Hello,
I am facing an RF interference problem involving two completely independent wireless systems operating at 433.92 MHz.

System 1:
- Wireless sensor network
- Sensor nodes communicate with an LCU
- Frequency: 433.92 MHz

System 2:
- Independent third-party transmitter/receiver system
- Frequency: 433.92 MHz

Both systems use different:
- RF modules
- Modulation
- Data rates
- Packet formats
- Protocols
- Addressing
- Firmware

There is no communication relationship between the two systems.

Observed behavior:
1. Both systems work normally when operated independently.
2. When brought close together, communication starts degrading.
3. When both systems transmit simultaneously, packet reception becomes unreliable.
4. If System 1 has higher TX power than System 2, System 2's receiver may fail to receive packets from its own transmitter.
5. Even if System 1 has higher TX power, if System 2 has two transmitters operating, System 1 can also experience packet loss/degradation.

My questions are:

1. What is the main RF mechanism causing this?
2. Is this co-channel interference, receiver blocking, desensitization, near-far effect, receiver saturation, or something else?
3. Why can different modulation/protocol systems still interfere when operating at the same 433.92 MHz frequency?
4. What practical RF/hardware/firmware techniques can be used to allow these independent systems to operate close to each other reliably?
5. Is it possible to solve this without changing the 433.92 MHz operating frequency?

Any technical explanation, practical experience, application notes, or references would be appreciated.

Thank you.

 

If both signals are narrowband, then they will strongly interfere. Effectively, each is acting like a barrage jammer.

Imagine that there is an AM and and FM transmitter that are transmitting on the same frequency. Now imagine that, at a point where the power from each is comparable, we place two receivers, one for each signal. Both signals will be heavily degraded, though the FM signal will suffer less than the AM signal (which will almost certainly be completely unintelligible) with comparable power.

The general solution is to use some form of spread spectrum so that the effective noise presented by the "wrong" transmitter appears as very low noise when the received signal is despread.