l resource block pair is mapped to one physical resource block and the other part of the virtual resource block pair is mapped to a physical resource block which is at a predefined gap away (which causes the inter-slot hopping) in order to achieve frequency diversity. This mechanism is especially important for small resource block allocations, due to inherently lower frequency diversity. Note that the localized and distributed allocations in 3GPP LTE are conceptually similar to contiguous and distributed resource units in IEEE 802.16m. 9.15.4 Modulation and Coding The baseband modulation schemes supported in the downlink and uplink of 3GPP LTE are QPSK, 16 QAM, and 64 QAM. While all three modulation schemes are supported in the downlink in all UE categories, the uplink 64 QAM is only supported in the highest UE category and lower UE cate- gories only support QPSK and 16 QAM. The channel coding scheme for transport blocks in LTE is turbo coding similar to UTRA, with a minimum coding rate of R = 1/3, two 8-state constituent encoders, and a contention-free Quadratic Permutation Polynomial (QPP) turbo interleaver [108]. Trellis termination is performed by taking the tail bits from the shift register feedback after all information bits are encoded. Tail bits are padded after the encoding of information bits. Before the turbo coding, transport blocks are segmented into octet-aligned segments with a maximum infor- mation block size of 6144 bits. Error detection is supported by the use of a 24-bit CRC. Link adaptation (adaptive modulation and coding) with various modulation schemes and channel coding rates is applied to the shared data channel. The same coding and modulation is applied to all groups of resource blocks belonging to the same MAC PDU scheduled to one user within one TTI and within a single stream. The downlink procedures for transport block processing are shown in Figure 9-68. The coding steps for each transport block include addition of CRC to the transport block, code block segmentation and code block CRC