HOME                                                                           

 

RESEARCH OVERVIEW

 

         My research falls in the area of communications and signal processing.  Currently, I am interested in various problems in wireless  

         communications.  See my publications for details. Here is a brief summary of my research.

        

 COOPERATIVE COMMUNICATION

 

  • Fundamental limits of cooperative networks

              A fundamental problem in wireless networks is determining the broadcast capacity, i.e. the maximum data transfer rate from a given 

              node  to every other node in a relay network. In this work, we study the scaling of the broadcast capacity for a network with a single 
              source and f(N) cooperative relays where N is the number of nodes (destinations) and f() is an increasing function. We study 

              random networks under different node configurations and channel fading models.

 

  • Asymptotic coverage analysis of cooperative transmission     

         Cooperative broadcast aims to deliver a source message to a locally connected network by means of collaborating nodes at the 

               physical layer. In this work, we studied the effect of network parameters such as source/relay transmission powers and the

               decoding threshold on the number of nodes reached by cooperative broadcast. Our approach is based on the idea of continuum

               approximation, which yields closed-form expressions accurate when the network density is high.

 

·         Decentralized diversity schemes for cooperative communication

In ad-hoc network, utilizing multiple-antenna systems is impractical for certain network applications. Cooperation among the nodes can provide spatial diversity gains without utilizing multiple transmit antennas. We introduced randomized strategies that decentralize the transmission of a space time code from a set of distributed relays. Furthermore, we provided design criteria and analyzed the performance of different strategies.

 

·        Power efficiency of cooperative transmission in dense wireless networks

In this work, we studied the optimal power allocation problem for cooperative broadcast in dense large-scale networks. We proposed practical distributed schemes that are almost optimal in terms of the scaling of power consumption and also compared their power consumption with those of conventional non-cooperative multi-hop broadcast.

 

 CONSTRAINED TOTAL LEAST SQUARES WITH APPLICATION TO HYPERSPECTRAL IMAGERY

 

Spectral unmixing is a pixel-by-pixel approach to the detection and localization of features by spectral analysis techniques. Usually, partial knowledge about the feature, noise, and clutter spectra are provided, and the problem is to ``unmix'' each pixel, or to estimate the relative concentrations of the reference spectra on a per pixel basis. We developed total least squares (TLS) based algorithms for spectral unmixing of hyperspectral images in case of dominant modelling errors.  We implemented the developed techniques to medical diagnosis and remote sensing problems.

 

 

RECENT TALKS

 

       Sep 21, 2007              SJSU/EE297 Seminar         Talk