We propose a covert communication protocol for the spread-spectrum multiple random access with additive white Gaussian noise (AWGN) channel. No existing paper has studied covert communication for the random access channel. Our protocol assumes binary discrete phase-shift keying (BPSK) modulation, and it works well under imperfect channel state information (I-CSI) for both the legitimate and adversary receivers, which is a realistic assumption in the low power regime. Also, our method assumes that the legitimate users share secret variables in a similar way as the preceding studies. Although several studies investigated the covert communication for the point-to-point communication, no existing paper considers the covert communication under the above uncertainty assumption even for point-to-point communication. Our protocol under the above uncertainty assumption allowsO(n) legitimate senders andO(n/logn) active legitimate senders. Furthermore, our protocol can be converted to a protocol for point-to-point communication that works under the above uncertainty assumption.

With the increasing demand for secure communication in optical space networks, it is essential to develop physical-layer scalable security solutions. In this context, we present the asymptotic security analysis of a keyless quantum private communication protocol that transmits classical information over quantum states. Different from the previous literature, our protocol sends dummy (decoy) states optimally obtained from the true information to deceive the eavesdropper. We analyze optical on-off keying (OOK) and binary phase shift keying (BPSK) for several detection scenarios. Our protocol significantly improves the protocol without decoy states whenever Bob is at a technological disadvantage with respect to Eve. Our protocol guarantees positive secrecy capacity when the eavesdropper gathers up to 90-99.9% (depending on the detection scenario) of the photon energy that Bob detects, even when Eve is only limited by the laws of quantum mechanics. We apply our results to the design of an optical inter-satellite link (ISL) study case with pointing losses, and introduce a new design methodology whereby the link margin is guaranteed to be secure by our protocol. Hence, our design does not require knowing the eavesdropper’s location and/or channel state: the protocol aborts whenever the channel drops below the secured margin. Our protocol can be implemented with state-of-the-art space-proof technology. Finally, we also show the potential secrecy advantage when using (not yet available) squeezed quantum states technology.

Our main contribution is the design of a spread spectrum random access scheme without pre-shared secret with asymptotically guaranteed availability against electronic/cyber-based jamming attacks. In order to establish asymptotic anti-jamming guarantees, first we develop the system model and show that for reactive jamming (only limited by the laws of physical propagation), the required location for a successful attack can be controlled by design. Then, for non-reactive protocol-aware jamming, we map a random selection of (publicly known) spreading codes to the computational birthday problem. Differently to the related literature, we formulate the birthday problem using entropic measures (Rényi entropy), which allows to obtain the optimal spreading code set sizes that guarantee asymptotically zero collision probability. Accordingly, the birthday attack is the best strategy to optimize the (trial and error) blind acquisition at the legitimate detector. We obtain numerical results that illustrate how to use our entropic method as a system design degree of freedom to identify realistic spreading code set sizes. We also derive an upper bound of the detection latency. Finally, we show that the resulting anti-jamming throughput is higher than the throughput under conventional operation (i.e. without anti-jamming guarantees) due to the control of collision probability by-design.

We consider two users A and B wanting to exchange their messages MAand MBvia a relay in a wireless communication network. To this aim, we have two methods: direct forward (DF) and computation and forward (CAF). In the first method, after an orthogonal multiple access (OMA) or non-orthogonal multiple access (NOMA) phase, the receiver decodes the two messages. In the second method, after a NOMA phase, the receiver decodes only the (modulo) sum. In the latter case the capacity region (computation region) is not known. This paper compares the two methods. To such aim, we propose a unified coding framework and identify a lower bound of achievable computation rates. We consider three constellations for the symmetric two-user Gaussian channel with Eisenstein constellation showing highest performance. We also show that a minimum signal-to-noise ratio is required for our CAF method to outperform DF, and we obtain the numerical values of such minimum ratios for the three constellations. Finally, we show achievability of our bounds, which is proved to require affine codes for computation, which has not been proved before. Overall, our results are useful for communication system designers towards practical implementation of multiple access methods in integrated wireless systems.

