The railway mobile communication system is undergoing a smooth transition from the Global System for Mobile Communications-Railway (GSM-R) to the Railway 5G. In this paper, an empirical path loss model based on a large amount of measured data is established to predict the path loss in the Railway 5G marshalling yard scenario. According to the different characteristics of base station directional antennas, the antenna gain is verified. Then we propose the position of the breakpoint in the antenna propagation area, and based on the breakpoint segmentation, a large-scale statistical model for marshalling yards is established.
Wireless communication technologies play an essential role in supporting railway operation and control. The current Global System for Mobile Communications-Railway (GSM-R) system offers a rich set of voice services and data services related with train control, but it has very limited multimedia service bearer capability. With the development of commercial wireless industry, Long-Term Evolution (LTE) mobile broadband technology is becoming the prevalent technology in most of commercial mobile networks. LTE is also a promising technology of future railway mobile communication systems. The 3rd Generation Partner Project (3GPP) and China Communications Standards Association (CCSA) have proposed two feasible LTE based broadband trunking communication solutions: the 3GPP Mission Critical Push to Talk (MCPTT) solution and B-TrunC solution. In this paper, we first introduce the development of railway mobile communications and LTE technology. The user requirements of future railway mobile communication system (FRMCS) are then discussed. We also analyze the suitability of the two LTE-based solutions for LTE based Next-Generation Railway Mobile Communication System (LTE-R) from different aspects.
Since Dalvik Executable (DEX) files are prone to be reversed to the Java source code using some decompiling tools, how to protect the DEX files from attackers becomes an important research issue. The traditional way to protect the DEX files from reverse engineering is to encrypt the entire DEX file, but after the complete plain code has been loaded into the memory while the application is running, the attackers can retrieve the code by using memory dump attack. This paper presents a novel DEX protection scheme to withstand memory dump attack on the Android platform with the name of DexDefender, which adopts the dynamic class-restoration method to ensure that the complete plain DEX data not appear in the memory while the application is being loaded into the memory. Experimental results show that the proposed scheme can protect the DEX files from both reverse engineering and memory dump attacks with an acceptable performance.
We propose a nonbinary byte-interleaved coded-modulation scheme with inner and outer turbo-like iterative decoder. The net coding gain is 0.6 dB higher than the state-of-the-art binary single parity check (SPC) low-density parity-check (LDPC) based turbo-product counterpart, with adjustable iterations and lower error-floor. We provide the details of Bahl-Cocke-Jelinek-Raviv (BCJR) based inner code decoder and optimum signal constellation design (OSCD) method in this paper. The single-mode fiber (SMF) channel simulation is also discussed.
The fifth generation (5G) communication has been a hotspot of research in recent years, and both research institutions and industrial enterprises put a lot of interests in 5G communications at some new frequency bands. In this paper, we investigate the radio channels of 5G systems below 6 GHz according to the 5G communication requirements and scenarios. Channel measurements were conducted on the campus of Beijing Jiaotong University, China at two key optional frequency bands below 6 GHz. By using the measured data, we analyzed key channel parameters at 460 MHz and 3.5 GHz, such as power delay profile, path loss exponent, shadow fading, and delay spread. The results are helpful for the 5G communication system design.
