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Recent publications have investigated and demonstrated new digital modulation techniques that allow realization of orthogonal frequency division multiplexing (OFDM) radar with relatively low hardware effort. This is especially interesting as the digitally defined signals offer additional freedom for multiplexing schemes of multiple-input multiple-output (MIMO) radar sensors. MIMO radar sensors rely on strictly orthogonal signals to distinguish between multiple transmitters (TX). To span a virtual array with a maximum number of antenna positions, a novel method that combines orthogonal signals with strongly correlated signals generated by space-time coding (STC) is introduced. This leads to virtual transmit antenna positions that are used to improve the unambiguous angular area of an otherwise ambiguous MIMO antenna array. The proposed method is validated with an integrated OFDM radar at millimeter-wave frequencies.

Full frequency reuse with nonorthogonal multiple access (NOMA) in heterogeneous networks (HetNets) can promisingly satisfy the fast-growing wireless transmission requirements, as the data of different users can be simultaneously delivered over the same frequency band. In HetNets, the transmissions from a micro base station (BS) to its cell-edge users often suffer from strong interference from the macro BS, which severely degrades the communication quality. The macro BS and the micro BS can transmit simultaneously to a common far-user using the distributed Alamouti coding technique to improve the communication robustness. Meanwhile, each BS also transmits data to a near-user using the NOMA protocol. The common far-user adopts the maximal ratio combining (MRC) technique to decode its desired data by treating the data of near users as interference. Each near-user decodes the data of far-user using the MRC technique and cancels it to decode its own data by treating the remaining undesired data as interference. Numerical results show that the Alamouti coding based NOMA transmission can greatly improve the throughput of HetNets.

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.

Nowadays, there is a need for wireless communications to operate over a variety of scenarios, including high mobility multiple-input multiple-output (MIMO) applications, that bring along a challenging problem. In channels where Doppler spread and delay spread are high, complexity of coherent detectors and pilot overhead are both raised. This work proposes a non-coherent reception technique, easily scalable to any number of antennas for the MIMO case, using simple coding and decoding structures which take advantage of channel diversity addition in three domains: time, frequency and space, by using virtual trajectories along with space time block-coding. Coarse analytics on the system performance in terms of the bit error rate are computed using Chernoff Boundaries as a function of the channel diversity and the order of the differential modulation, validating the efficiency of the proposed receiver.

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.

In this article, several extensions to an alternating space-time (ST) code (STC) physical layer security (PLS) scheme from the literature are proposed. These contributions include alternative orthogonal STCs as well as non-orthogonal and spatially-multiplexed (SM) STCs for improved bandwidth efficiency. Phase rotation (PR) algorithms are provided to build very large sets of unique alternative STCs for use with this scheme. Decoding methods are discussed for alternating non-orthogonal and SM STCs. Monte Carlo simulations are provided to compare bit error rate (BER) performance between different decoding methods. Secrecy system nomenclature is adapted to the alternative STCs and proposed algorithms. Information-theoretic security analysis including message and key equivocation is provided along with expected eavesdropper BER based on an assumed attack methodology. A comparison of security offered by the alternating STC PLS scheme with and without incorporation of proposed PR algorithms is performed. Substantially greater exhaustive key search attack complexity is achieved by using the PR algorithms proposed in this article.

The problem of interference alignment in multi-user multiple-input multiple-output communication systems is considered, in this paper. A specific transmission strategy is proposed to transmit the symbols of multiple users which enables a significant saving of transmission time slots as compared to a trivial time division multiplexing based strategy. In order to detect the symbols at different receivers, the concept of left null of channel vector is utilized. The statistical properties of received signal-to-noise ratio at receiving end are studied by using probability density function, cumulative distribution function. Further, analytical performance of the system is discussed in terms of symbol error rate and diversity order by using moment generating function based approach. It is observed through theoretical analysis that the error performance of the proposed scheme degrades with increasing number of users; but this loss in performance can be compensated by deploying more antennas at the receivers. It is also shown through simulations that the computational complexity of the proposed scheme is also very much less as compared to the existing schemes.

The optimization of joint source and channel coding for a sequence of numerous progressive packets has been a challenging problem. Further, the problem becomes more complicated if the space-time coding is also involved with the optimization in a multiple-input multiple-output (MIMO) system. This is because the number of ways of jointly assigning channel codes and space-time codes to progressive packets is much larger than that of solely assigning channel codes to the packets. To our knowledge, there is no complete and feasible solution for the optimization of joint source, channel, and space-time coding of progressive packets. This paper applies a parametric approach to address such a highly nonlinear optimization problem in MIMO systems. We use the parametric methodology and derive some relevant properties, which are exploited to propose an efficient optimization method where the joint assignment of channel codes and space-time codes to the packets can be optimized in a packet-by-packet manner. As a result, the computational complexity of the proposed method linearly increases in the number of packets, whereas that of the exhaustive search exponentially increases in the number of packets. The numerical results show that the proposed method significantly improves the peak-signal-to-noise ratio performance of the conventional rate-based optimal solution in a MIMO system.

