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POWER BUDGET AND SYSTEM PERFORMANCE ANALYSIS OF THE POF LINK FOR FUTURE AVIONIC APPLICATIONS
Sandy Cherian1, Holger spangenberg1, and Reinhard Caspary2
1Institut für Flugsystemtechnik, Deutsches Zentrum für Luft- und Raumfahrt (DLR) 2Institut für Hochfrequenztechnik, Technische Universität Braunschweig,
Braunschweig, Germany
Introduction The requirement of highly reliable and faster communication systems for future avionic data
transmission, in the range of 100Mbps– 1Gbps initiated the integration of avionics data buses from copper based networks to fiber based networks. Due to the ease of installation and lower costs, avionic industry finds great interest in multimode fiber for short range communication. It is possible to realize high speed, short range fiber optic link for avionics data communication with relatively low cost as a result of use of commercial off-the-shelf components (COTS) [1]. But the fact that avionic system data link consists of several components (due to the number of disconnects) and also the requirement that these COTS components must operate under stringent aircraft environmental conditions (e.g. RTCA DO-160) make the link loss power budgeting a major task in the avionics fiber optic system design. As the avionic fiber optic link has number of disconnects, this paper intends to evaluate the influence of POF (polymer optical fiber) connectors in the link loss budgeting. In this study, a point to point link is considered, as any of the avionic networks can be identified as a number of point to point links.
This paper aims to provide reliable and basic measurement data on the influence of flat connectors with an airgap (SMA) and connectors with physical contact (ST, SC) on the power margin and system performance on polymer optical fiber link for avionic applications.
Methods of Link Budget Analysis – An Overview Recommended methods for budget analysis based on MIL-STD 2052[2] and SAE AS5603 [3] are
numerical method, worst case method, and statistical method. In order to estimate the influence of different component loss in the link budget accurately, especially the connector loss, the Gaussian distribution of losses with each component and combined loss of the link are considered. Considering manufacture typical loss value as the population mean (µ) and worst case maximum as the three sigma standard deviation, the standard deviation (σ) for the connector as 0.36 dB(SMA) and 0.23 dB (connector with physical contact) is derived . The graph shown below is an example of probability density function of the loss of connectors. As we are intended to use the COTS components to an extended aircraft operating condition, test measurement data are adequate.
Figure 1. SC, ST Connector µ= 0, 3σ =0.7 SMA Connector µ=0.4, 3σ = 1.5
Test Setup and BER Measurement The test set up consists of 250Mbps transmitter, fiber link, connectors, optical attenuator (OA),
receiver, and a bit error rate (BER) generator. For all the test cases, the transceiver is modulated by coded mark inversion (CMI) pseudorandom binary signal for a data rate of 140Mbps, from the BER generator.
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3:15 PM – 3:30 PMWD3 (Contributed Oral)
978-1-4244-7345-8/11/$26.00 ©2011 IEEE
Figure 2. Experimental Setup
In order to get the reference BER curve, back to back measurement is performed [4, 5]. The loss is introduced in the link by OA and BER is measured. Thereafter the device under test (DUT), test fiber, and connectors are introduced in the link. One end of the DUT is connected to the OA and the other end to the mode mixer via SC/ST/SMA connectors. The output of the OA is then connected to the receiver via 2m long patchcord. In order to get the statistical estimate on the connector loss, we used different cases with many connector types in the link. The graph shows the relation between the receiver average power and BER. Before performing the BER test, receiver average power loss is measured separately using an optical power meter. Figure 3 shows an example of determining the power penalties due to the cable assemblies (Fig.3a) and due to connectors (Fig.3b). Power penalties can be estimated directly by taking the difference between reference curve and DUT curve.
Figure 3(a,b). BER Curve Estimate the Loss
Conclusion Statistical analysis provided an accurate estimate on the influence of different connectors in the link
performance. More link performance measurement data and test patterns for different cases under extended and normal operating conditions have been analyzed.
Reference: [1] Pignol, M, “COTS-based Applications in Space Avionics”, Conference on Design, Automation and Test in Europe, pp. 1213-1219, 2010 [2] MIL-STD 2052, Fiber Optic Systems Design; Department of Defence Design Criteria Standard, 10 October 1997 [3]AS 5603, Digital Fiber Optic Link Loss Budget Methodology for Aerospace Platforms, SAE Aerospace, November, 2007 [4] Marcus Müller, “Bit Error Ratio Testing,” Digital Communications Test and Measurement: High-Speed Physical Layer Characterization, Dennis Derickson, Marcus Müller, pp 169-241, December, 2007 [5] The Fiber Optic Association, Inc., Testing Fiber Optic Links, Reference Guide To Fiber Optics [Online]. Available: http://www.thefoa.org/tech/ref/testing/test/linktest.html
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