His present research interests are in detection and estimation, communication theory and coding, signal processing, and the theory of probability and stochastic processes in general. A major emphasis in recent years has been on wireless systems. Most of his work in communications is focused on the lowest physical layer, and his research contributions have been mainly in receiver design, carrier synchronization, and error performance analysis of digital modulation techniques.

His doctoral research at MIT was on modeling and estimation of stochastic processes in space and time. He developed his interest in communications during his work at Bell Labs, and decided to focus on communications research after joining NUS in 1978. In those days, coherent communication receiver design was based on the phase-locking principle of the phase-locked loop (PLL). The PLL is known to suffer from several nonlinear problems such as cycle-slipping, false-locking and hang-ups, and these problems are particularly common when the receiver operates in a fading or wireless channel. His early work in the early eighties resulted in the channel estimation concept for coherent receiver design on nonselective, Rayleigh fading channels, leading to a new class of  receivers which do not require the use of carrier loops for synchronization and coherent data detection.  These high-performance channel estimation receivers can be implemented digitally, and are more reliable than conventional carrier-loop receivers in the presence of fading.  Channel estimation is now the standard approach for receiver design on fading channels, and is commonly used in wireless communication receivers.  The concept has been extended from the symbol-by-symbol detectors to advanced sequence detectors.  In recent years, because of the increasing demands of wireless communications, his research group has contributed to the development of adaptive filter algorithms that can track nonstationary fading channel environments with unknown statistics.  Efforts are now being devoted to developing efficient channel-estimation receivers for modern space-time codes.

Another major research thrust is in carrier synchronization, and the design of sequence detectors which do not require explicit carrier phase recovery.  His work in the mid eighties has led to new carrier phase recovery structures that do not require voltage-controlled oscillators (VCO's) and carrier-loops in general.  More significantly, his sequence detection work has shown that coherent performance in the detection of a digital sequence can be achieved by merely increasing the observed sequence length, without explicit carrier phase estimation.  This has been followed in the literature with much subsequent work on the so-called "noncoherent" block detection.  Adaptive carrier phase estimators have also been developed, and the work of his group in recent years has focused more on fast frequency-offset estimation and carrier acquisition.  Recursive frequency and phase estimators with short acquisition times have been obtained based on advanced signal-modeling concepts, and high performance receivers with low acquisition overhead are expected soon that are suitable for burst-mode applications.

Error performance analysis of digital modulations is a very important theoretical problem that has attracted the attention of many researchers worldwide.  His research group has actively contributed to various areas of performance analysis, in particular, the performance of channel estimation receivers and differential detection receivers on fading channels, and the effects of phase noise on error performance.  Currently, the research effort here is concentrated on the performance of space-time codes, and the performance of multiple-antenna systems in general with interference.