In this article, we propose a $2 \times 2$ space–time code (STC) for backscatter communications. The interesting thing is that although the proposed code performs much worse than the classical Alamouti code in conventional channels, it achieves almost the same performance as the Alamouti code in backscatter channels. More importantly, it has a considerably lower tag circuit complexity, which is more preferred in hardware-limited backscatter devices. This article indicates that the sets of “good STCs” for conventional channels and backscatter channels are not heavily overlapped, and there may exist many simpler STCs, which were previously ignored and not reported in conventional channels, have high performance, particularly, in backscatter channels.

Maximum rank distance (MRD for short) codes lately attract more attention due to their various applications in storage systems, network coding, cryptography and space time coding. Similar to Reed-Solomon codes in classical coding theory, Gabidulin codes are the most prominent family of MRD codes. Due to their poor performance in list decoding or in constructing McEliece-type cryptosystems, the focus moves from Gabidulin codes to other non-Gabidulin codes. A natural following challenge is then to see if we can construct an infinite family of MRD codes that are not equivalent to Gabidulin codes. In this paper, we utilize Dickson matrices to construct an infinite family of $\mathbb {F}_{q}$ -linear MRD codes. Our codes are characterized by each of their codewords corresponding to a linearized polynomial with leading coefficient determined by one of any other coefficients. The family of codes corresponding to the set of linearized polynomials with leading coefficients dependent on the linear terms provides an extension to both Twisted Gabidulin codes and generalized Twisted Gabidulin codes for dimensions 1 and $n-1$ . Lastly, we also provide some analysis on the equivalence between our proposed codes with some known families of MRD codes.

Turbo-BLAST (T-BLAST) is a multiple-input multiple-output (MIMO) wireless communication system. It is based on three main concepts: Bell laboratories layered space-time (BLAST) architecture, random space-time interleaving, and the turbo principle. T-BLAST system has many advantages including high data rate, excellent performance, and low complexity. These advantages make T-BLAST one the most important choices for future wireless communication systems. In this article, the authors study the effect of the space-time interleaver on the performance of T-BLAST system. This interleaver is split into two separated stages, time interleaving followed by space interleaving. They show that, in a quasi-static channel, the enhancement in performance provided by the time interleavers is very small compared to the gain provided by space interleavers. They also propose a new technique to improve the system performance, called multiframe space-time interleaving (MUSTI). Simulation results show an improvement in performance up to 6 dB at BER=10-4 for a (2,2) configuration.

We provide a compact summary of our recent results and ongoing research on digital metasurfaces based on spatiotemporal coding. Examples of field manipulations include harmonic beam steering and/or shaping and programmable nonreciprocal effects. Possible applications range from wireless communications to radars and imaging.

In aeronautical telemetry Alamouti encoded Shaped Offset Quadrature Phase Shift Keying - Telemetry Group (SOQPSK-TG) modulated signal is used to resolve “Two antenna problem” due to simultaneous transmission from the two onboard antennae. Detection of this signal at the receiver requires estimation of channel impairments (channel gains, time delays and frequency offset). The Maximum Likelihood Sequence Estimation (MLSE) based decoder of Space Time Coding (STC) encoded SOQPSK- TG signal requires 512 states, which is too complex for implementation. In this paper, pulse shaping is performed on SOQPSK- TG frequency pulse to reduce the pulse duration. Pulse of length 2 bit interval is found to be approximately matching the SOQPSK- TG characteristic while reducing the decoder complexity to 8 number of states. Subsequently parameter estimation is carried out for STC encoded SOQPSK-2T by Maximum Likelihood (ML) estimation method. The performances of proposed pulse shaping functions are compared with those of SOQPSK- TG and Feher's Quadrature Phase Shift Keying (FQPSK-JR), and are found to be superior for aeronautical telemetry display and level flight operations.

To increase the energy and spectral efficiency of radio engineering systems, it is advisable to combine the methods of space-time coding with the use of multi-element receiving and transmitting antennas in promising radio communication systems and signal-code structures. The joint efficiency of spatiotemporal coding with two receiving and transmitting antennas, together with signal-code structures, is analyzed by modeling methods in the MATLAB environment. Based on the results of the analysis, a reasonable joint choice of methods of multi-position modulation in combination with noise-resistant and space-time coding in radio engineering systems for various purposes is possible.

