An Open-Loop Vector Receiver Architecture for GNSS-Based Scintillation Monitoring

GNSS-based studies of the ionosphere are typically conducted using navigation receivers which track both the carrier and code phase either on a satellite-by-satellite basis, or collectively via a vector structure [3]. Information relating to phase and amplitude scintillation is gathered from the receiver’s estimate of the carrier phase and the receiver correlators values, respectively. The quality of these parameters, however, is directly influenced by how well the receiver can track the GNSS signals. Under scintillation conditions these measurements are corrupted and degraded as the errors in the code and carrier tracking loops grow [1, 2]. Code-phase biases will manifest themselves as amplitude fades and carrier phase cycle-slips will appear as large, sudden phase fluctuations. Given such corrupted data it can be difficult to distinguish between receiver-induced artifacts and ionosphere anomalies. Moreover, if a receiver cannot acquire or track the signal, these measurements are simply not available [2]. In light of the limitations of navigation-receiver based monitoring, this paper explores the custom design of a scintillation-monitoring receiver (SMR). The navigation capabilities of a traditional SMR are often redundant as such receivers are typically fixed at known coordinates. Indeed the entire acquisition and tracking process is avoidable. This fact is exploited in the receiver design wherein an open-loop architecture is adopted. Rather than tracking the range and range-rate to each satellite in view, this architecture leverages knowledge of the receivers position in time and space and satellite ephemeris to demodulate the received signals in an entirely open-loop manner. The receiver clock employed is a GNSS-disciplined oscillator, ensuring a near-zero clock bias and drift and, even during GNSS outages, will typically ensure a holdover error of the order of tens millimeters per second [5]. In an inversion of the traditional navigation receiver, which uses measurements of signal parameters to compute an estimate of position and time, this architecture uses knowledge of position and time to estimate local-replica signal parameters for demodulation purposes in a pure feed-forward fashion. Essentially an open-loop vector demodulation scheme, it produces a series of baseband correlator values from which the deterministic phase process induced by satellite-to-user dynamics and receiver clock effects have been removed. What remains are a series of complex values modulated only by the amplitude and phase processes corresponding to the ionospheric activity. These can then be post-processed in a non-causal or batch mode to reconstruct the phase and amplitude processes and extract traditional metrics such as σϕ or S4, or even to explore new scintillation characterizations [6, 7].

CURRAN James Thomas;  BAVARO Michele;  FORTUNY GUASCH Joaquim; 

2014-11-21

Netherlands Institute of Navigation (NIN)

JRC89617

http://www.enc-gnss2014.com/proceedings/,    https://publications.jrc.ec.europa.eu/repository/handle/JRC89617,