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How are frequencies for different ITU regions handled when the satellite is in orbit?

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  • How are frequencies for different ITU regions handled when the satellite is in orbit?

    Originally there was no plan to handle or adjust frequencies to match the different ITU regions. However, we have since had communication from several organisations, including TTN, requesting that this be included. We are considering the possibility to include a GPS module and make frequency modifications to respect ITU & TTN.

  • #2
    Ave you had any success in sourcing a GPS module without COCOM limits?

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    • #3
      Yes, we have sourced GPS modules without COCOM limits. They range in price and performance. Here's a very expensive one: http://navspark.mybigcommerce.com/gp...ellite-cubesat

      Also, an interesting discussion on COCOm:
      https://space.stackexchange.com/ques...loons-and-cube

      Thoughts?

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      • #4
        Originally posted by Admin View Post
        Thoughts?
        Only that there seems to be a lot of confusion regarding cocom limits.

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        • #5
          Agreed. We've asked UK Space Agency for clarification.

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          • #6
            You asked for thoughts?

            Is gps really necessary? Don*t get me wrong, when i read, you want to add gps to the Ambasats i thought “how cool is that ”. I mean, the measurements we could do with the Ambasat are not very valuable if the location is not known.

            But when i see the effort (time, money and power consumption and also space on the pcb ), i changed my mind about a gps module on the Ambasat.

            As far as i understood the whole satellite stuff, each satellite must be trackable or must have a known location. So all of our Ambasats have to “fly” in a close formation to be processed as a single satellite. And somebody have to know its location.

            Or i am so wrong? %)


            The location of the “mothership” (the cubesat) will not be very far of the location of each Ambasat. And when its location in known it would be absolutely enough if you could provide us with this information. With a timestamp or something so we would be able to link measurement and location.

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            • #7
              Different geographical regions use different frequencies. Broadcasting in the wrong frequency is illegal. So the satellites will need to know where they are in order to switch frequencies, or to know when they are allowed the broadcast if they only use a single frequency band.

              Assuming we'll be allowed to use the ISM bands fram space (which is not yet clear I think) if we adjust frequency, the sprites will need to know when to switch frequencies. A gps could be a solution, but any other means could also be a solution.
              Last edited by mfalkvidd; 08-24-2019, 05:56 AM.

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              • #8
                Joerg, your suggestion is not something we'd considered so thank you very much for this. It certainly creates some possibilities and maybe in other areas of the project, too. As you write, the additional costs of adding the GPS, including time, effort, debugging etc is not a small undertaking. The issue we face and as mkalkvidd mentions, is the need to observe the ISM frequencies when flying over different regions. However, it is really not yet clear whether:

                a) There is international law covering the broadcast
                b) There is a real need to 'respect' these different frequencies

                It seems a bit to me like the situation a few years ago when flying - eg. All mobile phones and wifi devices must be turned off during flight due to critical interference with flight control. BUT, today we have a very different situation where there is onboard wifi available and mobile phones are no longer subject to earlier restrictions. It is the unknown that is feared...

                What we are currently doing is trying to find a definitive answer from those bodies who currently 'control' what we can do in space.

                Best regards,

                Martin.

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                • #9
                  Great that you are trying to fins definitive answers on the legal side.

                  While you get answers, let's focus on generating options for the the technical side.

                  Even if there is no legal requirement to respect the frequencies, TTN gateways will only listen on the frequency band for their region. So if we cannot switch frequency band, we should probably calculate which band would give us the best coverage.

                  We'll need an antenna that works well for the frequency band(s) we want to use.

                  If we need to switch frequency bands, we need to know when to switch. Gps on each satellite could be a solution, but as fiscussed above it might not be feasible.

                  How about putting a gps on the 3U satellite, and let the 3U satellit broadcast which frequency to use to the sprites? The sprites would have to cycle through the frequency bands until they hear the message from the 3U sat. We'd need to develop code for this, code that can coexist with the LoRaWAN stack.

                  Or maybe the 3U sat can get messages (with schedules) through its own radio link? In that case no gps would be needed. The 3U sat has a real time clock?

                  This assumes that the 3U satellite will be in proximity to the sprites during the entire lifetime though. I am not sure that's the case?
                  Last edited by mfalkvidd; 08-27-2019, 06:32 AM.

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                  • #10
                    mfalkvidd All good ideas and certainly the GPS on the 3U (as originally suggested by Joerg) seems like a good way to remove the need for a GPS on each AmbaSat-1. In fact, thinking about this logically, why not have the sprites communicate directly on a single 'low-power' channel with the 3U? The 3U effectively then becomes a LoRaWAN Gateway for the sprites and could relay sprite data using the correct regional frequency to the 'ground station' Gateways.

                    With regards to proximity, yes the 3U will be in proximity for the lifetime of the sprites.

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                    • #11
                      With the 1% duty cycle limit (at least for EU), the 3U sat will not be able to retransmit data for 200 sprites.

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                      • #12
                        Hi ladies and gents,

                        (Are there ladies in the team? )

                        I always thought (and please correct me if I'm wrong) that the sprites will all try to establish their own communication with what every gateway is available on the ground on either 868 MHz or 915 MHz.
                        This covers most parts of the world.

                        https://www.thethingsnetwork.org/art...miles-distance

                        Gerd
                        Last edited by gerdknese; 08-30-2019, 06:32 AM.

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                        • #13
                          Originally posted by mfalkvidd View Post
                          With the 1% duty cycle limit (at least for EU), the 3U sat will not be able to retransmit data for 200 sprites.
                          Hmm, we're still thinking all of this through at the moment but the 3U could transparently relay data from each sprite. The 3U could also 'store' the sprite data until it's over a particular region or until best conditions are met for transmission (eg. when not over polar regions). It could also contain properly tuned antennas with a much better chance of successful data transmissions.

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                          • #14
                            Originally posted by gerdknese View Post
                            Hi ladies and gents,

                            (Are there ladies in the team? )

                            I always thought (and please correct me if I'm wrong) that the sprites will all try to establish their own communication with what every gateway is available on the ground on either 868 MHz or 915 MHz.
                            This covers most parts of the world.

                            https://www.thethingsnetwork.org/art...miles-distance

                            Gerd
                            Hi Gerd,

                            Yes, we do have ladies on the team

                            The original intention was as you post. The problem we have is the need to respect regional frequency differences which is why the GPS was proposed. It's a costly addition for us both in price and time. Also, the current state of COCOM is not yet clear. We understand though that it is possible to request a GPS without COCOM restrictions but it may mean at a cost of $2,500 per GPS, plus other restrictions. We are still investigating...

                            Kind regards,

                            John.

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                            • #15
                              Originally posted by mfalkvidd View Post
                              With the 1% duty cycle limit (at least for EU), the 3U sat will not be able to retransmit data for 200 sprites.
                              Does the ability to transfer in different sub-bands help this situation? I'm new to this so this might be a dumb question. Is there a reason it couldn't communicate in the g3 subband and take advantage of a 10% duty cycle?

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