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With the increasing requirements on the quality of the wireless communication service and communication rate, many different techniques have been proposed to increase the channel capacity in order to improve signal quality, and reduce the error rate of the transmission of information. Distributed antenna system (DAS, Distributed Antennas System) has been a concern of the program as a way to effectively reduce the transmit power, increase channel capacity, reduce transmission bit error rate and effective coverage of the \The distributed antenna system is composed by a base station and a plurality of the antenna unit connected to the base station, the base station control the transmission of each antenna element signal, and each antenna element of the received signal processing, the distributed antenna system can be deemed a special a multi-input multi-output (MIMO, Multiple Input Multiple Output) system. Thesis studied channel characteristics of the distributed antenna system, and the quality indicators to measure the system performance of distributed antenna, and detailed description of the type of signal fading in wireless communication, as well as several commonly used channel model, focuses on distributed antenna system an integral factor of the channel model used, as well as composite shadow fading channel mathematical derivation. At the same time, a brief introduction to the performance evaluation parameters commonly used in wireless communication system - bit error rate and channel capacity. Distributed antenna system can be considered as a special MIMO system, in order to facilitate a more comprehensive and in-depth understanding of the distributed antenna system, the paper introduces the the various MIMO system model, including single-input single-output (SISO Single InputSingle Output) systems, single-input multiple-output (SIMO, Single Input Multiple Output) systems, multiple-input single-output (MISO, Multiple Input Single Output) systems as well as MIMO system, at the same time, in-depth analysis of the various system model error rate and channel capacity. Distributed antenna for existing cellular system structure (EDAS, the Existing the Distributed Antennas System) in the cell boundary area can not provide a sufficiently low bit error rate and a sufficiently high channel capacity problem, the paper proposes an improved cellular distributed antenna The system structure (IDAS, Improving Distributed Antennas System), the structure using a directional antenna unit and the antenna unit to give a reasonable placement. Papers in a single cell and multi-cell environment of IDAS, EDAS and traditional cellular systems (TC, Traditional Configuration) analysis and simulation results show that the phase for EDAS and TC, IDAS can better reduce the error rate and improve the channel capacity, especially in the cell channel quality is very poor a boundary area, and compared to the EDAS IDAS AS can largely reduce the complexity and lower costs in the network planning. At the same time, the paper also prove a larger shadow fading and shadow fading factor between different system BER performance and ergodic channel capacity.
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