Wireless system design : NB-IoT downlink simulator

Abstract: The newly defined NB-IoT standard currently lacks a toolkit and simulator. In order to develop algorithms for this new standard there is a need for channels and signals as reference during tests. MATLAB is commonly used for testing LTE signals and therefore the toolkit was developed in this environment. The toolkit focuses primarily on the Layer 1-relevant functionality of NB-IoT, the grid generation, encoding, rate-matching and modulation of channels. The simulator focuses on testing the developed toolkit in a virtual LTE NB-IoT environment. The virtual environment attempts to emulate a base station and a terminal. The path followed is scheduling, channel processing, grid generation, QPSK and OFDM modulation through a modeled channel, OFDM demodulation, channel estimation, equalisation, QPSK demodulation and reversal of channel processing. The simulator tests primarily the NPDSCH channel implementations. Measurements of bit error and block error rates were made and it was concluded that they follow the expected trends. More testing is required to validate the remaining channels. A sector equaliser and an interpolating equaliser were tested by measuring block error rate and checking constellation diagrams and it was concluded that the performance of the interpolation equaliser is more consistent. In order to improve the equalisation further the noise estimation must be reworked.