Alternative DME/N pulse shape for APNT

The Distance Measuring Equipment (DME, DME/Normal) based navigation method known as DME/DME positioning has been proposed as one of the possible Alternative Position, Navigation, and Timing (APNT) services for aviation during the outage of the Global Navigation Satellite Systems. A DME interrogator measures the slant range to a DME transponder by means of the elapsed time in exchanging a pair of DME pulses. A typical type of a DME pulse being used in practice is a Gaussian pulse, and the achievable DME ranging accuracy is primarily determined by the pulse shape. This paper presents an alternative DME pulse waveform that is able to provide much higher range accuracy than the conventional Gaussian pulse. The alternative pulse waveform is compliant with the pulse shape requirements in the current DME specifications to maintain the compatibility with existing DME ground transponders and avionics. This developed alternative DME pulse also takes into account the spectral density characteristics so that it does not cause interference to adjacent channels even when it is transmitted at the same high power of 1,000 Watts as the traditional Gaussian pulse. This paper will discuss the design approaches of the alternative DME pulse shape and show the improvement of range accuracy and multipath mitigation compared to the traditional Gaussian pulse. In addition, the paper will discuss the potential constraints in implementing the alternative pulse in the existing transponders and avionics.