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Vaidyanahtaswami Muralidharan (@Mannai_Murali)

Qualification MS in Electronics.I have over 20 years industrial experience in Digital Signal Processing/Wireless.I have worked in US with 3Com/Analog Devices.I know Matlab,Lab View,Assembly for DSP.At present work as Vice president Max Eye Technologies,Bangalore,India.I have simulated Kalman Filter/Viterbi Algorithm for CCI mitigation ,Sampling clock/Frequency offset mitigation for OFDM.

Re: Deriving velocity from accelerometer data

Reply posted 4 days ago (07/10/2024)
I think after IFFT you have taken absolute value for acceleration and has fed the absolute value to the velocity calculation.Actually you should take real part...

Re: Direct RF radio

Reply posted 4 weeks ago (06/14/2024)
This is not my area.But I am asking to get more exposure.Assuming we do not use RF filter interference close to 18 GHz can only alias andaffect the intended signal...

Re: Future of Signal Processing

Reply posted 1 month ago (06/10/2024)
Thanks

Re: Future of Signal Processing

Reply posted 1 month ago (06/09/2024)
Thank you for the detailed reply.

Future of Signal Processing

New thread started 1 month ago
Are all signal processing algorithms in communication and control going to be replaced by machine learning and AI.Is it still worth to look in to conventional signal...

Re: Acoustic Modems in Matlab

Reply posted 3 months ago (04/06/2024)
I selected 2000 Hz as the carrier frequency because if I choose higher carrier the Speaker and Mike frequency response will be poor.When I simulated at higher 2400...

Re: Acoustic Modems in Matlab

Reply posted 3 months ago (04/05/2024)
At present I tried 8 psk and symbol rate 24 symbols/sec.At high symbol rate the frequency offset detection failed even in simulation which was feed forward based.I...

Acoustic Modems in Matlab

New thread started 3 months ago
I want to try Acoutic Modems in Matlab and working with actual speaker and mike for transmission.I have designed 8 psk modem and another OFDM version QPSK Modem.Is...

Re: Learning Data Transmission for HF Channel

Reply posted 8 months ago (11/24/2023)
Is there any HF beacons with long sequence of known data transmitted through HF at high Symbol Rate so that I can design my receiver to tackle multipath and Doppler?This...

Learning Data Transmission for HF Channel

New thread started 8 months ago
I am trying to learn data transmission through HF Channel for various multi path and fading conditions.I will be designing and coding for simulation.I am planning...

Re: IFFT of Non causal signal?

Reply posted 9 months ago (10/24/2023)
As I understand you have frequency domain complex data which is present only for Negative frequencies.All positive frequencies are zero.In FFT for N frequencies...

Re: #OFDM point to point specification

Reply posted 1 year ago (05/09/2023)
I have some idea of OFDM.I will put my best effort to review it though I may not be very good.Mannai_Murali@hotmail.com

Re: Viva Ukraine!

Reply posted 2 years ago (02/27/2022)
US and its allies are symbol of evil.US acts as an international police man and what it did in Iraq,Afganistan,Syria,Vietnam every body knows.At least in Russia...

Re: Realisation the Decoder of the convolutional code

Reply posted 2 years ago (02/17/2022)
Due to 1/2 rate coding your EbNo of uncoded data will be 9+3=12;SNR=EbNo*BitRate/BandwidthT-->Bit periodBandwidth=1/(2*T)For Error calculation Decoded bits will...

Re: Fractionally Spaced Equalizer

Reply posted 3 years ago (12/21/2021)
Thank you for the reply.

Re: Fractionally Spaced Equalizer

Reply posted 3 years ago (12/21/2021)
Thank you for the kind reply

Re: Fractionally Spaced Equalizer

Reply posted 3 years ago (12/20/2021)
I was refering bursty transmission and not continuous transmission.Since Fractionally spaced equalizer can correct for unknown symbol timing offset even for commercial...

Fractionally Spaced Equalizer

New thread started 3 years ago
Can we get away with Sampling clock offset tracking and Symbol timing in a single carrier system if we use fractionally spaced equalizer for bursty transmission...

Re: Proving Time Invariance of a system

Reply posted 3 years ago (10/20/2021)
Understanding the mathematics is no doubt important.At the same time getting intution is equally important.Writing few lines of code in Matlab and plotting will...
Give the real part to a Hilbert Transformer.Hilbert Transformer will shift phase of all +ve frequencies by -Pi/2.All Negative frequencies will be shifted in phase...

Re: time recovery algorithm and CORDIC

Reply posted 3 years ago (05/25/2021)
You may refer Heinrich Meyr.Digital Communication Receivers.Vol2.You may find it in the net.

