ABSTRACT:The US Federal Aviation Administration (FAA) is developing alternative navigation concepts to maintain operational capacity and efficiency even with the loss of Global Positioning System (GPS). One concept being studied for alternative position navigation and timing (APNT) is a ground based passive ranging system. This system has few capacity constraints and can provide other benefits. The APNT passive ranging system would use existing FAA terrestrial infrastructure, particularly distance measuring equipment (DME) ground beacons. APNT project team has developed a DME Pseudolite (PL) concept that enables a passive ranging signal on DME that is compatible with existing DME operations. It can provide additional benefits for APNT and non-APNT users with its data transmission. This paper introduces the DME PL concept and assesses the potential performance of the system. The paper focuses on signal structure design for best data capacity. It formulates a methodology and modeling for the developing the design. Copyright # 2015 Institute of Navigation. OUTLINEThe paper is divided into four sections. The first section reviews basic DME operations and introduces the basic concept of DME PL. It discusses how DME PL and traditional DME differ and complement each other. Also discussed are the requirements and desired capabilities for the design.The next two sections analyze the performance of the DME PL signal design when it functions alongside DME. The second section examines measured signal precision. The third section focuses on determining the best signal structure design in terms of effective data rate. It develops a methodology and modeling tools to optimize the design. These tools represent an important outcome as the current design specification represents a starting point. As those specifications are refined, the tools can be applied to optimize the system based on the new limitations. Furthermore, the tools are useful in design trade-off studies. The paper examines modifications to the basic concept that would improve data capacity but at the expense of increased changes to the ground station. The tools help quantify the benefits of the modifications.The last section discusses signal design concepts to handle unique DME interference. In particular, DME Morse code transmissions, sent every 30-40 sec [1], can be problematic for DME PL if these are not accounted for. The section discusses how DME PL would operate during these occurrences to retain its ranging capabilities. BACKGROUND

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