Showing papers on "Transmit diversity published in 2021"

Performance Analysis of OTFS Modulation With Receive Antenna Selection

Abstract: In this paper, we analyze the performance of orthogonal time frequency space (OTFS) modulation with antenna selection at the receiver, where $n_s$ out of $n_r$ receive antennas with maximum channel Frobenius norms in the delay-Doppler (DD) domain are selected. Single-input multiple-output OTFS (SIMO-OTFS), multiple-input multiple-output OTFS (MIMO-OTFS), and space-time coded OTFS (STC-OTFS) systems with receive antenna selection (RAS) are considered. We consider these systems without and with phase rotation. Our diversity analysis results show that, with no phase rotation, SIMO-OTFS and MIMO-OTFS systems with RAS are rank deficient, and therefore they do not extract the full receive diversity as well as the diversity present in the DD domain. Also, Alamouti coded STC-OTFS system with RAS and no phase rotation extracts the full transmit diversity, but it fails to extract the DD diversity. On the other hand, SIMO-OTFS and STC-OTFS systems with RAS become full-ranked when phase rotation is used, because of which they extract the full spatial as well as the DD diversity present in the system. Also, when phase rotation is used, MIMO-OTFS systems with RAS extract the full DD diversity, but they do not extract the full receive diversity because of rank deficiency. Simulation results are shown to validate the analytically predicted diversity performance.

A Simple Multicarrier Transmission Technique Combining Transmit Diversity and Data Multiplexing for Non-Orthogonal Multiple Access

Abstract: Since the intra-group co-channel interference is introduced intentionally by the non-orthogonal multiple access (NOMA) technique, the reliability of NOMA based networks is limited by far users, while the sum-rate is mainly contributed by near users. In this paper, a NOMA based multiband scheduling policy is proposed to overcome this problem. Unlike conventional NOMA where all users are served in a single frequency band, the proposed scheme divides the entire band into multiple sub-bands, and accommodates the near and far users in different manners by exploring the sub-bands. Particularly, the far users employ repetition-based transmission in all sub-bands, and the maximum ratio combination (MRC) is integrated with successive interference cancellation (SIC) to jointly decode their intended symbols. Closed-form expression of the achievable sum-rate of the proposed scheme is derived, and the outage performance is characterized by the derived upper-bounded outage probability. Numerical results show that the proposed scheme enables NOMA systems to achieve both high reliability and high sum-rate.

Space-Time Coded Generalized Spatial Modulation for Sparse Code Division Multiple Access

Abstract: Space-time coded generalized spatial modulation-aided sparse code division multiple access (STC/GSM-SCDMA) is proposed, which exploits the two-dimensional transmit diversity potential of both the spatial and of the frequency domain. Hence, it constitutes a promising solution for the pervasive connectivity of devices in next-generation nonorthogonal multiple access (NOMA) systems. More explicitly, our STC/GSM scheme achieves diversity in the spatial-domain, while the sparse signal-spreading action of SCDMA results in frequency-domain (FD) diversity. A single-user bit error rate (BER) bound is derived as the benchmark of the BER performance of our STC/GSM-SCDMA system. Furthermore, a pair of novel detectors, namely a bespoke message passing aided (MPA) detector and a tailor-made approximate message passing (AMP) detector are conceived by designing a new factor graphs for our proposed STC/GSM-SCDMA system. The performance of these detectors is characterized in terms of their BER vs. complexity. Our simulation results show that the proposed AMP detector is capable of operating within 2 dB of the MPA detector’s signal-to-noise ratio (SNR) requirement, while supporting a normalized user load of 150%, despite its appealing low complexity, which is about 1000 times lower than the MPA detector.

Channel Estimation and Equalization for Alamouti SF-Coded OFDM-UWA Communications

