Start-Up Plots New Course For Modulating Signals

Feb. 26, 2016
Cohere Technologies has developed an air interface that uses wireless channel information to cut down on distortion and interference.

Over seven years ago, Shlomo Rakib, an engineer who has founded several wireless companies and even helped invent a new modulation scheme, 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. It completely turned upside down everything we knew about wireless at the time,” Rakib says. His instinct was so strong that he founded a new startup company 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 vying for its place in fifth-generation, or 5G, wireless technology.

Cohere claims to have devised a more efficient air interface for 5G networks. 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 networks with higher capacity and stronger reception at the network edge.

Their technology, 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,” says Phil Marshall, an analyst with Tolaga Research, a wireless research firm. “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, 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.

Larger companies like Qualcomm, Huawei, and Alcatel-Lucent have been tweaking OFDM, the modulation scheme that defines 4G technology, to meet new 5G requirements. But Cohere Technologies claims 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.

Overlaying instead of replacing OFDM could be a major benefit as the standards process for 5G moves forward. The 3G Partnership Project (3GPP), the standards group overseeing 5G standards, has the task of sorting through new air interfaces, wireless chips, and other technologies from research labs and universities.

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

At this point, it is difficult to predict what approach will make it into 5G. Rakib suggests that these plans 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.

In the view of industry analysts, time is not on the company's side. “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. In the next few years, new advances could "dull the luster" of its new modulation scheme, he said.

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

With the 5G standards process in its early stages, the company is hedging its bets with new equipment based on OFTS. The new equipment is designed to be “a wireless extension of fiber” with an eye toward delivering 1 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. “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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