Sumit Kumar (@cogwsn)

I am a Postdoc at SnT, University of Luxembourg.

Re: #OFDM material

Reply posted 4 months ago (07/25/2022)
This one is good. https://onlinelibrary.wiley.com/doi/book/10.1002/9...And the MATLAB code is also available. 

Re: Help with precoding (SDR implementation)

Reply posted 2 years ago (06/07/2020)
Ok, I will do this. 

Re: Help with precoding (SDR implementation)

Reply posted 2 years ago (06/07/2020)
Hi, so it is a proper OFDM signal with preambles (gold sequence). I use preambles for frame sync and channel estimation. No matter what I am doing at the transmitter,...

Re: Help with precoding (SDR implementation)

Reply posted 2 years ago (06/07/2020)
I am sorry. Here is a picture of the SDR I am using. https://www.ettus.com/wp-content/uploads/2019/01/USRP_B2x0_Enclosure_Rear_Diagonal_View.jpgI have two of them...

Re: Help with precoding (SDR implementation)

Reply posted 2 years ago (06/06/2020)
By phase lock, do you mean the PPS signal ? Right now I am not giving PPS, only Freq reference. 

Help with precoding (SDR implementation)

New thread started 2 years ago
I am trying to implement a very basic pre-coder using SDR (USRP B210). Both Tx and Rx have single antenna and the transmit and receive SDRs are frequency synced...
Ok, I see. Yes, it was indeed a simple explanation. 
Hi Kaz, :D Well the second part of the sentence I understood but the first part was not obvious:  "Why low number of subcarriers is needed for high path loss...
In one of the papers related to 5G numerology, I read this statement: "Low number of subcarriers is needed for high path loss scenarios because higher number of...

Re: Tunable power divider

Reply posted 3 years ago (03/03/2020)
Ok, thanks, this one I understood. And what should be the implementation for an active divider. So that I make sure power_out_1 + power_out_2 = power_in; I mean...

Re: Tunable power divider

Reply posted 3 years ago (03/03/2020)
Hi Neil, Thanks much for reply. I tried much to search. Upto 6 GHz should be OK for me. I would like to check both options, passive as well as active. If you can...

Tunable power divider

New thread started 3 years ago
Hi, Can anyone please suggest any tunable power divider available in market. I tried searching a lot, but found only research articles or patents. For a project...

Re: Generating Sine wave in C and Pwelch Plot

Reply posted 3 years ago (08/10/2019)
Yes I applied your suggestions and it works perfectly. Thanks :)

Generating Sine wave in C and Pwelch Plot

New thread started 3 years ago
I have made a C code to generate sine wave. I generate two sine waves of frequency 100 and 500 Hz respectively. The sampling rate is 2000 Hz.But when I see the dumped...

Re: Difference between bit-metrics and LLR

Reply posted 4 years ago (02/15/2019)
Thanks, the idea is more clear to me than before. I know the topic is very old, but can you share any reference (if you remember) about "LLR is just one way to...

Difference between bit-metrics and LLR

New thread started 4 years ago
Hi,My question may be very basic but I always get confused over this. What is the difference between bit-metrics and LLR. For example, in the attached paper, the...

Re: Understanding AD9364 Direct Conversion RFIC

Reply posted 4 years ago (01/02/2019)
Thank you very much. 

Re: Understanding AD9364 Direct Conversion RFIC

Reply posted 4 years ago (01/01/2019)
Got it! Thanks :) 

Understanding AD9364 Direct Conversion RFIC

New thread started 4 years ago
Hi all, New year wishes :) I am going through the specs of AD9364 which has direct conversion receiver architecture. https://www.analog.com/media/en/technical-document...When...

