Page 57 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 6 – Wireless communication systems in beyond 5G era

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 6

Fig. 2 illustrates the architecture of an analog RS. An all channel responses of BS-UE(considering all RSs)
analog RS node has two sides, of which one is the and BS-UE(direct path), as defined as follows.
receiving side and the other is the transmitting side. ℎ ( , , ) =
As shown in the figure, both sides are assumed to be URB UE BS
able to perform high-performance dynamic beam RS (4)
control. The analog RS is supposed to be an AF RS ∑ ℎ ( , , ) + ℎ ( , , )
that can amplify the received signal and transmit it =1 URB UE BS UB UE BS
without latency.
2.2 Artificial channel response by massive 2.3 Artificial MIMO channel matrix
analog relay In this paper, the hybrid beam-forming that

Artificial propagation channels generated by the combines analog BF and digital pre/post-coding is
massive analog RSs are shown in Fig. 1. The angles used to efficiently realize massive MIMO
of arrival RB and departure RU at the RS (BS side transmissions [18]. The BS prepares antenna
BS
and UE side) shown in Fig. 1 are described beam candidates and stacks them into BS × 1
by the azimuth angle and elevation angle, antenna directivity vector BS . According to the
i.e., RB = ( RB , RB ) and RU = ( RU , RU ). condition of the artificial channel response in
Eq. (4), the BS selects beams (spatial streams)
The channel response of BS-RSi is denoted as out of beam candidates for MIMO multiplexing.
BS
ℎ RB ( RB , , ) and that of RSi-UE is denoted as On the other hand, the UE always uses × 1
BS
UE
ℎ UR ( UE , RU , ). = 1, … , is RS index, and antenna directivity vector UE stacking
RS
RS
UE
is the number of analog RSs. The channel response antenna beams.
of BS-UE (direct path from the BS to the UE) is
defined as ℎ UB ( UE , , ). The channel response The UE × artificial MIMO channel matrix ( )
BS
BS
(including the RS antenna directivity) of BS-RSi, including antenna directivities of BS and UE is
denoted by ℎ RB ( , ), is defined as follows. defined as follows.
BS
)
ℎ RB ( , ) = ( ) = ∫ ∫ UE ( UE ⋅ ℎ URB ( UE , BS , )
BS
UE BS (5)
(1) T

∫ RS,r ( RB )ℎ RB ( RB , , )d RB ⋅ ( BS ( BS )) d BS d UE
BS
RB
where is BS × BS beam selection matrix

where RS,r ( RB ) is the antenna directivity of RSi defined as follows.
(BS side).
1 0
The channel response of RSi-UE, denoted by = [ ⋱ ] (6)
ℎ UR ( UE , ), is defined as follows. 0 BS
ℎ UR ( UE , ) = where ∈ {0,1}, ∑ BS = . is 1 if the

=1
(2) -th beam is selected, and 0 otherwise. In order to

∫ ℎ UR ( UE , RU , ) RS,t ( RU , )d RU determine , not only BS beams are selected, but
RU also RSs are used for relaying.
2.4 Noise vector with massive analog relay

where RS,t ( RU , ) is the antenna directivity of RSi
(UE side). In the process of relaying signals from the BS to the
UE, not only desired signals, but also noise are
The channel response of BS-RSi-UE, denoted by amplified and forwarded in each RS, which should
ℎ URB ( UE , , ), is defined as follows. be taken into consideration in the system analysis.
BS

RS
ℎ URB ( , , ) = ℎ UR ( UE , ) ℎ RB ( , ) (3) ( ) is the UE × 1 noise signal vector from all
BS
BS
UE
RSs received by UE and is defined as follows.

where is the amplification coefficient in RSi. ( ) =
RS
RS
(7)
The artificial channel response considering all RSs, ∫ UE ( UE ) ∑ ℎ UR ( UE , ) d

UE

denoted as ℎ URB ( UE , , ), is the summation of UE
BS

© International Telecommunication Union, 2021 45