A.5.1 General

37.5443GPPConformance testingRelease 16TSUniversal Terrestrial Radio Access (UTRA) and Evolved UTRA (E-UTRA)User Equipment (UE) Over The Air (OTA) performance

An OTA method based on the use of an Anechoic RF Chamber is described consisting of a number of test antenna probes located in the chamber transmitting signals with temporal and spatial characteristics for testing multiple antenna devices.

This clause describes the methodologies based on Anechoic RF Chamber, where a number of test antennas are located in different positions of the chamber, and the Device Under Test (DUT) is located at centre position. The DUT is tested over the air without RF cables.

A.5.1.1 Multi-probe Anechoic Chamber

An OTA method based on the use of an Anechoic RF Chamber is described consisting of a number of test antennas located in the chamber transmitting signals with temporal and spatial characteristics for testing multiple antenna devices. The method consists of a number of test antennas located in different positions of the chamber, and the device under test (DUT) is located at the centre position. The DUT is tested over the air without RF cables.

The Anechoic chamber techniques creates a realistic geometric based spatio-temporal-polarimetric radio channel for testing MIMO performance using Geometric based stochastic channel models as defined in Annex M.1.

The components of the solution include:

– Anechoic Chamber

– System Simulator (SS)

– N channel RF emulator, with OTA Channel Generation Features

– N linearly polarized antenna elements configured V, H or co-located V&H or slant X polarizations

– K azimuthally separated antenna positions with predefined angles at radius R

– Channel model definition for each test case

An illustration of an anechoic chamber is shown in Figure A.5.1.1-1 below.

Figure A.5.1.1-1: N-element Anechoic Chamber approach (Absorbing tiles and cabling not shown)

Figure A.5.1.1-2: OTA system level block diagram

A system level block diagram is shown in Figure A.5.1.1-2, which includes the SS to generate the M branch MIMO signal, and an RF Channel Emulator with an OTA Channel Generation Feature to properly correlate, fade, scale, delay, and distribute the signal to each test probe in the chamber. For the selected environmental conditions modelled by the SCME UMa and UMi channel models, the minimum setup configuration can be described as below:

Table A.5.1.1-1: Example of a minimum setup for Boundary Array implementations
using the Anechoic Chamber Methodology

Full Ring

Single Cluster

Minimum number of antenna positions

8

3

Antenna spacing

45°

Determined on the setup

Applicable channel model

SCME UMa/SCME UMi

Single Cluster UMa and Single Cluster UMi

The full SCME or Multi-Cluster channel models are defined in Annex M.1. The Single-Cluster model, which is not part of the set of channel models validated in clause 8, would be based on the channel models defined in Annex M.1 with a set of dithered AoAs around zero degrees.

A.5.1.1.1 Concept and configuration

For MIMO OTA modelling the geometric channel models are mapped into the fading emulator, converting the geometric channel models into the emulator tap coefficients. This process is illustrated in Figure A.5.1.1.1-1.

Figure A.5.1.1.1-1: Modelling process

The setup of OTA chamber antennas with eight antenna positions is depicted in Figure A.5.1.1.1-2. The DUT is at the centre, and the antennas are in a circle around the DUT with uniform spacing (e.g. 45 with 16 elements arranged in 8 positions, where each position contains a vertically and horizontally polarized antenna pair). Denoting directions of K OTA antennas with k, k = 1… K, and antenna spacing in the angle domain with . Each antenna is connected to a single fading emulator output port. In the figure, for example, antenna A1V denotes the first OTA antenna position and Vertically (V) polarized element, A8H denotes the eight OTA antenna position and horizontally (H) polarized element, etc.

Figure A.5.1.1.1-2: OTA chamber antenna setup with eight uniformly spaced dual polarized chamber antennas

NOTE: In the drawing the V-polarized elements are actually orthogonal to the paper (azimuth plane)

A.5.1.2 Radiated Two-Stage

The principle of two-stage MIMO OTA method is based on the assumption that the DUT far-field antenna radiation pattern will contain all the necessary information for evaluation of the DUT’s antenna’s performance like radiation power, efficiency and correlation and that with channel model approaches, the influence of antenna radiation pattern can be correctly incorporated into the channel model. Thus the method will first measure the DUT’s MIMO antenna patterns and then convolve the measured antenna patterns with the chosen MIMO OTA channel models for real-time emulation. The resulting test signal generated by the channel emulator and coupled back into the DUT receivers represents the signal that the DUT receivers would have seen if the DUT had been placed in the desired radiated field. Thus an ideal implementation of the two-stage method provides the same results as an ideal implementation of the boundary antenna array method.

