Page 601 - 5G Basics - Core Network Aspects

Transport aspects 2

SCM RoF signal

...
f
...
0 f opt
opt
f f – f eN f – f f f + f opt f + eN f
Electrical frequency multiplexer E/O converter O/E converter Electrical frequency demultiplexer
0 f e1 f opt – f e2 opt e1 opt e1 f opt + f e2 0 f e1
f f
0 f e2 0 f e2
.
. SCM signal
. ...

f 0 f e1 f e2 f eN f f
0 f eN 0 f eN
G Suppl.55(15)_F7-5

Figure 7-5 – Schematic block diagram of SCM transmission
7.3.1.2 Digital aggregation

The principle of aggregated analogue RoF is to aggregate wireless channels to/from multiple remote radio
heads (RRHs) so that they can be transported together in a single optical wavelength channel in a mobile
front-haul (MFH) system. By sharing the same optical hardware among multiple wireless channels, the cost
of the needed optical access components may be much reduced.
Figure 7-6 is a schematic diagram of an aggregated analogue RoF based MFH system. Multiple RRHs may
share the same optical fibre link to reduce overall cost. No baseband processing may be needed at the
remote radio unit (RRU), making the implementation energy-efficient. Also, the optical signal transmitted
over the optical fibre link may contain all the aggregated wireless channels with their bandwidths
unchanged (untouched). This means that this approach may be optical bandwidth efficient. The optical
bandwidth efficiency of this approach may be seen from the fact that the transmitted optical signal may be
viewed essentially as an analogue optical signal rather than as a binary on-off keying (OOK) optical signal
typically used with the Common Public Radio Interface [b-CPRI] or D-RoF.
Figure 7-7 is an illustration of the principle of channel aggregation through shifting the centre frequencies
of the input wireless channels and combining of frequency-shifted channels. The channel aggregation may
be implemented with relatively simple DSP. The reverse process can be applied to realize channel
de-aggregation.

Wireless channels typically have well-defined channel bandwidths and channel sampling rates, as shown in
Table 7-1 for the evolved universal terrestrial radio access (E-UTRA). In the long-term evolution advanced
(LTE-A) standard, carrier aggregation (CA) is specified such that the effective bandwidth of a wireless
channel may be increased beyond 20 MHz, e.g., to 100 MHz. The proposed channel aggregation method
may be overlaid on CA, but it does not touch (or change) each carrier-aggregated wireless channel in terms
of its bandwidth and baseband payload data.

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