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10 - Random access

Published online by Cambridge University Press:  28 February 2011

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

Random access is generally performed when the UE turns on from sleep mode, performs handoff from one cell to another or when it loses uplink timing synchronization. At the time of random access, it is assumed that the UE is time-synchronized with the eNB on the downlink. Therefore, when a UE turns on from sleep mode, it first acquires downlink timing synchronization. The downlink timing synchronization is achieved by receiving primary and secondary synchronization sequences and the broadcast channel as discussed in Chapter 9. After acquiring downlink timing synchronization and receiving system information including information on parameters specific to random access, the UE can perform the random access preamble transmission. Random access allows the eNB to estimate and, if needed, adjust the UE uplink transmission timing to within a fraction of the cyclic prefix. When an eNB successfully receives a random access preamble, it sends a random access response indicating the successfully received preamble(s) along with the timing advance (TA) and uplink resource allocation information to the UE. The UE can then determine if its random access attempt has been successful by matching the preamble number it used for random access with the preamble number information received from the eNB. If the preamble number matches, the UE assumes that its preamble transmission attempt has been successful and it then uses the TA information to adjust its uplink timing. After the UE has acquired uplink timing synchronization, it can send uplink scheduling or a resource request using the resources indicated in the random access response message as depicted in Figure 10.1.

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LTE for 4G Mobile Broadband
Air Interface Technologies and Performance
, pp. 226 - 250
Publisher: Cambridge University Press
Print publication year: 2009

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  • Random access
  • Farooq Khan
  • Book: LTE for 4G Mobile Broadband
  • Online publication: 28 February 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9780511810336.011
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  • Random access
  • Farooq Khan
  • Book: LTE for 4G Mobile Broadband
  • Online publication: 28 February 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9780511810336.011
Available formats
×

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.

  • Random access
  • Farooq Khan
  • Book: LTE for 4G Mobile Broadband
  • Online publication: 28 February 2011
  • Chapter DOI: https://doi.org/10.1017/CBO9780511810336.011
Available formats
×