Abstract: In this paper, a new channel estimation and equalization algorithm for underwater acoustic (UWA) communications is presented. The proposed algorithm is developed to meet the requirements of underwater time-varying sparse channels that undergo Rayleigh fading. In addition, the algorithm takes into consideration a path-based channel model which describes each received path with significant power by an attenuation factor, a Doppler scale, and a delay. Transmit diversity enabled by Alamouti space-frequency block coding coupled with orthogonal frequency division multiplexing is employed in the form of two transmitters and multiple receivers. The proposed, non-data-aided, expectation-maximization (EM)-based maximum a posteriori probability sparse channel estimation first estimates the channel transfer functions from each transmit antenna to the receiver. Then, the estimation performance is greatly improved by taking into account the sparseness of the UWA channel and refining the estimation based on the sparse solution that best matches the frequency-domain channel estimates obtained during the first phase of the estimation process. Sparse channel path delays and Doppler scaling factors are estimated by a novel technique called delay focusing . After that, slow time-varying, complex-valued channel path gains are estimated using a basis expansion model based on the discrete Legendre polynomial expansion. Computer simulation results show that the resulting channel estimation algorithm can achieve excellent mean-square error and symbol error rate for both generated data and semi-experimental data taken at Sapanca Lake in Turkey and is capable of handling some mismatch due to different fading models.

A Hybrid Approach to Joint Estimation of MIMO Channel and Antenna Impedance Matrices

Abstract: Antenna impedance matching significantly affects the channel capacity of compact MIMO receivers. When antenna impedance is known to the receiver, channel capacity can be optimized. However, channel capacity may diminish, when antenna impedance varies due to time-varying near-field loading. This motivates impedance estimation in real-time. In this paper, we derive joint MAP/ML estimators for channel and impedance matrices in closed-form. As one result, we develop a design principle leveraging a trade-off between channel and impedance estimation, which depends on transmit diversity.

On the Performance of Self-Concatenated Coding for Wireless Mobile Video Transmission Using DSTS-SP-Assisted Smart Antenna System

Abstract: In the current age of advanced technologies, there is an escalating demand for reliable wireless systems, catering to the high data rates of mobile multimedia applications. This article presents a novel approach to the concept of Self-Concatenated Convolutional Coding (SECCC) with Sphere Packing (SP) modulation via Differential Space-Time Spreading- (DSTS-) based smart antennas. The two transmitters provide transmit diversity which is capable of recuperating the signal from the effects of fading, even with a single receiving antenna. The proposed DSTS-SP SECCC scheme is probed for the Rayleigh fading channel. The SECCC structure is developed using the Recursive Systematic Convolutional (RSC) code with the aid of an interleaver. Interleaving generates randomness in exchange for extrinsic information between the constituent decoders. Iterative decoding is invoked at the receiving side to enhance the output performance by attaining fruitful convergence. The convergence behaviour of the proposed system is investigated using EXtrinsic Information Transfer (EXIT) curves. The performance of the proposed system is ascertained with the H.264 standard video codec. The perceived video quality of DSTS-SP SECCC is found to be significantly better than that of the DSTS-SP RSC. To be more precise, the proposed DSTS-SP SECCC system exhibits an gain of 8 dB at the PSNR degradation point of 1 dB, relative to the equivalent rate DSTS-SP RSC. Similarly, an gain of 10 dB exists for the DSTS-SP SECCC system at 1 dB degradation point when compared with the SECCC scheme dispensing with the DSTS-SP approach.

Cyclic Delay Diversity With Index Modulation for Green Internet of Things

Abstract: Cyclic delay diversity (CDD) is a simple and yet effective transmit diversity technique. Thanks to its strong power saving capability, CDD is very promising for green Internet of Things (IoT) networks. However, the reduced degrees of freedom in data transmission and the overhead of cyclic prefix lead to unsatisfactory spectral efficiency (SE), hindering the direct application of CDD to IoT networks where short-packet communication prevails. To tackle this problem, in this article, we propose to convey additional information via the varying cyclic delays for improving the SE of the CDD system based on the concept of index modulation (IM), which applies to both OFDM and cyclic-prefixed single-carrier (CPSC) signals. The methods to generate all possible cyclic delays and the optimal receivers are designed for both proposed systems. To aim at low computational complexity, we further propose a suboptimal receiver for the CDD-CPSC-IM system. Moreover, a closed-form upper bound on the bit error rate (BER) of the CDD-OFDM-IM system is derived, from which the coding gain is characterized. Simulation results in terms of BER corroborate the analysis and the superiority of the proposed systems over the pure CDD-OFDM and CDD-CPSC systems, uncovering the potential of CDD in the application to green IoT networks.

