Charlie Orlenius

Characterization of Reverberation Chambers for OTA Measurements of Wireless Devices: Physical Formulations of Channel Matrix and New Uncertainty Formula

The paper deals with reverberation chambers for over-the-air (OTA) testing of wireless devices for use in multipath. We present a formulation of the S-parameters of a reverberation chamber in terms of the free space S-parameters of the antennas, and the channel matrix in the way this is known from propagation literature. Thereby the physical relations between the chamber and real-life multipath environments are more easily explained. Thereafter we use the formulation to determine the uncertainty by which efficiency-related quantities can be measured in reverberation chamber. The final expression shows that the uncertainty is predominantly determined by the Rician K-factor in the reverberation chamber rather than by the number of excited modes, assumed by previous literature. We introduce an average Rician K-factor that is conveniently expressed in terms of the direct coupling between the transmitting and receiving antennas (corresponding to a line-of-sight contribution) and Hills transmission formula (corresponding to a multipath or non-line-of-sight contribution). The uncertainty is expressed in terms of this average K-factor and geometrical mode stirring parameters, showing strong reduction by platform and polarization stirring. Finally the formulations are verified by measurements, and the new understanding of uncertainty is used to upgrade an existing reverberation chamber to better uncertainty.

Corrections to “Channel Sounding of Loaded Reverberation Chamber for Over-the-Air Testing of Wireless Devices—Coherence Bandwidth Versus Average Mode Bandwidth and Delay Spread”

This letter finds the relation between different parameters that characterize the reverberation chamber as a channel emulator for over-the-air (OTA) testing of wireless devices and components. It is shown experimentally for the first time that the coherence bandwidth is proportional to the average mode bandwidth of the chamber. Both coherence bandwidth and average mode bandwidth increase when the chamber is loaded with absorbing objects, and thereby, the reverberation chamber can be controlled to emulate many different real-life environments. The relationship between RMS delay spread and coherence bandwidth are found from the measured channel response and are equal to the theoretical relation for isotropic multipath environments, being within previously published fundamental limits.

OTA Testing in Multipath of Antennas and Wireless Devices With MIMO and OFDM

New over-the-air (OTA) measurement technology is wanted for quantitative testing of modern wireless devices for use in multipath. We show that the reverberation chamber emulates a rich isotropic multipath (RIMP), making it an extreme reference environment for testing of wireless devices. This thereby complements testing in anechoic chambers representing the opposite extreme reference environment: pure line-of-sight (LOS). Antenna diversity gain was defined for RIMP environments based on improved fading performance. This paper finds this RIMP-diversity gain also valid as a metric of the cumulative improvement of the 1% worst users randomly distributed in the RIMP environment. The paper argues that LOS in modern wireless systems is random due to randomness of the orientations of the users and their devices. This leads to the definition of cumulative LOS-diversity gain of the 1% worst users in random LOS. This is generally not equal to the RIMP-diversity gain. The paper overviews the research on reverberation chambers for testing of wireless devices in RIMP environments. Finally, it presents a simple theory that can accurately model measured throughput for a long-term evolution (LTE) system with orthogonal frequency-division multiplexing (OFDM) and multiple-input-multiple-output (MIMO), the effects of which can clearly be seen and depend on the controllable time delay spread in the chamber.

Threshold Receiver Model for Throughput of Wireless Devices With MIMO and Frequency Diversity Measured in Reverberation Chamber

We present a simple theoretical model for the throughput data rate of a wireless LTE device including the improvements of data rate due to diversity in frequency (OFDM) and spatial domains (MIMO) under frequency selective fading. The model is based on defining an ideal threshold receiver for the line-of-sight (LOS) case, corresponding to reception with advanced error-correcting codes. The theoretical throughput model is in agreement with measurements in a reverberation chamber of a commercial LTE device for the 1 × 2 SIMO case, both regarding diversity and MIMO array gains, and it can therefore be used to complement measured results in evaluation of performance of LTE devices.

Calculated and measured absorption cross sections of lossy objects in reverberation chamber

Reverberation chambers can be used to measure radiation efficiency of small antennas when these are located close to lossy objects. The lossy objects represent a heavy loading of the chamber. This loading is characterized by the mean absorption cross section of the lossy objects. This paper describes how this mean absorption cross section can be calculated from the scattered far field of an object by using the forward scattering theorem, or from a more laborious near-field evaluation. Results for lossy spheres and cylinders are calculated by using three different codes, based on spherical mode expansion, finite difference time domain techniques, and moment methods, respectively. The results for the cylinder are compared with measured levels in a reverberation chamber.

Measurements of total isotropic sensitivity and average fading sensitivity of CDMA phones in reverberation chamber

The authors describe two ways to measure receive performance of active terminals by using a reverberation chamber, referred to as total isotropic sensitivity (TIS) and average fading sensitivity. The latter is a new method which can be measured very fast in a reverberation chamber. It is also more representative of the actual performance of a terminal in a real fading environment than the former. Based on measured results, they conclude that the average fading sensitivity is a promising alternative to TIS measurements for characterizing receive performance of mobile terminals. The reverberation chamber is well suited for both these measurements. Average fading sensitivity measurements can be done faster than TIS and give similar relative results i.e. the average fading sensitivity shows similar difference between the different phones as the TIS results, when they read the sensitivity levels at 0.5% error level.

In Situ Measurement of UHF Wearable Antenna Radiation Efficiency Using a Reverberation Chamber

The radiation efficiency and resonance frequency of five compact antennas worn by nine individual test subjects was measured at 2.45 GHz in a reverberation chamber. The results show that, despite significant differences in body mass, wearable antenna radiation efficiency had a standard deviation less than 0.6 dB and the resonance frequency shift was less than 1% between test subjects. Variability in the radiation efficiency and resonance frequency shift between antennas was largely dependant on body tissue coupling which is related to both antenna geometry and radiation characteristics. The reverberation chamber measurements were validated using a synthetic tissue phantom and compared with results obtained in a spherical near field chamber and finite-difference time-domain (FDTD) simulation.

Investigation of Heavily Loaded Reverberation Chamber for Testing of Wideband Wireless Units

Traditionally, the reverberation chamber has been used as a low-loss cavity to gain high signal levels. For testing of the radiated properties of wireless terminals and their antennas, this is not an issue, and lossy objects like for instance a head phantom can be introduced in the chamber without problem. However, for testing of active units, the bandwidth of the system itself plays an important role. In order to avoid distortion of the signal transmitted in the chamber, the bandwidth of the chamber must be larger than the bandwidth of the signal. This is one reason for loading the reverberation chamber. Another reason is a potential increase in the measurement accuracy, since an increased bandwidth makes more modes excited at a particular frequency. The purpose of this paper is to investigate the effect of loading on the statistics of the chamber and its bandwidth

Improved procedure for measuring efficiency of small antennas in reverberation chambers

We show that the accuracy of measuring the efficiency of an antenna in a reverberation chamber can be improved if the calibration antenna is located inside the chamber during the test measurements and visa versa, and they must together represent the same load in the chamber during both calibration and test measurements. The error by not doing so depends on the total loading of the chamber. In our case, with a cylinder, the systematic error is about 0.2 dB at 1800 MHz.

WLAN MIMO throughput test in reverberation chamber

The present paper describes the first repeatable full system measurement setting for WLAN link throughput at the transport layer payload. This is the effective rate of the link to be offered to the applications and determines the quality of the user experience. The measurement is done in a reverberation chamber.