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Investigating Bluetooth® Signal Strength (RSSI) in Noxturnal


Noxturnal now features a Received Signal Strength Indicator (RSSI) signal that allows users to check the quality of the Bluetooth® connection between the Nox A1s and Nox C1 during an online recording. Users can download a Noxturnal Sheet with the RSSI Signal already prepared, or create their own RSSI sheet. Aim for an RSSI between -40dB and -60dB range to reduce issues with Bluetooth transmission, and use the tool to determine if the connection between the Nox A1s and Nox C1 is the cause of any issues during an Online Recording. This feature requires Nox A1s firmware 3.0.6 or greater.


Received Signal Strength Indicator (RSSI)

Received Signal Strength Indicator (RSSI) is a measurement of the power present in a received radio signal. It is commonly used in wireless communication systems, such as Bluetooth, to estimate the distance between the transmitter and receiver, as well as to determine the quality of the received signal.

RSSI is typically measured in decibels (dB), and is normally reported as a negative value, indicating the strength of the received signal relative to a reference level. The reference level can vary depending on the system and the type of signal being measured.

Its ability to provide a rough estimate of signal strength and distance can help improve the reliability and performance of systems that utilize wireless transmission.


Adding the RSSI Signal to Noxturnal

Importing a pre-configured signal sheet:

You can download a Noxturnal Sheet with the RSSI Signal already prepared as an attachment below this support article. Download the sheet and import the .ndb file into Noxturnal using the Import settings (Tools - Import/Export Settings...). Now you can add the RSSI as an individual sheet during live recordings and when reviewing PSG data within Noxturnal as shown in the picture below.

Manually create a signal sheet

It is also possible to create your own RSSI sheet in Noxturnal with the steps below: 

  1. Navigate to the Workspace tab
  2. Find the Add Sheet option
  3. Add an Empty Sheet.

This will add an empty sheet to the current workspace layout.

From here go to the signals inspector menu on the right (1) of the window and locate or search for RSSI (2) to add the signal to the empty sheet (3).

The signal properties can be adjusted as below:

How to use the RSSI Signal with Noxturnal and the Nox A1s and Nox C1s

As mentioned in the introduction about RSSI, think about this signal as providing a rough estimate of the strength and reliability of the Bluetooth transmission between the Nox A1s and Nox C1. As mentioned, the values are negative, and can be considered a comparison of the signal strength from when it left the Nox A1s to when it was received by the Nox C1.

The Nox Medical team have done testing that shows that a theoretical optimal RSSI is around -30db (when the Nox A1s is next to the Nox C1). This can be seen in the screenshot below at point 2. This is not practical for the sleep laboratory setup so testing was also done on the optimal setup in relation to a real-world environment. The RSSI should aim for a signal around -60db (point 3 and 4) when determining the position of the Nox C1 in the room relative to the patient. Our testing shows that this provides a buffer for when the system is used with a patient. Our testing also shows that at RSSI less than -80dB (remember it’s negative!), the connection between the Nox A1s and Nox C1 will become less stable and result in a loss of connection. Always aim for a RSSI around the -60dB range to reduce issues with Bluetooth transmission.

The strength of the Bluetooth transmission between the Nox A1s and Nox C1 can be impacted by many factors. Refer to the optimal Bluetooth transmission guide for steps on how to improve the connection between the Nox A1s and Nox C1. Use the RSSI signal to test the placement of the Nox C1 in relation to the Nox A1s to find the optimal location. The RSSI signal will provide the information required to correctly place the Nox C1 and to ensure that external factors are not impacting the Bluetooth transmission. Testing the position while running an online study is optimal to see the best position during live acquisition.


*Please note that not all features or all products are available in all markets. Our products are medical devices and subject to registration/approval in each market area. For more information on product availability please contact

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