Distributed Cooperative Relaying Based on Space-Time Block Code: System Description and Measurement Campaign

Abstract: In cooperative relaying, intermediate stations are required to enhance the end-to-end transmission performance. The performance of the cooperative relaying scheme has been investigated theoretically and via computer simulations. However, cooperative relaying using transmit diversity techniques in actual environments has not been investigated thus far. This paper presents an experimental system for distributed cooperative relaying using space-time block code and evaluations of its transmission performances in real propagation channels. To this end, four wireless stations—specifically, one source, two relays, and one destination—were developed using analog transceivers and field-programmable gate arrays for real-time digital signal processing. Sample timing and frequency synchronizations among the four wireless stations were established by using the received signals as a reference. The end-to-end error performance of distributed cooperative relaying was compared to those of noncooperative relaying schemes, and the performances of three relaying schemes were evaluated quasisimultaneously in terms of their cumulative distribution functions of the bit-error ratios (BERs). The experimental results indicated that the BER performance of the two-hop distributed cooperative relaying scheme was substantially superior to those of noncooperative two-hop relaying schemes, including a route diversity scheme.

Performance Analysis of OTFS Modulation with Transmit Antenna Selection

Abstract: In this paper, we consider transmit antenna selection (TAS) in orthogonal time frequency space (OTFS) modulation and analyze its performance. We assume that the channel is quasi-static in the delay-Doppler (DD) domain and there is limited feedback from the receiver to the transmitter. The diversity performance of TAS is analyzed in a multiple-input multiple-output OTFS (MIMO-OTFS) system. Antenna selection is done based on the maximum channel Frobenius norm in the DD domain, where n s antennas are selected out of n t transmit antennas. Our analysis for one resolvable path in the DD channel (i.e., P = 1) shows that i) when n s = 1, full spatial diversity of n r n t (i.e., full receive diversity of n r and full transmit diversity of n t ) is achieved since the underlying symbol difference matrix is full rank, and ii) when n s > 1, only n r th order receive diversity is achieved because of rank deficiency. Simulation results are shown to validate the analytically predicted diversity performance. For P > 1, diversity orders are predicted through rank of the difference matrices, validated through computation of pairwise error probability (PEP) bounds and simulations.

A dCDD-Based Transmit Diversity Scheme for Downlink Pseudo-NOMA Systems

Abstract: In this paper, a new transmit diversity scheme is proposed for cooperative pseudo-non-orthogonal multiple access (Pseudo-NOMA) without assuming full channel state information at the transmitter (CSIT). To support two users under the near-far user pairing constraint, a distributed cyclic delay diversity (dCDD) scheme is adapted into NOMA by dividing a set of remote radio heads (RRHs) into two groups for multiple cyclic-prefixed single carrier transmissions. To maximize a far user’s rate and two users’ sum rate over independently but non-identically distributed frequency selective fading channels and under a near-far user pairing constraint, we first derive closed-form expressions for the rates of the two users with full CSIT. Considering that only partial CSIT is available, a new RRH assignment and power allocation scheme is proposed for dCDD-Pseudo-NOMA. For various simulation scenarios, the provided link-level simulations verify that higher rates can be achieved by dCDD-Pseudo-NOMA compared with the traditional orthogonal multiple access with dCDD and dCDD-Conventional-NOMA that uses the superimposed signals. Furthermore, the proposed RRH assignment and power allocation scheme makes dCDD-Pseudo-NOMA achieve almost the same rate as that of ideal dCDD-Pseudo-NOMA which requires full CSIT.

A Link Quality Estimation-Based Beamforming Training Protocol for IEEE 802.11ay MU-MIMO Communications

Abstract: The multi-user multiple-input-multiple-output (MU-MIMO) beamforming training (BFT) enables an access point (AP) and multiple stations (STAs) to determine appropriate directional antenna patterns; to this end, the AP transmits multiple action frames to the STAs during the MU-MIMO BFT. However, if the antenna weight vectors (AWVs) are determined to transmit the action frames inefficiently, this could lead to unnecessary transmissions, which could increase the BFT time. To mitigate the signaling overhead, the schemes used in our previous work employed AWVs, which use multiple beams simultaneously to transmit the action frames. Nevertheless, these existing schemes are still adversely affected by redundant transmissions because these schemes overlook the transmit diversity gain obtained from multi-beam concurrent transmission. Therefore, in this study, we propose a novel transmit antenna configuration scheme that mitigates the signaling overhead by considering the transmit diversity of the inter-symbol interference (ISI) channel incurred when multiple beams are used simultaneously. Our proposed scheme determines each candidate antenna weight vector (AWV) using multiple beams and efficiently identifies the STAs within reach of the corresponding multi-beam concurrent transmission. The numerical and simulation results demonstrate that our proposed scheme shortens the BFT time in comparison with existing schemes.

