Page 63 - 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

are done at three different UE positions result in Fig. 13 shows that the number of streams
y UE = 0,150, 360 m . It can be seen that as the in the LOS environment without hop is only one,
number of RSs is increased, channel capacity which indicates that MIMO transmission is not
increases, whereas when a certain number of RSs possible. The number of streams is obtained by both
are used, there is no more significant improvement single-hop and multi-hop more than seven, and it
of channel capacity. From different UE positions, it enables MIMO communications so that channel
can be understood that significant improvements of capacity is greatly improved. Especially at
channel capacity are contributed by RSs closer to intersections, number of streams is further
the UE. It indicates the effectiveness of dynamic RS increased in the multi-hop case compared to the
selection to improve channel capacity, and single-hop, because there are more available RSs
remaining RSs can be turned off to save power around these positions to create artificial channels.
consumption.
2) NLOS environment
4.2.2 Two-dimensional arrangement model Fig. 14 and Fig. 15 show channel capacities and

For the two-dimensional case, system performance number of streams plotted every 5m when UE
of multi-hop massive relay MIMO for mmWave moves along y-direction from (185, −55,3) to
communications is evaluated in three different (185,55,3). In the case of w/o hop, the result clearly
conditions: Condition 1) LOS environment where shows that without RS, mmWave communications
the UE moves along x-direction from (100,0,3) to are only possible when LOS path between the BS and
(210,0,3) in Fig. 8; Condition 2) NLOS environment UE exists. In the single-hop case, channel capacity is
improved in both LOS and NLOS positions compared
where the UE moves along y-direction from
(185, −55,3) to (185,55,3) in Fig. 8; Conditional 3)
Grid environment where the UE moves in a grid
among buildings in Fig. 8.
1) LOS environment

Fig. 12 and Fig. 13 show channel capacities and
number of streams plotted every 5 m when the UE
moves along the x-axis from (100,0,3) to (210,0,3).
Both single-hop and multi-hop relays improve
channel capacities when compared with the
conventional (w/o hop) method. Channel capacities
of more than 20 Gbps and 25 Gbps can be
respectively obtained. Multi-hop achieves a further
improvement over single-hop, especially at
intersections such as at UE =185 where available Fig. 12 – Position of UE(x-direction) and channel
RSs for single-hop are blocked by buildings. The capacity ( =0)

Fig. 13 – Position of UE (x-direction) and number of
Fig. 11 – The number of RS and channel capacity streams ( =0)
in one-dimensional arrangement model

© International Telecommunication Union, 2021 51