Space-time Codes Research Articles

A Fully Integrated GaN Dual-Channel Power Amplifier With Crosstalk Suppression for 5G Massive MIMO Transmitters

We present a broadband dual-channel power amplifier (PA) with crosstalk suppression for multi-input multi-output (MIMO) communications. Operation of MIMO system with crosstalk is theoretically evaluated for two popular coding schemes including the space-time coding and linear precoding. Design challenges of a multi-channel PA on a single chip are investigated and circuit techniques, including second-harmonic trapping integrated into the output matching network and the use of back-via lines to isolate the channels, are proposed to mitigate the inter-channel crosstalk. A fully integrated dual-channel PA prototype, implemented using a 250-nm GaN-on-SiC process, provides 34.9–36.3dBm output power, 44–49% power-added efficiency (PAE), 11.3–12.3 dB power gain, 31.0–34.2 dB second-harmonic rejection, and −28.1 dB to −25.7 dB inter-channel crosstalk across 4.5–6.5 GHz. For a 100-MHz 256-QAM signal with 7.2 dB peak-to-average power ratio (PAPR), the PA achieves 29.9dBm average output power, 30% average PAE, −38.2/−39.1 dBc adjacent channel leakage ratio (ACLR), and −28.2 dB (3.9%) rms error vector magnitude (EVM), without using digital predistortion (DPD). Effect of crosstalk on linearity of the dual-channel PA is also measured and it is shown that for a 256-QAM signal EVM can increase by 3–8 dB, depending on relative power levels of the two channels.

Space–Time Line Code for Enhancing Physical Layer Security of Multiuser MIMO Uplink Transmission

In this article, we investigate a secure uplink multiple-input multiple-output communication system, in which the multiple users transmit information to a legitimate access point (AP) when a passive eavesdropper exists. A secure multiple access method is proposed for single-antenna users by employing space-time line codes (STLCs), which enables noncoherent detection at the legitimate AP without channel state information (CSI) and achieves full spatial diversity. While extending the secure STLC scheme from the single-antenna to two-antenna users by combining the STLC with artificial noise (AN) injection, we design a low-complexity AN signals with the optimal power control scheme. The proposed AN is ensured to be eliminated after STLC decoding at the legitimate AP, while sustained in eavesdropper's received signals as interference. Theoretical sum secrecy rates are derived by considering time-varying fading channels with the uncertainty of CSI at the users, and the numerical results verify that the proposed STLC schemes outperform the existing secure transmission schemes in terms of the sum secrecy rate.

Enhanced Diversity-Achieving Quadrature Spatial Modulation With Fast Decodability

In this paper, based on the architecture of diversity-achieving quadrature spatial modulation (DA-QSM) transmission scheme, we propose an Enhanced DA-QSM (EDA-QSM) scheme. In the proposed EDA-QSM scheme, by using Kronecker product extension to the eight dispersion matrices of Sezginer-Sari-Biglieri (SSB) code, the size of the dispersion matrices set is doubled compared with DA-QSM. Consequently, EDA-QSM is shown to have higher spectral efficiency as well as nonvanishing determinant (NVD) property without requiring any parameter optimization. Furthermore, EDA-QSM with an appropriate ordering of the dispersion matrices is a block-orthogonal space-time code (BOSTC), which then makes the four real variables corresponding to the same block are independent and orthogonal. By utilizing this feature, for the detection of EDA-QSM we propose a state codewords matched block-by-block sphere decoding (SD) algorithm, which significantly decreases the decoding complexity of ML decoder. Simulation results of bit error rate (BER) performance show that the new EDA-QSM scheme outperforms some newly presented diversity-achieving SM schemes.

Super-orthogonal double space–time trellis code

This study develops a new class of super-orthogonal trellis codes for four transmit antennas based on double space–time codes. The transmit antennas are divided into two groups, each having two transmit antennas. The information bits are demultiplexed into two streams; each is encoded independently using a super-orthogonal trellis code and then is transmitted from the corresponding antenna group. The resultant parallel-trellis code structure offers a higher data rate and, at the same time, it has a smaller number of parallel branches in the trellis encoder compared to a single stream encoder. The decoding is done using the maximum likelihood (ML) decoder with an interference cancellation algorithm.It is shown that the proposed scheme reduces the required number of overall calculations by about half compared with super-orthogonal space–time trellis codes (SO-STTC) and super-orthogonal trellis coded spatial modulation (SOTC-SM).The performance of the designed codes is simulated and shows that an improvement in the frame error rate (FER) is achieved at 4 and 5 b/s.Hz compared with SO-STTC and SOTC-SM, while at 6 b/s.Hz, it achieved an improvement in the lower and medium range of signal-to-noise ratio (SNR) (<22 dB).

A Simple, High-Performance Space–Time Code for MIMO Backscatter Communications

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.

