The interconnection of all things is developing a new diagram of future information networks. However, it is difficult to realize future applications with only one single technique. Collaboration between multiple advanced techniques is leading the way for the development of future information networks. Optical communication is an enabling technique to achieve high speed, long reach, and low latency communication, which plays an important role on the transformation of information networks. To achieve these advantages that caters to the characteristics of future information networks, collaboration of multiple advanced techniques with optical, which is called “optical plus X, could realize the vision of “all things connected with networks. In this paper, we focus on the collaboration between optical networks with other techniques, mainly discuss four representative aspects, which are “optical plus IP, “optical plus radio, “optical plus computing, and “optical plus AI. We discuss the challenges, timely works, and developing trends. Finally, we give the future visions for optical network towards a collaborative, converged and co-automatic optical network.

Towards converged, collaborative and co-automatic (3C) optical networks

To accommodate the heterogeneous requirements of emerging 5G services, 5G Radio Access Network (RAN) will support the rising paradigm of network slicing, where a single physical RAN infrastructure is divided into multiple logical networks characterized by diverse requirements in terms of performance, cost, latency, and security, etc. The optimality of RAN slicing depends on various factors, such as slice requirements, resource availability and adopted network architecture. In 4G, RAN architecture evolved from a distributed architecture towards a 2-layer architecture that separates remote radio heads (RRHs) from baseband processing units (BBUs). However, this architecture has soon shown scalability limitations. To address this problem, the concept of flexible 5G functional split has been proposed, where RAN functions are distributed on a 3-layer architecture featuring a radio unit (RU), a distributed unit (DU), and a central unit (CU). Besides RAN architecture, isolation among different slices, which is necessary for slicing security, has a significant influence on the RAN slicing. In this work, we consider the isolation-aware RAN slice mapping problem considering advanced functional splits and a 3-layer RAN architecture. We propose a dual-objective heuristic algorithm for RAN slice mapping over a physical infrastructure represented by a wavelength division multiplexing (WDM) metro-aggregation networks. The proposed heuristic targets the minimization of 1) the number of active COs (i.e, hosting DUs and/or CUs) and 2) the number of established wavelength channels under constraints of network capacity and latency requirements. As our algorithm is also designed to map the RAN slices with least amount of physical resources for a given level of isolation, we also investigate the impact of slice isolation on resource utilization. Results show how higher isolation results in higher network cost.

Isolation-Aware 5G RAN Slice Mapping Over WDM Metro-Aggregation Networks

WDM-PON-based mobile edge computing (MEC)-enabled fiber wireless access networks (MFWAN) have been identified as a promising technology for next-generation broadband access. Low-latency oriented network planning of the WDM-PON-based MFWAN would be required for low-latency access to newly emerging latency-sensitive applications in the fifth-generation (5G) era. However, this would require a low-latency oriented network design in the network planning phase and has thus become a crucial challenge. In this paper, we investigate low-latency oriented network planning of the WDM-PON-based MFWAN under physical and management constraints. To this end, we develop a mathematical model to minimize total transmission latency for all latency-sensitive services. Our model is composed of the propagation latency on the paths and the processing latency on the network equipment and is subject to constraints of maximal transmission distance, maximal PON power budget, bandwidth requests, and the fronthaul latency limit under some functional split options. Given the model’s complexity, we also propose a heuristic algorithm called latency-minimized integrated multi-associated positioning and routing algorithm (LMI-MAPRA). The simulation results show that the proposed algorithm outperforms the benchmark algorithm with more total transmission latency reductions in both sparse and dense networks. We also analyze the impact of key parameters on comparisons of different approaches in terms of low-latency optimal performances.

