New trends in global navigation systems: implementation of a GPS antenna array receiver

ABSTRACTThis paper provides details about the implementation of anantenna array receiver devoted to GPS L1 navigation sig-nals. The design is based on the commercial RF front-endchip which performs the frequency down-shifting and thedigitization. On account of the use of array digital beam-formingalgorithms, theproposedplatformisequippedwitha calibration subsystem which ensures a phase reference,and a data acquisition subsystem for post processing meth-ods. Thisarchitectureallowsthetestofbeamformingstrate-gies with real-life data.1. INTRODUCTIONRecent developments in the design of Global NavigationSatellite Systems (GNSS) receivers point to the use of spa-tial diversity [1]. Although array theory has been deeplydeveloped in the literature, implementation is often omittedbut contains the key to demonstrate the concept of antennaarray devoted to GNSS. Besides the benets of the spatialdimension can bring to the synchronization performance,hardware technology seems to turn towards the SoftwareDened Radio (SDR) approach [2], replacing traditionalApplicationSpecicIntegratedCircuit(ASIC)deviceswiththemoreexibleFieldProgrammableGateArrays(FPGAs)[3]. The aim of this paper is to give some details about theimplementationofanantennaarrayreceiverwhichprovidesa data storage facility, allowing a test–bed suitable to be ex-plored by software–radio signal processing techniques.The proposed receiver is composed by eight RF front–endswhichprovidetheL1GPSsignalinananaloganddig-ital form. The system is intended to process the GPS L1signal, a spread spectrum signal centered at 1575 :42 MHz,BPSK modulated by the navigation Coarse-Acquisition(C/A) code at 1:023 Mcps and modulated again by a nav-igation data message on a 50 bps BPSK modulation. Eachfront-end comprises a Low Noise Amplier (described insection 2.2), three IF stages (section 2.3) and A/D conver-sion (section 2.4). In practical systems, one of the maindifcult aspects in an smart antenna is to calibrate the am-plitude and phase of every channel over temperature and