Re: OFDM Cyclic Prefix Understanding

Reply posted 4 years ago (12/05/2018)
Ok I think I got the point!. Thanks 

Re: OFDM Cyclic Prefix Understanding

Reply posted 4 years ago (12/05/2018)
But first 16 samples, i.e., CP may get corrupted due to ISI (right ?). Why do we use them to append :-/  

Re: OFDM Cyclic Prefix Understanding

Reply posted 4 years ago (12/05/2018)
Yes, if you have MATLAB with WLAN Tool Box, you can find this code in wlanOFDMDemodulate.m

Re: OFDM Cyclic Prefix Understanding

Reply posted 4 years ago (12/05/2018)
Yes the FFT length is 64 and CPlen is 16. symOffset = round(ofdmSymOffset * CPLen);

OFDM Cyclic Prefix Understanding

New thread started 4 years ago
I am going thru wlanOFDMDemodulate.m (script used by MATLAB to demodulate 802.11g OFDM symbols)wlanOFDMDemodulate(x, cfgOFDM, ofdmSymOffset)x is the array of received...

Re: LTE WiFi FFT Problem

Reply posted 4 years ago (10/20/2018)
Indeed! I also replicated and this happens without zero-padding. I was in the impression that taking 2048 point FFT of the LTE+WiFi will introduce some ICI in the...

LTE WiFi FFT Problem

New thread started 4 years ago
Hi, Suppose I have time domain LTE signal L and time domain WiFi signal W. L is generated by taking 2048 point IFFT and W is generated by taking 64 point FFT. Power...

Using stored channel for decoding data

New thread started 4 years ago
Suppose I am operating in an environment where Tx and Rx are static and channel does not change between them. In this case if I have channel estimate between Tx...
Ok in other words, the system acts as Selection Combiner. 
I am working on hardware implementation of Maximal Ratio Combiner for OFDM based system. Consider a two antenna receiver performing MRC over received signals y1...

Re: Arbitrary Resampling issue : 30.72 MHz to 20 MHz

Reply posted 4 years ago (05/29/2018)
Are you talking about polyphase resampler. 

Re: Arbitrary Resampling issue : 30.72 MHz to 20 MHz

Reply posted 4 years ago (05/29/2018)
My apologies, I should have used standard notations. So, 30.72 MHz is the sampling rate of LTE and 20 MHz is sampling rate of 802.11a.ADC performs sampling at 30.72...

Re: Arbitrary Resampling issue : 30.72 MHz to 20 MHz

Reply posted 4 years ago (05/28/2018)
Ok I might not have explained properly :) but here is a diagram which can explain better. 

Re: Arbitrary Resampling issue : 30.72 MHz to 20 MHz

Reply posted 4 years ago (05/28/2018)
No, provided that I can upsample/downsample it finally to 30.72 and 20 MHz. 30.72 MHz signal is coming from LTE and 20 MHz signal is coming from WiFi. Center freq...
Hi, I have two signals. Signal A, sampling rate 30.72 MHz and signal B, sampling rate 20 MHz. Their center frequency is same though. Now assuming a simultaneous...

Re: 802.11 Sync on MRC receiver

Reply posted 5 years ago (05/08/2018)
Hi, I have a followup question. Using STS we perform coarse frequency offset estimation and then using LTS , we refine the frequency offset estimation. When performing...

802.11 Sync on MRC receiver

New thread started 5 years ago
Hi,Is this correct that when we implement MRC in 802.11a/g (say with 2 antennas), the preamble based sync needs to be performed on both the antennas ? If yes, then...

Re: Square waves

Reply posted 5 years ago (02/21/2018)
Google is your friend ! :) https://en.wikipedia.org/wiki/Saturn%27s_hexagon

Re: Square waves

Reply posted 5 years ago (02/21/2018)
And here is the reason! http://www.lifeaspire.com/7342/the-cause-of-square...Very interesting indeed. 

Re: Frequency Shifting Confusion

Reply posted 5 years ago (02/08/2018)
Yes indeed. I found the mistake. I was supposed to transpose the carrier array by using ' operator but since carrier is complex, so ' operator was doing a conjugate...

Re: Frequency Shifting Confusion

Reply posted 5 years ago (02/08/2018)
So that the length of time array is equal to the length of interference. Apology these was a confusion in naming. load('zigbee_baseband.mat') % Baseband  loads...

Re: Frequency Shifting Confusion

Reply posted 5 years ago (02/08/2018)
Interference is zigbee. Yes when I plot it without multiplying with carrier, it lands on 0 MHz. The very first plot in the subplot. 

