ABSTRACT
In wireless asymmetric communication, broadcasting is an efficient way of simultaneously disseminating data to a large number of clients. Consider data services on cellular networks, such as stock quotes, weather infos, traffic news, where data are continuously broadcast to clients that may desire them at any instant of time. In this scenario, a server at the base-station repeatedly transmits data items from a given set over a wireless channel, whereas clients passively listen to the shared channel waiting for their desired item. The server follows a broadcast schedule for deciding which item of the set has to be transmitted at 484any time instant. An efficient broadcast schedule minimizes the client expected delay, that is, the average amount of time spent by a client before receiving the item he needs. The client expected delay increases with the size of the set of the data items to be transmitted by the server. Indeed, the client has to wait for many unwanted data before receiving his own data. The efficiency can be improved by augmenting the server bandwidth, for example, allowing the server to transmit over multiple disjoint physical channels and therefore defining a shorter schedule for each single channel. In a multichannel environment, in addition to a broadcast schedule for each single channel, an allocation strategy has to be pursued so as to assign data items to channels. Moreover, each client can access either only a single channel or any available channel at a time. In the former case, if the client can access only one prefixed channel and can potentially retrieve any available data, then all data items must be replicated over all channels. Otherwise, data can be partitioned among the channels, thus assigning each item to only one channel. In this latter case, the efficiency can be improved by adding an index that informs the client at which time and on which channel the desired item will be transmitted. In this way, the mobile client can save battery energy and reduce the tuning time because, after reading the index info, it can sleep and wake up on the proper channel just before the transmission of the desired item.
