Ambiguity in RMS Delay Spread of Millimeter-Wave Channel Measurements

The root mean square (RMS) delay spread is an important statistical parameter in channel modeling. This paper addresses the ambiguity in the estimation of the RMS delay spread from millimeter-wave (mm-wave) channel measurements, which is caused by the need for a threshold to exclude noise and spurious peaks. An overview of various thresholds used in literature is provided. The suitability of these threshold implementations and methods is investigated by applying them to mm-wave channel measurements. Based on the corresponding results, recommendations are proposed to ease the threshold selection and to enable more consistency in RMS delay spread estimates between different authors. These recommendations include the definition of a noise threshold, a 30 dB multipath threshold and the use of a sample method. The recommendations are derived from mm-wave data, but can also be applied to RMS delay spread measurements at other radio-frequencies.