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Packet collision

Discussion in 'Pro/Adv Discussion' started by Controls Weenie, May 21, 2016.

  1. Controls Weenie

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    Does anyone know how DJI keeps the packets collisions from happening between the rc and the drone? It is my understanding that an antenna is shared for transmit and receiving packets between the rc and drone. With so much data being transferred both directions, how does the 2.4ghz transceivers keep from loosing data while it is transmitting? Does it use time slices?
     
  2. Phantomix

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    magic
     
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  3. Shammyh

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    Lightbridge is a combination of a "control signal" using some variety of FHSS and the "video/telemetry signal" which is likely something similar-ish to DVB-T (aka, OFDM).
     
  4. RocketBrew

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  5. AJAX-14

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    There is no such thing as a packet collision... collisions take place at the media access/physical layers when two devices try to access the carrier at the same time..... and because the video is on a single, one way, point to point connections between the bird and the ground station, there can not be any collisions.

    Uh hate to break it to you RB, but the description of WiFi and Lightbridge operations in the post is significantly flawed. Lightbridge is NOT a "broadcast" technology, it IS a unicast (point to point) data stream over WiFi using standard WIFi technologies (FHSS, ODFM, MIMO etc.). I don't know where this stuff comes from... WiFi doesn't use a handshake, neither does IP for every packet, and TCP doesn't resend video or audio segments when streaming data. He states, "WiFi hinders the goal of "real time" video, .." My my MacBook, AppleTV, iPad, and Samsung TV stream 1080P video with multichannel audio over WiFi using TCP/IP just fine without buffering or .... Reading any further in that post is pointless...
     
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  6. Controls Weenie

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    What about the following two packets that do not include video? A joystick command goes towards the drone and a drone battery status come back towards the RC. How are these two signals kept from a collision?

    Maybe my answer lies in that there are two antennas on the RC.
     
  7. AJAX-14

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    DJI uses two independent, point-to-point communications channels (remember when Lightbridge was an add-on?), one for control and one for streaming video. The control channel is duplex (bi-directional), the video is simplex (one way). It's probably easier to understand as the earlier poster phantomix states... magic.
     
    #7 AJAX-14, May 22, 2016
    Last edited: May 22, 2016
  8. Ohiowoodsman

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    Hey bud, any idea what's wrong w/ this link? l get an error
     
  9. RocketBrew

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  10. Ohiowoodsman

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