Channelisation Codes
Transmissions from a single source are separated by channelisation codes, i.e. downlink
connections within one sector and the dedicated physical channel in the uplink from one
terminal. The spreading/channelisation codes of UTRA are based on the Orthogonal
Variable Spreading Factor (OVSF) technique, which was originally proposed.
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. In case the connection uses a variable spreading factor, the proper use of the code tree also allows despreading according to the smallest spreading factor.
This requires only that channelisation codes are used from
the branch indicated by the code used for the smallest spreading factor.
