Yu-Hsuan Chen

Design and Implementation of Real-Time Software Radio for Anti-Interference GPS/WAAS Sensors

Adaptive antenna array processing is widely known to provide significant anti-interference capabilities within a Global Navigation Satellite Systems (GNSS) receiver. A main challenge in the quest for such receiver architecture has always been the computational/processing requirements. Even more demanding would be to try and incorporate the flexibility of the Software-Defined Radio (SDR) design philosophy in such an implementation. This paper documents a feasible approach to a real-time SDR implementation of a beam-steered GNSS receiver and validates its performance. This research implements a real-time software receiver on a widely-available x86-based multi-core microprocessor to process four-element antenna array data streams sampled with 16-bit resolution. The software receiver is capable of 12 channels all-in-view Controlled Reception Pattern Antenna (CRPA) array processing capable of rejecting multiple interferers. Single Instruction Multiple Data (SIMD) instructions assembly coding and multithreaded programming, the key to such an implementation to reduce computational complexity, are fully documented within the paper. In conventional antenna array systems, receivers use the geometry of antennas and cable lengths known in advance. The documented CRPA implementation is architected to operate without extensive set-up and pre-calibration and leverages Space-Time Adaptive Processing (STAP) to provide adaptation in both the frequency and space domains. The validation component of the paper demonstrates that the developed software receiver operates in real time with live Global Positioning System (GPS) and Wide Area Augmentation System (WAAS) L1 C/A code signal. Further, interference rejection capabilities of the implementation are also demonstrated using multiple synthetic interferers which are added to the live data stream.

A Real-Time Capable Software-Defined Receiver Using GPU for Adaptive Anti-Jam GPS Sensors

Due to their weak received signal power, Global Positioning System (GPS) signals are vulnerable to radio frequency interference. Adaptive beam and null steering of the gain pattern of a GPS antenna array can significantly increase the resistance of GPS sensors to signal interference and jamming. Since adaptive array processing requires intensive computational power, beamsteering GPS receivers were usually implemented using hardware such as field-programmable gate arrays (FPGAs). However, a software implementation using general-purpose processors is much more desirable because of its flexibility and cost effectiveness. This paper presents a GPS software-defined radio (SDR) with adaptive beamsteering capability for anti-jam applications. The GPS SDR design is based on an optimized desktop parallel processing architecture using a quad-core Central Processing Unit (CPU) coupled with a new generation Graphics Processing Unit (GPU) having massively parallel processors. This GPS SDR demonstrates sufficient computational capability to support a four-element antenna array and future GPS L5 signal processing in real time. After providing the details of our design and optimization schemes for future GPU-based GPS SDR developments, the jamming resistance of our GPS SDR under synthetic wideband jamming is presented. Since the GPS SDR uses commercial-off-the-shelf hardware and processors, it can be easily adopted in civil GPS applications requiring anti-jam capabilities.

Phase/Frequency Tracking in a GNSS Software Receiver

In the paper, a software-based technique for the tracking of frequency and phase of Global Navigation Satellite System (GNSS) signals is proposed. It is shown that a software-based receiver with precomputed, zero-phase carrier replicas for phase tracking is subject to phase jump in phase tracking and ambiguity problems in frequency estimation. A phase/frequency tracking architecture is proposed in which the frequency of the incoming signal is estimated based on a lead-lag structure which is similar to a traditional delay locked loop and the phase, after de-rotation, is estimated using a frequency-aiding phase locked loop. The effects of thermal noise and resolution-induced noise are analyzed and verified using simulation. The significance of frequency aiding in enhancing the phase tracking response is also described.

Development of a PC-based software receiver for the reception of beidou navigation satellite signals

Beidou is the Global Navigation Satellite System (GNSS) being developed in China, with the aim to provide a global navigation service that is similar to the Global Positioning System (GPS) and Galileo navigation systems. In this paper, it is demonstrated that through the flexibility and re-configurability of a PC-based software receiver in which the baseband operations are realized in terms of software, it is possible to acquire, track, and demodulate Beidou satellite signals even when only a limited amount of information is known. Further, with the Beidou interface control document now available, the proposed PC-based software receiver can be easily adapted to perform navigation functions. This research lays the foundation for the further development of navigation receivers and exploration of multiGNSS applications.

