The spatial techniques currently used in accurate time transfer are based on GPS, TWSTFT, and GLONASS. The International Bureau of Weights and Measures (BIPM) is mandated for the generation of Coordinated Universal Time (UTC) which is published monthly in the BIPM Circular T. In 2009, the international Consultative Committee for Time and Frequency (CCTF) recommended the use of multitechniques in time transfer to ensure precision, accuracy, and robustness in UTC. To complement the existing GPS and TWSTFT time links, in November 2009 the first two GLONASS time links were introduced into the UTC worldwide time link network. By November 2011, 6 GLONASS time links are used in the UTC computation. In the frame of the application in the UTC computation, we establish the technical features of GLONASS time transfer: the short- and long-term stabilities, the calibration process, and in particular the impact of the multiple GLONASS frequency biases. We then outline various considerations for future developments, including the uses of P-codes and carrier-phase information. 1. Introduction GLONASS (from GLObal NAvigation Satellite System, GLN for short) is a radio-based satellite navigation system operated by the Russian Space Forces with the aim of providing real-time, all-weather, three-dimensional positioning, velocity measuring, and timing with a worldwide coverage. The completely deployed GLN constellation is composed of 24 satellites in three orbital planes of which the ascending nodes are 120° apart. Eight satellites are equally distributed in each plane. The first satellite was launched on 12 October 1982, and the constellation was completed in 1995, although until recent years it has not always been well maintained. With respect to present and future techniques for accurate time transfers, GLN is comparable to other global navigation satellite systems (GNSSs): the United States’ Global Positioning System (GPS), the upcoming Chinese Compass navigation system, and the Galileo positioning system of the European Union. To guarantee the accuracy and robustness of UTC generation, a multitechnique strategy for UTC time transfer is indispensable. Over the last two decades much effort has been devoted to introducing GLN in UTC. However, earlier GLN studies [1–9] remained at an experimental stage because there were only a few operationalGLN timing receivers, the GLN constellation was incomplete, and there were unsolved technical issues; among them the major difficulty was of the multiple GLN frequency biases. The situation has greatly improved in recent years. As of
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