In this paper, we present a unique word (UW)-based channel estimation approach for multiple-input multiple-output (MIMO) systems under doubly dispersive channels, which is applied to orthogonal time frequency space (OTFS) with space time coding (STC). The OTFS modulation has been recently proposed as a robust technique under time varying channels due to its property of spreading the data symbols over time and frequency. Yet another relevant aspect is the employment of multiple antennas at the transmitter and receiver. Therefore, we consider an STC MIMO system with cyclic delay diversity at the transmitter and maximum ratio combining at the receiver, where we develop a UW-based channel estimation scheme for multiple transmit antennas. We show a recently proposed frame optimization scheme for SISO is directly applicable to MIMO. In addition, we evaluate numerically the frame error rate (FER) of OTFS and OFDM with 2x2 and 4x4 MIMO, where the time varying channel is estimated using the UW-based approach. The FER results reveal that OTFS becomes more advantageous than OFDM for MIMO-STC systems with higher order modulation and code rate.

In this paper, we consider a wireless-powered dual-relay network consisting of one multi-antenna source, two single-antenna energy-constrained relays and one single-antenna destination without direct source to destination link. In order to establish the communication flow, the energy-constrained relays harvest energy from the radio frequency transmitted by the source firstly, then exploit the harvested energy to forward the source information to the destination based on distributed space time coding (DSTC). Under this network architecture, three decode-and-forward (DF) technique-based relaying protocols, i.e., time switching-based relaying (TSR) protocol, power splitting-based relaying (PSR) protocol, and hybrid relaying (HR) protocol, are considered to drive the energy transfer and information transmission. To maximize the network throughput, the joint design for the optimal energy and information beamforming vectors employed at the source, the optimal time switching, and power splitting ratios under these three protocols are investigated and solved efficiently by employing simple sequential optimization approach or alternating optimization approach. Simulations are conducted to show the superior performance achieved by our proposed scheme. Moreover, we find that the TSR protocol outperforms the PSR protocol in the low signal-to-noise ratio (SNR) region, while the latter outperforms the former in the high SNR region. And the HR protocol achieves the best performance in any SNR region. At the same time, the effect of the relays’ locations on the throughput performance of these three protocols is also investigated.

In this paper, the space-time code selection technique for multiple-inputs single-output systems is optimized using particle swarm optimization. We considered both variable-rate and constant-rate strategies. For a variable-rate technique, we address the problems of minimizing the bit-error rate for a given throughput objective and maximizing the throughput for a given bit-error rate objective. For a constant-rate technique, we address the problem of minimizing the bit-error rate. Results show that it is possible to find BER and throughput values close to those required when using a variable-rate technique with optimized threshold levels. For the constant-rate technique, we obtain considerable energy to noise gains when using optimized threshold levels.

The object of this research is the methods and algorithms of space-time block coding, which are also used in multi-antenna radio communication systems (Multiple Input Multiple Output – MIMO). The implementation of MIMO systems for coherent reception or precoding of data implies knowledge of information about the state of the communication channel and, accordingly, compensation for its impact. For channel estimation, together with information signals, pilot signals are transmitted, previously known at the receiving side. The frequency of sending these signals depends on factors that change the state of the communication channel, for example, one of which is the high speed of movement of mobile stations. But since the pilot signals do not carry user information, the resource of the system is consumed, which impedes the efficient use of the radio frequency spectrum. In the course of the study, a method was considered that admits the absence of the need for knowledge of the state of the communication channel – relative phase modulation, which was taken as a basis and distributed for use in MIMO systems. This method provides for incoherent reception, but, despite this, its use is fully justified, based on the results of the study. Effective tree coding and an algorithm for compensating the noise components of the received signal were also developed and integrated into the system. This, accordingly, allows to optimize the computational power of the system implementation and to approximate the proposed method of differential space-time block coding (DSTBC)to the methods of coherent reception. Using the MATLAB software package, the proposed DSTBC method is simulated for various options for the number of transmitting and receiving antennas and types of modulation. A comparison is made and the advantages of the DSTBC method are determined. The described method can find application in modern radio communication systems with rapidly changing communication channel parameters due to the high speed of movement of mobile stations.