Uplink NOMA Random Access Systems With Space–Time Line Code

This work proposes a random access system with uplink non-orthogonal multiple access (NOMA), where users transmit their packets by using the space-time line code (STLC) to fully exploit the spatial diversity without channel state information at the receiver. More specifically, users with a single antenna estimate channel gain from the base station (BS) with two antennas, encode the information using the STLC, and then transmit it using transmit power control so that the received power of their packets at the BS can be one of the predetermined values. The BS decodes the received packets via STLC decoding and the successive interference cancellation technique. Owing to spatial diversity, we show that the proposed scheme improves energy efficiency in comparison to the conventional system with a single antenna BS.

A Simple Time–Space Diversity Scheme Using Extended Shaping Pulse

This paper proposes a new time–space diversity scheme for data transmission through flat fading channels. Extended pulses are used to shape the modulated symbols at different time slots. The proposed transmitter does not change the transmission rate of the modulated symbols after the shaping process. One transmitting antenna is used to transmit the shaped symbols. Multiple antennas are used in the receiver to collect the transmitted symbols. The diversity gain in the proposed system is the product of the numbers of time slots through which the modulated symbol is transmitted and the number of receiving antennas. The proposed transmitter uses neither space–time codes nor spreading codes. The received signal suffers from intentional inter-symbol interference due to the correlation between the shaped symbols. Instead of using equalizers to remove this interference, multi-symbols detectors are used to exploit this interference to achieve the desired diversity gain. Buffers store the replicas of the desired symbol after the multi-symbols detector during its diverse period. Two-dimensional maximal ratio combiner adds these replicas in one decision variable. The proposed system achieves high diversity gain in flat fading channels with one transmitting antenna, and without affecting the used communication resources.

Quasi Orthogonal Space Time Block Code Over Nakagami-m Frequency Selective Fading Channels with Simple Decoding Complexity

In this paper, a Quasi Orthogonal Space Time Coding (QOSTBC) system over Nakagami-m frequency selective fading channels is introduced. The proposed scheme is carried out for the M-QAM modulation schemes assuming imperfect channel state information at the receiver. Inter symbol interference effect introduced due to the assumption of the frequency selective fading channels is eliminated by using the Orthogonal Frequency Division Multiplexing (OFDM) technology. Through the Bit Error Rate (BER) versus Signal to Noise Ratio (SNR) simulation results under different values of both Nakagami-m parameter and channel estimation error, the validity of the proposed technique is demonstrated. The results confirm that the BER in the case of frequency selective fading is overlapped with that of flat fading. This implies that the use of OFDM technology mitigates the effect of Inter-Symbol Interference (ISI) caused by frequency selectivity in the channel. Also, the results show that as the imperfect channel estimation error increases the performance degrades.

Joint Space-time Coding and Power Domain Non-orthogonal Multiple Access for Future Wireless System

According to information theory, non-orthogonal transmission can achieve the multiple-user channel capacity with an onion-peeling like successive interference cancellation (SIC) based detection followed by a capacity approaching channel code. However, in multiple antenna system, due to the unideal characteristic of the SIC detector, the residual interference propagated to the next detection stage will significantly degrade the detection performance of spatial data layers. To overcome this problem, we proposed a modified power-domain non-orthogonal multiple access (P-NOMA) scheme joint designed with space-time coding for multiple input multiple output (MIMO) NOMA system. First, with proper power allocation for each user, inter-user signals can be separated from each other for NOMA detection. Second, a well-designed quasi-orthogonal space-time block code (QO-STBC) was employed to facilitate the SIC-based MIMO detection of spatial data layers within each user. Last, we proposed an optimization algorithm to assign channel coding rates to balance the bit error rate (BER) performance of those spatial data layers for each user. Link-level performance simulation results demonstrate that the proposed time-space-power domain joint transmission scheme performs better than the traditional P-NOMA scheme. Furthermore, the proposed algorithm is of low complexity and easy to implement.

Improvement of FER using Differential Space-Time Block Code

Over recent years, various modulation and coding techniques have been proposed in MIMO wireless communication systems. A MIMO system uses the concept of spatial diversity which is very successful and promising technique. When a coherent transmission system is considered, the estimation of radio channel impulse response is done precisely. In MIMO systems, the radio channel is estimated among every transmitting and receiving antennas such that the complexity can be increased. For this reason, in MIMO systems differential modulation schemes are estimated. A Differential Space-Time Block Code (DSTBC) is useful in the Raleigh fading channel as they do not require channel estimates. Space-time coding with MIMO antennas at transmitting and receiving reduces the consequences of fading in multiple paths and therefore the performance of digital transmission throughout wireless radio channel can be improved. So it has been presumed that perfect CSI is available at the receiver and coherent detection is employed. This paper presents improvement of Frame Error Rate (FER) for differential space-time block code using various Doppler spectra. When the channels estimates are not available the DSTBC system noticed that at SNR of 10 dB, for two transmitting and four receiving antennas the FER is 0.0067 for rounded Doppler spectrum. The differential schemes attains full transmit diversity owing to orthogonal designs. However, the receiver or the transmitter needs the channel state information so these differential schemes are 3 dB worse than the STBC with coherent detection.

