Communication Engineering Tutorial

[Millard Winnin]

Inthis tutorial, the basic concepts of communications along with the important concepts of analog and digital communications have been covered. This tutorial is helpful for a beginner who wants to acquire knowledge on the communication systems. There are a few topics in this tutorial covering the concepts of digital communications, which are elaborately discussed in our Digital Communication tutorial.

The communication based on analog signals and analog values is known as Analog Communication. This tutorial provides knowledge on the various modulation techniques that are useful in Analog Communication systems. By the completion of this tutorial, the reader will be able to understand the conceptual details involved in analog communication.

A basic idea regarding the initial concepts of communication is enough to go through this tutorial. It will definitely help if you use our tutorial Signals and Systems as a reference. A basic knowledge of the terms involved in Electronics and Communications would be an added advantage.

At this moment, I am working on TCM and I read many times your tutorial on it. My goal is to prove that using TCM, with a 2/3 rate convolutional coder and a QAM-16 constellation mapping, I can acheive the same or better coding gain then a standard 8-PSK modulation scheme. My problem is to actually find a good 2/3 convolutional encoder with a good minimum squared distance. I tried the one in the tutorial, but with the suggested QAM-16 constellation mapping, the shortest path, is definitly too short to get a significant coding gain. Do you have any suggestion regarding a good convolutional encoder for QAM-16 TCM?

At this moment, I am working on fft/ifft for OFDM and I read many times your tutorial on it. My goal is to prove that using FFT/IFFT, with a 2/3 rate convolutional coder and a QAM-16 constellation mapping, I can acheive the same or better coding gain then a standard 8-PSK modulation scheme. My problem is to actually find a good 2/3 convolutional encoder with a good minimum squared distance. I tried the one in the tutorial, but with the suggested QAM-16 constellation mapping, the shortest path, is definitly too short to get a significant coding gain. Do you have any suggestion regarding a good convolutional encoder for QAM-16 TCM?

Hi,

I have been an electronics engineer for nearly a decade. Although I was only recently steered towards this site by a friend, the experience of going through these tutorials was like meeting a friendly and extremely interesting stranger whose charm does not fade with time, thank you for this excellent content and wishing you the very best.

I have a basic doubt. Consider a sine wave, if you take two times the sampling rate according to nyquist theorem. If 2 samples taken in a single period is at 0degree and 180degree.. Then we end up having all zeroes.. Can you please explain it?

Actually the 0 points mean that you have used a NYquist frequency that is exactly 2 timrs, but the definition says it needs to be larger than two tims the maximum frequency even if infinitesimally. Once you increase it a tiny bit, more than two times, you will not get those zeros and then can fit many harmonics through those points.

Just wanted to offer a sincere thanks for going to the trouble of putting together such a great site. You have a gift of making complex concepts easier to understand. This is a great use of the internet.

Best regards. Jim

I and my students are very thankful to you Charan for your tutorials and sincere efforts to make the tutorials easy and quick explanatory.especially your tutorial on Viterbi has helped me a lot to understand and teach precisely .

Hope to see some book on Communication soon.

Not clear if you are going a simulation or a closed form solution.

You will find the comparison of the closed form BER for a fading vs. a AWGN channel in my MIMO tutorial.

And yes, you should get a higher BER for for same SNR under a fading channel.

So you have some issue in your analysis.

I am asked to determine the required frequency spacing for the subcarriers such that each subchannel experiences a flat channel. Determine the resulting OFDM symbol period and Cyclic prefix to ensure no ISI among OFDM symbol.

hi Jorge, the frequency spacing should be more than the coherence bandwidth. Can you calculate that and see if it is near the 13 kHz. The other thing is that you need a power of two number of carriers so if your total bandwidth divided by the 13 kHz is not the power of 2 number, then you will have to zero pad those extra carriers and can not count them as carrying data.

I am going to assume that this is the max delay spread. Now the coherence BW is 1/DS = 666666 Hz. (I had a 2pi factor before, ignore) This is less than your bandwidth of 1 Mhz, so the channel will experience fading, but not a lot.

Coherence bandwidth relates more to total symbol rate. It is directly related to delay spread.

2pi/d. For the delay spread, you do not need four times the delay spread, that would be adding a lot extra overhead. No more than x2 would be my choice.

Yes, the spacing needs to be less, not more than coherence bandwidth not more. I said it wrong.

