Recent content by O.J.

  1. O

    Energy of the summation of two sinusoidal waves

    My question is very fundamental: adding two sinusoids in phase results in a sinusoid with twice the total energy of both sinusoids combined according to how we calculate power as A^2/2 with A being the amplitude. None of this answers the extremely fundamental question of how is energy conserved??!
  2. O

    Energy of the summation of two sinusoidal waves

    The energy (or power really) at the point of interference is twice the total energy/power of the two waves. How does that work in light of conservation of energy?
  3. O

    Energy of the summation of two sinusoidal waves

    Suppose we have two laser diodes that are made to transmit light at the same wavelength and intensity. Also, suppose that we place them in an open space and separate them by a distance such that when their generated beams intersect at one point in space and one point only. Further suppose that...
  4. O

    Question about hermitian operators

    Is there a proof? Can you link me to one? =)
  5. O

    Question about hermitian operators

    Theorem: For every Hermitian operator, there exists at least one basis consisting of its orthonormal eigen vectors. It is diagonal in this basis and has its eigenvalues as its diagonal entries. The theory is apparently making an assumption that every Hermitian operator must have eigen...
  6. O

    OFDM frequency sensitivity (MATLAB related)

    Hello everyone, I am trying to simulate an OFDM system and part of what I want to do is investigate the Bit Error Rate with respect to frequency offset. I understand how the offset vs BER curve should be looking like the curve obtained in the code in this link...
  7. O

    FFT question (MATLAB)

    Also another question. You said: "The FFT of 101 data points is doing the FFT of the periodic time series 1, [99 points defining the cosine wave], 1, 1, [99 points repeated], 1, 1, etc" But doesnt taking a larger point FFT mean padding the input with trailing zeros? Your input seems padded...
  8. O

    FFT question (MATLAB)

    Also, can you elaborate more on the role of windowing? Does having an FFT with N greater than signal length count as effectively windowing?
  9. O

    FFT question (MATLAB)

    Thanks alpha zero. That cleared up many things. Can you tell me what it mathematically means to use an FFT with a length more than the time domain signal length?
  10. O

    FFT question (MATLAB)

    Hello, I have a very basic FFT question. Correct me if I am wrong, but the FFT is a fast implementation of the DFT (which is essentially the same as Discrete Time fourier series). The DFT is periodic in time and frequency. Thus if you input a time domain made of 4 times samples for example to...
  11. O

    Fundamental OFDM question (MATLAB related)

    Upon feeding the IFFT block with the mapped date elements, shouldn't the binary data be upsampled by a sampling frequency that is equal to twice the highest subcarrier frequency (nyquist criterion)? I have written a code for a complete OFDM trasceiver system and I have not upsampled my binary...
  12. O

    Simulating OFDM system performance under different frequency offsets using MATLAB

    Homework Statement I am simulating an OFDM transceiver using MATLAB. I am trying to investigate the effect of frequency offsets on the system performance by measuring different offsets against their respective bit error rate with a SNR of 10 dB. Homework Equations All equations and...
  13. O

    Poisson's summation formula

    I do not understand how <ek , er> results in a delta function. Isnt the integrand going to be e^(2pi i k) * e^(-2pi i r). While this is equal to 1 if k = r, it isnt necessarily 0 if r isnt equal to k. How did u interpret it as delta? please clarify.
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