Section: 6.9.3 Mapping to resource elements
Content: The sequence for each of the PHICH groups is defined by where the sum is over all PHICHs in the PHICH group and represents the symbol sequence from the :th PHICH in the PHICH group. PHICH groups are mapped to PHICH mapping units. For normal cyclic prefix, the mapping of PHICH group to PHICH mapping unit is defined by where , and where is given by Table 6.9-1. For extended cyclic prefix, the mapping of PHICH group and to PHICH mapping unit is defined by where and where is given by Table 6.9-1. Let , denote symbol quadruplet for antenna port. Mapping to resource elements is defined in terms of symbol quadruplets according to steps 1–10 below: 1) For each value of 2) Let denote the number of resource element groups not assigned to PCFICH in OFDM symbol 3) Number the resource-element groups not assigned to PCFICH in OFDM symbol from 0 to, starting from the resource-element group with the lowest frequency-domain index. 4) Initialize (PHICH mapping unit number) 5) For each value of 6) Symbol-quadruplet from PHICH mapping unit is mapped to the resource-element group represented by as defined in clause 6.2.4 where the indices and are given by steps 7 and 8 below: 7) The time-domain index is given by 8) Set the frequency-domain index to the resource-element group assigned the number in step 3 above, where is given by in case of extended PHICH duration in MBSFN subframes, or extended PHICH duration in subframes 1 and 6 for frame structure type 2, or extended PHICH duration in subframe with the same duration as the DwPTS duration of a special subframe configuration in frame structure type 3 and by otherwise. 9) Increase by 1. 10) Repeat from step 5 until all PHICH mapping units have been assigned. The PHICH duration is configurable by higher layers according to Table 6.9.3-1. The PHICH shall not be transmitted in MBSFN subframes with zero-size non-MBSFN region. Table 6.9.3-1: PHICH duration in MBSFN and non-MBSFN subframes