Guray Acar

A Cross-layer Approach for Packet Scheduling in Reliable Multicast Data Transmission over Geostationary Satellite Networks

In this paper, we propose a channel-aware scheduling algorithm that exploits the reported channel state information (CSI) from all users in the multicast group for reliable transmission of multicast information over a geostationary satellite network. Reliability is guaranteed via a multicast transport protocol that retransmits lost segments to the multicast group. The proposed scheduling mechanism uses cross-layer CSI before making a decision whether or not a data segment is to be transmitted. As such, the algorithm avoids unfavourable channel conditions to reduce the forward link resources that would be wasted to retransmit lost segments. Scheduling delay and retransmission delay are found to be the elements of a trade-off, and simulations are conducted to attain optimal algorithm parameters to minimize session transfer delay in the face of L-band mobile channel conditions.

Multicast Link Adaptation in Reliable Transmission Over Geostationary Satellite Networks

The exploitation of fluctuating channel conditions in link adaption techniques for unicast transmission has been shown to provide large system capacity gains. However, the problem of choosing transmission rates for multicast transmission has not been thoroughly investigated. In this paper, we investigate multicast adaptive techniques for reliable data delivery in GEO satellite networks. An optimal multicast link adaptation is proposed with the aim to maximise terminal throughput whilst increasing resource utilization and fairness in the face of diverse channel conditions. Via simulation results and theoretical analysis, the proposed algorithm has shown to outperform other alternative multicast link adaptation techniques especially when the terminals are in vigorous channel conditions.

VoIP over DVB-RCS satellite systems: Trial results and the impact of adaptive speech coding using cross-layer design

VoIP is one of the most popular applications on the Internet. The DVB-S2 (digital video broadcasting-satellite version 2) and DVB-RCS (digital video broadcasting-return channel satellite) standards provide the potential for reliable and efficient voice and data transfer over satellite networks. This is important, as satellites can play a role in broadband service provision by addressing the cases of limited terrestrial access such as in rural or underserved areas. The first part of this paper presents the results of our VoIP trials with different commercial DVB-S/RCS satellite offers and popular internet telephony and videoconferencing applications (Skype, MSN, etc.). These results reveal that packet delay and jitter are strongly affected by the satellite network component as well as the type of speech codec used. Accordingly, research presented in the second part of this paper is focused on dynamic speech coding rate control adapted to the conditions of the underlying network, in which the satellite domain presents the most challenging portion of the end-to-end path. For this purpose, a novel cross-layer mechanism is proposed to facilitate and increase the accuracy of the speech coding rate adaptation mechanism. Cross-layer design is a relatively new idea aiming to exploit information exchange among layers of the protocol stack. Our simulation analyses show that the proposed cross-layer mechanism can help us in optimally adjusting the speech coding rate to maintain the user-perceived quality in terms of MOS (mean opinion score) in the face of time-varying available satellite channel capacity.

A Comparison of Multicast Adaptive Techniques in Reliable Delivery over GEO Satellite Networks

In this paper, we compare two multicast adaptive techniques for reliable data delivery in GEO satellite networks. Specifically, a channel-aware scheduling algorithm is compared with a multicast link adaptation technique, in the face of fluctuating channel conditions in downlink. The aim of the techniques is to maximise system throughput whilst increasing resource utilization. The scheduling technique is implemented within one forward bearer subtype, whereas the link adaptation mechanism considers transmission rates from a list of possible forward bearer subtypes. Simulation results are analysed and it is found that multicast link adaptation technique outperforms channel-aware scheduling algorithm, in terms of reduced session delay and retransmitted number of segments.

Channel-Aware Scheduling algorithms with Channel Prediction for reliable multicast data transmission over geostationary satellite networks

In this paper, real-time channel prediction (RTChP) technique is implemented with channel-aware scheduling algorithms to increase decision accuracy at the scheduler. The channel-aware scheduler receives feedback messages in the form of channel state information (CSI) from the terminals via reservation slots in the return link. In the face of reliable multicast transmission, the channel-aware scheduler aims to reduce the number of packets received in error at the terminals. As a consequence, additional retransmission passes can be decreased, resulting in higher resource utilization in the forward link and reduced session delay. Simulation results are presented with considerations of a channel-aware scheduling (CAS) algorithm. From simulation results, RTChP increases performance gain when a lower number of terminals are considered. However, when the scenario involves more terminals, the prediction technique is ineffective and its performance deteriorates. Essentially, the RTChP implemented at the scheduler is useful only for small multicast group.

Feedback Implosion Suppression Algorithm for Reliable Multicast Data Transmission over Geostationary Satellite Networks

In this paper, we propose a feedback implosion suppression (FIS) algorithm that reduces the volume of feedback traffic from receivers in a multicast group over a geostationary satellite network. The system considered in this paper includes a reliable multicast transport protocol that operates on top of a channel-aware scheduler (CAS) with receivers capable of measuring and feeding back to the scheduler their channel state information (CSI). The collected CSI becomes a valuable input to avoid unfavorable channel conditions to reduce the forward link resources that would be wasted to retransmit lost segments. Using a fixed number of available uplink slots, the Radio Network Controller (RNC) decides which receivers to update their feedback messages in the next collection period based on their CSI in the current cycle. The integration of FIS and CAS modules achieves a degree of full reliability in multicast transmission over a satellite network without relying on any collaboration between receivers, or on any infrastructure other than the satellite network.

