6 ms·

L5 GPS will address the multipath-in-urban-canyon problem that Uber worked on.

by c_o_n_v_e_x 4y ago

azinman2 4y ago
I don’t know much about L5. How does it do so?
- LeoPanthera 4y ago
  To oversimplify: It's on a different frequency and so will be subject to different forms of error. You can average the results of L1 and L5 to get a more accurate position.
  - skzv 4y ago
    Not just that. It's a higher frequency so the correlation peaks are more narrow and hence more easily distinguishable than L1 frequency
    - CamperBob2 4y ago
      That's not how it works at all. L5 at 1176 MHz has a different ionospheric delay than L1 at 1575 MHz. Since the timing data is identical, you can calculate and remove the ionospheric delay if you can receive both signals at once. Correlation peak width is an SNR property (and to a lesser extent dependent on receiver LO phase noise), not something that really corresponds to the RF band in use. Whichever signal is stronger (taking antenna gain into account) is the one that will yield better-quality baseband data.
      - fsh 4y ago
        L5 has a 10 times higher modulation ("chipping") rate than L1/2 which does lead to a narrower correlation peak width. However, it doesn't solve the multipath problem near tall buildings.
      - skzv 4y ago
        L5 is useful in many ways, but L5 really does produce more narrow correlation peaks than L1 as well [0] [0] https://insidegnss-com.exactdn.com/wp-content/uploads/2021/03/Fig.-10.png?strip=all&lossy=1&ssl=1 https://insidegnss-com.exactdn.com/wp-content/uploads/2021/0...
        CamperBob2 4y ago
        Yes, that's an SNR advantage due to processing gain. Works out to more or less 10 * log10(RF signal bandwidth / baseband data bandwidth) dB. They could have done something similar at L1, but that ship has pretty much sailed.
        skzv 4y ago
        I see, thanks for explaining
- skzv 4y ago
  It has a shorter wavelength so the correlation peaks are more narrow and hence more easily distinguishable. See this illustration [0] taken from this article [1] [0] https://insidegnss-com.exactdn.com/wp-content/uploads/2021/03/Fig.-10.png?strip=all&lossy=1&ssl=1 https://insidegnss-com.exactdn.com/wp-content/uploads/2021/0... [1] https://insidegnss.com/end-game-for-urban-gnss-googles-use-of-3d-building-models/ https://insidegnss.com/end-game-for-urban-gnss-googles-use-o...
FutureZeitgeist 4y ago
GekkePrutser 4y ago
It's not a perfect fix though. Even dual band multi network receivers will "jump around" a bit in deep canyons. Example: https://hikingguy.com/hiking-gear/garmin-gpsmap-66sr-review-test/ https://hikingguy.com/hiking-gear/garmin-gpsmap-66sr-review-...
- capableweb 4y ago
  Parent is talking about "urban canyons" which is just fancy wording for cities, while you're talking about actual canyons.
  - relaxing 4y ago
    It’s the same problem.
    - capableweb 4y ago
      Except the population density being different, I guess yeah.
dataflow 4y ago
If you're curious which phones support L5, check out the table linked on this page (SCROLL DOWN to "GPSTest Database" for the up-to-date table, since the first one is out of date): https://barbeau.medium.com/9be4bbb83a7b https://barbeau.medium.com/9be4bbb83a7b
ciupicri 4y ago
Also E5 Galileo [1]. It's such a shame that so few smartphones have support for dual frequency GPS and Galileo. [1]: https://gssc.esa.int/navipedia/index.php/Galileo_Signal_Plan https://gssc.esa.int/navipedia/index.php/Galileo_Signal_Plan
- sorenjan 4y ago
  Is it really so few? Snapdragon got support for dual frequency in Snapdragon 855 released in 2018. Use the GPSTest app to see if your phone supports it. https://github.com/barbeau/gpstest https://github.com/barbeau/gpstest
  - ciupicri 4y ago
    Here are a couple of phones that don't have dual frequency: - Samsung Galaxy A53 5G (https://www.gsmarena.com/samsung_galaxy_a53_5g-11268.php https://www.gsmarena.com/samsung_galaxy_a53_5g-11268.php) - Samsung Galaxy S10 (https://www.gsmarena.com/samsung_galaxy_s10_5g-9588.php https://www.gsmarena.com/samsung_galaxy_s10_5g-9588.php) - Samsung Galaxy S20 (https://www.gsmarena.com/samsung_galaxy_s20-10081.php https://www.gsmarena.com/samsung_galaxy_s20-10081.php) - Nokia G60 (https://www.gsmarena.com/nokia_g60-11826.php https://www.gsmarena.com/nokia_g60-11826.php) - Google Pixel 5 (https://www.gsmarena.com/google_pixel_5-10386.php https://www.gsmarena.com/google_pixel_5-10386.php) - Sony Xperia 10 IV (https://www.gsmarena.com/sony_xperia_10_iv-11522.php https://www.gsmarena.com/sony_xperia_10_iv-11522.php) - Apple iPhone 13 Pro (https://www.gsmarena.com/apple_iphone_13_pro-11102.php https://www.gsmarena.com/apple_iphone_13_pro-11102.php) If you want to have this feature you have to start looking at the high end models which are of course expensive. Last time I've checked only Chinese brands like Huawei, Xiaomi or Realme seem to offer it at a more affordable price range.
    - sorenjan 4y ago
      According to this list[0] some Samsung Galaxy S20 does support it, as does the Pixel 5 (and 4 and 6). Google also lists both models as having L5 support[1]. Of course the best way of knowing if your phone supports it is to test it yourself. [0] https://docs.google.com/spreadsheets/d/1jXtRCoEnnFNWj6_oFlVWflsf-b0jkfZpyhN-BXsv7uo/edit#gid=0 https://docs.google.com/spreadsheets/d/1jXtRCoEnnFNWj6_oFlVW... [1] https://developer.android.com/guide/topics/sensors/gnss.html#supported-devices https://developer.android.com/guide/topics/sensors/gnss.html...

