Filter Using Simulink Raised Cosine Filter Blocks
The Raised Cosine Transmit Filter and Raised Cosine Receive Filter blocks are designed for raised cosine filtering. Each block can apply a square-root raised cosine filter or a normal raised cosine filter to a signal. You can vary the roll-off factor and span of the filter.
The Raised Cosine Transmit Filter and Raised Cosine Receive Filter blocks are tailored for use at the transmitter and receiver, respectively. The transmit filter outputs an upsampled (interpolated) signal, while the receive filter expects its input signal to be upsampled. The receive filter lets you choose whether to have the block downsample (decimate) the filtered signal before sending it to the output port.
Both raised cosine filter blocks introduce a propagation delay, as described in Group Delay.
Combining Two Square-Root Raised Cosine Filters
This model shows how to split the filtering equally between the transmitter's filter and the receiver's filter by using a pair of square root raised cosine filters.
The use of two matched square root raised cosine filters is equivalent to a single normal raised cosine filter.
The filters share the same span and use the same number samples per symbol but the filters on the upper path have a square root shape while the filter on the lower path has the normal shape.
Run the model and observe the eye and constellation diagrams. The performance is nearly identical for the two methods. Note that the limited impulse response of practical square root raised cosine filters causes a slight difference between the response of two cascaded square root raised cosine filters and the response of one raised cosine filter.