Various information and materials about OFDM

[Aya2002]

Hi all,

I suggest to make this topic to be an open discussion about any thing in OFDM and to share any presented data.

what is your opinion?

 

[mashhur]

communications discussion montadar

hi all!

what are the main differences between OFDM and MC-CDMA?

i appreciate feedback!
thanks!

 

[Aya2002]

app.ofdm.cdma.rar

As I know:
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Multicarrier CDMA is the combination of OFDM signaling and CDMA scheme has one major advantage that it can lower the symbol rate in each subcarrier so that longer symbol duration makes it easier to quasi-synchronize the transmissions.

The MC-CDMA transmitter spreads the original data stream over different subcarriers using a given spreading code in the frequency domain. In other words, a fraction of the symbol corresponding to a chip of the spreading code is transmitted through a different subcarrier. Spreading code like the Hadamard Walsh code has been shown to be optimum in maintaining ortogonality between subcarriers, because here does not pay attention to the auto-correlation characteristics of the spreading code. Figure 1 shows the basic MC-CDMA system of the jth user, where GMC denotes the processing gain, NC the number of subcarriers, and Cj(t)=[C1j C2j …..CGMCj] the spreading code of the jth user. In this figure the MC-CDMA scheme is discussed assuming that the number of subcarriers and the processing gain are all the same. Therefore, in this figure the number of subcarriers is equal to the processing gain (GMC=NC).

figure 1

thanks

 

[Aya2002]

ofdmandmatlab yahoo

Hi members

no 1 want to join us!!!!!

Montadar

 

[Aya2002]

windowing in ofdm

Hi members:

is there any one has any information to share here?

Thanks

 

[bbatif]

ofdm wireless multimedia nee rapidshare

Some books:

Theory and Applications of OFDM and CDMA : Wideband Wireless Communications
By Henrik Schulze
*http://mihd.net/fc73is


Adaptive Wireless Transceivers: Turbo-Coded, Turbo-Equalized and Space-Time Coded TDMA, CDMA, and OFDM Systems
By Lajos Hanzo, C. H. Wong, M. S. Yee,
**broken link removed**

Wireless OFDM Systems : How to make them work? (The International Series in Engineering and Computer Science) By Marc Engels
***broken link removed**

Orthogonal Frequency Division Multiplexing for Wireless Communications (Signals and Communication Technology)
By Ye (Geoffrey) Li (Editor), Gordon L. Stuber (Editor)
*http://mihd.net/ir3dqs
***broken link removed**

 

[Aya2002]

basic dsp at mihd

Windowing

Sharp phase transitions that are caused by modulation exist between the symbol boundaries. This is illustrated in the following figure. Due to this there is out of band interference as the spectrum reduces very slowly. Windowing is a well-known technique to suppress the side-lobes level of the sinc functions and thus reduce the bandwidth occupied by the signal. Windowing an OFDM symbol makes the amplitude go smoothly to zero at the symbol boundaries. A commonly used window type is the raised cosine window, defined as



However, in an OFDM system, the applied window must not influence the signal during its effective period denoted as TFFT . Therefore, the cyclically extended parts of the signal are pulse-shaped as depicted in Figure Note that this additional prefix also helps to prevent ISI and lowers the SNR to some extent. It is to be noted that windowing reduces OOB but at the cost of reduced delay spread tolerance. The orthogonality between subcarriers holds only when amplitude and phase of the subcarriers are constant during the entire T-second interval

Hence, a roll off factor of β reduces the effective guard time by βTs. the Figure above shows the effect of β on OOB, it can been seen that as β increases the OOB decreases but with reduced effective guard time.

 

[mashhur]

matlab codes for ofdm .rar

hi all!
even though i am new for OFDM technique, i am understanding because of you guys.
thanks a lot!

and i am going to simulate a wireless channel (myself) by the M-QAM over an AWGN, so that i should choose one of the FEC codes such as LDPC, turbo, Red-Solomon, BCH or other, so first step is to create algorithm

could you help me please to create an algorithm, step by step.
(if it possible from input data till the real output information at the destination)

i really appreciate members of edaboard!
thanks a lot again!

 

[gayathri123]

basics of optical ofdm

hi aya2002.are u student. can u help me because i seen ur reports. i need some help from u. actually my aim of the project to reduce PAPR in OFDM . i think more ideas in OFDM. could u find me answer and some related coding in MATLAB.please it very urgent because i should implement this topic.

 

[Aya2002]

adaptive wireless transceivers rapidshare

hi gayathri123
i am a PhD student. I am interest in OFDM, but i am new for this system. but you can enjoy our group on yahoo named ofdmandmatlab by the following link as there are may researchers and Doctors in communications and PhD students and others available in this group.

**broken link removed**
see u in ofdmandmatlab

 

[Aya2002]

some ofdm explanations

hi friends: for the zero padding



regards

 

[mena2009]

any thing about OFDM

Hi aya2002,

thank you for your information but can i take your advise to start in digital communicatios?

thank you

 

[Aya2002]

any thing about OFDM

start with fourier transforms and before that try to study the digital modulation techniques and also the digital signal processing DSP.

Good luck

 

[gayathri123]

Re: any thing about OFDM

can you help me in coding in MATLAB because i should reduce PAPR in OFDM signal thgat why iam asking.iam helpless.

 

[Aya2002]

any thing about OFDM

i see you since some weeks, but firstly you must understand what is the OFDM and do your simulation and then decide to solve the problems step by step

 

[decode_done]

Re: any thing about OFDM

I am studying an OFDM system. I have adoubt on nulls. What is the significance to add nulls and DC subcarroers in an OFDM system?

 

[gayathri123]

Re: any thing about OFDM

i understand basic OFDM system . it says about some basic principle of orthogonality. i have done my coding serial to parallel converter and receiver p/s.

 

[Aya2002]

any thing about OFDM

this is the reference:
OFDM for Wireless Multimedia Communications
Richard van Nee, Ramjee Prasad 2000

chapter 2

 

[cachep]

Re: any thing about OFDM

Could you show some major applications of OFDM as well as state of the art on OFDM? I have heard some novel OFDM based system for example OFDM optical application, OFDM ultrasonics. Thank you!

 

[Aya2002]

any thing about OFDM

google it, i am sure you will find many applications