Measured GPS performance under LTE-M in-device interference
In this paper we present the measurement results for time-to-fix, position accuracy, and carrier-to-noise ratio of mass-market Global Positioning System (GPS) receivers under the in-device interference from an LTE-M transmitter. The laboratory measurement set-up is built using software-defined radio (SDR) platforms to conductively feed emulated GPS L1 signals and LTE-M interference signals to the antenna input of the GPS receivers. The LTE-M interference from second harmonics is accurately modelled taking into account the transmitter activity patterns in different coverage enhancement modes. According to measurements, there are large variations in interference tolerance between different GPS receivers. REC01 was able to tolerate high level of interference during tracking and also in acquisition as long as the interference pulse duration is not too long (tens of milliseconds). REC02 performed clearly worse and tolerated only low levels of LTE-M interference during both acquisition and tracking. The same measurement set-up can be used with any GPS receiver for designing proper isolation and filtering levels for co-existing LTE-M transmitters.