Page 618 - 5G Basics - Core Network Aspects

2 Transport aspects

Figure 9-6 – Measured EVMs vs. optical path loss
Figure 9-7 shows the measured EVM as a function of input RF power to evaluate the minimum input RF
power. In the case of electrical back-to-back (E-BtB), in which the LNA in the RoF Tx was directly connected
to the LTE vector signal analyser (VSA), it is estimated that the EVM of 17.5% was obtained when the input
RF power was about −100 dBm. Also in the case of RoF BtB, in which the RoF Tx was directly connected to
the RoF Rx without any optical amplifier, almost the same result was observed. Thus, no significant
degradation of the signal quality due to the introduction of the RoF Tx and Rx was observed. In the case of
36 dB optical path loss, it is estimated that the EVMs of 17.5% for 1.4 and 20 MHz-bandwidth QPSKs were
obtained at the input RF powers of less than −92 and −85 dBm, respectively. From this result, it can be seen
that the RoF transmission of uplink LTE signal over an ODN specified in the ITU-T G.98x series is feasible
under the condition of input RF power of more than −92 dBm. Hence, it is considered that the power
penalties are generally caused by the increase of total noise figure. However, the noise figure and the
operational power range of the whole system can be optimized.

Figure 9-7 – Measured EVMs vs. input RF power

9.2.3 Multiple downlink signals transmission
9.2.3.1 IF-band SCM RoF system with an analogue aggregation technique in ONU

Figure 9-8 shows the typical experimental set-up for measuring the transmission performances of typical
multiple LTE signals based on IF-band SCM RoF transmission scheme. This is a kind of IF-band SCM RoF
system with an analogue aggregation technique in ONU. It consists of an arbitrary waveform generator
(AWG) to generate multiple LTE signals, an RoF Tx, standard SMF of 20 km, a VOA, an EDFA, an ASE
rejection filter, an RoF Rx, a BPF, a frequency-up-converter (FUC), high power amplifier (HPA), antenna and
an LTE VSA. The AWG generated typical multiple LTE signals at the intermediate carrier frequency from 160
to 820 MHz with 60 MHz spacing. The bandwidth of each IF-band carrier was 20 MHz. The total summed RF
power for all IF carriers was about 0 dBm to obtain a proper optical modulation index (OMI) for better

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