Noise Modelling - Digital communication systems

In summary, the problem is that the noise figure in dBm is not referenced to any unit, so it is just a random number that the author picked.
  • #1
CMW328i
8
1
Hi all, Teacher here looking for some guidance. I'm teaching a class that I took myself a few years back, and I'm looking at my solution to a problem but I have a random value in my answer (which I know to be correct) but I can't for the life of me remember where this value came from! Can anyone help?

1. Homework Statement

A receiver in a digital mobile communication system has a noise bandwidth of 200 kHz and requires that its input SNR should be at least 10 dB when the input signal is -104 dBm.
What is the maximum permitted value of the receiver noise figure?2. Homework Equations

FdB = Ps -SNR -10log (kTB)

3. The Attempt at a Solution

FdB = (-104 -30)-10 -10log (1.399x10^-23*290*200000) = 6.9 dBI can't for the life of me figure out where the -30 comes from. I even have an excerpt from the book the question came out of and it just shows the -30 in the equation without explaining where it comes from. Any ideas?

I see the input at -104, I see the bandwith, the required SNR, but no origin for -30
 
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  • #2
CMW328i said:
Hi all, Teacher here looking for some guidance. I'm teaching a class that I took myself a few years back, and I'm looking at my solution to a problem but I have a random value in my answer (which I know to be correct) but I can't for the life of me remember where this value came from! Can anyone help?

1. Homework Statement

A receiver in a digital mobile communication system has a noise bandwidth of 200 kHz and requires that its input SNR should be at least 10 dB when the input signal is -104 dBm.
What is the maximum permitted value of the receiver noise figure?2. Homework Equations

FdB = Ps -SNR -10log (kTB)

3. The Attempt at a Solution

FdB = (-104 -30)-10 -10log (1.399x10^-23*290*200000) = 6.9 dBI can't for the life of me figure out where the -30 comes from. I even have an excerpt from the book the question came out of and it just shows the -30 in the equation without explaining where it comes from. Any ideas?

I see the input at -104, I see the bandwith, the required SNR, but no origin for -30
Is it a conversion between dB W and dB mW?
 
  • #3
Ah ha! That may be it actually!
 

What is noise modelling in digital communication systems?

Noise modelling is the process of representing the effects of noise on a digital communication system. This includes understanding the sources of noise, determining its characteristics, and developing mathematical models to simulate its impact on the system.

What are the sources of noise in digital communication systems?

The main sources of noise in digital communication systems include thermal noise, intermodulation noise, shot noise, and crosstalk. Thermal noise is caused by random fluctuations in the system's temperature, while intermodulation noise results from nonlinearities in the system's components. Shot noise is caused by the discrete nature of electrons in a circuit, and crosstalk is caused by unwanted signals interfering with the desired signal.

How does noise affect digital communication systems?

Noise can significantly degrade the performance of digital communication systems by introducing errors in the transmitted signal. This can result in signal distortion, reduced signal-to-noise ratio, and increased bit error rates, leading to decreased data throughput and overall system performance.

What are the common modelling techniques used for noise in digital communication systems?

The most commonly used modelling techniques for noise in digital communication systems include statistical models, such as Gaussian and Poisson distributions, and deterministic models, such as Fourier analysis and signal-to-noise ratio calculations. These models are used to predict the impact of noise on the system and optimize its performance.

How can noise be mitigated in digital communication systems?

There are several techniques that can be used to mitigate noise in digital communication systems. These include using error-correcting codes, increasing the signal power, using better filtering and equalization techniques, and implementing advanced modulation schemes. Additionally, proper system design, placement of components, and shielding can also help reduce the impact of noise on the system.

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