Research

Research Activities

(1) Coding and modulation schemes for communication systems

Coding and transmission techniques are crucial in modern communication systems. The progress in information theory and signal processing techniques has a tremendous impact on coding and modulation techniques. Recent advent in iterative decoding, codes on graphs, hybrid coding/modulation and loss recovery codes have shown that both capacity and performance of communication systems can be significantly enhanced. We have developed some very low complexity code and hybrid coded modulation methods, which can be ten times cost effective than the best existing schemes, yet with comparable or even better performances.

(2) Multiple access techniques of wireless cellular communication systems

The capacity of a cellular mobile communication system is limited by multi-user interference, from both same-cell users and other-cell users. Multiple access techniques, such as FDMA, TDMA and CDMA, are techniques to treat this interference problem. One basic approach (such as FDMA and TDMA) is to prevent interference by adopting orthogonal waveforms. Another quite different approach (such as CDMA) is to use random signals so as to reduce the correlation among signals from different users. Interference cancellation methods have also been widely studied to handle the problem. Our work in this area has revealed that the advantages of these methods can be combined so that the system architecture can be much simpler, the transmitter and receiver can be considerably simpler, and the performance can be greatly enhanced.

(3) Transmission and routing techniques for Internet and wireless data networks

As the broadband Internet keeps increasingly growing at speed, delivery of multimedia contents is expected to be one of the most popular broadband services in the near future. Handling multimedia contents is a very challenging issue as it involves a huge amount of storage capacity and a very wide transmission bandwidth. The current Internet architecture, however, uses a best effort delivery. It is not optimized for delivering multimedia contents because all types of data are treated as the same. To improve the performance of data delivery, designers of communication systems must pay special attention to each type of multimedia content. The delivery systems designed must also handle each type of contents in a unique way so as to provide optimal performance. Such systems can be called "content based multimedia delivery systems". We are currently studying and developing design strategy, performance analysis and demonstration prototypes for such systems.