SYMBOL LEVEL PRECODING TECHNIQUES FOR HARDWARE AND POWER EFFICIENT WIRELESS TRANSCEIVERS

Large-scale antennas are crucial for next generation wireless communication
systems as they improve spectral efficiency, reliability and coverage compared to
the traditional ones that are employing antenna arrays of few elements. However,
the large number of antenna elements leads to a big increase in power
consumption of conventional fully digital transceivers due to the one Radio
Frequency (RF) chain / per antenna element requirement. The RF chains include
a number of different components among which are the Digital-to-Analog
Converters (DACs)/Analog-to-Digital Converters (ADCs) that their power consumption
increases exponential with the resolution they support. Motivated by
this, in this thesis, a number of different architectures are proposed with the
view to reduce the power consumption and the hardware complexity of the
transceiver. In order to optimize the transmission of data through them, corresponding
symbol level precoding (SLP) techniques were developed for the proposed
architectures. SLP is a technique that mitigates multi-user interference
(MUI) by designing the transmitted signals using the Channel State Information
and the information-bearing symbols. The cases of both frequency flat and
frequency selective channels were considered.
First, three different power efficient transmitter designs for transmission over
frequency flat channels and their respective SLP schemes are considered. The
considered systems tackle the high hardware complexity and power consumption
of existing SLP techniques by reducing or completely eliminating fully digital
RF chains. The precoding design is formulated as a constrained least squares
problem and efficient algorithmic solutions are developed via the Coordinate
Descent method.
Next, the case of frequency selective channels is considered. To this end,
Constant Envelope precoding in a Multiple Input Multiple Output Orthogonal
Frequency Division Multiplexing system (CE MIMO-OFDM) is considered.
In CE MIMO-OFDM the transmitted signals for each antenna are designed
to have constant amplitude regardless of the channel realization and the information
symbols that must be conveyed to the users. This facilitates the
use of power-efficient components, such as phase shifters and non-linear power
amplifiers. The precoding problem is firstly formulated as a least-squares problem
with a unit-modulus constraint and solved using an algorithm based on
the coordinate descent (CCD) optimization framework and then, after reformulating
the problem into an unconstrained non-linear least squares problem,
a more computationally efficient solution using the Gauss-Newton algorithm is
presented.
Then, CE MIMO-OFDM is considered for a system with low resolution
DACs. The precoding design problem is formulated as a mixed discrete- continuous
least-squares optimization one which is NP-hard. An efficient low complexity
solution is developed based also on the CCD optimization framework.
Finally, a precoding scheme is presented for OFDM transmission in MIMO
systems based on one-bit DACs and ADCs at the transmitter’s and the receiver’s
end, respectively, as a way to reduce the total power consumption. The objective
of the precoding design is to mitigate the effects of one-bit quantization and
the problem is formulated and then is split into two NP hard least squares optimization problems. Algorithmic solutions are developed for the solution of the latter problems, based on the CCD framework.