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 Hill's 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.

https://publications.lib.chalmers.se/records/fulltext/local_164015.pdf

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

The constant evolution of wireless handheld devices together with the apparition of multiple wireless communication systems fosters the antenna community to design new radiating and measurements systems capable of satisfying the market demands. It is an object of the present paper to provide an overview of the evolution that wireless handheld technology has experienced in the last years. In this sense, a description of the evolution of wireless handheld devices, regulations, challenges in today’s smartphones, and handset characterization is reviewed. Finally, recent advances in antenna technology for wireless handheld or portable devices are presented.

/pdf/advances-in-antenna-technology-for-wireless-handheld-devices-3q0sayjyh0.pdf

Advances in Antenna Technology for Wireless Handheld Devices

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.

https://publications.lib.chalmers.se/records/fulltext/161662/local_161662.pdf

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

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.

http://publications.lib.chalmers.se/records/fulltext/153310/local_153310.pdf

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

This paper presents simple throughput models for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems with hybrid automatic repeat request (HARQ). In particular, we consider the long term evolution (LTE) systems. Antenna correlations and power imbalances are implicitly included in the models. In order to explicitly characterize the antenna effects on throughput, we resort to the spatial multiplexing (SM) efficiency. The SM efficiencies of a MIMO antenna with zero forcing (ZF), minimum mean square error (MMSE), and maximum likelihood (ML) receivers are studied via numerical simulations using the throughput models. To verify the throughput models, the throughputs of two LTE terminals (including antenna correlations and power imbalances) are measured in a reverberation chamber (RC). Good agreements between the measured and modeled throughputs are observed.

https://publications.lib.chalmers.se/records/fulltext/199237/local_199237.pdf

Throughput Modeling and Measurement in an Isotropic-Scattering Reverberation Chamber

This paper discusses the possibilities of using the reverberation chamber as a multipath emulator for testing of wireless terminals, especially those with multi-antenna solutions implemented. The tests are consisting of measurements of data bit throughput, in order to relate the performance of the terminal to an end-user experience. The experimental part includes HSDPA measurements with focus on overall system performance in different channel models, and LTE measurements of individual antenna parameters.

Over-the-air performance testing of wireless terminals by data throughput measurements in reverberation chamber

The evolution of measurement systems that can capture the performance of multi-antenna systems is an important and highly prioritized point of discussion for the antenna community. This paper gives a state-of-the-art recollection of the latest findings in MIMO OTA measurements utilizing reverberation chambers, specifically relating to LTE terminals.

Analysis of MIMO OTA measurements for LTE terminals performed in reverberation chamber

This paper presents a proposed measurement method utilizing the reverberation chamber to measure MAC layer throughput for LTE enabled wireless devices By using the reverberation chamber a statistically isotropic environment is produced, which is a suitable reference environment for terminal antenna testing

https://publications.lib.chalmers.se/records/fulltext/141297/local_141297.pdf

State-of-the-art measurements of LTE terminal antenna performance using reverberation chamber

This paper focuses on the latest advances in the use of reverberation chambers for active device testing. Contained are description and comparison of different figure-of-merits that are applicable to multi element antennas, with a specific focus on LTE devices with MIMO capability. There are two new parameter concepts introduced: Modified Total Isotropic Sensitivity measurements to include MIMO signaling, and a Throughput Threshold Level for simplified quantification of data bit throughput measurement results.

https://publications.lib.chalmers.se/records/fulltext/163387/local_163387.pdf

Evaluation of multi element antennas in reverberation chamber

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