# Channel Measurement and Feasibility Test for Wireless Avionics Intra-Communications
## 1 Introduction  
Wireless avionics intra-communications (WAIC) refers to radio communication systems that interconnect avionics components (e.g., sensors and actuators) installed in an aircraft [1]. Wireless technologies to enable communications outside an aircraft have been broadly investigated and developed to support various necessary functionalities such as aircraft-ground control, inter-aircraft communications, and radar. Contrary to this, applying wireless networks (e.g., intra-avionics sensor networks) inside the aircraft has been relatively less highlighted due to the concerns about wireless communication on reliability, safety, and security, compared to wired ones [2]. However, recent advances in wireless communication technologies show that mandatory operational-criteria (e.g.,reliability and robustness) of the aircraft can be sufficiently satisfied through wireless networks, which results in the overall weight reduction of the aircraft (e.g., removing the wired cables) [3]. In particular, statistics show that wireless networks will lead to 15% lighter designs than existing ones in terms of overall weight and will bring 12% increase in fuel efficiency in the aircrafts [4]. Accordingly, international telecommunication union (ITU) decided to allocate a frequency band from 4.2 GHz to 4.4 GHz for the WAIC at world radio-communication conference (WRC) 2015 [5]. Several studies related to WAIC are reported recently. [PERSON] and [PERSON] investigated the compatibility of WAIC systems with radio altimeters at 4.2-4.4 GHz by simulations [6], and analyzed the modulation performance in the WAIC systems with consideration of various factors such as modulation efficiency, net average application data rate, and protocol overhead [7]. [PERSON] et al. [2] investigated design issues in WAIC systems across several layers: from physical-layer to application layer. [PERSON] and [PERSON] [8] proposed a mathematical framework to evaluate wireless protocol candidates in terms of the deadline missing probability and the packet loss probability. [PERSON] et al. [9] estimated path loss between inside a passenger aircraft (Airbus 320-200) cabin to exterior near the tip of the main wing. Although various aspects of WAIC have been thoroughly investigated in previous work, the feasibility test on wireless protocol candidates of WAIC has not been explicitly validated via real-field experiments. To investigate the feasibility of wireless protocols, channel measurement should be preliminarily performed before the planning and design of any wireless systems. In this study, we performed a real-field experiment to measure channel characteristics of the WAIC bands (4.2-4.4 GHz) and to investigate the feasibility of IEEE 802.11 protocol in real aircraft environments. (IEEE 802.11 physical-layer specification is one of the most promising protocols for the high data-rate applications in WAIC systems [3]. In addition, we considered KAI KT-1 Woongbi ([[http://www.koreaaero.com/english/product/fixedwing_kt-1.asp](http://www.koreaaero.com/english/product/fixedwing_kt-1.asp)]([http://www.koreaaero.com/english/product/fixedwing_kt-1.asp](http://www.koreaaero.com/english/product/fixedwing_kt-1.asp))) for our experiment.) Further, reliable transmission techniques (e.g., maximum ratio combining and space-time block coding) in intra-avionics sensor network environments were evaluated using our measured data. (The notion of WAIC includes intra-avionics sensor networks. However, in this paper, we use the terms WAIC and intra-avionics sensor networks interchangeably to indicate applying wireless networks in the aircraft.) We believe that our field test shed light on the first step for implementing WAIC systems in practice. The main contributions of this paper are summarized as follows:  
* We used software-defined radio devices and modified the IEEE 802.11 application framework to measure wireless channel for WAIC systems (see Sections 2 and 3).