Real-Time Software Receiver for GPS Controlled Reception Pattern Antenna Array Processing

This paper demonstrates a real-time software receiver supporting GPS L1 C/A controlled reception pattern antenna (CRPA) processing. The software receiver is implemented on a widely-available recent generation multi-core processor and is capable of processing array signals from either radio frequency (RF) front-end modules or collected datasets. Most importantly, the receiver allocates dedicated satellite-tracking antenna patterns for each baseband receiver channel. The architecture of such a software receiver needs to be carefully developed so that it can process signals from each individual antenna, calculate the appropriate beam formed composite signals (one for each satellite/receiver channel) and then process those signals. Multitasking and synchronization mechanisms were developed to support the tracking of multiple channels in real time. To achieve real-time capability, parallel operations are necessary to reduce computation complexity. Bit-wise operations are exploited and implemented in the correlator. Additionally, Single Instruction Multiple Data (SIMD) instructions are used to efficiently calculate the covariance matrix for the beam steering algorithm. The architecture supports at least eighty tracking channels (ten channels from each of seven antennas plus ten composite beam formed signals) in real time. The CRPA software receiver was architected to operate without extensive set up and pre-calibration enhancing its suitability for commercial users. The algorithm design was architected to aid ease of set up. While conventional antenna array system receivers are used with the geometry of antennas and cable lengths known in advance, the algorithm implemented allows for operation without such a priori knowledge. Two beam steering techniques were tested. First is deterministic beam steering. An adaptive algorithm, Minimum Variance Distortion Response (MVDR) algorithm, was implemented to adaptively maximize signal power. The architecture determines of the carrier phase difference between signals from different antennas for a single satellite in order to build the steering vector. An experiment was conducted to show the enhanced C/No and controlled reception patterns through directing the CRPA toward the direction of satellite of interest. For evaluating interference rejection, a LI GPS simulator is used to build an environment with CDMA and CW interferences. The result shows that the MVDR algorithm has reliable performance than non beam steered and deterministic beam steering under the both type of interferences.