What is WCDMA/UMTS OVSF Code
• OVSF stands for Orthogonal Variable Spreading Factor. They are also referred as channelization codes.
They are used to separate data and control channels from same UE
• It preserves orthogonality between these control and data channels. Following are useful features of OVSF codes used in WCDMA system.
• The use of OVSF codes allows the spreading factor to be changed and orthogonality between different spreading codes of different lengths to be maintained
• The codes are picked from the code tree, based on the data rate and channel numbers requirement
|Property||Orthogonal property helps to reduce interference. Do not have good correlation properties. Needs additional long codes. Walsh code is an example.|
|Usage||Uplink- separation of DPDCH and DPCCH from same UE. Downlink- separation of DL connections to different users within one cells.|
|Length||Uplink- 4-256 Downlink- 4-512|
|Number of codes||Number of codes under one scrambling code = spreading factor|