Re: Frequency Shifting Confusion

Reply posted 5 years ago (02/07/2018)
As the baseband is it 0 MHz, either is applicable i.e. shifting to -7 MHz or shifting by -7 MHz.I have attached the picture now for downloading. untitled.pngLink...

Frequency Shifting Confusion

New thread started 5 years ago
Hi, It might be a very silly question. I have a baseband zigbee dump (zigbee._baseband.mat attached). I wish to shift it to -7 MHz, -2 MHz to the left and also...

Re: Generating Noise

Reply posted 5 years ago (02/05/2018)
Well in that case : Suppose your signal chunks are X1, X2, X3, ....Xn and your SNR requirement is SNR_dB1, SNR_dB2, SNR_dB3, .... SNR_dBnYou do as :  Y1 =...

Re: Generating Noise

Reply posted 5 years ago (02/03/2018)
Hi, check this linkhttps://www.gaussianwaves.com/2015/06/how-to-gener...

Re: WLAN Demodulation in MATLAB

Reply posted 5 years ago (01/26/2018)
Thanks much. Its very clear now. 

Re: WLAN Demodulation in MATLAB

Reply posted 5 years ago (01/08/2018)
New year Wishes to you too :) To be honest I couldn't understand your answer at all ... could you please share some link for details. 

Re: WLAN Demodulation in MATLAB

Reply posted 5 years ago (01/07/2018)
Well I found this reference where it says that soft Viterbi could be used with additional channel state information. http://ieeexplore.ieee.org/document/793537/I...

WLAN Demodulation in MATLAB

New thread started 5 years ago
I am using the WLAN Tool Box of #Matlab V2107b. A term named CSI for each data subcarrier is defined as CSI(i) = H(i) X conj(H(i)) + N(i)H(i) = channel estimate...

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

Reply posted 5 years ago (12/26/2017)
RF data i.e. passband data is never complex, it is real. It becomes complex only when you down convert it to baseband(using 2 ADC i.e. two channels). In MATLAB...
Ok its clearer to me now :) 
Ohh I see! So let me know if my understanding is correct (thanks much for your time :))Considering the case of 802.11g system where long training sequence(LTS) is...
As you said "If you do the combining first, you will get the SNR improvement of the combiner and will be equalizing on the combined channels."So for the equalization...
My basic question is that in SIMO OFDM system with Maximal Ratio Combining : Do we need to do equalization after MRC or just send the combined signal for further...

Re: Noise Generation Confusion

Reply posted 5 years ago (11/23/2017)
...

Re: Noise Generation Confusion

Reply posted 5 years ago (11/23/2017)
Okk thats solved the issue.. thanks much :) 

Noise Generation Confusion

New thread started 5 years ago
Hi, I have to generate AWGN noise whose power is -100 dBm I do the following calculation in MATLAB. np_dBm = -100; % desired noise power in dBm np_watts =...

Re: "Real" data?

Reply posted 5 years ago (11/15/2017)
It sounds like maybe the advantage of complex sampling is that you trade off one fast ADC for two ADCs operating at half the speed. Is this correct?YESAre there...

Re: "Real" data?

Reply posted 5 years ago (11/15/2017)
Normally we do complex sampling where the incoming data is splitted in two channels, each channel is multiplied with 2 sinusoids(which are 90 degree out of phase)...

Frame Synchronization ZigBee

New thread started 5 years ago
Hi, If my understanding is correct, most of the 802.15.4 receiver implementations perform frame synchronization i.e. find the start of the frame using the preambles...
What I have read so far, indicates that commercial multi-antenna wifi access points use selection combining i.e. uses only one antenna at a time (even if there are...
Thanks napierm for your reply :)However I was looking for suggestions on Fixed Point DSP books :) I am used to do floating point DSP, hence with fixed point DSP...
Hello, I am working with C and assembly code for DSP for some real time SDR applications and frequently get stuck in the basics. Can anyone suggest some reference...
See the figure attached. Use the crocodile connector to grab the part pointed by black arrow. 

