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Coding for OFDM

Started by kelvin83 in comp.dsp13 years ago 1 reply

Hey all, I am currently working on a set of trial data on OFDM communication. However, in order for my algorithm to work better, I need to have...

Hey all, I am currently working on a set of trial data on OFDM communication. However, in order for my algorithm to work better, I need to have as low a BER as I possibly can. My colleague suggested coding. However, my data wasnt encoded in the first place and since the trial data has already being collected, I have to make do with what I have, i.e post-coding. I have very little knowle...


OFDM-coherent

Started by Zeph80 in comp.dsp18 years ago

What is coherent OFDM? Does this refer to the type of modulation I use(coherent modulation - QPSk, BPSK)?

What is coherent OFDM? Does this refer to the type of modulation I use(coherent modulation - QPSk, BPSK)?


OFDM(doppler shift estimation)

Started by .avinash. in comp.dsp9 years ago 3 replies

Hey there everyone! I'm actually right now researching about ofdm based realization to efficiently estimate the doppler shift and I've kinda run...

Hey there everyone! I'm actually right now researching about ofdm based realization to efficiently estimate the doppler shift and I've kinda run into a block In the typical block diagram there's a IFFT/FFT block,I've read on many forums but I'm unable to determine the significance of the said block Also,if its possible could anyone help me understand why actually circular convolution is better ...


maximum likelihood in OFDM system

Started by mib in comp.dsp17 years ago 2 replies

I am looking for Matlab codes for maximum likelihood estimate of the OFDM How to do that? And could anybody point me to some samples,...

I am looking for Matlab codes for maximum likelihood estimate of the OFDM How to do that? And could anybody point me to some samples, resources, examples, Matlab codes? Thanks a lot!


ODFM Question

Started by naebad in comp.dsp18 years ago 3 replies

Idiots question on basic OFDM: Suppose I have data 1,1,1,1,0,0,0,0,1,1,1,1 and I want to convert this to OFDM. First of all - should...

Idiots question on basic OFDM: Suppose I have data 1,1,1,1,0,0,0,0,1,1,1,1 and I want to convert this to OFDM. First of all - should logic zero be -1 instead of zero? Also my understanding is that I convert the serial data to parallel and then take an Inverse FFT. Does this not generate complex data? If so do you take the real part only or the modulus? Also, should the parallel d...


Simulating Doppler Effects for OFDM

Started by idan82 in comp.dsp17 years ago 1 reply

Hello, I would like to simulate the Doppler effects on OFDM. What is the simplest way to do this in Matlab? I want to simulate ONLY doppler,...

Hello, I would like to simulate the Doppler effects on OFDM. What is the simplest way to do this in Matlab? I want to simulate ONLY doppler, without any fading, therefore I dont want to use the rayleigh or ricean channel function built into matlab. Any help is greatly appreciated. Thanks Idan


OFDM spectrum and sidelobes

Started by Zeph80 in comp.dsp16 years ago 2 replies

I would like to know why the OFDM Out of band sidelobes , reduce as the number of carriers/FFT size increases?What is the reason for this? Is...

I would like to know why the OFDM Out of band sidelobes , reduce as the number of carriers/FFT size increases?What is the reason for this? Is this ever a consideration in choosing the FFT size, because if I consider sidelobes due to PAPR driving PA to saturation, then its the other way round. More carriers will cause more spectral regrowth.


OFDM timing synchronization

Started by XYZ in comp.dsp14 years ago 1 reply

Hi, I've been struggling with OFDM timing synchronization using Schmidl algorithm for some time but I can't figure out how to find the sample...

Hi, I've been struggling with OFDM timing synchronization using Schmidl algorithm for some time but I can't figure out how to find the sample at which the symbol starts. Authors seem to have the same problem but apparently they don't mention how to deal with it -- or is it just me not understanding it? The timing metric shows me where to sample (I actually only use P metric because...


802.16e-2005 has different Rx SNR for OFDM and OFDMA

Started by minnows in comp.dsp16 years ago 5 replies

Hi, in 802.16e-2005, table 266 is Rx SNR for OFDM and table 338 is Rx SNR for OFDMA. I find that the Rx SNR is different for OFDM and OFDMA, why...

Hi, in 802.16e-2005, table 266 is Rx SNR for OFDM and table 338 is Rx SNR for OFDMA. I find that the Rx SNR is different for OFDM and OFDMA, why is that?


Queries Reg -OFDM transceiver Implementation

Started by Ammankumar in comp.dsp15 years ago 1 reply

Hi, I'm working in OFDM transceiver implementation in FPGA. I have following doubts. Kindly clarify . 1) How to determine number of...

Hi, I'm working in OFDM transceiver implementation in FPGA. I have following doubts. Kindly clarify . 1) How to determine number of points in IFFT with respect to bandwidth? 2) For given 1 MHz Bandwidth , what is the maximum amount of bandwidth that can be allowed for not having ISI and cross symbol interference. 3)How Receiver will take care of Doppler shift? Thanks


Baseband OFDM simulation - noise?

Started by Snowball in comp.dsp19 years ago 2 replies

Hi, I am simulating a baseband OFDM system in MATLAB Simulink. It looks similar to the adsl_sim demo, though I am not doing any CRCing,...

Hi, I am simulating a baseband OFDM system in MATLAB Simulink. It looks similar to the adsl_sim demo, though I am not doing any CRCing, scrambling or interleaving. I use a 256-carrier DMT modulator, and transmit my data over a channel which is basically a lowpass FIR filter with real coefficients. I am not sure how to model the noise though. Is it correct to add AWGN noise on each freque...


