IEEE Consumer Electronics Magazine - October 2016 - 83

DL Resource
Utilization (%)

Antonio Virdis (a.virdis@iet.unipi.it) is with the Dipartimento di Ingegneria dell'Informazione, University of Pisa, Italy.
Enzo Mingozzi (e.mingozzi@iet.unipi.it) is with the
Dipartimento di Ingegneria dell'Informazione, University of
Pisa, Italy.
Giovanni Stea (g.stea@iet.unipi.it) is with the Dipartimento di Ingegneria dell'Informazione, University of Pisa, Italy.

40
30
20
10
0
D2I Macro
1 pkt/s

D2I Femto
2 pkt/s

5 pkt/s

10 pkt/s

FIGURE 7. The DL resource utilization.

DL Resource
Utilization (%)

100
80
60
40
20
0
D2D Macro D2I Macro D2I Femto
1 pkt/s

2 pkt/s

5 pkt/s

D2D Femto
10 pkt/s

FIGURE 8. The UL resource utilization.

combining the two aforementioned approaches, that is, using
D2D within a house served by a femto eNB. In this last case,
resources are still requested to a serving node in proximity and
are then granted using D2D.
In Figures 7 and 8, we evaluate the benefits for the operator by showing the percentage of used UL and downlink (DL)
transmission resources, considering the macro in the first two
scenarios and the sum of the femto eNbs in the others. As we
can see, UL resources do depend on the traffic volume and are
lower when using D2D with the macro and D2I with the
femto. In the first case, most of the communications occurring
between couples of endpoints located in different homes can
benefit from frequency reuse, whereas in the second, UEs
experience better channel conditions and can achieve the same
data rate using fewer resources. Finally, DL resource utilization is shown only for D2I communications, as D2D occurs
only in UL. As we can see, using either macro or femto eNBs
lead to similar results. In fact, the stronger transmission power
used by the macronode compensates for its higher distance to
the homes, hence to devices, which is far shorter in the case of
femto eNBs. However, operators may select one solution or
the other also based on considerations on power consumption,
that is, depending on which node has better energy efficiency
and on the fact that the energy bill for femto eNBs can be
expected to be paid by the end user.

ABOUT THE AUTHORS
Carlo Vallati (c.vallati@iet.unipi.it) is with the Dipartimento
di Ingegneria dell'Informazione, University of Pisa, Italy.

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OCTOBER 2016

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