Understanding LTE with MATLAB

Chapter 5

OFDM

So far we have considered the modulation, scrambling, and coding specifications of the LTE standard and have used a simplistic channel model (Additive White Gaussian Noise, AWGN) to undertake performance evaluations. Understanding of Orthogonal Frequency Division Multiplexing (OFDM), which is the fundamental air interface in the standard, necessitates understanding and modeling of more sophisticated channel models.

In this chapter we consider realistic channel models that take into account the dynamic channel responses and fading conditions. Short-term fading effects such as multipath fading and Doppler effects resulting from mobility will lead to frequency-selective channel models. OFDM and Single-Carrier Frequency Division Multiplexing (SC-FDM) multiple-access technologies in LTE, for downlink and uplink respectively, use efficient frequency-domain equalizers to combat frequency-selective fading and contribute to its superior spectral efficiency. In this chapter we will focus on a single-antenna configuration, while in the next chapter we will combine Multiple Input Multiple Output (MIMO) and OFDM.

We will detail the basis of the OFDM technology and discuss OFDM frame structure and implementation in the LTE standard. We will then discuss the time–frequency mapping of the OFDM signal and the various resource element granularities used to adaptively exploit the channel bandwidth, followed by the frequency-domain equalization of the OFDM signal at the receiver. We ...