| 51. |
- Abdelaziz, Mahmoud, et al.
(författare)
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Digital Predistortion for Hybrid MIMO Transmitters
- 2018
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Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553.
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates digital predistortion (DPD) linearization of hybrid beamforming large-scale antenna transmitters. We propose a novel DPD processing and learning technique for an antenna sub-array, which utilizes a combined signal of the individual power amplifier (PA) outputs in conjunction with a decorrelation-based learning rule. In effect, the proposed approach results in minimizing the nonlinear distortions in the direction of the intended receiver. This feature is highly desirable, since emissions in other directions are naturally weak due to beamforming. The proposed parameter learning technique requires only a single observation receiver, and therefore supports simple hardware implementation. It is also shown to clearly outperform the current state-of-the-art technique which utilizes only a single PA for learning. Analysis of the feedback network amplitude and phase imbalances reveals that the technique is robust even to high levels of such imbalances. Finally, we also show that the array system out-of-band emissions are well-behaving in all spatial directions, and essentially below those of the corresponding single-antenna transmitter, due to the combined effects of the DPD and beamforming.
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| 52. |
- Adeogun, Ramoni, et al.
(författare)
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Polarimetric Wireless Indoor Channel Modeling Based on Propagation Graph
- 2019
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 67:10, s. 6585-6595
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Tidskriftsartikel (refereegranskat)abstract
- This paper generalizes a propagation graph model to polarized indoor wireless channels. In the original contribution, the channel is modeled as a propagation graph in which vertices represent transmitters, receivers, and scatterers, while edges represent the propagation conditions between vertices. Each edge is characterized by an edge transfer function accounting for the attenuation, delay spread, and the phase shift on the edge. In this contribution, we extend this modeling formalism to polarized channels by incorporating depolarization effects into the edge transfer functions and hence, the channel transfer matrix. We derive closed form expressions for the polarimetric power delay spectrum and cross-polarization ratio of the indoor channel. The expressions are derived considering average signal propagation in a graph and relate these statistics to model parameters, thereby providing a useful approach to investigate the averaged effect of these parameters on the channel statistics. Furthermore, we present a procedure for calibrating the model based on method of moments. Simulations were performed to validate the proposed model and the derived approximate expressions using both synthetic data and channel measurements at 15 GHz and 60 GHz. We observe that the model and approximate expressions provide good fit to the measurement data.
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| 53. |
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| 54. |
- Al-Ameri, Ali, et al.
(författare)
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A Hybrid Antenna Switching Scheme for Dynamic Channel Sounding
- 2023
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Ingår i: 2023 IEEE 97th Vehicular Technology Conference, VTC 2023-Spring - Proceedings. - 9798350311150 - 9798350311143
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Konferensbidrag (refereegranskat)abstract
- Channel sounding is essential for the development of radio systems. One flexible strategy is the switched-array-based channel sounding, where antenna elements are activated at different time instants to measure the channel spatial characteristics. Although its hardware complexity is decreased due to fewer radio-frequency (RF) chains, sequentially switching the antenna elements can result in aliasing in the joint estimation of angles and Doppler frequencies of multipath components (MPCs). Therefore, pseudo-random switching has been proposed to mitigate such aliasing and increase estimation accuracy in both angular and Doppler domains. Nevertheless, the increased Doppler resolution could cause additional post-processing complexity of parameter estimation, which is relevant when the Doppler frequencies are not of interest, e.g., for spatial channel modeling. This paper proposes an improved hybrid sequential and random switching scheme. The primary purpose is to maintain the estimation accuracy of angles of MPCs while decreasing the resolution of Doppler frequencies for minimized complexity of channel parameter estimation. A simulated-annealing algorithm is exploited to obtain an optimized switching sequence. The effectiveness of the proposed scheme is also demonstrated with a realistic antenna array.
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| 55. |
- Alayon Glazunov, Andres, et al.
(författare)
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A note on the Mean Effective Radiated Power and the Mean Effective Receiver Sensitivity of mobile handheld terminals
- 2008
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Ingår i: 2008 IEEE International Symposium on Antennas and Propagation and USNC/URSI National Radio Science Meeting. ; , s. 1-4, s. 4471-4474
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Konferensbidrag (refereegranskat)abstract
- In this paper we introduce the Mean Effective Radiated Power (MERP) and the Mean Effective Radiated Sensitivity (MERS) as alternative figures of merit of the uplink and downlink communication performance of wireless handheld terminals. We show how they are related to the Mean Effective Gain (MEG), the total radiated power (TRP) and total receiver sensitivity (TRS).
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| 56. |
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| 57. |
- Alayon Glazunov, Andres, et al.
(författare)
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Fading characterization in a semi-anechoic chamber with artificial scatterers for Mean Effective Gain measurements of wireless handheld terminals
- 2008
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Ingår i: 2008 IEEE Radio and Wireless Symposium, RWS. ; , s. 611-614
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Konferensbidrag (refereegranskat)abstract
- This paper presents the methodology and corresponding analysis of the scattered field measurements in a semi-anechoic ferrite-lined chamber. The focus is on recreating a Rayleigh fading environment with realistic cross-polarization ratio (XPR) with the purpose of measuring the Mean Effective Gain (MEG) of mobile handheld terminal operating in the 900 MHz GSM band. The emulated XPR was similar in each of the studied scenarios and approximately equal to 12 dB. The Rayleigh fading hypothesis for the statistics of the envelope of the measured signals could not be rejected in most cases at the 95 % level with the Kolmogorov goodness-of-fit test.
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| 58. |
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| 59. |
- Alayon Glazunov, Andres, et al.
(författare)
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Mean effective gain of antennas in a wireless channel
- 2009
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Ingår i: IET Microwaves, Antennas & Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725. ; 3:2, s. 214-227
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Tidskriftsartikel (refereegranskat)abstract
- The mean effective gain (MEG) is one of the most important parameters for the characterisation of antennas in wireless channels. An analysis of some fundamental properties of the MEG is provided and corresponding physical interpretations are given. Three points are analysed in detail: (i) closed-form expressions for MEG in a mixed environment with both stochastic and deterministic components are provided, showing that the MEG can be written as a sum of gains for the deterministic and stochastic components, (ii) it is shown that under some assumptions, the propagation channel and the antenna are equivalent in the sense that the impact of the channel cross-polarisation ratio (XPR) and the antenna effective cross-polar discrimination on the MEG are symmetrical, (iii) based on the fact that MEG depends on random variables, such as the XPR and antenna rotations because of user's movements, the average, the minimum and maximum MEG of antennas are defined, respectively. Finally, the maximum effective gain of antennas is derived and shown that it is bounded by 4 pi eta(rad), where eta(rad) is the radiation efficiency of the antenna.
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| 60. |
- Alayon Glazunov, Andres, et al.
(författare)
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On the mean effective gain expressed in terms of the spherical vector wave expansion of the electromagnetic field
- 2008
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Konferensbidrag (refereegranskat)abstract
- The mode expansion o®ers a general framework for the analysis of the interaction between antennas andpropagation channels. In this paper, the Mean E®ective Gain (MEG) of an antenna is expressed in termsof the spherical vector wave expansion of the electromagnetic ¯eld. An explicit expression of the MEG isprovided as a function of the normalized average power of modes excited in the propagation channel andthe correlation between the channel modes due to the polarization and spatial selectivity of plane wavesimpinging at the antenna.
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