The proposed project intends to explore the notion of overlay transmission as an alternative design criterion in wireless networks involving multiple transceiver pairs, i.e., the classical interference channels (IFC). Overlay transmission refers to the communication mode where the signals from multiple users superimpose in time and frequency. It is envisioned that, facilitated by the theory and technologies to be developed under this effort, more efficient spectrum utilization can be achieved by allowing concurrent transmissions without compromising each users Quality of Service. The intellectual merit of the project lies in its pursuit of the novel MIMO (multiple-input multiple-output) overlay transmission concept in wireless network design. This differs with existing overlay transmission, such as the code division multiple access systems, whose interference resistance comes at the cost of bandwidth expansion. Instead, we demonstrate that the interplay between spatial diversity and multiuser diversity in MIMO IFC enables overlay transmission to significantly outperform orthogonal transmission. This is also in sharp contrast to the single-input single-output system where overlay transmission has no tangible advantage in spectral efficiency over orthogonal transmission for IFC. The proposed MIMO overlay transmission has broad applications in wireless networks. For cellular networks, prudent use of MIMO overlay transmission will enable novel frequency reuse schemes to improve channel resource management. In ad hoc networks, incorporating MIMO overlay transmission into the networking protocols will help enhance both the network and end-to-end throughputs. MIMO overlay transmission, with its superior spectral efficiency and its potential to enable novel networking protocols, has the promise to bring relief to the spectrum scarcity issue encountered in todays wireless systems. Along with the proposed research project, the PI has designed a set of education initiatives. These include promoting active learning through innovative classroom teaching, enhancing graduate and undergraduate curriculum through course development, and involving undergraduate students with diverse background in this project. The broader impacts of this project are multi-faceted. By engaging students at both graduate and undergraduate levels in intellectually challenging activities, the students will assume a more active role in various education activities. Encouraging and facilitating graduate students participation in professional meetings and conferences will help instill enthusiasm in scientific research into the students. Involving undergraduate students in carefully designed research projects will help foster their interest in scientific activities. The curriculum development plan caters to the increasing needs of students in the area of communication and signal processing. At the graduate level, it will provide an important venue for many local industries and research institutions for the continuing education of their employees. The PIs enthusiasm in developing and teaching undergraduate courses will ensure the success of the ongoing undergraduate curriculum reform in the Department of Electrical Engineering and Computer Science at Syracuse University.
Interference refers to unwanted signals that may impair the reception of intended signal. It usually occurs when wireless users communicate simultaneously and has been considered a major limiting factor in wireless systems. The traditional approach of avoiding interference by placing different users in separate channels simplifies the design of communication systems but is known to be highly inefficient. The project investigate potential ways of improving upon this traditional approach by designing technologies that are robust to interference in radio communications thereby allowing users to communicate concurrently. This improves the efficiency in terms of frequency spectrum utilization and helps alleviate the spectrum scarcity issue that has confounded wireless network designers and operators. The most significant project outcome is the discovery that there exist situations in wireless, as well as wireline (e.g., digital subscriber line), communication systems where interference has no effect on the system throughput. That is, there incurs no penalty in network capacity if interference is completely ignored at individual receivers. This highly unusual result provides incentives for the communication engineers to identify, and perhaps create systems such that the simple scheme of disregarding unintended signals is completely optimal. One important situation is in communication systems where transmitters and receivers are equipped with multiple antennas. The presence of multiple antennas (i.e., the MIMO radios), and the fact that wireless channels varies drastically from one antenna element to another and from one user pair to another, give rise to more realistic situations where disregarding interference is practically optimal. The discovery, being highly counter-intuitive, enriches our understanding of the impact of interference as well as the way it ought to be handled in communication systems. It is expected that this discovery, when incorporated through creative engineering design, may significantly enhance the efficiency of future wireless networks.
