Instrumentation & Measurement Magazine 23-9 - 8

Fig. 2. E-field daily behavior for three operators in 800 MHz LTE downlink
bandwidth.

Fig. 3. E-field daily behavior for three operators in 1800 MHz LTE downlink
bandwidth.

instrument. In zero-span mode, only the PBCH channel has
to be monitored, and the overall power is computed by scaling the PBCH power with a scale factor in dependence on the
channel bandwidth. In this way, if the limits are not overcome
considering the whole channel at maximum power, then they
are not overcome for sure in real conditions, where the data
subchannels have less power than PBCH.
Furthermore, being a control channel, PBCH is expected
to be constant during the time and therefore the measurement
should be time-independent. Nevertheless, experimental results show that only operator 2, at 800 MHz, has a pretty
constant profile along the day. The other two operators have a
decrease during nighttime (especially operator 1) and a higher
and more constant value during the daytime.
A second consideration was made to address the variability. Indeed, reviewing the behavior from Fig. 2, operator 2 is
still much more stable than the other two operators in the same
band. This means that, whatever is the measurement point, it
will be a good approximation of the mean value since the observed dispersion is very small.
On the other hand, operators 1 and 3 show higher variability, and this condition is even worse if 1800 MHz bandwidth is
considered (Fig. 3), where all operators, and especially operator 3, have very high variability rates. This feature is reported
in Table 1, where the experimental standard deviation (σ) is
computed in decibel (dB) for each operator at each frequency
and each bandwidth. Furthermore, the observation day is divided into eight adjacent intervals (F1-F8), each of them being
three hours long, starting from midnight (0 a.m.), e.g., F1 = (0

a.m. to 3 a.m.). Similar behaviors have been observed for the
other days of the weeks and not reported for the sake of brevity.
It is interesting to note that qualitative observations that
can be drawn from Figs. 2 and 3 are quantitatively confirmed
in Table 1. Indeed, operator 2 shows the lowest variability at
800 MHz and operator 3 has constantly a variability equal to 1
dB at 1800 MHz on all day intervals. The other considerations
are related to day intervals. Therefore, higher variabilities
were observed for Operator 1 (at 800 and 1800 MHz) and Operators 2 and 3 (at 1800 MHz) during the nighttime (intervals
F1-F3) than during the daytime (F4 -F8). These issues are related to the evaluation of attention levels (24 hour-based).
When exposure limits are considered, only the 800 MHz
results are presented, both for the sake of brevity and the interesting results obtained. Different considerations can be
done in this situation. In particular, the normative establishes to consider any 6-minute interval throughout the day,
and to perform this measurement, two approaches are admitted: to measure the channel power for any 6-minute interval
or to apply the extrapolation technique (using PBCH) and
thus overestimate the value, to be in safe mode. Therefore, we
performed exactly 6-minute simultaneous measurements of
PBCH and channel power to compare the results achieved by
considering both approaches. The results are presented in Fig.
4, Fig. 5 and Fig. 6.
In particular, the purple line represents the reference E-field
obtained by direct channel power measurement and the other
lines (blue, red and orange) are the corresponding extrapolated E-field for each operator.

Table 1 - Variability analysis (in dB) in terms of average standard deviation over one week
Op/BW

F1

F2

F3

F4

F5

F6

F7

F8

1/800

0.94

0.83

0.86

0.38

0.35

0.36

0.34

0.35

2/800

0.17

0.12

0.20

0.23

0.25

0.20

0.20

0.22

3/800

0.52

0.25

0.34

0.56

0.50

0.55

0.55

0.53

1/1800

0.38

0.35

0.36

0.29

0.26

0.24

0.30

0.31

2/1800

1.12

2.24

1.91

0.35

0.32

0.29

0.28

0.26

3/1800

1.23

1.28

1.27

1.17

1.06

1.00

1.05

0.92

8	

IEEE Instrumentation & Measurement Magazine	

December 2020



Instrumentation & Measurement Magazine 23-9

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