OFDM-coherent

Started by Zeph80 in comp.dsp15 years ago

Im a little confused about how you employ coherent demod in OFDM. After the FFT at the receiver, how do I perform a coherent demodulation-dont I...

Im a little confused about how you employ coherent demod in OFDM. After the FFT at the receiver, how do I perform a coherent demodulation-dont I need a carrier for phase estimation in case of BPSK, QPSK etc. Also this is what coherent OFDM is, right?


Cylic prefix and postfix

Started by Ant_Magma in comp.dsp16 years ago 4 replies

Let's say my transmittid frame is like this: || Preamble || GI1 | OFDM symbol 1 || GI2 | OFDM symbol 2 || Removing GI1 would remove any...

Let's say my transmittid frame is like this: || Preamble || GI1 | OFDM symbol 1 || GI2 | OFDM symbol 2 || Removing GI1 would remove any interference effects caused by the preamble. But what if the last few samples of OFDM symbol 1 is interfered by GI2? Wouldn't a structure like this: || Preamble || GI1 | OFDM symbol 1 | GI1' || GI2 | OFDM symbol 2 | GI2' || With GI1' and GI2' p...


OFDM system

Started by patrick_dbg in comp.dsp13 years ago 2 replies

Hi, It is clear that OFDM systems may have different SNR values for each subcarrier due to frequency selectivity of the channel. If an OFDM...

Hi, It is clear that OFDM systems may have different SNR values for each subcarrier due to frequency selectivity of the channel. If an OFDM packet consists of n number of FEC blocks and in case of adaptive modulation and coding systems, a single FEC block may have different modulation scheme. However, is it possible for OFDM (e.g.IEEE 802.11a/n) systems that the block error probability of FEC b...


a mini question about the "sample sheme" of OFDM

Started by daor in comp.dsp15 years ago 6 replies

Hi all, I have a mini question and need yr help pls. It is simply about the understanding of sample scheme of OFDM. For convenience, the...

Hi all, I have a mini question and need yr help pls. It is simply about the understanding of sample scheme of OFDM. For convenience, the parameters of a OFDM system are presented as follows. .the sample period: T .FFT/IFFT point: N .the OFDM symbol period: N=B7T Then we obtain that, .the carrier spacing: 1/(N=B7T) .the frequency of the first "baseband" carrie...


MB-OFDM-UWB

Started by totohaha in comp.dsp13 years ago 1 reply

I want to simulate a MB-OFDM-UWB system in Matlab. I did pure OFDM system before which consist of convolution code block, modulation block,...

I want to simulate a MB-OFDM-UWB system in Matlab. I did pure OFDM system before which consist of convolution code block, modulation block, FFT block, Cyclic Prefix block, multipath block and corresponding receiver blocks. However, how to modify them to a MB-OFDM-UWB system, what kind of block I need to add into? thank!


AWGN channel in OFDM-System

Started by steffen in comp.dsp16 years ago 5 replies

Hallo everybody, I've just finished my OFDM-Simulation, but I'm still facing a little problem with the AWGN-function provided by Matlab. The...

Hallo everybody, I've just finished my OFDM-Simulation, but I'm still facing a little problem with the AWGN-function provided by Matlab. The transmitted OFDM-Signal s(k) consists of samples of the komplexe baseband signal. (As I've implemented a diskrete time OFDM-baseband-system). The channel should add white Gaussian noise n(k). An the resulting signal r(k) = s(k) + n(k) will than be process...


IFFT & DAC in IFFT

Started by Anonymous in comp.dsp15 years ago 1 reply

Hi, I am doing project in OFDM .I have doubts regarding the functionality of IFFT & DAC in OFDM TX. In OFDM block Where the carrier comes...

Hi, I am doing project in OFDM .I have doubts regarding the functionality of IFFT & DAC in OFDM TX. In OFDM block Where the carrier comes into picture?. After IFFT what is exactly done in DAC block?. There we are using any carrier suppliers?. IF possible anybody can explain the flow of data in OFDM Tx. can anybody help me out regarding the above queries. Thanks & Regards Lakku Raji...


synchronization in OFDM and others...

Started by rifo in comp.dsp14 years ago 8 replies

Hello, I am wondering there is so much literature about carrier and timing recovery in communications*. However as far as I understand, OFDM...

Hello, I am wondering there is so much literature about carrier and timing recovery in communications*. However as far as I understand, OFDM uses a different approach in synchronization. My question is since OFDM is becoming more and more popular does this mean that these algorithms will cease to be used in future? * synchronization in software radios (chris dick, fred harris, michael ric...


Simulation of symbol synchronization in a OFDM receiver

Started by Anonymous in comp.dsp15 years ago

Dear all I am doing a block for a OFDM receiver that receives as input the ofdm received signal and gives as output a rectangular signal...

Dear all I am doing a block for a OFDM receiver that receives as input the ofdm received signal and gives as output a rectangular signal (for synchronization) in which each pulse represents a peak in the autocorrelation function realised over the ofdm received signal. How can i define a threshold to detect this peak of the correlation function? Is there another way to do this? I will use di...


OFDM in SystemC

Started by Rezwan in comp.dsp15 years ago

Does anyone has experience of using SystemC for OFDM based design. Please share your experience. I'm new in SystemC so not sure how to start. If...

