The threat from LTE (4G) to 868MHz alarm systems

With a conservative figure of 33 million 868MHz receivers in situ, there’s a growing concern over the impact of 4G (LTE) and “Out Of Band” (OOB) interference.

Ofcom (UK) issued a consultation document [i.55] on the technical parameters for alarms.  

In this they acknowledge the threat to alarms, but propose to do nothing to mitigate it. Instead they suggest ([i.55], paragraph 3.13) that alarm manufacturers provide their own solutions “such as ensuring alarms use more robust signalling mechanisms”.

Improved signalling for Alarm systems?

Clearly, some products are more robust than others, like those using spread spectrum frequency hopping and systems that use line powered repeaters like the EE5000 from Inovonics

It is worth considering just how much improvement is needed. In practice, the minimum separation distance that could be enforced between an alarm receiver and a LTE TS is 5 m. A handset at that range would put -75 dBm into the input of a typical alarm receiver. In order to continue operating as before, the alarm system would have to improve by 45 dB, or become 32 000 times “more robust”.

Possible impact on equipment?

Missed alarm messages due to receivers being flooded with RF above signal level

Intermittent jam detection notification

Increased battery consumption on 2-way devices due to the receiver being “woken” and/or transmitter re-transmitting due to missed acknowledgment/handshake  

Possible solutions?

Move! Ofcom have proposed the use of 915-921 MHz within Europe to address the problem, this has clear benefits including cost reductions where a product has global reach i.e. aligns with the USA. The IoT (Internet of Things) may be the next step, 2.4GHz, this has true global reach, Samsung have just release their complete home security home automation system (See Smart Home) based around 2.4 GHz. Re visit products based on 433Mhz?   


The problem is only likely to get worse as greater adoption of 4G phones, 4G dongles and 4G routers take hold, sensitive 868MHz SRD and 800MHz 4G user equipment are totally incompatible when operated within tens of metres, in some cases hundreds of metres of one another, Ofcom report  confirms its official!

Scroll to Top