## Forums Search for: OFDM

## Q) MIMO-OFDM and freq-domain equalization

inHello, 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

inHi 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

inOK, 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 ...

## OFDM uses null DC. Why?

inHi~ 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...

## How does a time domain OFDM signal look like

inHi, 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 ??

## Four antennas OFDM receiver. How sum "in phase"

inHi guys, I have an OFDM signal (with DBPSK) received using four differents antennas (four unknown delays then). how i can sum the four...

Hi guys, I have an OFDM signal (with DBPSK) received using four differents antennas (four unknown delays then). how i can sum the four OFDM signals "in phase"? in others words, how i can estimate the phase compensation in each "bin" for each signal delayed? many thanks --------------------------------------- Posted through http://www.DSPRelated.com

## Channel correlation regarding OFDM.

inHello, 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 ...

## Baseband OFDM matlab simulation question

inI am attempting to simulate a baseband OFDM communication system in MATLAB. I have the parallelized QAM symbols feeding into an IFFT, but this...

I am attempting to simulate a baseband OFDM communication system in MATLAB. I have the parallelized QAM symbols feeding into an IFFT, but this produces a vector of complex numbers. I found much information about taking the real and imaginary parts and modulating them with an In-phase and Quadrature signal, however this is not what I am trying to do. I am simulating OFDM in the base band, ...

## DPSK's relation with OFDM and Demodulation

inHi, I understand that simplified equalization is one of the good reasons for going with OFDM. But, how do they manage it ? That is, The OFDM...

Hi, I understand that simplified equalization is one of the good reasons for going with OFDM. But, how do they manage it ? That is, The OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. So, The Differential modulation such as DPSK / DQPSK if applied to each sub-carrier, equalization can be completely omitted. ( Reason - ...

## OFDM Block-type Pilot, channel estimation

inHi, I am working on channel estimation in OFDM systems, and have a question related to block-type pilot arrangement. Block-type pilot...

Hi, I am working on channel estimation in OFDM systems, and have a question related to block-type pilot arrangement. Block-type pilot arrangement is one where all subcarriers in an OFDM symbol carry pilots. Does this mean that this OFDM symbol contains no null subcarriers, even at DC? Or is it assumed that these 'pilot' carrying OFDM symbols contain some minimum number of null-subcarriers a...

## Sampling Time Difference in OFDM Demodulator

inDear all, in my diploma thesis i am realizing an ofdm modem. i am working with two adsp bf533 ez-kit-lites. one as transmitter and one as...

Dear all, in my diploma thesis i am realizing an ofdm modem. i am working with two adsp bf533 ez-kit-lites. one as transmitter and one as receiver. for d/a and a/d conversion i use the implemented audio codec. this works with nominally 48khz. and here is my problem. these 48khz are only a nominally value. the "real" values differ slightly. after receiving my ofdm signal and detecting the sta...

## ofdm signal (dab) decoding problem

hi, i am working on the development of an ofdm receiver (dab receiver). After frequency synchronisation, when i differentially decode the ofdm...

hi, i am working on the development of an ofdm receiver (dab receiver). After frequency synchronisation, when i differentially decode the ofdm symbols, i get 5th symbol corrupted i.e. the constellation of 5th symbol is not centerd on the multiples of pi/4. When i shift the fft window for 5th symbol 7 samples backward, the contellation improves, but it is still very noisy and not centerd at the mu...

## oversampling in OFDM

inHi All,, Plz help me for ofdm simulation. I have tried to simulate ofdm signal with 64 subcarriers, with an oversampling of factor 4 in...

Hi All,, Plz help me for ofdm simulation. I have tried to simulate ofdm signal with 64 subcarriers, with an oversampling of factor 4 in frequency domain. Now I've got 256 QPSK symbols with zero paddings.I'm doing IFFT of 256 points. But I need to modulate my data on 64 subcarriers. then how would it be possible if i'm doing IFFT/FFT of 256 points. plz clarify me this thing, if i have zeronpadde...

## I am new to OFDM, I need help.. Thanks...

Recently, I am doing a project related to DAB receiver. And I knew very little about OFDM,and my question is very simple. In the DAB...

Recently, I am doing a project related to DAB receiver. And I knew very little about OFDM,and my question is very simple. In the DAB standard it said that there are some NULL symbols receiver can use to detect the begin of the OFDM Signal, after that there is the Phase reference symbol. I am wondering how can I get this phase reference symbol from the noise environment?

## flexible OFDM modulator

inHi all!! I'm a student and for my thesis I have to implement a flexible OFDM modulator in VHDL. That means that it has to be applicable in...

Hi all!! I'm a student and for my thesis I have to implement a flexible OFDM modulator in VHDL. That means that it has to be applicable in more than one systems. For example DVB and WiMAX. The elements to implement are the Mapper the OFDM and the Guard Interval Insertion. As you understand the mapper part should support all the possible constellations given from those two standards and th...

## OFDM simulation

inDear all, I am new to this group.I am bit confise about orthogonality in OFDM. I want to know what is orthogonal. Any help regarding this is...

Dear all, I am new to this group.I am bit confise about orthogonality in OFDM. I want to know what is orthogonal. Any help regarding this is greatly appreciate. Regards Lau

## Q) MIMO-OFDM better than AWGN performance. Why..

inHello. It's very shameful to ask this stupid question...but, if anyone woule help, can we have some discussion please? 1) I have a MIMO-OFDM...

Hello. It's very shameful to ask this stupid question...but, if anyone woule help, can we have some discussion please? 1) I have a MIMO-OFDM simulator. My problem is that, for example, if I use Alamouti's 2-by-2 diversity scheme, then my MIMO-OFDM curve in freq-selective channel works partially better than SISO QPSK curve in gaussian channel. The two curves also intersect. 2)It seems that t...

## MIMO - OFDM

Hi guys, my question is: What is the minimum frame length for SF-OFDM schemes(2x1 or 4x1)??Any help is really appreciated. Thanks

Hi guys, my question is: What is the minimum frame length for SF-OFDM schemes(2x1 or 4x1)??Any help is really appreciated. Thanks

## Modeling OFDM multipath channel in Matlab

Dear all, I have a basic question regarding modeling of a multipath channel for OFDM in Matlab and would appreciate your help. My intention...

Dear all, I have a basic question regarding modeling of a multipath channel for OFDM in Matlab and would appreciate your help. My intention is to simulate an 802.11a transmission which uses OFDM. From the 802.11a standard I know that: -Number of Subcarriers, Nsc = 64 -Sampling Rate at the receiver, fs = 20e6 samples/sec -BW = 20Mhz -Carrier Frequency, fc = 5.25 Ghz Now consider that I...

## OFDM average power

inHi, I understand the problem of high Peak to Average Power Ratio in OFDM. However, I am not sure how the average power of an OFDM signal...

Hi, I understand the problem of high Peak to Average Power Ratio in OFDM. However, I am not sure how the average power of an OFDM signal is calculated. Suppose you have an N-carrier transmitter where the average power per carrier is p, what would the average power of the OFDM signal be? Thanks.