## 1 Introduction  
It is well known that multipath (MP) effect is one of the main error sources that deteriorate positioning accuracy of Global Navigation Satellite System (GNSS) receivers. With technological advancement in both hardware and software, most of the common-mode errors such as satellite clock error and ionosphere error have been eliminated by methods like dual-frequency and differential techniques [1]. However, the multipath, which depends on the surrounding environment where the receiver is situated, is still one of the dominant error sources in applications that require high accuracy [2]. In the past decades, researchers and manufacturers have proposed a number of multipath mitigation techniques and they can be grouped into three categories according to the applied stages along the processing of the signal:  
1. Pre-receiver techniques suppress the reception of the MP signals via spatial diversity [3; 4; 5]. The spatial diversity is easy to understand for the fact that the line-of-sight (LOS) and MP signals propagate in different paths and arrive at the receiver antenna from different directions. Hence, the receiver antennas are designed to have either fixed or configurable radiation patterns to enhance the reception of the LOS signal while suppressing the reception of the MP signals. However, these techniques have either bulky antennas or complex hardware. 2. Receiver baseband signal processing techniques reduce the MP bias by discriminator design [6] or by estimating the parameters of the LOS signal from the compound of LOS and MP signals based on the estimation theory. The techniques based on discriminator design are adequate in mitigating medium to long delay multipaths, but the short delay multipath, which is one of the most challenging multipaths to mitigate, makes most of the algorithms in this category less effective [7]. The path parameter estimation techniques are often based on maximum likelihood estimation (MLE) such as the multipath mitigation technology (MMT) [8; 9; 10], the multipath estimating delay lock loop (MEDLL) [11; 12], the Newton method-based fast iterative maximum-likelihood algorithm (FIMLA) [13], and the space-alternating generalized expectation maximization (SAGE) algorithm [14; 15]. However, these methods are sensitive to the signal models and require high amount of computation. 3. Post-receiver or measurement domain techniques exploit the characteristics of the MP interfered measurements to average or compensate the multipath bias [16; 17]. They need prior knowledge about the multipath and are restricted to specific multipath environments [18]. Recently, dual-polarization antenna technology has become a research hotspot, for it provides an additional diversity to distinguish the LOS signal from the MP signals. The polarization diversity is exploited based on the fact that the GNSS satellite transmits right hand circular polarized (RHCP) signal and it turns partly to a left hand circular polarized (LHCP) signal upon reflection. The traditional receiver antenna is designed to be sensitive to RHCP signal; hence, it receives the LOS signal and the RHCP component of the MP signal, while the dual-polarization antenna has an additional LHCP channel to receive the LHCP component of the MP signal. Dual-polarization antenna technology has been used in various GNSS remote sensing applications, e.g., reflected signal analysis and altimetry [19; 20], precipitation detection [21], and vegetation sensing [22]. With the development of antenna hardware technology, the dual-polarization antenna has similar size with the RHCP antenna, which makes it easy to extend its applications, without extensively increasing the complexity, in the cases where there used to be an RHCP antenna, e.g., the survey receiver, vehicle navigation, and reference station. In the past decade, numbers of multipath mitigation techniques using dual-polarization antennas have been proposed and they can also be grouped into the aforementioned three categories.