ayer should support peak data rates of more than 100 Mb/s over the downlink and 50 Mb/s over the uplink. A flexible transmission bandwidth ranging from 1.25 to 20 MHz will provide support for users with different capabilities. These requirements will be fulfilled by employing In LTE, the base station is called enhanced NodeB (eNodeB). © 2009 by Taylor & Francis Group, LLC Radio-Interface Physical Layer new technologies for cellular environments, such as orthogonal frequency division multiplexing (OFDM) or multiantenna schemes (3GPP 36.201). Additionally, channel variations in the time/frequency domain are exploited through link adaptation and frequency-domain scheduling, giving a substantial increase in spectral efficiency. In order to support transmission in paired and unpaired spectra, the LTE air interface supports both frequency division duplex (FDD) and time division duplex (TDD) modes. This chapter presents a detailed description of the LTE radio-interface physical layer. For that purpose, this section provides an introduction to the physical layer, focusing on the physical resource structure and the set of procedures defined within this layer. Link adaptation techniques, including adaptive modulation, channel coding, and channel aware scheduling, are described in Section 3.2. The topic of multiple antenna schemes for LTE is tackled in Section 3.3. Finally, Section 3.4 addresses other physical layer procedures like channel estimation, synchronization, and random access. 3.1.1 Physical Resource Structure Physical resources in the radio interface are organized into radio frames. Two radio frame structures are supported: type 1, applicable to FDD, and type 2, applicable to TDD. Radio frame structure type 1 is 10 ms long and consists of 10 subframes length Tsubframe = 1 ms. A subframe consists of two consecutive time slots, each of 0.5 ms duration, as depicted in Figure 3.1. One slot can be seen as a time-frequency resource grid, composed of a set of OFDM subcarriers along several OFDM symbol intervals. The num