Due to the significant difference in speed between the user terminals (UTs) and the low earth orbit (LEO) satellites, it is necessary to solve the frequent handover of UTs at the edge of the moving satellite beams. Besides, as the development of LEO satellite communications, the scale of constellations and the number of UTs undergoing massive increase. Thus, in this paper, a satellite handover strategy is proposed to improve the handover performances of UTs and satellites. We define the utility function of handover jointly by considering the quality of experience of UTs, the throughput of satellites and the load balancing of network. Then, a coding method is proposed to represent the combinations of UTs and satellites. To reduce the calculational cost, an access and handover strategy based on a heuristic algorithm is proposed to search the optimal handover result. Finally, simulations show the effectiveness and superiority of the proposed strategy.

The technology advancement of satellite instruments requires increasingly fast interconnection technologies, for which no standardised solution exists. SpaceFibre is the forthcoming protocol promising to overcome the limitation of its predecessor SpaceWire, offering data-rate higher than 1Gbps. However, while several implementations of the SpaceFibre IP already exist, its Network Layer is still at experimental level. This article describes the architecture of an implemented SpaceFibre Routing Switch and provides synthesis results for common FPGAs.

Comparing with that of terrestrial networks, the location management in satellite networks is mainly restricted by three factors, i.e., the limited on-board processing (OBP), insufficient link resources and long propagation delay. Under these restrictions, the limited OBP can be smoothened by terrestrial gateway-based location management, the constraint from link resources demands the bandwidth-efficient management scheme and long propagation delay potentially lowers the management efficiency. Currently, the reduction of the management cost has always been the main direction in existing work which is based on the centralized management architecture. This centralized management has many defects, such as the non-optimal routing, scalability problem and single point of failure. To address these problems, this paper explores gateway-based distributed location management schemes for Low Earth Orbit (LEO) satellite networks. Three management schemes based on terrestrial gateways are proposed and analyzed: loose location management, precise location management, and the grouping location management. The analyses specifically analyze the cost of location queries and show their significant influence on the total cost which includes the location management and query. Starting from the above analysis, we speculate and prove the existence of the optimum scheme in grouping location management, which has the lowest total cost for the query frequency within given range. Simulation results validate the theoretical analysis on the cost and show the feature of latency in location queries, which provide a valuable insight into the design of the distributed location management scheme in satellite networks.

Border Gateway Protocol (BGP), with its advantages in routing isolation support and mature application, is a promising candidate to integrate satellite systems into the terrestrial IP network. However, with more and more ground stations accessing satellites by BGP, a significant amount of routing overhead can be produced on limited satellite links, especially for geostationary satellite networks with thousands of accessing terminals in extremely large areas. To solve this challenge, multicast transport of BGP was proposed, which takes advantage of the inherent broadcast property of wireless channels. However, its performance can be seriously degraded when interfered with the environment. In this paper, NCSR (Network Coding for Satellite network BGP Routing transport) [1] is explored in depth. Unlike existing counterparts, NCSR pays more attention to the lossy space links and can achieve reliability with more bandwidth savings. A greedy based coding algorithm is proposed to realize the network coding operation. To demonstrate the efficiency of NCSR, we conduct theoretical analyses and extensive simulations in typical scenarios of satellite systems. Simulation results show that NCSR can greatly reduce the bandwidth usage while achieving comparable latency. Discussions on practical considerations when applying network coding method for reliability assurance are also presented in detail.

The hop-limited adaptive routing (HLAR) mechanism and its enhancement (EHLAR), both tailored for the packet-switched non-geostationary (NGEO) satellite networks, are proposed and evaluated. The proposed routing mechanisms exploit both the predictable topology and inherent multi-path property of the NGEO satellite networks to adaptively distribute the traffic via all feasible neighboring satellites. Specifically, both mechanisms assume that a satellite can send the packets to their destinations via any feasible neighboring satellites, thus the link via the neighboring satellite to the destination satellite is assigned a probability that is proportional to the effective transmission to the destination satellites of the link. The satellite adjusts the link probability based on the packet sending information observed locally for the HLAR mechanism or exchanged between neighboring satellites for the EHLAR mechanism. Besides, the path of the packets are bounded by the maximum hop number, thus avoiding the unnecessary over-detoured packets in the satellite networks. The simulation results corroborate the improved performance of the proposed mechanisms compared with the existing in the literature.

This paper presents an inter-satellite link (ISL) reassignment method to optimize the snapshot routing performance for polar-orbit LEO satellite networks. When the snapshot routing tables are switching simultaneously in all satellites, we propose to reassign the inter-plane ISLs with regularity to improve the quality of the next snapshot, such as snapshot duration, on-board transceiver utilization ratio and end to end delay. Evaluations indicate that our method can attain equal-length snapshots regardless of the latitude of the polar area border, and so is superior to the natural partition method. Meanwhile, compared with the equal partition method which is used in the Iridium system, our method can prolong 82.87% snapshot duration, increase 8.68% on-board transceiver utilization ratio and reduce 5.30% average end to end delay of the whole network. Therefore, we believe that the ISL reassignment method can be efficiently applied in all practical polar-orbit LEO satellite networks.

In this paper, we analyze the rollback traffic in polar-orbit satellite networks that use the snapshot routing algorithm. The concept of diamond rollback links and polar rollback links are presented for the first time, and the numbers of diamond and polar rollback links in polar-orbit satellite networks are concisely formulated. Simulations are performed based on the Iridium and Teledesic system in NS2, and the results finally confirm our analysis. With this work, we can not only simplify the rollback loops avoidance scheme, but also provide guidance for future satellite network routing optimization and topology design.

