# What the disadvantages of up-sampling

Let's say we have a signal $$x[n]$$ upsampled at the transmitter by $$4$$ and then downsampled at the receiver by $$4$$ too. As known, the performance will be much better compared with transmitting the signal without upsampling. but what I need to understand, what is the disadvantage of using up-sampling ? Does that effect the data rate of the transmitted signal since we transmit $$4$$ times the signal $$x[n]$$ instead of $$x[n]$$?

• Upsampling is just a tool that is used in context. A couple of hints: $x[n]$ goes by different names BEFORE and AFTER it is upsampled at that point. The second hint would come from looking at the relationship between sampling frequency and symbol rate. Once you clarify these two points, then you can start thinking in terms of "pros and cons". What is the alternative to upsampling at that point? – A_A Jun 23 at 8:26

When you upsample a signal by a factor of 4, then, you have to churn out 4 times the number of samples in the same time in order to maintain the same Symbol Rate. Otherwise your symbol rate will be $$\frac{1}{4}$$ times the original symbol rate. This means your DAC needs to operate at least at 4 times the sampling frequency now. This can be costly. Also faster clocks need better synchronization techniques.