General Description
R&S
®
CMW-KM750/-KM751
19
User Manual 1173.9670.02 ─ 05
Fig. 3-6: Traffic timeslot structure
3.4.2 Channelization for CDMA
Channelization is applied to the data part of physical channels. This operation transforms
each data symbol into a number of chips. The number of chips per data symbol is called
Spreading Factor (SF). The symbol rate of the resulting channel equals the chip rate of
the total signal divided by the spreading factor: Symbol rate (Channel) = 1.28 Mcps / SF
(Channel). For uplink signals the allowed spreading factors are: 1, 2, 4, 8 and 16.
The transformation operation involves channelization codes c
SF,k
defined in terms of the
spreading factor SF and the index k ranging from 1 to SF (also called channelization code
number). The codes are defined in 3GPP TS 25.223 and are derived from a hierarchical
tree:
These codes are Orthogonal Variable Spreading Factor (OVSF) codes, allowing to
superimpose channels with different spreading factors in the same timeslot while pre-
serving the orthogonality. When assigning spreading factors and channelization codes
(code numbers) to channels, one rule has to be observed to preserve orthogonality:
Within each branch only one code can be used at the same time.
This means:
●
Other codes on the path between the code and the root of the tree must not be used.
●
Codes in sub-branches of the code (to the right of the code) must not be used.
For an example see the figure below. The red parts are blocked when c
4,4
is used.
TD-SCDMA Signal Properties
