## 1 Introduction
In addition to the spatial diversity, dual-polarization antennas provide polarization diversity to distinguish LOS and MP signals to enhance the suppression of the received MP signals. [PERSON] uses a pair of orthogonal dipoles instead of the directive antenna to suppress the ground-reflected multipath [23]. [PERSON] et al. use an array of LHCP antennas for better angle of arrival (AOA) estimations of multipath, which are used to suppress the received MP signals in the array of RHCP antennas [24]. Both of the works report benefits of using dual-polarization antennas to improve the multipath mitigation performance in the spatial domain. However, whether the usage of dual-polarization antennas always contributes to multipath mitigation in the spatial domain remains a question. In baseband signal processing, the dual-polarization antenna produces additional information about the reflected MP signal in the LHCP channel to enhance multipath parameter estimation. [PERSON] et al. utilize dual-polarization antennas in a statistical signal model to make the LOS signal easier to be distinguished from the MP signals in both time and spatial domains especially in cases where signals are highly spatially correlated [25]. However, in the time domain, he did not discuss if the utilization of dual-polarization antennas improves the multipath mitigation regardless of the relative time delay of multipath. Authors of [26; 27; 28; 29] also integrate the dual-polarization technique into the state-of-the-art baseband signal processing algorithms and obtain better multipath mitigation performance, but the question is still unsettled. The post-receiver techniques based on dual-polarization antennas have more measurements extracted from the additional LHCP channel to detect multipath or reduce the multipath bias, e.g., the estimated carrier power to noise ratios (CNRs) of the RHCP and LHCP channels in a dual-polarization antenna are combined to detect multipath [30; 31; 32; 33]. It is worth noting that, in [30], [PERSON] et al. conclude the cases where the dual-polarization antenna can or cannot help to detect multipath based on the CNR difference between RHCP and LHCP channels. However, this conclusion does not take the relative delay between the LOS and MP signals into consideration. To summarize, multipath mitigation techniques report performance improvement when using dual-polarization antennas. Meanwhile, as mentioned in [28; 23; 30], their DPMM algorithms are not always effective. However, few of these studies focus on the cases in which the multipath mitigation based on parameter estimation can or cannot benefit from dual-polarization antenna technology. On the other hand, the dual-polarization antenna technology requires high-quality circular polarization antennas, additional LHCP channel output, doubled correlators, and increased computational load. These are the weaknesses of DPMM technology. Therefore, before the adoption of dual-polarization technology or the design of DPMM algorithms, the fundamental question about the conditions under which the DPMM can outperform that of single-polarization and its theoretical performance improvement should be answered. In this paper, we model the received signal by a dual-polarization antenna concerning the polarization states of both the antennas and the reflected signals. Based on the typical parameters of the GNSS dual-polarization antenna and the electrical properties of the reflective materials, we analyze the characteristics of the received signals and classify them into strong LHCP signal and weak LHCP signal cases. After that we propose a MLE algorithm for multipath parameter estimation of a dual-polarization antenna to evaluate the performance of DPMM. By comparing the performance of the DPMM algorithm with that of the single-polarization-intended MLE algorithms in different received signals cases based on Monte Carlo simulations, we answer the fundamental question in some typical cases.