# How do I combine GNSS and cellular without interference?

**URL:** <https://forum.sequans.com/t/how-do-i-combine-gnss-and-cellular-without-interference/229>\
**Category:** LTE-M / NB-IoT (Monarch)\
**Tags:** rf\
**Created:** [October 7, 2025, 7:49am UTC](https://forum.sequans.com/t/how-do-i-combine-gnss-and-cellular-without-interference/229 "2025-10-07T07:49:28Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Brian\_TK](https://dub1.discourse-cdn.com/flex018/user_avatar/forum.sequans.com/brian_tk/32/42_2.png) [@Brian\_TK](https://forum.sequans.com/u/Brian_TK)\
**Post date:** [October 7, 2025, 7:49am UTC](https://forum.sequans.com/t/how-do-i-combine-gnss-and-cellular-without-interference/229/1 "2025-10-07T07:49:28Z")

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Hello there!

Do you have any guidelines for a design that includes GNSS and LTE-M to make sure that my LTE transmission will not interfere with the reception of the GNSS signal?

Thanks in advance!

Brian

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**Author:** ![Greg](https://dub1.discourse-cdn.com/flex018/user_avatar/forum.sequans.com/greg/32/7_2.png) [@Greg](https://forum.sequans.com/u/Greg)\
**Post date:** [October 7, 2025, 1:38pm UTC](https://forum.sequans.com/t/how-do-i-combine-gnss-and-cellular-without-interference/229/2 "2025-10-07T13:38:15Z")

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Dear Brian, please find my answers below:

### **GNSS and LTE-M Coexistence: Mitigation Measures**

1. **SAW Filtering**  
As a first mitigation measure, virtually every GPS receiver integrates one or two SAW (Surface Acoustic Wave) filters in the signal path to attenuate out-of-band signals.

2. **Antenna Isolation**  
Use a dedicated GNSS antenna and maintain physical separation between antennas — as much as possible within your device’s form factor. Good antenna isolation is the most effective protection, especially against in-band interference generated by the LTE-M modem.

3. **Transmission Indicator GPIO**  
The GM02S module includes a specific GPIO pin (#9), labeled “Transmission Indicator,” which can be used to notify the GNSS chipset when LTE transmission occurs. This requires the GNSS chipset to support an anti-jamming feature based on GPIO signaling (TX blanking).

4. **LTE-M Transmission Behavior**  
LTE-M operates in HD-FDD mode and therefore does not transmit continuously, reducing the risk of persistent interference.

* * *

### **Characterizing GNSS Sensitivity Impact**

To evaluate the impact on GNSS sensitivity, you can easily perform tests using the GM02S EVK and a GNSS EVK. By using an RF combiner and coupler, you can measure the Carrier-to-Noise (C/N) degradation on satellite reception as a function of modem output power.

Recommended test scenarios:

- **Continuous TX Tone Testing**  
Transmit a continuous tone at various output power levels. This represents a worst-case scenario and does not reflect the actual HD-FDD behavior.

- **Realistic Uplink Testing**  
Test in front of a call box with a defined amount of uplink data, using several output power levels (e.g., 23 dBm, 15 dBm, 0 dBm).