Page 12 - ITU Journal Future and evolving technologies – Volume 2 (2021), Issue 2

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 2

Low complexity full duplex MIMO systems: Analog canceler
architectures, beamforming design, and future directions

Pages 109-127
George C. Alexandropoulos

The hardware complexity of the analog Self-Interference (SI) canceler in conventional full duplex
Multiple Input Multiple Output (MIMO) designs mostly scales with the number of transmit and receive
antennas, thus exploiting the benefits of analog cancellation becomes impractical for full duplex MIMO
transceivers, even for a moderate number of antennas. In this paper, we provide an overview of two
recent hardware architectures for the analog canceler comprising of reduced number of cancellation
elements, compared to the state of the art, and simple multiplexers for efficient signal routing among
the transceiver radio-frequency chains. The one architecture is based on analog taps and the other on
AUXiliary (AUX) Transmitters (TXs). In contrast to the available analog cancellation architectures, the
values for each tap or each AUX TX and the configuration of the multiplexers are jointly designed with
the digital transceiver beamforming filters according to desired performance objectives. We present a
general optimization framework for the joint design of analog SI cancellation and digital beamforming,
and detail an example algorithmic solution for the sum-rate optimization objective. Our representative
computer simulation results demonstrate the superiority, both in terms of hardware complexity and
achievable performance, of the presented low complexity full duplex MIMO schemes over the relative
available ones in the literature. We conclude the paper with a discussion on recent simultaneous transmit
and receive operations capitalizing on the presented architectures, and provide a list of open challenges
and research directions for future FD MIMO communication systems, as well as their promising
applications.
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Infrastructure sharing model to connect the unconnected in rural areas

Pages 129-138
Ida Sèmévo Tognisse, Ahmed Dooguy Kora, Jules Degila

One of the major problems the telecommunication industry faces in providing connectivity to the
unconnected, particularly in rural and remote areas, is the lack of infrastructure in these areas. Indeed,
deploying a network in an isolated area can be more expensive for an operator than in an urban area,
while the return on investment is not possible. This is the primary cause of the coverage divide. To
remedy this, in this work, we propose a techno-economic analysis of infrastructure sharing. First, we
develop a mathematical model of the overall cost of extending a mobile network in rural areas. Different
scenarios involving infrastructure sharing at varying levels of deployment are then presented. Then,
using the models proposed in each scenario, we make a case study to deduce the most economically
advantageous scenario for operators to extend their networks to remote areas. This case involves the
sharing of passive infrastructure and also the sharing of active resources in a cloud-RAN. Based on the
proposed model, our simulation results show that while passive sharing is beneficial, active sharing
using cloud-RAN as technology increases this benefit. This work also indicates and highlights the
technical constraints to be respected in the sharing for this scenario.
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