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|Title:||Compatibility Analysis between LightSquared and L1/E1 GNSS Reception|
|Authors:||O'DRISCOLL CILLIAN; RAO MARCO; BORIO DANIELE; CANO PONS EDUARDO; FORTUNY GUASCH Joaquim; BASTIDE Frederich; HAYES Dominique|
|Citation:||2012 IEEE/ION Position, Location and Navigation Symposium p. 447-454|
|Publisher:||Institute of Electrical and Electronics Engineers (IEEE)|
|Type:||Articles in periodicals and books|
|Abstract:||In mid-November 2010 the US broadband wireless services delivery company LightSquared applied to the FCC for the right to deploy a ground based Long Term Evolution (LTE) 4G network with downlink in the 1525 – 1559 MHz band. This right was conditionally granted in January 2011, much to the consternation of the GNSS community. This concern was due to the proximity of the proposed downlink bands to the GPS L1 and Galileo E1 bands and the high power levels of the LTE transmitters. This band was previously allocated for Mobile Satellite Services (MSS), which typically has much lower Power Flux Density (PFD) than ground-based transmitters. The FCC grant was conditioned on the establishment of a technical working group (TWG) to investigate the impact of LightSquared transmissions on GPS receivers. The TWG was established in January 2011 with representatives from LightSquared and the GPS industry. It was divided into sub-teams focusing on different sections of the GPS receiver market: aviation; cellular; general location and navigation; high precision, timing and networks; space-based receivers. The final report of the TWG was published on 30th June 2011. The results of this report indicated two potential sources of interference with GPS: 1) Out of band interference; 2) In-band interference. The out of band interference arises due to the fact that GPS front-end filters are not perfect “brick-wall” filters and so let through some out of band signal power. The in-band interference arises due to intermodulation products between the two 10 MHz components of the LTE signal. While all receivers are affected by the in-band interference, high-precision receivers are the most affected by out of band interference, due to their larger front-end bandwidths. As is well known, ranging accuracy is dominated by high frequency components, hence high-precision receivers will always have larger front-end bandwidths. In this work we present an analysis of the impact of LightSquared on Galileo and modernised GPS Open Service (OS) signals. Following the joint EU-US agreement of 2008 both these OS signals are modulated by a Multiplexed BOC (MBOC) subcarrier, which has significant amounts of power in lobes spaced 1 and 6 MHz away from the L1/E1 centre frequency. The lower lobes are therefore closer to the LightSquared transmissions than the GPS C/A code, and hence these signals are potentially more susceptible to harmful interference effects. The analysis is derived from a combination of real data collection and theoretical signal and receiver models. The real data collection is based on a number of scenarios. To test the OS GPS and Galileo L1/E1 signals a Spirent GSS8000 simulator has been used to record IF samples of “clean” GNSS signals. A pair of Agilent vector signal generators with LTE simulation capabilities has been used to generate the interfering signals. The GNSS and LTE signals are subsequently broadcast from separate antennas in a large anechoic chamber and data from a number of receivers are collected for further analysis. For each receiver, the C/N0, pseudorange and navigation solution measurements are recorded for each signal tracked. The data analysis in this work focusses on the impact of the LightSquared signals on the C/N0 measured by each receiver. Future work will look also at the impact in the ranging and navigation domains. The methodology is to replay each GNSS scenario multiple times, once in the absence of the LTE signals and then again with the interferers turned on at various power levels and with different configurations (lower 10 MHz only, both upper and lower, etc). The primary metric is the difference in measured C/N0 between the “clean” and interference scenarios.|
|JRC Directorate:||Space, Security and Migration|
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