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Vector perturbation (VP) precoding is a promising technique to achieve near optimal capacity by exploring the channel state information (CSI) at the multiple-input multiple-output (MIMO) transmitter. To further enhance the bit error rate (BER) performance associated with forward error correction (FEC) coding, soft decision should be invoked in VP. However, the modulo operation in VP may influence the accuracy of soft decision. For alleviating this problem, the calculation of log-likelihood ratio (LLR) for VP is discussed and we further propose a sub-constellation shifted (SCS) scheme for VP precoding toward more accurate LLR. Simulation results demonstrate that the proposed scheme is capable of improving the BER performance of VP systems by accurate LLR calculation with moderate computational complexity.

In this letter, we propose a new convert information embedded spatial modulation (SM) system for secure communications, in which the transmitter tries to send covert information to the specific receiver while keeping the unintended receiver unaware of the transmission. In the proposed system, the covert information bits are conveyed via the activated antenna index while the common information bits are via the modulation symbols. Specifically, the convert information modulation is achieved by carefully designing the space-time mapping principle so that it is disguised as a conventional SM antenna index. Furthermore, an efficient detection scheme is designed for the proposed system. The simulation results show that the proposed scheme with the developed receiver can offer nearly the same performance gain as conventional SM, whereas the unintended receiver can hardly detect the information correctly. Moreover, the average bit error rate (BER) is analyzed, which also validates our simulation results.

In this paper, a novel scheme dubbed space-time block coded rectangular differential spatial modulation (STBC-RDSM) is proposed for multiple-input and multiple-out (MIMO) systems, which combines space-time block coding (STBC) and rectangular differential spatial modulation (RDSM) to reap their respective benefits while avoiding the drawbacks of conventional differential spatial modulation (DSM) systems. More specifically, in the proposed STBC-RDSM scheme, information bits are conveyed via the rectangular differentially encoded antenna index matrices, as well as the STBC blocks. Furthermore, a low-complexity detection scheme is proposed. Our simulation results demonstrate that STBC-RDSM outperforms its conventional DSM counterparts in various spectral efficiencies. Finally, a closed-form union bound on the bit error rate (BER) is derived and validated by our simulation results.

Orthogonal Frequency Division Multiplexing (OFDM) with Index Modulation (OFDM-IM), which conveyed information bits via the activated indices and constellation symbols is a promising technique in the next wireless communications. In the OFDM-IM scheme, only part of subcarriers are activated to transmit information, the inactive subcarriers transmit zero symbols, so that the conventional differential coding is not suitable for the adjacent subcarriers. In order to address this issue, in this paper, a novel Rectangular Differential OFDM-IM (RD-OFDM-IM) scheme is proposed to exploit the benefits of OFDM-IM dispensing with Channel State Information (CSI). In the proposed RD-OFDM-IM scheme, N subcarriers are partitioned into G subblocks and index modulation is employed in each subblock first. Then rectangular differential coding is invoked during two adjacent subblocks, so that non-coherent detection can be employed for the proposed RD-OFDM-IM scheme. Simulation results are shown that the proposed RD-OFDM-IM scheme is capable of providing considerable performance gain over conventional Differential OFDM (D-OFDM) scheme with lower Peak Average Power Ratio (PAPR).

In this paper, we investigate a class of new multiple-input multiple-output (MIMO) transmission schemes, dubbed space time line code (STLC), in the context of different mobility situations. We extend its original structure into space and frequency domains and propose a novel frequency line code (SFLC) for combining with orthogonal frequency division multiplexing (OFDM) in order to achieve potential diversity gains in time-varying multipath fading channels. Specifically, at the transmitter, the STLC/SFLC-OFDM scheme exploits the channel state information (CSI) to linearly encode successive modulated symbols in the time/frequency domain to achieve full diversity gain. At the receiver, it can retrieve the transmit symbols without full CSI, thanks to its special structure. We analyse the impact of time-variant channels to STLC and SFLC to show the expected performance degradation in practical channel, especially in the case of different mobile speeds. Our analysis and simulations show that the BER performance degrades with increasing correlation coefficient, which makes STLC-OFDM more robust in channels with abundant multipath spread, and SFLC-OFDM more robust in channels with high mobility speed. Meanwhile, a guideline is provided for switching when the communication environment changes. Finally, we carry out the practical implementation of STLC-OFDM and SFLC-OFDM schemes and characterize their performance with both computer simulations and an experimental testbed. Published version

Generalized Spatial Modulation (GSM), where both the Transmit Antenna Combination (TAC) index and the Amplitude Phase Modulation (APM) symbols convey information, is a novel low-complexity and high efficiency Multiple Input Multiple Output (MIMO) technique. In Conventional GSM (C-GSM), the legitimate TACs are selected randomly to transmit the APM symbols. However, the number of the TACs must be a power of two, hence the excess TACs are discarded, resulting in wasting some resource. To address these issues, in this paper, an optimal TAC set-aided Enhanced GSM (E-GSM) scheme is proposed, where the optimal TAC set is selected with the aid of the Channel State Information (CSI) by maximizing the Minimum Euclidean Distance (MED). Furthermore, a Hybrid Mapping GSM (HM-GSM) scheme operating without CSI knowledge is investigated, where the TAC selection and bit-to-TAC mapping are both taken into consideration for optimizing the Average Hamming Distance (AHD). Finally, an Enhanced High Throughput GSM (E-HT-GSM) scheme is developed, which makes full use of all the TACs. This scheme is capable of achieving an extra one bit transmission rate per time slot. Moreover, rotated phase is employed and optimized for the reused TACs. Our simulation results show that the proposed E-GSM system and HM-GSM system are capable of outperforming the CGSM system. Furthermore, the E-HT-GSM system is capable of obtaining one extra bit transmission rate per time slot compared to the C-GSM system.

In this paper, a novel space-time block coded rectangular differential spatial modulation (STBC-RDSM) is proposed for multiple-input and multiple-out (MIMO) system, which combines the space-time block coding (STBC) and rectangular differential spatial modulation (RDSM) to take the advantages of RDSM and STBC systems, while avoiding the drawbacks of conventional differential spatial modulation (DSM) systems. More specifically, in the proposed STBC-RDSM scheme, the information bits are conveyed via the rectangular differential encoded antenna indices matrices, as well as the STBC blocks. Our simulation results demonstrate that STBC-RDSM outperforms the existing DSM systems for various spectral efficiencies.