Generalized Quadrature Space-Frequency Index Modulation for MIMO-OFDM Systems

Abstract: In this paper, motivated by the framework of diversity-achieving quadrature spatial modulation (DA-QSM), we propose a generalized quadrature space-frequency index modulation (GQSF-IM) transmission scheme for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The dispersion matrices potentially transmit some combination of each symbol from each antenna at every subcarrier, and their structures lead to desirable coding properties. By setting two well-designed dispersion-matrix sets for both the in-phase (I-) and quadrature (Q-) dimensions, each resource block (RB) of MIMO-OFDM independently selects part of dispersion matrices from each set to modulate the real and imaginary parts of complex symbols, respectively. Thus a simple and systematic method which easily generates dispersion-matrix set with large size is presented. It can be verified that the proposed GQSF-IM scheme subsumes the existing QSF-IM scheme as its special case. Moreover, it can be proved that the GQSF-IM scheme automatically achieves the second order transmit diversity without requiring any parameter or matrix optimization. Owing to obtaining higher transmit diversity order, simulation results of bit error rate (BER) performance show that GQSF-IM outperforms QSF-IM in different channels such as independent and identically distributed (i.i.d.), correlated Rayleigh fading, and Rician channels. Furthermore, GQSF-IM can achieve obvious better BER performance when it combines with interleaving for more diversity gains.

Study of 5G-NR-MIMO Links in the Presence of an Interferer

Abstract: Many communication systems are based on the Multiple Input, Multiple Output (MIMO) scheme, and Orthogonal Space–time Block Transmit diversity Coding (OSTBC), combined with Maximal Ratio Receive Combining (MRRC), to create an optimal diversity system. A system with optimal diversity fixes and optimizes the channel’s effects under multi-path and Rayleigh fading with maximum energy efficiency; however, the challenge does not end with dealing with the channel destruction of the multi-path impacts. Susceptibility to interference is a significant vulnerability in future wireless mobile networks. The 5th Generation New Radio (5G-NR) technologies bring hundreds of small cells and pieces of User Equipment (UE) per indoor or outdoor local area scenario under a specific Long Term Evolution (LTE)-based station (e-NodeB), or under 5G-NR base-station (g-NodeB). It is necessary to study issues that deal with many interference signals, and smart jammers from advanced communication equipment cause deterioration in the links between the UE, the small cells, and the NodeB. In this paper, we study and present the significant impact and performances of 2×2 Alamouti Phase-Shift Keying (PSK) modulation techniques in the presence of an interferer and a smart jammer. The destructive effects affecting the MIMO array and the advanced diversity technique without closed-loop MIMO are analyzed. The performance is evaluated in terms of Bit Error Rate (BER) vs. Signal to Interference Ratio (SIR). In addition, we proved the impairment of the orthogonal spectrum assumption mathematically.

On the Performance of DVB-T2 MISO System: Special Fixed Transmission Scenarios

Abstract: The Second Generation Digital Video Broadcasting Terrestrial (DVB-T2) system has the most complex and flexible configuration among the second generation DVB standards. It also supports the multiple-input single-output (MISO) transmit diversity to improve terrestrial TV broadcasting in the Single Frequency Networks (SFNs). This paper deals with the performance study of DVB-T2 using MISO at special fixed transmission scenarios. These scenarios are characterized by different channel conditions between the transmitters (TXs) and receiver (RX) and different power imbalances between TXs. A laboratory workplace enabling to measure the DVB-T2 MISO signal on both objective and subjective levels is realized. Results show that the considered transmission conditions have different influence on the overall performance of MISO-based DVB-T2 system.

Space-Frequency Coded Quadrature Index Modulation With Linear Maximum Likelihood Detection

Abstract: This paper focuses on the issue of achieving transmit diversity for the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system working with quadrature index modulation (QIM). Inspired by the ideas of quadrature spatial modulation (QSM) and quadrature space-frequency index modulation (QSF-IM), parts of the space-frequency resource units in each resource block (RB) of the MIMO-OFDM system are activated twice independently to send the in-phase and quadrature components of a space-frequency code, respectively, to achieve the second order transmit diversity. Thus the proposed scheme is called space-frequency coded QIM (SFC-QIM). The SFC-QIM scheme allows for a linear-complexity maximum likelihood (ML) receiver, which benefits from the orthogonality between the real and imaginary parts of the symbols in the SFC codewords. Owing to obtaining higher diversity order, simulation results of bit error rate (BER) performance demonstrate that the new SFC-QIM scheme outperforms some existing IM schemes in both independent and identically distributed (i.i.d.) and correlated Rayleigh fading channels.

