ceiver can discriminate between them-and one plus one is one. A few paragraphs cannot give an intuitive sense of how radio signals combine. The best we can do is help you understand that adding radio signals is a tricky business. Engineers doing this for decades still forget factors and components from time to time. 1.12 Conclusion In this chapter we have reviewed the basics of radio engineering and their application to wireless technology. In the next chapter we will look at the challenges radio engi- neers face in making wireless systems work. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Source: CDMA CAPACITY AND QUALITY OPTIMIZATION Chapter Radio Signal Quality This chapter briefly defines the theoretical issues behind major challenges for cellular engineers. We look at noise, interference, and related issues, as well as issues related to radio signal measurement. The practical consequences of these issues will be ad- dressed in depth throughout the remainder of this book. 2.1 Radio Impairments Between a modulated and transmitted signal at one end and the received and demod- ulated version at the other end, a lot of bad things can happen. Since code division mul- tiple access (CDMA) demands more of our radio links than most earlier technology, these impairments have to be understood and managed more carefully than before. We can divide radio impairments into four basic categories: noise, interference, dis- tortion, and multipath. 2.1.1 Noise Every radio receiver has some internal electrical activity that has nothing to do with the electromagnetic radiation it is designed to receive. There is a quantum-level atomic component called thermal noise that increases with temperature and frequency band- width. 1 Other than operating our radio telephones in Dewer flasks of liquid helium, there isn't much we can do about thermal noise. Noise is 