Spatial Index Modulation Research Articles

Dual-mode spatial index modulation for MIMO-OWC.

In this Letter, we propose and demonstrate a dual-mode spatial index modulation (DM-SIM) scheme for spectral efficiency enhancement of band-limited multiple-input multiple-output optical wireless communication (MIMO-OWC) systems. By performing dual-mode index modulation in the spatial domain, DM-SIM can transmit both spatial and constellation symbols. Since constellation design plays a vital role in the proposed DM-SIM scheme, we further propose three dual-mode constellation design approaches including phase rotation, amplitude scaling and joint phase rotation and amplitude scaling. Moreover, we also designed a differential log-likelihood ratio (LLR) detector for the proposed DM-SIM scheme. Experimental results show that the joint phase rotation and amplitude scaling approach can achieve a remarkable 3.2 dB signal-to-noise ratio (SNR) gain compared with the phase rotation approach in a 2×2 MIMO-OWC system applying DM-SIM.

Spatial-Index Modulation Based Orthogonal Time Frequency Space System in Vehicular Networks

In this paper, a spatial-index modulation (SIM) based orthogonal time frequency space (OTFS) system, named SIM-OTFS, is proposed to enhance the effectiveness and the reliability of high mobility vehicular networks in intelligent transportation systems. The SIM-OTFS system adopts a three dimensional index modulation (IM) technique which utilizes the transmit antenna, delay, and Doppler indexes in the space and delay-Doppler domains, respectively, to achieve a higher transmission rate. Considering the characteristics of vehicular networks, we first present the SIM-OTFS system design and the corresponding signal processing. Then, we derive the average bit error rate (ABER) upper bound of the SIM-OTFS system by the union bound theory. Moreover, the diversity, the coding gain, and the complexity of the SIM-OTFS system are further investigated. Numerical results verify the theoretical analysis of the ABER and the diversity of the SIM-OTFS system, which shows the superiority of the SIM-OTFS system in the ABER performance over the multiple-input and multiple-output (MIMO) based OTFS (MIMO-OTFS) system. Meanwhile, the SIM-OTFS system realizes better performance than the spatial modulation (SM) and IM based orthogonal frequency division multiplexing (SM-OFDM-IM) system in high mobility vehicular communication with reasonable complexity sacrifice. Furthermore, the influence of the resolvable multipaths of the channel in vehicular networks on the ABER performance of the SIM-OTFS system is also illustrated.

Index Modulation Recognition Based on Projection Residual Analysis

Index modulation recognition (IMR) at secondary user (SU) receiver is a challenging topic for MIMO-OFDM cognitive radio network (MIMO-OFDM-CRN) with index modulation scheme, in order to make SU preferably adapt to the communication environment by adjusting own parameters. For index modulated signals, this paper proposes an effective IMR algorithm based on projection residual analysis (PRA). The proposed algorithm is suitable for various types of modulation such as spatial index modulation (SIM), frequency index modulation (FIM) and space-frequency index modulation (SFIM). Firstly the sparse structure of primary user (PU) signal is detected through removing the joint sparsity of signal matrix. Secondly, according to the detected sparse structure, the problem of whether the signal is index modulation (IM) or unindexed modulation (UIM) is addressed by projection residual analysis with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${z}$ </tex-math></inline-formula> -test. The hypothesis test judges whether the projection residual power of the received signal is significant compared with that of the UIM case, where the projection residual is obtained through projecting the subcarrier signals in the current index modulation symbol into the subspace of those in the previous symbol. The distribution of the test statistic is derived theoretically under UIM case. Thirdly, combining the detected sparse structure and the results of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${z}$ </tex-math></inline-formula> -test, the index modulation mode of PU signal is identified. Simulation results verify the performance of the proposed algorithm in terms of bit error rate (BER) and recognition rate, respectively.

Linearized Model for MIMO-MFSK Systems With Energy Detection

For user terminals, energy-detection based multiple-input-multiple-output (MIMO) has the advantages of low complexity and anti-Doppler capability. However, the energy detector makes it difficult to linearly separate the signals in spatial multiplexing. In this letter, the linearized model is introduced in <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> M-ary frequency-shifted keying (MFSK) V-BLAST system with energy detection. To avoid rank deficiency of the model, we propose nonlinear virtual antennas (NVA) to increases both the dimension and receive diversity gain of MIMO system. Then the full-rank condition is discussed. In multiple-antenna systems, NVA is further generalized by spatial index modulation with dual antennas selection. By simulations, linear detectors are verified to be feasible for non-coherent spatial-multiplexing MIMO, and its diversity gain is obviously increased by the proposed NVA.

Spatial Index Modulation With the Combination of Both Antenna Indexes and Two Constellations

In this paper, in order to further exploit the antenna index (AI) domain for increasing the spectral efficiency, we propose a new schematic of enhanced generalized spatial modulation with both three dimension constellation and QAM constellation (EGSM-3DQ) to enhance the active AI combinations with the construction of three dimension (3D) signal constellation. In the EGSM-3DQ, a transmit vector symbol (TVS) consists of two spatial vector symbols (SVS) with the aid of one vector index bit, one SVS of which is obtained by modulating three components of a 3D signal symbol on two or three active transmit antennas (TAs) through the 3D Signal Mapper and AI Vector Modulator, another SVS of which is obtained by modulating one or multiple mapped QAM symbols on one or multiple active TAs through the AI Vector Selector. In addition, by jointing the AIes and multiple constellations such as the 3D and QAM, PAM constellations, grouping EGSM (gEGSM) is proposed to develop the group index combinations to increase extra index information. Finally, the comparisons of squared minimum Euclidean distances (MED) and the average bit error probability are provided. Simulation results show that the proposed schemes improve the bit error rate performance as compared with conventional systems.

All-optical temporal phase correction scheme for few-cycle optical pulses using diffractive optics

All-optical phase correction scheme for few-cycle optical pulses has been proposed. The temporal phase structure of a phase-modulated pulse is recorded as spatial index modulation in a two-photon recording medium. This scheme drastically relaxes complicacy in stretcher design for few-cycle chirped pulse amplification (CPA) systems.

Direct characterization of the spatial effective refractive index profile in Bragg gratings

We propose a pulse response method to directly characterize the phase of the spatial index modulation, including the dc refractive index distribution (distributed phase shift), discrete phase, and chirp of fiber Bragg gratings (FBGs). This method is based on the observation that the spatial phase of gratings is directly related to the temporal phase of its pulse response. Therefore, the phase of the spatial index modulation can be characterized directly by measuring the temporal phase of the pulse response of FBGs. This method is then used to characterize an FBG with a current-induced phase shift.

Antisymmetric taper of distributed feedback lasers

In a distributed feedback (DFB) laser with spatial index modulation, an antisymmetric taper of the feedback parameter, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> , removes the threshold degeneracy, which is characteristic of uniform structures, and leads to one mode of particularly low threshold. Exact solutions are presented for the special case of an antisymmetric step of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> . An approximate perturbation method is developed which gives simple expressions for the threshold gains, and external <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> 's of some tapered distributed feedback structures. The method is tested against two exact solutions, the uniform, and the stepped- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> DFB laser. It is shown that the threshold of the stepped- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</tex> DFB laser is the lowest of any structure with an antisymmetric taper and a prescribed maximum value of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">|k|</tex> .