Research Problem:

    Software radio


    The superheterodyne principle has been employed for more than 80 years in the design and realization of radio receivers.  These receivers are basically analog in nature.  The received signal is first processed by an analog RF front end.  The amplified signal is then downconverted into the IF by means of an analog mixer.  At the IF stage, only the components of the signal at desired frequencies are retained and the others are filtered out.  Finally, the IF signal is further downconverted into the baseband frequency.  One can use an analog-to-digital converter to convert the analog baseband signal into the digital domain.  Digital signal processing is then used to process the signal in order to estimate the transmitted information data sequence.  Advantages of receiver implementation based on the aforementioned principle are that the system architecture is proven, the RF/IF analog technology is mature, and the requirements on analog-to-digital converters and digital signal processors are relatively undemanding.  However, one of the greatest disadvantages of analog receivers is their lack of flexibility.  One receiver is designed for one communication system.  As more and more mobile communication standards emerge and coexist around the world, a multimode radio receiver would certainly be a significant advantage.  One approach for achieving multimode capability is to pack several discrete receivers for different standards, but this approach greatly increases the weight and size of the resultant composite receiver.  

    Fundamentally, a software radio uses an analog-to-digital converter to digitize the received signal when the signal frequency is still at the RF band or has been downconverted to the intermediate frequency (IF) band, and processes the digitized signal in the discrete-time domain by programmable processors.  For different communication standards, different programs (in the form of software) are loaded into the processors to demodulate the received signal.  Multimode capability is therefore supported without the need to duplicate hardware.

   Software radio is a broad topic and covers a large number of research areas.  It can be analyzed from many different perspectives, including the network level, terminal level, device level, hardware implementation aspects, and software aspects.  In this study, only the signal processing aspects in the receiver design were considered.  In particular, bandpass sampling, decimation filtering, channelization, and fractional sampling-rate conversion were emphasized, all of which being important components in the implementation of software radios.

Representative Publications:

Yik-Chung Wu, Tung-Sang Ng and Kun-Wah Yip, “Chapter 7 -- Software-Radio: A Prospective Technology for the Future Broadband Communication Systems,” in Advances in 3G Enhanced Technologies for Wireless Communications, edited by J. Wang and T. S. Ng, Artech House, 2002.  (This book has been translated into chinese language)

Yik-Chung Wu and Tung-Sang Ng, “New Implementation of a GMSK Demodulator in Linear Software Radio Receiver,” Proceedings of the 11th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC2000), pp. 1049-1053, Sept., 2000.