Hi Hamid,
The maximum throughput of your communication is dependent on the microcontroller clock, and the speed of the transfer. There are a certain amount of clock cycles to perform each function. For example, it will take a certain amount of time to retrieve the data, some more time to structure the data, some more time to prepare to print out the data, then the time to actually send the data. If all the micro did was to send data, you could send no more than 960 characters per second. The more characters (including non-printable characters like new line and carriage return) the longer it will take to transmit the data.
It will also take a certain amount of time to capture the data, process and store it. All these events take a certain amount of time. As you have a processing loop, you need to consider how much time it takes to run the process completely. It is not clear to me what is happening in this loop.
One thing you could do is see how fast you can print without capturing new data. Just keep printing the time over and over (with data characters printed as well) and see what the maximum print rate is as this will determine the speed of printing. Then add one data capture and add that to the print to see the difference in time.
Best regards,
Bob B