Error-control Scheme On The High Timeliness Demand Of Aerospace Communication

Promoted by the increasing importance of real-time status update applications,diverse services have put forward increasing demands for accurate description and optimization of transmission timeliness.In the status update system,the value of information changes diminishingly over time.Strong timeliness is the basis for ensuring safe and effective completion of tasks.The timeliness of information is determined by the freshness of the information at the receiver,and is affected by multiple factors such as the update process and number of sources,the number of servers and the reliability of transmission.Therefore,the optimal design of the transmission scheme is of great importance in improving the timeliness of the system.However,the existing research lacks analysis of timeliness for practical communication environment,especially the aerospace communication scene characteristic of long distance and dynamic channel fading.The metric age of information(AoI)is employed to analyze the timeliness of information.Optimized transmission schemes are analyzed in different systems.A general model of the state update system is established,and the stationary characteristics of AoI are analyzed.For the design of the source update process and transmission strategy,the transmission process under ideal channel conditions is first analyzed.The source monitors the status process in real time,and randomly generates new updates according to the Poisson process.The server processes the updates according to a specific service policy and sends them to the channel.Under several different service strategies,the average AoI performance is analyzed and the optimal source update rate and service strategy are obtained.Since AoI is related to transmission reliability,and the channel in aerospace communication is dynamic,it is important to ensure the required reliability by error-control channel coding.Since feedback in transmission introduces additional propagation delay which will cause the received updates to be stale,the open-loop FEC(Forward Error Correction)scheme is employed.Due to resource constraint,long updates need to be divided into packets for transmission.Inthis case,it is difficult to ensure reliability by pure physical-layer coding.Therefore,a two-layer error control coding scheme is proposed,which employs a channel coding scheme combing the packet-layer erasure coding and physical-layer error-correction coding to achieve reliable and timely delivery of status updates.Under this transmission scheme,the average AoI performance is analyzed and the factors such as update rate and channel environment are analyzed.Under the optimal update rate and scheduling policy,an age-optimized code-rate allocation is designed.Some real-time status update systems,such as satellite monitoring systems for the Internet of Things,need to transmit status updates from multiple sensors to an interested receiver within strict reliability constraints.The status updates are generally short packets.According to the finite block-length coding theory,the transmission reliability is positively correlated with the codeword length.Aiming to improve the age performance of the considered system,a waiting-and-batching transmission scheme is proposed.Specifically,earlier generated updates are waiting for late ones and then batching into a long packet before being coded and transmitted.This transmission scheme can improve transmission reliability and thus improve timeliness.The average AoI of the proposed scheme is compared with that of the traditional independent transmission scheme.Results reveal that the proposed scheme is more beneficial to AoI if the update generation rate is high or the propagation delay is non-trivial.