Spatial Transmit Diversity for GFDM via Low Complexity Transceiver Design

Abstract: Generalized frequency division multiplexing (GFDM) is a novel multi-carrier technique that provides the flexibility required by various emerging applications, thanks to the low out-of-band emissions due to better prototype filters and lower loss in spectral efficiency due to combined cyclic prefix for a group of sub-symbols. To improve robustness in multipath fading wireless channels, GFDM can be combined with transmit and receive multi-antenna diversity. In this work, we propose a generic framework for achieving multi-antenna transmit diversity in GFDM via standard orthogonal space time block codes in combination with time reversal coding and simple linear receivers. We have shown the attainment of full diversity order for four and eight transmit antennas. Appropriate array and diversity gains are also achieved by increasing the number of antennas at receiver side. Moreover, a mechanism to reduce GFDM transceiver computational complexity via the use of chirp Z-transform has been proposed along with benchmarking with prior works.

OFDM-Based Generalized Spatial Modulation for Optical Wireless Communication

Abstract: In this paper, we propose two orthogonal frequency division multiplexing (OFDM)-based generalized spatial modulation (GSM) techniques, i.e., frequency domain GSM (FD-GSM) and time domain GSM (TD-GSM), for indoor multiple-input multiple-output optical wireless communication (MIMO-OWC) systems. Specifically, FD-GSM selects a subset of parallel OFDM modulators to transmit the same quadrature amplitude modulation (QAM) constellation symbol in the subcarrier level, while TD-GSM selects a subset of light-emitting diode (LED) transmitters to transmit the same time domain sample after OFDM modulation. Compared with the existing OFDM-based spatial modulation (SM) scheme, OFDM-based GSM can provide additional transmit diversity. For both FD-GSM and TD-GSM, maximum-likelihood (ML) detectors are employed to recover the spatial and constellation symbols. Moreover, TD-GSM usually requires a secondary direct current (DC) bias to work properly. The simulation results show that in a typical indoor $4\times 4$ MIMO-OWC system, OFDM-based TD-GSM outperforms OFDM-based FD-GSM by adding a proper secondary DC bias.

Ergodic Capacity of High Throughput Satellite Systems With Mixed FSO-RF Transmission

Abstract: We study a high throughput satellite system, where the feeder link uses free-space optical (FSO) and the user link uses radio frequency (RF) communication. In particular, we first propose a transmit diversity using Alamouti space time block coding to mitigate the atmospheric turbulence in the feeder link. Then, based on the concept of average virtual signal-to-interference-plus-noise ratio and one-bit feedback, we propose a beamforming algorithm for the user link to maximize the ergodic capacity (EC). Moreover, by assuming that the FSO links follow the Malaga distribution whereas RF links undergo the shadowed-Rician fading, we derive a closed-form EC expression of the considered system. Finally, numerical simulations validate the accuracy of our theoretical analysis, and show that the proposed schemes can achieve higher capacity compared with the reference schemes.

Space-Time Coding Technique for Coherent Frequency Diverse Array

Abstract: Coherent frequency diverse array (FDA) radar is able to cover all directions with a stable gain by transmitting a single frequency-shifted waveform. However, it is revealed in this work that the range resolution scales linearly with the number of elements, which is limited by the fixed element number. By leveraging the relationship between the beam direction and the signal frequency, we link the sub-bands of the emitted signal to angular sectors. Based on the fact, a novel transmit diversity technique, referred to as two-dimensional (2-D) space-time coding (STC), is proposed to improve the range resolution. For a specific observation direction, the frequency band of each pulse is shifted by STC to synthesize a full bandwidth after the pulse accumulation. Furthermore, the piecewise LFM (linear frequency modulation) waveform design can be combined with the STC technique to synthesize the transmit beampattern flexibly without range resolution degradation for each pulse. Compared with the state-of-the-art technologies, the proposed STC technique has superiorities in range resolution improvement, ultra-low range sidelobe level, interference suppression, and beampattern design capability. In addition, multi-dimensional ambiguity functions are derived to assess the performance in range-angle-Doppler domain, including the range and angle resolutions, the sidelobe level (SLL) and the angular coverage. To satisfy practical demands, the general receive processing procedures are also designed. The proposed method and corresponding theoretical analysis are verified by extensive numerical results.

