# SDR-Based 28 GHz mmWave Channel Modeling of Railway Marshaling Yard
## 5 Conclusions  
In this work, the railway marshaling yard mmWave propagation scenario is deeply analyzed and classified into three typical categories, involving open scene with Catenary poles, a locomotive parked on the adjacent track, and a building near the testing track. A measurement campaign is conducted at the National Railway Track Test Center of CARS according to the three propagation scenarios, using an SDR channel sounding system, the hardware of which mainly consists of a USRP-2974 transceiver and a mmPSA-TR64 MX phased-array antenna. A self-developed software under the LabVIEW platform is used to derive the channel parameters; to achieve this, a ZC sequence of 200 MHz sample rate and 2048 points is selected, and a discrete algorithm of cross-correlation is designed. Parameters involving received power, delay, and time-spread are successfully derived for every sampling position on our selected tracks of \(T_{162}\) and \(T_{3}\), and the following four conclusions can be drawn based on these parameters:  
(1) As the distance between Tx and Rx increase, there is no significant change in the number of MPCs, which fluctuates randomly between 7 and 11, with a mean value of \(\mu=9.55\) and variance of \(\delta=0.868\). (2) The relationship between parameter and position is deeply analyzed and fitted with proper equations. The relationship between the delay of the first effective path and position conforms to the equation \(y=a\times x^{b}\), the relationship between the time-spread and the position conforms to the equation \(y=\frac{q}{1+e^{i(-x\times(a-x))}}\), and the relation between received power and position conforms to the equation \(y=b\times\ln(x-a)\). Figure 23: Comparison of the locomotive and the building. (**a**) Number of MPCs. (**b**) Received power. (**c**) Delay of the first effect path. (**d**) Time-spread. (3) The impact of the Catenary is an important factor. As the distance between Tx and Rx increases, the number of Catenary between the Tx and Rx increases, and the density of Catenary increases accordingly; therefore, the probability of being blocked by Catenary increases. This phenomenon affects mmWave propagation in two ways: With respect to received power, at all the blocked positions, deep fading occurs, with a penetration loss of 5.07 dB. As for time-spread, at the blocked position of 37.4 m, the time-spread does not change much, only increasing by 118 ns compared with the expected value; however, at the blocked positions of 152.4 m and 202.4 m, the time-spread compared with the expected value is increased by 2970 ns and 2853 ns, respectively, which means that as the distance between Tx and Rx increases, the time-spread increases accordingly at blocked positions. (4) The impact of the locomotive parked on the adjacent track is not obvious; the time-spread slightly increases, with a _MAPE_ of 38.63%. However, due to the larger size and more irregular shape of the building, the received power, delay, and time-spread channel parameters within a small position range show dramatic random variations, so the recommendation that locomotives with unloading data tasks travel on the tracks away from buildings is proposed. The conclusions of this paper are helpful for facilitating the design of mmWave communication systems for railway marshaling yards, to fully exploit the potential of mmWave communications. In the meantime, 6G networks are expected to utilize ultra-high-frequencies such as mmWave in typical scenarios involving smart factory and cell-free communication, as well as non-terrestrial communication [34]. The relevant analysis methods employed in this paper can also be further extended and applied to research of mmWave utilization in 6G and future communication technologies for more scenarios. Moreover, meteorological effects are of great importance in the research of mmWave. In the future, we will conduct further data collection and analysis based on different weather conditions. Conceptualization, Y.L. ([PERSON]) and H.L. ; methodology, Y.L. ([PERSON]), Y.T., and Y.L.