In this paper we propose a two-way protocol of physical layer security using the method of privacy amplification against eavesdroppers. First we justify our proposed protocol by analyzing the physical layer security provided by the classic wiretap channel model (i.e. one-way protocol). In the Gaussian channels, the classic one-way protocol requires Eve's channel to be degraded w.r.t. Bob's channel. However, this channel degradation condition depends on Eve's location and whether Eve's receiving antenna is more powerful than Bob's. To overcome this limitation, we introduce a two-way protocol inspired in IEEE TIT (1993) that eliminates the channel degradation condition. In the proposed two-way protocol, on a first phase, via Gaussian channel, Bob sends randomness to Alice, which is partially leaked to Eve. Then, on a second phase, Alice transmits information to Bob over a public noiseless channel. We derive the secrecy capacity of the two-way protocol when the channel to Eve is also Gaussian. We show that the capacity of the two-way protocol is always positive. We present numerical values of the capacities illustrating the gains obtained by our proposed protocol. We apply our result to simple yet realistic models of satellite communication channels.

In this work, we focus on the classical optical channel having Poissonian statistical behavior and propose a novel secrecy coding-based physical layer protocol. Our protocol is different but complementary to both (computationally secure) quantum immune cryptographic protocols and (information theoretically secure) quantum cryptographic protocols. Specifically, our (information theoretical) secrecy coding protocol secures classical digital information bits at photonic level exploiting the random nature of the Poisson channel. It is known that secrecy coding techniques for the Poisson channel based on the classical one-way wiretap channel (introduced by Wyner in 1975) ensure secret communication only if the mutual information to the eavesdropper is smaller than that to the legitimate receiver. In order to overcome such a strong limitation, we introduce a two-way protocol that always ensures secret communication independently of the conditions of legitimate and eavesdropper channels. We prove this claim showing rigorous comparative derivation and analysis of the information theoretical secrecy capacity of the classical one-way and of the proposed two-way protocols. We also show numerical calculations that prove drastic gains and strong practical potential of our proposed two-way protocol to secure information transmission over optical channels.

We present the comparative modelling and analysis of one-way and two-way physical layer security protocols using privacy amplification for the Gaussian satellite channel. It is known that one-way protocols based on the classic Wyner?s wiretap channel require Eve's channel to be degraded w.r.t. Bob?s channel. Here, to overcome this limiting performance condition, we introduce a two-way protocol inspired in Maurer?s protocol in IEEE TIT (1993), which differently to other proposals of two-way protocols, fully eliminates the channel degradation condition (i.e. secrecy capacity is always guaranteed to be positive). We present the description of the two protocols and the comparison of secrecy capacity when Eve uses any type of orbit. We show their realistic performance taking into consideration orbital dynamics, i.e. the only assumption made on Eve is that she has to comply with orbit mechanics. Our numerical security analysis results confirm that the two-way protocol outperforms the one-way protocol in different degrees depending on the orbit and legitimate antenna radiation patterns.

Secure communications are becoming increasingly relevant in the development of space technology. Well-established cryptographic technology is already in place and is expected to continue to be so. On the other hand, information theoretical security emerges as a post-quantum versatile candidate to complement overall security strength. In order to prove such potential, performance analysis methods are needed that consider realistic legitimate and eavesdropper system assumptions and non-asymptotic coding lengths. In this paper, we propose the design of secure radio frequency (RF) satellite links with realistic system assumptions. Our contribution is three-fold. First, we propose a wiretap channel model for the finite-length regime. The model includes a stochastic wiretap encoding method using existing practical linear error correcting codes and hash codes. Secrecy is provided with privacy amplification, for which the finite-length secrecy metric is given that upper bounds semantic secrecy. Second, we derive a novel RF (broadcast) satellite wiretap channel model that parameterizes the stochastic degraded channel around the legitimate channel, a necessary condition to enable secure communication. Finally, we show the design of a secure satellite physical layer and finite-length performance evaluation. In doing so, we define as sacrifice rate the fixed fraction of the overall coding rate budget for reliability that needs to be allocated to secrecy. Our methodology does not make use of channel side information of the eavesdropper, it only makes assumptions on Eve's noise power. We illustrate our proposed design method with numerical results using practical error correcting codes in current standards of satellite communication.