/pdf/low-latency-oriented-network-planning-for-mec-enabled-wdm-4yczia5h2e.pdf

Low-Latency Oriented Network Planning for MEC-Enabled WDM-PON Based Fiber-Wireless Access Networks

To meet emerging mobile traffic requirements, Centralized Radio Access Network (C-RAN) has been proposed to split the base station (BS) into two functional entities: the baseband units (BBU) and the remote radio heads (RRH). In C-RAN, by centralizing BBUs into BBU pools and leaving the RRHs in the cell sites, significant cost and energy savings and improved radio coordination can be achieved. However, C-RAN requires a costly high-capacity and low-latency access/aggregation network to support fronthaul traffic (i.e., digitized baseband signal). Hence, more recently, a new C-RAN architecture has been proposed (i.e., by 3GPP, IEEE 1914 WG), that defines three baseband function entities (or “splits”): central unit (CU), distributed unit (DU) and remote unit (RU). These three entities are expected to be interconnected by two external interfaces, called F1 and Fx. By transforming the RAN into a 3-layer (CU-DU-RU) architecture, more flexible deployment of the baseband functions can be achieved that better adapts to the heterogeneous characteristics of incoming 5G service requirements. It is also expected that, by properly placing CUs and DUs in the metro/aggregation network, higher benefits in terms of cost and power consumption can be achieved with respect to the previous 2-layer (BBU-RRH) architecture. In this paper, we investigate the optimal CU/DU placement problem in a 3-layer RAN architecture and formalize it by integer linear programming. We evaluate the benefits of the 3-layer architecture compared to the 2-layer architecture, showing that the consolidation degree of baseband processing depends heavily on fronthaul traffic latency, transport network capacity and processing capacity.

/pdf/du-cu-placement-for-c-ran-over-optical-metro-aggregation-259n5s80cf.pdf

DU/CU Placement for C-RAN over Optical Metro-Aggregation Networks

Massive multiple input multiple output (mMIMO) enabled beamforming is a promising technology in the next generation of mobile communication. It allows multiple antennas transmit the same data to a user to improve the signal strength and quality. However, beamforming may incur redundant data transmission over fronthaul in the centralized radio access networks. When accommodating a set of beam requests, a key problem is how to coordinate radio and optical resources to maximize the beamforming throughput and minimize the fronthaul bandwidth. In this paper, we study on the joint wavelength, antenna, radio resource block allocation (WARA) in a time and wavelength division multiplexed passive optical network, which is an economic fronthaul solution for the mMIMO. We formulate the WARA into an integer linear programming (ILP) model. Three heuristic algorithms are proposed to optimize fronthaul bandwidth, radio resource block (RB) utilization, and both. We compare ILP with the proposed algorithms under different sizes of antenna arrays. A tradeoff is shown to exist between fronthaul bandwidth and radio RB utilization. Also, we find that the optimization goal depends on the number of antennas in an optical network unit.

Joint Wavelength, Antenna, and Radio Resource Block Allocation for Massive MIMO Enabled Beamforming in a TWDM-PON Based Fronthaul

The BBU aggregation for mobile tidal traffic is proposed, which is achieved by a SDN-enabled flexible optical fronthaul network. Two lightpath reconfiguration strategies for the BBU aggregation are experimentally demonstrated on the cloud radio over flexible optical fronthaul transport networks (C-RoFlex) testbed.

Demonstration of Lightpath Reconfiguration for BBU Aggregation in the SDN-Enabled Optical Fronthaul Networks

We propose a passive wavelength division multiplexing based fronthaul architecture for heterogeneous cellular networking, and a threshold based on/off algorithm for micro cells. Simulation results show that our algorithm significantly saves energy than traditional solutions.

Energy Optimization with Passive WDM Based Fronthaul in Heterogeneous Cellular Networking

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Papers

Joint Wavelength, Antenna, and Radio Resource Block Allocation for Massive MIMO Enabled Beamforming in a TWDM-PON Based Fronthaul

Demonstration of Lightpath Reconfiguration for BBU Aggregation in the SDN-Enabled Optical Fronthaul Networks

Energy Optimization with Passive WDM Based Fronthaul in Heterogeneous Cellular Networking