Received Signal Modelling for Millimeter Wave and Terahertz Systems with
Practical Impairments
Abstract
For wideband transceivers operating at millimeter wave and terahertz
frequencies, the implementation of conventional digital predistortion
for nonlinearity mitigation faces significant challenges due to the
limited availability and/or complexity of high-speed digital signal
processing. In this paper, a simple received signal model is proposed
for wideband system with nonlinearity and other practical impairments,
such as transmitter (Tx) and receiver (Rx) I/Q imbalances (IQIs),
carrier frequency offset (CFO), and phase noise, to enable
low-complexity impairment mitigation. An expanded memory polynomial
(EMP) model is firstly proposed to capture Tx IQI and the nonlinearity
over the entire transceiver chain. Exploiting the CFO and a novel
transmission protocol, a blind Rx IQI estimation is also proposed. The
noise enhancement after Rx IQI and CFO compensation is then evaluated as
a noise factor related to the mean-square-error of the Rx IQI
estimation. As a result, the received signal of the wideband system is
finally modelled as an EMP plus additive noises followed by a
band-limited noisy receiver filter. Simulation results using a
millimeter wave system with 2.5 GHz bandwidth and 73.5 GHz carrier
frequency are presented to verify the accuracy of the EMP modelling and
validate the theoretical analyses.