Wireless Transceiver Architecture

6 RF Impairments

A final set of limitations classically encountered in the implementation of wireless transceivers is related to what are called RF impairments. What do we mean by this term? We have in fact already encountered phenomena caused by what could be called RF impairments. A good example of this is even order nonlinearity, detailed in Chapter 5, which is for the most part related to the mismatch between, or the impairment of, elements expected to be identical in RF/analog devices.

In wireless transceivers, the term “RF impairments” is classically associated with degradations linked to the implementation of complex frequency conversions in the analog domain. Given that the implementation of such functionality requires the use of two LO waveforms in quadrature, any imbalance between those LO signals indeed results in a degradation of the processing. The corresponding system limitations are of particular importance as such complex frequency conversion is widely used, for various reasons discussed in this chapter. It even necessarily occurs at some point in a line-up when dealing with complex modulating waveforms as introduced in Chapter 1. However, before going any further, it is of interest to review the frequency conversion processing itself. This allows us to understand in greater depth the mechanisms involved in what are called real and complex frequency conversions and thus the associated system limitations we can expect in the presence of such impairments. It also ...