Page 629 - 5G Basics - Core Network Aspects

Transport aspects 2

a predefined IF frequencies plan. These uplink signals centred at IF frequencies were combined with RF
combiner and then input into the RoF transmitter after being amplified or attenuated to obtain proper OMI
for obtaining better transmission performances. As shown in the inset of Figure 9-22, the number of uplink
signals was four due to supporting two MIMO antennas and two FAs at the same time. In the RoF
transmitter, the uplink LTE signals were optically converted with a directly modulated distributed feedback
laser diode (DFB-LD). The generated IF band RoF signal with a centre wavelength of 1548.5 nm and a power
of +2.5 dBm was transmitted over SMFs (up to 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 driving current of pump LD was fixed to 70 mA to operate the EDFA under the automatic current
control (ACC) mode. The OBPF has a 3 dB bandwidth of 0.5 nm and was utilized to eliminate undesired ASE
noise from the EDFA. The optically amplified RoF signal was detected by the RoF receiver to regenerate the
LTE signals, where the RoF receiver consisted of a PD and a PA with a variable gain of up to 18 dB. Finally,
the EVMs and the electrical spectra of regenerated LTE signals were measured by the LTE VSA.

UNI ONU S/R ODN R/S OLT SNI
Air propagation loss
emulation: 50~90 dB
Ant. –2 Ant. –1 2.39 GHz SMF up
LTE-VSG to 40 km
(vector
signal VEA G = 48 dB Filter
generator) RoF LTE-VSA
splitter LNA Combiner VEA transmitter VEA receiver (vector
RoF
w/wo
signal
LNA LNA EDFA and analyzer)
OBPF
λ: 1548.5 nm Optical
• LTE band-7 (up): 2.5 ~ 2.57 GHz BW: < 3 GHz propagation EVM and
• 2 FA uplink signals at 2.54 and 2.56 GHz with loss emulatio n spectrum
20 MHz bandwith 2.27 GHz measurement
Frequency plan for uplink in the IF domain
RF power
150 170 270 290 Frequency [MHz]
G Suppl.55(15)_F9-22

Figure 9-22 – Typical experimental set-up

Figure 9-23 shows the measured EVM as a function of optical path loss to evaluate the available dynamic
range of uplink transmission system. EVMs of the uplink signal centered at 270 MHz after receiving LTE
signals at OLT were measured. The measurement was done when the input RF power to the RoF
transmitter was set to −65 dBm. For an optical path loss ranging from 5 to 15 dB, the observed EVMs
appear to be below 3% for a 20 MHz-bandwidth of 64-QAM signal (which provides the maximum bit rate)
without using EDFA in front of the RoF receiver. Similarly, for an optical path loss varying from 5 to 30 dB,
the observed EVMs appear to be below 4% when using EDFA in front of the RoF receiver. They were well
below the required EVM thresholds for 64-QAM of 8%, 16-QAM of 12.5% and QPSK of 17.5% (see [b-3GPP
TS 36.104]). From this measurement, the available dynamic range to satisfy the required EVM of 8% was
approximately 20 and 36 dB without using EDFA and with EDFA, respectively. It can be seen that the optical
path loss budget can thus be as high as 36 dB, meeting the N1, N2, E1 and E2 loss budget requirements for
passive optical networks.

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