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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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'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's the rationale behind this pulse shaping function?

Section 13.2 of the HD Radio standard for AM defines a pulse shaping function that appears to be some strange variant on a raised cosine filter: More specifically, H(ξ) is a raised cosine filter with total width (1+α)T, and W(ξ) appears to be a…
JP Sugarbroad
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OFDM synchronisation Schmidl and Cox method - question

If somebody has good knowledge about the synchronisation method (related to the OFDM topic) developed by Schmidl and Cox, then you will probably be able to help me with my question about their synchronisation method. I understand that their method…
Kenny
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doesn't OFDM inherently deals with ISI? why cyclic prefix is needed?

As far as I can understand, the motivation to OFDM and multi carrier communication in general was alot due to the ISI caused by multi-path which is equivalent to frequency selective channel. Now, by using OFDM, we send our symbols over sub-carriers,…
user3921
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Why do we need FFT pairs for OFDM?

this is a basic question, but i barely find any tutorial to explain this. Most of tutorial dont talk about why use IFFT and FFT, they just say "oh, at transmitter, we just take this information time domain as frequency domain, then we need IFFT". I…
Sunson29
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VOFDM (Vector OFDM) advantages and disadvantages

What are the advantages and disadvantages of using VOFDM over OFDM? I know that one advantage is frequency diversity, what are others? edit : By VOFDM I mean Xia's method as shown here.
Gabizon
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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 existing algorithms, depending on the specific…
Alex2014
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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 me to understand this mathematically? How is…
rajez79
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How does DFT-s-OFDM precoding reduces PAPR?

I would like to understand how does DFT-s-OFDM reduces PAPR compared to CP-OFDM. I am not able to locate any mathematical explanation for this. If anybody can provide an explanation it will be great. Thanks.
user3005720
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Why does OFDM need cyclic prefix?

As I understand, by using multiple carriers, OFDM can mitigate the effects of multi-path delay as the symbol duration is larger than the delay. In this case, why do we still need to add cyclic prefix in OFDM? I have looked into several related…
Fzzyy
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Relation between QAM size and Number of subcarrier in OFDM

I am trying to understand the OFDM system. If i am using 16 QAM with 16 subcarriers that means one constellation point mapped to one subcarrier. What will happen to mapping of constellation point to subcarrier when number of subcarrier goes to 8 or…
PRAVEEN YADAV
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Comparison between two OFDM schemes

I am wondering about two scenarios that I came across for OFDM systems. Say we have a station transmitting to an access point and say we have the following two scenarios: 1- N1 subcarriers and transmit power per subcarrier is Pt1 2- N2 subcarriers…
Tyrone
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Intercarrier Interference (ICI) with OFDM signals

What is the relationship between Intercarrier Interference (ICI) in OFDM signals and Doppler spread? Is there a mathematical property to determine what OFDM parameters, such as subcarrier spacing, should be selected to overcome X hertz of Doppler…
BigBrownBear00
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Ofdm and subcarrier modulation

I was learning about OFDM systems and the different subcarriers. My understanding is thay each subcarrier carries one symbol. One question come to mind, can these different subcarriers be modulated differently for example one subcarrier with BPSK…
Tyrone
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