Complexity of I and Q signals in OFDM and method of simpler decoding and error detection
Keywords:OFDM, multicarrier modulation, I/Q signals, PSK modulation, Bit Error Rate (BER), IEEE 802.11 standards
The modulation schemes in the IEEE 802.11 radio frequency communication protocols are based on two carriers at right angles, called I and Q signals. These two signals, which are formed for the data symbols, are further modulated at radio frequency on two main carriers, which have a phase shift of 90° to each other. The critical analysis of the methods for generating the I/Q signals is given here. The phase and amplitude imbalance errors caused by using two signals to decode one data element are shown. This scheme is used mainly together with the orthogonal frequency division multiplexing (OFDM), employing the Inverse Fourier Transform (IFFT) at the transmitter and direct Fast Fourier Transform (FFT) at the receiver. An alternative better method is described, which does not need to use IFFT and FFT. This method involves the sequential demodulation of subcarriers one by one, and finally the error prone subcarriers are ascertained. It is also feasible to employ this method for correcting the symbol errors.
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