Frequent inter-satellite link(ISL)handovers will induce service interruption in large-scale space information networks,since traditional distributed/centralized routing strategy-based route convergence/update will con...Frequent inter-satellite link(ISL)handovers will induce service interruption in large-scale space information networks,since traditional distributed/centralized routing strategy-based route convergence/update will consume considerable time(compared with ground networks)derived from long ISL delay and flooding between hundreds or even thousands of satellites.During the network convergence/update stage,the lack of up-to-date forwarding information may cause severe packet loss.Considering the fact that ISL handovers for close-to-earth constellation are predictable and all the ISL handover information could be stored in each satellite during the network initialization,we propose a self-update routing scheme based on open shortest path first(OSPF-SUR)to address the slow route convergence problem caused by frequent ISL handovers.First,for predictable ISL handovers,forwarding tables are updated according to locally stored ISL handover information without link state advertisement(LSA)flooding.Second,for unexpected ISL failures,flooding could be triggered to complete route convergence.In this manner,network convergence time is radically descended by avoiding unnecessary LSA flooding for predictable ISL handovers.Simulation results show that the average packet loss rate caused by ISL handovers is reduced by 90.5%and 61.3%compared with standard OSPF(with three Hello packets confirmation)and OSPF based on interface state(without three Hello packets confirmation),respectively,during a period of topology handover.And the average endto-end delay is also decreased by 47.6%,9.6%,respectively.The packet loss rate of the proposed OSPF-SUR does not change along with the increase of the frequency of topology handovers.展开更多
Communities in developing country mountain areas,in part due to their remoteness,find themselves excluded from social,political and economic systems; and excluded from access to resources. This paper aims to study the...Communities in developing country mountain areas,in part due to their remoteness,find themselves excluded from social,political and economic systems; and excluded from access to resources. This paper aims to study the impact of information and communication technologies (ICTs) on remoteness and exclusion. It utilises two models - the resource movement framework,and the "information chain" - to analyse a telecentre in one district of mountainous Huancavelica,Peru's poorest region,set in the high Andes. It finds ICTs enabling new and positive resource flows for the two key user groups:teenaged school students and young farmers. These help to maintain social networks. They also support information searches that have improved agricultural practice where other information chain resources have been available. But non-use and ineffective use of the telecentre are found where information chain resources are lacking. ICTs have some impacts on intangible elements of remoteness. In this particular example,they also offer access to some previously-excluded resources. But they have not really addressed the systematic exclusions faced by mountain communities. And they so far appear to be a technology of inequality; favouring those residents who begin with better resource endowments.The paper concludes by offering some recommendations for mountain ICT project practice.展开更多
This paper proposes a joint network-channel codingbased on turbo codes for user cooperation. The scenario under consideration is one in which two ＂partners＂--UE1 and UE2---cooperate in transmitting information to th...This paper proposes a joint network-channel codingbased on turbo codes for user cooperation. The scenario under consideration is one in which two ＂partners＂--UE1 and UE2---cooperate in transmitting information to the base station （BS）. Each partner transmits both locally generated information and the relayed information that originated at the other partner. The local information and relayed information are jointly network-channel coded to form a superimposed codeword, and the adjacent codewords transmitted in turn by the two partners are tightly correlative like a chain. It is shown via simulation that the proposed scheme achieves full diversity gain compared with the other user cooperation schemes, including those based on coded cooperation and distributed space-time coded cooperation.展开更多
基金the National Natural Science Foundations of China(Nos.61771074,62171059)。
文摘Frequent inter-satellite link(ISL)handovers will induce service interruption in large-scale space information networks,since traditional distributed/centralized routing strategy-based route convergence/update will consume considerable time(compared with ground networks)derived from long ISL delay and flooding between hundreds or even thousands of satellites.During the network convergence/update stage,the lack of up-to-date forwarding information may cause severe packet loss.Considering the fact that ISL handovers for close-to-earth constellation are predictable and all the ISL handover information could be stored in each satellite during the network initialization,we propose a self-update routing scheme based on open shortest path first(OSPF-SUR)to address the slow route convergence problem caused by frequent ISL handovers.First,for predictable ISL handovers,forwarding tables are updated according to locally stored ISL handover information without link state advertisement(LSA)flooding.Second,for unexpected ISL failures,flooding could be triggered to complete route convergence.In this manner,network convergence time is radically descended by avoiding unnecessary LSA flooding for predictable ISL handovers.Simulation results show that the average packet loss rate caused by ISL handovers is reduced by 90.5%and 61.3%compared with standard OSPF(with three Hello packets confirmation)and OSPF based on interface state(without three Hello packets confirmation),respectively,during a period of topology handover.And the average endto-end delay is also decreased by 47.6%,9.6%,respectively.The packet loss rate of the proposed OSPF-SUR does not change along with the increase of the frequency of topology handovers.
基金a grant from the International Development Research Centre, Canada, and Microsoft Corporationsupport of the Seminario Permanente de Investigacion Agraria (Permanent Seminar on Agricultural Research), SEPIA
文摘Communities in developing country mountain areas,in part due to their remoteness,find themselves excluded from social,political and economic systems; and excluded from access to resources. This paper aims to study the impact of information and communication technologies (ICTs) on remoteness and exclusion. It utilises two models - the resource movement framework,and the "information chain" - to analyse a telecentre in one district of mountainous Huancavelica,Peru's poorest region,set in the high Andes. It finds ICTs enabling new and positive resource flows for the two key user groups:teenaged school students and young farmers. These help to maintain social networks. They also support information searches that have improved agricultural practice where other information chain resources have been available. But non-use and ineffective use of the telecentre are found where information chain resources are lacking. ICTs have some impacts on intangible elements of remoteness. In this particular example,they also offer access to some previously-excluded resources. But they have not really addressed the systematic exclusions faced by mountain communities. And they so far appear to be a technology of inequality; favouring those residents who begin with better resource endowments.The paper concludes by offering some recommendations for mountain ICT project practice.
文摘This paper proposes a joint network-channel codingbased on turbo codes for user cooperation. The scenario under consideration is one in which two ＂partners＂--UE1 and UE2---cooperate in transmitting information to the base station （BS）. Each partner transmits both locally generated information and the relayed information that originated at the other partner. The local information and relayed information are jointly network-channel coded to form a superimposed codeword, and the adjacent codewords transmitted in turn by the two partners are tightly correlative like a chain. It is shown via simulation that the proposed scheme achieves full diversity gain compared with the other user cooperation schemes, including those based on coded cooperation and distributed space-time coded cooperation.
