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7 - Diversity

Published online by Cambridge University Press:  05 June 2012

Andrea Goldsmith
Affiliation:
Stanford University, California
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Summary

In Chapter 6 we saw that both Rayleigh fading and log-normal shadowing exact a large power penalty on the performance of modulation over wireless channels. One of the best techniques to mitigate the effects of fading is diversity combining of independently fading signal paths. Diversity combining exploits the fact that independent signal paths have a low probability of experiencing deep fades simultaneously. Thus, the idea behind diversity is to send the same data over independent fading paths. These independent paths are combined in such a way that the fading of the resultant signal is reduced. For example, consider a system with two antennas at either the transmitter or receiver that experience independent fading. If the antennas are spaced sufficiently far apart, it is unlikely that they both experience deep fades at the same time. By selecting the antenna with the strongest signal, a technique known as selection combining, we obtain a much better signal than if we had just one antenna. This chapter focuses on common methods used at the transmitter and receiver to achieve diversity. Other diversity techniques that have potential benefits beyond these schemes in terms of performance or complexity are discussed in [1, Chap. 9.10].

Diversity techniques that mitigate the effect of multipath fading are called microdiversity, and that is the focus of this chapter. Diversity to mitigate the effects of shadowing from buildings and objects is called macrodiversity.

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Publisher: Cambridge University Press
Print publication year: 2005

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  • Diversity
  • Andrea Goldsmith, Stanford University, California
  • Book: Wireless Communications
  • Online publication: 05 June 2012
  • Chapter DOI: https://doi.org/10.1017/CBO9780511841224.008
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  • Diversity
  • Andrea Goldsmith, Stanford University, California
  • Book: Wireless Communications
  • Online publication: 05 June 2012
  • Chapter DOI: https://doi.org/10.1017/CBO9780511841224.008
Available formats
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Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Diversity
  • Andrea Goldsmith, Stanford University, California
  • Book: Wireless Communications
  • Online publication: 05 June 2012
  • Chapter DOI: https://doi.org/10.1017/CBO9780511841224.008
Available formats
×