This work proposes an inter-symbol data-mapping (ISDM) precoding scheme, which allows the receiver to adaptively select its most suitable data decoder based on the estimated SNR or channel conditions, for single carrier systems. For conventional modulation schemes, the only decoding method for traditional modulations, such as PSK and QAM, is to apply the maximum likelihood (ML) method after channel equalizations. Moreover, if the estimated SNR is unreliable enough to correctly decode the incoming signal, the received frame is usually discarded. As such, the communication system has to lower the symbol modulation order and re-transmit the data. The proposed ISDM scheme rearranges and re-maps a block of data bits to be transmitted so that they are correlated. Then, the receiver can decode the received signal by dynamically selecting the following three proposed decoders: post-equalization ML (PEML) decoder, full-rate most-significant-bit (FR-MSB) decoder and down-rate (DR) decoder based on estimated channel SNRs. For the FR-MSB decoder, its performance is close to the conventional BPSK decoder. On the other hand, PEML decoder can have roughly 2dB better performance than the FR-MSB one, while the DR decoder performs poorer than the FR-MSB one but with a lower computational complexity. Although the DR decoder has lower performance than the other two, its major advantage is able to decrease the ADC sampling rate with the help of multi-phase PLL. As such, the ISDM precoding scheme can provide the system better flexibility in data decoding.
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