| 41. |
- Jansson, M., et al.
(author)
-
Optimal Subspace Techniques for DOA Estimation
- 2005
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In: Space-Time Wireless Systems: From Array Processing to MIMO Communications / edited by Helmut Bölcskei et al..
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Book chapter (other academic/artistic)
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| 42. |
- Johansson, Eija, 1982, et al.
(author)
-
Interpolation based on stationary and adaptive AR(1) modeling
- 2011
-
In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. - 9781457705397 ; , s. 4052-4055
-
Conference paper (peer-reviewed)abstract
- In this paper, we describe a minimal mean square error (MMSE) optimal interpolation filter for discrete random signals. We explicitly derive the interpolation filter for a first-order autoregressive process (AR(1)), and show that the filter depends only on the two adjacent points. The result is extended by developing an algorithm called local AR approximation (LARA), where a random signal is locally estimated as an AR(1) process. Experimental evaluation illustrates that LARA interpolation yields a lower mean square error than other common interpolation techniques, including linear, spline and local polynomial approximation (LPA).
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| 43. |
- Khademi, Seyran, 1981, et al.
(author)
-
Peak-to-Average-Power-Ratio (PAPR) reduction in WiMAX and OFDM/A systems
- 2011
-
In: EURASIP Journal on Advances in Signal Processing. - : Springer Science and Business Media LLC. - 1687-6180. ; , s. Article Number: 38-
-
Journal article (peer-reviewed)abstract
- A peak to average power ratio (PAPR) reduction method is proposed that exploits the precoding or beamforming mode in WiMAX. The method is applicable to any OFDM/A systems that implements beamforming using dedicated pilots which use the same beamforming antenna weights for both pilots and data. Beamforming performance depends on the relative phase shift between antennas, but is unaffected by a phase shift common to all antennas. PAPR, on the other hand, changes with a common phase shift and this paper exploits that property. An effective optimization technique based on sequential quadratic programming is proposed to compute the common phase shift. The proposed technique has several advantages compared with traditional PAPR reduction techniques in that it does not require any side-information and has no effect on power and bit-error-rate while providing better PAPR reduction performance than most other methods.
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| 44. |
- Kolomvakis, Nikolaos, 1985, et al.
(author)
-
Downlink Performance of Regularized ZF in Massive MIMO Systems Subject to IQ Imbalance
- 2017
-
In: IEEE International Conference on Communications. - 1550-3607.
-
Conference paper (peer-reviewed)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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| 45. |
- Kolomvakis, Nikolaos, 1985, et al.
(author)
-
Massive MIMO Systems with IQ Imbalance: Channel Estimation and Sum Rate Limits
- 2017
-
In: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 65:6, s. 2382 - 2396
-
Journal article (peer-reviewed)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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| 46. |
- Kolomvakis, Nikolaos, 1985, et al.
(author)
-
Reconstruction of clipped signals
- 2023
-
Patent (other academic/artistic)abstract
- Using information contained in clipped samples from aualog-to-digital (ADC) conversion to improve receiver performance, by, for example, reducing the clipping distortion caused by ADCs due to its data resolution constraints. This provides an advantage over existing solutions, which perform suboptimally because the existing solution discard information in tire clipped samples.
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| 47. |
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| 48. |
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| 49. |
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