Stavroula Vassaki

A survey of architectures and scenarios in satellite‐based wireless sensor networks: system design aspects

This paper is not a survey related to generic wireless sensor networks (WSNs), which have been largely treated in a number of survey papers addressing more focused issues; rather, it specifically addresses architectural aspects related to WSNs in some way connected with a satellite link, a topic that presents challenging interworking aspects. The main objective is to provide an overview of the potential role of a satellite segment in future WSNs. In this perspective, requirements of the most meaningful WSN applications have been drawn and matched to characteristics of various satellite/space systems in order to identify suitable integrated configurations. Copyright

Power Allocation in Cognitive Satellite Terrestrial Networks with QoS Constraints

The increasing demand for high-speed multimedia services and the underutilization of scarce satellite spectral resources have recently led the researchers to propose the concept of cognitive satellite terrestrial networks. Considering this novel architecture, we propose an efficient resource management mechanism for the terrestrial network that acts as the secondary system. We introduce a new power allocation algorithm that optimizes the effective capacity of the terrestrial link for given Quality of Service (QoS) requirements while guaranteeing a specified outage probability for the satellite link. Both perfect and imperfect channel estimation cases are considered in the power allocation scheme and analytical results are presented. Numerical calculations evaluate the performance of the proposed scheme.

Effective Capacity and Optimal Power Allocation for Mobile Satellite Systems and Services

Satellite communication networks play a significant role to worldwide telecommunication infrastructure providing direct-to-mobile user satellite services. Quality of Service requirements should be taken into account in the satellite power allocation schemes that follow the channel variations. Employing a shadowed Rician model for land mobile satellite communications and an adaptive modulation scheme, closed form expressions are derived for the optimal power allocation and the effective capacity. The effective capacity of the system under specific Quality of Service constraints is maximized. Finally, the impact of the elevation angle on the power allocation and the effective capacity is investigated.

Interclass and Intraclass Modulation Recognition using the Wavelet Transform

This paper presents an algorithm for modulation recognition of received signals in the presence of additive white Gaussian noise (AWGN) with the use of the wavelet transform. The decision is made based on the extraction of some special features of the continuous wavelet transform of the received signal. The Haar wavelet was used as the mother wavelet. Besides the SNR, the algorithm needs no further information for the received signal such as signal bandwidth or carrier frequency. It is able to classify PSK, QAM, FSK and ASK signals, as well as to identify the modulation order. Effort was made in order to reduce the computational workload, so that the algorithm can be suitable for real-time recognition. After extended simulation the algorithm proved to be practically inerrable for SNR>12 dB and achieves low rates of false detection for SNR=10 dB.

Optimal power allocation under QoS constraints in cognitive radio systems

Cognitive radio technology aims at the efficient utilization of the limited radio resources and the improvement of flexibility of spectrum usage in wireless networks. The main idea of this technology is the development of intelligent networks where the unlicensed secondary users may coexist with the licensed primary users, always limited by the obligation not to affect their communication. In this paper, we consider a spectrum underlay cognitive radio system operating in fading environment. Guaranteeing that the average interference limit constraint to primary users is satisfied, we propose a quality of service (QoS)-driven power allocation scheme, with a view to maximizing the effective capacity of the secondary users. The proposed scheme takes into consideration the interference of primary user to the secondary user, in order to accomplish the optimal allocation more realistically. Finally, the proposed allocation scheme has been evaluated through numerical simulations that confirm the presented theoretical analysis.

