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Mitigation of interference radio altimeter signals by bit Interleaving of wireless avionics communications transmit signals

IP.com Disclosure Number: IPCOM000244010D
Publication Date: 2015-Nov-05
Document File: 5 page(s) / 1M

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Mitigation of interference radio altimeter signals by bit Interleaving of wireless avionics communications transmit signals: IP.COM

Abstract

Transmission techniques for wireless communication networks are well specified in the IEEE 802 15 4 WirelessHART Highway Addressable Remote Transducer Protocol or ISA 100 11a standards The use of interleaving techniques increasing the robustness of the wireless communication networks onboard aircraft against radio altimeter signals is not part of these standards Wireless Avionics Intra Communication WAIC Systems are operated in a frequency band from 4 2 to 4 4GHz on board of an aircraft This frequency band is also used by aeronautical Radio Altimeters RA employing a Frequency Modulated Continuous Waveform FMCW type signals WAIC systems and FMCW RA are typically installed and operated on board of the same aircraft Therefore mutual interference between these systems is to be expected and needs to be avoided Signals of FMCW RA have the potential to significantly interfere wireless communication between WAIC systems This document suggests and describes a method for mitigating FMCW RA signals causing interference The new approach concerns the specific application of the interleaving algorithm and parameters J and L to waveform parameters duration and bandwidth of the Radio Altimeter and the WAIC channel bandwidth and data rate Subsequently a Forward Error Correction revises all bits errors caused by an FMCW RA within the period L after de interleaving

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Mitigation of interference radio altimeter signals by bit Interleaving of wireless avionics communications transmit signals

Transmission techniques for wireless communication networks are well specified in the IEEE 802.15.4, WirelessHART (Highway Addressable Remote Transducer Protocol), or ISA-100.11a standards. The use of interleaving techniques increasing the robustness of the wireless communication networks onboard aircraft against radio altimeter signals is not part of these standards.

Wireless Avionics Intra Communication (WAIC) Systems are operated in a frequency band from 4.2to 4.4GHz on board of an aircraft. This frequency band is also used by aeronautical Radio Altimeters (RA) employing a Frequency Modulated Continuous Waveform (FMCW) type signals. WAIC systems and FMCW RA are typically installed and operated on board of the same aircraft. Therefore mutual interference between these systems is to be expected and needs to be avoided.

Signals of FMCW RA have the potential to significantly interfere wireless communication between WAIC systems.

This document suggests and describes a method for mitigating FMCW RA signals causing interference.

WAIC systems are digital wireless communications systems, which can be installed at any location inside and outside the aircraft fuselage. WAIC systems enable a wireless communication between avionic systems installed on board the same aircraft. Data packet transmissions between WAIC systems are performed via radio channels with a fixed bandwidth BWand center frequency within the 4.2 to 4.4GHz frequency range, cp. Figure 1.

In order to measure its altitude civil passenger aircraft are typically equipped with an FMCW Radio Altimeter. FMCW RA generally use saw tooth or triangle shaped waveforms with an in- or decreasing instantaneous frequency. Therefore, FMCW RA signals can be described by an infinitely repeating sequence of frequency ramps. Frequency ramps are characterized by their duration TS, Bandwidth BSand their center frequency, cp. Figure
1.

WAIC systems and FMCW RA are operated in a common frequency range on board the same aircraft. Therefore mutual interference between these systems is likely: The wireless communication between WAIC systems will be interfered by an FMCW RA signal when its instantaneous frequency falls within the bandwidth of the utilized WAIC communication signal. Due to the continuously in- or decreasing instantaneous frequency of the RA signal, this interference is limited in time. For each frequency ramp the duration in which the RA signals resides within the bandwidth Ti of WAIC communication signal is described by

Ti= BWTS/ BS.

Considering a single frequency ramp, interference between WAIC systems will only occur within a duration Ti potentially resulting in a burst of bit errors in the received WAIC communication signal (cp. Figure 1). Assuming that all bits received by a WAIC system during the time Tiare erroneous, the number of bit errors Necan be estima...