OFDM stands for **o**rthogonal, **f**requency-**d**ivision **m**ultiplexing.

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Sparse Channel Estimation in OFDM System

Compressive sensing methods are used in channel estimation when the channel is thread as sparse where there are zero points in the signal representation. I am in the beginning of the sparse signal ...
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16 views

Alamouti scheme, what is the SF to ST transformation?

I have been inspecting a MATLAB code, that performs Alamouti scheme for LTE downlink. Alamouti scheme has been known to achieve full diversity gain. Assuming we have DATA of length L. The code I ...
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17 views

What is the purpose of oversampling the QAM signal in OFDM?

What is the purpose of oversampling the constellation mapper output QAM in OFDM? After the constellation mapper the signal is mapped into QAM and then with IFFT the subcarriers are created in OFDM ...
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38 views

DAC implementation in OFDM

In an OFDM transmitter, after IFFT & CP block, a DAC block is used.Since the output of IFFT is complex, and the input to DAC should be an integer, how can we integrate the two blocks? I ...
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15 views

Resource Mapping LTE

I am having a hard time understand what resource allocation means in LTE. Below is one example of resource block over one subframe. Can anyone please explain to me, what does this mapping mean? ...
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54 views

SFBC Alamouti Scheme LTE

That a 2$\times$1 Alamouti SFBC is referred to as a rate 1 code, two symbols are sent over two adjacent subcarriers. Reference: Fundamentals of LTE Book. This question is regarding this SFBC encoder ...
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69 views

OFDM modulator in LTE

My understanding of what an OFDM modulator does, is that it takes a parallel sequence of QAM symbols of size M, pads it with zeroes corresponding to the zero subcarriers, then passes them through an ...
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1answer
36 views

Questions Downlink OFDMA in LTE

I am looking for a clear and precise explanation of how an OFDMA modulator in downlink LTE operates. I have many books that explain it but each has its own way and do not answer my questions ...
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25 views

How does the OFDM system receiver decide the OFDM symbol length? [duplicate]

I am trying to understand how the receiver decides the length of OFDM symbol in time domain before it goes into DFT process at the receiver. The complete OFDM symbol (with Cyclic Prefix added) is ...
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17 views

position of null carriers in N=256 subcarier OFDM

can anyone tell me the position of null subcarrier in $N=256$ subcarrier OFDM. since edges re assigned null to prevent interference from an adjacent symbol, i assuming that the subcarrier $-127$ to ...
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25 views

Principle of Mapper in frequency diversity in OFDM

I am trying to understand frequency diversity in OFDM. An extra block 'MAPPER' is introduced in conventional OFDM transmitter to apply frequency diversity. Can anyone explain the principle of this ...
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88 views

What is difference between OFDM and GFDM?

I am trying to understand the difference(s) between OFDM (Orthogonal Frequency Division Multiplexing) and GFDM (Generalized Frequency Division Multiplexing) which are used as a multicarrier modulation ...
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20 views

Sub-carriers spacing in DVB-T2

Looking at DVB-T2 technical specifications I see that sub-carriers spacing has, in the worst case, a value of few hundred hertz, (something like 279 Hz). 32K sub-carriers are used to reach such a low ...
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3answers
54 views

Can OFDM modulate analog signal?

I suppose that OFDM can't modulate analog signal. The basic mathematical description for OFDM is $$ v(t)=\sum_{k=0}^{N-1}X_{k}\exp(j2\pi k t /T),\quad 0<t<T$$ In this equation, $X_k$ is a ...
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1answer
28 views

Must OFDM signal be time-division in a multiple-transmitter and SFN system when the signal is free of spread-spectrum?

The OFDM baseband signal can be demodulated since each subcarrier is orthogonal to another. But In SFN system, i.e., Single Frequency Network, all OFDM signals from several transmitters are in the ...
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38 views

Does the OFDM MMSE Channel Estimator Require Prior Channel Knowledge?

