To solve the irreconcilable contradiction between data sharing demands and requirements of privacy protection， federated learning was proposed. As a distributed machine learning， federated learning has a large number of model parameters needed to be exchanged between the participants and the central server， resulting in higher communication overhead. At the same time， federated learning is increasingly deployed on mobile devices with limited communication bandwidth and limited power， and the limited network bandwidth and the sharply raising client amount will make the communication bottleneck worse. For the communication bottleneck problem of federated learning， the basic workflow of federated learning was analyzed at first， and then from the perspective of methodology， three mainstream types of methods based on frequency reduction of model updating， model compression and client selection respectively as well as special methods such as model partition were introduced， and a deep comparative analysis of specific optimization schemes was carried out. Finally， the development trends of federated learning communication overhead technology research were summarized and prospected.

Oblivious Random Access Machine （ORAM） is one of the key technologies to protect the privacy security of the user access behaviors. However， existing ORAM schemes mainly focus on the single-user access requirements and cannot support data sharing between multiple users. Combined with Ring ORAM scheme and Attribute Based Encryption （ABE） technology， a multi-user sharing ORAM scheme was designed and implemented based on attribute encryption， namely ABE-M-ORAM. Attribute encryption was adopted to achieve the fine-grained access control， which can not only protect user access behavior security， but also realize the convenient data sharing between different users. Theoretical analysis and simulation experiments verify the high security， practicability and good access performance of the proposed scheme.

Based on the detailed analysis of UC/OS-II kernel task scheduling, this paper discussed the limitation of the scheduling algorithm in practical application, and then put forward the design that achieved time slice circular scheduling. It made the operating system have two kinds of task scheduling-task scheduling based on priorities and time slice circular scheduling, and it also preferably repaired the lack of the UC/OS-II kernel. Finally the new kernel obtained good effect in practical application.