Channel Capacity of an Asymmetric Constellation in Rayleigh Fading With Noncoherent Energy Detection

Abstract: The channel capacity of noncoherent reception of multi-level one-sided amplitude-shift keying (ASK), which is an asymmetric constellation, in Rayleigh fading with receive diversity and energy detection is considered. The asymmetries result in capacity achieving input probability distributions, that is, a priori probability distributions, that deviate from uniformity. An analytical expression for the mutual information in terms of a single integral is derived, and from it the set of equations, which can be solved to obtain the optimum or capacity achieving input probabilities, is obtained. High and low signal-to-noise ratio (SNR) approximations of the optimum input probabilities and the capacity are derived next. Furthermore, a logarithmic upper bound on the mutual information is obtained. Numerical results confirm that the uniform distribution of input probabilities is not capacity achieving. For example, with average SNR per symbol per branch of 6 dB, the relative deviation of the mutual information (with uniform input distribution) from the capacity is nearly 20% for 4-level ASK with one transmit diversity branch and two receive diversity branches. Furthermore, the derived high and low SNR approximations to the capacity are shown to be reasonably accurate.

A Cluster-Based Transmit Diversity Scheme for Asynchronous Joint Transmissions in Private Networks

Abstract: In this paper, a multiple cluster-based transmission diversity scheme is proposed for asynchronous joint transmissions (JT) in private networks, in which the use of multiple clusters or small cells is preferable to increase transmission speeds, reduce latency, and bring transmissions closer to the users. To increase the spectral efficiency and coverage, and to achieve flexible spatial degrees of freedom, a distributed remote radio unit system (dRRUS) is installed in each of the clusters. When the dRRUS is disposed in the private environments, it will be associated with multipath-rich and asynchronous delay propagation. Taking into account of this unique environment of private networks, asynchronous multiple signal reception is considered in the development of operation at the remote radio units to make an intersymbol interference free distributed cyclic delay diversity (dCDD) scheme for JT to achieve a full transmit diversity gain without full channel state information. A spectral efficiency of the proposed dCDD-based JT is analyzed by deriving the closed- form expression, and then compared with link-level simulations for non-identically distributed frequency selective fading over the entire private network.

Quaternion Codes in MIMO System of Dual-Polarized Antennas

Abstract: The use of quaternion orthogonal designs (QODs) to describe point-to-point communication among dual-polarized antennas has the potential to provide higher rate orthogonal and quasi-orthogonal complex designs exploiting polarization diversity among space and time diversities. Furthermore, it is essential to have a space time block code (STBC) which offers a linear and decoupled decoder which quasi-orthogonal designs fail to attain. In this paper, we show how the realm of quaternions unexpectedly offers us a possible solution and codes obtained from quaternion designs mostly achieve both linear and decoupled decoders. This motivated us to perform an indispensable search for QODs such that the code rate is bounded below by 1/2 and does not sharply decrease as the number of transmit antennas increases. It is shown that three famous recursive techniques do not satisfy this criteria and their code rates decrease rather rapidly. Therefore, we propose another method of constructing quaternion designs suitable for any number of transmit antennas and verify that these attain linear and decoupled decoders with the system model based on quaternionic channel. It is shown that such designs outperform others in terms of transmit diversity, code rates and the optimality of the proposed decoder is validated through simulation results.

Antenna Grouping Based Generalized Spatial Modulation System

Abstract: Spatial modulation (SM) technology [1], compared with the vertical Bell Labs layered space-time (V-BLAST) [2] and multiple-input and multiple-output (MIMO) [3] schemes, can significantly combat the inter-channel interference (ICI) and reduce the detection complexity at the receiver. SM exploits both the signal and the spatial domains to convey the information bits. However, traditional SM cannot obtain both the transmit diversity gain and the multiplexing gain effectively. As an extension of SM, generalized SM (GSM) [4] [5] can achieve the diversity gain and improve the spectral efficiency (SE) by simultaneously allowing multiple active transmit antennas (TAs) to convey the information. In order to enhance the multiplexing gain, current research on GSM with multiple TAs, such as multiple active spatial modulation (MA-SM) [6] and generalized spatial index modulation (GSIM) [7], allows several activated TAs to transmit different signals at the same time. To further achieve the multiplexing and diversity gains, the related literature also investigated the in-phase and quadrature index dimensions of SM, named as quadrature spatial modulation (QSM) [10], to transmit more index bits.

