Performance advantages of time-frequency-sliced systems

The time-frequency-code-slicing technique allows multiple users with different speed requirements access to a communications resource in a manner that is cost effective over a wide range of access speeds. For instance, with a time-frequency-slicing approach, users are assigned different portions of the 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. By efficiently packing the time-frequency space, better system utilization is attained. We illustrate the performance advantages of time-frequency-sliced systems by computing the reduction in blocking probability achieved under the constraint of a single transmitter/receiver per user. The dramatic reduction in blocking probability is attained at the expense of a variable-bit-rate transmitter/receiver with fast (slot-by-slot) tunability. For example, at a 90% traffic load, with 30 frequency bands and 15 time slots per frame, the time-frequency-slicing technique reduces the blocking probability from 90% (for the traditional allocation scheme) down to only 1% for a new connection that requests 13 “time-frequency slices.” The main focus of the paper is to determine how much performance advantage is gained by allowing mobiles to modulate more than just one unit (frequency) slice per time slot