OFDM transmitter

Started by Zeph80 in comp.dsp14 years ago 8 replies

I'm simulating a DVB-T OFDM 8 Mhz BW transmitter with 2K tones, DVB-T sample rate is 9MHz. I'm doing this by using a 4K IFFT and 18 MHz...

I'm simulating a DVB-T OFDM 8 Mhz BW transmitter with 2K tones, DVB-T sample rate is 9MHz. I'm doing this by using a 4K IFFT and 18 MHz sample rate (I arrange the IFFT input with 1K tones (worth 4 MHz) having QPSK data, then zero out all the central tones, and put remaining QPSK data on the last 1 K tones ( worth the remaining 4 MHz BW).So I get a base-band OFDM spectrum to begin with. I'm then ...


OFDM Frequency Synchronizations

Started by Eric C. in comp.dsp17 years ago

Hello all, I'm a student working on a problem about frequency synchronization for OFDM. I just wonder if the Moose's approach (using repeat...

Hello all, I'm a student working on a problem about frequency synchronization for OFDM. I just wonder if the Moose's approach (using repeat training symbols) is the best way to this issue. Besides Moose's and Schmidl's approachs, is there any other pilot-based approach? Also, I have an immature new idea to estimate the frequency offset but it can only estimate half the range. Is it still...


Have i done this right? OFDM spectrum

Started by Ant_Magma in comp.dsp18 years ago

Guys, i've finished my basic ofdm model and i'm currently working on the synchronization & later the modelling of the power line...

Guys, i've finished my basic ofdm model and i'm currently working on the synchronization & later the modelling of the power line transfer function... But i just wanna check out with you guys first whether my spectrum is correct or not... This is my model (50kb), the AWGN SNR is set at 30... http://geocities.com/antonio_magma/model.jpg And this is my output Tx spectrum, averaged about ...


orthogonality not acheived after IFFT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Started by awais in comp.dsp17 years ago 5 replies

Guys i am working on ofdm simulation.after taking the ifft of my crriers (having baseband data in the form of matrix) mycarriers are not...

Guys i am working on ofdm simulation.after taking the ifft of my crriers (having baseband data in the form of matrix) mycarriers are not orthogonal. As the ifft is responsible for making carriers orthogonal in order to acheive OFDM. I am using built in command of ifft in matlab. For eg x=ifft (carrier_matrix,128) then when i take dot product of my vectors the result is a non-zero number or...


FFT or DFT with large N (for OFDM/DMT)

Started by Anonymous in comp.dsp18 years ago

Hello, I have a question about the DFT that is used in OFDM and DMT. Emerging standards such as VDSL, DVB and Powerline allow transfrom ...

Hello, I have a question about the DFT that is used in OFDM and DMT. Emerging standards such as VDSL, DVB and Powerline allow transfrom sizes which can be as large as N = 1024, 2048 or 4096. Associated with this there is the problem of large peak to average ratio, clipping and non-linearities at the power amplifier. But there are methods to reduce these effects (see Tellado and Cioffi...


Why OFDM is better than CDMA in theory?

Started by phil in comp.dsp16 years ago 2 replies

I heard that OFDM is better than CDMA in theory, e.g., from capacity point of view. And I found the following from this group by James...

I heard that OFDM is better than CDMA in theory, e.g., from capacity point of view. And I found the following from this group by James K., which I do not fully follow though (the two equations). Especially for CDMA, where does the term 1/(1/r1+1/r2) come from? Any idea ? Thanks. Below is from James K, http://groups.google.com/group/comp.dsp/browse_thread/thread/d976778329c3af6d/36dac...


Content of the preamble for OFDM channel estimation

Started by skywalker601 in comp.dsp18 years ago 2 replies

Hello, i'm currently working on a channel estimation algorithm for OFDM. I already programmed the main part according to the implementation in...

Hello, i'm currently working on a channel estimation algorithm for OFDM. I already programmed the main part according to the implementation in DVB-T. But my system is rather abstract. First a symbol will be sent only with pilots to make the channel estimation. All the other symbols after that are full of purely real data (without pilots). With the help of the channel freq. resp. (which calculat...


OFDM Question

Started by Crisanquito in comp.dsp15 years ago 2 replies

Hello I have got a simple question about the OFDM transmitter and the spectrum we obtain after IFFT processing-DAC-IQ modulator. It must be...

Hello I have got a simple question about the OFDM transmitter and the spectrum we obtain after IFFT processing-DAC-IQ modulator. It must be very simple because I have not found anything to clear my mind. I just do not understand how we can obtain a symmetric location of all the subcarriers after a N-IFFT processing, with N even, if one of the subcarries is located at 0 frequency: even numbe...


Use of channel estimation in OFDM

Started by m26k9 in comp.dsp16 years ago 2 replies

Hello, I have a confusion with the use of channel estimation in the context of OFDM. Suppose subcarrier 'k' has a channel gain of H(k) and...

Hello, I have a confusion with the use of channel estimation in the context of OFDM. Suppose subcarrier 'k' has a channel gain of H(k) and this subcarrier is used to transmit data to some user U(k). (1) If the required data to send is, for example, X(k), the transmitter multiplies X(k) by 1/H(k) to compensate for the channel attenuation. Then at the receiver, after FFT, the received sign...