ulation Reference Zadoff-Chu Signal (DRS) (narrowband) Sounding Reference Signal Based on Zadoff-Chu (SRS) (wideband) that are later mapped to one or several transmission layers. The complex-valued modulation symbols on each layer are precoded for transmission and are further mapped to resource elements for each antenna port. The complex-valued time-domain OFDMA signal for each antenna port is then gener- ated following these stages [107]. The continuous-time signal (p) (t) on antenna port p in OFDM symbol l in a downlink slot can be expressed as follows: (9-40) where + NDLNRB/2 RB SC and k" - 1. The variable N is equal to 2048 for = 15 kHz sub-carrier spacing and 4096 for Af=7.5kHz sub-carrier spacing. CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) Input Bit Stream (User Antenna Data) Layers Ports Modulation Scrambling Resource OFDM Signal Mapper Element Mapper Generation Layer Mapper Precoding Modulation Resource Scrambling OFDM Signal Mapper Element Mapper Generation Downlink PHY Processing Resource SC-FDMA Modulation Transform Scrambling ELement Mapper Precoder Signal Mapper Generation Input Bit Stream(User Uplink PHY Processing Data) Sub-carrier CP Insertion Mapping FIGURE 9-70 Overview of physical channel processing [107] In the uplink, the baseband signal is processed by scrambling the input coded bits and then by modulation of the scrambled bits to generate complex-valued symbols. The complex-valued modu- lation symbols are transform-precoded (DFT-based precoding) to generate complex-valued symbols that are later mapped to resource elements. The complex-valued time-domain SC-FDMA signal for each antenna port is then generated. The continuous-time signal si(t) in SC-FDMA symbol l in an uplink slot is defined as follows: (9-41) where + RB JRB SC /2 N = 2048, Af = 15 kHz, and akl is the content of resource element (k, 1). The detailed physical channel processing in the downlink, as shown in Figure 9-70, can be described as follows. For each codeword Nc=0,1 1, the block of bits (1), b(Nc) (MCNe) - 1), wh