Civil aviation is considering the use of wireless transmission technology for safety-related on-board machine-tomachine communications. The crucial factor is the availability of a globally harmonized radio frequency band with predictable characteristics in terms of signal propagation and interference induced by other users of that frequency band. Currently the International Telecommunication Union and the International Civil Aviation Organization are establishing the regulatory environment allowing the usage of the band 4. 2-4.4 GHz for socalled Wireless Avionics Intra-Communications. A WirelessAvionics Intra-Communications system essentially provides highly reliable short-range radio links between two or more points on board an aircraft. Since the frequency band 4.2-4.4 GHz is also used for radio altimetry on board civil and state aircraft, it is important to understand the coupling mechanisms between WAIC systems and the Radio Altimeter system onboard the same aircraft as well as onboard different aircraft. For this reason an extensive measurement campaign as described in this paper was carried out. The purpose of this campaign was to assess the degree of coupling between the antennas of both systems for a variety of antenna constellations involving one or two commercial short-haul aircraft of type Airbus A320-200 and A321-200. Keywords-wireless avionics intra-communications (WAIC), coupling measurements, radio altimeter, wireless sensor network.I.

Abstract-Ultra-wideband (UWB) techniques are recently targeted as a broadband short range solution for in-flightentertainment (IFE) systems. Despite the in-cabin channel can be considered as an indoor channel, under the current aviation regulations, and due to the usual metal cabins and cylindrical shapes, these scenarios are particular for wireless applications. In this paper it is presented an experimental characterization of the UWB channel within an Airbus 319 aircraft cabin based on a real-time multiple-input-multiple-output (MIMO) UWB channel sounder. Here, the delay spread and coherent bandwidth have been calculated for different antennas configurations and distances. Besides, the in-cabin path-loss exponent has been calculated based on a large amount of data. Moreover, dynamic range metrics have been introduced for channel analysis and performance comparisons along the cabin.