheme uses both time and frequency data about wireless channels to alleviate signal fading and multipath noise. The result, the company claims, is higher capacity and stronger reception at the network edge.

Their technology, also known as Orthogonal Time Frequency and Space (OTFS), captures accurate data about wireless channels that, when combined with algorithms, can help compensate for distortion, interference, and other wireless handcuffs. The technology also combats the Doppler effect in mobile applications, such as the antennas embedded in smartphones and that could find their way into autonomous cars.

In recent field tests, the company says that OFTS modulation enabled “perfect linear scaling” of multiple-input multiple-output (MIMO) radios, which are expected to be a major component of 5G networks. MIMO links together multiple transmit and receive antennas to increase network capacity. But adding more antennas to the array has been difficult without introducing more signal fading and interference.

“From a technical perspective, the approach makes sense,” said Phil Marshall, an analyst with technology research firm Tolaga Research. “There is a great deal of value that can be garnered from techniques that capitalize on the time and frequency domain diversity of wireless channels.”

Rakib, now Cohere's chief executive, claims that existing technology too often has high overhead for accessing a wireless channel. OFTS technology spends only 0.15% of the network’s capacity to acquire a wireless channel, whereas today’s modulation schemes require about 7% overhead per stream.

Google Earth image showing the range of OFTS when compared to other technologies in recent field tests. (Image courtesy of Cohere Technologies).

Larger companies like Qualcomm, Huawei, and Alcatel-Lucent have been tweaking OFDM, the modulation scheme codified in 4G, to meet new 5G requirements. But Cohere says that their technology sits on top of OFDM. It preserves what works with OFDM—high spectral efficiency and multipath noise canceling—while also bolstering capacity, coverage, and data rates.

Rakib says that the other interfaces are not a significant departure from the OFDM waveform. Nokia, Alcatel-Lucent, and others have designed a filter band modulation scheme, while Qualcomm is using another approach. Huawei and others are promoting a sparse-code multiple access approach and have tested the technology in China.

At this point, it's difficult to predict what approach will make it into 5G. Rakib suggests that these technologies will eventually consolidate around one main proposal. But he thinks it will not be until around 2018 that the 3GPP agrees on one. If OFTS technology gets into the new standard, Cohere will be able to license it to other companies.

For some analysts, time is not on the side of a start-up company. “Like any startup, Cohere will face sustainability challenges during a long technology acceptance cycle,” says Ken Rehbehn, an analyst with 451 Research, in a research note. His concern is that research and development in the next few years might “dull the luster” of OFTS.

For now, Cohere Technologies still has a certain luster. In three rounds of venture funding, the company has raised around $90 million with investments from Telstra, an Australian telecommunications company, and other investors like Lightspeed Ventures and New Enterprise Associates.

With the 5G standards process in its early stages, the company is hedging its bets with equipment based on OFTS. The new equipment is designed to be “a wireless extension of fiber” that delivers gigabit wireless service, presumably to enhance current LTE networks. The company is also preparing MIMO radios with 64 × 64 antenna arrays.

Even with all their technology in the works, Rehbehn is not certain of the end game for Cohere Technologies. “Is this an intellectual property firm like InterDigital? Is it a silicon supplier like Qualcomm? It is too early to tell, but Cohere’s intellectual assets are attractive and should set the stage for an interesting journey.”

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