| CDMA Reference Blockset | |
Hints for Using the CDMA Reference Blockset
This section describes some conventions that the CDMA Reference Blockset uses. Understanding these conventions helps you interpret the demo models, construct your own models, and troubleshoot models.
Understanding Rates and Rate Sets
The IS-95A CDMA standard allows for data transmission at four different rates. The four rates together form a rate set. The CDMA Reference Blockset supports two rate sets. The first is based on the IS-95A standard, while the second is based on the J-STD-008 requirement. Both rate sets allow for varying-rate speech coders.
Some blocks in this blockset, such as the IS-95A Fwd Ch Repeater/Derepeater, behave differently depending on the data transmission rate. In such blocks, you specify the rate set as a dialog box parameter (called Rate set in the block dialog box) and you select the data transmission rate using an input signal (marked Rate near the input port of the block icon). After a simulation begins, you can change the data rate by changing the Rate input, but you cannot change the Rate set parameter.
The following table shows how different values for the Rate input determine the data transmission rate, for each of the two Rate set parameter values.
Because the Rate value is an input to a block rather than a dialog box parameter, you can easily change the data rate during a simulation. However, the vector lengths of the input and output signals are fixed throughout the simulation at the maximum possible size for any data rate. This means that if, at a given time in the simulation, the data rate is smaller than the maximum, then the input and output signals consist partially of relevant information and partially of placeholder bits that the block does not process. To find out how many bits are relevant for a particular block with a particular data rate, see the block's online reference page by pressing the block's Help button.
| Note To ensure compatibility of blocks within your model, use the same Rate set parameter and Rate input for all blocks that process a given frame of data. |
The modulation bit rate is the same for all rate sets and data rates, as a result of different convolutional coding and code repetition procedures. The symbol rate after interleaving is 28.8 ksps for the reverse channel and 19.2 ksps for the forward channel. However, for Rate Set II, data puncturing is performed before interleaving to bring the symbol rate from 28.8 to 19.2 ksps. This means that two of every six symbols are deleted. Therefore, the symbol rate of the forward link after the interleaver is 19.2 ksps for all rates and rate sets.
| | IS-95A Common Library | Understanding Frame Contents and Padding | |