【摘要】：深空探測(cè)具有十分重要的科學(xué)價(jià)值與經(jīng)濟(jì)意義,其中深空通信的有效進(jìn)行是保障深空探測(cè)任務(wù)成功的關(guān)鍵。隨著深空通信任務(wù)的日益艱巨,未來將選用具備更高傳輸速度和更寬帶寬的Ka波段。但是Ka波段盡管能夠增加通信下行鏈路的數(shù)據(jù)吞吐量,卻容易受到天氣變化的影響繼而導(dǎo)致傳輸過程的有效性降低。由于近地天氣的動(dòng)態(tài)變化,使得Ka波段下行鏈路呈時(shí)變信道。針對(duì)于時(shí)變信道而言,使用傳統(tǒng)的固定傳輸速率的鏈路方案使得鏈路的有效吞吐量受限甚至鏈路中斷,所以本論文擬提出自適應(yīng)傳輸速率方案以應(yīng)對(duì)時(shí)變信道的誤碼率變化,在保證通信鏈路連續(xù)性的同時(shí),深空Ka波段下行鏈路的系統(tǒng)吞吐量也會(huì)增加。設(shè)計(jì)自適應(yīng)傳輸方案首先需要基于深空Ka波段下行鏈路進(jìn)行信道建模,在信道模型的基礎(chǔ)上,對(duì)信道進(jìn)行預(yù)測(cè)。然而信道的預(yù)測(cè)結(jié)果相較于實(shí)際信道狀態(tài)會(huì)存在誤差,因此需要接收端反饋與前向糾刪技術(shù)來降低預(yù)測(cè)誤差對(duì)于系統(tǒng)吞吐量的影響,本文重點(diǎn)關(guān)注如何進(jìn)一步提高系統(tǒng)吞吐量。本文為了減少由于近地天氣變化所帶來的下行鏈路吞吐量損耗,結(jié)合近地大氣雨衰參數(shù)與等價(jià)噪聲溫度,建立時(shí)變信道預(yù)測(cè)模型——Gilbert-Elliot模型。同時(shí)基于此信道模型,計(jì)算出兩種信道閾值策略中的閾值,在深空背景下設(shè)計(jì)出具有最優(yōu)閾值策略的GE信道模型,為下一步設(shè)計(jì)結(jié)合傳輸協(xié)議的信道預(yù)測(cè)算法提供平臺(tái)。為了避免由于預(yù)測(cè)步長過長而引起預(yù)測(cè)誤差過大的問題,本課題采用能夠處理間斷傳輸,大時(shí)延,高誤碼率的LTP/BP協(xié)議反饋地面天氣狀態(tài),從而避免了預(yù)測(cè)步長過長的問題。本文提出基于異步LTP/BP(Licklider Transmission Protocol/Bundle Protocol)協(xié)議的文件傳輸模式,并結(jié)合LTP傳輸模式特點(diǎn),設(shè)計(jì)一種基于Ka波段的信道狀態(tài)預(yù)測(cè)模型,從而提高Ka波段下行鏈路的全局吞吐量。在前向糾刪技術(shù)中引入了系統(tǒng)噴泉碼,系統(tǒng)碼是無碼率碼,沒有固定的傳輸速率,因此當(dāng)信道條件為“好”狀態(tài)時(shí),發(fā)送端選擇用高傳輸碼率傳輸;當(dāng)信道條件為“壞”狀態(tài)時(shí),則選用低傳輸碼率傳輸。根據(jù)天氣狀態(tài)轉(zhuǎn)變對(duì)Ka波段下行鏈路丟包率變化的影響,自適應(yīng)的調(diào)節(jié)系統(tǒng)噴泉碼碼率,從而保證Ka波段的數(shù)據(jù)鏈路能夠連續(xù)通信并且有效的提高Ka波段下行鏈路吞吐量。
[Abstract]:Deep space exploration has very important scientific value and economic significance, among which the effective implementation of deep space communication is the key to ensure the success of the deep space exploration mission. With the increasingly arduous task of deep space communication, Ka band with higher transmission speed and wider bandwidth will be selected in the future. However, although Ka band can increase the data throughput of the downlink, it is vulnerable to the weather change, which leads to the decrease of the efficiency of the transmission process. Because of the dynamic change of near-earth weather, the downlink of Ka band is time-varying channel. For the time-varying channel, the traditional fixed transmission rate link scheme is used to limit the effective throughput of the link and even interrupt the link, so this paper proposes an adaptive transmission rate scheme to deal with the change of BER in time-varying channel. At the same time, the system throughput of deep space Ka band downlink will be increased. The design of adaptive transmission scheme requires channel modeling based on deep space Ka band downlink and channel prediction based on channel model. However, compared with the actual channel state, the channel prediction results will have errors, so the receiver feedback and forward erasure techniques are needed to reduce the impact of prediction errors on the system throughput. This paper focuses on how to further improve the system throughput. In order to reduce the downlink throughput loss caused by the variation of near-Earth weather, a time-varying channel prediction model, Gilbert-Elliot model, is established by combining the rain decline parameters and equivalent noise temperature of the near-Earth atmosphere. At the same time, based on this channel model, the threshold of two channel threshold strategies is calculated, and the GE channel model with optimal threshold strategy is designed under the background of deep space, which provides a platform for the next design of channel prediction algorithm combined with transmission protocol. In order to avoid the problem that the prediction error is too large because the prediction step is too long, the LTP/BP protocol, which can deal with discontinuous transmission, large delay and high bit error rate, is adopted to feedback the ground weather state, thus avoiding the problem of long prediction step. In this paper, a file transfer mode based on asynchronous LTP/BP (Licklider Transmission Protocol/Bundle Protocol) protocol is proposed. Combining the characteristics of LTP transmission mode, a channel state prediction model based on Ka band is designed to improve the global throughput of downlink in Ka band. The system fountain code is introduced into the forward erasure technology. The system code is no bit rate code and has no fixed transmission rate. Therefore, when the channel condition is "good", the sender chooses to transmit at high transmission rate. When the channel condition is "bad" state, select low transmission rate transmission. According to the influence of weather state change on the downlink packet loss rate of Ka band, the fountain code rate of the system can be adjusted adaptively to ensure the continuous communication of the Ka band data link and improve the downlink throughput of Ka band effectively.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TN927.3

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