Virtual MISO with joint device relaying and beamforming in 5G networks

In this paper, a novel scheme is proposed in which mobile users organize a virtual multiple-input single-output (MISO) structure with the aid of relaying based on device to device (D2D) communication in a 5G cellular network. The performance of distributed quasi-orthogonal space–time code (D-QOSTC) based virtual MISO for the cooperation among four communication nodes is investigated. Error propagation in the second hop of relaying in decode and forward (DF) relaying protocols, is one of the main challenges of virtual MISO systems and it can be mitigated by the joint use of selection relaying and beamforming techniques. We propose a novel beamforming technique for removing the end to end inter-symbol interference (ISI) of D-QOSTC scheme. By means of our proposed scheme, even though we have error propagation in the second hop of relaying, without any loss in bandwidth or rate, the full diversity order can be achieved. Moreover, the performance of bit error rate (BER) with closed form result is analyzed and compared to the simulation results. The results exhibit that the theoretical BER curves coincide with the simulation ones and the system achieves full diversity order. The simulation results also indicate a significant gain in power efficiency for the optimal selection relaying and fixed relaying compared to conventional schemes.

Dickson Matrix Based Construction of Linear Maximum Rank Distance Codes

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 Fq-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.

High-Rate Spatial Modulation Transmission Scheme With Block-Orthogonal Structure and Block-by-Block Sphere Decoding

The work in this paper is an extension of the recently proposed stacked Alamouti based spatial modulation (SA-SM) scheme. The motivation is that by taking advantage of the existing full-diversity full-rate (FDFR) space-time code, to construct SM transmission with the properties of higher spectral efficiency, non-vanishing determinants (NVD) property, as well as fast decoding. In the proposed scheme, we still use the stacked structure to construct the signal matrix, but Alamouti code in the SA-SM scheme is replaced by the FDFR Sezginer-Sari-Biglieri (SSB) code. The combination of stacked structure with SSB code can contribute to attaining the goals of our motivation. Since the proposed SM scheme has block-orthogonal (BO) property, we call it as BO-SM. We then present a low-complexity block-by-block sphere decoding for the BO-SM scheme owing to the variables corresponding to the same block are independent. Simulation results of bit error rate (BER) performance show that the proposed BO-SM scheme outperforms some newly presented diversity-achieving SM schemes.

Asymptotically Optimal Codebooks Derived From Generalised Bent Functions

Codebooks are required to have small inner-product correlation in many practical applications, such as direct spread code division multiple access communications, space-time codes and compressed sensing. In general, it is difficult to construct optimal codebooks. In this paper, two kinds of codebooks are presented and proved to be optimally optimal with respect to the Welch bound. Additionally, the constructed codebooks in this paper have new parameters.

Space-Time Adaptive Processing Techniques (STAP) for Mitigation of Jammer Interference and Clutter Suppression in Airborne Radar Systems: A MATLAB Implementation-based Study

Radar Systems are used for the detection of objects by transmitting the electromagnetic waves in the free space. They operate in environments where there is a high possibility that the desired echo signal interferes with the signals from other sources. These signals include clutters and jammer signals. The jammer is a device that continuously emits the wideband radio signals in the radar environment, to saturate the receiver with noise or false information. Thus, the total received signal has three components- returns from target, clutter, and jammer combined i.e. it is a three dimensional signal. The use of conventional signal processing techniques is not desirable, as they cannot separate the desired echo signal from the other components, because the statistics of these components present in the received signal is not known. This problem needs to be accounted for, in airborne surveillance radars, as they have to identify and locate the targets in multiple interference environments. The Space-Time Adaptive Techniques (STAP) is a combination of spatial and temporal filtering that can nullify the jammer signal, and recognize the slow-moving targets. These techniques filter the signal in the angular and the Doppler domain for suppressing the unwanted signals. This paper presents a theoretical study of space-time adaptive coding techniques, and the MATLAB implementation of STAP algorithms; namely, SMI, DPCA, and ADPCA, to suppress clutter and jammer interference in the received pulse.

