Experimental Evaluation of User Influence on Test Zone Size in Multi-probe Anechoic Chamber Setups

Over-the-air (OTA) radiated testing for multipleinput
multiple-output (MIMO) capable mobile terminals has
been actively discussed in the standardization in recent years,
where multi-probe anechoic chamber (MPAC) method has been
selected, together with the radiated two-stage (RTS) method. The
supported test zone size is a key parameter to determine for an
MPAC design, and the test zone size is restricted by the number
of OTA antennas. A larger test zone would necessitate more OTA
antennas, each port of which is driven by an expensive channel
emulator radio frequency (RF) interface. Results available in the
literature are typically limited to free space scenarios, where no
user effect in the vicinity of MIMO terminal is present. There is
a concern whether or not the test zone size should encompass the
user phantom, together with the mobile terminal in the MPAC
setup. To address this issue, an extensive measurement campaign
was carried out in the paper. Two realistic LTE mockups were
designed and their performance were evaluated under standard
spatial channel models with and without the presence of user
phantom. The measurement results have shown that the nearby
user phantom can significantly affect the MIMO performance.
However, its impact on the test zone size of the MPAC system is
negligible, since emulation accuracy in terms of received power,
branch power ratio (BPR), antenna correlation and measured
throughput under the target and the emulated channels is not
affected by the presence of user phantom. Moreover, results
measured with the synthetic MPAC method generally match those
obtained with the reference two-stage method. These findings are
valuable inputs for the ongoing MIMO OTA harmonization work
in the standardization.