Databases Reference
In-Depth Information
from multiple sources and delivers them, possibly modified according to pri-
vacy requirements, to other parties. Users define their privacy preferences in
terms of a minimum distance representing the maximum location accuracy
they are willing to accept. Bellavista et al. [29] present a solution based on
a middleware that balances the level of privacy requested by users and the
need of service precision. Location information is perturbed depending on pri-
vacy/eciency requirements negotiated by the parties and it is returned with
lower precision and lower geographical granularity.
In summary, although obfuscation-based techniques are compatible with
users specifying their privacy preferences in a common and intuitive manner
(usually as a
minimum distance
), they do not provide a quantitative esti-
mation of the provided privacy level, and they usually implement a single
obfuscation technique, which provide an obfuscation effect by scaling up the
extent of the location area.
4 Obfuscation Techniques for Location Privacy
Protection
An interesting research direction is to use obfuscation-based techniques for lo-
cation privacy protection in LBAC systems [30, 31, 32]. These recent propos-
als provide privacy by degrading the location accuracy of each measurement
while offering a measurable accuracy to service providers and are based on
two working assumptions that simplify the analysis with no loss of generality:
i)
the area returned by a location measurement is planar and circular, which
is the actual shape resulting from many location technologies;
ii)
the distri-
bution of measurement errors within a returned area is uniform. The first
assumption derives from the fact that user location information is affected by
an intrinsic measurement error introduced by sensing technologies, resulting
in spatial areas rather than geographical points. This assumption represents
a particular case of the general requirement of considering convex areas and a
good approximation for actual shapes resulting from many location technolo-
gies (e.g., cellular phones location). A location measurement is then defined
as follows.
Definition 2 (Location measurement).
A location measurement of a user
u is a circular area Area
(
r, x
c
,y
c
)
, centered on the geographical coordinates
(
x
c
,y
c
)
and with radius r, which includes the real user's position
(
x
u
,y
u
)
with
probability P
((
x
u
,y
u
)
∈
Area
(
r, x
c
,y
c
)) = 1
.
Definition 2 comes from observing that sensing technologies based on cel-
lular phones usually guarantee that the real user's position falls within the
returned area.
The second assumption is introduced to discuss the effects of obfusca-
tion techniques. Consider a random location within a location measurement