It is becoming clear that softwarization and virtualization of networking entail fundamental changes in how networking industry can control or troubleshoot traffic flows or enforce network-wide policies. Also application developers bystander major changes, with new opportunities for fast development of innovative applications and services. Network functions (NFs) are key building blocks to realise such potential. Indeed, NFs are currently subject of great development by diverse vendors for a large range of applications beyond traditional well known networking functionalities. Such new capabilities may benefit from flexible and scalable design as opposite to current blackbox view of NFs. In this paper we propose one such novel NF with flexible and scalable design. Our NF exploits the capabilities of the network coding (NC) concept to improve different metrics of service performance, hence resulting in a NC service that can be offered either to external customers or used as internal service by the network provider. Our main contribution is three-fold. First, we justify our approach of internal logical visibility of network coding functions (NCFs), which allows proprietary while interoperable NCFs. Second, we propose the modelling of NCFs internal logic in terms of their software functional architecture. Finally, we show that our functional logic naturally maps to softwarized network architectures, which in turn facilitates NCFs virtualization. We also discuss the applicability of our architectures to representative conceptual scenarios and identify next steps.

In this paper, we present the functional design and experimental validation of network coding technology over hybrid networks including satellite links. We first describe our design framework based on a holistic modelling of (overlay) heterogeneous networking satellite scenarios. We then define different types of logical nodes depending on their encoding, re-encoding and decoding functionalities and whether or not the satellite (overlay) application designer has control over them. Nodes are assumed strategically chosen to recode, which may result in a small number of re-encoding nodes that suffice to optimize selected performance metrics. Our main contribution is a system-oriented functional design of network coding that enables flexible instantiation of different types of network codes via configurable network coding (C-NC) functions. Random or structured NC coefficients can be remotely or locally generated and a packet scheduler can forward packets according to different policies. The choice of coefficients and overall NC scheme depend on the SATCOM-specific performance target, namely delay or bandwidth constraints. Here, we present a preliminary design and experimental testebed validation for the case of delay constrained transmission. Our results show the practical benefits of re-encoding and performance tradeoffs of different network coding schemes. In particular, our results show the good structural properties and delay-reliability tradeoffs of our novel proposal of structured network codes using Pascal matrices due to the regenerative properties of the coding coefficients.

We discuss secure transmission via an untrusted relay when we have a multiple access phase from two nodes to the relay and broadcast phase from the relay to the two nodes. To realize the security, we construct a code that securely transmits the modulo sum of the messages of two nodes via a multiple access channel. In this code, the relay cannot obtain any information for the message of each node, and can decode only the messages of the two nodes. Our code is constructed by simple combination of an existing liner code and universa12 hash function.

In this paper, we propose a design solution for the implementation of Virtualized Network Coding Functionality (VNCF) over a service coverage area. Network Function Virtualization (NFV) and Network Coding (NC) architectural designs are integrated as a toolbox of NC design domains so that NC can be implemented over different underlying physical networks including satellite or hybrid networks. The design includes identifying theoretical limits of NC over wireless networks in terms of achievable rate region and optimizing coding rates for nodes that implement VNCF. The overall design target is to achieve a given multicast transmission target reliability at receiver sides. In addition, the optimization problem uses databases with geo-tagged link statistics and geo-location information of network nodes in the deployment area for some computational complexity constraints. Numerical results provide validation of our design solution on how network conditions and system constraints impact the design and implementation of NC and how VNCF allows reliable communication over wireless networks with reliability and connectivity up to theoretical limits.

We propose the joint study of function computation (arithmetics) and lattice coding gain (geometry) to derive the (complex modulo) arithmetics of compute and forward over Euclidean geometry. First, we demonstrate that only five families of complex alphabets exist that admit euclidean complex modulo arithmetics. Second, we prove that the (per-dimension) euclidean division algorithm is equivalent to a closest vector algorithm hence a natural framework for compute and forward. Third, we derive the nominal coding gains of the five resulting families of (nested) lattice codes obtained as preimages of linear block codes. Finally we apply the proposed arithmetic geometry framework to the MAC channel and show graphical illustration of the 2-user case over the Eisenstein numbers.

