185 research outputs found
Joint Optimization for Secure and Reliable Communications in Finite Blocklength Regime
To realize ultra-reliable low latency communications with high spectral
efficiency and security, we investigate a joint optimization problem for
downlink communications with multiple users and eavesdroppers in the finite
blocklength (FBL) regime. We formulate a multi-objective optimization problem
to maximize a sum secrecy rate by developing a secure precoder and to minimize
a maximum error probability and information leakage rate. The main challenges
arise from the complicated multi-objective problem, non-tractable back-off
factors from the FBL assumption, non-convexity and non-smoothness of the
secrecy rate, and the intertwined optimization variables. To address these
challenges, we adopt an alternating optimization approach by decomposing the
problem into two phases: secure precoding design, and maximum error probability
and information leakage rate minimization. In the first phase, we obtain a
lower bound of the secrecy rate and derive a first-order Karush-Kuhn-Tucker
(KKT) condition to identify local optimal solutions with respect to the
precoders. Interpreting the condition as a generalized eigenvalue problem, we
solve the problem by using a power iteration-based method. In the second phase,
we adopt a weighted-sum approach and derive KKT conditions in terms of the
error probabilities and leakage rates for given precoders. Simulations validate
the proposed algorithm.Comment: 30 pages, 8 figure
Coverage Analysis of Dynamic Coordinated Beamforming for LEO Satellite Downlink Networks
In this paper, we investigate the coverage performance of downlink satellite
networks employing dynamic coordinated beamforming. Our approach involves
modeling the spatial arrangement of satellites and users using Poisson point
processes situated on concentric spheres. We derive analytical expressions for
the coverage probability, which take into account the in-cluster geometry of
the coordinated satellite set. These expressions are formulated in terms of
various parameters, including the number of antennas per satellite, satellite
density, fading characteristics, and path-loss exponent. To offer a more
intuitive understanding, we also develop an approximation for the coverage
probability. Furthermore, by considering the distribution of normalized
distances, we derive the spatially averaged coverage probability, thereby
validating the advantages of coordinated beamforming from a spatial average
perspective. Our primary finding is that dynamic coordinated beamforming
significantly improves coverage compared to the absence of satellite
coordination, in direct proportion to the number of antennas on each satellite.
Moreover, we observe that the optimal cluster size, which maximizes the ergodic
spectral efficiency, increases with higher satellite density, provided that the
number of antennas on the satellites is sufficiently large. Our findings are
corroborated by simulation results, confirming the accuracy of the derived
expressions
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