云南 大学 学报 ( 自然 科学 版)? 1998, 20 (5): 329 332CN 53- 1045/N? ISSN 0258- 7971 Journal of Yunnan University The Analyzing of Key Techniques for Software Radio? Shen Dongya ?Zhen Changquan?Zhen Wenxing (Department of Information and Electronic Science, Yunnan University, Kunming, Yunnan, 650091) Abstract? This paper compares software radio with traditional receiver firstly, then discussed the architecture ad - vanced features and applicationsof software radio in details. Furthermore, the key techniques and its functions for soft - ware radio are proposed. Finally, technique difficulties current status on ADC, DSP, and RF front end are chiefly ana - lyzed and studied. Key words? software radio, ADC, DSP ? ? Since the invention of the superheterodyne re - ceiver in the early this century, radio architecture has remained remarkably unchanged. While it is true that development has not stood still ?increasing in - tegration, ever more sophisticated devices, and the use of digital circuitry to implement baseband func - tions are just some examples of technological ad - vancement ? it is also true that none of these deve- l opments can be said to have revolutionized the orig- i nal concept. It seems however, that such a revolution may already be in progress, in the guise of the so - called software radio. Software radio, first presented by Joe Mitola1, an American, is mainly applied to military services which have, over the years, developed many kinds of radios, each having a special purpose and, usually, not interoperable with each other. To solve this interop - erablility problem, the Department of Defense is de - velopingthe Speakeasysoftware -definedradio. Speakeasy also has powerful business applications as a wireless broadband/ multimedia platform for trans - mitting voice/ data and multimedia information in the 2MHz -2GHz spectrum range. Some analysis has been done examining other commercial waveforms that might be implemented in speakeasy 3. Celullar telephone standards, Paging systems, mobile satellite telephone standards, PCS, Wireless data and mobile radio standards have all been analyzed for potential inclusion in the speakeasy software suite. Most of these waveforms will be able to be implemented through the inclusion of software thus producing a truly multimode and multimedia business system. Software radio makes a feature of standardiza - tion, modularzation, versatility. An additional benefit is the ability to easily upgrade the system when com - munications standards change or evolve. Therefor, it is of great value to military services but of much great to mobile communication systems which are confronted with a lot of new standards and environ - ments. Software radio is of two advantages: flexibility and centrality. Flexibility means that channel access mode can be transferred randomly, modulation mode can be changed at will and, various signals can be re - ceived, e. g. software radio can presents a opportunity for business travelers to easily overcome the cha- l lenge of different wireless standards in different countries and regions through reprogramming their multimode handset to meet local conditions. central- i ?The project is supported by the Applied Basic Fundation of Yunnan Prvince. Received 1998- 05- 08 ty implies that many channels can share the same RF front end and wideband A/ D/ A converter, each channel can be processed digitally at lower cost. The cost for software radio is much more than that for traditional receiver, but the cost of each channel can be decreased on the large scale. this increases great abstraction of software radio for people. 1? Architectures of software radio A traditional modern receiver is shown in figure 1. Essentially, all functions -filtering, amplification, downconversion -up to the demodulation stage are implemented using analogue technology. At this point the baseband signal is digitized, and operations such as channel equalization, channel decoding, de - cryption and source decoding are then carried out us - ing a programmable digital signal processing ( DSP) chip. Obviously, this architecture consists of quite a number of components. It is always attractive for the circuit designer to minimize the component count, thereby potentially minimizing cost and complexity. One approach to this forms the basis of the software radio concept, namely the moving of analogue -to -dig- ital converter( ADC) as far up the antenna itself. ( as shown Fig. 2) ? ? BPF ? LNA ? ? Mixer Synthesiser ? BPF ? IF ? Amplifiers DemodADCDSP Output format Fig. 1 Traditional Narrowband Receiver ? RFADCDSPDecode Audio Video Data Fig. 2 Ideal Software Radio ? RF RF front end and down - conversion IFADCDSPOutput foemat Fig. 3 Radio with IF digization However, radio frequency ( RF) digitization as represented in Fig. 2 is currently not feasible in the real world. At the very least, a pre -selection filter and an amplifier would be required between antenna and ADC. A more realistic archite