Fast Prototyping of Receiver Accelerators Using NI Labview FPGA

A. Soghoyan, D. Kinjarapu, D. Akopian

Abstract:	The modernization of Global Navigation Satellite Systems (GNSS) and the availability of more complex signals and modulation schemes boost the development of civil and military applications while the accuracy and coverage of receivers gradually improve [1]. The GNSS receiver performance is highly efficient in strong signal environments but the researchers continuously explore new ideas and methods in an effort to design less costly, faster and more sensitive receivers considering also weak/distorted signal environments. The developers address software and hardware accelarators or their hybrids for testing and prototyping more robust and flexible receivers for various conditions. Thus there is a need for reference receivers, associated SDKs, development platforms, simulators and testbeds to accelerate and facilitate their research. Traditional hardware incorporated design of a GPS receiver employing massive correlators on hardware accelerators such as Application Specific Integrated Circuits (ASICs), offers high performance but is less flexible, costly and time consuming. As alternative approach software defined radio (SDR) concept has emerged where all the digital signal processing tasks of the receiver are accomplished in software or on a flexible programmable processor such as Field Programmable Gate Array (FPGA) and Digital Signal Processor (DSP). Flexibility of the system is particularly important when GPS needs to be used indoors with an augmentation such as Assisted GPS, or A-GPS. This paper presents new aspects on a hybrid software/hardware (FPGA peripheral) solution for GPS receiver design and A-GPS support [2]. For fast prototyping the benefits of National Instruments (NI) LabVIEW [3] environment is utilized. With an optimal distribution of tasks between hardware reconfigurable peripherals and software components it would be possible to achieve higher performance. LabVIEW is a data flow programming platform with rich integrated digital signal processing libraries and interactive interface design essential for the simulation and testing of the software receiver. As a peripheral we consider NI PXIe 7966R FPGA [4] module and convenient host-target co-design using LabVIEW FPGA tool from National Instruments. Selected modular block correlator algorithms for GPS acquisition and tracking allow using standard modules and distributing tasks between the FPGA target and the PC host achieving high performance solution. Thus the paper overviews fast prototyping process and applies it for SDR performance acceleration. As a user friendly graphical programming language LabVIEW makes it easier to build systems with fast application prototyping and deployment. The testing GPS signal is generated using NI RF PXI signal generator along with the NI GPS Simulation Toolkit software. This paper also studies real-time GPS receiver operation with advanced correlator algorithms incorporated in GNU Radio design [5]. GNU Radio is a free and open-source software development toolkit that provides signal processing blocks to implement software radios. As an example application of the GNU Radio is GPS receiver and in our studies it is fully integrated in NI LabVIEW environment using dynamic linked libraries. The testing GPS signal is acquired by USRP databoard as a low-cost external RF hardware. A dedicated Labview A-GPS support is also developed to generate assistance data for available satellites. A-GPS significantly improves the acquisition of satellite signals, and relieves the receiver from the data demodulation tasks [3]. A-GPS receivers perform satisfactorily even with weak signals using external assistance such as satellite orbit parameters, reference time and coarse locations. Our solution is integrated with NI’s GPS simulator to provide aiding data both to a handheld device and also a laptop PC where the GPS receiver is located. The process follows the guidelines of Secure User Plane Location (SUPL) [6] which defines the assistance delivery format and communication between the user (client) and SUPL server. SUPL is the Internet Protocol (IP)-based network service to deliver information through a User Plane bearer between a SUPL Enabled Terminal (SET) (e.g. mobile devices) and a SUPL Location Platform (SLP) (e.g. A- GPS servers) for wireless communications developed by Open Mobile Alliance (OMA) [6]. The assistance data (ephemeris and almanac parameters) are generated by extracting navigation bits which are obtained by GPS simulator for RF signal generation using NI RF equipment. These generated assistance data are according to Radio Resource Location Protocol (RRLP) [7] and delivered through the RRLP Payload wrapped in the SUPL message. Coarse receiver location is either specified by the user or acquired from WLAN network if available or Internet using WLAN access point or IP address location databases. References [1] P. Misra, P. Enge. Global Positioning System, Signals, Measurements, and Performance. Ganga-Jamuna Press, Lincoln, MA. 2001 [2] N. Agarwal et al, “Algorithms for GPS operation indoors and downtown,” GPS Solutions. 2002, vol. 6, no. 3, pp. 149-160, Springler-Verlag Heidelberg [3] Labview, GPS Simulator, RF Signal analyzers and generators from National Instruments, www.ni.com [4] NI PXIe 7966R, NI FlexRIO FPGA Module for PXI Express, http://sine.ni.com/nips/cds/view/p/lang/en/nid/210272 , Accessed Jan. 11, 2013 [5] GNU Radio, http://gnuradio.org/redmine/projects/gnuradio/wiki/WikiStart , Accessed Jan. 11, 2013 [6] Open Mobile Alliance. Secure User Plane Location Architecture, OMA-AD-SUPL-V1_0-20070615-A. User Location Protocol, OMA-TS-ULP-V1_0-20070615-A, www.openmobilealliance.org. [7] 3GPP TS 44.031 Third Generation Partnership Project; Technical Specification Group GSM/EDGE Radio Access Network; Location Services (LCS); Mobile Station (MS) – Serving Mobile Location Centre (SMLC) Radio Resource LCS Protocol (RRLP), 2010.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	1517 - 1526
Cite this article:	Soghoyan, A., Kinjarapu, D., Akopian, D., "Fast Prototyping of Receiver Accelerators Using NI Labview FPGA," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 1517-1526.
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