Study On Slot Assignment Protocol And Its Simulation For Tactical Data Links

In tactical data links (TDLs), the medium access control (MAC) protocol determines the mode of nodes accessing to shared channel and the availability of channel resources, and, which has a direct impact on the performance of TDLs. Among the MAC protocols, Time Division Multiple Access (TDMA) has good anti-interception and anti-jamming capabilities, and is flexible in networking, so it has been widely used in TDLs. In TDMA, how to design effective slot assignment protocols in order to obtain better system performance is the technical problem. Therefore, this dissertation researches the design and evaluation method of slot assignment protocols for TDLs, and aimed to design slot assignment protocols which can meet the needs of tactical operation under certain network environment. The main research production of this dissertation includes the following aspects:1) Design and Evaluation Method of Slot Assignment Protocol for TDLsIn order to design slot assignment protocols for TDLs, a three-stage slot assignment protocol design strategy is proposed based on the analyzing of the problems of slot assignment and the influencing factors of the design of slot assignment protocols. In order to meet the dynamic slots demands of nodes for massages transmission, the design of slot assignment protocols in our strategy includes three stages: the initial solving, the dynamic adjusting and optimizing, and the scheme generating. For evaluating the slot assignment protocols of TDLs, the evaluation indexes of slot assignment protocols are proposed, and the simulation evaluation framework is designed, moreover, the demands of simulation models and the process of the framework are discussed.2) Dynamic Slot Assignment Protocol for TDLsThe traditional centralized polling protocols of TDLs are not accomplished in meeting the dynamic slots demands of nodes. In order to solve the problem, an adaptive polling MAC protocol (APMP) is proposed. With an adaptive polling scheduling algorithm, which is built based on the Queue length, the message priority and the delay requirements, APMP can poll the node with more high-priority packets in a great probability, then, the channel utilization is increased and the differentiated services are provided. At the same time, APMP can meet the tactical demands of random joining and leaving of nodes with the corresponding mechanism, and can solve the empty polling problem caused by the node beyond the scope of the coverage of the network control station.Distributed slot assignment protocols can facilitate meet the needs of distributed applications for TDLs, however, the existing distributed slot assignment protocols have poor adaption to the dynamic slot demands of the nodes and can not meet the needs of nodes'random joining and leaving preferably. So, an adaptive-frame-based dynamic slot assignment protocol (ADSAP) is proposed. The protocol does not require a central control node, and allows of nodes'random joining and leaving. Furthermore, based on special frame structure, the protocol can automatically expand or shrink the frame length to adapt to the dynamic changes of the nodes'slot demands.3) Hybrid Slot Assignment Protocol for TDLsIn order to improve the adaptability of dynamic slot assignment protocols for the changes of load and node density, the hybrid slot assignment protocols are studied. After analyzing of the characteristics of the message stream in TDLs, we divide the message stream into fixed message stream and random message stream, and design the corresponding message stream models, then, a message-stream oriented hybrid slot assignment protocol (MOHSAP) was proposed. In this protocol, the fixed slot assignment algorithm assigns slots for fixed message streams, and the assignment process does not depend upon the topology information; the dynamic slot assignment algorithm assigns slots for random message streams, and the assignment process needs the certain topology information. So the protocol is a hybrid slot assignment protocol with the characteristics of both fixed slot assignment protocol and dynamic slot assignment protocol. Furthermore, MOHSAP has a conflict detection mechanism, so it is able to solve the problem of slot conflicts caused by dynamic slot assignment effectively.4) Modeling and Simulation of Slot Assignment Protocols for TDLsIn order to evaluate slot assignemnt protocols for TDLs, the tactical data link protocol simulation platform (TDLPSP) is designed, and the running process of TDLPSP is introduced. Based on the support of a variety of tools, TDLPSP was composed mainly of the database module, the scenario generation module, the simulation configuration and operation module and the analysis modules, and can be used for modeling and simulation of different slot assignment protocols. Then, the link model, the messages generated model, the mobile model, and the node models with different protocols are established based on TDLPSP. And then, the proposed three slot assignment protocols are evaluated under different schemes respectively.