This project deals with models of wireless multi-terminal networks incorporating practical constraints such as individual links that experience fading, applications that are delay-sensitive, network communication that is subject to broadcast and interference constraints and nodes that are constrained to operate in half-duplex mode. The network is assumed to be static for the duration of the message, but can change from one message to the next and channel-state information is assumed to be present only at the receiver. In such settings, cooperative communication in which intermediate nodes facilitate communication between a particular source-sink pair, is key to efficient operation of the network.
A key goal of any communication system, is one of achieving an optimal rate-reliability tradeoff. The diversity-multiplexing gain tradeoff (DMT) determines the tradeoff between relevant first-order approximations to the rate and reliability of communication. The DMT of point-to-point communication links has been extensively studied and signal sets are available that are optimal under any statistical distribution of the fading channel. There now exist protocols and codes for two-hop relay networks that come close to achieving the corresponding min-cut upper bound on DMT. Goals of this project include: 1) determining the DMT of various classes of multiterminal networks ranging from broadcast, cooperative-broadcast and multiple-access channel networks to layered multi-hop networks; 2) identifying the classes of networks for which the DMT of the network is given by the DMT of the min-cut; 3) assessing the impact of asynchronous operation of the network, as well as of the presence of feedback along one or more links in the network; 4) the construction of codes with lesser decoding complexity.
In this project, we have developed numerous novel coding and modulation schemes for wireless communications systems where multiple antennas and/or relay nodes are used. New space-time codes for two use MIMO-X channels, new space-time-frequency codes with simplified decoding, new space-time codes for interference channels, new space-time codes with fast decoding have been obtained. We obtained a new space-time coding for massive MIMO systems with omni directional transmission property that achieves spatial diversity. We have obtained new precoding schemes for massive MIMO and OFDM systems. New coding schemes for full-duplex relay systems have been obtained, with which, the performance is more stable to the channel errors. We obtained new theoretical results on linear receivers for single antenna vector OFDM systems and also a cyclic delay diversity transmission for multiple antennas with VOFDM. We have found some new applications of robust Chinese remainder theorem in error correction coding. We have also obtained some new transmission schemes and theoretical results with high wireless communication security. It is believed that these schemes may impact the coming new cellular systems, such as the 5th generation. These newly developed coding and modulation schemes may impact our daily life telecommunications and our research provides good training to graduate students.
