Chapter 4
Introduction to OFDMA and SC-FDMA and to MIMO in LTE
4.1 Introduction
As discussed in Chapter 1, LTE multiple access is different to that of WCDMA. In LTE the downlink multiple access is based on the Orthogonal Frequency Division Multiple Access (OFDMA) and the uplink multiple access is based on the Single Carrier Frequency Division Multiple Access (SC-FDMA). This chapter will introduce the selection background and the basis for both SC-FDMA and OFDMA operation. The basic principles behind the multi-antenna transmission in LTE, using Multiple Input Multiple Output (MIMO) technology, is also introduced. The intention of this chapter is to illustrate the multiple access principles in a descriptive way without too much mathematics. For those interested in the detailed mathematical notation, two selected references are given that provide a mathematical treatment of the different multiple access technologies, covering both OFDMA and SC-FDMA.
4.2 LTE Multiple Access Background
A Single Carrier (SC) transmission means that information is modulated only to one carrier, adjusting the phase or amplitude of the carrier or both. Frequency could also be adjusted, but in LTE this is not affected. The higher the data rate, the higher the symbol rate in a digital system and thus the bandwidth is higher. With the use of simple Quadrature Amplitude Modulation (QAM), with the principles explained, for example in [1], the transmitter adjusts the signal to ...
