Zero-Forcing Equalisation of Measured Optical Multimode MIMO Channels
Within the last years multiple-input multiple-output (MIMO) transmission has reached a lot of attention in the optical fibre community. Theoretically, the concept of MIMO is well understood. However, practical implementations of optical components for mode combining, mode maintenance and mode splitting are in the focus of interest for further computer simulations. That’s why in this contribution the specific impulse responses of the \((2 \times 2)\) MIMO channel, including a 1.4 km and 1.9 km multi-mode fibre respectively and optical couplers at both ends, are measured for operating wavelengths of 1326 nm and 1576 nm. Since pulsed semiconductor diode lasers, capable of working at different wavelengths, are used for the characterization of the underlying optical MIMO channel, inverse filtering is needed for obtaining the respective impulse responses. However, the process of inverse filtering also known as signal deconvolution is critical in noisy environments. That’s why different approaches such as Wiener and parametric filtering are studied with respect to different optimization criteria. Using these obtained impulse responses a baseband MIMO data transmission is modelled. In order to create orthogonal channels enabling a successful transmission, a MIMO zero forcing (ZF) equaliser is implemented and analysed. Our main results given as an open eye-diagram and calculated bit-error rates show the successful implementation of the MIMO transmission system. Finally, for practical investigations regarding mode combining, mode maintenance and mode splitting a \((2 \times 2)\) MIMO testbed using fusion couplers and a multi-mode fibre (MMF) length of 1.9 km is set up for an operating wavelength of 1326 nm. Together with the MIMO receiver-side signal processing the successful transmission of parallel data streams is presented.
KeywordsMultiple-Input Multiple-Output System Optical fibre transmission Multimode fibre (MMF) Signal deconvolution Equalisation
This work has been funded by the German Ministry of Education and Research (No. 03FH016PX3).
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