The train signaling organization in the world is developing several technologies for high-speed train, one of which is the Future Railway Mobile Communication Systems (FRMCS) technology to be implemented in the world in 2022. This paper studies FRMCS for Indonesian high-speed train and possibility of being interfered by Global System for Mobile Communication (GSM) cellular because of the use of the same or adjacent frequency bands. This paper evaluates the performance of FRMCS in Indonesia with and without interference from GSM cellular networks. The effect of interference to the FRMCS is analyzed in term of Bit Error Rate (BER) against Signal-to-Noise Power Ratio (SNR) for several given speed and inzterference levels. The evaluation was performed using the Indonesian FRMCS channel model obtained from New York University Simulation (NYUSIM), where outage probability is functioning as the best performance (lower bound). The results of this paper are the performance of FRMCS Indonesia with and without interference from GSM cellular to FRMCS signals along railroads in Indonesia, in term of BER curve of FRMCS performance and GSM-R performances. The result of this paper shows that the performance of FRMCS is better than GSM-R in the aspect of resistance to interference. The results of this paper are expected to be a reference for the implementation of FRMCS in Indonesia.
Communication systems for high-speed flying devices, such as drones and missiles, have performances with error-floor caused by the Doppler effect, which causes inter-carrier interference (ICI) and destroys real-time data transmission. Channel coding cannot reduce error-floors, but channel coding may still achieve performance with turbo-cliff. This paper proposes a broadband communication system for high-speed flying devices using soft 4 quadrature amplitude modulation (4-QAM) modulations with the optimal threshold S for practical implementation assuming that the maximum/minimum log-likelihood ratio (LLR) values of ±709. We use orthogonal frequency division multiplexing (OFDM) with low-density parity-check (LDPC) codes as the channel coding scheme and minimum mean squared error (MMSE) equalization. To reduce the computational complexity and to keep the data rate high, we use only a single pilot for the channel estimation. Computer-based simulations for several high speeds are performed to evaluate the performance of the proposed high-speed flying devices system. The bit error rate (BER) performance is evaluated based on LLR under additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. The results confirmed that the proposed system with the optimal threshold S can avoid unstable jumping error with better turbo-cliff and lower error-floor. The maximum speed the system can achieve for BER of 10 −2 is 400 km/h. The results of this paper are expected to contribute significantly to the development of communication systems on flying devices.
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