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doc:lps:twr-tdma [2017-07-18 15:39]
arnaud [Abstract]
doc:lps:twr-tdma [2018-10-19 07:24] (current)
arnaud
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 ====== TWR-TDMA ====== ====== TWR-TDMA ======
 +
 +<WRAP center round important>​
 +**Note**: TWR-TDMA is now considered obsolete and replaced by the TDoA modes. TDoA will generally have better performance than TWR-TDMA, TWR might still be useful to you though but if you are setting up a single room system TDoA is most likely the way to go.
 +</​WRAP>​
 +
  
 ===== Abstract ===== ===== Abstract =====
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 The disadvantage is that the tag has to actively send packets, it means that two tag cannot range at the same time and so some synchronization mechanism has to be put in place to allow multiple tag to use TWR measurement concurrently. The disadvantage is that the tag has to actively send packets, it means that two tag cannot range at the same time and so some synchronization mechanism has to be put in place to allow multiple tag to use TWR measurement concurrently.
  
-TWR-TDMA is implementing this concurrent mode using a Time Division Multiple Access algorithm. To do so, we define a time slot width and number of time slot for the system. Each tag is assigned a time slot and is only allowed to communicate in its assigned time slot. All the tags are synchronized on the Anchor 0 clock, they use it to calculate the position, in time, of the time slots.+TWR-TDMA is implementing this concurrent mode using a Time Division Multiple Access algorithm. To do so, we define a time slot width and number of time slot per frame. Each tag is assigned a time slot and is only allowed to communicate in its assigned time slot. All the tags are synchronized on the Anchor 0 clock, they use it to calculate the position, in time, of the time slots.
  
 ===== Compiling Crazyflie for TWR-TDMA ranging ===== ===== Compiling Crazyflie for TWR-TDMA ranging =====
  
 In order to activate TWR-TDMA, you need to recompile the Crazyflie firmware. Add the following to '​tools/​make/​config.mk':​ In order to activate TWR-TDMA, you need to recompile the Crazyflie firmware. Add the following to '​tools/​make/​config.mk':​
-<​code>​+<​code ​make>
 LPS_TDMA_ENABLE=1 LPS_TDMA_ENABLE=1
 CFLAGS += -DTDMA_NSLOTS_BITS=1 CFLAGS += -DTDMA_NSLOTS_BITS=1
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   * **LPS_TDMA_ENABLE=1** Enable the TDMA mode for TWR   * **LPS_TDMA_ENABLE=1** Enable the TDMA mode for TWR
-  * **TDMA_NSLOTS_BITS=1** Configures 2 time slot (good for 2 tags). The number of time slot is 2^TDMA_NSLOTS_BITS +  * **TDMA_NSLOTS_BITS=1** Configures 2 time slot (good for 2 tags) per frame. The number of time slot per frame is 2^TDMA_NSLOTS_BITS 
-  * **TDMA_SLOT** Optionally hardcode the time slot. See bellow for time slot auto-configuration.+  * **TDMA_SLOT** Optionally hardcode the time slot. See bellow for time slot auto-configuration
  
 ===== Configuring time slots ===== ===== Configuring time slots =====
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 ===== System performance ===== ===== System performance =====
  
-TWR-TDMA is currently implemented with time slots of 4ms. Each time slot is used by one tag to range with one anchor. This means that the ranging rate is of //1/(0.004 * (2^TDMA_NSLOTS_BITS)//​ and the rate of update of the full system is //1/(0.004 * (2^TDMA_NSLOTS_BITS* nAnchors)// where nAnchors is the number of anchors in the system.+TWR-TDMA is currently implemented with time slots of 4ms. Each time slot is used by one tag to range with one anchor. This means that the ranging rate is of //1/(0.004 * 2^TDMA_NSLOTS_BITS)//​ and the rate of update of the full system is //1/(0.004 * 2^TDMA_NSLOTS_BITS * nAnchors)// where nAnchors is the number of anchors in the system.
  
-The more timeslots, the less often measurements can be used to estimate the tag position and so the performance of the position estimate will deteriorate. For a great number of tag the [[doc:​lps:​tdoa|TDoA]] mode is better suited.+The more timeslots ​per frame, the less often measurements can be used to estimate the tag position and so the performance of the position estimate will deteriorate. For a great number of tag the [[doc:​lps:​tdoa|TDoA]] mode is better suited.
doc/lps/twr-tdma.1500385147.txt.gz · Last modified: 2017-07-18 15:39 by arnaud