Krishna Sankar Madhavan Pillai

Krishna Sankar M is a Signal Processing Engineer based out of Bangalore, India. His typical activities on a working day involve identifying and modeling digital signal processing algorithms for wireless receivers.
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The blog started some in February 2007 on the free Blogger platform and was hosted at http://dsplog.blogspot.com with the following objective:

Explain and discuss the basic text book concepts in digital signal processing and digital communication using simple Octave scripts.

Seeing consistent increase in traffic over the 6-7 months from inception, it was decided to move to an independent platform hosted at www.dsplog.com.

Target audience

(a) Students taking courses in digital signal processing/digital communication and requiring help to understand some of the concepts.
(b) Practicing engineers who are fresh to the domain of digital signal processing and requiring help.
(c) Ofcourse, the experienced engineers can share tips and tricks associated with the digital signal processing trade. 🙂

Probable contents

(a) Understanding basic concepts pertaining to FIR/IIR filtering
(b) Sample rate conversion
(c) Bit and Symbol error probabilities for typical digital communicatio
(d) Orthogonal Frequency Division Multiplexing
(e) more… 🙂

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46 thoughts on “About

  1. hi krishna,

    can u plzzz get me VHDL codes for viterbi decoding both using traceback and register exchange method.thanks

  2. …………..pls help me…..
    my project on femtocell power control……..
    i have theoretical knowledge but i don’t know how to simulate in MATLAB. so please help me giving sample code for power conterol in cellular communication

    1. @prasad: Power control should be relatively easy to simulate. How’s the transmitter getting a sense of it’s transmitted power – feedback from the power amplifier and/or feedback from the receiver system?

  3. Sir,

    I am working on spectrum sensing on TV band.
    I need to help on how to model a digital TV signal for null and alternate hypothesis.
    Pls help me with this.

  4. Hello, In this website I have learn much knowledge. Now I am studying LDPC channnel coding.
    Do you have some source code about block fading channel? I can not know it exactly?

  5. Hi Krishna Sankar,
    I am doing research in MIMO and Transmition Antenna Selection (TAS), may you give me some links or examples matlab codes on this topic?
    i am a beginer in using matlab.

  6. Mr.Krishna I’m working in co-operative spectrum sensing for cognitive radios.. Currently in energy detection based on neyman-pearson criterion and likelihood ratio test.. Is there any blogs for hypothesis testing(DETECTION THEORY ) pls provide me if u have any materials or links

  7. Sir…

    is there a reason between the choosing a MIMO 2×2 with the 64-QAM constellation?
    are they connected each other?
    i mean, why don’t we choose 2×3 or 2×4 which have a higher throughtput?

    the square configuration (MIMO 2×2) and the square constellation of 64-QAM, are they correlated each other?

    thank you for your answer

    1. @Dewa: The MIMO configuration (2×2, 3×3 etc) and the constellation (64-QAM, QPSK, 16QAM etc) are independent design choices. For eg, if you see 11n/11ac standard, can see the MIMO configurations with upto 8 antennas, with constellations from BPSK all the way to 256QAM.

  8. sir we are implementing 2×2 MIMO system..using almouti scheme and also mrc at receiver side…actually we have to transmit text file wirelessly through zigbee module and receiver should add both the signal…i dnt knw how the SNR will increase and also the original signal should get back…

    1. @snehaa diwan: Couple of points:
      a) Using two transmit antennas and two receive antennas, you can potentially double the data rate
      For articles relating the equalization with a 2x2MIMO case, please look at

      b) To increase the reliability, one can chose to keep the data rate and have more antennas at the receiver
      – Maximal Ratio Combining (1tx and 2 receive antennas)
      – Alamouti coding (2tx and 1 receive antenna)
      – Alamouti coding (2tx and 2 receive antenna)

      Hope this helps

  9. hi Krishna
    Good to see you solving problems of technocrates
    i want some suggestion from you on my project.
    i am doing MSK modulation using DDS centered at 60 mhz. please suggest me some demodulation scheme at receiving End.

  10. If we increase the number of subcarriers on OFDM, but keep the bandwidth the same, why do you think the BER increases with higher carriers

    1. @Mat: If the number of subcarriers are more, then the chances of the frequency offset, phase noise affecting the orthogonality between the subcarriers gets higher.

  11. Hello Mr krishna

    Currently im doing research on ofdm with qpsk and 64-qam modulation technique. I also need to generate a simulation of it.
    But im a little bit confuse now…what is the equation for the BER of QPSK and 64-QAM?

    it will be helpful if you can guide me on how to generate the MATLAB codes.

    Thanks in advance

  12. sir,
    we are trying to implemnt UWB subsampling receiver for 3.1to 10.6 ghz input signal(gaussian pulse).can u help us with matlab code for subsampling receiver..
    please sir .kindly help us..

  13. hi dude,
    i am stuck with coding in matlab of simulation environment for mobile communication system (mose) for power control in mobile radio system.
    please help me

  14. Hi Krishna,
    Yesterday I sent a mail to your address and also posted a question on forum asking about plotting eye diagram. On one of the thread I found this and had few doubts.
    When you say you are plotting 2 bits I see that high and low of that bit are at center of plot. So is it plotted as half of previous bit-current bit-half of next bit

  15. Mr. Kri Index to Various dashnan, I want to know , While assigning Subcarrier
    Index to each data, You have used -26 to +26 neglecting 0. may know how this process is done. WHY Such change in subcarrier index is followed

    1. @Selvi: 0th subcarrier is not used by controlling the assignment of symbols to subcarriers. In general, modulating the DC subcarrier is not preferred as the DC impairments in RF etc will corrupt the information.

  16. I have been asked to write a 1/4 soft input viterbi decoder in VHDL or Verilog (I use VHDL as I’m more familiar with it). I have a decent knowledge of Convolutional Codes and Viterbi Decoding and I have access to a 1/2 Viterbi decoder (which I didn’t create). My question is..is a 1/4 decoder much more complicated to design or is there anyway I can use the existing 1/2 decoder?

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