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  • Case ID: 341205
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throughout sample TX power

Ziyao Zhou

Hi

I am using 4 nrf52833 DK to see the relationship with RSSI and Dara rate. I have two running the nordic uart service and print out the RSSI, they are using TX=0. And another pair is running throughput sample to test datarate. I need to make sure the TX power for both pair is identical so that the RSSI of central uart could be the RSSI for throughput sample.

Could you please advice me whether throughput TX is 0. And whether my way to test is OK?

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  • 0

    You did not mention which SDK you are using, assuming that you are using our nRF Connect SDK.

    You need to add CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL=y in your prj.conf 

    You would also need CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL=y.

    Just look at the SDK\zephyr\samples\bluetooth\hci_pwr_ctrl\src\main.c to see how it works.

    Could you please advice me whether throughput TX is 0. And whether my way to test is OK?

    Testing both test devices with TX power 0 is a good way to compare when there is another peer listening to the packets and then comparing RSSI. I cannot comment on the technical details of the experiment as I know very little technical details from your description.

  • 0 in reply to Susheel Nuguru

    Hi,

    Thank you for your reply! Yes, I am using the NCS and did not add CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL=y and CONFIG_BT_CTLR_TX_PWR_DYNAMIC_CONTROL=y. As I barely remember if there is no config the TX power will be default 0 dbm for both throughput sample and NUS sample. So I just want to confirm that two samples are both runnning with 0 dbm.

    By the way, I have check the result and found that Datarate is not sensitive to the RSSI, is it correct? Are that highly relative or not. Thank you so much for your help!

  • 0 in reply to Susheel Nuguru

    Hi,

    Thank you for your information. How about throughput sample, if no thing change it is running on TXP = 0dbm?

  • 0 in reply to Susheel Nuguru

    Hi, today I have do the test again and found different result. I am doing with 2M phy 251 bytes 320ms interval. All the environment is the same (open space). the first one is previous, the second is today's. Why they have such large difference. I have done many sets of experiments and all shows this difference

    Or do you have some materials for the relationship between RSSI and datarate.Thank you so much!

  • +1 in reply to Ziyao Zhou

    With the BLE testing, even a small variation of one in hundreds of variable can give you a difference. Even small differences in antenna positioning, reflections, or interference can affect RSSI values. 

    Was the throughput test running with exactly the same connection interval & PHY settings?

    We cannot provide a direct relationship between RSSI and data rate because throughput depends on PHY mode, interference, packet retransmissions, temperature and scheduling. I myself have done a lot of testing on this and with the DKs I was getting predictable behavior at the open space. If you see the same behavior with different DKs, then there might be some issue with the application? please log more data to see more detailed info.

    Turnon these configs in your prj.conf just for debugging

    CONFIG_BT_LOG=y
CONFIG_BT_CTLR_PROFILE_ISR
CONFIG_BT_CTLR_SCHED_ADVANCED # might need more dependencies to be enabled

    In short, it is not easy for me to analyze the environment and interference around your test setup. But this should normally have a clear repeatable results in less interference open space setups with proper antenna direction set correctly and not moving between tests.

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  • +1 in reply to Ziyao Zhou

    With the BLE testing, even a small variation of one in hundreds of variable can give you a difference. Even small differences in antenna positioning, reflections, or interference can affect RSSI values. 

    Was the throughput test running with exactly the same connection interval & PHY settings?

    We cannot provide a direct relationship between RSSI and data rate because throughput depends on PHY mode, interference, packet retransmissions, temperature and scheduling. I myself have done a lot of testing on this and with the DKs I was getting predictable behavior at the open space. If you see the same behavior with different DKs, then there might be some issue with the application? please log more data to see more detailed info.

    Turnon these configs in your prj.conf just for debugging

    CONFIG_BT_LOG=y
CONFIG_BT_CTLR_PROFILE_ISR
CONFIG_BT_CTLR_SCHED_ADVANCED # might need more dependencies to be enabled

    In short, it is not easy for me to analyze the environment and interference around your test setup. But this should normally have a clear repeatable results in less interference open space setups with proper antenna direction set correctly and not moving between tests.

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