RFWCDMA/UMTS OVSF Codes Explained
wcdma
ovsf code
channelization
umts
wireless communication
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Understanding OVSF Codes
OVSF stands for Orthogonal Variable Spreading Factor. These codes are also known as channelization codes and are primarily used to separate data and control channels originating from the same User Equipment (UE).
- Key Function: Preserves orthogonality between control and data channels, minimizing interference.
Key Features of OVSF Codes in WCDMA
OVSF codes bring several advantages to WCDMA systems:
- Variable Spreading Factor: OVSF codes allow the spreading factor (which determines data rate) to be dynamically adjusted.
- Maintained Orthogonality: Crucially, orthogonality is maintained even when using different spreading codes of varying lengths.
- Code Tree Selection: Codes are chosen from a pre-defined code tree based on the required data rate and available channel numbers.
OVSF Code Properties and Usage
| Code OVSF (channelisation code) | Property |
|---|---|
| Orthogonal property | Helps to reduce interference. |
| Correlation properties | 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 |
| Spreading | Increases bandwidth |
