IEEE/ION PLANS 2010, Session C4, Indian Wells/Palm Springs, California, 4-6 May 2010 1/8 Comparing Detection Performance of Polarization and Spatial Diversity for Indoor GNSS Applications Mohammadreza Zaheri, Ali Broumandan, Gérard Lachapelle Schulich School of Engineering Position, Location and Navigation (PLAN) Group University of Calgary Abstract—GPS signal detection is limited in indoor areas due to signal attenuation and multipath fading. Considering diversity systems can provide two major benefits: increasing overall average received signal power and decreasing signal fading margins by combining independent signal sources. In this paper, detection performance of spatial and polarization diversity systems applied to the received GPS signals in indoor environments is investigated. Herein, the polarization diversity is formed using two different combinations of orthogonal polarized antennas: one with Right Hand Circular Polarized (RHCP) and Left Hand Circular Polarized (LHCP) antennas and another one by vertical and horizontal antennas. Theoretical comparison of these antenna diversity structures is investigated along with real GPS signal collection in different indoor locations to evaluate their performance experimentally. The diversity gain metric has been introduced to quantify the performance of the combining method theoretically and experimentally. Since diversity gain is a function of correlation coefficient and average signal input, these parameters are measured and compared as well for the target diversity systems. Keywords- Antenna diversity, indoor GNSS, detection performance I. INTRODUCTION Global Navigation Satellite System (GNSS) signal suffers from attenuation and deep fading in dense multipath environments such as indoor and urban areas due to propagation through building materials and interference between multiple reflected signals. In order to overcome these problems and improve position estimation under weak GNSS signal conditions, several techniques including High-sensitivity GPS (HSGPS), assisted GPS (AGPS), and diversity techniques have been utilized. There are various techniques to implement a diversity system such as antenna, time and frequency diversity [1]. In the antenna diversity technique, a receiver utilizes multiple antennas known as diversity branches to capture independent copies of the transmitted signal. Different techniques including spatial, polarization and pattern diversities have been implemented and analyzed in the literature (see [2] and references therein). Among them, spatial diversity and polarization diversity are widely utilized in communication systems. The spatial diversity system is developed based on the fact that in a multipath fading environment the received signals on different antenna elements decorrelate spatially [3]. In [4] an optimum spatial post-correlation signal processing and detection algorithm for two-antenna array GPS receivers is proposed. Reference [5] analyzes theoretically and experimentally the processing gain achievable through spatial combining of a pair of antennas. The spatial diversity performance of three different antenna configurations in indoor 902-928 MHz propagation channel is evaluated in [6]. In this work, it has been shown that the indoor propagation channel has either Rician or Rayleigh models and the fading distribution characteristics are discussed. Reference [7] has recently proposed a new spatial diversity structure based on the synthetic array concept to enhance the detectability of GPS signal in indoor locations. In the polarization diversity system, antennas with orthogonal polarization can be considered as diversity structure branches. In indoor environments, since the signal path is cluttered by multiple scatters the received signal polarization changes randomly. The polarization diversity and channel characteristics at 1800 MHz are extensively analyzed in [8]. The effect of correlation between two polarization branches on diversity gain has been discussed in [8] as well. In addition, the performance of polarization diversity using different antenna configurations in both Rayleigh and Rician environments was evaluated. The concept that the received GNSS signal in high multipath environments is no longer circularly polarized has been used by [9] with introducing GNSS signal detectability enhancement approach using circular polarization diversity by a dual-polarized RHCP and LHCP antennas. Using real GPS signal in various environments, it has been shown that up to 5 dB diversity gain can be achieved by a dual-polarized antenna in dense multipath environments. In addition to the circular polarization diversity, the enhancement of GNSS signal detection performance utilizing dual linear polarized antenna is considered herein. The paper is organized as follows. Second II describes indoor fading channel and its corresponding considerations. In Section III, the spatial and polarization diversity systems are introduced. The important factors leading to higher detection performance and diversity gain in a diversity system are discussed in Section IV. In continue the test setup and experimental results are explained and analyzed in Section V. Conclusions are given in Section VI. II. FADING CHANNEL MODEL: Since in indoor environments the receiver antenna receives multiple signals from many reflections and different directions, the received signal becomes a complex vectorial sum of the signals reflected from various obstacles with different