## 1 Introduction  
Achieving a high data rate is one of the key challenges for the next-generation wireless communication systems. Hence, large frequency bandwidth is required. Such large bandwidth cannot be achieved on radio links operating at low frequency bands (below 6 GHz). Therefore, high frequency bands (above 6 GHz) have been widely considered for future applications [1]. It is well known that the design of a wireless system requires a deep understanding of the propagation channels. However, most available channel models, e.g., WINNER II/+ and International Mobile Telecommunications-Advanced models, have been designed for the frequency range below 6 GHz. Thus, Mobile and wireless communications Enablers for the Twenty-twenty Information Society (METIS) indicates that measurement data above 6 GHz is crucial for the needed extensions/modifications of available channel modeling [2]. In this paper, measurement-based characterization for the corridor scenario at 14.6 GHz is presented. To reveal the influence of frequency on the channel characteristics, characterization for the same scenario at 3.6 GHz is also presented.  
As one of the candidate frequency bands for the fifth generation (5G) system, the 14 GHz band has more than 0.7 GHz bandwidth (14.3-15 GHz) to be allocated [3]. Some 5G tests using this frequency band demonstrate data rates up to 4.5 Gbps [4]. The 3.6 GHz band is also suitable for providing capacity to fulfill the increasing traffic requirements, especially for small coverage with denser network deployment [3].  
Stochastic channel models reproduce the statistics of the channel parameters based on the realistic measurements and have been widely used [5; 6; 7]. Based on measurements, several papers have provided comparisons between some different frequency bands [8; 9; 10]. In [8], a multi-frequency outdoor-to-indoor path loss model for different frequency bands ranging from 0.8 GHz to 28 GHz was presented. In [9], the path loss and wideband characteristics were measured at 1.7 GHz and 60 GHz for small cell systems. Omnidirectional and directional antennas were used for 1.7 GHz and 60 GHz, respectively. The difference between the antennas limited the effectiveness of the comparison. In [10], measured data and empirical models for 2-10 GHz and 57-66 GHz were presented. In this work, the measurements were performed in a laboratory and the distance between the transmitter and receiver was less than 4 m. The scenario is different from our work and leads to different results on the frequency dependency for some channel characteristics (for details, see the Comparative Analysis section).  
This paper focuses on the reflective environments where free space propagation and/or reflection are the main mechanisms. A comparative analysis of the channel characteristics between the low and high frequency bands is presented. The main contributions of our work are summarized as follows:  
* A detailed insight into the channel characteristics of the path loss, RMS (root-mean-square) delay spread and coherence bandwidth in the corridor scenario with the directional antennas at 3.6 GHz and 14.6 GHz frequency bands is presented.
* A comparative analysis is made for statistical metrics of the propagation channel between the two frequency bands.
* The underlying factors that lead to the influence of frequency on the channel characteristics are investigated. It is found that, in the corridor, the differences between the two frequency bands in RMS delay spread are minimal (less than 1 ns). Measurements in the reverberation chamber (RC) verify this inference.  
The remainder of this paper is organized as follows: Section 2 describes our measurement system and measurement scenario. Section 3 presents the measurement results. Section 4 focuses on the comparative analysis. In Section 5, some auxiliary experiments in an RC are described to support the analysis. Section 6 concludes this paper.