Re: ZigBee Preamble

Reply posted 6 years ago (05/17/2017)
Hi Tarik, In the receiver side what is the Error threshold used chip errors. I mean when a symbol is decoded from  32 bit sequence, how many chip error could be...

Re: Correct method to add AWGN

Reply posted 6 years ago (05/09/2017)
Hi Tim, Now I am trying to come out of theory-land :)I have another related question. I am using an SDR USRP B210 which shows me approx -100 dBm noise floor on...
Yes I am counting the PER for WiFi already, So with your suggestion, I think I have no option but to mark all the bits as error in the dropped packet !  
Hi,I am performing some tests with WiFi and ZigBee. There are some situations when the header of the frame is lost and hence the receiver discards the packet. In...

Re: ZigBee Preamble

Reply posted 6 years ago (04/28/2017)
So that means, a total of 256 bits for the preamble part. And since zigbee uses oqpsk, there will be total 256/2 = 128 complex symbols in the front of a zigbee frame....

Re: sum of sinusoids

Reply posted 6 years ago (04/26/2017)
Visual interpretation and understanding in time domain is difficult, but if you plot the fft, you will start seeing peaks at different frequencies.

Re: Spectrum Sensing HW.

Reply posted 6 years ago (04/14/2017)
I would append to motilito's reply by saying that : if you want to go with AD9361 , USRP B210 from Ettus Research is the best option you can have. It will not only...

Re: Correct method to add AWGN

Reply posted 6 years ago (04/14/2017)
Okk.. I just got it ..so awgn(a) = a + noise awgn(b) = b + noise awgn(a) + awgn(b) = a + b + noise + noise = a + b + 2 * noise :) Thanks ! 

Re: LTE Uplink transmit

Reply posted 6 years ago (04/14/2017)
Not sure about sub carrier interference but due to PAPR there is also inter modulation(IP3) which will distort the transmitted constellation. 

Re: LTE Uplink transmit

Reply posted 6 years ago (04/13/2017)
For uplink, lte uses sc-fdma which has relatively low PAPR compared to OFDM. A low PAPR is required in order to avoid high power consumption in the mobile terminal,...

Re: Correct method to add AWGN

Reply posted 6 years ago (04/11/2017)
I could not understand this properly. Can you explain it again please "For Eb/N0 you should normalize the values according to signal bandwidth"

Correct method to add AWGN

New thread started 6 years ago
Hi, I have to mix two signals WiFi and ZigBee. What should be the correct method to add AWGN after chanel effects A . awgn(WiFi + ZigBee) OR B. awgn(WiFi) +...
Hi, In the commercial cell phones mostly we have WiFi, ZigBee and Bluetooth working. I was wondering if they use the same RF front end for sampling the signals...

ZigBee and Multipath

New thread started 6 years ago
Hello, How does ZigBee copes up with multipath. I don't see any inherent support for channel estimation ? TIASumit 

ZigBee Preamble

New thread started 6 years ago
Hello, In ZigBee (802.15.4), is there a preamble like WiFi (STS, LTS). I have not studied much details, but from first view it looks like there are sequence of...
As of now my WiFi and ZigBee Rx are working in real time independently. Yes I will try your suggestion also, to make them working independently in vicinity of each...
Hahaha, I agree with you Tim. But this is more than that :D (Devil is in the details :D)Following to this, I have to generalize it for other standards where there...
No actually I have to decode both WiFi and ZigBee at the same time. So during interference, assuming most of the time WiFi will be strong, I can detect the WiFi...
Yes, I am trying to do ZigBee and WiFi simultaneously in real-time. So far I found successive interference cancellation the most suitable one. 
Hello, thanks for your reply. Yes, I have a confusion because for Successive Interference Cancellation, I have to recreate the entire OFDM symbol. ZigBee signal (4...
Hello,I am planning the following.First sample the 20 MHz WiFi channel (WiFi channel-1 in figure).Put band pass filters (5 MHz wide) around each of the ZigBee center...
Hello, I am working on SIC between WiFi(802.11g) and ZigBee(802.15.4). First I am decoding the #WiFi signal. Once decoded I have to regenerate the WiFi signal with...

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