Sensors 2014, 14 22710
such as e-government, e-commerce and e-banking, fast QoS optimization is the key to promote the
successful development, application and extension of the SCAs [32], which provides a flexible and
effective mechanism of QoS measure for SCAs by deduction and adoption based on the summative
evaluation of operating information.
In recent years, many previous studies have focused on the security guarantees at the network layer
in WSNs [33,34]. However, it is impossible to assure the overall security of SCAs in WSNs only
depending on the security guarantees of the network layer [35–37]. Therefore, the security must be
considered together with other QoS indices in analyzing comprehensive QoS of SCAs in WSNs.
Therefore, this paper focuses on the comprehensive evaluation of multiple QoS indices including
security for SCAs in WSNs, which aims at providing a selection criterion for some potential solutions
for designers of SCAs. On this basis, this paper further focuses on analyzing the contribution of each SN
to the total evaluation, which aims at providing some potential optimization probabilities to the
designers. The current solutions cannot solve the above problems well. Most current researchers separate
performance, reliability, and security into different fields and study them individually. However, in fact,
performance, reliability and security are closely related and affect each other, in particular when the
WSA is implemented [38–41]. For example, when a task is divided into different ASs simultaneously
executed by SNs, the performance is high, but the reliability can be low because failure of any SN will
make the entire task incomplete. This causes the task to restart, which inversely increases its execution
time (i.e., reduces its performance). Therefore, it is worth having some redundant SNs to execute the
same AS, especially for those failure-prone SNs. However, too many redundancies, even though
improving the reliability, can decrease the performance by not fully parallelizing the execution of
different AS and considerably reduces data security as multiple replicas of the same data are processed
by different SNs, which increases the chances of unauthorized access. For different types of users (or
different usage scenarios), the security requirements may be different, which relates to the security
levels of data accessed by users. That is to say, the security of service applications based on wireless
sensor networks is interconnected with the security levels of the accessed data. In the design of the
service application system, the high security level should be used for the data with high confidentiality
to prevent the occurrence of unsafe events. For example, the probability of the occurrence of
unauthorized access can be reduced by limiting the number of redundant key nodes. Obviously, doing
so may reduce the system performance and/or reliability. Therefore, ensuring absolute security is
unrealistic in the design of a service application system. Designers usually have to compromise
between the security, the performance and the reliability. Thus, performance, reliability and security
should be studied together in WSN service analysis.
In order to assure the lowest security strength of SCAs in WSNs satisfying users’ individualized
security requirements and improve other QoS indices as much as possible, this paper studies the
analysis method for the comprehensive QoS with security constraints of SCAs in WSNs based on the
VUGF technology. Our contributions are as follows: (I) We present the working mechanisms of SCAs
in WSNs and analyze the necessity of comprehensive assessment on multiple QoS indices; (II) We
analyze the disadvantages of the classic UGF, and present a VUGF technique that can obviously
improve the efficiency on comprehensive QoS assessment in a parallel computing environment;
(III) Employing our VUGF, we present a composition calculation method of multiple QoS indices for
SCAs in WSNs, which can work out the total comprehensive QoS assessment by using a fast algebraic