Multiple important topics are being considered in the domain of 5G Cellular Networks within the RAN and the EPC. These topics include massive MIMO, millimeter-wave technologies, Dual connectivity, LTE Unlicensed within the RAN and technologies for optimization within the mobile core using Mobile-edge Computing and EPC virtualization.
a) Technologies for deploying Massive-MIMO Systems: In this project, two key problems are being considered. Given the scale of such antenna systems, low-complexity beamforming techniques have become a requirement. Such techniques have been developed using a combination of two-level beamforming and compressive sensing. Another key problem is the design of a low-complexity scheduler. We have developed solutions where we exploit the de-correlation property in Massive-MIMO systems to avoid unnecessary precoder computations, thereby reducing scheduler overhead.
b) Millimeter-wave Technologies: In this project, the key problems that are being considered are, 1) beam tracking technology for millimeter wave which is required to track mobile users when deployed for mobile access (as opposed to backhaul) – the problem is made complex by the inability to get accurate channel measurements. We are developing technology that does not require explicit channel measurement, 2) We are also developing a novel design framework for MU-MIMO scheduling in millimeter-wave networks that considers hybrid beamforming (analog plus digital precoding) at the transmitter as well as receiver nodes. We use transmit and receive analog precoding to reduce the CSI feedback overhead.
c) Dual-connectivity: Dual connectivity (DC) is a feature that targets emerging practical HetNet deployments that will comprise of non-ideal (higher latency) connections between transmission nodes, and has been recently introduced to the LTE-Advanced standard. DC allows for a user to be simultaneously served by a macro node as well as one other (typically micro or pico) node and requires relatively coarser level coordination among serving nodes. For such a DC enabled HetNet , we comprehensively analyze the problem of determining an optimal user association, and are developing efficient solutions for this problem.
d) Unlicensed LTE: We have developed a system (ULTRON) for LTE-LAA (Licensed-Assisted Access) systems where we have implemented a technology to embed CTS-to-self within LTE frames to increase the performance of the LTE-LAA without any changes to the current LTE-LAA standard. The project is being extended to study transmission in the CBRS band (without any LAA) as this mode of transmission is becoming important.
e) Mobile Core Optimization Techniques: As part of the ACACIA project, we have developed efficient solutions for redirecting MEC traffic to the edge-servers without the need for either splitting the GTP tunnels at the base –station or performing deep-packet inspection. Additionally, within the context of the SCALE project, we have implemented solutions to virtualize and scale the control-plane elements of a virtualized EPC. The work is now being continued to include the data-plane as well as IP services deployed within the operator IP network.
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