## Implementation of a Vector-based Tracking Loop Receiver in a Pseudolite Navigation System  
**[PERSON] 1, [PERSON] 1, [PERSON] 1,*, [PERSON] 1, [PERSON] 1, [PERSON] 2 and [PERSON] 2**  
positioning availability. A pseudolite (PL) is one of the powerful candidates [1]. A PL is a transmitter broadcasting a GNSS-like signal that can enable conventional GNSS users to do positioning. By installing PLs indoors or other places where the GNSS signal is not available, users can navigate seamlessly with a conventional GNSS receiver. To improve GNSS navigation availability, PLs are very useful because the conventional GNSS user is not required to change receiver hardware. In this paper, meter-level PL navigation utilizing pseudorange measurements is a main consideration. There could be many applications. For indoor navigation, a meter-level PL is applicable to large-scale area where a GNSS receiver-equipped vehicle and equipment could be operated. A large-scale warehouse of a logistics center, an indoor shipbuilding plant, an indoor or underground parking lot of a big supermarket, an indoor amusement park, a large and long tunnel are good examples. Indoor PL navigation system has an advantage over the other indoor systems in that indoor/outdoor seamless navigation with only one user equipment could be achievable. Outdoor use of PLs is useful to cooperate with GNSS to improve navigation availability where the visibility of GNSS satellites is not fully obtained. It could be applicable to urban canyons or mountain valley regions. Maritime navigation is a good application of meter-level accuracy system. PLs could increase integrity of ship docking, harbor loading and unloading applications. PLs also could be an independent navigation system as a backup for wartime. PLs could enable the consistent use of GNSS-related equipment. There are, however, still some limitations in managing PL navigation systems [2]. The near-far problem is one of the most critical limitations, especially for indoor PL navigation. The near-far problem refers to the variation in received signal strength with respect to the relative distance between the user and a PL. Because PLs are installed in a small area relative to GNSS satellites, the distances between the user and the PLs change rapidly compared with GNSS navigation. When the user approaches a specific PL, the received signal power from it is much higher than that from the others and it saturates the automatic gain control (AGC) of the receiver's RF front end. This AGC saturation causes signal to noise ratio degradation of more distant PL signals. Because of this, PL navigation coverage is restricted to regions that are almost equidistant from all the PLs. Even when all the PLs are in appropriate locations, tuning the transmitting power of each PL remains a problem, and is very troublesome in indoor navigation [3]. There are some techniques to mitigate the near-far problem. A pulsing scheme is one of the most popular solutions [4]. Each PL signal transmission is turned on and off in fixed duty cycles so that they do not interfere with each other. While some near PLs saturate the user's AGC during their own duty cycles, the other PL signals can be received during their own duty cycles. Pulsing is effective but cannot be a complete solution, because its performance decreases as the number of signal sources increases. In addition, fine scheduling on the pulsing timing according to the PL constellation and AGC characteristics is required. While pulsing is a solution for the near-far problem in PL systems, we propose a vector tracking loop (VTL) algorithm with PL systems as a new solution, to be implemented in a receiver. Combining a pulsing scheme in PLs and a VTL in a receiver could make a more robust PL navigation system and improve navigation availability. The main feature of the VTL is that it has one big loop that combines tracking and navigation. Conventional receivers use an independent tracking loop (ITL) and navigation functions.