espectively. The sub-carriers in each OFDM symbol are indexed from 0 through NFFT - 1, where NFFT is given by the TotalNumSub-carriers field of the Overhead Messages Protocol. The guard sub-carriers on the other hand are not modulated. Table 6.3 represents the OFDM symbol numerology for the different FFT size. Each FFT size is linked to a different channel bandwidth ranging from 2.5 to 20 MHz. The cyclic prefix duration, chip rate, and symbol duration for each FFT size is also listed in the Table 6.3. 6.5.1.2.2 Channel Structure Each of the PHY frames is further divided into a CDMA segment and an OFDMA segment. The uplink consists of three pilot, four control and two data channels which are divided between CDMA and OFDMA segments. During the uplink PHY frame portion of the transmission, the sub-carriers of each OFDM symbol uses a second indexing scheme known as hop-port indexing. In this scheme, each OFDM symbol consists of QSDMA,RL NFFT individually-modulated hop-ports. The QSDMA,RL represents the number of SDMA (Space Division Multiple Access) dimensions on the uplink. There is a mapping between the QSDMA,RL NFFT hop-ports and the NFFT sub-carriers, called a hop-permutation. The hop-permutation may change Guard Interval No Transmission during Forward Reverse Link Reverse Link Reverse Link Link Superframe PHY Frame PHY Frame PHY Frame Preamble 8 OFDM 8 OFDM Symbols Symbols Figure 6.9 FDD Reverse Link superframe structure if FDDHalfDuplexTDDPartition = 1. Reproduced with permission from C 2008 IEEE [4] IEEE 802.20 Mobile-Fi Equate the Symbols Mapping of the modulation from the Z Sequences to Symbol to O on OFDM Symbols the R-ACKCH Segment of a PHY Frame Subcarriers as Defined by FLSS R-ODCCH Wrap-Around Modulated R-DPICH Hop-Port OFDM-Symbol Mapping R-DPICH Insert in All Using FLSS Modulation Quarter-Tiles Hop Patterns Symbols with R-ODCCH R-ACKCH Sum all Modulation instances of Symbols R-ACKCH Wrap-Around R-ODCH R-DPICH, Modulated R-ACKCH, Hop-Port and R-ODCCH Subcarriers as OFDM-Symbol Defined by RLSS Mapping U