The objective of this paper is to investigate whether or not network coding offers increased throughput with respect to routing in satellite multibeam communications. To this aim, we depart from the traditional system level oriented design of multibeam communications and propose a novel networking approach based on graph modelling. Specifically, for the multi-beam geometry, a graph model based on Kronecker product of matrices is presented. The model captures the broadcasting transmission nature as it embeds a physical description of the underlying multibeam coverage. In order to introduce the interference limitation inherent to multibeam communications, we propose realistic system and transmission models which render connectivity constraints that we introduce into the graph model. Cut-capacity analysis adapted to the multibeam scenario is proposed and the comparison of the cut-capacity achievability for the derived graphs is investigated under routing and network coding assumptions. We obtain that, under the assumed system and transmission models, network coding gain is 1.75.

In this paper we investigate capacity optimization mechanisms for multi-beam satellite systems built on a realistic payload model. The first proposed mechanism deals with long term traffic variations, for which capacity optimization algorithms are proposed based on per-beam traffic requests. Due to the high asymmetry of the traffic, our algorithms provide time and spatial flexibility illuminating a specific set of beams within a window of several time-slots. Our algorithms maximize the amount of capacity actually offered while providing reduced power consumption. The second proposed mechanism deals with short-term traffic variations, for which we propose Network Coding (NC) based techniques at the link layer. The aim is to increase the offered capacity taking advantage of overlapping beam coverage, usually considered as a source of interference. This technique is meant to be applied not only in classical multi-beam systems, but also on top of the per-beam capacity optimization as a method to deal with fast traffic unbalances not evaluated in the first mechanism. Analysis and simulations results show that system capacity can be increased up to 13% in the first case and up to 90% in the second case.

In this paper, a novel precoding technique is proposed for implementing Physical layer Network Coding (PNC) based on Compute and Forward (CF). In particular, an integer forcing precoder (IFP) is proposed that avoids the maximum rate achievability limitation due to channel approximation at the receiver in previous proposals. The probability of error from the proposed in previous proposals. The probability of error from the proposed scheme is shown to have up to 2 dB of gain over the existent lattice network coding based implementation of CF. Further, it is shown that the extra power penalty which is paid due to precoding is upper bounded with finite value. It is also shown that the achievable rate using IFP approaches the upper bound for CF. Our precoder requires Channel State Information (CSI) at the transmitter but only that of the channel between the transmitter and relay, which is a feasible assumption.

For the two-user interference channel, the Han-Kobayashi (HK) scheme is known to achieve optimal rates within one bit of the capacity for Gaussian codebooks. In this paper, we propose its practical implementation based on finite M-QAM constellations. For the very strong interference regime, we derive the interference level conditions and its geometrical interpretation. For the weak interference regime, we propose a joint private/common constellation design which utilizes the interference-free constellation spaces and induces the geometrical conditions for this regime. Our results show that for the very strong interference regime, the desired signal is transmitted interference-free over a larger range of channel values than in the Gaussian case. Furthermore, for the weak interference regime, the achievable rates of the proposed scheme are compared with 1) the theoretical limit of the HK scheme when Gaussian codebooks are used [8] and 2) the orthogonal rates. In particular, the proposed scheme achieves upto 150% increase in the transmission rates as compared to the orthogonal rates.

We present a framework for optimizing content delivery in disaster recovery scenarios using a holistic network design. Our methodology proposes two main novelties compared to state-of-the-art. First, we propose to model the communication network following a holistic approach. This framework guarantees generality and robustness of the overall design since any network can be considered as part of the different instantiations of a disaster scenario. Second, we characterize the particular network instantiations via their min-cut (well-known parameter from graph theory), which we use to formulate a cross-layer optimization problem aiming at procuring Quality of Service (QoS) and Quality of Perception (QoP) of content delivery. Our results show the benefits of our proposal compared to non-cross layer strategies not designed holistically, by maintaining a level of QoS and QoP in spite of changing network conditions.

Trading delay and rate in upcoming satellite networks are of paramount interest. In this paper, we present a solution to optimally distribute resources across MAC, IP and APP layers to deal with the problem of efficiently and reliably delivering low latency and high rate inelastic services over such networks. In order to do so, we formulate the problem of rate/delay balancing according to a Network Utility Maximization (NUM) paradigm assuming Scalable Video Coding (SVC) feeding a cross-layer DiffServ architecture, and an adaptive physical layer. We solve not only the bit loading balancing across the IP queues but also the video layers distribution to be sent among the adaptive physical layers, all constrained by delay requirements. The solution, which provides a fair rate-delay trade-off, happens to be on a water filling load across the queuing architecture, and it is suitable for multicasting scenarios. Finally, we propose a full protocol design, implementation, and performance evaluation based on truly available standardized tools, hence, it is ready-to-use. Our solution significantly outperforms non cross-layer approaches in terms of delay and video quality, and it dynamically adapts to channel and traffic variations.

