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4 - Single-carrier FDMA

Published online by Cambridge University Press:  28 February 2011

Farooq Khan
Affiliation:
Samsung Telecommunications America, Richardson, Texas
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Summary

The design of an efficient multiple access and multiplexing scheme is more challenging on the uplink than on the downlink due to the many-to-one nature of the uplink transmissions. Another important requirement for uplink transmissions is low signal peakiness due to the limited transmission power at the user equipment (UE). The current 3G systems use the wideband code division multiple access (WCDMA) scheme both in the uplink and in the downlink. In a WCDMA downlink (Node-B to UE link) the transmissions on different Walsh codes are orthogonal when they are received at the UE. This is due to the fact that the signal is transmitted from a fixed location (base station) on the downlink and all the Walsh codes received are synchronized. Therefore, in the absence of multi-paths, transmissions on different codes do not interfere with each other. However, in the presence of multi-path propagation, which is typically the case in cellular environments, the Walsh codes are no longer orthogonal and interfere with each other resulting in inter-user and/or inter-symbol interference (ISI).

The problem is even more severe on the uplink because the received Walsh codes from multiple users are not orthogonal even in the absence of multi-paths. In the uplink (UE to Node-B link), the propagation times from UEs at different locations in the cell to the Node-B are different. The received codes are not synchronized when they arrive at the Node-B and therefore orthogonality cannot be guaranteed.

Type
Chapter
Information
LTE for 4G Mobile Broadband
Air Interface Technologies and Performance
, pp. 70 - 87
Publisher: Cambridge University Press
Print publication year: 2009

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  • Single-carrier FDMA
  • Farooq Khan
  • Book: LTE for 4G Mobile Broadband
  • Online publication: 28 February 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9780511810336.005
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  • Single-carrier FDMA
  • Farooq Khan
  • Book: LTE for 4G Mobile Broadband
  • Online publication: 28 February 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9780511810336.005
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.

  • Single-carrier FDMA
  • Farooq Khan
  • Book: LTE for 4G Mobile Broadband
  • Online publication: 28 February 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9780511810336.005
Available formats
×