Does anyone has experience of using SystemC for OFDM based design. Please share your experience. I'm new in SystemC so not sure how to start. If you know any good books/websites for OFDM in C/C++ please post here. kind regards, Rezwan


OFDM Transmit diversity

Started by Shahin in comp.dsp14 years ago 3 replies

Hello, Assume you have 2 OFDM transmitters that are simultanously transmitting different data and the data is somehow coded (ie...

Hello, Assume you have 2 OFDM transmitters that are simultanously transmitting different data and the data is somehow coded (ie CDMA). After IFFT the ofdm symbol of each transmitter , X1 and X2, passes a freq. selective fading channel: Y = X1.G1 + X2.G2 + N My question is at the receiver, before or after the FFT, how to remove the effect G1 and G2 which are the fading coeffici...


implementing rayleighchan in OFDM

Started by burky in comp.dsp14 years ago

Hi everbody, I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". I have very limited time, if you can help me I will be...

Hi everbody, I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". I have very limited time, if you can help me I will be grateful to you.... I can implement the OFDM structure in AWGN channel, it works very well.. But when i try to implement the system in a "rayleighchan", I obtain very bad BER results. -------------------------- N=3D256 ; % carriers GI=3DN/4;...


OFDM symbol

Started by harishm in comp.dsp7 years ago 1 reply

Hi, I have a question on IFFT input in OFDM systems. Why center tone is always set to ZERO for IFFT input ? is it one method to reduce...

Hi, I have a question on IFFT input in OFDM systems. Why center tone is always set to ZERO for IFFT input ? is it one method to reduce PAPR in OFDM systems ? _____________________________ Posted through www.DSPRelated.com


OFDM Simulink problem, SOS!

Started by Ant_Magma in comp.dsp16 years ago 13 replies

I'm simulating an OFDM transceiver to be later converted and implemented on a C6713 DSK. I'm currently facing a problem with the simulation and...

I'm simulating an OFDM transceiver to be later converted and implemented on a C6713 DSK. I'm currently facing a problem with the simulation and i'm at my wits end trying to figure out what is wrong. Thus i'm really hoping you guys can lend me some help otherwise i can't proceed anymore... Here are 2 pictures of my OFDM simlation in Simulink. Pic1 is the model with the convolutional enco...


Q) MIMO-OFDM and freq-domain equalization

Started by lsw00kor in comp.dsp14 years ago 1 reply

Hello, everyone. In SISO-OFDM, we usually employ a frequency domain equalization after the receiver FFT module, as a way to compensate for the...

Hello, everyone. In SISO-OFDM, we usually employ a frequency domain equalization after the receiver FFT module, as a way to compensate for the channel distortion along frequency bins. We depend on OFDM channel estimation and simple inversion for this purpose. In MIMO-OFDM, either multiplexed system or diversity system, what is the best way to implement a frequency-domain equalization for the...


Questions about OFDM

Started by pozz in comp.dsp18 years ago 7 replies

Hi all, I'm studying OFDM from documents available from Internet for free and I have some doubts. I understand that guard interval was added...

Hi all, I'm studying OFDM from documents available from Internet for free and I have some doubts. I understand that guard interval was added to solve problems with multipath-signal delayed. So, because symbol duration in OFDM is long, a little fraction of it can guarantee immunity against long-delayed multipath-signals. So, if I have: ....-------+-------------------------------+-----...


simple-minded non-OFDM signal design question

Started by Randy Yates in comp.dsp15 years ago 48 replies

OK, now that I've got my OFDM question off my chest, here's a related question. If one used a normal single-carrier signal in place of OFDM,...

OK, now that I've got my OFDM question off my chest, here's a related question. If one used a normal single-carrier signal in place of OFDM, you'd have a relatively huge bandwidth to deal with, which means your single-carrier data rate is going to be many times higher than the rate across any one carrier of a comparable OFDM signal. Well, given all that freakin' bandwidth, it seems that ...


How does a time domain OFDM signal look like

Started by walter2k in comp.dsp14 years ago 6 replies

Hi, The ofdm symbols when placed in the freq domain say for QPSK, all the spectrum components have the same value. Hence it results in a flat...

Hi, The ofdm symbols when placed in the freq domain say for QPSK, all the spectrum components have the same value. Hence it results in a flat square frequency spectrum. Hence the time domain OFDM symbol shoul be a sinc pulse. Am I right ??


OFDM uses null DC. Why?

Started by Mabinogi in comp.dsp15 years ago 1 reply

Hi~ everybody~ I have one thing about OFDM to want to know. In general OFDM system, DC sub-carrier is not used, that is, null is inserted...

Hi~ everybody~ I have one thing about OFDM to want to know. In general OFDM system, DC sub-carrier is not used, that is, null is inserted there. Suddenly I come to curious about the reason. According to the some documents that I found in the web, the reason is due to direct conversion which cannot pass DC component. Is it correct? and is it the only reason why DC sub-carrier was stuf...


Channel correlation regarding OFDM.

Started by m26k9 in comp.dsp14 years ago 2 replies

Hello, I have a confusion regarding the channel correlation of an OFDM system. In the OFDM receiver, after the FFT, the frequency-domain...

Hello, I have a confusion regarding the channel correlation of an OFDM system. In the OFDM receiver, after the FFT, the frequency-domain output is given as: Y = XH + W Y,X,H and W are matrices with X being a diagonal matrix with constellation points. My question is regarding channel estimation. Usually in MMSE, we need the channel correlation R_HH ('_' denotes the subscript}. And it ...