Challenges and Solutions in Full Duplex Communication

This article discusses the challenges and possible solutions in full duplex communication, including self-interference cancellation, hardware limitations, receiver combining, and more. It also highlights the need for efficient SI suppression and full duplex-based MAC layer protocols. The article concludes with future research opportunities in the field.

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Introduction
Further improvements must be done to the spectral efficiency of various networks in a bid to enhance the
delivery of the ever increasing rates of data. The operational systems of wireless communication
nevertheless depend upon the operation of the half-duplex that is turn cause exploitation of resource
erosion. The pledge of full duplex on contrary promotes the attainable spectral efficiency wireless
communication systems through ever having the transmission as well as reception within the whole
bandwidth (Arachchillage et al., 2018).
The pledge of almost twice channel capacity in comparison with existing half duplex communication
remains the main driving force for the further development that occurs to full duplex communication
hence providing the ability of complimenting as well as sustaining the progressive evolution in the
technologies of fifth generation in the direction of denser heterogeneous networks associated with flexible
relaying modes.
Investigations have been carried out in the recent past on an avalanche of practical as well as theoretical
aspects of full duplex through quantification of the gains of performance of full duplex modes which
show benefits over half duplex mode with regard to having lowered outage probability or increased
throughout even though attained at expense of enhanced complexity. Still, the recent advances
experienced in full duplex communications have resulted in an increase in attainable throughput alongside
orders of diversity of systems of wireless communication (Vial et al., 2017).
Nevertheless, a drawback of the full duplex gain revolves around erosion by self-interferences as a result
of the enormous power difference that exists between the imposed power by own transmission of device
and receiver signal having low power as generated from a remote signal antenna.
Challenges associated with full duplex and possible solutions
In as much as very little full duplex realizations have been adopted in the commercial set ups as a result
of the technical as well as economic challenges, a significant level of research has been undertaken
already through addressing numerous challenges as shown below:
Self-interference cancellation
Existing research demonstrate that it is of importance to precisely measure as well as supress the self-
interference in full duplex communication. For instance, the self-interference power and spatial reuse may
to signficnt levels lower the full duplex gain over half duplex with regard to the capacity of network
levels making it less than 2 in frequent cases (Wang and Zhang, 2016). Suppose the self-interference level
at the full duplex relay input however be at least less than 3 dB less than the level of noise, the remaining
self-interference is least likely to degrade t end to end throughput. Self-interference methods are often
grouped into passive as well as active suppressions.
Passive self-interference suppression: This refers to the attenuation of path loss imposed signal power as
resulting from physical separation between receivers as well as transmit antennas of the very device
(Poncha et al., 2018). Among the various techniques of a typical passive self-interference suppression are
inclusive of:
Directional SI suppression where key radiation lobes of antennas of transmit or receiver of a full duplex
device bear minimal intersection resulting in partial suppression of the Si before the FR front end of the
receiver.
SI cancellation & antenna separation: Enhancing the path loss that exists between the transmitter and
receiver antennas compose a proper approach for attenuation of the SI power where a higher separation of
antenna means better performance of SI suppression. The natural isolation is as well likely to exploit the

neighbouring structures or the advantageous inclusion of a shielding plate when depending on antenna
separation, offered strict limitations is put on the size of the device may be attained (Liu et al., 2016).
Active self-interference suppression: Active self-interference suppression techniques have experimentally
been illustrated to be able to facilitate full duplex communication within ranges to the tune of 6 meters as
well as transmit powers ideal for Wi-Fi devices, showing the level of interference may be lowered by 50
dB as well as 40 dB respectively under static and dynamic channel scenarios of fading interference in
case an RF self-interference is joined with baseband canceller. The group of active suppression methods
may be further grouped unto digital cancellation, analog cancellation as well as combined digital and
analog cancellation as determined by the various features (Li, Fei and Zhang, 2018).
Hardware Limitation
Co-channel FDM-based MIMO nodes’ performance has been studied within the contexts of modeling the
realistic hardware features. An FDM system with an infinite dynamic range as well as perfect estimation
of channel is able to significantly remove the SI signal. Nevertheless, the limitations in hardware
inclusive of quantization of transmission/receive signal, quadrature as well as in-phase mismatch as well
as nonlinearities among others all may erode the realistic implementation of FD systems.
Receiver combining
other than impairments as a result of SI signals as well as the challenge of hardware limitations, another
issue is derived from notion full duplex based systems may be unable to invoke some complicated
combining schemes for instance maximum ratio combining otherwise if source node as well as full
duplex-based relay are phase-synchronized in a perfect manner. A co-phasing scheme may be included in
direct as well as relay joins that serve to facilitate a relatively high coherent combining gain at destination
(Hu et al., 2016).
Relaying of Hybrid HD/FD
It is not automatic and obvious that full duplex will always perform better than half duplex with regard to
throughput or outage probability of channels especially in cases where full duplex is suffering from high
residual self-interference power. A hybrid HD/FD scheme that allows switching between full duplex and
half duplex may hence be anticipated to perform better than full duplex or half duplex operating alone
(Jagyasi and Ubaidulla, 2019).
Conclusion & Future research
In as much as full duplex methods are able to enhance to significantly levels achievable spectral
efficiency and network throughput in comparison with the classic half duplex approach, efficiency SI
suppression as well as full duplex based MAC layer protocols are significantly needed. Among the
opportunities that can be used for future research which include problems that have not been solved
include:
Issues of full duplex-based device sophistication: The cost as well as the complexity of full duplex based
devices is increased by conducting powerful SI cancellation majorly since complex computations have to
be carried out at transceiver. Still, hardware limitations would as well contain full duplex gain
performance.
Design of full duplex-based MAC-layer protocol: Other than the solutions of physical layer that have
been discussed, an adequately designed full duplex MAC-layer protocol that ought to be backward-
compatible with current half-duplex based MAC-layer protocol is needed to aid in avoidance of problems
including hidden terminal within multihop networks. Still, full duplex based MAC-layer protocol ought
not to favour the chances of full duplex unduly over the flows of half-duplex that needs the mechanism of

access to be in a position to provide fair chance for all nodes for accessing shared platform (Chalise, Li
and Ma, 2019).
Issues with low energy consumption: As most of the terminals tend to be battery driven and are of limited
capabilities of energy, the dissipation of energy of full duplex-based MAC-layer protocols is still
challenge. IT is of importance to come up with cost effective full duplex-based MAC-layer protocols
having low consumption of energy to make longer the recharge time of the battery as well as the overall
survivability of the network.

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