WSU Master of Engineering: Full-Duplex Communication Systems Report

This report delves into the complexities of full-duplex communication systems, a crucial technology for 5G networks. It examines the concept of simultaneous data transmission and reception, highlighting its potential to double data rates without increasing bandwidth. The report identifies key challenges, including self-interference cancellation due to signal distortion from both linear and non-linear impairments of analog equipment, antenna sharing, and the need for wideband RF cancellation. It explores various solutions, such as circulators, electrical duplexer balances, and active RF cancelers, while addressing issues like circulator leakage, impedance mismatch, and the impact of environmental reflections. The report emphasizes the importance of both analog and digital domain signal attenuation to achieve the necessary level of self-interference suppression, and the need for adaptive RF cancelers. The conclusion underscores the need for full-duplex mobile devices to accommodate antenna sharing, adapt to channel variations, and overcome circuit-induced impairments to realize the full potential of this technology for increased data rates in 5G and beyond.

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FULL-DUPLEX COMMUNICATION
By (Student’s Name)
Tutor’s Name
University
City
Date

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Introduction
Full-duplex communication ensures data transfer simultaneously in two directions (Pirinen,
2014). Full-Duplex communication systems are majorly taken to be among the better solutions to
greater wireless networks that are spectrally efficient (M et al., 2015). The reason behind this
notion is to make it possible for utilizing the already existing spectral and temporal resources to a
great deal of extent during the simultaneous transmission and reception of data signals using a
similar data frequency centre. In theory, achieving such technology would be doubling the rate of
data without needing additional bandwidths (Ma et al., 2015). This important in the development
of the 5G era (Ma et al., 2015). The full-duplex communication, therefore, could be a crucial step
and an enabler to the required huge increase in data transmission. Hence, the implementation of
full-duplex is one tempting project. This article will be looking into the challenges, possibilities
and solution for implementing the full-duplex on personal communication systems.
Issues
In theory, the well-known cancelling self-interference is well achieved by the subtraction of the
transmitting signal from the total receiving signal waveform (Ma, et al., 2015). In practice,
however, the SI signals are always distorted in a nonlinear or linear manner during attempts for
propagating and reception. Hence, there exist trivial difficulties in accurately reproducing a
sufficient signal cancellation. How the SI signals are attenuated using enough quantity is the
central problem for researching that requires resolving before the implementation of practical
full-duplex communication systems.
There is a non-linear distortion of coming from impaired analogue equipment (Fettweis &
Alamouti, 2014). This issue is prominent in mobile scale devices that make use of low-cost RF

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components that are mass-produced. This reason creates a typical assumption that the personal
communication networks have their base stations able to use the full-duplex mods for
communication while the mobiles are half-duplex.
On the other hand, giving a limit to only the network element side’s operation for full-duplex is
not the way to capitalize on the full-duplex principle’s full potential. When the mobile devices
have the capability to use full-duplex, is when the total rate of data for corresponding personal
communication increase (Zhang, et al., 2017).
Challenges
Firstly, there exists a restricted dimension within the full-duplex personal communication
transceiver and this gives a possibility of a non-existing space for separating the receive and
transmit antennas. Therefore, it means that the receiver and the transmitter will have to share the
antenna (Boccardi, et al., 2013). Despite sharing the antenna, the devices have to maintain a good
quantity of isolation between their operation goals (Thompson, et al., 2014).
Additionally, due to the wide bandwidth exhibited by the modern communication waveforms,
technical wideband cancellation process within the analogue domain should be achieved in a
related full-duplex personal communication link. These RF circuits for cancellation feasibility
have been tried out in practice to see their success. What remains is the implementation of
wideband RF scaling for personal communication hence enabling the receiver and the transmitter
to use the same antenna (Aijaz, et al., 2017).
One more aspect lies in the quality within the analogue components (Aijaz, et al., 2017). In
particular, the components that are costing low, hence leading to SI signal distortion. The linear
digital processing circuit then fails to reproduce as well as cancel the SI residual waveform with

