Enabling High Capacity for Next Generation Fiber-Wireless System with MIMO and DSP Technologies

• Main Authors: Huang, Hou-Tzu, 黃厚茨
• Other Authors: Lin, Chun-Ting
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/2246wn

博士 === 國立交通大學 === 光電系統博士學位學程 === 105 === In this dissertation, two MIMO systems are investigated for indoor or outdoor application in next-generation communication systems. First, it shows the overview of wireless communication systems and introduces RoF technology for the current state of fiber to overcome the challenges of mm-wave transmission in next-generation communication systems. By applying MIMO technology to 60-GHz radio-over-fiber system to increase data rate, we analyse the characteristic of wireless channel by change the location of antenna. From the measurement, some of the antenna location arrangement can cause extremely low performance due to the high condition number of channel. Hence, to mitigate the penalty caused by higher CN, lattice reduction-aided detection with Lenstra-Lenstra-Lovasz algorithm is utilized and experimentally investigated. On the other hand, comparing to our past work, we improve the fiber transmission distance from 4 km to 12 km by choosing proper carrier frequencies of two MZM driving signals. However, the generated 60 GHz OFDM signal will have beat noise after square-law photo-detection. Because the beat noise is analytically analyzed, and the beat noise re-construction technique is derived, the beat noise mitigation algorithm with the beat noise re-construction technique is utilized to reduce beat-noise-induced interference and improve signal-to-noise ratio. Based on the acknowledge of MIMO technology, we combine two transmission data streams and two corresponding SSBIs using multiple-output technology to expand transmission capacity. Training symbols were used to characterize the information of MIMO channels in order to separate the two data streams using their own SSBI. The use of iterative SSBI mitigation for the separation of data streams enables the recovery of the two data streams without affecting the MIMO channel or SSBI. To provide a system which both optical and wireless are operated with MIMO technique, optical layer signal multiplexing with polarization division multiplexing (PDM) has been investigated to transmit the optical signals for wireless MIMO transmission. A new method for tracking the polarization of a DD-PDM-OFDM system without employing extra optical components at the optical receiver is proposed. The key is that two polarization-orthogonal reference optical carriers are separated with an OFDM subcarrier frequency spacing, so that the issue of polarization tracking is converted to the issue of inter-subcarrier interference. With appropriate training symbol design, this approach makes it possible to combine both PDM and MIMO signal processing with the same DSP algorithm. However, noise enhancement due to channel inversion is observed with the proposed system. Therefore, the method of OFDM empty tone insertion is proposed, and the corresponding penalty of increasing overhead is also well analyzed. Also, subcarrier power pre-compensation is also adopted to improve the overall system performance and meet the BER forward error correction (FEC) limit for all states of polarization (SOP). For the last part of our work, to exploit the full potential of MIMO technique, we study the massive MIMO technique which is one of the candidate solutions for next generation mobile communication system. Using the law of large numbers, in a rich scattering environment, the full potential of massive MIMO systems can be achieved by utilizing simple digital beamforming techniques such as zero forcing (ZF) and maximum ratio transmission (MRT). However, using unlimited number of antenna is not realistic. Therefore, we focus on the improvement of system by applying M-MIMO technique with limited number of antenna by utilizing simulation with Matlab. In the simulation, the scenario is outdoor with carrier frequency of 2.1 GHz because most of the massive MIMO system in practice is at this frequency and it helps us to verify the simulation results. Besides, because the cost of setup and implementation are increased with M-MIMO system, we adopt the hybrid beamforming technique to further reduce the cost of implementation.