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With the rapid development of mobile communication technology, wireless mobile, broadband and IP-based communication system showing trends, to improve the competitiveness of 3G broadband wireless access market, as well as respond to from WiMAX, Wi-Fi and other wireless broadband challenges of access technology, 3GPP organization UTRA and UTRAN LTE (Long Term Evolution, LTE) technology research plans to implement 3G technology to B3G and 4G smooth transition. Modern 3G, including LTE, 4G mobile communication base station mainstream distributed base station, its greatest feature traditional macro base station is divided into the baseband processing unit (BBU) and remote radio unit (RRU), both connected by optical fiber , flexibility, construction easier, faster, and greatly reduces the difficulty of engineering, installation and saves engineering time required, and the advantages of the engine room select unrestricted. LTE distributed base station of a pre-research project 2.3 to 2.4GHz band two-channel RRH unit (RRU), developed for the background, LTE distributed base station RRU digital front-end part of its structure, algorithm principle and concrete realization. This paper briefly describes the characteristics and composition of LTE, the background, the development of the main technical features, as well as distributed base station system, then in the proposed introduction of digital front-end LTE distributed base station RRU digital front-end design before the concept and introduces a few commonly used wireless communication system transceiver structure, after in-depth analysis of the software radio digital front-end principle on the basis of a single FPGA-based LTE distributed base station two antennas RRU digital front-end design, combined with software-defined radio thinking program, and given the system block diagram and working principle of the design can handle two 20MHz bandwidth LTE signal, the system clock 368.64MHz. Then the author detailed description of the key modules of the system design methods, including DDC, DUC using the industry increasingly popular and efficient graphical FPGA development tools, System Genetator design, integrated in the FPGA greatly shorten the development cycle. This program FPGA integrated digital predistortion module to improve the linearity of the amplifier up to 20dBc ACLR improvement of the transmitted signal EVM improvement of about 2% rms. Finally, the design of good digital front-end combined analog front end linked to reconcile test, the test results show that the digital front-end to reach a predetermined design requirements. Compared with other commonly used transceiver digital front-end design, digital front-end design of the program with a broadband high-speed, high integration, cost savings, flexibility, the design is simple and quick, and can handle both multi-channel and debugging easy. Apply the digital front-end TD-LTE distributed base station RRU has high practical value in the rapid development of 4G communication.
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