5 ms·

Demodulation of the LTE uplink

123 points by picture 5y ago

dboreham 5y ago
Very nice example of math in a web page!
kevmo314 5y ago
I've never read so many words and understood so few of them. This is some really complex stuff, kudos to the author for this deep dive, it clearly took a lot of work.
- deleted 5y ago
  [deleted]
- Reventlov 5y ago
  >This is some really complex stuff No that's just I and Qs ! (sorry couldn't resist)
birdyrooster 5y ago
I couldn’t recreate the work of this single page in my entire life. Very cool work.
- drmpeg 5y ago
  Dani is definitely smarter than the average bear. Also, I believe English is a second language for him.
- oh_sigh 5y ago
  Not to diminish the very cool work of the author - I'd bet you $1,000,000 you could understand this work with 3 years of dedicated study or 10 years of passionate part-time study.
  - drmpeg 5y ago
    Software Defined Radio is a pretty steep learning curve. You need to know about RF, digital signal processing, math, software and computers all at the same time. On the GNU Radio Matrix server, we see Masters and Ph.D students have a difficult time with at least one of the above all the time. The most successful SDR hackers usually have a ham radio background.
bjt2n3904 5y ago
Daniel also did a really fun write up decoding data from the JWST.
londons_explore 5y ago
I think it's really sad that there is no readily available LTE wireshark... I should be able to put any phone into 'monitor mode' and dump all LTE cell data that flows past. And then I should be able to decrypt my own data by getting keys out of my test phone - which should be a thing any phone owner can do through a debug menu. Why doesn't such tooling exist?
- fragmede 5y ago
  Basebands are very much still closed proprietary mostly black boxes, with DMA access to your phone. Such a thing doesn't exist because it's not in test equipment suppliers interests to undercut their existing market so thoroughly, where they'd rather sell you an analyzer that costs the same as a car. Combined with how patent encumbered LTE is in the US, there's only a slim chance of seeing such a thing.
  - xxpor 5y ago
    That's an interesting point. Thinking about the timing, how much of the 5G push is due to LTE patents getting ready to expire?
    - nfriedly 5y ago
      I'm sure that plays a part, but I think the primary reason for the 5G push is better spectrum utilization. (And marketing is probably a close second.)
      - deleted 5y ago
        [deleted]
    - g_p 5y ago
      There's a new "G" every ten-ish years. Usually there is a lot of hype in the 2 to 3 years before the next G launches, at which point the early release standards are frozen. If equipment has a nominal 5 year replacement span, you deploy early release equipment, then at the half-way point, replace it with newer eqiupment, while looking for the next "G". The "G"s are driven by marketing and hype - "5G" is better than "4G" and promises a pile of use-cases that haven't materialised. It's pointless even trying to dispel the hype. 1ms latency was heralded, 10 Gbit throughput, etc etc. You can't really do a round-trip measured to the radio (across just the air interface) yet with 1ms latency, let alone 1ms to anywhere meaningful. I'm reminded of Carmack's famous statement [0] about latency. ARPU (average revenue per user) is not going up, at least in the European markets I'm aware of. Customers were not willing to pay more for 4G or 5G. In fact, I think many are ending up paying less - I negotiated a better deal this time around than last time around (anecdote, n=1, but far from alone) - competition is tight in a 4-operator market. I don't think patents are necessarily driving the push - the push comes from operators competing to win churn from rivals. This comes from a race to the bottom on price. As soon as someone has "5G", everyone needs it, whether it's really 5G, or just 4G with the string changed on the screen [1]. "Another G" helps drive sales, and coverage helps drive sales. The operators drive the market, as they own the relationship with the customer. Vendors sell whatever operators want, and try to help them make a more compelling differentiated product (which is a dumb pipe now...) - they have fought over "fastest" and "coverage", now they are fighting over "lowest latency" and "best experience" and "most reliable"... Ultimately, LTE is going nowhere fast, in my view. It varies by market, but will still be the underlying dominant tech for a few more years - unless you are on T Mobile USA or one of a few other carriers, your 5G is "non-standalone" and fully reliant on the 4G network and radios - the 5G cell is carrier-aggregated in as extra capacity. In early systems, uplink was only over 4G, so the only place the 5G radio was used for was downlink. Therefore I'm not convinced it's really patents that drive this, rather marketing and attempts to differentiate and sell to win over others' churn in a reasonably competitive marketplace with limited barriers to switching, and huge cross/up-sell opportunity when you do win a customer. [0] https://twitter.com/id_aa_carmack/status/193480622533120001 https://twitter.com/id_aa_carmack/status/193480622533120001 [1] https://www.xda-developers.com/att-fake-5ge-icon-added-aosp/ https://www.xda-developers.com/att-fake-5ge-icon-added-aosp/
krazerlasers 5y ago
Absolutely amazing writeup, and I love that he released the work in jupyter notebook format (which is rendered perfectly by github no less) which only needs numpy and matplotlib so basically anyone can dig in and start messing with it with minimal effort. I wish more SDR projects were documented in this form, it is so much more accessible than gnuradio or matlab etc based projects (albeit, these don't run in realtime so it is a bit different usecase than the gnuradio ecosystem).

