Single Carrier FDMA: A New Air Interface for Long Term Evolution

3

Single Carrier FDMA

3.1 Introduction

Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) are modified versions of the OFDM and SC/FDE schemes described in Chapter 2. In contrast with the techniques described in Chapter 2, the multiple access techniques presented in this chapter transmit several signals simultaneously. All the orthogonal frequency division techniques employ a discrete set of orthogonal subcarriers distributed across the system bandwidth. They all include discrete transforms to move signals between the time domain and frequency domain. To transmit several signals simultaneously the multiple access techniques assign the signals to mutually exclusive sets of subcarriers. Because broadband channels experience frequency-selective fading, the FDMA techniques can employ channel dependent scheduling to achieve multi-user diversity, and because the fading characteristics of the terminals in different locations are statistically independent, the scheduling techniques can assign each terminal to subcarriers with favorable transmission characteristics at the location of the terminal.

The WiMAX cellular system uses OFDMA for transmission of signals both from the base station and from the mobile terminals. By contrast, 3GPP prescribes OFDMA for downlink transmission and SC-FDMA for uplink transmission in the long term evolution (LTE) of cellular systems in order to make the mobile terminal power-efficient. Anticipating ...