Performance evaluation of avionics communication systems with radio frequency interference

Abstract

Telemetry, Tracking and Command (TTC) subsystems are crucial for avionic designs. To ensure the integrity, robustness, and security of the TTC communication link, we developed physical layer reliability techniques, where direct-sequence spread spectrum and turbo coding with soft-input-soft-output decoding are applied. Different from personal communication system where Rayleigh fading channel is a good estimation, we investigated the Rician fading channel due to the line-of-sight (LoS) link between the ground station and the avionic system. Specifically, the performances of our proposed techniques are evaluated in the presence of unintentional and intentional jammer situations. To test and verify TTC link performance with the proposed techniques, we used the Intelligent Fusion Technology, Inc. (IFT) communication data link simulator (ICDLS). Results demonstrate that the TTC link with our proposed techniques increase reliability as compared to traditional channel coding schemes. Avionic reliability robustness is shown when there exists intentional jammers that can cause large jamming interference. Introduction In wireless communications, bit error rate (BER) and frame error rate (FER) are two crucial metrics in physical (PHY) layer Telemetry, Tracking and Command (TTC) communication link evaluations [1]. BER quantifies the quality of end-to-end data transmission in wireless environments, where signals are often distorted by wireless channels and disrupted by intentional or unintentional interferences. FER is another metric to quantify the quality of a data transmission link; however, different from BER, it is an interface to upper layers in an open systems interconnection (OSI) model for system-level performance evaluation and communication protocol stack designs. It is important to evaluate the performance of a proposed communication system before implementing to avoid unnecessary unavailing efforts. For instance, in Figure 1, BER versus Eb/N0 at a receiver are plotted for uncoded system with binary phase shift keying (BPSK) modulation in two kinds of wireless channels, where Eb represents the received bit energy and N0 represents single-sided power spectral density of noise. The two wireless channels are additive white Gaussian noise (AWGN) channel and Rayleigh fading channel. Figure 1. BER v.s. Eb/N0 for Various Wireless Channel Situations It can be seen that to achieve a given BER, such as 10−3 for voice transmission, it requires received Eb/N0 is around 7dB in AWGN channel, but 24 dB in Rayleigh fading channel. Therefore, after field testing for wireless channel modeling, the power control module at the transmitter must provide the required Eb/N0 to ensure voice transmission, if only BPSK modulation scheme is employed. However, at the same time, for a TTC link, due to the low probability of intercept (LPI) and low probability of detection (LPD) requirements [2, 3], conflicts on transmission power could be raised, such as in Rayleigh fading channel, while ensuring both metrics. Therefore, link-level data transmission -5 0 5 10 15 20 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 Eb/N0 (dB) Bi t e rro r r at e (B ER ) AWGN channel Rayleigh fading channel