Y9071B Datasheet, PDF (21/29 Pages) Keysight Technologies – Measurement Applications For the E6640A EXM Wireless Test Set

21 | Keysight | Measurement Applications for the E6640A EXM Wireless Test Set - Solution Brochure
Implicit transmit beamforming calibration
Beamforming is a technique in which the beamformer (the transmitter in beamforming)
uses the knowledge of the MIMO channel to generate a steering matrix that improves
reception in the beamformee (the receiver in beamforming). (See Figure 14.) It enables a
dramatic improvement in WLAN 802.11n and 802.11ac performance in terms of reliability,
range, and coverage. There are two categories of beamforming based on the methods of
getting channel knowledge:
Category 1: Explicit feedback
Here, the beamformee makes a direct estimate of the channel from training symbols sent
from the beamformer to the beamformee.
Category 2: Implicit feedback
Here, the beamformer receives long training symbols transmitted by the beamformee.
Implicit transmit beamforming is based on the assumption that the channel between
the beamformer and beamformee is reciprocal. The beamformer obtains a reverse link
channel estimate from a long training sequence in acknowledgements (ACKs). This
method also:
–– Calculates forward link HAB channel information, as shown in Figure 14
–– Applies channel compensation (and radio calibration) to a transmitted signal
For this to work, the transmit chain radio performance needs to be calibrated to com-
pensate for the transmit phase response. Implicit transit beamforming calibration testing
can be easily performed using EXM Option V9077B-KFP or V9077B-KTP.
H_AB
EXM WLAN MIMO Test
Solutions Summary
Small form
factor
Up to 4 TRXs to
support 4X4 True
MIMO in one 4U box
Easy set up
Easy to set up,
no need complex
connection for
synchronization
High
performance
Fast, accurate
and reliable MIMO
measurement and
detailed measurement
results
Beamformer
Beamformee
H_BA
Figure 14. The implicit feedback method assumes that the channel between the beamformer and beamformee is identical in the uplink and downlink
directions. Computation of correction matrices is required to eliminate any mismatch between the uplink and the downlink channels.
Table 10. E6640A MIMO test solutions summary and comparison
True MIMO
Use case
WLAN MIMO R&D and design and
validation
Test methods
Multiple analyzer/source pairs for
simultaneous test of all MIMO channels
EXM capability
Up to 4X4 MIMO
Hardware
EXM with multiple TRXs
(N TRXs for NxN MIMO )
Product option
E6640A-M22/M33/M44 for up to
2x2/3x3/4x4 MIMO
Switched MIMO
Cost-sensitive manufacturing
Sharing analyzer/source pair to measure
each MIMO channel in turn
Up to 3x3 MIMO
EXM with 1 TRX
Combined Stream MIMO
Implicit Tx beamforming
calibration test
Calibrate transmit chain radio
performance
Up to 8 streams
EXM with 1 TRX
V9065B-SFP/TP for up to 3x3 Switched V9077B-KFP/TP for up to 8
MIMO
streams