We consider an environment in which a collection of mobile clients interacts with a stationary database server. Due to the low bandwidth of wireless communication channels, it is necessary to broadcast highly popular data items and deliver other data items on a demand basis to the mobile clients. This broadcast wireless media can be considered as an extra layer of cache storage, which we term air-storage. we investigate several mechanisms in selecting the data items to be placed over this new layer of air-storage, and illustrate their effectiveness by means of simulation.
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