A Study On The Communication System Based On The Software Radio

The software radio is the multi-functional intelligentization radio communication set of various functions of definition that is definited and realized by software. Its nucleus is: makes A/D and D/A commutator close to the antenna as far as possible, and realize the wireless communication function by software as far as possible based on the basic hardware platform. The hardware is regarded the basic platform that can realize wireless communication in the software radio, and its function of wireless communication is realized by software as far as possible. So, the wireless communication system has a very good commonality and flexibility, and the systems interconnection and update becomes convenient very much. The software radio is thought to be the third breakthrough following the analogue communication to digital communication and fixed communication to mobile communication. In the paper, we introduce the background and definition of the software radio, and discuss the key technologies of the software radio such as open bus structure to the software radio ,wideband/multi-frequency ranges antenna technology ,wideband A/D transformation technology, DDC technology , high speed DSP technology and so on.In this paper , we study the basic structure of the software radio ,and entirely analyze the three structures of software radio which are RF low-band direct sampling digital structure, RF pass-band sampling digital structure and wide-band IF pass-band sampling digital structure. The software radio is a new wireless communication system structure based on the modern communication theory, takes the digital signal processing as the nucleus, and takes microelectronic technology as the support. Its basic theory chiefly includes signal sampling theory, multi-frequency signal processing theory, high efficiency digital filter as well as orthogonal theory. In this paper, we also study these basic theories deeply.In this paper, we have a deep research of modulation and demodulation of communication signal with the angle of signal space, and the process of the modulation and demodulation can be comprehend:(1) The modulated signal can be expressed by N's dimension orthogonal base function, and its expanding coefficients are corresponding to the points in the signal space formed by orthogonal base function. After the mapping that from the defining modulated signal to N's dimension signal space, according to the defining modulation mode, we can accomplish the modulation process .(2) Under the circumstances of no noise, demodulation is a point to point remapping , but under the circumstances of noise and distortion, remapping can not accomplish the demodulation, unless we can introduce the definition of spatial distance, and establish a multi-point to one point optimal signal detection theory, according to the relationship of modulation mapping.(3) For analog demodulation and waveform estimation, we can establish the optimal filter and optimal estimation theories based on the definition of the orthogonal projection.The paper goes deep into the study on the general platform of the analog and digital communication signal modulation and demodulation based on the software radio, and on this foundation, we can calculate the modulation and demodulation arithmetic of the mode in common use such as AM, FM, DSB, SSB, 2ASK, 2FSK, 2PSK, MASK, MFSK, MPSK, MQAM and so on. We also carry on simulation on the arithmetic by MATLAB, so that we can prove its correctness and feasibility.The paper accomplishes the general platform software of communication signal modulation and demodulation based on the software radio, so that we validate the correctness of the general structure of the software radio modulation and demodulation, and realize the compatibility of multi-mode modulation and demodulation. We also introduce a hardware structure of the software radio general platform, in order to establish the foundation of the deeper research of the software radio.