Re: Joint Research in Base Band Signal Processing

Reply posted 3 years ago (05/09/2021)
Thank you Fred Harris.I will look in to them.

Joint Research in Base Band Signal Processing

New thread started 3 years ago
With in a month I will start doing research on Signal Processing related to Receiver Design (Mainly related to one or more of Synchronization (Frequenbcy Offset/Sampling...

Re: Viterbi equalizer

Reply posted 3 years ago (05/08/2021)
Instead of single carrier when we use OFDM the symbol duration becomes large to combat delay spread.For the same mobile speed and hence the doppler the normalized...

Re: Soft-output Hamming decoder

Reply posted 3 years ago (04/28/2021)
There are logical mistakes in your code.First you have to get syndrome from soft LLRs by taking hard decision.From these n tuples get syndrome consisting of n-k...

Re: How to compute a phase? [phase estimation]

Reply posted 3 years ago (03/26/2021)
In genral receiver will have carrier frequency offset not only mere phae offset.You may have to correct for difference in frequency and phase of DAC (At Transmitter),ADC...

Re: time recovery algorithm and CORDIC

Reply posted 3 years ago (03/26/2021)
The QPSK Receiver code with NDA Timing Recovery is attached.I wrote it long back.If some one needs help I have to go through for a day.It uses NDA Timing Algorithm.I...
I have replied in detail.Please do NOT use AWGN even reading my reply.After convolving with fading channel do the following.If you want SNR of 30 dB after Channel...
It is incorrect to use measured option while using for fading channel.example:If you use snr of 20dB measured it means AWGN is added 20dB below the faded signal...

Re: How to test my FFT implementation?

Reply posted 3 years ago (03/08/2021)
You can give real only cosine waves from f0=Fs/N to Fs/N*N/2 with imaginary zeros as input.You will see +Ve going impulse pairs at Fs/N Fs/N*(N-1) ,Fs/N*2&Fs/N(N-2)...

Re: time recovery algorithm and CORDIC

Reply posted 3 years ago (03/06/2021)
Please read Meyr 'Digital Communication Receivers Vol2' and Phase lock techniques By Gardner.I have a reference code for QPSK Receiver, NDA Timing Recovery.If you...

Re: LTE Uplink Timing

Reply posted 4 years ago (12/31/2020)
I am not suggesting any modification of LTE.Since the receiver design is up to individual and anyhow Demodulation reference signal for each uplink UE is available...
As for as I know the simplest way to get fraction delay is to use an All pass filter (Truncated Sinc) with the given delay.These type of filters is used as interpolator...
I did not go through the code and I do not understand it fully.But see whether my suggestion will be useful.If the FFT or IFFT is decimation in time input must be...

LTE Uplink Timing

New thread started 4 years ago
In LTE Uplink timing is calculated at Base Station using cross correlation of PRACH when UE joins the network.Can I use Demodulation reference signal of two successive...

Re: Autocorrelation of OFDM Signal ?..

Reply posted 4 years ago (12/21/2020)
I think in any ofdm if the channel is not AWGN any dispersive channel may cause multiple peaks.You may take the first peak.

Re: PMCW Radar for cars

Reply posted 4 years ago (12/15/2020)
Phase Modulated Continuous Wave (PMCW) radar is different from Linear FMCW radar.It has PN sequences (+1/-1) generated modulated BPSK and transmitted.By cross correlating...

Re: Carrier frequency correction using real IQ

Reply posted 4 years ago (11/26/2020)
If Z is real it means it is in pass band.Give Z to a hillbert transformer and find the imaginary part.Get the imaginary part.Now Z will have real and imaginary part.Down...
Hi,I can help anybody in Baseband Digital Signal Processing by providing some ideas if anyone needs.I will not charge anything.I can help in design and debugging...

Re: OFDM Pilot Detection

Reply posted 4 years ago (11/13/2020)
There are 3 IEEE papers I can give you as reference.Two by Heinrich Meyr and another by different authors.If you give your email I can mail you those papers.Generally...

Re: OFDM Pilot Detection

Reply posted 4 years ago (11/08/2020)
Are you interested to work in blind algorithms.If you are working whatever knowledge I have I can share with you.Mannai_Murali@hotmail.com

Re: OFDM Pilot Detection

Reply posted 4 years ago (11/08/2020)
For pilot tones phase will not be constant from ofdm symbol to next symbol.Also in pilot group phase rotation of pilots due to ADC sampling clock offset will be...

Re: OFDM Pilot Detection

Reply posted 4 years ago (10/31/2020)
Assume like DVB-T continuous pilots are available every Symbol.Let 'M' maximum spacing between pilots.Let 'N' minimum spacing between pilots.Let 'P' be starting...

