Study On Multi-band, Multi-rate, Multi-mode Software Radio Receivers

With wireless communication technologies progressing and communication services expanding, problems on compatibility, scalability, and adaptability of various communication systems are arising, either in civil or in military field. J. Mitola proposed Software Radio (or Software Defined Radio, SDR) technology to deal with those problems, i.e., digitizing waveforms as near as possible to RF, and modulating / demodulating signals by software. It is considered the most promising way to resolve the problems. After several years' investigation, it is convinced that not only wireless modems should be implemented via software, but also the architecture of wireless systems should be reconstructed. Generally, software radio systems should be greatly flexible, and new communication modes can be provided by the system only through software update, or download. Furthermore, a software radio system is an open structured, standardized, modularized and extendable system. To achieve compatibility, scalability, and adaptability, the key technologies of software radio may be divided into three classes. Firstly, to construct an open, standardized and extendable hardware & software architecture. Secondly, to produce very powerful RF & DSP devices. Thirdly, to investigate multi-band, multi-rate, and multi-mode (MMM) signal processing methods and theories for software receivers.Though software radio technology is widely discussed, lucubrated and meticulous work on the subject is not so much, especially on the third point noted above. Based on much pre-work on modem technology, the author investigated the MMM technology for software receiver and build a SDR testbed.Firstly, with a description of open and standardized hardware & software architecture and RF/ADC/DSP devices, we discussed the bypass sampling theory and applied it in software radio receivers. Two multi-band (all band) sampling schemes are also proposed for software radio. Based on the quadrature sampling, uniform sampling and high order sampling techniques, we investigated how to compute and choose a reasonable sampling frequency.Secondly, another important technique, multi-rate signal processing for software receivers, is investigated. In fact, multi-rate processing is corresponding to sampling rate conversion. Sampling rate conversion methods of integral ratio, fractional ratio, and NCO controlled positive real ratio are investigated. In consideration of resource consuming, high efficient universal rate conversion structures are discussed. And sampling rate conversion with timing variable interpolator controlled by NCO (from high rate to low rate) is applied to software radio receivers. The controlling principle and implementation of interpolator are presented. Moreover, based on poly-phase signal processing and interpolation, a timing variable CIC (Cascaded- Integrator -Comb) filter based method for sampling rate conversion is analyzed.Thirdly, multi-mode signal receiving is investigated. Multi-mode demodulation is one of the essential techniques of software radio. Under the same restriction of a universal SDR hardwareplatform, the demodulation of linear modulated waveform, continuous phase (no-linear) modulated waveform, and multi-carrier modulated waveform, are investigated. Corresponding to those three modulation schemes, bust mode MPSK, OMSK, and OFDM signals are taken as the examples to implement a multi-mode SDR receiver, and results are presented. Most of the work is focused on frame detection, carrier and symbol timing offset estimation, and their implementation structures. Tracking loops and performances of three demodulation modes are also discussed respectively. Most of the work has been demonstrated on our self-built software radio, testbed.At last, based on the universal software & hardware architecture, COST devices, bypass sampling techniques, and multimode demodulation methods, a SDR testbed for software radio is described.