Section: 6.9.2 Resource group alignment, layer mapping and precoding
Content: The block of symbols should be first aligned with resource element group size, resulting in a block of symbols , where for normal cyclic prefix; and for extended cyclic prefix. For normal cyclic prefix, , for . For extended cyclic prefix, for . The block of symbols shall be mapped to layers and precoded, resulting in a block of vectors , , where represents the signal for antenna port , and the number of cell-specific reference signals . The layer mapping and precoding operation depends on the cyclic prefix length and the number of antenna ports used for transmission of the PHICH. The PHICH shall be transmitted on the same set of antenna ports as the PBCH. For transmission on a single antenna port, , layer mapping and precoding are defined by clauses 6.3.3.1 and 6.3.4.1, respectively, with . For transmission on two antenna ports, , layer mapping and precoding are defined by clauses 6.3.3.3 and 6.3.4.3, respectively, with . For transmission on four antenna ports, , layer mapping is defined by clause 6.3.3.3 with and precoding by if for normal cyclic prefix, or for extended cyclic prefix, where is the PHICH group number and , and by otherwise for .