Bit Error Rates of Digital Modulation Techniques 1

[suanruey]

Hi everyone. I am new to this forum and this is my first post. It is an honor to meet all of you.

Currently i am working on a communication system design for a line of sight communication link. I need to find out the bit error rate of these following techniques: BPSK, QPSK, 16QAM and 32QAM.

My thoughts are that, to demonstrate the efficiency of the given techniques, I should be using graphs of BER vs Signal-to-Noise ratio and/or BER vs Eb/N0. My trouble is that, i was able to calculate BER using the set values of transmitted power, bandwidth and data rate. However, my supervisor advised that the calculated BER values are wrong and i should refer to the typical graphs of BER vs Eb/N0 in illustrated in books, such as the link stated below.

http://www.keysight.com/upload/cmc_upload/ck/4W/images/w1712fig2.png

(view the ones in black headings)

Knowing the given concepts, the eb/n0 is found against using a typical value of 10^-7 BER value to demonstrate the effectiveness of a real-life receiver sensitivity threshold. However, given the set parameters, the eb/n0 for the different modulations is set to be lower and these values are perceived to be wrong by my supervisor.

In that case, what are the methods that i could do to demonstrate the effectiveness of my communication systems, and also to show that it meets the requirements of a minimum 10^-7 value with the set values of transmitted power, bandwidth, and data rates?

The given values are as follows:
1) Transmitted Power - 10 Watts
2) Bandwidth - 20 MHz
3) Data rate - 16Mbps
4) Frequency used - 800Hz, 900Hz, 1.24GHz, 1.8GHz, 2GHz, 2.1GHz, 2.4GHz, and 5GHz

Thank you so much everyone who had viewed this post. I greatly appreciate everyone whom is able to give me guidance on this matter. Thank you so much again

Regards,
Jay

 

[IRstuff]

Given your parameters, there is no error rate, since you've not specified anything related to noise, i.e, N₀, nor have you specified anything related to receiver sensitivity, or range. What is your link budget?

Beyond that, the analysis is done; there's nothing else to do. Every modulation scheme described is cast in concrete relative to the basic BPSK, and is worse. That relationship cannot change, since the fundamental benefit is higher data rate, which comes at the expense of the energy per bit. Since the higher data rate automatically reduces E_b, which increase BER. You "simply" need to figure realistic values for the noise characteristics.

TTFN
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[suanruey]

Hi Mr IRstuff

No. I do not have any sorts of error rate because i'm assuming an ideal system with no internal resistance. The BER vs Eb/N0 graph i'm referring to is as shown below.

http://www.keysight.com/upload/cmc_upload/ck/4W/images/w1712fig2.png

The link budget is:

Gains
Tx gain - 20 dB
Rx Gain - 20 dB

Losses
Loss - Terrestrial losses. Due to ground bounce, or the Two-ray ground reflection model, and refraction; no multipath, fading, or shadowing. Followed by rain attenuation.

Noise - N = k * T * B; where the k is Boltzmann constant of 1.38 x 10^-23 and T is assuming room temperature, which is 290 Kelvins.

Does that mean that for the analysis, all i have to explain is how the different modulation schemes affect the system's performance isnt't it?

Regards
Jay

 

[suanruey]

In addition to the previous post,

range - 2km, 50km , and 100km
Receiver sensitivity - (-60) dB, minimum threshold which receiver can receiver signal power

Regards
Jay

 

[IRstuff]

I suggest you dig out your college text books or read some of the tutorials on the web. You need to determine your E_b and N₀. Given your link budget, one or more of your modulation schemes will meet the BER requirement.

TTFN
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[suanruey]

I see. Sure. Thank you Mr IRstuff for the guidance.

Regards
Jay

 

[suanruey]

Hi everyone again. I would like to refer you to the first post of this thread.

"Knowing the given concepts, the eb/n0 is found against using a typical value of 10^-7 BER value to demonstrate the effectiveness of a real-life receiver sensitivity threshold. However, given the set parameters, the eb/n0 for the different modulations is set to be lower and these values are perceived to be wrong by my supervisor. "

I had made a mistake for the highlighted section. The Eb/N0 that i had actually calculated is higher than the perceived Eb/N0 of each modulation scheme to meet 10^-7 BER value. Hence, this means that the BER that is obtained from the higher Eb/N0 is lower than the minimally required BER.

In that case, as i had iterated before, what are the methods that i could do to demonstrate the effectiveness of my communication systems, and also to show that it meets the requirements of a minimum 10^-7 value with the set values of transmitted power, bandwidth, and data rates without relying on the obtained lower BER values?

Regards
Jay

 

[VEBill]

Real world system designs don't usually have such lovely round numbers, nor a selection of values as input.

Are you sure that this isn't a homework assignment?

 

[IRstuff]

"I had made a mistake for the highlighted section. The Eb/N0 that i had actually calculated is higher than the perceived Eb/N0 of each modulation scheme to meet 10^-7 BER value. Hence, this means that the BER that is obtained from the higher Eb/N0 is lower than the minimally required BER.

In that case, as i had iterated before, what are the methods that i could do to demonstrate the effectiveness of my communication systems, and also to show that it meets the requirements of a minimum 10^-7 value with the set values of transmitted power, bandwidth, and data rates without relying on the obtained lower BER values?"

You appear to be confused about the purpose of the analysis. I suspect that your boss thinks your calculations are OVERLY optimistic and that you should re-check how you arrived at your E_b/N₀. It may be that you are correct, but given your apparent lack of experience, and his presumed abundance of experience, the odds are not in your favor. If you have so much margin, then you should be able to do a number of things to reduce the margin, like reducing transmit power, or using a cheaper, noisier receiver, or increasing the data bandwidth. Excess margin equates to excess cost, which is anathema to a tightly run business.

As to your question, it's moot. The accepted characterization of a comm system is its BER, so anything else is irrelevant, since there's no other accepted method for comparing systems.

TTFN
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