The first two generations of TV broadcasting are almost history, at least from the standardization perspective. Analog and digital satellite distributions both have addressed mass markets. The next-generation TV systems are close to primetime deployments: HDTV, 3DTV, interactive services, hybrid services, and additional innovations will dominate the next-generation TV. With the efficiency and maturity of DVB-S2, satellite distribution is a cost-efficient and well-established broadcast technology with significant potential for extensions. In this paper, the future perspectives of digital TV and HDTV broadcasting will be first explored, considering ongoing and future standardization activities that will be carried out. Particular attention to innovative solutions based on adaptive modulation and coding, source and channel coding, and error resilience techniques for satellite TV transmission is paid. In addition to broadcast TV, also the perspectives of hybrid and IPTV will be considered in a satellite scenario with their pros and cons, trying to understand if satellite IPTV will be in competition with “conventional” broadcast satellite TV services (like it already happens in terrestrial scenarios).

In this paper, we study multibeam satellite secure communication through physical (PHY) layer security techniques, i.e., joint power control and beamforming. By first assuming that the channel state information (CSI) is available and the beamforming weights are fixed, a novel secure satellite system design is investigated to minimize the transmit power with individual secrecy rate constraints. An iterative algorithm is proposed to obtain an optimized power allocation strategy. Moreover, suboptimal beamforming weights are obtained by completely eliminating the cochannel interference and nulling the eavesdroppers' signal simultaneously. In order to obtain jointly optimized power allocation and a beamforming strategy in some practical cases, e.g., with certain estimation errors of the CSI, we further evaluate the impact of the eavesdropper's CSI on the secure multibeam satellite system design. The convergence of the iterative algorithm is proven under justifiable assumptions. The performance is evaluated by taking into account the impact of the number of antenna elements, number of beams, individual secrecy rate requirement, and CSI. The proposed novel secure multibeam satellite system design can achieve optimized power allocation to ensure the minimum individual secrecy rate requirement. The results show that the joint beamforming scheme is more favorable than the fixed beamforming scheme, especially in the cases of a larger number of satellite antenna elements and higher secrecy rate requirement. Finally, we compare the results under the current satellite air-interface in DVB-S2 and the results under Gaussian inputs.

In this paper, we investigate two new candidate transmission schemes to replace current ones in satellite communication systems. They operate in different domains (frequency and time-space), and we want to know which domain shows overall best performance. The two new transmission schemes are: Non-Orthogonal Frequency Reuse (NOFR) and Beam-Hoping (BH). We propose a novel formulation of the Signal-to-Interference-plus-Noise Ratio (SINR) and spectral efficiency of these two schemes and prove the theoretical duality between them. Further, we also develop a general methodology to include the technological constraints due to realistic implementation, which is common for the two domains and obtain the main factors that prevent the two technologies be in practice dual of each other (what we have called the technological gap). Moreover, we solve the frequency/time-space resource optimization problem with two different cost functions for an asymmetric traffic distribution. Both Gaussian codes and current state-of-the-art adaptive coding and modulation transmission over time division multiplexing (DVB-S2) are assumed in the simulation. It is shown that the Beam Hopping system turns out to show a less complex design and performs better specially for non-real time services.

A novel multibeam satellite system design is proposed in this paper based on jointly optimizing power and carrier allocation in order to best match the asymmetric traffic requests. This design introduces higher and asymmetric interference levels throughout the coverage. However, both power and bandwidth will be used more efficiently. Even though the problem of power and bandwidth allocation has been addressed in terrestrial wireless communications, it is new in satellite systems and since architecture and channel are different, available results and algorithms are not applicable to satellite payload systems. In this paper we formulate the resource allocation problem as max-min SINR balancing based on the recently introduced axiomatic-based interference model, but in addition, we also optimize the carrier allocation when performing the SINR balancing problem. An analytical solution for the optimal carrier allocation is proposed and we iteratively find the optimal power allocation for each beam. The Shannon (upper bound) and current state-of-the art PHY layer technology: DVB-S2 are proposed to be implemented in order to obtain the gap between them. Simulation results show significant improvements in terms of power gain, spectral efficiency and traffic matching ratio comparing with conventional system, which is designed based on uniform bandwidth and power allocation.

