Research On Intermediate Frequency Technology For Distributed Antenna System

In the last decades, seamless coverage and high bit rate transfer are very crucial to the evolution of wireless communication system, the research and application of Distributed Antenna System (DAS) and Smart Antenna is drawing great attentions. Remote Antenna Technique is the basic foundation of realizing Distributed Antenna System (DAS). At present, Remote Radio Head (RRH) is commonly utilized in the DAS Solutions. But comparing to RRH, Intermediate Frequency (IF) Remote Connection has a large sum of advantages, which are requiring less wires, lower fading, lower cost and more flexible in assembling the system.In this thesis, a IF Remote Connection solution is proposed, which is based on the basic theory and research results of the Software Radio conceptions. The structure of the IF Remote Connections that contains Digital Down Converter (DDC) and Digital Up Converter (DUC) is designed. To insure the validity of the system, the structure is simulated via Matlab, as well as the DDC is realized on a FPGA chip. In the thesis, we mainly focus on the simulation and realization of the DDC module, as DDC and DUC are symmetrical to each other. The main function of DDC is that translating digital IF signal received from ADC to baseband for follow-up process, the whole process contains mixing with orthogonal signal, decimating the sample sequence, low pass filtering and channel shaping. The DDC module consists of Numerical Controlled Oscillator (NCO), frequency mixer, low pass decimating filter. Based on this structure, a Numerical Controlled Oscillator (NCO) which is implemented by the method of ROM Look-Up-Table (LUT) and a low-pass decimating filter algorithm that combines Cascaded Integrator Comb (CIC) filter and poly-phase filter are designed, which is to achieve the high-rate data-processing requirements and to minimize resource consumption of FPGA. In this blue print, numerical Controlled Oscillator (NCO) meets the requirement of flexibility and high frequency resolution. Cascaded Integrator Comb (CIC) filter has simple structure without coefficients, it carries filtering through delay units and adders, which is suitable for FPGA implementation. While poly-phase filter can combine signal extracting and anti-aliasing filtering together to achieve an parallel operation, in this way, it reduces the amount of computing and the implementation complexity.