Transmit Antenna Selection for Space–Time Line Code Systems

In this study, we consider a space-time line code (STLC) system with N transmit antennas and two receive antennas. Although the STLC system is scalable to an arbitrary number of transmit antennas, a large number of them will increase the hardware cost and complicate the implementation of the system. To resolve this practical limitation, we propose a transmit antenna selection (TAS) scheme for the N-by-2 STLC system. If S ≤ N antennas are used for the transmission, the STLC transmitter selects the S antennas such that the instantaneous signal-to-noise ratio (SNR) is maximized. For a comprehensive performance analysis, the instantaneous SNR of the proposed TAS is characterized in terms of the statistical mean and moment-generating function (MGF). To investigate the performance of the proposed TAS approach, the approximated expression of error rate is derived based on the MGF method. Moreover, using asymptotic analysis, we show that the proposed TAS-STLC system achieves full spatial diversity of 2N, while the coding gain is affected by N, S, and the modulation order. As a special case, we also provide a mathematical analysis of the error rate of the conventional STLC system when N = S.

Hierarchical Trellis Based Decoder for Total Variation Sequence Detection (TVSD) in Space-Time Trellis Coded (STTC) Wireless Image/Video Communication

This paper proposes a robust reconstruction scheme for image/ video transmission in space-time trellis coding (STTC) based MIMO wireless multimedia sensor networks (WMSN). The information bits of the image/ video stream are modulated using STTC prior to transmission over the MIMO wireless channel between the multimedia sensors and the cluster head. At the receiver, a novel total variation sequence detector (TVSD) is developed that employs an anisotropic total variation (TV) regularized cost function to leverage the bounded variation property of the image/ video stream, in addition to the coding and diversity advantages of the STTC, for improved image/ video recovery. For reconstruction, a novel bi-layered hierarchical trellis based modified Viterbi decoder is developed to decode the optimal bit sequence corresponding to the least TV cost function using appropriately modified node and branch metrics. Simulation results using several test images and video sequences demonstrate the improved reconstruction performance of the proposed scheme, especially in the low SNR regime (0 - 10 dB), in comparison to the conventional maximum likelihood (ML) decoder, which makes it ideally suited for implementation in practical WMSN.

Double Space–Time Line Codes

In this paper, an M × 4 double space-time line code (D-STLC) is designed for a system with M-transmit and four-receive antennas whose channel state information is available at the transmitter. By delivering two independent STLC data streams simultaneously, both spatial diversity and multiplexing gains are obtained, like a 4 × M double space-time transmit diversity (DSTTD) system that transmits two space-time block coded data streams. It is analytically shown that the decoding signal-to-interference-plus-noise ratios of D-STLC and DSTTD are identical to each other, and furthermore, it is numerically verified that the proposed D-STLC significantly outperforms a conventional M × 4 STLC scheme and other existing spatial-diversity and spatial-multiplexing schemes, such as precoded space-time block code and precoded spatial multiplexing, in terms of achievable rate and bit-error-rate performance as the signal-to-noise ratio and/or transmission data rate increase.

Performance Analysis of Grouped Multilevel Space-Time Trellis Coding Technique Using Cognitive Radio in Different Deployment Models

In this era, the number of users in a network is increasing tremendously at a faster rate; as a consequence, quality of service (QoS) is drastically deteriorating. To compensate such kinds of problems, we attempted to enhance the QoS of the network, which leads to an improvement in throughput, link quality, spectral efficiency, and many more. To meet the requirements mentioned above, many researchers intervene to advance and propose different techniques with an appropriate design methodology. In this work, we try to emphasize symbol error rate (SER) and frame error rate (FER) by implementing some of the existing space-time coding techniques like Space-Time Trellis Coding (STTC), multilevel space-time trellis coding (MLSTTC), and grouped multilevel space-time trellis coding (GMLSTTC). Though all these techniques are proved to be efficient enough, we explicitly included a powerful method of cooperative diversity-based spectrum sensing in cognitive radio scenario. From this analysis, we landed on to the conclusion that this technique is far better to deal with all these parameters, which can improve the QoS of the network. This paper has also analyzed the effect of the proposed model of GMLSTTC with cognitive radio on various deployment setups such as urban, suburban, and rural macrodeployment setup of the ITU-R M.2135 standard.

Power Allocation for Self-Coded Distributed Space-Time Codes in FD Two-Way Relaying Networks

In this paper, a power allocation space-time coding scheme based on the self-coding property of residual loop interference (RLI) for two-way full-duplex (FD) amplify-and-forward (AF) relaying networks is proposed. The relay and direct link cooperate to forward the received signals to destination node, forming the self-coded distributed space-time code, in which the relay performs self-coding using the RLI after implementing some self-interference cancellation techniques. Then, an iterative power allocation algorithm is presented. With the proposed power allocation algorithm, both amplifying factor and transmit powers of terminal nodes are jointly optimized to maximize the smaller signal-to-interference-plus-noise ratio (SINR) of terminal nodes under a total power constraint when estimated instantaneous channel state information is available. We theoretically demonstrate the benefits of the proposed power allocation algorithm compared to equal power allocation. Simulation results show that the proposed scheme achieves significant improvement in performance compared with existing schemes for FD relaying systems and half-duplex relaying systems.