Accounting for data intermittency in a software gnss receiver

In a GNSS software receiver, blocks of digitized intermediate-frequency (IF) data are prepared at the front end and sent to the processing unit for signal acquisition, tracking, demodulation, and position fix. A problem that is observed in practice when the GNSS software module is co-located with a mobile phone device is that the digitized IF data are subject to data intermittency. The intermittency results from the use of mobile phone when the GNSS signals are being received or the execution of higher priority routine in the host computer. An improper buffering scheme at the front end may also lead to such phenomena. Such data intermittency leads to burst-type errors (rather than bit-type errors) on the data to be processed, posing a challenge for the tracking of the GNSS signals. Indeed, if not properly handled, a typical tracking algorithm is not able to accommodate such a large data gap. In the paper, a decision-aided tracking algorithm is developed for a seamless tracking of codes and phases. The effects of data intermittency on code and phase tracking are analyzed. To accounting for the effect without going through the reacquisition process, a detector based on signal power and continuity is then implemented to facilitate decision making. It is shown, through the processing of field gathered data, that the proposed algorithm can indeed be able to continuously track codes and phases in the presence of data intermittency.

Evaluation & comparison of ranging using Universal Access Transceiver (UAT) and 1090 MHz Mode S Extended Squitter (Mode S ES)

The FAA Alternative Position Navigation and Timing effort is developing technologies to provide navigation service capable of sustaining operations in the event of the loss of Global Navigation Satellite Systems (GNSS). APNT will utilize existing ground infrastructure to support this capability. One effort is to examine the use of the Automatic Dependent Surveillance Broadcast (ADS-B) ground infrastructure for ranging. This paper examines the use the two transmitted ADS-B signals: 1) 1090 MHz Mode S Extended Squitter (Mode ES) and Universal Access Transceiver (UAT). It uses the transmitted, on-air signal to examine multipath, ranging and timing performance.

Using Traffic Information Services Broadcast (TIS-B) signals for aviation navigation

Airspaces around the world are introducing capabilities and infrastructure to handle higher traffic densities. Highly capable satellite based navigation is being adopted to help aircraft operate more efficiently in the future. Furthermore, Automatic Dependent Surveillance Broadcast (ADS-B), where aircraft and other users broadcast their precise position, velocity and intent, is being introduced to help manage these airspaces. This allows air traffic and other aircraft to have excellent awareness of the airspace users. Adoption of new systems and technologies will only intensify as future airspaces will have to handle more varied traffic such as unmanned aerial vehicles (UAV). GNSS is critical to both future air navigation and ADS-B. Many of improvements in future airspace are primarily achieved with GNSS. This makes a robust, accurate terrestrial alternate essential should GNSS be unavailable. This paper examines using the Traffic Information Services Broadcast (TIS-B) service that is part of ADS-B implementation to provide terrestrial navigation. TIS-B would broadcast an aircraft position report generated using radar measurements. Conceptually, an aircraft may be able to use the reception of its own TIS-B report to provide knowledge of its position. This paper provides an overview of the concept and of the potential capabilities of the system.

Direct comparison of the multipath performance of L1 BOC and L1 C/A using on-air Galileo and Quasi-Zenith Satellite System (QZSS) transmissions

New Global Navigation Satellite System (GNSS) satellites will bring common, interoperable GNSS signals on L1. These new signals, L1C Global Positioning System (GPS)/Quasi-Zenith Satellite System (QZSS) L1C and Galileo E1 Open Service (OS), promise performance improvements in many areas. One key area is that these signals, which use binary offset carrier (BOC) and multiplexed BOC (MBOC), will provide better multipath performance over the binary phase shift keyed (BPSK) GPS L1 C/A. This paper evaluates the benefit of difference using on-air measurements of these signals. The evaluation will utilize signals from to-be operational Galileo and QZSS satellites. The assessment conducts BPSK and BOC processing using signals from the same satellite to eliminate the effects of geometry.