Ensuite la surface d'absorption équivalente moyenne est évaluée en fonction de la bande de cohérence selon. Extraire le gain de l'antenne de la relation (16) nécessite de connaître la distance de propagation dans l'espace libre d.
Introduction
Working context
Overview of reverberation chambers
The mean field in a well-operated reverberation chamber (over the stirring process) is considered to be statistically isotropic and homogeneous in a limited volume of the chamber. The main property of the reverberation chamber is the statistical uniformity and isotropy of the average electric field in the working volume of the cavity.
Description of this thesis
Threshold receiver model for throughput of wireless devices with MIMO and frequency diversity measured in reverberation chamber,” Antennas and Wireless Propagation Letters, IEEE, vol. Besnier, "On the K-factor estimation for Rician channel simulated in reverberation chamber," Antennas and Propagation, IEEE Transactions on, vol.
Friis propagation model
Two fading models
Each position of the mixer blade corresponds to a measurement of the pth channel in the pth propagation environment. For our chamber, the minimum time for a full rotation of the stirrer (corresponding to the maximum speed of the stirrer) is 30 s.
Overview on channel measurements in reverberation cham- ber
A better presentation of the variation of the signal level depending on the position of the mixer is in Figure 2.5. This figure represents the normalized amplitude of the signal with mixer position to the lower neighbor: (r(p) −r(p−1)) /r(p−1). For example, Figure 2.11(a) shows the decay constant τ of a chamber with multiple amounts of absorbers, 2.11(b).
Conclusions
We can easily obtain an approximation of the average absorbing cross section if the absorber is parallelepiped (or any other shape for which any face of the absorber does not partially mask other faces). Our results show a good agreement between simulated and measured values of the mean absorbing cross section. Moreover, the estimation of the average absorbing cross section is affected by random fluctuations of much lower amplitude than the classical method.
Introduction
The goal of our estimators is to expand the useful range of values and reduce estimation uncertainties, while using a small sample size for the estimation. For the second estimator, the maximum likelihood estimate (MLE) (see Appendix B.8) of the probability density function (PDF) of the fading envelope is calculated using an approximation of the modified Bessel function of the first kind (see Appendix C. 1). The performance of both proposed estimators is compared with other envelope-based estimators, including analyzes regarding the measured sample size and signal-to-noise ratio (SNR).
Methods to estimate K-factor
In [3,20], the estimated K-factor is extracted from the ratio of the second and the 4th moment of the blurred envelope. In [12] a method is presented that uses the maximum likelihood applied to the realizations of the fading phase. Q is the total quality factor (ie it is generally affected by the quality factor of the room).
Our proposal for new K -factor estimators
The estimators ̂µ1 and µ̂2 are the first and second non-central moments of the signal envelope, respectively. For values of K <5 dB, the CI of the second new estimator has a maximum value of ~5.7 dB. Validation of the second new estimator in a real environment takes place with measurements in our echo chamber.
Introduction
The average absorbing cross section (AACS) is obtained by calculating the average absorbing cross section for any plane wave directions and polarizations. In this chapter we calculate in frequency domain the average absorbing cross-section of a quantity of absorbers from the estimated coherence bandwidths of the empty and charged chamber. Since the coherence bandwidth is inversely proportional to the quality factor, the average absorbing cross section can be easily estimated.
Estimating the average absorbing cross section from measurements in reverberation chamber
Conversely, it turns out that changes in wireless transmissions in the presence of absorption can be approximated a priori by estimates of the average absorbent cross section if the geometric and electromagnetic parameters of the absorbers are known. In this chapter, the analysis of the frequency selectivity of the absorption rate channel is done by calculating the bandwidth of the complex coherence for each mixing position at a correlation level of 0.7. The cross section represents an apparent area used to describe the amount of radiation interacting with this target.
Prediction of the average absorbing cross section of the par- allelepiped absorbers
This results in the average reflection coefficient over all angles and polarizations of the absorber being: R = 1−T. In other words, we mean that the depth of the absorber is high enough to completely scatter the incoming waves regardless of their angles of incidence. Without including the effects of the re-radiation of the electromagnetic waves after they have passed through the absorber, the simulated average absorbing cross section is overestimated.
Validation of the method
Because the hypothesis of a plane wave spectrum of the field is not respected, the measured average absorbing cross-section will be underestimated in respect of the situation in which the absorbers are illuminated uniformly. The variation of the measured coherence bandwidths with frequency for different number of absorbers is shown in Fig. As expected, the level of the coherence bandwidth increases with the number of absorbers in the chamber.
Conclusions
Issac, “On the power dissipated by an antenna in transmit mode or in receive mode in a reverberation chamber,” Electromagnetic Compatibility, IEEE Transactions on, vol. Kildal, "Theoretical derivation and measurements of the relation between coherence bandwidth and RMS delay spread in reverberation chamber," in Antennas and Propagation, 2009. Hill, "Plane wave integral representation for fields in reverberation chambers," IEEE Transactions on Electromagnetic Compatibility, vol.
