While integer ambiguity resolution (IAR) enables GNSS to achieve real-time sub-centimeter-level positioning in open-sky environments, it can be easily hindered if the involved receivers are situated in areas with limited satellite visibility, such as in dense city environments. In such GNSS-challenged cases, commercial Low Earth Orbit (LEO) communication satellites can potentially augment GNSS by providing additional measurements. However, LEO satellites often lack code measurements, mainly transmitting satellite-specific frequency-varying carrier phase signals. This contribution aims to study the ambiguity-resolved baseline positioning performance of such phase-only signals, addressing the extent to which LEO constellations can realize near real-time positioning in standalone and GNSS-combined modes. Through a simulation platform, we analyze the distinct response of each LEO constellation (Iridium, Globalstar, Starlink, OneWeb, and Orbcomm) to IAR under various circumstances. Although achieving single-receiver high-precision positioning can be challenged by inaccuracies in the LEO satellite orbit products, the relative distance between two receivers can help overcome this limitation. As a result, centimeter-level relative positioning over short baselines can be made possible, even with a satellite elevation cut-off angle of 50 degrees, making it suitable for GNSS-challenged environments. This can be achieved with high-grade receiver clocks over very short baselines ( $$\sim $$ ∼ 5 km) and access to decimeter-level orbit products.

Precise point positioning with ambiguity resolution (PPP-AR) based on multiple global navigation satellite system (multi-GNSS) constellations is an important high-precision positioning tool. However, some unmodeled satellite and receiver biases (such as errors in satellite attitude) make it difficult to fix carrier-phase ambiguities. In order to fix ambiguities of eclipsing satellites, accurate integer clock and satellite attitude products (i.e., attitude quaternion) have been provided by the International GNSS Service (IGS). Nevertheless, the quality of these products and their positioning performance in multi-GNSS PPP-AR have not been investigated yet. Using the PRIDE PPP-AR II software associated with the corresponding rapid satellite orbit, integer clock and attitude quaternion products of Wuhan University (WUM), we carried out GPS/BDS PPP-AR using 30 days of data in an eclipsing season of 2020. We found that about 75% of GPS, 60% of BDS-2 and 57% of BDS-3 narrow-lane ambiguity residuals after integer clock corrections fall within ±0.1 cycles in the case of using nominal attitudes. However, when using attitude quaternions, these percentages will rise to 80% for GPS, 70% for BDS-2 and 60% for BDS-3. GPS/BDS daily kinematic PPP-AR after integer clock and nominal attitude corrections can usually achieve a positioning precision of about 10, 10 and 30 mm for the east, north and up components, respectively. In contrast, the counterparts are 8, 8 and 20 mm when using attitude quaternions. Compared with the case of using attitude quaternions only at the network end for the integer clock estimation, using attitude quaternions only at the user end shows a pronounced improvement of 15% in the east component and less than 10% in the north and up components. Therefore, we suggest PPP users apply integer clock and satellite attitude quaternion products to realize more efficient ambiguity fixing, especially in satellite eclipsing seasons.

Integer ambiguity resolution (IAR) is crucial for fully exploiting the ultra-precise carrier phase measurements in global navigation satellite system positioning. To achieve IAR, phase biases that violate the integer property of ambiguities are typically either estimated together with other model parameters or eliminated through differencing techniques. Observing that these biases can be bounded, exploring the impact of constraining their extreme bounds on IAR performance is a logical next step yet one that has received limited attention in existing research. This study proposes a bias-weighted model that constrains the random variations in GLONASS between-receiver single-difference phase biases to enhance IAR. Real-world short-baseline ( $$\sim $$ ∼ 1–5 km in length) positioning results demonstrate that the bias-weighted model enables instantaneous, centimeter-level dual-frequency GLONASS-only ambiguity-resolved positioning. For longer baselines (from 10 to 100 km), instantaneous, centimeter-level ambiguity-resolved positioning can also be achieved by combining dual-frequency GLONASS and GPS observations based on the proposed bias-weighted model, showing improvements over its counterpart in which the phase biases are treated completely unknown, i.e., the bias-unknown model. A formal analysis for both standalone GLONASS and combined GLONASS+GPS constellations at 1-km and 100-km baselines across various global locations, further highlights the improvements brought by the bias-weighted model in enhancing IAR performance worldwide. The bias-weighted model shows strong potential for improving GLONASS-included IAR and positioning performance, especially in weaker models where ionospheric parameters must be estimated–such as those typical of medium-to-long baselines.