Praise for Fundamentals of WiMAX

8.8 Transmit Diversity and MIMO 295Odd SymbolEven SymbolAntenna 0 Antenna 1(a)Antenna 2 Antenna 3Odd SymbolEvenSymbolAntenna 0 Antenna 1(b)Figure 8.17 PUSC Clusters for (a) two- and four-antenna transmissions• Symbol 3: Antenna 2 uses variable set 1 and constant set 1, and antenna 3 uses variable set0 and constant set 0.For the PUSC subcarrier permutation, a separate cluster structure, as shown in Figure 8.17,is implemented when multiple antennas are used. When three antennas are used for transmission,the pilot pattern distribution is the same as in the case of four antennas, but only the patternsfor antennas 50, 1, and 2 are used for transmission.8.8.2 Frequency-Hopping Diversity CodeIn the case of space/time encoding using multiple antennas, the entire OFDM symbol is operatedby the space/time encoding matrix, as shown in Figure 8.15. IEEE 802.16e-2005 also defines anoptional transmit diversity mode, known as the frequency-hopping diversity code (FHDC), usingtwo antennas in which the encoding is done in the space and frequency domain, as shown inFigure 8.18 rather than the space and time domain. In FHDC, the first antenna transmits theOFDM symbols without any encoding, much like a single-antenna transmission, and the secondantenna transmits the OFDM symbol by encoding it over two consecutive subchannels, using the2 × 2 Alamouti encoding matrix, as shown in Figure 8.18.