It’s quite common for new wireless user equipment (UE) devices to support multiple radio transceivers. For example, a single UE device may support LTE, WiFi, Bluetooth, and GNSS. This makes it challenging to prevent coexistence interference between different co-located radio transceivers.

Figure 1 shows an example of such a situation.

Figure 1: Coexistence interference in a UE device supporting LTE, GPS, and WiFi

This blog post describes some of potential solutions for coexistence interference. For more information, I encourage you to look at 3GPP’s technical report

[1] on the subject.

Frequency Division Multiplexing (FDM)

The basic idea is to shift LTE or ISM signals away from an interfering band via the frequency domain. This can be done by performing inter-frequency handover within E-UTRAN or by removing secondary cells (SCells) from the set of serving cells.

Figure 2: Moving LTE signal away from ISM band

Figure 2: Moving LTE signal away from ISM band

Time Division Multiplexing (TDM)

The basic idea is shown in Figure 3. This solution relies on avoiding the overlapping of signal transmission in the time domain. In LTE, a discontinuous reception (DRX) mechanism can provide TDM patterns for the scheduling of  LTE transmissions.

Figure 3: Time division multiplexing for coexistence interference avoidance.

Figure 3: Time division multiplexing for coexistence interference avoidance. 

LTE and ISM Power control

This solution relies on reducing the power of the transmitting signal (LTE or ISM) in order to mitigate interference on the other receivers.

Figure 4: LTE power control for coexistence interference mitigation

Figure 4: LTE power control for coexistence interference mitigation

Furthermore, in some cases the UE can autonomously deny ISM transmission in order to protect important LTE signaling (e.g. RRC connection configuration).

In-device coexistance development platforms

In one of our previous blog posts, we showed how the PicoSDR can serve as the perfect SDR platform when working on LTE systems. On top of that, the PicoSDR can also serve as an ideal platform to validate your own algorithms for resolving in-device coexistance issues.

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