tern of the type-2 subframes (seven OFDM symbols) is obtained by repeating the first OFDM symbol of the type-1 subframe at the end of the subframe. A Collision-Free Interlaced Pilot (CoFIP) pattern is specifically designed for use in the type-1 open- loop MIMO region (see Section 10.5) to reduce inter-cell interference. Figure 9-36 shows the CoFIP 9.9 Pilot structure and channel estimation Type A Type B Type C Common Pilot structures for 2TX Antennas 2x2 PedB 3km/h 2x2 VehA 120km/h Ideal Ideal 2Tx Type A 2Tx Type A 2Tx Type B 2Tx Type B 2Tx Type C 2Tx Type C SNR (dB) SNR (dB) Spatial Multiplexing 2x2 PedB 3km/h 2x2 VehA 120km/h Ideal Ideal 2Tx Type A 2Tx Type A 2Tx Type B 2Tx Type B 2Tx Type C 2Tx Type C SNR (dB) SNR (dB) Space-Frequency Block Code FIGURE 9-33 Channel estimation accuracy of various pilot patterns for two transmit antennas and QPSK 1/2 in different mobility and channel conditions [123] CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) Table 9-5 Characteristics of Typical Radio Channel Models Maximum Sampling Rate in Frequency (Number of Sub- RMS Delay Maximum Delay carriers) Tu Channel Model Spread (ns) VRMS Spread (us) Tmax 2Tmax ITU-T Pedestrian A (PedA) ITU-T Pedestrian B (PedB) ITU-T Vehicular A (VehA) 370.4 ITU-T Vehicular B (VehB) Typical Urban 6-Ray Model (TU) Maximum Sampling Rate in Time Maximum (Number of OFDM Doppler Spread Coherence Time Symbols) Vehicular Speed Range (km/h) (Hz) Vmax (ms) Tc 2T s v max ~ 27.78 15.23 15-120 ~ 222.22 120-350 ~ 648.15 pilot pattern for subframes consisting of six OFDM symbols. The index of the pilot pattern set used by a particular BS with IDcell = k is denoted by Pk = (k mod 3). The index of the pilot pattern set is deter- mined by the IDcell. For subframes consisting of seven OFDM symbols, the first OFDM symbol which contains pilot sub-carriers and null sub-carriers in each pilot pattern set is inserted as the seventh symbol. Note that in order to reduce the inter-cell interference due to overlapping data and pilot sub-carriers, the pilot sub-carrier