Browsing by Author "Wichman, R."

Now showing 1 - 3 of 3
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    A Closed-Form Approximation of the SIR Distribution in a LEO Uplink Channel
    (2023-01-12) Angervuori, Jouko; Wichman, R.; Risto Wichman Group; Dept Signal Process and Acoust
    The Low Earth Orbit (LEO) satellite networks will improve the quality of future communication networks. The rapid expansion of LEO networks brings up considerations of man-made interference from terrestrial networks or other LEO terminals. Especially the future terrestrial networks will cause interference in satellite receivers as higher frequency bands will be utilized in the emerging 5G and beyond networks. We study the distribution of signal-to-interference ratio (SIR) in a narrow beam LEO satellite receiver affected by a dense heterogeneous set of interfering transmitters. We propose that the distribution of interference power approximates the Gaussian distribution for the positive values. Furthermore, we suggest that the distribution of SIR follows the gamma distribution. We use the tools of stochastic geometry and derive the location, shape, and scale parameters for the distributions of interference and SIR. The parameters depend on the amount of interfering transmitters inside the receiving satellite’s3 dB footprint, the transmitting powers, and the slow and fast fading conditions.
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    The Joint Impact of Fading Severity, Rotation Angle, and Non-Gaussian Noise on Signal Space Diversity-Based Relaying Networks
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2019-08-15) Ilter, M. C.; Sokun, H. U.; Yanikomeroglu, H.; Wichman, R.; Hämäläinen, J.; Dept Signal Process and Acoust; Department of Communications and Networking
    This work focuses on the interplay between rotation angle, transmit power, fading severity, and noise impairment severity in signal space diversity-based three time-slot decode-and-forward two-way relaying networks. Specifically, we develop a joint design for rotation angle selection and transmit power allocation, while taking into account the performance impact of fading severities on the channels and noise impairment severities on the receivers. To model different severities of fading and noise impairment, Nakagami distribution and additive non-Gaussian noise are used respectively. The objective in doing so is to promote the reliable reception of end-sources, while satisfying individual and total power budgets as well as average error probability. To this end, we start by deriving average error probabilities of end-sources for non-uniform constellations, which capture all possible signal constellations produced by using various rotation angles. Next, we formulate the joint design problem in an optimization form. Unfortunately, the resulting formulation is a non-convex optimization. To find the solution, we resort to numerical optimization. The numerical results not only validate the derived error probability expressions, but also demonstrate the efficacy of the proposed framework and provide useful insights on the interaction between rotation angle, transmit power, fading severities of the channels, and noise impairment severities at the end-sources.
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    Power Adaptation in Buffer-Aided Full-Duplex Relay Networks with Statistical CSI
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018-08) Nomikos, N.; Charalambous, T.; Vouyioukas, D.; Wichman, R.; Karagiannidis, G. K.; Department of Electrical Engineering and Automation; Dept Signal Process and Acoust; Distributed and Networked Control Systems; Risto Wichman Group; University of the Aegean; Aristotle University of Thessaloniki
    In networks with multiple wireless nodes and especially in fast changing environments, the continuous acquisition of Channel State Information (CSI) may become infeasible. In this paper, we study the relay selection problem for a cooperative network, where Full-Duplex (FD) relays are equipped with buffers and only statistical CSI is available at the transmitters (CSIT). For this setting, a novel relay selection algorithm is proposed, named HyQoS, relying only on statistical CSIT and performing power adaptation. HyQoS solves an optimization problem for selecting the optimal set of relays. We consider two optimization approaches: 1) minimization of the total power consumed in the network, and 2) maximization of the throughput per energy unit, while guaranteeing a specific Quality of Service (QoS), in terms of Successful Transmission Probability (STP). The power allocation problem is formulated as a nonlinear optimization one, taking into account inter-relay interference and residual loop interference. Numerical results show that HyQoS can reduce the power expenditure and increase the throughput, by using only statistical CSIT.