Intermediate Frequency Digital Receiver Of SDR Design & Realization

Receiver is a key part of radio communication system. The traditional radio receiver suffers simple function and poor signal processing. Hardware plays an important role in the traditional radio receiver world so its expandability is limited. But Software Defined Radio (SDR) is more advanced than the traditional. It is characterized of module and standard simple hardware. In SDR, it adopts Digital Signal Processing technology and its design theory is to realize radio communication function through upgrading application software. The key technology in SDR include wideband/multiband antenna, wideband RF signal processing, wideband A/D/A conversion, DSP technology and real-time operation system etc.The emergency of SDR brings about the renovation of receiver. Its working principle is to sample RF signal first, then load different software to DSP signal to obtain different waveform modulation and demodulation. Owing to the limited component level, currently we cannot directly sample RF signal instead of sampling wideband IF (intermediate frequency). Moreover, the receiver is composed of special chips to strengthen its powerful function. Such kind of receiver meets the communication requirements of modern military forces, in a word, interoperability and compatibility. This design scheme also makes maintenance cost reduce considerably and development cost decrease.In my design of "IF digital receiver in Software Defined Radio", the center frequency is 10MHz, IF modulation signal with 5MHz bandwidth, channel bandwidth with 25KHz is being sampled and demodulated. The data flow is sampled by AD then processed by DDC (Digital Down Converter) HSP50216, the data, in one way, output from D/A to form analog signal, then in another way, it is sent to signal processor through DMA transmission path of DSP, then signal processor will test the carrier. In my development, only the carrier signals more than 10MHz are digitally demodulated, it is analyzed as follows:1. Samples the IF carrier signals based on the "Over Sample Theory", to avoid the overlapping aliased components and avoid signal distortion caused by spectrum overlapping so that the original signal is much easier recognized.2. Filters the signals by applying FIR digital filter algorithm so as to improve the technical specifications.