Current multibeam satellite systems perform centralized power and carrier allocation assuming a multi-frequency time division multiple access (MF-TDMA) scheme with fixed regular frequency reuse. This approach is not optimal when individual SINR constraints are to be met. In this paper, we formulate the problem of joint power and carrier allocation allowing non-regular frequency reuse. This setting will increase the interference levels but in turn will allow a more efficient use of the power increasing the spectral efficiency. We focus on a distributed formulation of the problem and compare it with the conventional power balancing solution. Numerical results show that the centralized power balancing approach performs better for high SINR constraints, balancing the co-channel interference among all the users and beams. Conversely, the decentralized approach optimizes the satellite terminals' self-interest deteriorating SINR of high loaded beams resulting in worse performance for highly loaded beams.

Unequal protection mechanisms have been proposed at several layers in order to improve the reliability of multimedia contents, especially for video data. The paper aims at implementing a multi-layer unequal protection scheme, which is based on a Physical-Transport-Application cross-layer design. Hierarchical Modulation, in the physical layer, has been demonstrated to increase the overall user capacity of a wireless communication. On the other hand, unequal erasure protection codes at the transport layer turned out to be an efficient method to protect video data generated by the application layer by exploiting their intrinsic properties. In this paper, the two techniques are jointly optimized in order to enable recovering lost data in case the protection is performed separately. We show that the cross-layer design proposed herein outperforms the performance of hierarchical modulation and unequal erasure codes taken independently.

This paper aims at providing different cost-efficient solutions for the channel impairments in tropical areas. In order to extend service to isolated areas, we propose hybrid architecture based on DVB-S2/RCS+Wi-Fi networks. In this scenario the satellite channel is affected by deep rain events that do not allow ACM modes to protect data. Moreover, the delay in the ACM reaction to fade changes can affect the quality of the video transmission. In order to avoid the QoS reduction, we focus on different fading mitigation techniques (FMT), designing a multi-layer scheme protection, using LL-FEC and AL-FEC in higher layers, and optimizing the intervention threshold and super-frame length in the physical layer.

Research interest related to hybrid networks for mobile users has rapidly evolved in order to extend service to all users. In particular, DVB-SH provides an efficient way of carrying multimedia services over hybrid satellite and terrestrial networks for a big diversity of terminals. Also a variety of possible hybrid system architectures can be chosen due to the two different physical layers specified: OFDM and TDM. Although DVB-SH has been designed for broadcast transmission, we propose to use it for multicast applications, which is more competitive over satellite systems. New system techniques implemented in the hybrid scheme, such as ACM and resource allocation, make the system strongly dependent on the channel conditions. Thus the capacity optimization in a multicast scenario becomes a powerful research challenge, mainly in mobile scenarios. In this paper, we aim at optimizing the multicast transmission over the satellite link and the terrestrial link of a DVB-SH based system. The architecture proposed includes resource allocation techniques depending on the scenarios considered (mobility and transmission mode). We first investigate a Hierarchical Allocation algorithm based on SC (HA-SC) for the OFDM air interface of DVB-SH, which is constrained to serve a minimum rate to all users. We later propose a Time Scheduling (TS) algorithm, more appropriate for TDM satellite-based systems, which finds the optimal number of users to be served in order to achieve the highest throughput in the multicast group. We show that with the TS algorithm, the spectral gain is 20-40% with respect to the worst case user. Moreover, the HA-SC is more suitable for the satellite since it outperforms TS in 300%.

