Location: #9521, Jiuli campus
Dr. Konstantinos Nikitopoulos is a Lecturer (assistant professor) of Institute of Communication Systems (ICS) and 5G Innovation Centre (5GIC) at University of Surrey. His research interests lie in the field of signal processing for wireless communication systems. In particular, his work strives to realize pragmatic, energy-efficient wireless communication systems able to provide the performance predicted by cutting-edge theoretical trends; with a focus on those trends that hold a great potential to form the basis of 5G wireless networks. Targeting high-throughput systems that scale their capacity to a large number of users, Dr. Konstantinos Nikitopoulos’s current research bridges two complementary areas: (a) centralized and distributed, mobile, multi-antenna (MIMO) systems and advanced detection and channel encoding/decoding schemes, including sphere decoding and iterative soft-input, soft-output techniques.
In this talk we are going to discuss Geosphere, a physical- and link-layer design for access point-based MIMO wireless networks that consistently improves network throughput. To send multiple streams of data in a MIMO system, practical designs rely on a technique called zero- forcing, a way of “nulling” the interference between data streams by mathematically inverting the wireless channel matrix. In general, zero-forcing is highly effective, significantly improving throughput. But in certain physical situations, the MIMO channel matrix can become “poorly conditioned,” harming performance. With these situations in mind, Geosphere uses sphere decoding, a more computationally demanding technique that can achieve higher throughput in such channels. To overcome the sphere decoder’s computational complexity when sending dense wireless constellations at a high rate, Geosphere introduces search and pruning techniques that incorporate novel geometric reasoning about the wireless constellation. These techniques reduce computational complexity of 256-QAM systems by almost one order of magnitude, bringing computational demands in line with current 16- and 64-QAM systems already realized in ASIC. Geosphere thus makes the sphere decoder practical for the first time in a 4×4 MIMO, 256-QAM system. Results from our WARP testbed show that Geosphere achieves throughput gains over multi-user MIMO of 2× in 4×4 systems and 47% in 2×2 MIMO systems.