• State Verified Answer
  • Replies 3 replies
  • Subscribers 74 subscribers
  • Views 1554 views
  • Users 0 members are here
Attachments (0)
Nordic Case Info
  • Case ID: 291817
Options

Impact of TX power and RSSI

TilakL

Hi,

The attached picture below captures all the RSSI of our beacons in the field. These devices were set to transmit at maximum transmit power of +4dBm. This max value was set as we wanted to maximize the coverage and we were afraid of shadowing (pathloss) problems.

Histogram of RSSI

Now we see that the battery life needs improvement and that Low Energy Power Control (LEPC) is not yet supported. Hence, with the help of your online-power profiler for BLE, +4dBm (max) results in 96uA and the default setting of 0dBm results in 88uA. This results in 8uA of average savings in current consumption.

Questions:

  1. We would like to improve the battery life of the beacons by configuring the transmit power to 0dBm. Then, how much of the RSSI can we expect to lose in the above chart? Will the expected lowest RSSI value be -85 or -80 or something else? Your input will help us configure our deployed network better.
  2. I am unable to explain why there is dip in the RSSI for values between -46 and -56. If possible, based on Nordic's experience, please help me understand why there could be a dip here at these healthy values of RSSI. Note that this is years of data.
  3. Is 0dBm the default settings for Nordic devices that is used in the products out there?
  4. Do you have any cases/scenarios where +4dBm should be used?

I would like to make an informed decision to change to 0dBm and convince my manager to make this change. Please let me know your thoughts on this.

Thanks,
Tilak

Parents
  • +1

    Hi

    First off, you shouldn't base too much off of the RSSI values you see, as these will only give an indication of what the sensitivity is, and not be very accurate. I would recommend testing that you receive the expected data at the range you're looking for instead of basing your tests off RSSI alone. As I don't know what your application/ use case is, I'm not sure what to recommend. What range is the application going to operate in, and in what kind of environment?

    1. Yes, you will get worse RSSI values when decreasing the TX power, but if you're still happy with the effective range you get at 0dBm this should be fine. The RSSI will vary a lot depending on what environment you're testing in, so I can't come with an expected RSSI number I'm afraid.

    2. I think this is just random as RSSI is not too reliable for measurement. I'm sure if you do the same test again the highs and lows will be different.

    3. I can't speak for what the customer base is using, as everyone must choose what fits their specific use case. Some use +4dBm, some use 0dBm, and some use -40dBm. By default most of our example projects are set to 0dBm at least, to give good range as well as good power consumption results.

    4. If you find that the higher dBm helps your transmissions/connection be more stable at the range you need them in, and power consumption does not matter as much, +4dBm could be a useful setting.

    Best regards,

    Simon

Reply
  • +1

    Hi

    First off, you shouldn't base too much off of the RSSI values you see, as these will only give an indication of what the sensitivity is, and not be very accurate. I would recommend testing that you receive the expected data at the range you're looking for instead of basing your tests off RSSI alone. As I don't know what your application/ use case is, I'm not sure what to recommend. What range is the application going to operate in, and in what kind of environment?

    1. Yes, you will get worse RSSI values when decreasing the TX power, but if you're still happy with the effective range you get at 0dBm this should be fine. The RSSI will vary a lot depending on what environment you're testing in, so I can't come with an expected RSSI number I'm afraid.

    2. I think this is just random as RSSI is not too reliable for measurement. I'm sure if you do the same test again the highs and lows will be different.

    3. I can't speak for what the customer base is using, as everyone must choose what fits their specific use case. Some use +4dBm, some use 0dBm, and some use -40dBm. By default most of our example projects are set to 0dBm at least, to give good range as well as good power consumption results.

    4. If you find that the higher dBm helps your transmissions/connection be more stable at the range you need them in, and power consumption does not matter as much, +4dBm could be a useful setting.

    Best regards,

    Simon

Children
  • 0 in reply to Simonr

    Thank you Simon for your detailed comments. The range is expected to be in a typical indoor environment where the assets can move and can experience shadowing effects with people moving around or constantly shadowing the line of sight communication.

    As RSSI does not seem reliable, please suggest suitable alternatives to RSSI.

  • 0 in reply to TilakL

    Do you need RSSI or something similar in your application? For testing you should set the devices up in a control environment and make sure that the packets are transmitted and received at a satisfactory success rate. Using a receiver that acknowledges and prints out the transmitted data so you can see. If you get the expected data at 0dBm TX power there's no need to use 4dBm in your application. The environment you describe shouldn't require more than 0dBm in my experience.

    Best regards,

    Simon

Related
Terms of service