## 2 Synchronization Issues with Various Part-to-Picker Systems and a Literature Review
### Synchronization Problems in Hospitals
Preemption and mixed service modes, limited departure times, replaceable products, internal congestion, value-added activities, and robustness against deviations should be prioritized. To improve solution quality, it should focus on more advanced metaheuristics and generalizations of the truck scheduling problem with fixed outbound departures (TSFD). It is important to investigate the unifying scheduling algorithms for all four sorting systems, including pure shuttle systems and rubber-tired lift and shuttle systems. New problem solving procedures and TSFD generalizations for dealing with release dates in real-world applications should be the focus. The parcel hub scheduling problem (PHSP) should be simplified by simplifying the assumptions, such as unequal batch size trailers, linked unload and load docks, and incoming and outgoing trailer replacement periods. A comprehensive review of multistudin multishuttle systems (MSMSSs) implemented across various global locations was presented in this study. And the main focus is on their applications in the manufacturing sector. The review encompasses several key aspects. They include design considerations, operational control strategies, congestion effects analysis, dead-lock prevention techniques, and queuing network models. And the heuristic algorithms employed to address the challenging NP-hard problem of assigning automated guided vehicles (AGVs) within these systems are also considered. This study examines the introduction of automated storage/retrieval systems (ASRSs). Then, the problem of storage location assignment in warehouse transportation, as well as conventional storage and order picking methods, is introduced. In addition, the mixed-integer linear programming (MILP) model has been suggested as a viable approach. Parts-to-picker systems aim to decrease picker travel and minimize the unproductive time of expensive equipment during warehouse transportation, thereby reducing both wasted picker trips and excessive personnel charges. We also identified some overhead hoist transport models that are now utilized in hospitals, such as semiopen queuing networks (SOQNs). This can help simulate the automated overhead distribution of medicine in healthcare facilities, as well as the HABOR approach. The synchronization issues that were observed at airports were addressed by this research. And this also specifically focuses on the baggage handling system (BHS), aircraft landing problem (ALP), mixed-integer linear programming (MILP), and airport gate assignment (AGAP) difficulties. The works suggested that the vector assignment problem (VAP) and stochastic vector assignment problem (SVAP) are potential solutions for these issues. It is clear that the impact of multistation multishuttle systems on the industry and human life is significant. This research is solely focused on the analysis of a single workstation, but it is important to note that real-world systems may have several parallel workstations. Therefore, it is crucial to take into account the synchronization task when allocating orders among workstations and coordinating the demands for SKU bins across multiple workstations. Parts-to-picker systems face uncertainty, which can include inventory discrepancies, tardy deliveries, and the effort required to locate items in mixed bins containing numerous stock-keeping units (SKUs). Understanding the influence of variables on picker search time can lead to the development of synchronization models that are more representative of real-world scenarios. Increasing the stock-keeping unit (SKU) variety not only enhances operational flexibility but also improves the accuracy and reliability of modeling. Warehouses that utilize mobile robots to lift shelves may be able to benefit from the wide variety of racks that are available in their inventory pods. There is a lack of literature on the subject of OHT in Vietnam. The main objective of this study was to examine the current literature on MSMSS in industrialized nations in an extensive manner.