| 1. |
- Özdogan, Özgecan, et al.
(författare)
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Uplink Spectral Efficiency of Massive MIMO with Spatially Correlated Rician Fading
- 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 ; , s. 216-220
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Konferensbidrag (refereegranskat)abstract
- This paper considers the uplink (UL) of a multicell Massive MIMO (multiple-input multiple-output) system with spatially correlated Rician fading channels. The channel model is composed of a deterministic line-of-sight (LoS) path and a stochastic non-line-of-sight (NLoS) component describing a spatially correlated multipath environment. We derive the statistical properties of the minimum mean squared error (MMSE) and least-square (LS) channel estimates for this model. Using these estimates for maximum ratio (MR) combining, rigorous closed-form UL spectral efficiency (SE) expressions are derived. Numerical results show that the SE is higher when using the MMSE estimator than the LS estimator, and the performance gap increases with the number of antennas. Moreover, Rician fading provides higher achievable SEs than Rayleigh fading since the LoS path improves the sum SE.
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| 2. |
- Özdogan, Özgecan, et al.
(författare)
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Massive MIMO With Dual-Polarized Antennas
- 2023
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Ingår i: IEEE Transactions on Wireless Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 1536-1276 .- 1558-2248. ; 22:2, s. 1448-1463
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers a single-cell massive MIMO (multiple-input multiple-output) system with dual-polarized antennas at both the base station and users. We study a channel model that includes the key practical aspects that arise when utilizing dual-polarization: channel cross-polar discrimination (XPD) and cross-polar correlations (XPC) at the transmitter and receiver. We derive the achievable uplink and downlink spectral efficiencies (SE) with and without successive interference cancellation (SIC) when using the linear minimum mean squared error (MMSE), zero-forcing (ZF), and maximum ratio (MR) combining/precoding schemes. The expressions depend on the statistical properties of the MMSE channel estimator obtained for the dual-polarized channel model. Closed-form uplink and downlink SE expressions for MR combining/precoding are derived. Using these expressions, we propose power-control algorithms that maximize the uplink and downlink sum SEs under uncorrelated fading but can be used to enhance performance also with correlated fading. We compare the SEs achieved in dual-polarized and uni-polarized setups numerically and evaluate the impact of XPD and XPC conditions. The simulations reveal that dual-polarized setups achieve 40-60% higher SEs and the gains remain also under severe XPD and XPC. Dual-polarized also systems benefit more from advanced signal processing that compensates for imperfections.
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| 3. |
- ÖZEN, MUSTAFA, 1984
(författare)
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Advanced Transmitter Architectures Based on Switch Mode Power Amplifiers
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays the main driving parameters for the research in radio transmitters in wireless infrastructure are energy efficiency, frequency agility, and integration.This thesis presents new solutions at the device waveform-, circuit-, and transmitter level which exploit the inherent high efficiency potential of switch-mode power amplifiers (SMPAs) for realization of energy efficient, wide-band, highly integrated transmitters for wireless communication applications.In the first part of the thesis, a continuum of novel high efficiency class-E power amplifier modes are derived, significantly extending the known SMPA design space. In contrast to conventional SMPA modes, the new continuum allows some variation for the switch impedances, providing important possibilities on wide-band SMPA designs. This is experimentally verified in a 1 W SiGe BiCMOS SMPA design having a drain efficiency of above 70% over a 1.3-2.2 GHz bandwidth.In the second part a novel combiner synthesis technique is developed that enables realization of wide-band highly efficient outphasing transmitters. The technique is based on the calculation of the combiner network parameters from the boundary conditions required for highly efficient switch-mode operation of the transistors in each branch. The approach is validated in a CMOS-GaN outphasing transmitter design providing a peak output power of 44 dBm and a 7.5 dB output power back-off efficiency exceeding 52% over a 750-1050 MHz bandwidth. It is further shown that the same theoretical approach can also be used for design of Doherty PA combiner networks. A 28 W 3.5 GHz Doherty PA is designed and manufactured for experimental verification providing a record-high power added efficiency of 51% at an adjacent channel leakage ratio (ACLR) of -50 dBc with carrier-aggregated 100 MHz LTE test signals.In the third part a new SMPA topology particularly suitable for amplification of RF pulse-width modulation (RF-PWM) signals is presented. In classical pulse width modulated SMPAs the varying pulse width leads to switching losses and hence efficiency degradation. We present an electronically tunable load output network that alleviates this problem.A 10 W 2 GHz CMOS-GaN RF-PWM transmitter demonstrator is constructed and characterized to demonstrate the feasibility of the proposed technique. ACLR after digital pre-distortion linearization is -45 dBc at a drain efficiency of 67% with W-CDMA communication signals.The solutions presented in this thesis will facilitate realizations of frequency agile, energy efficient and highly integrated/digitalized radio transmitters for future wireless communication systems.
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| 4. |
- ÖZEN, MUSTAFA, 1984
(författare)
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Class-E Power Amplifiers for Pulsed Transmitters
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays the main driving parameters for the radio transmitter research are: energy efficiency, frequency re-configurability and integration. Pulsed transmitter architectures have attracted large interest in the recent years due to their potential to meet these demands. In pulsed transmitters, a highly efficient switch mode power amplifier (SMPA) is used in conjunction with a pulse modulator to achieve high efficiency linear amplification. Digital implementation of the modulator enables wide bandwidth for the signal generation path and improves the level integration. The bandwidth in a pulsed transmitter is however typically limited by the load matching network of the SMPA. This thesis presents two main contributions in the field of pulsed transmitter architectures.In the first part focus is given to bandwidth improvement of class-E switch mode PAs. A continuum of novel closed-form class-E modes is derived extending the traditional class-E design space. The extended design space provides important possibilities for wide band design of the class-E load networks and for further efficiency optimization of class-E PAs. A wide band design methodology is thus developed based on the analytical design equations.In the second part, focus is given to efficiency improvement of RF pulse width modulation (RF-PWM) based transmitters. A new SMPA topology particularly suitable for energy efficient amplification of RF-PWM signals is derived. It is analytically shown that high efficiency can be maintained over a wide power dynamic range if the imaginary part of the class-E load impedance is varied along with the pulse width. Using in-house (Chalmers University) SiC varactor diodes to implement the tunable load impedance, a 2 GHz 10 W peak output power CMOS-GaN HEMT RF-PWM transmitter demonstrator is realized. The static measurements show that a drain efficiency >70% can be obtained over a 6.5 dB dynamic range. A digital pre-distortion based linearization scheme is proposed to enhance the linearity of the transmitter. An adjacent power ratio of -45 dBc and average drain efficiency of 67% is achieved using a realistic W-CDMA communication signal. These results clearly demonstrate the feasibility of the proposed pulsed transmitter topology for high efficiency linear amplification.
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| 5. |
- Aad, G., et al.
(författare)
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- 2012
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swepub:Mat__t (refereegranskat)
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| 6. |
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| 7. |
- Ax, Christian, et al.
(författare)
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- 2002
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Bok (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Aad, G., et al.
(författare)
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- 2015
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Ingår i: The European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6052. ; 75:7
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Tidskriftsartikel (refereegranskat)
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| 9. |
- Persson, A., et al.
(författare)
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- 2008
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 455:7216
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Aad, G., et al.
(författare)
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- 2012
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swepub:Mat__t (refereegranskat)
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