The paper studies the performance of the bandwidth request procedure for a proactive digital video broadcasting - return channel satellite (DVB- RCS) terminal in comparison with a reactive one. The proactive terminal uses an adaptive predictor to forecast the future input traffic flow along with a predictive bandwidth controller to generate bandwidth requests according to a receding horizon policy. On the other hand, the reactive terminal generates requests, at the end of each frame, depending on the current queue lengths [1] [2]. The simulated scenario involves adaptive coding and modulation (ACM) techniques and Quality of Service (QoS) management. Simulation experiments highlight the effectiveness of the proactive bandwidth control under different traffic load and channel conditions.

The problem of dynamic bandwidth allocation (DBA) is inherent to systems that employ bandwidth on demand (BoD). An important issue in such systems is to be able to react efficiently to the always-changing traffic requests of users. Moreover, it is realistic to assume large populations sharing system resources and thus efficient methods to distribute bandwidth are mandatory. Further desirable system features include guarantees on fairness and on quality of service (QoS). Actual trends propose to reach convergence among networks at IP-level. This encourages the design of algorithms that sustain IP-defined QoS (e.g. in DiffServ) and forces to exchange information between layers. We talk then about cross-layer designs. In this paper, we propose a novel method to compute the allocation accomplishing the previous requirements of fairness, QoS and time efficiency. Our work departs from known results on decomposition techniques (primal and dual) and combines these in a novel, interleaved and coupled fashion. In the dual decomposition technique, the subgradient method is typically used to adaptively compute the price the resource is charging to the users. In our approach, the price is selected taking into account the value that users are willing to pay, which comes from the primal decomposition. The method is compared to the well-known bisection one and results effectively demonstrate superior performance in terms of convergence speed and computational complexity.

This paper focuses on the broadcast channel of an interactive multibeam broadband satellite (MBS) system with a transparent architecture. In particular, a cross-layer design is proposed for the packet scheduling on a forward link that implements adaptive coding and modulation (ACM). A cross-layer approach is considered whereby the physical and medium access control (MAC) layers share knowledge of the channel dynamics in presence of ACM. Transmission power and symbol rate are assumed to be constant, and hence the bit rate is time and space dependant according to the channel conditions. An architecture is proposed which relies on the physical characteristics of the Ka-band satellite propagation channel and the definition of "correlated areas". The stable throughput region has been derived assuming full-queue traffic conditions. Moreover, the proposed architecture is simple but flexible enough to allow the implementation of different scheduling policies like the proportionally fair or opportunistic ones. Finally, a new time-fair policy appropriate for wet seasons is proposed. It has the property of isolating users in clear-sky conditions from the effects of the reduced transmission rate experienced by users under a rain fade

This paper introduces a novel operational framework for the problem of time slot assignment in a digital video broadcast-return channel via satellite (DVB-RCS) system. The approach is compliant with the latest technical specifications emitted by the European telecommunications standards institute (ETSI) about quality of service (QoS) in satellite earth stations and systems (SES). It is a cross-layer MAC-PHY optimization approach sustained by the powerful framework of convex optimization. The paper proposes a hierarchical dynamic bandwidth allocation approach, which is motivated by the computational complexity of the single-step solution. More specifically, we obtain and analyze the optimal time duration of the time slots and jointly, we make a fair allocation of slots to areas, which is the highest level in the bandwidth allocation hierarchy. Results show up to a 10% increase in transported capacity.

This paper presents a general framework and the corresponding solution for the problem of fair resource allocation among entities with absolute and relative QoS requirements. It is described how the framework can be applied to a variety of scenarios, in particular to the scheduling of the TDM transmission in DVB-S2 and to the dynamic bandwidth allocation needed in DVB-RCS systems. A usual need in this type of problems is that the allocation has to be computed in (almost) real-time even when the number of entities is very large. The paper proposes a low-complexity algorithm. The algorithm provides the exact solution and numerical simulations shows its low computation time.

Future broadband satellite access networks will provide user connectivity via a return channel from a centralized hub. The forward channel can be embedded into the broadcast channel yielding asymmetric bandwidth ratios of 10:1 or greater. To meet such a bandwidth asymmetry as well as the required quality of service, QoS, selection of multiple access and media access control protocols plays a significant role among other design issues. In most of the recent satellite access networks, the forward traffic is broadcasted to satellite interactive terminals (SITs) using the ETSI specified DVB-S protocol. For the return channel multiple access protocol, options based on multi-frequency time division multiple access (MF-TDMA), code division multiple access (CDMA) and random multiple access (RMA) are available. We present a comparative overview of connection- and contention-oriented multiple access and focus on the use of spread ALOHA by using one single long code.