123 points by picture 5y ago

Very nice example of math in a web page!

I've never read so many words and understood so few of them. This is some really complex stuff, kudos to the author for this deep dive, it clearly took a lot of work.

deleted 5y ago
[deleted]
Reventlov 5y ago
>This is some really complex stuff No that's just I and Qs ! (sorry couldn't resist)

birdyrooster 5y ago

I couldn’t recreate the work of this single page in my entire life. Very cool work.

drmpeg 5y ago
Dani is definitely smarter than the average bear. Also, I believe English is a second language for him.
oh_sigh 5y ago
Not to diminish the very cool work of the author - I'd bet you $1,000,000 you could understand this work with 3 years of dedicated study or 10 years of passionate part-time study.
- drmpeg 5y ago
  Software Defined Radio is a pretty steep learning curve. You need to know about RF, digital signal processing, math, software and computers all at the same time. On the GNU Radio Matrix server, we see Masters and Ph.D students have a difficult time with at least one of the above all the time. The most successful SDR hackers usually have a ham radio background.

bjt2n3904 5y ago

Daniel also did a really fun write up decoding data from the JWST.

londons_explore 5y ago

I think it's really sad that there is no readily available LTE wireshark... I should be able to put any phone into 'monitor mode' and dump all LTE cell data that flows past. And then I should be able to decrypt my own data by getting keys out of my test phone - which should be a thing any phone owner can do through a debug menu. Why doesn't such tooling exist?

fragmede 5y ago
Basebands are very much still closed proprietary mostly black boxes, with DMA access to your phone. Such a thing doesn't exist because it's not in test equipment suppliers interests to undercut their existing market so thoroughly, where they'd rather sell you an analyzer that costs the same as a car. Combined with how patent encumbered LTE is in the US, there's only a slim chance of seeing such a thing.
- xxpor 5y ago
  That's an interesting point. Thinking about the timing, how much of the 5G push is due to LTE patents getting ready to expire?
  - nfriedly 5y ago
    I'm sure that plays a part, but I think the primary reason for the 5G push is better spectrum utilization. (And marketing is probably a close second.)
    - deleted 5y ago
      [deleted]
  - g_p 5y ago
    There's a new "G" every ten-ish years. Usually there is a lot of hype in the 2 to 3 years before the next G launches, at which point the early release standards are frozen. If equipment has a nominal 5 year replacement span, you deploy early release equipment, then at the half-way point, replace it with newer eqiupment, while looking for the next "G". The "G"s are driven by marketing and hype - "5G" is better than "4G" and promises a pile of use-cases that haven't materialised. It's pointless even trying to dispel the hype. 1ms latency was heralded, 10 Gbit throughput, etc etc. You can't really do a round-trip measured to the radio (across just the air interface) yet with 1ms latency, let alone 1ms to anywhere meaningful. I'm reminded of Carmack's famous statement [0] about latency. ARPU (average revenue per user) is not going up, at least in the European markets I'm aware of. Customers were not willing to pay more for 4G or 5G. In fact, I think many are ending up paying less - I negotiated a better deal this time around than last time around (anecdote, n=1, but far from alone) - competition is tight in a 4-operator market. I don't think patents are necessarily driving the push - the push comes from operators competing to win churn from rivals. This comes from a race to the bottom on price. As soon as someone has "5G", everyone needs it, whether it's really 5G, or just 4G with the string changed on the screen [1]. "Another G" helps drive sales, and coverage helps drive sales. The operators drive the market, as they own the relationship with the customer. Vendors sell whatever operators want, and try to help them make a more compelling differentiated product (which is a dumb pipe now...) - they have fought over "fastest" and "coverage", now they are fighting over "lowest latency" and "best experience" and "most reliable"... Ultimately, LTE is going nowhere fast, in my view. It varies by market, but will still be the underlying dominant tech for a few more years - unless you are on T Mobile USA or one of a few other carriers, your 5G is "non-standalone" and fully reliant on the 4G network and radios - the 5G cell is carrier-aggregated in as extra capacity. In early systems, uplink was only over 4G, so the only place the 5G radio was used for was downlink. Therefore I'm not convinced it's really patents that drive this, rather marketing and attempts to differentiate and sell to win over others' churn in a reasonably competitive marketplace with limited barriers to switching, and huge cross/up-sell opportunity when you do win a customer. [0] https://twitter.com/id_aa_carmack/status/193480622533120001 https://twitter.com/id_aa_carmack/status/193480622533120001 [1] https://www.xda-developers.com/att-fake-5ge-icon-added-aosp/ https://www.xda-developers.com/att-fake-5ge-icon-added-aosp/

krazerlasers 5y ago

Absolutely amazing writeup, and I love that he released the work in jupyter notebook format (which is rendered perfectly by github no less) which only needs numpy and matplotlib so basically anyone can dig in and start messing with it with minimal effort. I wish more SDR projects were documented in this form, it is so much more accessible than gnuradio or matlab etc based projects (albeit, these don't run in realtime so it is a bit different usecase than the gnuradio ecosystem).