For UL communication, the PHY uses TDMA and Demand Assigned Multiple Access
(DAMA) to allow communication from multiple SSs to a BS. The UL transmission
frame is further divided into a number of timeslots, each of which is assigned by the
BS for various purposes, including transmission of data by an SS to the BS. Two slots
are reserved for contention-based communication; a large number of the timeslots are
reserved for communication from SSs to the BS on an assignment basis. The assignment
information is provided as part of the DL frame (referred to as UL-MAP). The SS
that is assigned a timeslot transmits its data during the slot using the burst profile
specified as part of the UL-MAP. The burst profile for one timeslot may be different
from the burst profile for another timeslot.
480 Chapter 15
This ability to adjust transmission properties, such as modulation scheme and FEC
code types during transmission, allows for varying degrees of transmission robustness
and throughput based on the channel condition experienced by each SS and the quality
of service needed by each service.
Forward Error Correction Forward Error Correction (FEC) techniques are used to
correct for or detect errors in received data, which allows for additional robustness to
the channel at the cost of information overhead and/or processing complexity.
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