# Future Is Unlicensed: Private 5G Unlicensed Network for Connecting Industries of Future
## 4 Challenges and Research Directions
### Challenge 2: Seamless Connection due to Small Cell Architecture  
When operating an NR-U network with mobility in the unlicensed bands, several potential problems arise from the combination of low transmit power requirements, coexistence requirements, and device mobility. The low transmit power of nodes will cause the cell sizes to become relatively small. In contrast, device mobility might cause the system to have a short time to handle the entire handover procedure when UEs move towards a cell having better link conditions. On top of this, the LBT procedure that is required for coexistence may cause a blocking of the transmission from either the eNB or the UE, which results in lost or delayed messages and delayed/outdated measurement reports. Having delays during the handover procedure in such small cells can potentially cause the UE to be out of coverage of its original source cell before it can complete the handover towards a target cell. Furthermore, this condition becomes more severe when mobility from a standalone LTE in the unlicensed spectrum to a standard LTE network on the licensed spectrum is expected to be seamless.  
The current handover procedure is controlled by centralized eNB in LTE [45; 46]. However, as we are operating solely in the unlicensed band, seeing the aforementioned challenges of small cell deployment and its regulatory requirements, a centralized eNB controlled handover procedure is not feasible. Thus, we need some advanced user-controlled handover similar to WiFi [47], where users are pre-configured with one or more potential target cells. Upon certain conditions being met, the UE may autonomously contact the target cell without informing the current cell. The pre-configuration of the UE for autonomous handover may be based on reported measurements of nearby cells such as the signal-to-noise ratio (SNR). In addition to this, we also can implement handover decisions to skip frequent transfers for fast-moving nodes such as UAV vehicles, warehouse robots, etc. [48; 49]. This skipping decision can be achieved based on the upcoming cell's topology; we can consider three criteria: (a) the area of the cell, (b) the trajectory distance within the cell, and (c) the distance of the BS from the cell edge. When a cell area is small, the sojourn time of the user inside that cell is limited; hence, the time for two successive handovers is short. Similar to the cell area, trajectory distance within the cell attempts to prevent frequent handovers. This option is more significant because it covers the situations where the area is wide, but the distance inside the cell of the consumer is small. The final criterion is the perpendicular distance between the BS of the upcoming cell and the boundary, which will be crossed by the user. This distance determines how close the current and next cell's BSs are. Therefore, connecting to either BS will carry identical path loss results. Thus, as shown in Figure 4, the cell having less trajectory (red dotted line) can be skipped based on the combination of the above decision parameters. Here, we can use the TOPSIS [50] method, which is a multi-criteria decision analysis method to choose the correct option, integrated with the Q-learning [51] approach to provide intelligence in the system for managing a good QoS during the skipping phase (to find the right time). However, retaining the upcoming cell's topology information for the user is still challenging.