## 1 Introduction
Since the receiver is only for a time transfer application, it makes a direct beam toward a single satellite (_i.e._, single-beamsteering-channel SDR). The receiver processes intermediate frequency (IF)-sampled data with 16 Msps (mega samples per second) rate (16 Msps real samples). This sampling rate is sufficient for GPS L1 C/A signals because L1 C/A-code bandwidth is about 2 MHz, but it is not enough for future GPS L5 signals whose code bandwidth is about 20 MHz. Further, 2-bit sampling resolution of this previous work does not provide necessary dynamic range for anti-jamming applications. In this paper, we present a novel SDR architecture for GPS anti-jamming reference station receivers with CRPA using COTS general-purpose parallel processors. The GPS SDR for CRPA presented in this paper has capabilities far exceeding those described in this previous work. Figure 1: Illustration of the functionality of our GPS SDR for processing a four-elememt controlled reception pattern antenna (CRPA) array. The receiver adaptively rejects jammers while steering high gains toward all GPS satellites in view. We achieved required computational power by parallel processing on a new generation general-purpose Graphical Processing Unit (GPU) and a novel design scheme (see [30] for the evolution of GPUs for general-purpose computing). Among many applications, GPUs can be used for sensor systems which require significant processing power (e.g., [31]) because GPUs provide very high computational throughput from their massive number of threads. GPU-based GPS SDRs without beamsteering capability have been previously developed by several researchers [32-35]. [PERSON] _et al._[32] developed an 8-channel GPS SDR capable of processing 40 Msps and 8-bit resolution data in real time using a single-core 3.0 GHz CPU and an NVIDIA GeForce 8800 GTX GPU. [PERSON] _et al._[33] developed a real-time GPS SDR supporting 12 channels with 8 Msps and 4-bit resolution data using an Intel Core 2 Q9450 CPU and an NVIDIA GeForce GTX 280 GPU. [PERSON] _et al._[34] stated that they developed a GPS SDR running 150 channels with 5 Msps and 14-bit resolution data using an Intel Xeon 5150 CPU and an NVIDIA GeForce GTX 285 GPU, however their paper does not present the design details. All these developments in [32-34] utilized GPUs for correlation operations for code tracking. On the other hand, [PERSON] _et al._[35] used an NVIDIA GTX 480 GPU to expedite GNSS signal acquisition. The GPUs that have been used by these previous studies are summarized in Table 1.  
Our GPS SDR for CRPA presented in this paper has 12 beamsteering channels for all-in-view satellite tracking (Figure 1), and it processes IF-sampled data at a 40 Msps rate (20 Msps inphase and quadrature samples) which enables future GPS L5 signal tracking whose bandwidth is ten times wider than the L1 C/A-code bandwidth. Further, our receiver processes digitized samples with 14-bit resolution. Although most commercial GPS receivers process 2-bit resolution data, more dynamic range is required for anti-jamming applications. As a very rough comparison, the GPU-based SDR in [34] effectively processes 750 Msps (5 Msps data and 150 tracking channels), but our GPU-based SDR for CRPA effectively processes 2,400 Msps (40 Msps data and 60 tracking channels because 12 channels for each antenna element of a four-element array and additional 12 channels for beamsteering). In addition, our receiver calculates signal covariance matrix for adaptive interference rejection which requires additional computational power. To the authors' knowledge, a real-time capable GPS SDR for CRPA with comparable functionalities on general-purpose CPU and GPU has not been previously demonstrated.