The IEEE 802.16 MAC layer makes use of two access
techniques, frequency division duplex (FDD) and time
division duplex (TDD). Bandwidth requests and data from
SSs to the BS are carried in an uplink (UL) frame.
Transmissions from the BS to SSs are carried by a downlink
(DL) frame. Upon receiving a bandwidth request, the BS
handles bandwidth allocation by assigning uplink grants
based on requests from the SSs. A typical signaling frame
for TDD includes an UL-frame (see Fig. 1a) and a DL-frame
(see Fig. 1b) using a single channel frequency as illustrated
in Fig. 1c. In FDD these frames are transmitted at the same
time using different frequencies as illustrated in Fig. 1d (see
[2] for further details on the frame structure).