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Private Femtocells for Indoors

UltraSON™ Mobility Management Suite

Femtocells operate on licensed spectrum and provide excellent user experience through better coverage for voice and very high data throughputs. When a mobile camping on a macro-only frequency approaches a femtocell, it is essential that the mobile searches and reselects to the femtocell so as to facilitate efficient offloading of macro traffic. However, in good macrocell coverage, the mobile may not perform inter-frequency search for other cells and, hence, the reselection procedure may not be triggered and thus user may not be able to discover and camp on its own femtocell. The objective of an efficient discovery scheme is not only to find the femtocells quickly but also minimize any potential impact on the battery life of all mobile devices served both by macro and as well as femtocells.

Details

UltraSON™ Mobility Management Suite provides the following features:

  • Idle Mode Femto Discovery: This feature provides a fast and reliable discovery via beacon transmission with minimal impact on macro mobile performance.
  • Active Hand-in: This feature provides a reliable method to handover from macro to femto in active mode via beacon and target femtocell disambiguation.
  • Transmit Diversity: This feature implements dual femto transmit antennas to reduce number of handovers and improve voice quality especially in indoor environments.

To address the femtocell discovery issue, an innovative approach based on cell-reselection-beacons is proposed in which the femtocell transmits a beacon on macro–only frequencies. The beacon is designed to trigger mobile device to search the femtocell carrier and reselect to a femtocell.

Further, beacon transmission is used to  facilitate inter-frequency hand-in of macro users to femtocells in active mode.  Beacons solve key challenges of active hand-in namely (1) absence of a reliable inter-frequency hand-in trigger and( 2) presence of PSC confusion arising from PSC reuse among femtocells.

The Femtocells R&D group has performed extensive research in the area of femto mobility management, conducted numerous simulations and lab experiments to show the effectiveness of the innovations in addressing the femtocell discovery issue in both idle and active modes.