Challenges and Solutions in Full Duplex Communication

This article discusses the challenges and solutions in full duplex communication systems. It explores the concept of full duplex operation and its potential in improving spectral efficiency and data rates. The article also delves into the self-interference cancellation methods and the limitations of hardware. It concludes by highlighting the potential of full duplex technology in enhancing wireless communication systems.

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Introduction
The spectral efficiency network requires intense and elaborate improvements if the aim of
ensuring the ever increasing data rates is anything to go by. The wireless communication system
operation nevertheless to a great extent depend on half duplex operations that often resulting in
deterioration of exploitation of resource. The anticipation of radical full duplex operation which
is an advancement of the half duplex operation is usable in improving the attainable spectral
efficient of wireless communication systems through receiving as well as transmitting all time
round in the whole bandwidth (Bi, Zeng and Zhang, 2016). The promise of almost twice capacity
of the channel in comparison s with conventional half duplex communication is the major
driving force for the advances in full duplex wireless communication systems hence providing
possibility of sustaining as well as complementing the evolution in the technologies of the fifth
generation in the direction of denser homogenous networks associated with high flexible relaying
modes.
Challenges with full duplex communication
In the recent past, a range of practical as well as theoretical components of full duplex
communications have been studies through quantification of the gains in the performance of full
duplex modes that show benefits in comparison with the half duplex modes with regard to either
having an enhanced throughput otherwise a greatly lowered outage probability, despite this being
attained at the expense of enhanced complexity (Chung et al., 2015). Still, the recent
development in full duplex communication has raised the diversity orders as well as the
throughput of wireless communication systems. It is highly possible for a full duplex device to
lower the bit rate error as soon as the complexity of the software or hardware is tolerated towards

facilitation of more complicated signal processing. Besides, the packet loss ratio of dull duplex
modes may as well be lowered as long as larger buffer size is offered by full duplex device.
Nevertheless, as a limitation or drawback, full duplex gain is deteriorated by self-interference as
due to large difference in power that exists between imposed by transmission of a device and
lower power that is received coming from remote transmit antenna. Excessive self-interference
may even lead to lowered capacity for full duplex systems which fall beneath the values of half
duplex system (Liu et al., 2015). An agreement arrived at by the scholars and the industry
illustrated that it is of importance to carry out efficient self-interference cancellation or
suppression in implementation of radical full duplex communication systems.
Other than above mentioned issues with physical layers, there is need for more refined and
further studies on the conception of the protocols of full duplex Media Access Control expected
showed that full duplex schemes may not often shown better performance than their half-duplex
counterparts as well hybrid schemes which change between half duplex modes and full duplex
modes may as well be developed for exploitation of the radio resources adaptively even as they
maximize spectral efficiency. Still, a full duplex scheme might often perform better than the half
duplex thereby resulting in the need to have a hybrid scheme implemented to enjoy the benefit
over either of the individual schemes.
Self-interference cancellation
The available literature demonstrated that it is of importance to precisely take measurement as
well as suppress the self-cancellation in full duplex communication. For instance, a study
conducted showed that the power of self-interference as well as spatial reuse might significantly
lower full duplex in comparison with half-duplex mode with regard to the capacity of the

network level making it be less than 2 in most cases. Suppose the self-interference levels of the
full duplex relay input may be not less than 3 dB less than the level of noise, the residual self-
interference may not have a significant degradation effects to the end to end throughput. There
are two main classifications of the SI cancellation methods: passive suppression as well as active
suppression (Mehmood et al., 2017)
I. Passive SI suppression
Passive suppression in self-cancellation refers to a situation in which the attenuation of signal
power imposed by path loss as a result of physical separation between receives as well as
transmits antennas of the very device. Among the techniques of passive SI suppression is:
SI cancellation & Antenna separation: One of the most effective approaches to attenuation the
SI power is through an increase in path loss between receive & transmit antennas in which
method higher separation of antenna means a netter performance of SI suppression. The natural
isolation may as well exploit neighbouring buildings or even beneficial incorporation of
shielding plate when depending on antenna separation as long as the strict limitations on device
are satiable.
Directional SI suppression: The key radiation modes of receive/transmit antenna for full duplex
device in this technique have limited intersection allowing partial suppression of the SI before
the radio frequency front end of the receiver (Noh et al., 2017).
II. Active SI suppression
Experimental studies demonstrated that the methods of SI suppression are able to enhance full
duplex communication at limits to the tune of 6 meters as well as transmit powers of the normal
WiFi devices showing the level of interference may be lowered by a range of 50 dB and 40 dB

