RF Analog Impairments Modeling for Communication Systems Simulation: Application to OFDM-based Transceivers

3.1 Introduction

The major RF analog impairments we find in modern transceivers have been described and mathematically modeled in Chapter 2. The aim of this chapter is to address the system simulation of these imperfections in OFDM-based transceivers so as to study their impact on the RF analog transmitter and receiver performance. To summarize, here are the RF analog impairments we will take into account:

• In transmission:
  • DAC resolution, clipping, and clock sampling jitter;
  • LO phase noise;
  • quadrature imbalance;
  • PA distortions.
• In reception:
  • LNA nonlinearities IP2 and IP3;
  • quadrature imbalance;
  • LO phase noise;
  • CFO and SFO;
  • ADC resolution, clipping, and clock sampling jitter.

The resulting analysis will be based on EVM estimation as a function of each of the RF analog impairments. The principle is to vary all the impairments individually and to observe their impact on the system performance through EVM estimation. In addition we will illustrate the results using PSDs, showing the noise and the distortion generated by the imperfections inside and outside the channel bandwidth. In order to target OFDM-based transceiver performance, we will compare the simulation results for two deployed standards: WLAN (OFDM WiFi: IEEE 802.11a/g) and mobile WiMAX (IEEE 802.16e). Actually, the choice of these two technologies is significant from an RF analog point of view because they use different subcarrier spacings; large for WLAN (312.5 kHz) and narrow for WiMAX (∼11 kHz). Indeed, we will ...