Digital Compensation for Analog Front-Ends: A New Approach to Wireless Transceiver Design

5

Generic OFDM System

Since the end of the 1990s, OFDM and OFDMA have become two of the most widely used modulation techniques. They can be found now in major digital television and radio broadcast standards (DVB-T/H, DAB, ISDB-T, DMB), in major outdoor cellular systems (IEEE802.16-2004, IEEE802.16e-2005, 3GPP-LTE), in WLANs (IEEE802.11a/g/n) and WPANs (IEEE802.15.3c, Ecma 368). The reasons for the success of OFDM are many: elegant multi-path mitigation in the frequency domain, very flexible multiplexing and multiple access by sub-carrier allocation, simple per-sub-carrier processing in MIMO-OFDM, etc.

OFDM has been described in detail in Chapter 2 and its sensitivity to non-idealities was addressed in Chapter 4. The goal of this chapter is to describe how non-idealities can be tackled in OFDM transmitters or receivers. We will start by describing a generic OFDM system, with a frame format containing a preamble and pilots, as with most modern burst transmission systems. This generic OFDM system will then be used to show how the OFDM modem receiver is designed to process the OFDM burst and, at the same time, compensate for the non-idealities introduced by the front-end. We will delve into the details of the acquisition schemes (burst detection, timing, CFO estimation), estimation of the channel and front-end parameters and tracking of the CFO, SCO and phase noise.

5.1 Definition of the generic OFDM system

For the purpose of describing how estimation and compensation of front-end ...