Why Does NASA Claim 10-100x Better Bandwidth from Optical Communications?

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In summary, NASA claims that optical communications can achieve 10-100 times better bandwidth compared to traditional radio frequency systems due to the higher data transmission capacity of light. This technology utilizes lasers to send information, allowing for greater data rates and improved efficiency in space communications. The advancements in optical technology promise to enhance the volume and speed of data transfer, which is crucial for future space missions and scientific research.
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berkeman
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The DSOC (deep-space optical communication) experiment on the Psyche spacecraft had a successful test (even though the test distance was mouse nuts, IMO):

https://www.nasa.gov/directorates/s...bout-nasas-deep-space-optical-communications/

But NASA seems to be suggesting that optical comm has a 10x to 100x better bandwidth for deep-space comms compared to traditional RF comms. I have not been able to figure out where this improvement is coming from given the articles by NASA and in the popular press. Does anybody have links to where this improvement is coming from? Is it because of a lower noise floor at those optical wavelengths (NIR), or maybe higher directivity or something else?

Thanks for any insights...
 
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  • #2
I think it is the usual difference between an analog and a digital signal. I have found an example for phone frequencies: ~3kHz versus 100kBits/s = 100kHz for VoIP, which gives a factor of 30.
 
  • #4
DaveE said:
Higher carrier frequency means more modulation BW typically. Like how the internet runs better on fiber optics than cables.

https://www.ll.mit.edu/r-d/projects/terabyte-infrared-delivery-tbird
Good point, but the noise floor in optical fiber is very low. Is the noise floor in the NIR way lower than the RF bands they are currently using for satellite probe comms?
 
  • #5
Sorry, link to Quora didn't work, for whatever reason, so it has to be a picture:

1701128360097.png
Here are the data from the lunar test:
https://www.nasa.gov/mission/lunar-laser-communications-demonstration-llcd/
 
  • #6
It may be due to the size of the remote antenna, measured in wavelengths.
 
  • #7
berkeman said:
Good point, but the noise floor in optical fiber is very low. Is the noise floor in the NIR way lower than the RF bands they are currently using for satellite probe comms?
IDK. It's really about SNR of the recovered signal though. More noise can be fixed by more source power. Absorption is also a thing; what about clouds and such. It's also about the filtering and detection functions at the receiver front end. It's hard to find good comparative data since they each live in their own silos.

From mostly unrelated laser comm work I was a bit involved with; you might be surprised at how far a bright laser can travel through "stuff" and still be detected.
 
  • #8
It's frustrating to me that NASA didn't link to more technical artices...
 
  • #10
Baluncore said:
It may be due to the size of the remote antenna, measured in wavelengths.

Transmitting antenna large in terms of wavelengths --> Narrow transmit beam --> Less spread of energy --> More energy picked up by receiver.

Given a certain area, the receiving antenna intercepts the same amount of energy, irrespective of the wavelength. (The transmit antenna produces a certain flux density around the receiver, and that's it).

However, engineering formulas often contain a "receiving antenna gain" but this doesn't reflect anything physically going on, but rather is a side effect of the way gain was historically defined.
 
  • #12
Swamp Thing said:
Given a certain area, the receiving antenna intercepts the same amount of energy, irrespective of the wavelength.
That is misleading. It assumes the incident energy density is the same at RF as at optical wavelengths.

The optical wavelength employed is so much shorter than the RF wavelength, that the beam widths are much narrower for optical systems than for manageable RF antennas.
Optical transmission has a narrower beam, so produces a higher Effective Incident Radiated Power at the receive-antenna, which also has a narrower beam, so captures less noise through the unnecessary sides of the beam, noise that would otherwise enter the receiver and signal processor. Both those effects improve the signal-to-noise ratio, and both are due to the size of the antenna, measured in wavelengths.
Now is the decade of optical communications.
 
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  • #13
fresh_42 said:
https://www.nasa.gov/wp-content/uploads/2015/03/tglavich_dsoc.pdf

Considering more details: there might be patents involved.
Good point. I didn't find any info on the modulation scheme, other than that they were "counting photons" at that distance. Does that mean OOK (on-off keying)? It did mention 1kbit/s, but I don't know if that is 100x what RF comms is at those distances, or just starting out at slow datarates as a proof of concept for the optical comms...
 
  • #14
They first tested it with the moon. I found dozens of papers about LLOC (Lunar Laser Optical Communication) by a Google (scholar) search, e.g. https://arc.aiaa.org/doi/pdf/10.2514/6.2014-1685.

Searching for DSOC also produces a lot of hits, e.g. https://www.spiedigitallibrary.org/...ons-DSOC-transceiver/10.1117/12.2256001.short.

However, as has been said already,
DaveE said:
Yes, but soooo much stuff on google scholar.
I cannot assess whether and where the information you're looking for is hidden.
 
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  • #15
fresh_42 said:
e.g. https://arc.aiaa.org/doi/pdf/10.2514/6.2014-1685.
Thanks!
Prior to transmission, the data are encoded using a ½-rate serially concatenated turbo code8. The
encoded data are modulated using 16-ary pulse position modulation (PPM). The resulting symbols are interleaved with a ~1-second convolutional channel interleaver prior to being amplified to a nominal 0.5-W for transmission on the optical downlink. The combination of this powerful forward error correction code with channel interleaving
enables reliable error-free communication through the turbulent Earth atmosphere with >1 received bit per detected photon,
 

FAQ: Why Does NASA Claim 10-100x Better Bandwidth from Optical Communications?

What is DSOC and why is it significant for NASA's communication systems?

DSOC stands for Deep Space Optical Communications. It is significant because it uses laser-based technology to transmit data, which allows for much higher bandwidth compared to traditional radio frequency (RF) communications. This increased bandwidth is crucial for transmitting high-resolution images, videos, and large volumes of scientific data from distant space missions back to Earth.

How does optical communication achieve 10-100 times better bandwidth performance compared to RF?

Optical communication uses lasers to transmit data via light waves, which have much higher frequencies than the radio waves used in RF communication. Higher frequency waves can carry more data per second, resulting in significantly higher bandwidth. Additionally, optical systems can focus the transmission beam more precisely, reducing signal loss and allowing for more efficient data transfer.

What are the technical challenges associated with implementing DSOC?

Implementing DSOC comes with several technical challenges, including the need for precise alignment between the transmitter and receiver due to the narrow beam of laser communication. Atmospheric interference, such as clouds and turbulence, can also affect signal quality. Additionally, developing and deploying the necessary ground and space-based infrastructure to support optical communication is complex and costly.

How will DSOC impact future space missions?

DSOC will have a significant impact on future space missions by enabling the transmission of larger volumes of data more quickly. This will enhance scientific research and exploration by providing higher-resolution images and more detailed data from distant planets, moons, and other celestial bodies. It will also improve communication with spacecraft, allowing for better mission control and real-time decision-making.

When can we expect DSOC to become operational in NASA missions?

NASA has been testing DSOC technology through various projects and demonstrations. While there isn't a specific timeline for when DSOC will become fully operational, it is expected to be integrated into upcoming missions within the next decade. Continuous advancements and successful demonstrations will pave the way for its widespread adoption in future space exploration efforts.

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