Efficient data broadcast schemes for mobile computing environments with data missing

Data broadcast is an efficient method for disseminating data items in a mobile computing environment. With the data broadcast method, data items are broadcast periodically according to a predetermined schedule. If a data item is retrieved from a storage device with a nondeterministic access time, the content of the data item may not be ready when it is required in a broadcast cycle. We call this problem the data-missing problem. To handle this problem, we revise the existing data broadcast schemes using two approaches. The reaccess approach requires a mobile client to access a missing data item in the next broadcast cycle, while the add-missing approach allows a mobile client to access a missing data item in an attached missing data segment. We compare the performance of the revised schemes in terms of access time and tuning time. The comparison shows that, except latency_opt, the access time of an add-missing-based revised scheme is shorter than that of its reaccess-based counterpart. On the contrary, the tuning time of the former is longer than that of the latter. For latency_opt, both the access time and the tuning time of its add-missing-based revised scheme are shorter than those of its reaccess-based revised scheme. The comparison also shows that the access times of the revised schemes increases dramatically as the data missing probability increases, while the tuning times of the revised schemes are not so sensitive to the data missing probability.