Efficient data retrieval scheduling for multi-channel wireless data broadcast

Wireless data broadcast is an efficient technique of disseminating data simultaneously to a large number of mobile clients. In many information services, the users may query multiple data items at a time. In this paper, we study the data retrieval scheduling problem from the client´s point of view. We formally define the Largest Number Data Retrieval (LNDR) problem with the objective of downloading the largest number of requested data items in a given time duration, and the Minimum Cost Data Retrieval (MCDR) problem which aims at downloading a set of data items with the minimum energy consumption. When the time needed for channel switching can be ignored, a Maximum Matching optimal algorithm is exhibited for LNDR which requires only polynomial time; when the switching time cannot be neglected, LNDR is proven to be NP-hard and a greedy algorithm with constant approximation ratio is developed. We also prove that the MCDR problem is NP-hard to be approximated within to any nontrivial factor and a parameterized heuristic is devised to solve MCDR non-optimally.