Admission control and handover management for high-speed trains in vehicular geostationary satellite networks with terrestrial gap-filling

Following a recent upgrade, the Digital Video Broadcasting—Return Channel Satellite (DVB-RCS) standard sets up to support terminal mobility. In this scenario, integration with terrestrial systems becomes a primary concern to ensure network connectivity in urban areas. This article proposes an integrated satellite–terrestrial architecture for the provision of broadband services onboard high-speed trains, in which terrestrial cellular networks are seen as viable gap-fillers for discontinuous satellite coverage. We derive an analytical model of the hybrid DVB-RCS-cellular system by exploiting analogies between the mobility pattern predictability of LEO constellations and that of high-speed trains. Terminals whose QoS cannot be guaranteed by the satellite segment are proposed to temporarily divert the connections towards the terrestrial infrastructure, where available. Using an iterative approach based on the Erlang fixed-point approximation, we show performance improvements with respect to stand-alone satellite systems in terms of handover failure probability and overall resource utilization. The analytical model is also validated via our ns2-based DVB-RCS packet-level simulator. Detailed modelling of synchronization and signalling mechanisms confirms the accuracy of the analytical results, and shows that topology and mobility information can contribute to refine radio resource utilization optimality when used jointly. Copyright

VoIP over DVB-RCS Satellite Systems: A Novel Capacity Request Mechanism for Improved Voice Activity Detection

Satellites can complement terrestrial networks in Internet service provision by addressing the market which lies out of their reach. Despite of the global coverage, satellite networks entail high propagation delays and usually limited user bandwidth. VoIP is an example of an application which is subject to performance impairments due to these characteristics. VoIP trials over existing broadband satellite offers reveal that the application can be carried out with an acceptable quality. However results also reveal the need for further improvement of the bandwidth on demand scheme in order to reduce delay or improve bandwidth utilization. This paper presents a novel capacity request mechanism based on the accurate modeling of VoIP traffic as well as cross-layer design. Our analysis and simulation results show that our approach outperforms fixed capacity allocation mechanisms in terms of bandwidth efficiency or traditional bandwidth on demand schemes in terms of QoS.

Predictive Reservation Based Connection Admission Control for Mobile DVB-RCS Networks

[Abstract] This paper presents a novel Connection Admission Control (CAC) strategy for vehicular DVB-RCS satellite networks. Using estimations of arriving and departing traffic in each spot-beam our proposal aims to maximize user satisfaction and minimize at the same time resource reservation. Via GPS measurements, terminals periodically estimate their time to handoff and encapsulate mobility information within signaling bursts. Upon reception of a mobility update, the NCC (Network Control Centre) is able to estimate the amount of traffic roaming around the spot-beams as well as the probabilities that active terminals will eventually handoff. As a consequence, the NCC reserves only the necessary amount of resources for handover purposes in each spot-beam in order to minimize the percentage of connections forced to termination. No overhead is introduced for the implementation of our CAC solution as it makes use of the existing DVB-RCS signaling for providing the NCC with the extra mobility parameters driving the admission control module. Through an accurate ns-2 modeling of existing DVB-RCS signaling mechanisms, we demonstrate that our lightweight CAC scheme outperforms static channel reservation schemes in terms of handover failure rate as well as traffic prediction strategies using mobility information in terms of channel utilization.

Change Detection Mechanism in Feedback Implosion Suppression Algorithm for Reliable Transmission of Multicast Data over Geostationary Satellite Network

[ Abstract] In this paper, we propose a channel change detection mechanism implemented at UE to support feedback implosion suppression algorithm for reliable transmission of multicast data over GEO satellite networks. In this framework, reliability is guaranteed via MFTP that retransmits lost segments to the multicast group. A channel-aware scheduling mechanism is used at the Gateway that behaves like a switch to allow downlink transmissions of MFTP packets. The scheduler uses CSI values collected from group members through the CSI collection policy before making a decision as to whether or not to transmit a multicast packet in the forward link. As such, the scheduling algorithm aims at avoiding unfavorable channel conditions to reduce the forward link resources that would be wasted for retransmissions and to allow downlink transmissions only when users are in good channel condition, in the face of L-band mobile satellite channel conditions. The integration of channel-aware scheduling algorithm and CSI collection policy aims to reduce session duration and traffic volume in the return link by updating only relevant information back to Gateway. In order to achieve this objective, change detection mechanism is proposed. The performance parameters such as change detection rate and downlink resource utilization are analyzed. Two change detection algorithms are compared; it is shown that there is a trade-off in performance, in particular between uplink signalling load and downlink resource utilization. The work presented in this paper is executed within IST SatNEx II (EU IST FP6 – Contract No. 027393), JA2330 “Radio Resource Allocation and Adaptation” activity. Nomenclature