Page 617 - 5G Basics - Core Network Aspects

Transport aspects 2

9.2.2 Single uplink signal transmission

Figure 9-5 shows the typical experimental set-up for measuring the transmission quality of a typical LTE
signal. It consists of an LTE VSG, a variable electrical attenuator (VEA), an RoF Tx, three SMFs, a VOA, an
EDFA, an OBPF, an RoF Rx, and an LTE SA. The LTE VSG generated a typical uplink LTE signal with the radio
carrier frequency of 2.535 GHz, the bandwidth of 1.4 to 20 MHz, and the power of −10 dBm, in which the
LTE band #7 was assumed (see [b-3GPP TS 36.101]). To emulate a free-space propagation loss, the
generated LTE signal was manually attenuated by 50 to 90 dB with the VEA. To generate a desired RoF
signal, the LTE signal was input into the RoF Tx, which corresponded to an ONU. In the RoF Tx, the LTE
signal was electrically amplified by 52 dB with a low noise amplifier (LNA) and then was converted with a
laser diode (LD) to an optical signal. The generated RoF signal with a centre wavelength of 1 551.7 nm and a
power of about 10 dBm was transmitted over 25 km, 5 km, and 15 km cascaded SMFs (total: 40 km) and
the VOA to an OLT. The VOA emulates an additional optical path loss. In the OLT, the received RoF signal
was amplified with the EDFA followed by the OBPF. The gain of EDFA was fixed to 20 dB and the OBPF with
the 3 dB bandwidth of 1 nm was used to eliminate undesired ASE noise from the EDFA. The optically
amplified RoF signal was detected with the RoF Rx to regenerate the LTE signal, where the RoF Rx consisted
of a photodetector (PD) and a post-amplifier (PA) with the variable gain of 25 to 40 dB. Finally, the EVM and
the electrical spectrum of regenerated LTE signal were measured with the LTE SA.

UNI S/R R/S SNI
ONU ODN OLT
E/O converter O/E converter
f RF : 2.535 GHz
BW: 1.4 to 50-90 dB λ c : 1551.7 nm 25+5+10 km 0-30 dB
20 MHz BW: 3 GHz Gain: 20 dB BW: 1 nm BW: 3 GHz
LTE VSG VOA RoF Tx VOA EDFA OBPF RoF Tx LTE SA
3 cascaded
LTE band #7 SMFs EVM
Additional Additional measurement
propagation optical path
loss emulation loss emulation
52 dB 25-40 dB
LNA LD PD PA
G Suppl.55(15)_F9-5

Figure 9-5 – Typical experimental set-up

Figure 9-6 shows the measured EVM as a function of optical path loss to evaluate the available dynamic
range of optical path loss. The measurement was done when the input RF power to the RoF Tx was
−65 dBm. For an optical path loss ranging from 10 to 40 dB, the observed EVMs appear to be constant at
approximately 3% for both a 20 MHz-bandwidth 64-QAM signal (which provides the maximum bit rate) and
a 1.4 MHz-bandwidth QPSK signal (which provides the minimum bit rate). They were within the required
EVM for a 64-QAM of 8% and QPSK of 17.5%, respectively (see [b-3GPP TS 36.104]). From this
measurement, the available dynamic range of optical path loss was larger than 16 dB at least. These results
show that the uplink transmission of an LTE signal over a fibre-optic link can be applicable to all the ODN
classes specified in the ITU-T G.98x series under the condition of relatively high modulation index.

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