How Alexa’s engineers overcame limited bandwidth to communicate over the Deep Space Network

Recently, Alexa went into space aboard the Orion spacecraft as part of Artemis I, the first of a series of NASA missions that will pave the way for human exploration to the moon and Mars. Alexa joined the mission as part of Callisto, a technology demonstration payload embedded into NASA’s Orion spacecraft and built in collaboration with engineers from Amazon, Cisco, and Lockheed Martin. In this series, we are exploring how Amazon’s brightest minds have developed innovative solutions to support Alexa’s journey.

Zhengran Li is a software development manager at Amazon. Li joined the Alexa team 5 years ago, before which he helped build devices like the Echo Show at Amazon Lab126, the inventive San Francisco Bay Area research and development team that designs and engineers high-profile consumer electronic devices.

In this article, Li explained how Alexa’s engineers overcame issues related to limited bandwidth to communicate over NASA’s Deep Space Network.

Understanding the Deep Space Network

The Deep Space Network (DSN) is NASA’s proprietary communications network. According to NASA, the DSN is the largest and most sensitive scientific telecommunications system on the planet, made up of satellite and antenna installations located around the world. While designing the DSN, NASA placed the related facilities strategically so that the DSN could stay in constant communication with spacecraft as the earth rotates, providing a critical link to explorers in space.

In addition to its communications capabilities, the DSN also has powerful applications for tracking, monitoring, and commanding spacecraft. The network can acquire and distribute telemetry data, provide a place for teams to control space missions, and track spacecraft with incredible precision. Scientists also use the DSN to conduct advanced scientific research, such as mapping asteroids and exploring the interiors of planets.

Though the DSN is powerful, it does have significant bandwidth restrictions for different applications. Its upload speed, for example, can achieve a maximum bandwidth of only 200 Kbps for Alexa payload device– only four times as fast the speeds achieved by the typical modem. 

“With Alexa, we often work with the high bandwidth and low latency of commercial internet. But the DSN is not like broadband,” says Li. “The limited bandwidth results in long round-trip delay, and there’s a risk for packet loss.”

Establishing a Connection with Alexa in space

The DSN allocates a majority of the bandwidth to its main application, which is responsible for mission critical activities. Alexa-related communications took place on the second payload for the data pipe NASA allocated a total of 200 Kbps to the Alexa team which was shared across several components including voice commands, video channels, and data whiteboards.

The Alexa team had to carefully budget the allocated bandwidth, and ensure that communications with Alexa were as streamlined possible. Amazon’s engineers also had to minimize delays while maintaining high audio quality so that Alexa would be able to accurately detect wake words, in addition to being able to a wide variety of accents and voices. 

“We simulated the DSN in our lab environment, and focused on issues related to delay, bandwidth, and packet loss,” says Li. “We used an off-the-shelf network simulator that we configured to match the characteristics that NASA gave us.”

Li and his team examined how Alexa’s voice recognition technology worked at three bandwidths: 64 Kbps, 32 Kbps, and 16 Kbps. They brought in real people to test voice commands on each bandwidth, analyzing how Alexa responded to people of different ages, genders, and other characteristics. 

“We sent the recordings to our Alexa backend speech engineer to perform an analysis. We also gave each participant a scorecard so that they could tell us how well Alexa performed in terms of responding to their requests. We utilized the findings from these experiments to configure a solution.”

The pioneering work carried out by Amazon’s engineers and scientists technology has powerful implications for people both in space and on Earth. 

“Space is only one instance of a network-challenging environment,” says Li. 

He points to the use of Alexa being able to serve areas with low bandwidth internet: to give just a few examples, people living in rural areas, or far flung regions like mountains and deserts around the world.

“The ability to make a positive impact on the lives of people on earth and beyond– that’s what’s most meaningful for me,” he says.