Q:   What should be the entropy formula ? 

A: There is a typo in the lecture 5 notes page 7 about entropy. The entropy of the source is:  

         H= - S p(a_j) log₂ (p(a_j))  , here p(a_j) is the prob. of the event that the source will produce a symbol a_j.

Q:   How to create a OPEN Directory in Unix account ? 

A: Suppose my directory name is ~/cs3242/assign1, type the following commands: (Please be familiar with basic Unix commands. )

    chmod 711 ~

    chmod 711 ~/cs3242

    chmod 711 ~/cs3242/assign1

    chmod 755 ~/cs3242/assign1/*

Q:   What is High pass filtering? (Is it some kind of filtering to produce convolution resulting in higher spectra of y(n) (contrast to  h(n) which is a low pass filtering?)

A: No. high pass filter will filter out the low frequency components and only keep the high ones, so called only "High" ones can "Pass". low pass filter keeps the low ones. band pass filter keeps the components within a certain range. band stop filter keeps the components outside a certain range.

Q:  I wonder is there a minimum requirement of pages of Assignment 1report? Because I find that I really don't have much to write down in  my report. Could you provide us some necessary points?

A : objectives, development environment, background / introduction , necessary formula and explanation, calculation, result analysis, summary and necessary figures, etc.

Q: For lec 2, notes pg 5 slide 1, there is a Digital Filter Example. I do not understand how to derive magnitude response from  |H(ejw)|2 to |H(ejw)| because when I expand the equation & sq root, I do  not get the 2*sqrt(2) in front. Is this a typo error? If not how to derive? 

A: you are right. there is a typo. please eliminate either the 8 or 2*sqrt(2).

Q: What are the relationships between Frequency and Bandwidth?. When do we talk about frequency and when do we talk about Bandwidth?

A: frequency is the number of times a specified phenomenon occurs within a specified interval, measured in cycles/s, i.e. Hertz. 

     Bandwidth has 2 meanings: 1) The difference, expressed in Hertz, between the two limiting frequencies of a band.   2) The data transfer capacity (in bits per second) of a bit-parallel bus.  so, when you are talking about freq. vs bandwidth, bandwidth is the difference between two freq.

Q:  What does wideband mean?

A: wideband channel is a channel of bandwith which is equivalent to a batch of frequencies.

Q:  What is the relationship between bit rate and bandwidth?

A: bit rate is one of the measurement for bandwidth.

Q:  As suggested in the assignment, I am trying to implement band-pass, high-pass and band-stop filter for experiment purposes. I am just wonderingif you can kindly provide the filter coefficients for those filters, so that we can actually do the exercise.

A: If you want to do it, you should design your own filter coefficients, and this is what part c means.

Q:  For assignment1 part b, we are asked to find out and plot the amplitude spectra of x(n) and y(n). What is it mean by amplitude spectra??? Is it the same as the amplitude response in part a shall we also plot from 0 to PI and convert to decibel? or it is something else?

A: no. it's just the raw value of x(n), y(n).

Q: Can we use Excel to do Assignment 1? 

A: No. For your assignment 1, you are not allowed to key in the values into Excel, or Matlab to get the graph. You have the following 2 options:
   1) Write your own program to do plotting, e.g. Visual c++, Visual Basic, java, etc.
   2) If you can write an interface program so that the tools, like Excel or Matlab, accepts the data as a file and then generate the plots from these files, it should be fine.

You have to write computer programs to generate all the values for plotting and need to submit a report and executable  source codes in your Unix open directory.

Q: For tutorial One, question 1.5 - Calculate the frequency response 

    H(e^jw) = e^3jw - 2(e^2jw) - 3(e^jw) + 4 

   Where do we go from here? I'm not too sure how to resolve the  omega(w) in the equation.

A: use the formula : e^jw = cosw + jsinw. You can calculate the value for cos and sin one you know the value of w. If you don't know yet, jet leave it as a function contains variable w. 

     e.g. e^3jw = e^j(3w)= cos3w + jsin3w 

Q: tutorial one question 1.7, calculate the DFT of h(n) > I've found that H(0) = H(1) = H(2) = H(3) = 4 This is due to the fact that h(n) = 0 for n = 1 to n = 3,  So how do I show that G(k) is the complex conjugate of H(k) .

A:  I guess some of your values for h(k)is wrong. anyway, if you get h(0) = 4, if g(0) = 4, too, then we can say they are complex conjugate. Note: the definition for complex conjugate: two complex numbers, their ONLY difference is the sign of their imaginary part. i.e. their real part should be identical.

     BTW, you should calculate DFT for h(-3) to h(0), the n value now should be from -3 to 0. The given formula only shows most of the cases while we count frequency components starting from 0. However,  in this case, our components should be counted from -3. DO remember, DFT is to convert any periodic signal in to a sum of several frequency components, which  will represented as sin and cos.  

Q: How to form a project group?

A: You may follow the instruction below.

  1) 5 persons from the same tutorial group form a group . 

  2) After tutorial registration, please sign up for project groups at your 1st tutorial or come to Ms Yang Hui's Office (S16  07-02) to sign up. You need to clarify your group member's matric number, name in the matric card, group leader's email address and the public attraction your group chosen. You may state three of your choices.

  3) The deadline for project group signing is 1200 Sat 26 Jan.