In this paper, we propose a two-hop MIMO multi-relay system with tensor space-time coding (TSTC) at the source and the relays. The multiple relays use orthogonal channels (parallel relaying) to increase the diversity order, assuming that all the relays can communicate directly with the destination. The signals received at destination form a fifth-order tensor that satisfies a new tensor model, called coupled nested Tucker decomposition (CNTD). This model is a generalization of the nested Tucker decomposition (NTD) and extends the coupling concept, introduced for PARAFAC models, to Tucker-based decompositions. The CNTD consists of a coupling of NTD models that share a common factor, resulting in the concatenation of a generalized Tucker model with a Tucker one. This tensor modeling is exploited to derive a semi-blind receiver for jointly estimating the information symbols and the channels. The uniqueness property of the proposed tensor model and the identifiability conditions of the receiver are established. Monte Carlo simulation results are provided to illustrate the effectiveness of the proposed system and the advantage of exploiting cooperative diversity based on tensor modeling.

In this paper, we utilize a space-time coding (STC) scheme to synthesize the multiple-input multiple-output (MIMO) radar transmit beampattern and meanwhile consider the matched filtering loss (MFL) of equivalent signal in waveform design. To solve the MFL optimization problem, we propose a simulated annealing based (SA-based) algorithm to effectively find the optimal solution of STC waveform matrix. Our STC method for waveform design has suppressed the fluctuation of equivalent signal so that has the advantage of achieving the minimum MFL nearly, compared to the conventional methods for constant-envelope constraint waveform design (e.g. cyclic algorithm (CA) method). Simulation results demonstrate the effectiveness of the proposed algorithm.

A multi-hop multi input multi output (MIMO) relay system with tensor coding at the source and relays is proposed in this paper. The tensor of signals received at destination satisfies a high-order nested Tucker decomposition (HONTD), generalizing an existing tensor decomposition. Exploiting this HONTD model allows to derive a closed-form semi-blind receiver for jointly estimating the information symbols and the individual channels. Identifiability conditions and ambiguity relations are derived. Monte Carlo simulation results are provided to evaluate the performance of the proposed receiver in terms of channels and symbols estimation, and the impact of the number of relays is illustrated.

Orbital angular momentum (OAM) multiplexing has recently received considerable interest in free space optical (FSO) communications. Propagating OAM modes through free space may be subject to atmospheric turbulence (AT) distortions that cause intermodal crosstalk and power disparities between OAM modes. In this paper, we are interested in multiple-input-multiple-output (MIMO) coherent FSO communication systems using the OAM. We propose a selection criterion for the OAM modes to minimize the impact of the AT. To further improve the obtained performance, we propose a space-time (ST) coding scheme at the transmitter. Through numerical simulations of the error probability, we show that the penalty from AT is completely absorbed for the weak AT regime, and considerable coding gains are obtained in the strong AT regime.

The known methods of signal processing of information transmission systems with space-time coding are quite successful in combating signal fading. However, these methods do not reduce the influence of external interference signals correlated in different reception channels. The article proposes a method for compensating external interference to systems with space diversity. The structure of the interference compensator is described. The method has been experimentally investigated. The experiments used a communication system with 2x space diversity. The proposed interference compensator showed the ability to suppress external narrow-band radio interference by at least 40 dB, and broadband barriers by 15 dB.

The paper presents a methodology for assessing the probability of communication disruptions in one beam of a radio communication system operating on the technology of space-time coding of signals. Expressions are given for an accurate and for an approximate estimate of the probability of communication disruptions in radio channels with multipath and signal fading. Long-term experimental studies of signal fading on a long-range tropospheric radio link have been carried out. It has been experimentally proven that the Rayleigh description of interference fading in multipath propagation of signals is observed in 60% of the time of communication sessions. For the rest of the communication sessions, other laws of probability distribution are observed. It is confirmed that they, together with Rayleigh's description of fading, are special cases of the four-parameter law of probability distribution. Convenient for practical use formulas are obtained for estimating the noise immunity of a communication channel. The graphs of the dependence of the probability of communication failure on the ratio of the average received signal power and the threshold level of the receiver signal are given.

This report on research in progress demonstrates a machine learning (ML) approach to array-based free-space optical communication using mobile devices. Spatial codes are transmitted using arrays of lasers or light emitting diodes for increased resilience and throughput, and ML models are trained on the channel alphabet to provide efficient decoding at the receiver. Various ML models, transmission array configurations, and spatial codes are compared for performance, and a proof-of-concept system is demonstrated. ML decoding of spatial symbols under noisy/perturbed channel conditions was successfully accomplished, however significant challenges are identified with throughput on mobile devices. Future experimentation is outlined to incorporate testing over greater distances under more realistic conditions.

