6.2 Channelisation codes

25.2233GPPRelease 17Spreading and modulation (TDD)TS

The elements ; k=1,…,K_Code; q=1,…,Q_k; of the real valued channelisation codes

; k=1,…,K_Code;

shall be taken from the set

(3)

The are Orthogonal Variable Spreading Factor (OVSF) codes, allowing to mix in the same timeslot channels with different spreading factors while preserving the orthogonality. The OVSF codes can be defined using the code tree of figure 1.

Figure 1: Code-tree for generation of Orthogonal Variable Spreading Factor (OVSF)
codes for Channelisation Operation

Each level in the code tree defines a spreading factor indicated by the value of Q in the figure. All codes within the code tree cannot be used simultaneously in a given timeslot. A code can be used in a timeslot if and only if no other code on the path from the specific code to the root of the tree or in the sub-tree below the specific code is used in this timeslot. This means that the number of available codes in a slot is not fixed but depends on the rate and spreading factor of each physical channel.

For the 3.84Mcps and 1.28Mcps TDD options, the spreading factor goes up to Q_MAX=16; for the 7.68Mcps TDD option, the spreading factor goes up to Q_MAX=32.