Implementation details of a deeply integrated GPS/INS software receiver

The goal of this paper is to describe the implementation details of an embedded GPS/INS software receiver. Several different methods of improving performance in difficult environments have been studied for the past few decades, but vector tracking and deep integration (or ultra-tight coupling) has been especially popular in the past few years. Vector tracking algorithms boast the ability to maintain signal lock in weak signal-to-noise ratio environments such as urban canyons or heavy foliage. Another touted benefit is the ability to instantly reacquire GPS signal lock after an outage. The addition of an inertial sensor to aid the vector tracking algorithms is known as deep integration or ultra-tight coupling. The addition of this inertial sensor further boosts immunity to jamming and receiver dynamics. Implementing vector tracking and deep integration on a real-time platform does not come without its drawbacks. Besides the typical real-time deadlines, a full traditional (non-vector) GPS receiver must be implemented to initialize the vector tracking algorithm. The addition of an IMU also requires the algorithm to track attitude and inertial bias states, which increases the size and complexity of the algorithm. In this paper, the design of an FPGA hardware platform to perform both traditional and vector tracking/deep integration is described in detail along with some preliminary computational results.