L5 GPS will address the multipath-in-urban-canyon problem that Uber worked on.

azinman2 4y ago

I don’t know much about L5. How does it do so?

LeoPanthera 4y ago
To oversimplify: It's on a different frequency and so will be subject to different forms of error. You can average the results of L1 and L5 to get a more accurate position.
- skzv 4y ago
  Not just that. It's a higher frequency so the correlation peaks are more narrow and hence more easily distinguishable than L1 frequency
  - CamperBob2 4y ago
    That's not how it works at all. L5 at 1176 MHz has a different ionospheric delay than L1 at 1575 MHz. Since the timing data is identical, you can calculate and remove the ionospheric delay if you can receive both signals at once. Correlation peak width is an SNR property (and to a lesser extent dependent on receiver LO phase noise), not something that really corresponds to the RF band in use. Whichever signal is stronger (taking antenna gain into account) is the one that will yield better-quality baseband data.
    - fsh 4y ago
      L5 has a 10 times higher modulation ("chipping") rate than L1/2 which does lead to a narrower correlation peak width. However, it doesn't solve the multipath problem near tall buildings.
    - skzv 4y ago
      L5 is useful in many ways, but L5 really does produce more narrow correlation peaks than L1 as well [0] [0] https://insidegnss-com.exactdn.com/wp-content/uploads/2021/03/Fig.-10.png?strip=all&lossy=1&ssl=1 https://insidegnss-com.exactdn.com/wp-content/uploads/2021/0...
      - CamperBob2 4y ago
        Yes, that's an SNR advantage due to processing gain. Works out to more or less 10 * log10(RF signal bandwidth / baseband data bandwidth) dB. They could have done something similar at L1, but that ship has pretty much sailed.
        skzv 4y ago
        I see, thanks for explaining
skzv 4y ago
It has a shorter wavelength so the correlation peaks are more narrow and hence more easily distinguishable. See this illustration [0] taken from this article [1] [0] https://insidegnss-com.exactdn.com/wp-content/uploads/2021/03/Fig.-10.png?strip=all&lossy=1&ssl=1 https://insidegnss-com.exactdn.com/wp-content/uploads/2021/0... [1] https://insidegnss.com/end-game-for-urban-gnss-googles-use-of-3d-building-models/ https://insidegnss.com/end-game-for-urban-gnss-googles-use-o...

