uplink is single-carrier transmission (SC-FDMA) with a cyclic prefix to achieve uplink inter-user orthogonality and to enable efficient frequency-domain equalization at the receiver side. The frequency-domain generation of the SC-FDMA signal, also known as DFT-spread OFDM, is similar to OFDMA and is illustrated in Figure 9-10. This allows for a relatively high degree of commonality with the downlink OFDMA baseband processing using the same parameters, e.g., clock frequency, sub-carrier spacing, FFT/IFFT size, etc. The use of SC-FDMA in the uplink is mainly due to the relatively inferior peak-to-average power ratio properties of OFDMA that result in worse uplink coverage compared to SC-FDMA. The PAPR characteristics are important for cost-effective design of UE power amplifiers. The sub-carrier mapping determines which part of the spectrum is used for transmission by inserting a suitable number of zeros at the upper and/or lower end, as shown in Figure 9-10. Between each DFT output sample L - 1 zeros are inserted. A mapping with L = 1 (as shown in Figure 9-10) corresponds to localized transmissions, i.e., transmissions where the DFT outputs are mapped to consecutive sub-carriers. There are two sub-carrier mapping schemes (localized and distributed) that could be used in the uplink. However, 3GPP LTE only specifies localized sub-carrier mapping in the uplink. 9.15.2 Frame Structure Downlink and uplink transmissions are organized into radio frames with 10 ms duration. 3GPP LTE supports two radio frame structures, Type 1, applicable to an FDD duplex scheme, and Type 2, applicable to a TDD duplex scheme. Frame structure Type 1 is illustrated in the upper portion of Figure 9-66. Each 10 ms radio frame is divided into 10 equally sized subframes. Each subframe consists of two equally sized slots. For FDD, 10 subframes are available for downlink transmission and CHAPTER 9 The IEEE 802.16m Physical Layer (Part I) Table 9-16 3GPP Band Classes [111,112] Uplink Operating Band eNB Downlink Operating Band eNB Receive/UE Transmi