| 1. |
- Cerullo, Livia, 1982, et al.
(författare)
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Microwave measurement system for dispersive dielectric properties of densely packed pellets
- 2017
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Ingår i: Measurement: Journal of the International Measurement Confederation. - : Elsevier BV. - 0263-2241. ; 106, s. 179-189
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Tidskriftsartikel (refereegranskat)abstract
- We present a microwave measurement system that is intended for the estimation of the dispersive dielectric properties for densely packed pellets. In particular, we estimate the Debye parameters for the effective permittivity of a mixture of air and densely packed moist microcrystalline cellulose pellets for the frequency band 2.7–5.1 GHz. The Debye parameters are estimated by means of minimizing the misfit between the measured scattering parameters and the corresponding computed response given a model of the measurement system. This minimization is performed by means of a nonlinear iterative optimization procedure, which is supported by continuum sensitivities, and the optimum is found in 10–60 iterations for the cases presented in this article. We find that increasing moisture content yields an increase in the static permittivity and a decrease in the relaxation time.
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| 2. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
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Downlink Performance of Regularized ZF in Massive MIMO Systems Subject to IQ Imbalance
- 2017
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Ingår i: IEEE International Conference on Communications. - 1550-3607.
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Konferensbidrag (refereegranskat)abstract
- This paper studies the impact of in-phase and quadrature imbalance (IQI) on the downlink of a single-cell multiuser multiple-input multiple-output (MU-MIMO) system with large antenna arrays. Moreover, we consider a time-division duplex (TDD) system where we assume uplink/downlink channel reciprocity in the downlink precoding design and study the impact of uplink/downlink channel mismatch on the downlink rate caused by different IQI on the base station (BS) and users equipment (UEs). A tractable analytical expression to predict the achievable downlink rates is derived for the regularized zero-forcing (RZF) and based on this expression, we prove that, as the number of BS antennas grow large, the achievable downlink rate of each UE is limited either by the RX IQI at the UEs or by the simultaneous presence of the transmit/receive IQI at the BS and TX IQI at the UEs, when there is uplink/downlink channel mismatch.
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| 3. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
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Massive MIMO Systems with IQ Imbalance: Channel Estimation and Sum Rate Limits
- 2017
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 65:6, s. 2382 - 2396
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the impact of in-phase and quadrature imbalance (IQI) on single-cell multiuser multiple-input multiple-output (MU-MIMO) systems with large antenna arrays. Moreover, we consider a time-division duplex (TDD) system where we assume uplink/downlink channel reciprocity in the downlink precoding design. First, we investigate the effect of transceiver IQI on the uplink channel estimation by deriving the linear minimum-mean-square-error (LMMSE) estimator for the IQ-impaired model and prove that only the receiver IQI at the base station (BS) limits the estimation accuracy. Then, we study the impact of uplink/downlink channel mismatch on the downlink rate caused by different IQI on the BS and user equipments (UEs). We prove that the achievable downlink rate of each UE is limited either by the receiver IQI at the UEs or jointly by the transmit and receive IQI at the BS, when there is mismatch between the uplink and downlink channels.
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| 4. |
- Ozcelikkale, Ayca, 1982, et al.
(författare)
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MIMO Linear Precoder Design with Non-Ideal Transmitters
- 2015
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Ingår i: Proceedings of the International Symposium on Wireless Communication Systems. - 2154-0217 .- 2154-0225. ; 2016-April, s. 681-685
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Konferensbidrag (refereegranskat)abstract
- We investigate the linear precoder design problem for multiple-input multiple-output (MIMO) channels under non-ideal transmitter hardware.We consider two different non-ideal hardware models: i) an additive noise model in which the level of the noise at an antenna is proportional to the signal power at that antenna, ii) an additive precoder error model. We focus on the problem of minimizing mean-square error at the receiver under transmit power constraints at the transmitter. For the first hardware impairment model, this scenario leads to a non-convex formulation for which we propose a block-coordinate descent technique. The proposed method has a convergence guarantee and provides rank-constrained solutions.For the second model, analytical expressions for the optimum designs are provided. We compare the performance of our hardware impairment aware designs with that of designs developed with ideal hardware assumptions. Our results suggest that significant gains can be obtained by the proposed designs for sufficiently high signal-to-noise ratio values.
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| 5. |
- Ozcelikkale, Ayca, 1982, et al.
(författare)
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Performance Bounds for Remote Estimation with an Energy Harvesting Sensor
- 2016
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Ingår i: IEEE International Symposium on Information Theory - Proceedings. - 2157-8095. - 9781509018062 ; 2016-August, s. 460-464
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Konferensbidrag (refereegranskat)abstract
- Remote estimation with an energy harvesting sensor with a limited data buffer is considered. The sensor node observes an unknown correlated circularly wide-sense stationary (c.w.s.s.) Gaussian field and communicates its observations to a remote fusion center using the energy it harvested. The fusion center employs minimum mean-square error (MMSE) estimation to reconstruct the unknown field. The distortion minimization problem under the online scheme, where the sensor has only access to the statistical information for the future energy packets is considered. We provide performance bounds on the achievable distortion under a slotted block transmission scheme, where at each transmission time slot, the data and the energy buffer is completely emptied. Our bounds provide insight to the trade-off between the buffer sizes and the achievable distortion. These trade-offs illustrate the insensitivity of the performance to the buffer size for signals with low degree of freedom and suggest performance improvements with increasing buffer size for signals with relatively higher degree of freedom.
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| 6. |
- Ozcelikkale, Ayca, 1982, et al.
