Signal Processing Stack Exchange
Signal Processing Stack Exchange

Questions tagged [ofdm]

OFDM stands for Orthogonal, Frequency-Division Multiplexing.

OFDM stands for orthogonal, frequency-division multiplexing.

See the wikipedia page for more details.

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How is symbol synchronization with OFDM done?

I'm trying to understand how symbol synchronization is done in OFDM using pilot tones, cyclic prefixes, or any other technique. I've read the following answers which provide some explanation, but I still don't totally understand it. How to…
Dan Sandberg
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How to demodulate an OFDM signal

I'm looking at decoding an OFDM signal which consists of 6 carriers (or tones) which are BPSK modulated and a pilot tone which aids tuning. This is the first time I have worked with OFDM so I need to know if I'm approaching this in the right…
IanW
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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 techniques in wireless communication. As far as…
tuner
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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 has to encounter flat and slow fading? If not,…
Noor
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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 x(n-3)x(n-2)x(n-1)x(n)x(0)x(1)x(2)x(3)........…
srk_cb
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What Is the Difference between RLS, LMS and Wiener Filter? When Is One Preferred Over Another?

I'm dealing with a channel equalization problem where the channel is modeled as a WSS process. I understand LMS utilities a Wiener-like approach, ie it converges to the optimal (wiener) solution. I understand RLS converges to the normal solution,…
Marco Datola
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Flat fading criterion of OFDM subcarrier spacing

I have always thought that the OFDM subcarrier spacing $\Delta f$ is chosen such that not too small because Doppler spread can destroy subcarrier orthogonality not too large to avoid Cyclic Prefix (CP) overhead because OFDM symbol period $T_u =…
AlexTP
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OFDM training symbol format

For OFDM synchronisation, we are using two training symbols according to the Schmidl and Cox method of frequency synchronization and timing synchronization. The paper says: The first OFDM training symbol has only even numbered subcarriers applying…
Karan Talasila
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What's the reasoning behind changing pilot tones in OFDM?

Many OFDM wireless protocols (e.g. 802.11, DVB-T2, LTE, etc.) utilize pilot tones to provide channel state information for the receiver. Within the transmission, the pilot tones generally assume a BPSK or QPSK modulation depending on the protocol.…
eUser
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What does the one-tap equalizer used with OFDM accomplish?

I've read that OFDM normally uses a one-tap equalizer. It seems that a one-tap equalizer could only scale and delay a signal. Why is this useful? I thought multipath was handled through the cyclic-prefix and by choosing a symbol width that is…
Dan Sandberg
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Why does OFDM use cyclic-prefix while QPSK uses root-raised cosine filters?

My understanding is that BPSK/QPSK/... are often implemented with root-raised cosine (RRC) filters to reduce ISI and bandwidth. OFDM can be understood to be BPSK/QPSK/... implemented on multiple orthogonal carriers, with some additional…
Dan Sandberg
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The necessity of null subcarrier in OFDM?

In looking to LTE specifications, with the subcarrier spacing $\Delta f = 15 \textrm{kHz}$, for bandwidth $10 \textrm{MHz}$, fft size $N_{fft} = 1024$ that needs a sampling rate $F_s \geq 1024 \times 15\textrm{kHz} = 15.36 \textrm{MHz}$. The useful…
AlexTP
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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 32,-31,...0,1,...31. I have read in the book that…
Tyrone
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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 processing and trying to understand how to model…
tuner
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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. Theoretically, the spectrum (assuming BPSK modulation for…
aslan
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