# Channel Measurement and Feasibility Test for Wireless Avionics Intra-Communications
## 4 Measurement Results
### Feasibility Test and Power Delay Profile  
To verify the feasibility of adopting IEEE 802.11 physical layer specification in KT-1 Woongbi, we checked block error rate (BLER), constellation, and throughput during packet transmissions. During our experiments, we set a transmit power of USRP as 20 dBm (=100 mW). Note that the transmit power set in our experiment can be a reference value for the minimum required power for the communication in the aircraft since SDR devices (i.e., USRPs) usually have less performance in terms of radio transmission/reception compared to commercial radio devices. (It would be interesting to see the performance result (i.e., transmission success/fail) with commercial grade radio devices. However, unfortunately, as mentioned in Section 3, there are no commercial antennas that support those band since the 4.2-4.4 GHz bands are allocated for WAIC by ITU. Thus, we only considered the results measured by the self-produced monopole antennas.) Figure 8 shows feasibility test in our experiment. Figure 8a indicates success of packet transmission, determined by almost zero BLER, clear constellation points, and a certain level of throughput. On the other hand, Figure 8b represents fail of packet transmission, which shows 100% BLER, none constellation points, and zero throughput. Based on the feasibility test, we classified the measurement points in Figure 6 into the communication regions summarized in Table 3. The criterion of classification was the success/fail of packet transmissions between the given measurement points. Fortunately, we could clearly differentiate the success/fail of packet transmissions, as shown in Figure 8, between any measurement points. Specifically, we chose any two measurement points among P0-P7. If a packet transmission was successful (i.e., zero BER, clear constellation points) between those two points, then those two points were considered as the same communication region. In other words, in our context, communication regions mean an area where reliable wireless packet transmissions are feasible between any points in each region under the transmit power constraint (\(\leq\)20 dBm). (The power constraint under 20 dBm was sufficient in our experiments since we considered intra-avionics sensor network environments.) For example, reliable wireless packet transmissions were feasible between P0 and P2 since they were in the same Region 2. However, if we considered P0 (Region 1 and 2) and P7 (Region 4), then we would experience a transmission failure. Figure 9 shows APDP measurement results at each communication region. We omit the result for Region 3 (left wing) in Table 3 since it was similar to that in Region 4 (right wing). Since we used OFDM transmission in 20 MHz (effectively, 52 subcarriers with 16.6 MHz) at 4.3 GHz, we had about 0.06 \(\upmu\)s \((=\frac{1}{16.6\,\mathrm{MHz}})\) time resolution in our measurements. For all measurements, line-of-sight (LOS) signal path was a dominant component of measured APDP since the measurement distances were relatively short (less than 2 m). We notice that the engine room (P1) contained more electrical devices and wires compared to the left rear room (P2), and those contributed to more reflections (please refer to Appendix A for detailed inside photos). Accordingly, Figure 8(a) shows a relatively clear non-LOS (NLOS) effect (i.e., multiple prominent peaks) rather than Figure 8(b). Although NLOS effects were observed in each measurement, those were not a crucial factor for implementing wireless networks in this environment. **Remark 1**. : _It is worth noting that we performed our experiment in both LOS and NLOS environments where electronic devices and mechanic components are filled in the measurement points, as shown in Figure 8(a). Interestingly, our measurement results properly fit a single tap channel model rather than multi-tap channel model due to the dominant LOS channel effect rather than the NLOS one. Accordingly, our measurement results and feasibility test provided insight for WAIC system design.