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Description: Downlink othogonal codes allocation
Library: 3GPPFDD 10-99, Spreading & Modulation









types of OVSF sequences



int array

[2, ∞)


numbers of code channels



int array

[1, 2TT ]

Pin Outputs




Signal Type



OVSF sequences

multiple int

  1. This model is used to generate single or multiple orthogonal variable spreading factor (OVSF) sequences as spreading codes for downlink transmission. The OVSF sequence family has a tree-structure; the length of each OVSF sequence varies to meet multi-rate transmission. Orthogonality is maintained among all output spreading sequences. The maximal length of these spreading sequence output tokens is produced for each output signal.
  2. The matrix size of TypeArray must be equal to that of ChannelNumberArray.
  3. Layered OVSFs are generated from recursions:

    = 1


    All OVSF sequences of the same layer are orthogonal to each other. From each OVSF sequence Cn (m), two additional OVSF sequences ( Cn+ 1 (2m) and Cn+ 1 (2m+1) ) are generated. These two sequences are not orthogonal to the sequence from which they are generated-the mother sequence. However, the other 2n − 2 sequences are orthogonal to this mother sequence. So the sequences generated from a mother sequence cannot be used as spreading codes if this mother sequence is applied. This restriction is imposed on the spreading code allocation to maintain orthogonality among all output OVSF sequences as spreading codes.
    In downlink transmission, sequence C8(0) is dedicated to the Primary CPICH and sequence C8(1) is dedicated to the Primary CCPCH. Therefore, all mother sequences of C8(0) and C8(1) are set occupied.
    Since the cycle of a spreading code is one symbol in length as defined in [1], the cycle of a spreading code of the same chip rate varies according to the symbol rate; and, the number of spreading codes available varies according to the symbol rate. Spreading code rates are listed in the following table.
    Spreading Code Rates for 3.84 Mcps Chip Rate
    Condition Symbol Rate
    7.5 15 30 60 120 240 480 960
    Spreading code type 9 8 7 6 5 4 3 2
    Spreading code length 512 256 128 64 32 16 8 4
    Number of spreading codes 512 256 128 64 32 16 8 4

  1. 3GPP Technical Specification, TS 25.213, V3.0.0, "Spreading and modulation (FDD)," Oct 1999.
  2. K. Okawa and F. Adachi, "Orthogonal Multi-Spreading Factor Forward Link for Coherent DS-CDMA Mobile Radio," in Proc. 47th IEEE VTC'97, Phoenix, May 1997.
  3. L. Tie and X. Haige, "A Improved Multi-rate Scheme for DS-CDMA System" (in Chinese), in Journal of China Institute of Communications, Vol. 19, pp.24-28, March 1998.
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