# Resource Management in Converged Optical and Millimeter Wave Radio Networks: A Review
## 2 Background Concepts
### Converged Optical and Mmwave Radio Networks  
An essential source for capacity enhancement in dense networks is the use of mmWave spectrum bands around 28, 38, 71-76 and 81-86 GHz frequencies [7]. A total of 16 GHz bandwidth is available to use in these spectrum regions. In spite of the availability of large bandwidth, these bands were not used in cellular networks due to their high power consumption [8] and the challenging propagation characteristics due to high path loss, poor signal penetration and reflection, the sensitivity to blockage from various objects outdoors and the high Doppler effect observed in frequency bands deployed until long term evolution (LTE) technology [9].  
Extensive studies are carried out in order to understand whether mmWave spectrum bands can be used in dense networks despite these unwanted characteristics. Interested readers are referred to [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. Here, we only provide a list of some of the key challenges that are addressed by the resource management solutions in the selected studies: In order to reach the extreme data rates, beamforming with adaptive antenna arrays and highly directional transmissions are required for narrow beam operations [10; 11], bringing in the problem of dynamic adjustment of antenna elements to support multiple directed beams with massive multiple input multiple output (MIMO) [12; 13]. Synchronization and broadcasting should also be designed properly for these directional transmissions [14], as narrow beams can cause loss of connectivity in mmWave mobile networks when they are misaligned [15]. In addition, efficient beam-tracking and alternative directed spatial channels need to be provided to users in case of outage [16] or blockage [11]--one probable solution can be to serve a UE at the same time over several APs [7].  
Integration of capacity enhancement techniques, namely the use of mmWave and massive MIMO is also complementary to the small cell evolution [13]. Utilizing higher frequency spectrum bands for capacity gains also drives toward use of more small cells, as the propagation characteristics of mmWave signals lead to higher attenuation and reduced coverage area, requiring the deployment of more APs. Ultra-dense networks (UDN) is an attractive technology to boost the capacity in a coverage area [17], as increasing the number of access nodes enables radio frequency reuse in a certain coverage area. To unfold the added capacity provided by UDN, end-to-end network management has to deal with increased dynamics of radio access due to the complexity of the architecture with increasing number of nodes, massive data generation, and dynamic topology changes requiring quicker network reconfiguration.  
The introduction of mmWave frequency bands for wireless access with dense deployments also leads to a major increase in fronthaul capacity, and fiber network solutions can provide the required data rates for this fronthaul [21; 22; 23]. Radio-over-fiber (RoF) implementations for mmWave have long been considered to create distribute mmWave radio signals to dense APs from a central station [24; 25]. Multiple wireless services can thus share the huge amount of bandwidth in the same optical fronthaul network, achieving optical-wireless convergence [3].  
A data plane design for converged optical and wireless networks [26], and aligning this design with the control plane inside an ANM framework allows the dynamic reconfiguration of the end-to-end data plane channels with AI-ML-based solutions, such as beamforming and steering [27] or service-aware slicing [28].