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2 Transport aspects
Figure 9-23 – Measured EVM as a function of optical path loss to evaluate
the available dynamic range of optical path loss
Figure 9-24 shows the measured EVM as a function of input RF power to evaluate the minimum input RF
power. In the cases of E-BTB and E-BTB with LNA, in which the LNA inside the RoF transmitter was directly
connected to the LTE VSA, it is estimated that the EVM thresholds of 8 and 12.5% were obtained when the
input RF powers were about −76 and −82 dBm, respectively. Also in the case of optical BTB, in which the
RoF transmitter was directly connected to the RoF receiver without any optical amplifier (the received
optical power was fixed at −10 dBm for the RoF receiver), similar results were observed. As increasing the
input RF power level from −62 to −57 dBm, a slight EVM degradation caused by LD clipping was observed.
Thus, no significant degradation of the signal quality due to the introduction of the RoF transmitter and
receiver was observed in the input RF power range from −85 to −62 dBm. In the case of 36 dB optical path
loss, it is estimated that the EVMs of less than 8% for 20 MHz-bandwidth 64-QAM mapped signals were
obtained at the input RF powers of more than −67 dBm. Similarly, it is also estimated that the EVMs of less
than 12.5% for 20 MHz-bandwidth 16-QAM mapped signals were obtained at the input RF powers of more
than −72 dBm. From these results, it is necessary to manage the input RF power level in order to achieve
sufficient uplink transmission performance and to reduce overall system degradations.
Figure 9-24 – Measured EVM as a function of input RF power to evaluate
the minimum input RF power
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