Highly Reliable Mobile Computing Systems(II)

Mobile computing is a hot research
area in recent years. It consists of a set of
fixed hosts and mobile hosts to form a
distributed processing system. In this
system architecture, the fixed hosts are
connected to each other by a static
network. A mobile host communicates
with other nodes in the system through a
fixed host. The communication between
the mobile host and the fixed host is via a
wireless network. The main characteristic
of the mobile computing system is as
follows: The mobile computing system
can provide users to access information at
anywhere and anytime.
A large body of literature concerning
the fault tolerance problem exists, but most
of them deal with distributed systems
rather mobile computing systems. The
fault-tolerant approaches for distributed
systems can not be directly applied to
solve the fault-tolerant problem in mobile
computing systems. The reasons are as
follows.
(1) In mobile computing systems,
the location of a mobile host changes with
time.
(2) A mobile host is usually powered
by a stand alone energy source, like a
battery pace, that has to be replenished
after a certain period of time.
(3)Wireless communication is lower
bandwidth and higher error rate than wired
communication
The goal of this integrated project is
to design a responsive information service
system for mobile environment. However,
as the number of hosts in the system and
running time of distributed applications
increase, the probability of one or more
failures also increase. Here, the failures
can occur in the fixed nodes and mobile
hosts, or on the wireless links between the
mobile host and the fixed host. The
failures in the mobile computing system
will result in the system to restart from
beginning. Therefore, if an error occurs,
the system can not respond the user
request with a predetermined interval.
This behavior contradicts the goal of our
integrated project. In the first year, we
utilized the log-based approach to
implement a mobile information system
with the capability for tolerating fixed
hosts and mobile hosts' failures. In the
second year, we proposed a new error
detection method to detect more errors
and identify the sources of errors correctly.
In addition, we used the replication
technique to reconstruct the lost location
information, and used the dynamic
channel allocation technique to improve
the quality of wireless communication.