Sanjeev Gunawardena

Closed-Loop Sequential Signal Processing and Open-Loop Batch Processing Approaches for GNSS Receiver Design

Global navigation satellite system (GNSS) receiver design is considered in terms of closed-loop and open-loop receiver architectures that utilize sequential and batch processing techniques. The paper uses the Global Positioning System (GPS) as a case study to demonstrate that an open-loop approach that combines batch and sequential signal processing improves GNSS signal tracking characteristics as compared to the traditionally applied closed-loop sequential receiver design for a number of important application areas. Particularly, for flight test scenarios considered, it is demonstrated that open-loop batch/sequential processing improves the GPS tracking margin by 8 dB as compared to the closed-loop sequential tracking for the case of deep GPS/Inertial Navigation System (INS) integration mode that performs code and carrier phase tracking and data bit recovery.

Decoding Navigation Data Messages from Weak GPS Signals

A new method for decoding navigation data bits from very weak Global Positioning System (GPS) signals is presented. Coherent signal integration is applied over a time period that includes multiple navigation data bits. A search is performed for a combination of bits that maximizes the signal energy during the coherent integration.

Controller-pilot communications using a VDL Mode 2 datalink for the NASA runway incursion prevention system

NASAs Runway Incursion Prevention System (RIPS) was tested between September and October 2000 at the Dallas Fort-Worth International Airport (DFW). Controller-Pilot Datalink Communications (CPDLC) represented one component of the RIPS program. Air traffic controllers relayed surface operations instructions to NASAs 757 research aircraft via a Controller Communications and Situational Awareness Terminal (C-CAST). The Onyx mainframe computer aboard the 757 decoded these messages and sent automatic acknowledgements back to the C-CAST. The CPDLC messages were sent over a datalink utilizing the ICAO-defined VHF Digital Link (VDL) Mode 2 protocol. This paper presents implementation and performance details of the datalink. The paper describes the VDL Mode 2 protocol, the overall architecture of the CPDLC system, hardware-software interfacing details, CPDLC message formats, signal coverage data for the DFW airport, and design details of the Airborne Datalink Manager (ADLM) software used for this work.

Mitigation of GPS Cross-Correlation Errors using Semi-Codeless Tracking

Cross-correlation properties of the Global Positioning System (GPS) coarse acquisition (CA)-code can significantly degrade measurement performance for high precision applications. The use of semi-codeless P-code measurements of the Link 1 (L1) carrier signal for the mitigation of CA-code cross-correlation errors is investigated. The trade-off between cross-correlation error mitigation and squaring loss (SL) of the semi-codeless tracking is discussed. Test results are used to demonstrate the efficacy of using P-code measurements for the cross-correlation error mitigation.