In this work, we propose a new multiple-input multiple-output (MIMO) concept, which is called coordinate interleaved orthogonal design with media-based modulation (CIOD-MBM). The proposed two novel CIOD-MBM schemes provide improved data rates as well as diversity gain while enabling hardware simplicity using a single radio frequency (RF) chain. Moreover, using the equivalent channel model, a reduced complexity can be obtained for maximum likelihood (ML) detection of the proposed system. Using computer simulations, it is shown that CIOD-MBM schemes provide remarkably better performance against the conventional MBM and CIOD systems., Scientific and Technological Research Council of Turkey (TÜBİTAK)

Figure 23.1 shows the principle block diagram of a MIMO transmitter with space-time encoding. The incoming bit sequence b(n) is fed into the QAM mapper, which periodically maps \(\kappa \) consecutive bits to a QAM symbol \(c(k')\), constituting a \(2^{\kappa }\)-ary QAM. b(n) may contain redundancy bits from a forward error correction encoder, Friedrichs (Error Control Coding. Springer, Berlin, 2017 [1]), Richardson and Urbanke (Modern Coding Theory. Cambridge University Press, Cambridge, 2008 [2]), Moon (Error Correction Coding - Mathematical Methods and Algorithms. Cambridge University Press, Cambridge, 2008 [3]).

Layered space–time coding is one of space–time codes with the maximum multiplexing gain. In the paper, we investigate the using of iterative detection in the field of mobile satellite communication systems and analyze the performances of the algorithm in three typical channels. The performances of the simulation results meet the law that the open case is better than the urban case and suburban case. During the process of implementing the receiver, a new method of implementation with FPGA is proposed. The comparison between results by soft simulation and ones by hardware implementation shows the performance of soft simulation is a little better than the one of hardware implementation. At last, we analyze the differences of the situation.

The coding metasurface is a type of two-dimensional (2D) metamaterial, which has been widely employed to manipulate the electromagnetic (EM) waverfront in a controlled manner [1]. The meta-atoms with 2n phase states have been introduced to simplify the design procedure, making it possible to synthesize the radiation or scattering pattern of the metasurface by optimizing the digital codes of finite elements. Recently, a time-domain coding metasurface was further proposed for nonlinear manipulation of the EM waves. The spectral properties of reflected/transmitted waves can be effectively adjusted by periodically changing the reflection or transmission coefficients, leading to the emergence of high order harmonics [2], [3]. It has also been proved that a high conversion efficiency could be achieved from the fundamental to the specific order harmonic, by changing the coding strategy in the time domain [4]. In this talk, we will talk about the design of the space time coding metasurface, which enables the control of the wavefronts for multiple harmonics simultaneously, and facilitate the increase the capacity of the wireless communication systems due to the multi-channel transmissions. A new method is discussed to achieve multi-modulation schemes in wireless communication, such as BFSK, QPSK and 16QAM [5].

We provide a compact summary of our recent results and ongoing research on digital metasurfaces based on spatio-temporal coding. Examples of field manipulations include harmonic beam steering and/or shaping and programmable nonreciprocal effects. Possible applications range from wireless communications to radars and imaging.

A new design of MIMO-OFDM channel estimation using complementary codes is proposed in this paper. In the proposed algorithm a 2x2 space time code MIMO-OFDM system is considered. Instead of using single sided channel estimation techniques as in previous investigation [1], a two-sided approach is considered in. The suggested code on frequency-antenna distribution covers all the OFDM subcarriers. This is an advantage of our algorithm as previous investigations use only half of the subcarriers of the channel estimation. The considered channel model is a multi-tap fading channel model with doppler shift. The simulation results of the proposed algorithm are done assuming multi taps Rayleigh fading channel. Good results are obtained compared to other previous approaches of using complementary code in the estimation of MIMO-OFDM channels at low SNR and channel taps equal one and two.

The present communication system demands high data rate, spectral efficiency, and reliability. By employing numerous antennas in transmitter and receiver sides of a wireless channel, the spatial multiplexing or diversity gains can be explored. The modern communication network can be designed to attain a high data rate, enhanced link reliability, and improved range. MIMO technique can increase spectral efficiency without using extra bandwidth. This paper reviews recently published results on MIMO—Multiple Input Multiple Output. This paper describes the BER performance using Alamouti Space-Time Block Code and Average Channel Capacity has been discussed for different antenna system, i.e., SISO—Single Input Single Output, SIMO—Single Input Multiple Output, MISO—Multiple Input Single Output, and MIMO—Multiple Input Multiple Output systems under Rayleigh and Rician fading conditions. The simulated BER of MIMO has been compared with its theoretical result and with all other antenna configuration systems. Finally, the Average Channel Capacity for all the systems is analyzed and simulated under both Rayleigh and Rician Fading Channels.