Page 68 - Kaleidoscope Academic Conference Proceedings 2021

2021 ITU Kaleidoscope Academic Conference

throughput of the uplink to the same level as the downlink. Received and filtered Convert to Transmit spectrum
Due to the finite frequency bandwidth, the enhancement of Transmitted spectrum in spectrum in THz band access-link in access-link band
band and
MIMO technology in the spatial domain is expected. In the THz band Power Amplify Power #1
#3
configuration of a conventional user terminal such as a Power #1 THz band #M Freq.
#2
Freq.
smartphone up to 5G, the number of transmit RF front-end #1 #2 #3 #M Freq.
modules and antennas and layers for MIMO transmission in THz band Device #1
the uplink are limited to two due to restrictions such as power Device #2 Access
Point #1
consumption and terminal size. In order to realize CF-
mMIMO, the user terminal also needs a multi-antenna Device #3 Access
Point #2
configuration that can efficiently achieve MIMO Main user
performance. On the other hand, wearable terminals terminal Access
equipped with wireless functions such as smart watches and THz band Point #3
smart glasses are becoming increasingly popular, and the Frequency division Device #M
multiplex in super
number of peripheral devices equipped with wireless wide terahertz band Access
Access-
functions around us is increasing in addition to PCs, tablets, Virtualized Terminal link band Point #N
and vehicles. Therefore, we think that it is practical to Cell-free massive MIMO in
configure a virtualized terminal by utilizing these peripheral the same frequency band
devices as MIMO antennas. We believe that transmission
from user terminals to peripheral devices can be achieved Figure 6 – Structure and uplink transmission of virtualized
with a small number of transmitters by using a super- terminals using terahertz communications
wideband and tremendously high frequency like the terahertz to be the same for the main user terminal and peripheral
band. Research has been conducted on applying the terahertz devices. Since the required SNR of QPSK is about 10 dB, it
band to the access link between the AP and the user terminal is confirmed that the virtualized terminal with the terahertz
[13], but research on applications such as virtualized band can be sufficiently realized with an antenna gain of 5
terminals used for relaying in the vicinity of the human body dBi when wearable terminals are assumed as peripheral
has not been conducted. devices. However, considering the feasibility of noise figures
of the terahertz band amplifier, it is considered necessary to
Figure 6 shows the structure and uplink transmission of a assume the use of an antenna that forms a high gain multi-
virtualized terminal using the terahertz band. The main user beam.
terminal is equipped with a terahertz transmitter and a broad
directional antenna, and simultaneously transmits super- Table 2 – Terahertz link budget conditions
wideband signals composed of sub-bands for the number of
peripheral devices. The peripheral devices filter and extract Parameter Value
only the corresponding sub-band, and convert terahertz
bands to access-link bands, amplify them, and transmit them Carrier frequency 300 GHz
to the access points. All access-link transmission signals Bandwidth 5 GHz / Peripheral device
from each peripheral device use the same frequency, and CF- Transmission power 10 dBm
mMIMO achieves high-speed transmission equivalent to the Propagation loss Free space path loss,
terahertz band. The downlink has a similar configuration, Atmospheric and rain
and vice versa. attenuation
Noise Thermal noise (290 K)
With such a simple analog frequency conversion function,
implementation in small wearable devices as peripheral
devices can be expected. In addition, regarding RF-front-
ends and antennas in the terahertz band, R&D aimed at
increasing output and gain is already underway with the aim
of applying them to fixed wireless access over long distances
[13]. Application of short-range wireless to peripheral
devices such as wearable devices can be expected as a new
realistic use case.

A case study was calculated for the feasibility of the link
budget when the terahertz band is applied to virtualized
terminals. Table 2 shows the conditions of the link budget.
In this case, assuming polarized MIMO and QPSK
modulation, 100 Gbps transmission can be achieved in the
transmission of a virtualized terminal by using five
peripheral devices. Figure 7 shows the distance Figure 7 – Distance characteristic in terahertz link for
characteristics of the SNR with respect to the antenna gain virtualized terminals
based on this link budget. Here, the antenna gain is assumed

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