Interleave-division multiple-access (IDMA) is a multiple-access technique, which uses an elementary signal estimator (ESE) to achieve simple chip-by-chip detection. In this paper, we propose a new ESE which can be calculated directly based on the two-dimensional received signals. Hence, the proposed ESE can be applied to IDMA using signal modulation with either Gray labelling or non-Gray labelling. In contrast, the original ESE is calculated either based on the one-dimensional received signals or separately based on the real parts and the imaginary parts of the two-dimensional received signals. In fact, the original ESE can only be applied to IDMA using BPSK or Gray-labelled QPSK. From the proposed ESE, we can predict that the IDMA using the non-Gray labelling will be superior to the IDMA using the Gray labelling at the high signal-to-noise ratio (SNR) region. With EXIT (extrinsic information transfer) chart analysis, we can estimate the SNR region for which there is advantage of using non-Gray labelling for IDMA. The simulation results fit well with the theoretical analysis.

Partial transmit sequence (PTS) is a well-known peak-to-average power ratio (PAPR) reduction scheme based on the concept of multiple candidates. In this paper, we propose multiple-candidate separation at the receiver by turbo decoding. Both blind and semi-blind methods are proposed and applied to both the phase-rotation-based PTS scheme and cyclical-shift-based PTS scheme. The blind method in general achieves better error performance at the cost of higher complexity compared to the semi-blind method. Compared to the conventional method, both methods can provide better error performance. The proposed blind method can achieve similar error performance compared to using the perfect side information.

We propose a multiple-candidate shaping technique for turbo coded modulation systems. Shaping gains are obtained by encoding each message into multiple turbo coded modulation sequences, called candidates, and then selecting the candidate with the lowest energy for transmission. Multiple candidates are generated by adding various scrambling sequences to each message sequence. The proposed shaping technique can also be applied to turbo coded modulation systems equipped with some other shaping methods to obtain additional shaping gains.

Luby Trasform (LT) codes are regarded as packet-based codes which are useful for multicast communications. High Peak-to-Average Power Ratio (PAPR) is a notorious problem inherently existing in OFDM systems. In this paper, we propose to take the PAPR constraint into account in the encoding of LT codes for OFDM multicast systems. Substantial PAPR reduction can be obtained without sacrificing the decoding performance of LT codes.

A selective-mapping (SLM) scheme which does not require the transmission of side information and can reduce the peak to average power ratio (PAPR) in turbo coded orthogonal frequency-division multiplexing (OFDM) systems is proposed. The candidates of the proposed SLM are respectively generated by a turbo encoder using various interleavers. The waiver of side information can avoid the degradation of error rate performance which results from the incorrect recovery of side information at receiver in the conventional SLM OFDM system.

In this paper, we propose deliberate power boost (DPB) to reduce the PAPR (peak-to-average power ratio) in an OFDM (orthogonal frequency-division multiplexing) system. Although both the average power and peak power are increased by using DPB, we show that the PAPR can be reduced by the proposed method. DPB can be combined with other PAPR-reduction techniques such as deliberate clipping and repeated clipping and filtering (RCF) for further PAPR reduction. Although selective mapping (SLM) is originally proposed for PAPR reduction, we apply a concept similar to SLM to clipping-based OFDM systems for improved error performance. We show that turbo coded OFDM systems using both RCF and DPB can achieve better PAPR performance without degrading the error performance as compared to the case of using only RCF if SLM is used for improved error performance in both systems.

In a turbo coded orthogonal frequency-division multiplexing (TCOFDM) system, low peak-to-average power ratio (PAPR) can be achieved by selective-mapping (SLM). In this paper, we propose to generate multiple candidates used in SLM by employing the tail-biting bits in a tail-biting turbo code. In our method, no explicit side information is needed and no error propagation is observed. Low PAPR can also be achieved by distortion-based techniques such as deliberate clipping. Although SLM is originally proposed for PAPR reduction, we also apply a concept similar to SLM to clipping-based TCOFDM systems for improved bit error rate (BER). With these proposed techniques, a tail-biting TCOFDM system can achieve both low PAPR and low BER.