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accuracy. Therefore, advanced processing and modelling are in need of producing sufficient and
accurate cancellation signals.
Problems and Solutions
Signals are mostly difficult to reproduce due to distortion (Thompson, et al., 2014). However, the
circulator is one constituent that allows the receiver and transmitter in full-duplex mobile devices
using one antenna. The circulator links the transceiver with the antenna. The signals enter using a
single port and leave the circulator using the other port, based on the rotation direction. Every
circulator ports apply this principle, which makes sure that there is some specific isolation
quality between the receiver and the transceiver (Zhang, et al., 2017).
Another approach for receiver and transmitter isolation using a single antenna is by the
application of the electrical duplexer balance (Fettweis & Alamouti, 2014). Substantial isolation
volumes between the receiver and the transmitter will be obtained where the hybrid transformer
has been applied. There are various ways of implementing the electrical duplexer balance into a
significantly compact form rather than circulators. This renders it highly preferable devices for
mobiles. An electrical duplexer balance is the most suitable candidate to be implemented in
future.
Two great constituents present in the SI signal are seen towards the path for the receiver when
the architectural circulator is applied (Zhang, et al., 2017). First, attenuation of the SI at a
minimum of 20dB results in the circulator leakages. The reflected power from the mobile
antenna is the second great feature brought about by the failure of the impedance to match during
input. The antenna only feeds in upon the accurate matching of the input. The mismatch always
results in the reflection of partial power back to the line of transmission. Therefore, greater

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matching values are excellent because of their direct translation to lower SI volumes. It is rare to
achieve higher values that match above -20 dB despite the application of the off-the-shelf
antenna.
Components that are very weak inside the SI signal composite are majorly formed by the
reflection of the many paths from the around environment which are eventually transmitted into
the antenna (Zhang, et al., 2015). The numerous path reflections are in most cases very weak
compared to the antenna reflections or the leakages via the circulator. Therefore, variations in the
closer antenna zones will have an impact on its matching resulting in the direct variations in the
volume of power reflected.
It is important to have extra SI attenuations for the digital and RF or analogue domains due to
reflections resulting from the environment around and from the antennas as well as the leakages
via the circulator (Zhang, et al., 2015). Generally, before getting into the receiver chain, the SI's
attenuation analogue signals need to be enough to make sure that:
 The dynamic ADC’s ranges are very high in order for the SI residual to be captured and
also the interesting received signals that are weak comprising enough precision.
 The levels of power are not very high for the low-noise amplifier receiver so as to avoid
saturation of the receiver.
Depending on whether these could also be the limitation factors or not, lies on the receiver itself.
The passively attenuated SI produced by the matched antenna and isolation of the circulator is
not enough to meet the given requirements (Talwar, et al., 2014). Significant motivation is
formed which actively cancels the RF that offers additional suppression of SI prior to the real
receiver chain. The canceler of an active RF in the full-duplex mobile device should be able to

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cancel wideband efficiently (Ratasuk, et al., 2015). This is achieved through the analogue SI
multi-tap canceler in which many transmit signals copies are differently delayed will play as
reference signals whereby, every signal has tunable phase and amplitude. The cancellation circuit
aims at matching the amplitudes and phases of the reference signal, that is to say, that the
cancellation signals generated are matching with the SI composite signals resulting from the
antenna and circulator prior the receiver chain at the summing node (Eid, et al., 2011).
The full-duplex mobile devices have other concerns to be put into account such as enough
adaptability within the RF canceler. In order for the cancellation signals’ control of the
amplitudes and phases to obtain self-adaptability, so as to be able to detect sudden variations in
the antenna at closer proximity, the SI cancellation must be efficiently supported under actual
states. For example, the control may be automated by the application of the analogue or digital
tracking circuits if the level of power is being monitored at the point of canceller output (Talwar,
et al., 2014). Therefore, the SI cancellation analogue signal can tune itself.
Additionally, the SI analogue cancellation independently is typically insufficient for attenuation
lower than the noise floor receiver. Therefore, the residual SI final attenuation should be
conducted within the digital domain. The construction of the cancellation signal may be obtained
from the original data transmitter through filtration in regards to the remaining SI effective
channel, if it is performed in the digital domain (Wu, et al., 2014). The major advantage of SI
digital cancellation is that it is very easy to add the SI waveform’s nonlinear modellings. The SI
channel by nature accommodates the self-tracking features by adaptive filtration. Hence, the
processing of the nonlinear digital adaptive signal makes sure that the tracking and cancellation
of residual Si are done efficiently.
Conclusion

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This paper has investigated the enormous problems in regards to the full-duplex communication
devices as well as a description of the solutions to the challenges (Fettweis & Alamouti, 2014).
To be specific, full-duplex mobile devices should be able to accommodate the operation of
sharing an antenna, and also be able to adapt to the variations in the channel surroundings (Wu,
et al., 2014). Given that mobile devices depend on affordable materials, the many impairments
induced by the circuit are supposed to be taken into account because they impact directly on the
capability of self-interference cancellation. Moreover, mobile devices currently should be able to
accommodate enormous wideband signals and make sure that a higher rate of data is achieved
(Fettweis & Alamouti, 2014).

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