Your coherence BW comes to about 4 MHz, but you are allocated 1 MHz. So you are limited in spacing by how much data you want to transmit. The maximum is 1 Msps which would require app. 1 Hz spacing and 1 kHz of data would need app 1 kHz spacing. (minus the CP overhead in each case). Hope this helps.

For this I calculated the first moment of the power delay profile (taking into account the multipath profile), which came to 1.51us. Then I calculated the second moment of the power delay profile, which resulted in: 4.53us.

The freeway is the electromagnetic spectrum, for 0 Hz to infinity Hz. We divide it into lanes of certain frequency band and those are called bands. Each media is capable of operating in only a few of these bands. Energy can travel in wires only in the lower bands, wireless can operate in pretty much all. The regulatory bodies control at which frequency you can transmit and assign you a small part of a band, and that is the bandwidth that you are assigned. You as an operator can then further subdivide the allowed band if you want, or use all in one channel.

For example, a satellite operator is allowed to use a band of 12 GHz to 13 GHz for downlink. He can take this 1000 MHz and then subdivide into ten 100 MHz channels. Then he would design his system for 100 MHz (often called transponders) and then place these like lanes on a freeway next to each other separated by 100 MHz center frequency. Each of these sub-bands then has a center frequency and a bandwidth, which is of course 100 MHz, the width.

The allowed frequencies are allocation by the ITU and best thought of as lanes on a road where you may drive and the media capability is best thought of as the with of the car that travels in that lane. The car with width is the media capability and it is always less than the allowed band in which it operates.

i will be glad to see the analysis of blind channel equalization algorithms, especially adaptive one basing on stochastic gradient methods. honestly i have to thank you a lot for your support in academic success.

Hi, your website has really helped a lot in understanding of digital communication. Tutorial of raised cosine pulse shaping and isi Are explained in much simple and clear form. Thanks a lot for your efforts.

Charan, simlpy the best explanation of modulation techniques I have come across in my 20 years in Broadcast engineering. Others tend to leave out the realisation of the modulators, however your step by step and diagramtic approach is simply magic.

EXTREEMELY INFORMATIVE AND INTERESTING TUTORIALS IN DIGITAL MODULATIONS PRINCIPLELS UNDERSTANDING AND THE FUNDAMENTAL CONCEPTS ARE MADE VERRY CLEAR-I AM AN ELETRICAL ENGINEER TRYING TO UNDERSTAND THE FUNDAMENTALS IN COMMUNICATION THEORY AND PRACTICALS IN THIS ERA OF COMMUNICTIONS.-I AM EXTREEMELY THANKFULL TO YOU FOR PROVIDING THIS INSIGHT INTO DITAL MODULATIONS SO CLEARLY AND IN SIMPLE CONCEPTUAL MANNER WITH APPROPRIATE DIAGRAMS AND WAVE FORMS-I AM HIGHLY OBLIGED TO YOUR TUTORIALS PUBLISHED ON LINE.-THANK YOU IMMENSELY.

Firstly i want to thank you for putting together such good tutorials. I am doing my masters in Communications and Signal Processing. This forum has helped me a lot since the commencement of my degree. I have a request if you can take out some time to prepare a tutorial on FBMC (Filter Bank Multi Carrier) modulation scheme. Currently, I am about to start a project on this topic but can not find a specific and to the point tutorial on this topic. Your effort would be really appreciated.

Thank You

Hello Ms. Charan! Your tutorials have helped much more than entire semesters of wireless comm classes combined. Please keep up the good work.

Will you be posting any tutorials on wireless channel modeling and MIMO-OFDM? It would be very beneficial as channel modelling is a common but challenging topic and MIMO-OFDM is the technology of choice, but the mathematics and concepts may be difficult to grasp at first hand. Please let me know

On the whole, the couple paragraphs below it make it seem like all complex exponentials have a spectrum only in the positive domain which is slightly confusing. For instance, e^-jwt does not. A proof that the hilbert transform results in positive frequency would be great.

Your tutorials are exellent regarding the explanation but there are so many mistakes with the math. You need to go through them as it can be confusing when equations make no sense! however i still value your work. if you correct this then it is perfect.

Thank you very much Charan. This site is really helpful for understanding Digital Communications.

I had gone through Turbo Coding and Decoding. It really helped me alot in getting a big picture of Turbo Codes.

Thank you once again for explaining the concepts and on creating such a wonderful website for wireless Communications. Eagerly waiting for your explanations/teachings on contemporary wireless communication topics.

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