The OFDM MMSE channel estimator seems to require a-priori knowledge of the channel to calculate the MMSE estimate. See equation 8 here: http://cache.freescale.com/files/dsp/doc/app_note/AN3059.pdf. ...
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239 views

OFDM transmitter bandwidth

Theory Suppose an OFDM transmitter with four subcarriers is implemented using the structure shown below. If the serial data input rate is 40 bps, each parallel stream will run at 10 bps. ...
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2answers
127 views

Simulating noise in OFDM

I'd like to simulate a certain $E_s/N_0$ in a baseband OFDM MATLAB modem to generate SER curves. I randomize 50 QAM symbols with $N$ subcarriers each in frequency domain, add null frequencies (guard ...
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17 views

calculating average PSD of N radio frames

i've written a matlab code for the basic ofdm with bpsk modulation. there is no channel coding or compression used at this point. i just want to see the PSD of the transmitted packet. i am getting a ...
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42 views

How to simulate two OFDM Users with low complexity FFT/IFFT?

have two User one of them sending over freq (0-B] and the other transmit over (B-2B]. Both of them are using OFDM and each one has Nc subcarriers. I wanted to simulate the received signal using ...
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76 views

Spectral location of individual OFDM symbols

The generic IFFT OFDM transmitter takes $N$ serial input data symbols, parallelizes them, maps them to their signal constellation points, and processes all $N$ resultant complex values using the IFFT ...
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109 views

OFDM violates sampling theorem

The "textbook" OFDM block diagram is as the below figure. But I wonder if it satisfies the sampling theorem. Here, we have N points $X[k]$ before IFFT, and $$x[n]=\frac{1}{\sqrt{N}}\sum_{k=0}^{N-1} ...
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23 views

OFDM intra-block multipath interference

We know that OFDM eliminates the inter-block intereference. But there are still multipath interference in a single OFDM block(symbol). How does LTE handle this intra-block interference induced by ...
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54 views

Q and I part in QAM

I have one confusion in QAM about in-phase I and quadrature Q part, i.e. do they transmit identical data or not? For e.g. if i have 11001001 as a byte to be transferred, so will 4-QAM separate it ...
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1answer
331 views

why LTE doesn't use DC subcarrier in the downlink?

I know LTE doesn't use the DC subcarrier for OFDM/OFDMA modulation for the downlink, but no author gives a detailed explanation to this stuff. Can you tell me the reason behind it? Thank you!
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375 views

Sampling rate in Wifi 802.11 -> 20 MHz enough with a BW of 20 MHz?

In a Wifi 802.11n context, I'm looking to find the sampling rate to perform some processing on the signal and I've something I cannot understand : in the book Next Generation Wireless LAN's: 802.11n ...
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975 views

How to calculate bandwidth require for OFDM

I read LTE PHY profile and do not understand the relationship between number of FFT and bandwidth. For example LTE downlink channel bandwidth 1.25MHz and 5MHz have 128 FFTs and 512 FFTs accordingly. ...
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3answers
169 views

Time-frequency synchronization algorithm for OFDM continuous stream

I am studying on the implementation of a continuous stream OFDM baseband modem. Googling and also searching here on stackexchange for synchronization techniques I found the descriptions of several ...
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1answer
109 views

How may samples per symbol in ieee 802.11 g

I am doing a baseband simulation for IEEE 802.11 g. The standard uses 64 IFFT length ($3.2 \mu s$) and 20 Msamples per second. This result in one sample per symbol. I am wondering what the structure ...
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95 views

Additional prefix and suffix required when windowing an OFDM symbol?

To reduce out of band energy, it is common to apply a Raised Cosine filter to the front and back of an OFDM symbol. It is also common to overlap the windowed portions of adjacent symbols to eliminate ...
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433 views

Hermitian symmetry in OFDM systems

I am trying to understand the usage of Hermitian symmetry in OFDM systems and have a couple of questions regarding this. What is the reason of using the Hermitian symmetry in OFDM? How can we ...
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1answer
226 views

Alamouti code after or before IFFT block in OFDM

We are trying to implement Alamouti STBC on underlying ofdm signal. We were thinking as to where to write alamouti coder block. I thought we could write it after the cyclic prefixer block as we get a ...
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284 views

What is the advantages of BPSK+OFDM over usual BPSK (with no OFDM Modulation)?