Introduction
Signal model
When the received signal also contains unperturbed components, the envelope of the steady-state electric field becomes Rician-distributed. AunSti is the maximum level of the envelope of the electric field of unstirred components, which remains constant with the stirring mechanism;. This results in the estimated power of the signal in steady state being equal to/or smaller than.
Relating K-factor with various time parameters
This section deals with the relationships between the average absorbing cross section of the loads, the decay constant of the chamber and the K factor. In the first situation, the decay constants of the chamber without and with absorbers: τE and τL are considered known. In [18] this is done using the decay constants of the chamber with and without absorbers:.
Validation
When received, the total duration of the recorded signal (i.e. the transient regime and the steady state) is 19 µs. Fig.5.10 shows the variation of the decay constant of the chamber with the increase in the number of absorbers. The estimates of the average absorbing cross-sections with the number of absorbers are shown in Figure 5.11.
Conclusions
Eyring, “Reverberation Time in "Dead" Rooms,” The Journal of the Acoustical Society of America, vol. Besnier, “On the estimation of the K-factor for a Rician channel simulated in an echo chamber,” Antennas and Propagation, IEEE Transactions on, vol. The following application evaluates the use of an echo chamber to characterize diversity gain.
Introduction
We then investigate the issue of the propagation distance estimate to further determine the antenna gain for a given position/orientation relative to the chamber wall towards which the antenna is directed. An uncertainty analysis of the free space propagation distance shows the conditions under which this parameter is estimated. Results show that providing a careful estimation of time inputs and of the distance between free space, antenna pattern and half-power beamwidth is measured in good agreement with reference results.
The Method
Deriving the antenna gain as shown in (6.2), requires knowledge of the free-space propagation distance d. The quality of the estimation of this parameter has a direct influence on the estimation of the antenna gain, since the error of the estimation of the antenna gain is identical to the error of the estimation of the propagation distance in free space. To find the propagation distance in free space, one solution is to extract the time corresponding to the maximum of the amplitude of the impulse response, which corresponds to the propagation distance of the first reflection, dIR.
Data processing and Results
When the signal is strongly truncated (example "a" in Fig. 6.6), the energy of the first reflection is underestimated. We calculate the relative difference of the measured value in the reverberation chamber over the value measured in the near-field chamber. 6.15(b) for the vertical polarization by calculating the relative difference between the half-power beamwidth measured in the reverberation chamber over that measured in the near-field chamber.
Conclusions
Raisanen, “An antenna pattern correction technique based on an adaptive array algorithm,” Antenne and Propagation, IEEE Transactions on, vol. An improved method for characterizing the performance of UWB antennas,” Antennas and Propagation, IEEE Transactions on, vol. Gupta, “A single-antenna method for measuring antenna gain and phase,” Antennas and Propagation, IEEE Transactions on, vol.
Introduction
The performance of the maximum-ratio combination method for the Rician fading channels is analyzed in [10]. In this chapter, we discuss the diversity in a simulated wireless channel in reverberation room (RC). This is done using Monte Carlo simulations, while the measurements in the reverberation chamber confirm our theoretical results.
Computing the diversity gain
So far in this thesis we have analyzed different parameters of the reproductive tracts and different methods to evaluate and control these parameters. The goal is to analyze and obtain the same improvements on the reproductive tract in the presence of blur as in a real environment. In these settings, the use of envelope or power correlation as a parameter to characterize the quality of the diversity techniques is not recommended as it may bias the conclusions.
Linear diversity combining techniques
For this diversity, the same piece of information is repeatedly transmitted at different time intervals, which are well separated compared to the delay distribution of the environment.
Definitions of the diversity gain
Methods to combine the signals for diversity gain
Compared to previous techniques, combining selection combinations introduces transients in the output signal due to switching. The SNR at the output of the combiner is the sum of the instantaneous SNRs of each branch. For a Rayleigh environment, considering a two-branch diversity combiner, receiving uncorrelated signals (i.e. ρ≈0), the theoretical maximum diversity gain estimated from Monte Carlo simulations is less than: 11.5 dB for maximum ratio combining, 10 dB for combining selection, and 8 dB for equal gain combining.
Parameters which may influence diversity gain
The correlation (see appendix B.1) is mainly caused by mutual coupling between the elements of the antenna arrays at emission and reception [3]. The measured signals at the output of the two branches can also be complex envelopes, voltage envelopes or power envelopes, and different types of correlation between branches can be calculated: complex correlation, envelope correlation and power correlation. In spatial diversity systems, the complex correlation between antenna branches is a function of the spacing distance between the dipole antennas.
Results
With increasing the minimum K-factor, diversity gain depends on both the power imbalance and the value of K-factor. Also, with the increase of the distance between horn and dipole antennas, secondary unstirred components reflected by walls but not by the stirrer may appear. 50MHz from the horn and two dipole antennas when the separation distance between them is 10cm.