Received signal strength

The received signal strength indicates the signal power measured in dBm that a UE receives from a BS in a cellular network. In NPO, engineers aim at providing the best possible signal level to ensure good user experience, which in turn gives a measure of the system performance.

Since only outdoor users are considered, some BSs did not have enough traffic at all serving the outdoor users and were therefore eliminated from the analysis. After filtering of outdoor users was done, the resulting outdoor users were 115 for the 2.1 GHz and 104 users for the 28 GHz scenario. Due to the limited number of users, the smoothness of the curves is not as expected. The system performance is also affected by the position of the user relative to the position of the serving cell. The mean and median values of the received signal strength are given below.

Mean and median of received signal strength at 2.1 GHz.

Scenarios Reference Masking Masking with down tilt

Mean(dBm) -60.70 -41.11 -37.41

Median(dBm) -59.03 -40.17 -36.59

From Table 5, the mean of the reference received signal strength between the 3 scenarios have highly varying values, with the reference values lower than those of the masking and masking with down tilt scenarios.

CDF of received signal strength of all simulation scenarios in 2.1 GHz.

Figure 22 illustrates the power received by the users in all scenarios in the 2.1 GHz frequency transmission simulation. There is a stark difference in the average values of the received signal strength between the reference scenario with the average received signal strength being 59.8 dBm. The average received signal strength with the masked antenna is -40 dBm and -36.8 dBm for the antenna masking with the down tilt angle scenario. Therefore, the conclusion is that antenna masking improves the signal strength to users, avoiding wastage of signal power because of radiating equally in all directions as it is the case with the isotropic antenna. There is a difference of about 4 dB between the sectorized antenna with masking but no tilting and the scenario with both masking and down tilt. The received signal strength with the latter scenario is stronger, with the conclusion that it is the best implementation in a cellular network.

The received signal strength was also evaluated in the 28 GHz frequency scenario, and the results show a similar pattern to those of the 2.1 GHz frequency band. Table 6 gives the mean and median values of the received signal strength in all scenarios.

-90 -80 -70 -60 -50 -40 -30 -20 -10 0

Received signal strength (dBm)

10 20 30 40 50 60 70 80 90 100 C D F

CDF of received signal strength for all sites: 2.1 GHz

Reference sum power 2.1 GHz

sum power with antenna masking 2.1 GHz sum power with masking and down tilt 2.1 GHz

Mean and median of received signal strength at 28 GHz.

Scenarios Reference Masking Masking with down tilt

Mean(dBm) -87.58 -66.33 -49.26

Median(dBm) -83.52 -66.68 -42.74

From Table 6, the mean of the reference received signal strength between the 3 scenarios have significant differences compared to the 2.1 GHz frequency band. The reference values are once again lower than those of the masking and masking with down tilt scenarios. The masking with down tilt scenario gives better performance than earlier two scenarios.

CDF of received signal strength of all simulation scenarios in 28 GHz.

Figure 23 shows the received signal strength for all users being served by all the sites in the 28 GHz frequency band. There are significant differences between all the scenarios than in the 2.1 GHz frequency band. The difference between the reference and the masked antenna scenario is about 21 dB, while the difference between the reference and the masking with down tilt scenario is 38 dB. Therefore, signal losses when using an isotropic antenna are significant in millimetre waves, and sectorization, masking and tilting have a big effect in high frequency band transmission.

-120 -100 -80 -60 -40 -20 0

Received signal strength (dBm)

10 20 30 40 50 60 70 80 90 100 C D F

CDF of received signal strength for all sites: 28 GHz

Reference sum power 28 GHz

sum power with antenna masking 28 GHz sum power with masking and down tilt 28 GHz

Figure 24 (a) – (d) illustrates the comparison between the 2.1 GHz frequency and the 28 GHz frequency in each simulation scenario. For the reference scenario has the largest difference between the 2.1 GHz and the 28 GHz. Since the isotropic antennas radiate equally in all directions, it is expected that the 28 GHz scenario experiences more losses as discussed in earlier chapters due to shorter wavelengths and higher diffraction and reflection losses.

(a) (b)

(c) (d)

CDF of received signal strength comparison between each simulation

scenario for 2.1 GHz and 28 GHz. (a) Reference, (b) Antenna masking, (c) Antenna masking with down tilt, (d) All scenarios in 2.1 GHz and 28 GHz comparison.

Figure 24 (b) also shows that the system performance of the 2.1 GHz system is better in comparison to that of the 28 GHz system. This is expected because of the losses experienced by mmWaves. The performance of the masking and down tilt scenario as shown in figure 24 (c) follows the expected trajectory as the reference and masking scenarios, but without the markedly large margins in the performance. It is therefore observed that the 28 GHz systems experience larger losses during transmission than those at 2.1 GHz. Figure 24 (d) gives a better view of the comparison of all scenarios in 2.1 GHz and 28 GHz for better analysis. The figure shows that the 2.1 GHz system has a better performance overall.

-120 -100 -80 -60 -40 -20

Received signal strength (dBm) 20 40 60 80 100 C D F

Reference sum power 2.1 GHz Reference sum power 28 GHz

C

D