SGUM-based Database Assisted Spectrum Access - Social Group Utility Maximization - page 32

Fig. 4.6 Normalized
system-wide interference
with number of nodes
N =

Non−Cooperative Spectrum Access
Social Group Utility Maximization
Network Utility Maximization

1.3

100 and different social
network density

1.2

1.1

1

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Social Link Probability P L

Similar to the price of anarchy in non-cooperative game [ 10 ], we normalize the
system-wide interference of these solutions with respect to that of the social optimal
solution (i.e., network utility maximum solution). The results are given in Fig. 4.6 .
We see that the performance of the SGUM solution always dominates that of the
non-cooperative spectrum access. This is non-trivial since non-cooperative game
promotes the competition among users to increase the system-wide utility and has
been widely adopted to devise efficient distributed resource allocation mechanisms
in wireless networks [ 11 ]. Moreover, we observe that the performance gain of the
SGUM solution increases as the social link probability P L increases. When the
social link probability P L =

1, the SGUM solution achieves the same performance
of the network utility maximization and can reduce 23 % system-wide interference
over the non-cooperative spectrum access. This also demonstrates that the proposed
SGUM framework spans the continuum space between non-cooperative game and
network utility maximization—two extreme paradigms based on drastically different
assumptions that users are selfish and altruistic, respectively.

4.5.3 Real Trace Based Social Graph

We next evaluate the SGUM solution by the distributed spectrum access algorithm
based on the social graph represented by the friendship network of the real data
trace Brightkite [ 12 ]. We implement experiments with the number of users N =
200, 300, ... , 600, respectively. As the benchmark, we also implement the solutions
of non-cooperative spectrum access and network utility maximization.
The results are shown in Fig. 4.7 . We see that the non-cooperative spectrum access
solution will increase the system-wide interference up-to 29 % over the network util-
ity maximization solution. Upon comparison, the system-wide interference by the the
SGUM solution will increase at most 15 %, compared with the network utility maxi-
mization solution. This verifies the effectiveness of leveraging social tie to stimulate
user cooperation for achieving efficient distributed spectrum access in practices.