Dear all,
Recently a lot of emails and questions have been received on "what is expected in the last lab."
The most important things are as follows:
1. Which system (modified 4FSK, modified 4ASK, your 4ASK+FSK) is better w.r.t BER for your parameters and why?
2. Which system (modified 4FSK, modified 4ASK, your 4ASK+FSK) is better w.r.t spectrum usage for your parameters and why?
3. Which system do you consider ideal in real conditions and why? Under which condition will you prefer your 4ASK+FSK over that ideal system and why? What are pros and cons of all these systems?
4. Are conventional 4FSK and 4ASK better than the above mentioned systems (in terms of BER and spectrum usage) and why?
Very long reports are not required for this 1 credit lab. I think you may use 5 pages for this if possible for you. Discussions like explanations on look-up tables, multiport switch to select signals, use of float for matching the data types, etc are not useful. You have to discuss Digital Communication Systems (not simulink usage).
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1. If you wish, you are free to reduce your fc and fd by a factor of 10 if your computer is not able to ensure enough sampling time for it. Prof. Silage gave you 200KHz so that you understand how crucial/costly the speed of analog-to-digital conversion becomes in real systems. In fact, it makes a very huge contribution in the cost of all the practical systems. The price of ADC increases (more than) exponentially with their speed and the number of bits used by them.
2. If you wish, you are free to use any other values of fd (only if) your current values result in non-orthogonal signal set. This means that you can select cos(2pi(fc+fd)t), cos(2pi(fc+2fd)t), cos(2pi(fc-fd)t) and cos(2pi(fc-2fd)t) such that they are orthogonal to each other during one symbol time.
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I must put a note on the importance of ASK ad FSK based systems which might be useful in overall understanding of all the labs. There are practical constraints which have resulted in emergence of these different types of systems.
-For 4-ASK systems
Standard ASK uses different amplitudes but only one frequency. Therefore, they might use less spectrum than FSK to transfer same amount of information in a given time. However, they may need more power and if the frequency band used by the ASK observes severe environmental perturbations/jammers, all the data can be lost or damaged.
-For 4FSK system
Standard FSK uses only one amplitude but different frequencies. If a band of frequency is jammed (or even perturbed), it is still possible to send data on other frequencies. Recent techniques use more than 1024 orthogonal subcarriers.
---For your FSK+ASK system
In real systems, different frequency signals may be transmitted with different gains. This is because the channels can be frequency selective (different loss for different frequency signals). Moreover, note that as the frequency increases, the propagation loss also increases.
I thought above notes were important before ending this very pleasant semester. I hope you enjoyed the course as well as the lab.