oise and interference. Considering the resource elements associated with a certain block Xn output from the precoder and assuming that the channel is constant over the block, i.e., the block size L is small and the resource elements are localized in the resource element grid, the following block-based received data model is obtained Yn = ynL+1---YnL+L-1) = HnXn + Wn. The transmission rank is given by the average number of complex-value symbols per resource element. Since Q symbols are transmitted over L resource elements, the transmission rank r is obtained as r = QIL. The 3GPP LTE supports rank-1 transmit-diversity through Alamouti-based space-time codes in frequency-domain (SFBC). The encoding operation is performed over space and frequency SO the output block X from the precoder is limited to consecutive data resource elements over a single OFDM symbol. If single-codeword transmission is assumed, the modulated symbols of a single codeword are mapped to all layers. The transmit-diversity schemes for two and four cell-specific antenna ports are supported. Note that these transmit-diversity schemes are also used for the PBCH, PDCCH, and PCFICH. Furthermore, the number of cell-specific antenna ports used to encode the PBCH is the same as the total number of configured cell-specific antenna ports and these are also used for other control channels. Thus, all UEs must support up to four cell-specific antenna ports and the CHAPTER 10 The IEEE 802. 16m Physical Layer (Part II) corresponding transmit-diversity schemes. For the case of two antenna ports, the output from the precoder is as follows: (10-56) where the rows corresponds to the antenna ports and the columns to consecutive data resource elements over the same OFDM symbol. In the case where four antenna ports are utilized, a combi- nation of SFBC and frequency-switched transmit diversity is employed to provide robustness against the correlation between channels from different transmit antennas and for less-complex UE receiver implementation. The output from the 