when in scenarios of static as well as dynamically eroding interference channel respectively
suppose the RF SI canceller is joined with baseband canceller. Active suppression methods may
be classified further into analog cancellation, digital cancellation as well as combination of
analog/digital cancellation.
Analog cancellation: In such method, the group of time domain cancellation algorithms
including the methods based on training may be adopted by SISO as well as multiple input
multiple output based methods in which multiple input multiple output methods may carry out SI
suppression through exploitation of the spatial diversity attained by related multiple transmit or
receive antenna (Siddique et al., 2015).
Digital cancellation: As the analog SI cancellation is often non perfect, remaining residual SI
upon analog cancellation ought to be further lowered using digital cancellation. Zigzag shows
higher advantage among the current methods of digital cancellation with regard to attainable full
duplex gains. It should be noted than Zigzag does not impose any changes on conventional IEEE
802.11 MAC protocols in cases there are no collision hence keeping the very throughput like
colliding packets were meant priori in different time slots in transmission collision presence.
Besides numerous other challenges have to be dealt with regard to extra challenges in the context
of the available active suppression methods. Some of possible solutions are as discussed:
Combining Active and Passive Suppression: A scheme with high capability can be attained
through combining active as well as passive techniques as none of each of the techniques of
cancellation is able to meet the requirements of the system with regard to the achievable SI
cancellation ability.

Configuration of antenna for limited size full duplex devices: The best possible antenna with
regard to the attainable SI suppression in passive SI configuration schemes may be attained upon
installation of the antennas of transmit and receive on the device’s opposite sides to generate
enough separation demanding that the device be sufficiently large (Wang et al., 2015).
Approaches of low capacity spatial domain: Most of the available spatial domain SI techniques
depending on computations of complex matrix may to a great extent erode the full duplex gains
as a result of infeasibility hence low complexity algorithms conceived for MMO channels that
have high dimensions are able to significantly enhance the capability of SI cancelation at
relatively reasonable cost of hardware or software.
Transmission of power for enhancing SI suppression: A higher transmit power will
automatically result in a reduced estimation error of the SI channel even the absolute level of
remaining SI power may still enhance for high power of SI, in spite of ratio between residual
error and entire SI may be lowered (Zhang et al., 2016).
Other challenges of full duplex transmission have addressed in the context of the economical or
technical challenges that have made realization of full duplex implementation in the commercial
setup a nightmare:
I. Hardware limitations
An analysis of performance of co-channel full duplex modes based MIMO output modes was
done with regard to modelling of their realistic hardware features. A full duplex system that has
an infinite dynamic range as well as perfect estimation in the theoretical aspect may eliminate the
SI signal to perfect levels (Wei et al., 2016). Nevertheless, the imitations of hardware among

them non-linearities, quantization of transmit/receive signal among other all may deteriorate
practical applications of full duplex systems.
II. Receiver combining
Other than the drawbacks as a result of SI signal and hardware limitations, the notion that full
duplex based systems may not be able to invoke certain complicated combination of schemes
including maximum ratio combining not unless the full duplex based really and source not are
phase synchronized perfectly is yet another challenge. This may be addressed by deployment of
a co-phasing scheme in the in the direct as well as relaying links which result in significant
coherent combining gain at end (Zhang et al., 2015).
Conclusion
The full duplex technology has been suggested with anticipation of almost doubling rate of data
when compared with conventional half duplex system since throughput needs may not be met
readily without enhancing attainable self-efficiency in bits per second per Hertz. The full duplex
device possibly promotes simultaneous transmission as well as reception with the same band of
frequency. Self-interference which induces erosion of performance is one of the greatest
challenges of implementation of full duplex communications that needs to be cancelled to
suppress to levels that can be tolerated.

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