Mobile Intelligence

9.2 PRELIMINARIES

9.2.1 Basic Concepts

In air indexing, a broadcast cycle consists of index segments to hold index information and data segments to hold data items. The two segments are organized as a sequence of buckets, where the bucket is the smallest logical unit of information delivery and all buckets are of the same size like disk page [1]. Therefore, mobile clients access data items in the unit of buckets. Index buckets refer to buckets in index segments and data buckets to buckets in data segments. Every bucket contains a bucket header that keeps the following information: bucket_id referring to a bucket identifier, bucket_type indicating the kind of the bucket, index bucket or data bucket, bcast_pointer referring to the offset to the beginning of the next broadcast cycle, and index_pointer referring to the pointer to the next index segment. Bcast is defined as the length of a broadcast cycle.

Tuning time consists of initial probe, index listening time, and data listening time [1]. Initial probe refers to determining the time when the next index segment appears on the wireless channel and is completed within 1.5 buckets on average after tuning into the wireless broadcast channel. Index listening time is the amount of time the mobile client listens to index segments for predicting the arrival time of the desired data items. Data listening time is the amount of time the mobile client downloads the desired data items from the wireless broadcast channel. Access time is the ...