The other days I read a useful article (on BER v.s. Eb/N0 curve of ofdm) whose link is as bellow. While watching the plot inside, a question was arisen in my mind. I wonder if the BER v.s. Eb/N0 curve ...
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145 views

Really basic question about OFDM

I am new to signal processing and am currently doing research into the subject. I am learning about Orthogonal Frequency Division Multiplexing and have a question. Most definitions of OFDM mention its ...
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3answers
94 views

How do you perform OFDM modulation?

I'm new to OFDM modulation. During OFDM modulation in the frequency domain, are the negative frequencies modulated with a conjugate version of the data of the positive frequencies, or do the negative ...
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3answers
95 views

comparison between frequency offset estimators

I have been working frequency offset estimation in OFDM. The objective was to compare different frequency offset estimation techniques. By using MATLAB, I have simulated three different estimation ...
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63 views

How to calculate BW ofdm?

HI I have these specification for an OFDM program I was wondering, what is the bandwidth and the sampling frequency? I'm not a student of Digital signal processing, hence I am so confused. ...
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1answer
279 views

Simulate a simple multipath channel for OFDM Modulation test. MATLAB [closed]

Hi I need to simulate a simple multipath channel in matlab through which I can send my OFDM transmission signal, I want to test my OFDM receiver design. So far I have: ...
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1answer
90 views

What type of correlation is this equation?

In a book [1], gives an equation (equation 5.31 in the book) for estimating frequency offset in OFDM systems proposed by Classen. the procedure is: first, two OFDM symbols, $y_l [n]$ and $y_{l+D} ...
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383 views

IFFT and OFDM upconversion

I am trying to understand some basic concepts with IFFT as represented here OFDM Modem page 50-53, and 108-114. Some basics that are represented - The base sampling rate is 8khz. The symbol period ...
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728 views

generating pilot sub-carriers in matlab

I wanted to simulate OFDM system in MATLAB. I'm using Fixed WiMAX OFDM parameters in my simulation, where the number of data sub-carriers are 192, number of Pilot sub-carriers are 8, number Null ...
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278 views

Using Pilot tones to estimate carrier frequency offset in ofdm

I have been studying carrier frequency offset estimation techniques in OFDM systems. I have understood several of them. when using Pilot tones, as stated in paper (1), the process involves two methods ...
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1answer
305 views

Oversampling in OFDM

Why do we need an oversampling in OFDM signal? and how to do it? If around half of the Sub-carriers are only used to send data, then do we need to perform oversampling to the signal? Is it necessary ...
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183 views

Carrier frequency offset (CFO) estimation based on Symbols

In (1), it's said that: If two identical training symbols are transmitted consecutively, the corresponding signals with CFO of $\epsilon$ are related with each other as follows: ...
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1answer
115 views

Choosing clock frequency and number of bits of an OFDM transceiver [closed]

I want to implement an OFDM transceiver chip and my question is how to choose the clock frequency of the IFFT block? The number of output bits of the IFFT block? Also, how has the clock frequency and ...
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2answers
907 views

Carrier frequency offset (CFO) estimation using cyclic prefix

I understand the cyclic prefix, but in (1) it's said that: "If we consider that the channel effect is minimal and can be neglected. then the phase difference of the CP and the OFDM symbol which the ...
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140 views

Software-based sound card OFDM

I'm trying to implement an sound card-based OFDM modem. A paper says: ...A serial to parallel converter is applied and the IFFT operation is performed on the parallel complex data. Say I have ...
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1answer
79 views

OFDM DA conversion problem

I'm working on a sound card based OFDM system and ran into some problems: How can I perform DAC on the real and imaginary parts of the IFFT? I think they are real numbers instead of 0 and 1. ...
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2k views

How to Show A OFDM Symbol's PSD in Matlab

I'm trying to suppress the sidelobe of OFDM but having troubles showing its spectrum in Matlab. After IFFT, I get a time-domain signal, but in which way I can get its spectrum(or PSD)? I want to ...
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2k views

Coherence bandwidth and coherence time in an OFDM system

While studying an OFDM system, I have encountered statements like coherence bandwidth is the reciprocal of delay spread and coherence time is the reciprocal of the Doppler spectrum. Can somebody help ...