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Introduction

Historical Background

GSM

EDGE

WCDMA

  WCDMA

Carrier Spacing and Deployment Scenarios

Logical Channels

Control Channels

Uplink Physical Channels

Downlink Physical Channels

Packet Data

Handovers

Soft Handovers

Chapter Summary

UMTS

The Future

Final Thoughts

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Handovers

The WCDMA system's base stations do not need to be synchronized, and hence, there is no need for an external source of synchronization such as GPS. Asynchronous base stations have to be considered, especially when designing soft handover algorithms and when implementing position location services.

Before a soft handover happens, the MS measures observed timing differences of the downlink SCHs from the two base stations. The timing of a new downlink soft handover connection is adjusted with a resolution of one symbol. For example, dedicated downlink signals from the two base stations that are synchronized with an accuracy of one symbol. This enables the mobile RAKE receiver to collect the micro diversity energy from the two base stations. From this the timing adjustments of dedicated downlink channels can be carried out with a resolution of one symbol without losing orthogonality of downlink codes.

 

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