10using channel estimation techniques. The demodulator can simply use these estimated channel gains to recover the original symbols: X[k] = Y[k]/H[k]. This procedure is called frequency-domain equalization and reduces the complexity of the receiver considerably. However, frequency-domain equalization also enhances the noise because the noise for the kthsubcarrier is scaled by a factor of 1/H[k]. Even though this type of equalization removes the effects of flat fading on X[k], the received SNR of the signal is unchanged. Pre-coding, adaptive loading, and coding across subcarriers are better approaches to mitigate the effects of flat fading. After the effects of flat fading have been mitigated, the symbol detector attempts to recover the originally sent symbols. The parallel-to-serial converter finally recreates the bit sequence of the original message. Now that we understand the basics of OFDM, let us continue on our journey towards resource allocation in OFDMA systems. But first, let us take a quick look at the multiple-access version of
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