5G Radio Access Networks (RANs) are supposed to increase their capacity by 1000x to handle growing number of connected devices and increasing data rates. The concept of cloud-RAN (CRAN) has been recently proposed to decouple digital units (DUs) and radio units (RUs) of base stations (BSs), and centralize DUs into central offices. CRAN can ease the implementation of advanced radio coordination techniques, e.g., Coordinated Multi-Point (CoMP) Transmission/Reception, to enhance its system throughput. However, separating DUs and RUs, and implementing CoMP in CRAN require low-latency and high-bandwidth connectivity links, called "fronthaul". Today, consensus has not yet been achieved on how BSs, fronthaul, and central offices will be orchestrated to enhance the system throughput. In this study, we present a CRAN over Passive Optical Network (PON) architecture called virtualized-CRAN (V-CRAN). V-CRAN leverages the concept of virtualized PON (VPON) that can dynamically associate any RU to any DU so that several RUs can be coordinated by the same DU, and the concept of virtualized BS (V-BS) that can jointly transmit common signals from multiple RUs to a user. We propose a novel mathematical model based on constraint programming for joint allocation of radio, optical network, and baseband processing resources to enhance RAN throughput, and we solve it by optimally forming VPONs and V-BSs. Comprehensive simulations show that V-CRAN can enhance the system throughput and the efficiency of resource utilization.

In recent years, the increasing traffic demand in radio access networks (RANs) has led to considerable growth in the number of base stations (BSs), posing a serious scalability issue, including the energy consumption of BSs. Optical-access-enabled Cloud-RAN (CRAN) has been recently proposed as a next-generation access network. In CRAN, the digital unit (DU) of a conventional cell site is separated from the radio unit (RU) and moved to the “cloud” (DU cloud) for centralized signal processing and management. Each DU/RU pair exchanges bandwidth-intensive digitized baseband signals through an optical access network (fronthaul). Time-wavelength division multiplexing (TWDM) passive optical network (PON) is a promising fronthaul solution due to its low energy consumption and high capacity. In this paper, we propose and leverage the concept of a virtual base station (VBS), which is dynamically formed for each cell by assigning virtualized network resources, i.e., a virtualized fronthaul link connecting the DU and RU, and virtualized functional entities performing baseband processing in DU cloud. We formulate and solve the VBS formation (VF) optimization problem using an integer linear program (ILP). We propose novel energy-saving schemes exploiting VF for both the network planning stage and traffic engineering stage. Extensive simulations show that CRAN with our proposed VF schemes achieves significant energy savings compared to traditional RAN and CRAN without VF.

In recent years, the increasing traffic demand in radio access networks (RAN) has led to considerable growth of the number of base stations (BS), posing a serious scalability issue with respect to the energy consumption of BSs. Optical-access-enabled Cloud RAN (CRAN) has been recently proposed as a next-generation access network, where the digital unit (DU) of a conventional cell site is separated from the radio unit (RU), by an optical access network (fronthaul), and moved to the “cloud” (DU pool) for centralized signal processing and management. Time-Wavelength Division Multiplexing (TWDM) Passive Optical Network (PON) is a promising fronthaul solution due to its low energy consumption and high capacity. In this study, we propose the concept of Virtual Base Station (VBS), which is dynamically formed for each cell by assigning virtualized network resources, including i) a virtualized PON link connecting the DU and RU and ii) virtualized functional entities performing baseband processing in DU pool. We propose a novel energy-saving scheme exploiting VBS formation for CRAN and compare its performance with the optimal results of an Integer Linear Program for VBS formation optimization problem. Numerical evaluation shows that CRAN with VBS formation achieves significant energy savings compared to traditional RAN and CRAN without VBS formation.

Time- and wavelength-division multiplexed passive optical network allows wavelength sharing by optical network units (ONUs) in a time-division multiplexing fashion. When ONUs are lightly loaded, they can share fewer wavelengths to reduce energy consumption. In such a dynamic system, the configuration of wavelength sharing should adapt to the traffic changes for energy saving and load balancing (which affects the quality of service). However, going from one configuration to another is nontrivial, as it usually involves wavelength reassignment and potential service disruptions. The optimization and algorithm design have to account for such reconfiguration (along with other aspects). In this study, we have developed optimization models and online algorithms that incorporate the reconfiguration dimension. Various underlying tradeoffs (e.g., energy saving versus reconfiguration and load balancing versus reconfiguration) are investigated for both static planning and dynamic operations.