Description:
OBJECTIVE: The objective is to develop a software-defined navigation receiver with an improved assurance level for position, navigation, and timing (PNT). To mitigate the jamming, interference, and spoofing vulnerability of the Global Positioning System (GPS) receiver, the receiver gathers signals from GPS as well as other emerging global navigation satellite systems (GNSSs). Furthermore, the receiver can use opportunistic non-GNSS signals to extract useful information to assist the GNSS signals in order to improve PNT assurance. DESCRIPTION: Current Army operations rely heavily on Global Positioning System (GPS) signals to provide position, navigation, and timing (PNT) information. Most current navigation receivers rely on GPS signals only and are vulnerable to jamming, interference, and spoofing. GPS signal gaps often exist in urban and indoor environments, where the signals are susceptible to line-of-sight blockage and multi-path reflection. With the modernization of GPS satellites and the emergence of other global navigation satellite systems (GNSSs), including Galileo, GLONASS, and COMPASS, many more new GNSS signals other than the widely used GPS L1 signal is available. PNT information can also be extracted from signals of opportunity. These signals of opportunity include both satellite and terrestrial signals, such as Long Range Navigation (LORAN), cellular code division multiple access (CDMA), Global System for Mobile Communications (GSM), 4G Long Term Evolution (LTE), broadcast TV/Radio, Iridium, and much more. Dedicated pseudolites can also be set up to broadcast PNT information. These signals of opportunity can be combined with GNSS signals to increase the availability and assurance of PNT information, and create seamless situational awareness for Soldiers in combat. For example, it has been demonstrated that precision timing can be extracted from cellular CDMA signals and used to improve the coherent integration time of a GPS receiver to recover weak GPS signals in an indoor environment. Although GNSS receiver technology has matured significantly over the past 20 year, most receivers can only acquire signals at one or two GPS frequencies. Multi-GNSS, multi-frequency receivers are at the early stage of development as new GNSS signals are being broadcasted. Ways to develop techniques and algorithms to recover PNT or PNT-related information from the signals of opportunity mentioned above to assist and complement GNSS receivers in GNSS-denied and weak signal environments are being actively pursued by many researchers. However, computationally efficient implementations of these signal fusion techniques to improve PNT assurance and create devices that are suitable for portable use and have a low power form factor still require significant development. The goal of this program is to develop a reprogrammable, software-defined, multi-GNSS, multi-frequency receiver with signals of opportunity fusion. The receiver will leverage recent developments in high-speed analog-to-digital converters and field-programmable gate arrays (FPGAs) for signal capturing, digitizing, and processing. An efficient digital signal processing algorithm will be developed to integrate multi-GNSS signals and signals of opportunity. A broadband radio frequency (RF) front end that can cover the ~500-MHz band occupied by GNSS signals at L-band as well as other frequencies used by signals of opportunity will also be developed as part of the receiver. PHASE I: In Phase I, the proposer will analyze and select a suitable receiver architecture for receiving, capturing, and analyzing multiple GNSS signals at multiple frequencies as well as a select number of signals of opportunity. The receiver must cover GPS, Galileo, GLONASS, and COMPASS signals. The analysis must show integration of at least three signals of opportunity and demonstrate a path to incorporate more signals if necessary. The receiver can be implemented using a wideband direct digital RF front end or a channelized RF front end. In order to integrate signals of opportunity, an alternative architecture using a wideband RF channel for GNSS signals and a number of narrowband RF channels for signals of opportunity is permissible. The proposer will analyze the trade-off between the speed and vertical resolution requirements of the analog-to-digital converters and the digitized signal distortion. The proposer will investigate digital signal processing algorithms to process and track multiple GNSS signals. The tracking can be performed using Kalman filters as well as other innovative approaches. The tracking must be able to incorporate signals of opportunity. Performance metrics, such as receiver sensitivity, interference rejection, etc., will be defined in the study to quantify the improvement in PNT assurance level. The proposer will analyze the implementation of the signal processing algorithms in FPGAs and determine the computational resource requirements. The overall power consumption and performance of the receiver will be analyzed and compared to current state-of-the-art GPS receivers. PHASE II: In Phase II, the proposer will demonstrate a prototype of a multi-GNSS receiver with signals of opportunity fusion by implementing the receiver architecture and signal processing algorithm developed in Phase I. The receiver must be a complete receiver including a broadband antenna, an RF front end, digitizers, and a signal processing unit. A single broadband antenna must be used to cover all signals of interest. The signal processing unit must be implemented in an FPGA for programmability. Either evaluation boards or a dedicated developmental system can be used for the implementation. The proposer will perform a field demonstration of the prototype against state-of-the-art GPS receivers under adverse environments such as weak signal (indoor), intentional jamming, etc., using metrics developed in Phase I. The proposer will demonstrate the programmability of the receiver by using different numbers of GNSS signals and signals of opportunity. Programmability should also be demonstrated using the new and updated signal processing algorithm. PHASE III: In Phase III, the proposer will develop a portable version of the multi-GNSS receiver with signals of opportunity fusion. The receiver should be implemented in an application-specific integrated circuit (ASIC) form factor to lower the size, weight, power, and cost (SWAP-C). Initially, the SWAP-C of the multi-signal receiver could be worse than that of a state-of-the-art, single-signal GPS receiver because of the increase in functionality. At the commercialization stage of the program, the SWAP-C of the multi-signal receiver should be comparable to that of a state-of-the-art, single-signal GPS. Also, a military version of the multi-signal receiver capable of receiving, processing, and integrating military GNSS signals (for example, GPS L2 M code) will be developed for transition to PD PNT.