(författare)
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Remote Estimation of Correlated Sources under Energy Harvesting Constraints
- 2018
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Ingår i: IEEE Transactions on Wireless Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2248 .- 1536-1276. ; 17:8, s. 5300-5313
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Tidskriftsartikel (refereegranskat)abstract
- Remote estimation with an energy harvesting sensor with a limited data and energy buffer is considered. The sensor node observes an unknown temporally correlated field and communicates its observations to a remote fusion center using the energy it harvested. The fusion center employs linear minimum mean-square error (LMMSE) estimation to reconstruct the unknown field. We provide performance guarantees for the estimation error under a block transmission scheme, where at each transmission block, data and energy buffers are completely emptied. Our bounds provide insights into how statistical prop- erties of the energy harvesting process and buffer sizes may affect the estimation error. In particular, these bounds suggest insensitivity of the performance to buffer sizes for signals with low degree of freedom and suggest performance improvements with increasing buffer sizes for signals with relatively higher degree of freedom. Depending only on the mean, variance and finite support of the energy arrival process, these results provide insights for the energy and data buffer sizes for deployment in future energy harvesting wireless sensing systems.
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| 7. |
- Ozcelikkale, Ayca, 1982, et al.
(författare)
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Simultaneous Information and Power Transfer with Transmitters with Hardware Impairments
- 2016
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Ingår i: Proceedings of the International Symposium on Wireless Communication Systems. - 2154-0217 .- 2154-0225. - 9781509020614 ; 2016-October, s. 114-118
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Konferensbidrag (refereegranskat)abstract
- We investigate the performance of a communication system with simultaneous wireless information and power transfer capabilities under non-ideal transmitter hardware. We adopt an experimentally validated additive noise model in which the level of the noise at an antenna is proportional to the signal power at that antenna. We consider the linear precoder design problem and focus on the problem of minimizing the mean-square error under energy harvesting constraints. This set-up, in general, constitutes a non-convex formulation. For the single antenna information user case, we provide a tight convex relaxation, i.e. a convex formulation from which an optimal solution for the original problem can be constructed. For the general case, we propose a block coordinate descent technique to solve the resulting non-convex problem. Our numerical results illustrate the effect of hardware impairments on the system.
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| 8. |
- Ozcelikkale, Ayca, 1982, et al.
(författare)
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Transmission Strategies for Remote Estimation under Energy Harvesting Constraints
- 2016
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Ingår i: European Signal Processing Conference. - 2219-5491. - 9780992862657 ; 2016-November, s. 572-576
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Konferensbidrag (refereegranskat)abstract
- We consider the remote estimation of a time- correlated field using an energy harvesting (EH) sensor. The sensor observes the unknown field and communicates its observa- tions to a remote fusion center using an amplify-forward strategy. We consider the design of optimal transmission strategies in order to minimize the mean-square error (MSE) at the fusion center. Contrary to traditional approaches, the degree of correlation between the field values constitutes an important aspect of our formulation. We provide the optimal power allocation strategies for a number of illustrative scenarios, including the circularly wide-sense stationary (c.w.s.s.) signals with static correlation coefficient and the sampled low-pass c.w.s.s. signals. Based on these results, we propose low-complexity policies for the general case. Numerical evaluations illustrate the performance of the optimal and the low-complexity policies.
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| 9. |
- Ozcelikkale, Ayca, 1982, et al.
(författare)
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Transmission Strategies for Remote Estimation with an Energy Harvesting Sensor
- 2017
-
Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 16:7, s. 4390-4403
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the remote estimation of a time-correlated signal using an energy harvesting (EH) sensor. The sensor observes the unknown signal and communicates its observations to a remote fusion center using an amplify-and-forward strategy. We consider the design of optimal power allocation strategies in order to minimize the mean-square error at the fusion center. Contrary to the traditional approaches, the degree of correlation between the signal values constitutes an important aspect of our formulation. We provide the optimal power allocation strategies for a number of illustrative scenarios. We show that the most majorized power allocation strategy, i.e. the power allocation as balanced as possible, is optimal for the cases of circularly wide-sense stationary (c.w.s.s.) signals with a static correlation coefficient, and sampled low-pass c.w.s.s. signals for a static channel. We show that the optimal strategy can be characterized as a water-filling type solution for sampled low-pass c.w.s.s. signals for a fading channel. Motivated by the high-complexity of the numerical solution of the optimization problem, we propose low-complexity policies for the general scenario. Numerical evaluations illustrate the close performance of these low-complexity policies to that of the optimal policies, and demonstrate the effect of the EH constraints and the degree of freedom of the signal.
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| 10. |
- Ozcelikkale, Ayca, 1982, et al.
(författare)
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Wireless Information and Power Transfer in MIMO Channels under Rician fading
- 2015
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. - 9781467369978 ; 2015-August, s. 3187-3191
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Konferensbidrag (refereegranskat)abstract
- Simultaneous wireless information and power transfer (SWIPT) offers an attractive alternative to the traditional battery limited or grid dependent communication system design. In this paper, we investigate robust precoder designs for systems with SWIPT capabilities under a stochastic Rician fading framework. Under a multiple-input multiple-output (MIMO) channel model, we formulate the problem of minimizing the average mean-square error at the information receiver (IR) while keeping the average energy harvested at the energy receiver (ER) above given levels. We consider two different strategies that can be adopted by the IR: i) simple estimation filters based solely on the channel mean, ii) robust estimation filters aiming to minimize the average mean-square error. Both of these scenarios lead to non-convex formulations. For the first scenario, we propose a convex relaxation that is tight. For the second scenario, we propose an alternating minimization method that provides precoder designs even in the scenarios where the number of transmit antennas is larger than the length of data vector. Our numerical results show that the proposed designs provide significant performance gains especially when the scattering component of the channel is strong.
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