How to receive OFDM signals?

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In summary, the conversation discusses the spacing and carriers of an OFDM signal, as well as different approaches to demodulating and receiving the signal in practice. The use of a sparse spectrum and resource efficiency are also mentioned. The conversation ends with a request for further information on how OFDM reception is done in practice.
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divB
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Hi,

Suppose you have an OFDM signal, e.g. DVB-T. In this case the spacing between the carriers is 4464 Hz and there are 1705 carriers. So the total bandwidth is 7.61 Mhz in baseband.

First: Am I right that the spectrum is wide but very sparse? So There is a peak at 0Hz, 4464 Hz, 8928 Hz, ..., 7606656 Hz? And nothing between?

How does a real OFDM receiver work in practice?

The first approach would be to demodulate each subcarrier. But this yields a 1705 oscillators ... not really good.

The second approach, as suggested by Wikipedia [1] is to sample the whole baseband signal and then apply the FFT to obtain the carriers. However, the bandwidth is 7.61 Mhz and this would require at least an ADC of 15.22 Mhz!

On the other hand this is a waste of resources because it is known that only 1705 frequencies are active and even the locations are known!

Can anyone give me a hint how OFDM reception is done in practice?

Regards, divB



[1] http://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing#Receiver
 
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Several recent threads may help.

Use this PF search https://www.physicsforums.com/search/32970/?q=odfm&o=date
 

1. What is OFDM and how does it work?

OFDM stands for Orthogonal Frequency Division Multiplexing. It is a type of signal modulation technique used in wireless communication systems. OFDM works by dividing a high-speed data stream into multiple lower-speed substreams and transmitting them simultaneously over different frequency bands. This allows for more efficient use of the available bandwidth and helps to reduce interference.

2. What equipment is needed to receive OFDM signals?

To receive OFDM signals, you will need a receiver that is capable of demodulating the signal. This can be a specialized OFDM receiver or a software-defined radio (SDR) that can be programmed to demodulate OFDM signals. Additionally, you will need an antenna that is tuned to the frequency of the OFDM signal you want to receive.

3. What is the difference between OFDM and other signal modulation techniques?

Unlike other modulation techniques, such as AM or FM, which use a single carrier frequency, OFDM uses multiple carrier frequencies. This allows for a more robust and efficient transmission of data over a wider frequency range. OFDM is also less susceptible to interference and can support higher data rates.

4. Can OFDM signals be received over long distances?

Yes, OFDM signals can be received over long distances, just like other wireless signals. However, the range may be affected by various factors such as the frequency, power, and interference levels. In general, higher frequencies have shorter ranges, while lower frequencies can travel longer distances.

5. Are there any limitations to receiving OFDM signals?

Yes, there are some limitations to receiving OFDM signals. One limitation is that OFDM signals are more susceptible to frequency-selective fading, which can cause parts of the signal to be lost or distorted. Another limitation is that OFDM requires more complex processing and decoding compared to other modulation techniques, which can be a challenge for low-power or low-cost devices.

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