| 1. |
- Abrahamsson, Olle, 1988-
(författare)
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On Aggregation and Dynamics of Opinions in Complex Networks
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis studies two problems defined on complex networks, of which the first explores a conceivable extension of structural balance theory and the other concerns convergence issues in opinion dynamics. In the first half of the thesis we discuss possible definitions of structural balance conditions in a network with preference orderings as node attributes. The main result is that for the case with three alternatives (A, B, C) we reduce the (3!)3 = 216 possible configurations of triangles to 10 equivalence classes, and use these as measures of balance of a triangle towards possible extensions of structural balance theory. Moreover, we derive a general formula for the number of equivalent classes for preferences on n alternatives. Finally, we analyze a real-world data set and compare its empirical distribution of triangle equivalence classes to a null hypothesis in which preferences are randomly assigned to the nodes. The second half of the thesis concerns an opinion dynamics model in which each agent takes a random Bernoulli distributed action whose probability is updated at each discrete time step, and we prove that this model converges almost surely to consensus. We also provide a detailed critique of a claimed proof of this result in the literature. We generalize the result by proving that the assumption of irreducibility in the original model is not necessary. Furthermore, we prove as a corollary of the generalized result that the almost sure convergence to consensus holds also in the presence of a fully stubborn agent which never changes its opinion. In addition, we show that the model, in both the original and generalized cases, converges to consensus also in rth moment.
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| 2. |
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| 3. |
- Boyvalenkov, P., et al.
(författare)
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Refinements of Levenshtein Bounds in q-ary Hamming Spaces
- 2018
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Ingår i: Problems of Information Transmission. - : Pleiades Publishing. - 0032-9460 .- 1608-3253. ; 54:4, s. 329-342
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Tidskriftsartikel (refereegranskat)abstract
- We develop refinements of the Levenshtein bound in q-ary Hamming spaces by taking into account the discrete nature of the distances versus the continuous behavior of certain parameters used by Levenshtein. We investigate the first relevant cases and present new bounds. In particular, we derive generalizations and q-ary analogs of the MacEliece bound. Furthermore, we provide evidence that our approach is as good as the complete linear programming and discuss how faster are our calculations. Finally, we present a table with parameters of codes which, if exist, would attain our bounds.
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| 4. |
- Chandhar, Prabhu, 1986-, et al.
(författare)
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Massive MIMO for Communications With Drone Swarms
- 2018
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1536-1276 .- 1558-2248. ; 17:3, s. 1604-1629
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Tidskriftsartikel (refereegranskat)abstract
- We illustrate the potential of Massive MIMO for communication with unmanned aerial vehicles (UAVs). We consider a scenario, where multiple single-antenna UAVs simultaneously communicate with a ground station (GS) equipped with a large number of antennas. Specifically, we discuss the achievable uplink (UAV to GS) capacity performance in the case of line-of-sight conditions. We develop a realistic geometric model, which incorporates an arbitrary orientation, of the GS and UAV antenna elements to characterize the polarization mismatch loss, which occurs due to the movement and orientation of the UAVs. A closed-form expression for a lower bound on the ergodic rate for a maximum-ratio combining receiver with estimated channel state information is derived. The optimal antenna spacing that maximizes the ergodic rate achieved by an UAV is also determined for uniform linear and rectangular arrays. It is shown that when the UAVs are spherically uniformly distributed around the GS, the ergodic rate per UAV is maximized for an antenna spacing equal to an integer multiple of one-half wavelength.
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| 5. |
- Chandhar, Prabhu, 1986-, et al.
(författare)
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On the Zero-Forcing Receiver Performance for Massive MIMO Drone Communications
- 2018
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Ingår i: 2018 IEEE 19th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538635124 - 9781538635117 - 9781538635131 ; , s. 930-934
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Konferensbidrag (refereegranskat)abstract
- We study the uplink ergodic rate performance of the zero-forcing (ZF) receiver in a Massive multiple-input and multiple-output (MIMO) enabled drone communication system. Considering a 3D geometric model for line-of-sight (LoS) propagation, approximate but accurate analyses of lower and upper bounds on the uplink ergodic rate with estimated channel state information (CSI) are provided.
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| 6. |
- ChengWen, Xing, et al.
(författare)
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Statistically robust resource allocation for distributed multi-carrier cooperative networks
- 2013
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Ingår i: Science China Information Sciences. - : Springer. - 1674-733X .- 1869-1919. ; 56:2, s. 109-121
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate joint subcarrier and power allocation scheme for distributed multi-carrier cooperative networks with imperfect channel state information. Using practical channel estimation algorithms, the statistic model of the channel estimation error is first derived. Then based on the channel error model, the resource allocation scheme aims at maximizing the sum rate of the overall network. Specifically, both subcarrier allocation and power allocation are taken into account. In the subcarrier allocation, a realistic problem of the power leakage between neighboring subcarriers is also addressed. Furthermore, based on Lagrange dual-decomposition algorithm, a practical power allocation algorithm is proposed. Finally, the simulation results demonstrate the performance advantages of the proposed robust design.
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| 7. |
- Danev, Danyo, 1973-, et al.
(författare)
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A Family of Constacyclic Ternary Quasi-Perfect Codes with Covering Radius 3
- 2009
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Ingår i: Proceedings of the International Workshop on Coding and Cryptography (WCC'09). ; , s. 111-118
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Konferensbidrag (refereegranskat)abstract
- In this paper a family of constacyclic ternary quasi-perfect linearblock codes is presented. This family extends the result presented ina previous work by the first two authors, where the existence of codeswith the presented parameters was stated as an open question. The codes have a minimum distance 5 and covering radius 3.
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| 8. |
- Danev, Danyo, 1973-, et al.
(författare)
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A Family of Ternary Quasi-Perfect BCH Codes
- 2008
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Ingår i: Designs, Codes and Cryptography. - : Springer Science and Business Media LLC. - 0925-1022 .- 1573-7586. ; 49, s. 265-271
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a family of ternary quasi-perfect BCH codes. These codes are of minimum distance 5 and covering radius 3. The first member of this family is the ternary quadratic-residue code of length 13.
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| 9. |
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| 10. |
- Danev, Danyo, 1973-, et al.
(författare)
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Efficient Message-Passing Decoding of LDPC Codes using Vector-based Messages
- 2006
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Konferensbidrag (refereegranskat)abstract
- In this paper we investigate reduced complexitydecoders for LDPC codes over M-PSK modulation. Capacitycalculations show only minor losses if only phase informationis considered in the decoder. We device a decoder based onphase angle summation, which unfortunately does not work forcodes over Galois fields (but shows promising results for codesover integer rings). For codes over Galois Fields we constructtable-based decoders which gives performance close to BeliefPropagation decoders at substantially reduced complexity.
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