erarchical synchronization scheme with two stages. There are two downlink synchronization signals; the Primary Advanced Preamble (PA-Preamble); and the Secondary Advanced Preamble (SA- Preamble). The PA-Preamble is a narrowband synchronization signal and is common to a group of cells that is used for initial acquisition, superframe synchronization, and broadcast of essential system information. The SA-Preamble is a wideband and cell/sector-specific synchronization signal that is used for fine time/frequency synchronization and cell/sector identification. The PA-Preamble and 9.13 Synchronization channel IEEE 802.16-2009 - 1st Transmission IEEE 802.16m - 1st Transmission IEEE 802.16-2009 - 2nd Transmission IEEE 802.16m - 2nd Transmission IEEE 802.16-2009 - 3rd Transmission IEEE 802.16m - 3rd Transmission IEEE 802.16-2009 - 4th Transmission IEEE 802.16m - 4th Transmission SNR (dB) FIGURE 9-54 A comparison of the downlink/uplink channel coding and HARQ performance in IEEE 802.16m and IEEE 802.16-2009 [87] SA-Preamble are time-division multiplexed across time. One PA-Preamble OFDM symbol and two SA-Preamble OFDM symbols present in every superframe period. The PA-Preamble is located at the first OFDM symbol of the second frame in a superframe, while the SA-Preamble is located at the first OFDM symbol of the first and third frames in the superframe. When the new and the legacy systems are co-deployed, the legacy preamble is located at the first OFDM symbol of the legacy frame. The locations of the A-Preamble OFDM symbols are fixed within the superframe. Figure 9-58 shows the structure of the IEEE 802.16m preambles in time and frequency. The timing and Cell-ID acquisition in IEEE 802.16m is substantially different from that of the legacy system. In the IEEE 802.16-2009 standard, the preamble is the first OFDM symbol of the frame. For each FFT size, three different preamble sub-carrier sets are defined (i.e., frequency reuse-3), differing in the allocation of sub-carriers. These sub-carriers are modulated using a boosted 