The two-stage method can be used to measure the following figures of merit:

1) Throughput

2) TRP and TRS

3) CQI, BLER

4) Antenna efficiency and MEG

5) Antenna correlation, MIMO channel capacity.

In order to accurately measure the antenna pattern of the intact device, the DUT chipset needs to support received amplitude and relative phase measurements of the antennas. The validity of antenna pattern measurement is predicated on the assumption that for the frequency being tested, the DUT antenna pattern is static. Devices than can alter their antenna pattern in real time as a function of the radiated environment is not supported. The method of coupling the base station emulator and DUT uses a specially calibrated radiated connection (radiated two-stage or RTS method) to do the test on throughput, etc., to test how the MIMO antennas will influence the performance. The conducted method of coupling is straightforward but does not capture the impact of radiated leakage from the DUT transmit antennas to the DUT receive antennas, thus in its current form without additional interference estimation the conducted method of coupling in the second stage is not proposed for use in conformance testing. Its description is included for historical completeness of the development of the two-stage method. The radiated method of coupling in the second stage does fully capture radiated leakage and is the method defined for conformance testing.

A.5.1.2.1 Concept and configuration

The assumption of the two-stage MIMO OTA method is that the measured far field antenna pattern of the DUT’s multiple antennas can fully capture the mutual coupling of the multiple antenna arrays and their influence on radiated performance.
Thus to do the two-stage MIMO OTA test, the antenna patterns of the antenna array needs to be measured accurately in the first stage. In order to accurately measure the antenna pattern of the intact device, the chipset needs to support amplitude and relative phase measurements of the antennas. To achieve this, two new UE measurements have been defined called Reference Signal Antenna Power (RSAP) and Reference Signal Relative Antenna Phase (RSARP). These measurements are defined in TS 36.509 [34].

Stage 1: The measurement of the DUT’s multiple antennas takes place in a traditional anechoic chamber set up as described in Annex A.3, where the DUT is put into the chamber and each antenna element’s complex far zone pattern is measured using the RSAP and RSARP measurements defined in TR 36.509 [34]. The influence of human body loss can also be measured by attaching the DUT to a SAM head and or hand phantom when doing the antenna pattern measurements. The characteristics of the SAM phantom are specified in Annex A.2. The chamber is equipped with a positioner, that makes it possible to perform full 3-D far zone pattern measurements for both Tx and Rx radiated performance. As specified in A.3, the measurement antenna shall be able to measure two orthogonal polarizations (typically linear theta () and phi () polarizations as shown in Figure A.5.1.2.1-1).

Figure A.5.1.2.1-1: The coordinate system used in the measurements

Stage 2: Convolve the antenna patterns measured in stage 1 with the chosen MIMO channel model, using a channel emulator and then use the resulting signal to perform the OTA throughput test. The signal is coupled into the DUT using a radiated connection.

The radiated two-stage (RTS) method is illustrated in Figure A.5.1.2.1-2. The BS emulator is connected to the MIMO channel emulator and then to the DUT using a calibrated radiated connection in an anechoic environment. This coupling technique exploits the Eigen modes of the transmission channel in the anechoic chamber to provide isolated radiated connections between the probe antennas and each DUT receiver after the DUT antenna.

To convolve the DUT antenna patterns with MIMO channel model.

a) Apply antenna patterns to correlation-based channel models. With a correlation matrix calculation method for arbitrary antenna patterns under multipath channel conditions, the correlation matrix and the antenna imbalance can be calculated and then emulated by the channel emulator.

Figure A.5.1.2.1-2: Radiated two-stage (RTS) test methodology for MIMO OTA test

Figure A.5.1.2.1-2 shows the radiated coupling method for the second stage. Two probe antennas with polarization V and H are co-located in the anechoic chamber. Note, unlike in the first stage where the V and H probes are used at different times, in the second stage both V and H probes are used simultaneously. An example implementation of this would be the dual polarized configuration described in Annex A.3. Due to the propagation channel in the chamber, signals transmitted from each probe antenna are received by both DUT antennas. However, by precoding the transmitted signals using spatial multiplexing techniques it is possible by calculating the radiated channel matrix and by applying its inverse to the transmitted signals, to create an identity matrix allowing the transmitted signals to be received independently at each DUT receiver after the DUT antenna.

The establishment of the radiated connection is explained as follows. Assume and are the transmitted signals from the base station emulator, after applying the desired channel model and convolution with the complex antenna pattern we get:

and .

The radiated channel matrix between the probe antennas and the DUT antennas is .

If the channel emulator applies the inverse of the radiated channel matrix to and , the signal received after the DUT antennas is same as if the channel emulator were directly connected to equivalent antenna connectors:

The above example of RTS using two probe antennas is applicable to UE with two Rx antennas. For UE with > 2 Rx antennas, the RTS method is FFS.