# Feasibility Test and Analysis for Heavy Haul Freight Using WDPS Based on MIMO-OFDM
## 4 Conclusions  
In this paper, we describe that the results of field tests for a heavy-haul freight with WDPS was applied for the first time in Korea. WDPS has designed an electric interface with the main devices of existing vehicles. Among the electrical interfaces of the WDPS, a safety circuit was constructed to stop the train without driver intervention. If the communication between WDPS is lost for more than 2 s, or the safety loop of the master loco or the slave loco is disconnected, the emergency stop is executed.  
Figure 5: SNR in the test section.  
\begin{table}
\begin{tabular}{c p{142.3 pt}} \hline \hline
**Test Item** & **Result** \\ \hline Pantograph function & Valid raise/down pantograph signal is detected and pantograph state is correctly displayed on DU. \\ \hline Main circuit breaker function & Valid Main circuit breaker close signal is detected and main breaker state is correctly displayed on DU. \\ \hline Air compressor control & Valid air compression on signal is detected and air compressor state is correctly displayed on DU. \\ \hline Emergency brake function & Valid EB signal is detected and brake mode is correctly displayed on DU. \\ \hline Service brake function & Valid SB signal is detected, command is executed and cylinder pressure is correctly displayed on DU. \\ \hline Safety circuit function & Valid safety circuit cutoff is detected, emergency brake mode is correctly displayed on DU. \\ \hline \hline \end{tabular}
\end{table}
Table 3: Functional test results.  
MIMO-OFDM, which is strong in multipath is adopted as a communication method. When constructing a 50 freights, the distance between the locomotives equipped with WDP is about 670 m, so a repeater was installed for the 25 th freight to secure communication coverage.  
Through this test, we obtained as the following results.  
1. We confirmed the operational applicability of distributed control technology for heavy haul freight with WDPS based on WiFi for the first time in Korea. Communication performance, braking performance, and train operation functions (propulsion/braking command, pantograph function, MCB function, and safety circuit) were verified on the track.
2. Due to the distributed control by WDPS, the braking tube pressure of the master locomotive and the slave locomotive was simultaneously controlled. Therefore, it was confirmed through measurement that the braking and release time of the heavy haul freight was about 1.5 times faster. This can be expected to improve the operational efficiency of freights.
3. Through SNR measurement of WDPS, it was confirmed that the topography of the track is a major influence on communication performance. Although the same tunnel section, the difference of SNR was confirmed according to the meandering section and the straight flat section due to continuous curves and gradients, that is, whether the LOS was guaranteed.
4. For the stable operation of WDPS, the first method should be arranged so that the wireless device satisfies the LOS condition when applying the high-frequency band. The second method when choosing a frequency, we can allocate two or more other channels in the 2.4 GHz band or consider the latest communication methods in the band below the 2.4 GHz band (e.g., LTE in 850, 950, 900 MHz, 1.8 GHz, etc.).  
We verified the technical feasibility of the WiFi- and WDPS-based heavy-haul freight, and we expect to operate heavy haul freight trains in Korea through additional research such propagation modeling, optimizing transceiver locations and freight dynamic analysis, etc.  
[PERSON], [PERSON] conceived and designed the main concept; [PERSON] performed test and simulation; [PERSON] wrote the original draft and edited. [PERSON] reviewed and supervised. All authors have read and agreed to the published version of the manuscript.  
This research was supported by a grant number PK2004A1 from the R&D program of the Korea Railroad Research Institute, Republic of Korea.  
The authors declare no conflict of interest.