Today’s fourth generation (4G) cellular mobile communication networks are tasked
with providing service for an ever increasing number of mobile users and their demand for
increased data rates. The fifth generation (5G) of cellular mobile communications will be
required to be able to handle the burden currently on 4G networks and also service new
technologies as they are introduced. Massive multiple-input multiple-output (MIMO), Millimeter
Wave (mmWave) and beamforming have recently been identified as a key enabling
technologies for the fifth generation (5G) of cellular mobile communications. Current
transmitter typologies exhibit non-idealities that are non-negligible in practical hardware,
especially when transmitting wideband mmWave signals. This leads to the requirement
that RF building blocks, such as PAs and quadrature modulators, and their respective
nonlinearity, and I/Q imbalance must be corrected for.
This thesis proposes a new method to concurrently identify and compensation the I/Q
imbalance in mmWave MIMO direct-conversion transmitters (Tx) using a single transmitter
observation receiver (TOR). New 5G standards for mm-wave transmitters have
strict error vector magnitude (EVM) requirements; however, adjacent channel power ratio
(ACPR) requirements are typically relaxed. Therefore, this thesis also proposes judiciously
engineered uncorrelated training signals for minimizing the error vector magnitude (EVM)
while maintaining acceptable performance in the out-of-band region. The latter is necessary
to ensure proper Tx linearization when applying digital predistortion (DPD). The
proposed method was validated using a 4 GHz signal in ADS simulation for 1, 2, 4 and 8
Tx chains as well as in measurement using a custom built transmitter comprised of 1, 2
and 4 mm-wave Tx chains utilizing commercially available quadrature modulators. NMSEs
of 19.9% before and 2.25% after I/Q imbalance compensation were obtained. Finally,
the compensation accuracy of the proposed method was further confirmed when the I/Q
compensation filters are calculated in back-off and applied during the DPD linearization
of a mm-wave power amplifier (PA)