FutureZeitgeist 4y ago

GekkePrutser 4y ago

It's not a perfect fix though. Even dual band multi network receivers will "jump around" a bit in deep canyons. Example: https://hikingguy.com/hiking-gear/garmin-gpsmap-66sr-review-test/ https://hikingguy.com/hiking-gear/garmin-gpsmap-66sr-review-...

capableweb 4y ago
Parent is talking about "urban canyons" which is just fancy wording for cities, while you're talking about actual canyons.
- relaxing 4y ago
  It’s the same problem.
  - capableweb 4y ago
    Except the population density being different, I guess yeah.

dataflow 4y ago

If you're curious which phones support L5, check out the table linked on this page (SCROLL DOWN to "GPSTest Database" for the up-to-date table, since the first one is out of date): https://barbeau.medium.com/9be4bbb83a7b https://barbeau.medium.com/9be4bbb83a7b

ciupicri 4y ago

Also E5 Galileo [1]. It's such a shame that so few smartphones have support for dual frequency GPS and Galileo. [1]: https://gssc.esa.int/navipedia/index.php/Galileo_Signal_Plan https://gssc.esa.int/navipedia/index.php/Galileo_Signal_Plan

sorenjan 4y ago
Is it really so few? Snapdragon got support for dual frequency in Snapdragon 855 released in 2018. Use the GPSTest app to see if your phone supports it. https://github.com/barbeau/gpstest https://github.com/barbeau/gpstest
- ciupicri 4y ago
  Here are a couple of phones that don't have dual frequency: - Samsung Galaxy A53 5G (https://www.gsmarena.com/samsung_galaxy_a53_5g-11268.php https://www.gsmarena.com/samsung_galaxy_a53_5g-11268.php) - Samsung Galaxy S10 (https://www.gsmarena.com/samsung_galaxy_s10_5g-9588.php https://www.gsmarena.com/samsung_galaxy_s10_5g-9588.php) - Samsung Galaxy S20 (https://www.gsmarena.com/samsung_galaxy_s20-10081.php https://www.gsmarena.com/samsung_galaxy_s20-10081.php) - Nokia G60 (https://www.gsmarena.com/nokia_g60-11826.php https://www.gsmarena.com/nokia_g60-11826.php) - Google Pixel 5 (https://www.gsmarena.com/google_pixel_5-10386.php https://www.gsmarena.com/google_pixel_5-10386.php) - Sony Xperia 10 IV (https://www.gsmarena.com/sony_xperia_10_iv-11522.php https://www.gsmarena.com/sony_xperia_10_iv-11522.php) - Apple iPhone 13 Pro (https://www.gsmarena.com/apple_iphone_13_pro-11102.php https://www.gsmarena.com/apple_iphone_13_pro-11102.php) If you want to have this feature you have to start looking at the high end models which are of course expensive. Last time I've checked only Chinese brands like Huawei, Xiaomi or Realme seem to offer it at a more affordable price range.
  - sorenjan 4y ago
    According to this list[0] some Samsung Galaxy S20 does support it, as does the Pixel 5 (and 4 and 6). Google also lists both models as having L5 support[1]. Of course the best way of knowing if your phone supports it is to test it yourself. [0] https://docs.google.com/spreadsheets/d/1jXtRCoEnnFNWj6_oFlVWflsf-b0jkfZpyhN-BXsv7uo/edit#gid=0 https://docs.google.com/spreadsheets/d/1jXtRCoEnnFNWj6_oFlVW... [1] https://developer.android.com/guide/topics/sensors/gnss.html#supported-devices https://developer.android.com/guide/topics/sensors/gnss.html...