Experimental Evaluation of UL-NOMA system with FD-STBC

Abstract: In this paper, we propose a novel uplink non-orthogonal multiple access (UL-NOMA) for massive communications under the number of user equipments (UEs) that send signals simultaneously is larger than the number of receive antennas. The base station (BS) separates the superimposed signals through minimum mean square error (MMSE) spatial filtering with successive interference cancellation (SIC). In order to improve the signal separation performance, frequency domain-space time block coding (FD-STBC) is adopted as transmit diversity in the uplink. As FD-STBC, we examine two ways of transmit power allocation method for each UE. The proposed methods are evaluated by computer simulations and also experiments, which were performed under condition when up to 6 UEs transmit signals simultaneously. Performance evaluation is given by packet error rate (PER) by sending 16 bytes a packet as the signal. The results of the computer simulation and the experiments show good agreement, and the experimental results with the power difference for each UE, show that PER is less than 10% in single transmission without repetition when the number of UEs is up to 6. These are the results when the overloaded ratio, which is the ratio of the number of UEs to the number of the receive antennas, is up to 300%. And these results showed that it is effective to make a power difference for each UE.

Low Complexity Anti-Interference Equalization for Broadband Single-Carrier Systems With Transmit Diversity

Abstract: In this paper, we consider single carrier system with transmit diversity and a new multi-antenna transmission waveform is carefully designed to enable low-complexity anti-interference adaptive equalization. We propose a new space-frequency adaptive equalization method which makes use of the mutual interferences among different antennas from the desired user rather than attempts to completely remove them. We further propose two different ways to significantly reduce the computational complexity based on the idea of subband-wise processing with little sacrifice of equalization performance. Simulation results show that the proposed method exhibits a significant gain over conventional anti-interference schemes.

Wireless power transfer with transmit diversity

Abstract: Background: Wireless power transfer is important for energizing and recharging the Internet-of-Things (IoT) cordlessly. Harnessing energy effectively from radio waves has become a crucial task. It is known that diversities at the transmitting antenna and waves (i.e. simultaneous continuous waves with center frequencies separated apart) can enhance the radio frequency (RF) to direct current (DC) energy conversion. What remains unknown is the extent of which the wave diversity enhances the conversion gain. This study attempts to examine the RF-to-DC conversion gain of applying wave diversity. This paper investigates the effects of wave diversity on the energy conversion efficiency, and contributes the analytical expression that relate the conversion efficiency to the diversity count, i.e. the number of simultaneously transmitted sinewaves. Methods: We adopted a theoretical approach to the problem. First, we derived and presented a theoretical model that incorporated different forms of transmit diversity, i.e. antenna and wave diversities. This model then connected a RF-to-DC energy conversion model resulting from polynomial fitting on circuit simulation results. With the availability of these two models, we determined the theoretical energy conversion gain of simultaneously transmitting multiple sinewaves. Results: The results showed that transmitting multiple sinewaves simultaneously yields diversity gain and higher energy conversion efficiency. Most importantly, the gain and conversion efficiency can now be theoretically quantified. For example, at certain RF power measured at the receiver circuit, the diversity gain of transmitting four sinewaves is 2.6 (as compared to transmitting single sinewave). In fact, both the diversity gain and conversion efficiency increased with the number of simultaneously transmitted sinewaves. In another example, the conversion efficiency of transmitting four sinewaves is 0.1 as compared to 0.075 of two sinewaves. Conclusions: In summary, this paper presents a novel analytical expression for wave diversity in the context of wireless power transfer.

Constellation-Based Index Modulation: A Permutational Approach

Abstract: In this chapter, we implement constellation-based index modulation for orthogonal frequency division multiplexing (OFDM) systems via a permutational approach. First, we propose the multiple-mode OFDM with index modulation (MM-OFDM-IM) scheme and extend the principle to the in-phase (I-) and quadrature (Q-) components of OFDM signals. Then, we propose the scheme of generalized (G-)MM-OFDM-IM, which allows a different subcarrier to utilize a signal constellation of a different size while conveying the same number of index bits. Finally, two transmit diversity schemes are designed for MM-OFDM-IM(-IQ).