Robust QoS-Aware Multi-Service Transmission with Hierarchical Modulation in High-Speed Railway

摘要

Adaptive hierarchical modulation is an effective technique to improve the spectral efficiency for multi-service transmission in high-speed railway (HSR) communication systems. Many efforts have been devoted to studying this technique with the perfect channel state information (CSI) assumption. However, the fast time-varying fading channels and feedback delay lead that the perfect CSI cannot be obtained in HSR scenario. Therefore, the performance of the existing non-robust hierarchical modulation schemes degrades severely. This paper proposes a robust adaptive hierarchical modulation scheme, which can bear multiple services in one symbol with different QoS requirements. The closed form bit error rate (BER) expressions of the robust hierarchical modulation scheme are derived, then the adaptive transmission strategy of the HSR communication system is designed. Finally, the performance of the robust hierarchical modulation scheme is evaluated by extensive simulations. Comparing with the uniform modulation scheme, the overall spectral efficiency increases by 15% when the train is at 500 km/h.