Page 59 - 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

ℎ ( , ) =
BS
R 1 B
∫ ( , ) ℎ ( , , ) d (12)
R 1 r R 1 r R 1 B R 1 r BS R 1 r

R r
1
where is the receiving antenna directivity of
R r
1
the 1st-hop RSi.
The channel response between k-1th hop in RSi and
( ), is defined as
k-th hop in RSj, denoted by ℎ
R R
−1
follows.
Fig. 4 – System model for mmWave massive ℎ ( ) = ∫ ∫ ( , )
multi-hop relay MIMO R R R r R r
−1

R r R −1 t

∙ ℎ ( , , ) (13)
R R R r R −1 t
−1

, )
∙ (
R −1 t R −1 t
d
d
R −1 t R r

where = 1, … , RS is the RS index in k-th hop,
, are the antenna directivities in k-1th

R −1 t R r

hop in RSi in the transmitting side, and in k-th hop in
RSj in the receiving side.
The channel response between the k-th hop in RSi
and the UE, denoted by ℎ ( UE , ), is defined as
Fig. 5 – Multi-hop artificial channel UR
follows.
this one-dimensional arrangement is repeated for
the maximum number of hops. Assuming that the ℎ UR ( UE , ) = ∫ ℎ UR ( UE , , )
R t
maximum number of hops is K, the system consists
R t
of K times repeating of the one-dimensional (14)
arrangement of RSs as shown in Fig. 5. Finally, it ∙ ( , ) d
enables us to exhaustively represent all the routes, R t R t R t

including routes to the UE with 1 hop, routes with 2
hops, and routes with K hops. Then, RSs and routes where is the antenna directivity in k-th hop in
R t

for relay are picked up to form the artificial the RSi (transmitting side).
propagation paths. The single-hop channel response between the BS
As shown in Fig. 5, the angles of departure and and UE using RSi at 1st-hop, denoted by
(
arrival at the k-th hop of the RSi in the receiving ℎ UR B UE , , ), is defined as follows.
BS
1
side and transmitting side are defined ℎ ( , , ) =
as = ( , ) and = ( , ), where UR 1 B UE BS
R r R r R r R t R R (15)

= 1, … , RS is the RS index, = 1, … , is the ℎ ( UE , ) ℎ ( , )

BS
R 1 B
number of hop, and K is the maximum number of UR 1
hops. Both receivers and the transmitters of RSs are
assumed to be able to actively perform beam- The channel response between the BS and UE with
(
forming. The channel response between the BS and K hops, denoted by ℎ UR R ⋯R B UE , , ), is

BS
1
−1
RSi, denoted by ℎ ( , ), is defined as follows. defined as follows.
BS
R B
1

© International Telecommunication Union, 2021 47