ancy to the information vector, resulting in a longer vector of coded symbols. This functionality includes code block segmentation, turbo or convolutional coding (depending on the channel type), rate matching, and code block concatenation (see Section 3.2 for further details). Scrambling. Scrambling of the coded data helps to ensure that the receiver- side decoding can fully utilize the processing gain provided by the channel coding. Scrambling in LTE downlink consists of multiplying (exclusive or operation) the sequence of coded bits (taken as input) by a bit-level scram- bling sequence. Modulation mapping. The block of scrambled bits is modulated into a block of complex-valued modulation symbols. Because LTE uses adaptive modu- lation and coding (AMC) to improve data throughput, the selected modu- lation scheme is based on the instantaneous channel conditions for each user. The allowed modulation schemes for downlink and uplink are shown in Table 3.2. Antenna mapping. Signal processing related to multiantenna transmission is performed at this stage. This procedure is responsible for mapping and Resource Element OFDM Signal Channel Modulation Mapping Generation Coding Scrambling Mapping To radio From MAC Antenna interface layer Mapping Channel Modulation Coding Scrambling Mapping Resource Element OFDM Signal Mapping Generation Number of Number of codewords antennas Figure 3.6 Physical layer processing sequence in the base station (downlink). © 2009 by Taylor & Francis Group, LLC Radio-Interface Physical Layer Table 3.2 Modulation Schemes Direction Channel Modulation Schemes Downlink PDSCH QPSK, 16 QAM, 64 QAM QPSK, 16 QAM, 64 QAM PCFICH PDCCH PHICH Uplink PUSCH QPSK, 16 QAM, 64 QAM PUCCH BPSK, QPSK PRACH uth Root Zadoff-Chu precoding the modulation symbols to be transmitted onto the different antennas.* The antenna mapping can be configured in different ways to provide different multiantenna schemes, including transmit diversity, beam forming, and spatial multiplexing. More details-regarding the antenna mapping 