Time-Frequency-Code Slicing: Efficiently Allocating the Communications Spectrum to Multirate Users

The time-frequency-code slicing technique allows multiple users with different data-rate requirements access to a communications resource in a manner that is cost effective over a wide range of access rates. For instance, with a timefrequency slicing (TFS) approach, users are assigned different portions of the frequency spectrum (e.g., on a slot-by-slot basis), granting them access to a fraction of the shared resource that is commensurate with their needs and their own end equipment. Users with high-data-rate requirements can “grab all the bandwidth” when no one else needs it. Also, by efficiently packing the time-frequency space, better system utilization is attained. For the specific case of TFS, we compute the reduction in blocking probability achieved under the constraint of a single transmitter/receiver per user. As an example, consider the case of 70% traffic load with ten frequency bands and 15 time slots per frame. Using the traditional allocation scheme in which users can be assigned only a single-frequency band per time slot, there is a 10% blocking probability for new connections that request 14 “time-frequency slices.” The TFS technique reduces this blocking probability to well below 0.01%.