ucture The transmission is divided into units of superframes and a transmitter is present in each sector of the access network. Superframe is a structure formed from a superframe preamble and multiple physical layer frames. In FDD, each superframe consists of a superframe preamble followed by a sequence of 25 downlink PHY frames. If FDDHalfDuplexTDDPartition = 1 and Duplexing = FDD, then each of the Forward Link PHY frames is separated by a guard interval, whereas there is no separation when FDDHalfDuplexTDDPartition = 0 and DuplexingMode = FDD, where FDDHalfDuplexTDDPar field of the Overhead Messages Protocol. 2 The superframe structures for the cases of FDDHalfDu- plexTDDPartition = 0 and for (DDHalfDuplexTDDPartition = 1 are shown in Figure 6.5 and Figure 6.6 respectively. OMP provides broadcast messages containing information that is mostly used by Connection Control Plane protocols. Next Generation Mobile Communications Ecosystem Forward Forward Forward Superframe Preamble PHY Frame PHY Frame PHY Frame 8 OFDM 8 OFDM Symbols Symbols Figure 6.5 FDD Forward Link superframe structure if (FDDHalfDuplexTDDPartition. Reproduced with permission from C 2008 IEEE [4] Each superframe has an associated SuperframeIndex and both the superframe preamble and the PHY frames further consist of a sequence of OFDM symbols. Each superframe preamble and PHY frame consists of eight OFDM symbols. An OFDM symbol consists of NFFT (Fast Fourier Transform) individually modulated sub-carriers that carry complex-valued data. Table 6.3 presents OFDM symbol numerology which shows support for multiple FFT size and the numerology remains the same for both uplink and downlink. The different FFT size corresponds to different carrier bandwidths ranging from 5 to 20 MHz, chip rates, cyclic prefix duration and OFDM symbol duration. This flexibility and robustness contributes to ease of implementation. 6.5.1.1.2 Channel Structure Figure 6.7 shows the channel structure for the single-transmit-antenna case. The channel structure for MIMO and Space t