Re: CFO correction in OFDM

Reply posted 4 years ago (10/02/2020)
If you do not use interlevers can you use the data symbols decoded and find the channel estimate.If you refine channel estimate from symbol to symbol the channel...

Re: Reflectometry in power lines (spread spectrum TDR)

Reply posted 4 years ago (08/12/2020)
You can have a long PN sequence.Also you may repeat the same sequence many times(periodic) and find the average.This will perform better against white noise.The...
If the channel has no memory then we can do symbol by symbol demodulation.One matched filter which will match to transmitted pulse shape(which is common for all...

Re: Proof of Correlation Theorem for DFT

Reply posted 4 years ago (06/10/2020)
split u=1-N= -(N-1) in to two parts. -(N-1) to -1 and 0.Here everything is modulo N.So -(N-1) to -1 corresponds 1 to N-1.Added with 0 it gives 0 to N-1.This is because...

Re: Help with precoding (SDR implementation)

Reply posted 4 years ago (06/08/2020)
If PPS is the timing reference signal (DAC/ADC Sampling) and if you use it may stop rotation.While simulating you may not have introduced sampling clock offset and...

Re: Help with precoding (SDR implementation)

Reply posted 4 years ago (06/07/2020)
If it is not possible to use same DAC and ADC clock in transmitter and receiver(No time reference) and the hardware does not support you may do the following test.In...

Re: Help with precoding (SDR implementation)

Reply posted 4 years ago (06/07/2020)
In OFDM other than frequency offset and channel the sampling clock offset between DAC in the transmitter and ADC in the receiver can cause phase rotation.The phase...

Re: LTE IFFT Sampling and Nyquist Rate

Reply posted 4 years ago (05/16/2020)
Just recollect sampling theorem.The band limited signal in analog domain (Whether real or complex signal) is convolved by train of impulses(Periodic ) in frequency...

Re: Block Floating Point in FFT.

Reply posted 4 years ago (05/11/2020)
Block floating point uses the same exponent for the entire stage unlike floating point which use different exponent for each butterfly.Excellent reference can be...
I have used only matlab not simulink. Try giving ZERO delay if it allows as hard coded.If it finds delay probably it may look for a particular sync bit pattern in...

Re: ICI avoidance in OFDM

Reply posted 5 years ago (07/05/2019)
Suppose there are two paths.Path1 will have theeta1 as angle of arrival.path2 will have theeta2 as angle.The doppler for path1 will be deltaf1.For path2 it is deltaf2.Subcarrier...

Re: ICI avoidance in OFDM

Reply posted 5 years ago (07/04/2019)
Since Doppler in Hz=V*Cos(Theeta)/Lambdav-->velocity;Lambda-->Wave length;Theeta -->Angle for different pathsEach resolvable path having different (theeta)...

Re: ICI avoidance in OFDM

Reply posted 5 years ago (07/03/2019)
Is it because with multi path each path will have different frequency shift due to different arrival angle and hence different velocity.Frequency offset estimation...

ICI avoidance in OFDM

New thread started 5 years ago
In standards like DVB-T2 there is a iterative decoder to mitigate ICI.Since the effect of high doppler is to introduce ICI due to frequency offset why we can NOT...
1.For practical digital communication to work we need some excess band width above minimum.This is because we need timing and frequency synchronization to be done...

Re: How to downconvert a Complex RF signal in Matlab?

Reply posted 7 years ago (12/26/2017)
The signal once modulated by RF carrier will be real.The channel also will be real and pass band.There will be a single ADC with real output.You can down convert...

Re: Synchronization For Fading Channels

Reply posted 7 years ago (10/26/2017)
I am working for OFDM system.The auto cyclic prefix correlation based OFDM symbol boundary detection and and ineteger frequency offset detection while workfor AWGN...

Synchronization For Fading Channels

New thread started 7 years ago
How do synchronization for Frequency selective fading channels differ from AWGN channels.The reason is many algorithms work for AWGN does not work for fading channels.How...
For ANY bin in the frequency domain the FFT coefficient will be linear combination of gaussian.So real and imaginary part will be gaussian.However the magnitude...
Let the data length be 2N samples.Then centered at sample N/2 find auto correlation for0 to N-1 sample.Similarly centered at N+N/2 find Auto correlation for N/2...

Re: Aliasing effect in RRC filter

Reply posted 7 years ago (06/06/2017)
In the transmitter I sample 2*symbol rate.Due to 100% excess band width signalfrequency upto symbol rate are passed through matched filter receiver.When I dosymbol...

Aliasing effect in RRC filter

New thread started 7 years ago
Suppose I transmit digital data(BPSK/QPSK/QAM) with symbol period T.Then minimum band width needed is 1/(2*T).If I use a transmit Root Raised Cosine Filter with...

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