WCDMA: Difference between Channel Bit Rate and User Data ? (Is it the half , why?)

[UnSolved1994]

Given the following Diagram:

41696

It seems that the UserData (kb/s) is halft the Channel bit Rate (kb/s):

41697

Why the User Data seems to be half the Channel Bit rate , is it beacuse the modulation , if so? How can I get to that conclusion?


Thanks , Im stuck in this !

[Nyquist]

Hi.
First, you need to have clear both definitions: Channel Bit Rate and User Data Rate.
Always User Data Rate will be smaller than Channel Bit Rate.
WCDMA was designed (as all digital radio transmissions do) to protect user data against interferences and losses.
One bit of information could be transformed into two or even more depending on the protected method.
This is the general reason.
In order to know the exact Channel/User rates you should dive into the WCDMA method of coding the different channels.

Hope it helps

[firstmaxim]

On the downlink, the downlink channel also contains control information in addition to the user data. Furthermore, there are protection bits.

[UnSolved1994]

Thanks I understand ! So,in the case of the picture it seems they are using channeling codes of spreading factor of 2. That'ts why it is reduced by half.

[UnSolved1994]

@firstmaxim , yes that is why the user rate is less than the half.