BPSK modulation with a specific Pseudo-Noise (PN) code. The timing and frequency acquisition in the legacy system is a non-hierarchical procedure, i.e., both timing and Cell ID information are acquired in a single step. The legacy preamble sequences carry 114 distinct Cell IDs. One of the problems with the legacy preamble design is that when an MS is turned on at a location with a similar distance to CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) 1st Transmission (IEEE 802.16-2009) 1st Transmission (IEEE 802.16m) 2nd Transmission (IEEE 802.16-2009) 2nd Transmission (IEEE 02.16m) 3rd Transmission (IEEE 802.16-2009) 3rd Transmission (IEEE 802.16m) 4th Transmission (IEEE 802.16-2009) 4th Transmission (IEEE 802.16m) SNR (dB) FIGURE 9-55 A comparison of the downlink channel coding and HARQ performance with MCS and resource adaptation in IEEE 802.1 16m and IEEE 802.16-2009 [87] three base stations using three different segment preambles, the received preamble would lose its quasi-repetition property because all sub-carriers would be non-zero (except the DC carrier and the guard-band sub-carriers). Without this repetition property, the initial frame synchronization algorithms would only rely on the cyclic prefix in every observed OFDM symbol in a radio frame to decide the symbol boundary and to detect the PN sequence with unknown channel impulse response and frequency offset over 114 possible sequences. This would consume the power of the MS and increase the scanning time. The latter would result in poor cell selection/re-selection at the cell edge. Other problems with the legacy preamble design include the timing accuracy and an insufficient number of preamble sequences for cell planning and deployment (at least 256 distinct sequences are required based on information obtained from early deployments of mobile WiMAX Release 1.0). The IEEE 802. 16m timing and Cell ID acquisition, on the other hand, is based on a hierarchical scheme, where the timing and Cell ID and other information are obtained in two steps. Also t