In a digitally implemented OFDM system, the input bits are grouped and mapped to source data symbols that are a complex number representing the modulation constellation point e.
These complex source symbols are treated by the transmitter as though they are in the frequency-domain and are the inputs to an IFFT block that transforms the data into the time-domain. Each of these N input symbols has a symbol period of T seconds. These orthogonal sinusoids each have a different frequency and the lowest frequency is DC. The input symbols are complex values representing the mapped constellation point and therefore specify both the amplitude and phase of the sinusoid for that subcarrier.
After some additional processing, the time-domain signal that results from the IFFT is transmitted across the radio channel. At the receiver, an FFT block is used to process the received signal and bring it into the frequency domain which is used to recover the original data bits.
An To begin the OFDM signal creation process, the input data bit stream is encoded with convolutional coding and Interleaving. Note that the bit-rate will be different depending on the modulation format, a QAM constellation 6 bits at a time can have a bit rate of 54 Mbps while a QPSK constellation 2 bits at time may only be 12 Mbps.
Then 52 bins of the IFFT block are loaded. The samples are clocked out at 20 Msps to create a 3. To complete the OFDM symbol, a 0. This produces a "single" OFDM symbol with a time duration of 4 us in length, 3. The process is repeated to create additional OFDM symbols for the remaining input data bits. Learn more. Waves of differing frequency are orthogonal - help me understand Ask Question. Asked 8 years, 2 months ago.
Active 8 years, 2 months ago. Viewed 12k times. Add a comment. Active Oldest Votes. In the integral, those positive contributions will exactly cancel the negative contributions, leading to an average of zero: That's the intuition. Neal Neal 30k 2 2 gold badges 61 61 silver badges bronze badges. There's more to say about this, but let's not. Gordan Segon Gordan Segon 73 4 4 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
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