Optimal iSINR-based power control for cognitive satellite terrestrial networks

The incorporation of cognitive radio techniques in satellite communications has recently become a significant research challenge leading to the proposal of a novel network infrastructure known as cognitive satellite terrestrial networks. However, efficient resource management mechanisms should be proposed to provide a complete system analysis for this promising architecture. Towards this direction, this article focuses on the problem of power management in cognitive satellite terrestrial systems, where the satellite system has the role of the cognitive system, while the terrestrial represents the primary one. Particularly, a power control scheme for the satellite terminal is proposed. Taking into account the peculiarities of both systems and considering the uplink case, the goal of the proposed scheme is to optimise the performance of the satellite link without deteriorating the communication quality of the terrestrial link. To safeguard the communication of the terrestrial system, we introduce a novel interference-based constraint, which ensures a specific level for the inverse signal-to-interference plus noise ratio of the terrestrial link. Both the cases of perfect and imperfect channel estimation of terrestrial link are considered in order to study a more realistic scenario. Furthermore, for the imperfect case, a protection mechanism is proposed to guarantee the communication quality of the primary link that offsets the uncertainty of channel estimation. Simulation results evaluate the performance of the proposed scheme for various system parameters and verify its superiority compared with the well-known water-filling based power control scheme for both cases of perfect and imperfect channel estimation. Copyright

QoS-Driven Power Allocation Under Peak and Average Interference Constraints in Cognitive Radio Networks

Efficient radio spectrum utilization can be improved using cognitive radio technology. In this work, we consider a spectrum underlay cognitive radio system operating in a fading environment. We propose an efficient power control scheme that maximizes the effective capacity of the secondary user, provisioning quality of service while on the same time the communication of the primary user is guaranteed through interference constraints. The specific power allocation scheme uses a policy in which the outage events of the primary user are exploited leading to a significant increase of the secondary user’s effective capacity. Moreover, the interference of the primary link to the secondary is taken into account so as to study a more realistic scenario. In order to safeguard primary user’s communication, two types of restrictions are considered: the traditional interference power constraint and the proposed inverse signal to interference plus noise ratio constraint. Different scenarios depending on the nature of the constraints (peak/average) are studied and their impact on the performance of the primary and secondary users is investigated. The superiority of the proposed schemes is demonstrated through their comparison with two reference power control schemes. Finally, numerical calculations, validated with simulation results, confirm the theoretical analysis and evaluate the performance of the proposed scheme for all the different scenarios.

Proactive radio resource management using optimal stopping theory

In this paper, we focus on proactive radio resource management schemes that retain the quality of the individual connections by pre-reserving the needed resources in a cellular network. We propose a new scheme, which improves older proactive solutions. Typically, in such solutions an improvement in call dropping probability negatively impacts new call blocking probability. We improve this framework by careful, fine-grained time scheduling of the proactive resource management. We adopt optimal stopping theory for our solution. Our findings are quite promising for the broader framework of proactive resource management and mobile computing.

Spectrum Leasing in Cognitive Radio Networks: A Matching Theory Approach

In this paper, we analyze the problem of spectrum leasing in cognitive radio networks using principles from matching theory. More specifically, we deal with the pairing problem among the primary and the secondary users and we propose two different matching schemes that take into account the preferences of each user in terms of performance. The first scheme is a one-to-one matching scheme that is based on the deferred acceptance algorithm whereas the second one refers to a one-to-many matching algorithm where each primary user may cooperate with more than one secondary user. The performance of both proposed schemes is finally investigated for various network parameters and some useful conclusions are drawn.

Satellite-based sensor networks: M2M Sensor communications and connectivity analysis

In this paper, we study the performance of satellite-based sensor networks. In particular, we consider dense networks of M2M sensor devices deployed in several geographical locations. The M2M sensor devices are locally grouped into clusters and communicate with a satellite gateway. The proposed network architecture is a potential solution for remote monitoring and surveillance networks usually deployed on border and non-habitable areas. We also consider the employment of Ka band for the broadband satellite connection. Consequently, an efficient clustering methodology is proposed for the M2M sensor devices while the feasibility of the proposed system in terms of connectivity of the satellite gateways using high data rate terrestrial links operating at frequencies above 10 GHz, is investigated. Finally, we present realistic satellite link budget analysis using either GEO or LEO Ka band satellites.