Research On The MAC Protocol Of Wireless Network For The Fractionated Payload

Space technology is one of the most comprehensive engineering technologies,which is used for exploration, development and utilization of the outer space. It has huge effect and represents a country’s comprehensive strength. For Earth System Monitoring purpose, small satellites need to be deployed in the near-Earth orbit according to a specific position, posture. One of the key technologies to the space exploration missions is the reliable inter-satellite links(ISLs). However, the intersatellite communications network has the characteristics of long propagation delay,three-dimensional dynamic ad hoc network, satellite resource limitation,.etc. All this disadvantages challenge the inter-satellite communications network technology.In this thesis, the key technology of MAC protocol for inter-satellite wireless communication network is investigated. Firstly, IEEE 802.11 MAC protocol which is reliable for inter-satellite communication network is studied. In this part, it is researched about the impact of long distance on the behaviour of IEEE 802.11 DCF and presented a Markov chain analytical model for verification purpose. This model is validated by simulation results. Then the adaptability and optimization of IEEE802.11 MAC protocol are carried out in three aspects including long ISL, the known information of satellite network scale, data transmission characteristics. Secondly,a novel MAC protocol based on CSMA with Adaptive Wait Collision Avoidance is proposed. Using this protocol, we designed the wireless networking solutions for the fractionated payload. Finally, the protocol performance and feasibility analysis are validated and simulated in the NS3 network simulation platform.The main research contents are as follows:1. Inter-satellite communication network has characteristics like long communication distance, the limited SWa P of the micro-satellite, changing network scale,etc. A fixed allocation protocols such as TDMA, FDMA, CDMA, scheduling protocols such as polling, competition protocols such as ALOHA, CSMA, etc.,are analysed. The research is based on CSMA/CA which is used in IEEE802.11 MAC protocol(Wi Fi technology).2. The impact of long propagation delay on the IEEE 802.11 MAC protocol is analysed, including the timeout wait mechanism, the virtual carrier sense mechanism, the set of inter-frame time space and so on. The slot is the base time unit for MAC protocol. The research is focused on the relationship between the slot and the propagation delay and the concept of conflict intervals is proposed. Meanwhile, A Markov chain model for long distance with MAC protocol is established, analysed and verified.3. To solve the problem of the high propagation delay and hidden terminal, the IEEE 802.11 MAC protocol workflow is improved, and inter-frame interval is adapted. The calculation method for the minimum data frame length, NAV, slot time is proposed. To accommodate the changes in communication distance,a dynamically adjustment MAC protocol parameter solution is given.4. By taking advantage of the known information about inter-satellite communications network scale, a novel algorithm is proposed, which uses the deterministic backoff value based on network size to avoid the conflict. The CSMA/AWCA protocol can significantly improve the network throughput and decrease the end-to-end delay compared with traditional CSMA/CA protocol.5. A MAC protocol for the fractionated payload formation network is designed and implemented according to the flight formation topology, satellite node types and application requirements. There are two physical communication channels. One is responsible for managing the communications network, and the other one is used for the transmission of scientific data, navigation and control data. The flow chart of the protocol for ad hoc network is given. And finally the system is tested in the NS3 satellite network simulation platform.