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

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What benefits can we get from the use of GFDM?

Existing literatures say that the generalized frequency division multiplexing (GFDM) has lower out-of-band emission (OOBE) levels compared to orthogonal frequency division multiplexing (OFDM). ...
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How to calculate energy of an OFDM signal?

What is the difference between power and energy of OFDM signal. How to calculate energy of an OFDM signal, if we consider OFDM symbol size is 64, and QPSK is used as modulation scheme?
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channel estimation in OFDM systems(MMSE Estimator)

I want to use the mmse estimator to estimate the channel in ofdm systems. I find the formula: h=Rgy*(Ryy)^-1*y[1],while Rgy is RggF'X'. My question is: in the ...
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89 views

OFDM channel estimation

As we know, if we want to get the time domain response of the channel $h[n]$, we can first get the frequency domain response of the channel $H[k]=Y[k]/X[k]$. And then we do IFFT. But now one OFDM ...
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57 views

How to simulate High Power Amplifier(HPA), like Solid State Power Amplifier (SSPA)

I cannot understand how to simulate Solid State Power Amplifier (SSPA). When I directly write the Rap's SSPA model in Matlab, it does not produce BER of OFDM like published papers by other ...
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57 views

Crest Factor of OFDM signal

I have been given a OFDM signal of crest factor of 12dB. The crest factor is the ratio of peak power to the average power of the signal. Does anyone have any idea how crest factor of 12dB is derived ...
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Practicality of the assumption of i.i.d. for Rayleigh channels

I would like to understand how far the assumption of having i.i.d. is accurate/valid (from the practical point of view) when an OFDM system is working in Rayleigh channels. Is this means the channel ...
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78 views

Number of samples in one period of subcarrier after IFFT

I have a quick question about the number of samples in one period of a sub carrier in OFDM systems. The IFFT process generates N-parallel sub carriers in discrete time domain which are sent ...
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20 views

Conceptual questions on MC-CDMA - where to perform equalization?

I have some basic questions on MC-CDMA technology. Below are the steps involved and the Questions. Please correct me if there is any mistake in the steps. An intuitive answer will be very helpful. ...
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17 views

Guard Interval Correlation for a given Impulse Response in OFDM system

I've been given a channel response of $$ h(n) = \delta(n) + A \delta(n -D) $$ where A and D are arbitrary constants. What would be the output of Guard Interval Correlation (GIC) symbol ...
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Bandwidth of OFDM symbol

In 802.11a, channels of 20 MHz bandwidth are available for wireless transmission. With OFDM modulation, the protocol uses 64 pt IFFT for transmission. This means we take a stream of symbols apply ...
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31 views

A General Question regarding OFDM symbol

I have cross across an OFDM modulator that says that A frequency domain sequence is passed into a 64 point IFFT. A cyclis prefix is added (0.8 $\mu$sec) and creates as a result a 4 $\mu$sec time ...
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32 views

Which MIMO scheme is implemented in a modem?

Hope I phrased the title in a sense. I'm trying to get more knowledge on MIMO , so I read a few paper and i've understood that MIMO system can provide 3 types of improvements : array gain, diversity ...
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82 views

Can we do cyclic prefix with zeros in OFDM rather than with samples from end of the ofdm symbol?

considering an OFDM symbol of x(0)x(1)x(2)x(3)x(4)....x(n-2)x(n-1)x(n). To perform cyclic prefix we prefix some samples from end of this OFDM symbol to the beginning of the OFDM symbol, like ...
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223 views

Purpose of interleaving in OFDM systems

Interleaving is often encountered in digital communication systems. I have seen interleaving between codewords in a single OFDM symbols as follows Assume the bits are denoted by ...
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105 views

Necessity of Cyclic Prefix in OFDM

I have a question on CP-OFDM. In recent years people are talking about filter bank approach where they are trying to filter out the out of band side lobes using filters. Besides they are presuming ...
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46 views

A sequence OFDM modulated with normalization factor

The following sequence is used to modulate 52 subcarriers. Twelve out of 52 are non zero. I was wondering $S_{[–26, 26]} = \sqrt{13/6} \{0, 0, 1+j, 0, 0, 0, –1–j, 0, 0, 0, 1+j, 0, 0, 0, –1–j, 0, 0, ...
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205 views

Pilot symbols in IEEE 802.11a

In IEEE 802.11a standards, there are many fields. Of which is the Data field which has 52 available sub-carriers used for transmission of coded bits. If the subcarrier locations are numbered from ...
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35 views

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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52 views

What is the purpose of oversampling the QAM signal in OFDM? [on hold]

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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173 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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201 views

SFBC Alamouti Scheme LTE

A sentence I copied from book. That a 2$\times$1 Alamouti SFBC is referred to as a rate 1 code, two symbols are sent over two adjacent subcarriers. This question is regarding this SFBC encoder ...
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146 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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80 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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66 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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48 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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67 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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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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28 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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104 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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36 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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68 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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570 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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282 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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51 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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160 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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148 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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40 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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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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748 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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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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2k 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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234 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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156 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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167 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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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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306 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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453 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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233 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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138 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 ...