A transmission control protocol (TCP) using an additive increase multiplicative decrease (AIMD) algorithm for congestion control plays a leading role in advanced Internet services. However, the AIMD method shows only low link utilization in lossy networks with long delay such as satellite networks. This is because the cwnd dynamics of TCP are reduced by long propagation delay, and TCP uses an inadequate congestion control algorithm, which does not distinguish packet loss from wireless errors from that due to congestion of the wireless networks. To overcome these problems, we propose an exponential recovery (ER) TCP that uses the exponential recovery function for rapidly occupying available bandwidth during a congestion avoidance period, and an adaptive congestion window decrease scheme using timestamp base available bandwidth estimation (TABE) to cope with wireless channel errors. We simulate the proposed ER-TCP under various test scenarios using the ns-2 network simulator to verify its performance enhancement. Simulation results show that the proposal is a more suitable TCP than the several TCP variants under long delay and heavy loss probability environments of satellite networks.

In Low Earth Orbit (LEO) satellite networks, the user distributions are unbalanced due to the geography and the population dispersion. As a result, some satellites have few traffic loads, while others have heavy traffic loads which often lead to congestion events. In this paper, we propose a novel load balancing method based on congestion prediction. In the proposed method, each satellite detects areas where congestion often occurs and conveys their positions to its adjacent satellites. In those areas, the concerned satellites perform load balancing algorithms to prevent congestion. The performance of the proposed method is evaluated through a number of simulations. The simulation results demonstrate that the proposed scheme improves packet drop rate, end-to-end delay, and throughput.

There are many system proposals for satellite-based broadband communications that promise high capacity and ease of access. Many of these proposals require advanced switching technology and signal processing on-board the satellite(s). One solution is based on a geo-synchronous (GEO) satellite system equipped with on-board processing and on-board switching. An important feature of this system is allowing for a maximum number of simultaneous users, hence, requiring effective medium access control (MAC) layer protocols for connection admission control (CAC) and bandwidth on demand (BoD) algorithms. In this paper, an integrated CAC and BoD algorithm is proposed for a broadband satellite communication system with heterogeneous traffic. A detailed modeling and simulation approach is presented for performance evaluation of the integrated CAC and BoD algorithm based on heterogeneous traffic types. The proposed CAC and BoD scheme is shown to be able to efficiently utilize available bandwidth and to gain high throughput, and also to maintain good Grade of Service (GoS) for all the traffic types. The end-to-end delay for real-time traffic in the system falls well within ITU's Quality of Service (QoS) specification for GEO-based satellite systems.

In this paper, we propose an adaptive compensation algorithm to compensate cell delay variation (CDV) occurring during ATM/TDMA transition in a satellite ATM network. The proposed CDV compensation algorithm uses two types of additional information: cell position information (Cp)--indicating the number of cells (N) arriving within a control unit time (Tc) and positions of cells at a given time--and the number of cells in bursts--to take into account the characteristics of localized bursts. To evaluate the performance of the proposed algorithm, we performed a computer simulation based on an OPNET environment, using the Markov modulated Poisson process (MMPP) traffic model and assessed its effectiveness from varied standpoints. The results of the performance testing indicate that the proposed algorithm, while requiring significantly less additional information than previous CDV compensation algorithms, is able to more efficiently compensate CDV in localized burst traffic than the previous ones.

Low Earth Orbit (LEO) satellite constellations have been proposed in recent years to provide broadband network access. This research focuses on Walker Delta type constellation. Walker Delta has overlapping ascending and descending orbits. Although Inter Satellite Links (ISLs) can be utilized between satellites orbiting in the same direction, ISLs cannot be utilized between satellites orbiting in opposite directions. As a result, a Walker Delta Constellation with ISLs has two locally separate overlapping meshes, an ascending and a descending mesh. To reach from one local mesh to the other, the traffic has to pass through the highest latitude intra-plane ISLs. Therefore the propagation delay between terminals connected to different meshes is greater than between terminals connected to the same mesh. Due to characteristic handover of LEO satellites, terminals can connect to a satellite in the other mesh during communication, causing drastic variation of propagation delay which results in degradation of communication quality. These issues can be solved by continuously connecting the communication terminals to the same mesh. In this paper, a satellite selection method for Walker Delta Constellations with double mesh coverage is proposed. It employs geographical location information of the communicating terminals, to connect them to the same mesh. In addition, the proposed method selects the mesh that minimize propagation delay for that communication session. It is shown through simulation that the proposed method is effective in reducing delay and jitter for a connection while improving overall communication quality of the network.

In this paper, we propose a teletraffic model and evaluate the performance in the terrestrial/satellite integrated mobile communication networks having hierarchical structure consisting of terrestrial microcell and satellite spot beam. In the proposed teletraffic model, both the subscriber terminal mobility in the terrestrial microcell and the satellite mobility in the LEO satellite spot beam are considered. The overflow traffic from microcell can be accommodated by the satellite spot beam and is analyzed by IPP (Interrupted Poisson Process) which is often used to analyze non-random overflow traffic. Various reservation channels for handoff calls in terrestrial microcell and satellite spot beam are considered. New calls initially directed to the satellite spot beam are also considered for reservation channels. Carried traffic, blocking, forced termination and non-completion probabilities are evaluated for the overall integrated networks.