Mobile communications devices or User Equipment (UE) often contain a number of different radio technologies that enable the UE to connect or communicate with various other devices or base stations using different formats, which may or may not use other frequencies. Thus, for example, a UE may include Bluetooth connectivity, Wi-Fi connectivity, GPS connectivity, as well as LTE connectivity. Often, some or all of these radio technologies will be operative at the same time, so that the UE is connected to several of these systems at once (sometimes known as in-device coexistence). Depending on the frequencies, it will be appreciated that UE transmissions on one radio technology may cause interference to the receivers of the others. This problem may be particularly acute in certain LTE frequency bands, some of which lie adjacent the Industrial, Scientific and Medical (ISM) frequency band, where the Wi-Fi and Bluetooth channels are located.
This problem of in-device coexistence interference, has been considered in, for example Technical Report 3GPP TR 36.816 v1.0.0 entitled “3rd Generation Partnership Project; Technical Specification Group Radio Access Networks; Evolved Universal Terrestrial Radio Access (E-UTRA); Study on signalling and procedure for interference avoidance for in-device coexistence; (Release 10)” available at http://www.3gpp.org/ftp/specs/archive/36 series/36.816/36816-100.zip. The objective of this report is to investigate suitable mechanisms for interference avoidance from the signalling and procedural point of view to facilitate the coexistence scenario that LTE and GPS/ISM radio within the same device working in adjacent frequencies or sub-harmonic frequencies. The work under this study evaluates whether existing Radio Resource Management (RRM) mechanisms could be utilized to effectively solve the coexistence problems that arise with such scenarios and provide the required Quality of Service (QoS) in LTE with proper GPS/ISM operation, and also, if legacy signaling and procedure are not sufficient to ensure required performance in the particular coexistence scenario, whether enhanced mechanisms would better avoid interference and mitigate the impact caused by ISM radio.
In the report, three modes of operation in which in-device coexistence interference may occur were considered. In the first, uncoordinated, mode, different technologies in the UE operate independently, without any internal coordination between each other. In the second mode, different radio technologies within a UE are coordinated to the extent that one radio technology is aware of what another one is doing so that, if there is co-existence interference, the UE may be able to adjust operation to remove or at least minimise the effects of such interference. The third mode is where there is coordination not just within the UE, but also between the UE and the network, which allows the network to take action to try to minimise any coexistence interference that the UE has informed it about. Some solutions that are discussed in the report are UE controlled and include moving the LTE signal away from the ISM band or moving the ISM signal away from the LTE band. In another solution, the UE tries to Time Division Multiplex (TDM) the signals so that interference is avoided. Other solutions are LTE-network controlled with the assistance of the UE. In the latter solutions, the UE informs the network base station of interference problems and the base station may then apply mitigation techniques to try to reduce or avoid the interference. The mitigation may be either Frequency Division Multiplexing (FDM) or TDM to change the signal frequencies or times, or may increase power on the downlink to try to reduce or avoid the interference. The UE therefore sends a signal to the network that there is an interference problem, for example when there is on-going interference on the serving frequency. This may be considered as a reactive indication. However, the problem with the LTE-network controlled UE assisted solutions is that they rely on the indication signal from the UE. More particularly, the solutions require that the indication signal be triggered within the UE based on a measurement of the interference, and such measurement can be unreliable, and can cause unnecessary indication signals to be sent to the network too frequently, thereby unnecessarily burdening the network.