Research On Digital Intermediate Frequency For CDMA2000 Based On Software Radio

Telecommunication system has been transformed from analogy system to digital system. In this period software radio has been raised. The clou of Software Radio(SR) is to establish a open, standard and modular universal hardware Platform where the A/D converter is moved as closed as Possible to antenna and all of the communication function is realized by software. We should convert IF analog signal even RF analog signal into digital signal. However, limited by the current technical level of the chip, it is difficult to realize RF signal digitalization. Thus, IF signal digitalization becomes the inter-specific choice.This paper is a research project of transceivers in an CDMA2000 base-station. Its main content is about how to treat with the signal sampling in IF band with digital method completely for CDMA2000 System.This thesis firstly introduces SR base theory, then the system architectures of BTS digital IF are investigated and compared in this report in researching CDMA2000 digital IF. A kind of broadband-architecture is selected and designed. According to the architectare, the system design in detail is implemented, and selecting the key components based on the analyzing result. The circuit designs of Up Link (UL) and Down Link (DL) units, as well as their PCB designing, debugging and testing are finished. A modified CIC compensation filter is realized to reduce the CIC's passband error that distorts the original signal. The channel shape filter is implemented by a programmable TDD inverse architecture FIR filter, which makes good use of FPGA resource and display the FPGA parallel ability. The paper presents a DAGC algorithm, which has been achieved the dynamic limits of 96dB with the flatness of 0.1 dB. AGC produces a constant demodulated signal level to the baseband unit regardless of the RF signal level. The circuit unit can support 4 channels of CDMA2000 digital IF.Compared with the original analog BTS system, the architecture of this system is improved much and more simple. And the cost is lower too. The measurement results of it are accorded, with the requirement of 3GPP specifications. The results of this, thesis reveals that the application of SDR in 3G are reasonable.