We focus on a non-GEO scenario and investigate the effect of actual power control performance on the return capacity dynamics of a DS-CDMA system. We consider mobile users at different speeds and transmission rates yielding several classes of service. We compute analytically the ideal maximum return capacity of the system which is shown not to be fixed but limited by a hyperplane in the space of the considered quality of service (QoS) so that different resource assignment criteria can be applied. At maximum ideal capacity, it is shown that, for the different percentages of users that can be served, the more restraining the QoS the more resources that must be assigned. We then explore the appropriate efficiency of the system, i.e., the actual used resources as a function of the distribution of QoS. We finally look into the inter-beam effect by applying different degrees of diversity gains and we show the trade-off between improving the capacity efficiency which is poor due to power control error and the net capacity achieved by the overall system.

In this paper three statistical models frequently used to describe the land mobile satellite (LMS) propagation channel under narrowband conditions are compared. The models are those of Loo (1985), Corazza and Vatalaro (1994), and Suzuki (1979). Statistical models are very well suited for the production of time-series (generative models) for simulation studies. Methodologies to produce synthetic time-series corresponding to the three models are discussed and results are compared.

A simple three-segment model quantifying the cross-correlation coefficient of shadowing effects in multiple satellite systems for "street canyons" is presented. The assumption of uncorrelated blockage in two satellite-to-mobile links is not always accurate: positive or, even negative correlation may exist. Shadowing cross-correlation information is needed in the assessment of multi-satellite system availability.

In this paper a simple methodology to assess the availability of multi-satellite systems for terminals in urban areas is presented. Urban environments are defined in terms of a mixture of basic or canonic scenarios, namely, street canyons, street crossings T-junctions, single walls. For each of these basic scenarios "masking functions" are defined which are well suited for a quick, approximate evaluation of the availability.

We focus on a non-GEO scenario and investigate the effect of actual power control performance on the return capacity dynamics of a DS-CDMA system. We consider mobile users at different speeds and transmission rates yielding several classes of services. We compute analytically the ideal maximum return capacity of the system which is shown not to be fixed but limited by a hyperplane in the space of the considered quality of service (QoS), so that different resource assignment criteria can be applied. At maximum ideal capacity, for the different percentages of users that can be served, it is shown that the more restraining the QoS, the more resources that must be assigned. We then explore the appropriate efficiency of the system, i.e. the actual used resources as a function of the distribution of QoS. We finally look into the inter-beam effect by applying different degrees of diversity gains and we show the trade-off between improving the capacity efficiency which is poor due to power control error and the net capacity achieved by the overall system.

We present a wideband land mobile satellite channel model based on a three-state Markov chain model valid for any kind of satellite constellation and for L, S, and Ka bands. Data from measurement campaigns was used to extract the parameters for the statistical distributions involved in the model. We also present a methodology describing how to use the proposed channel model to interface with system-level analysis. We use the time series generated by the model to parameterize power control (PC) imperfection as a function of the environment and user speed by acting upon the time series through a seven-level PC algorithm. We then apply the obtained parameterization to the analysis of a direct sequence-code division multiple-access scenario with users requiring different quality-of-service (QoS). It is shown that request of different QoS produces an unbalance in the users power distribution and less users can be served with the most demanding QoS. PC error worsens this effect and considerably reduces capacity efficiency which is highly dependent on the environment and mobile speed. Bit-error rate statistics are also investigated through the log-normal characterization obtained by using the channel model obtaining results on the effect of required E/sub b//(N/sub o/+I/sub o/) of a particular user.

Abstract This paper reviews the state of the art and current trends towards 3G and 3G+ mobile satellite systems that are being planned in parallel or within the International Mobile Telecommunications (IMT‐2000) framework. The subject is firstly approached by introducing the key and enabling technologies both for satellites and high altitude platform stations. After having introduced an overall picture, another review is presented on physical layer research activities including propagation and channel modeling. Finally, the use of the reviewed channel models for Code Division Multiple Access system level analysis is introduced and some current efforts towards system design are presented. Copyright © 2002 John Wiley & Sons, Ltd.