Page 100 - 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

proposed method and its characteristics in a variety
of environments, we assume a propagation channel
model featuring identically distributed (i.i.d.)
Rayleigh fading (uncorrelated paths). In short, we
substitute values for the Rayleigh distribution and
uniform distribution in the amplitude and phase
components, respectively, of Eq. (3) and Eq. (4).
Furthermore, we set the SNR of each receiver, i.e., γ
in Eq. (12) and Eq. (13), to 10 dB and interference
threshold (INR) to 1 dB.

Now, denoting SNR as γ, the channel capacity of
directly SISO communications not using IRS
reflectors can be written as follows:

SISO = log (1 + ), (19) Fig. 4 – Channel capacity when partitioning into 5 clusters
2
Since γ in this simulation is 10 dB, a channel
capacity exceeding approximately 3.5 bit/s/Hz
would demonstrate the effectiveness of
propagation path control by IRS reflectors.

4.1 Comparison of channel capacities
We evaluated the Cumulative Distribution Function
(CDF) of channel capacity obtained by receiver D

(see Eq. (12)) when partitioning a total of 100 IRS
reflectors into 5 or 10 clusters and inputting the
representative values of those clusters into the
solver. Here, to clarify the characteristics of the
proposed method, we compare its results with
those of a method that selects IRS reflectors
randomly (random method) and a method that Fig. 5 – Channel capacity when partitioning into 10 clusters
applies k-means clustering with no cut-offs (k-
means method).
The results of selecting 5 IRS reflectors from out of
100 IRS reflectors are shown in Fig. 4. With the
proposed method, approximately half of the
channel capacity values were greater than 4
bit/s/Hz thereby exceeding the channel capacity of
SISO communications while maintaining the
allowed amount of interference. Since the amount of
interference is constrained as in Eq. (15), it is
always less than the interference threshold. On the
other hand, the performance of the k-means method
was worse than that of the random method with
approximately half of the channel capacity values
falling under 1 bit/s/Hz. We consider the reason for Fig. 6 – Number of cluster partitions versus channel capacity in
this to be that the number of combinations the proposed method
satisfying the allowed INR of interfered receiver P The results of selecting 10 IRS reflectors from out of
was small since the difference in amplitudes among 100 IRS reflectors are shown in Fig. 5. For the
the clusters was large, which decreased the number random method and k-means method, the worst
of combinations that could improve the capacity of value was still 0 bit/s/Hz, but that of the proposed
receiver D.
method was greatly improved to 2.5 bit/s/Hz so
that the channel capacity of SISO communications

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