Initial performance evaluation of spatial modulation OFDM in LTE-based systems

The combination of orthogonal frequency division multiplexing (OFDM) and spatial modulation (SM) can enhance the capacity of optical wireless communication (OWC) systems with low complexity. In this paper, we propose a novel SM scheme for intensity modulation/direct detection (IM/DD) OWC systems by employing discrete Hartley transform based OFDM (DHT-OFDM). Due to the use of DHT with one-dimensional constellations, the Hermitian symmetry constraint, which is generally imposed in conventional discrete Fourier transform based OFDM (DFT-OFDM) to obtain a real-valued output signal, is not required in DHT-OFDM. As a result, DHT-OFDM based SM can achieve much higher spectral efficiency than that of DFT-OFDM based SM in OWC systems. Simulation results show that, for an indoor 4×4 SM-OWC system with a spectral efficiency of 6 bits/s/Hz, DHT-OFDM achieves a remarkable 4.5-dB transmit signal-to-noise ratio reduction for an overall bit error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> in comparison to conventional DFT-OFDM.

In this paper, two different configurations to drive multi-services OFDM signals in a dual electrode Mach-Zehnder modulator (DEMZM) to generate an optical hybrid signal (OHS) are investigated. The linearity of the configurations and their performance in the transmission of an OHS composed by a custom 4-quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) gigabit Ethernet (GbE) signal, a 20 MHz quadrature phase shift keying (QPSK) Long Term Evolution (LTE) signal and three OFDM-ultra-wideband (UWB) signals of the first group of the ECMA-386 standard are compared.

Future communication systems such as 5G will require high interoperability between standards, obligating current designs to contemplate the inclusion of multiple standards into a single device. Therefore, the main communication blocks must be designed with high capability in terms of reconfigurability. This paper presents the architecture and implementation of a reconfigurable Orthogonal Frequency Division Multiplexing (OFDM) transmitter with such capabilities. The proposed architecture is capable of generating frames for the Long Term Evolution (LTE) standard and with minimal modifications can also generate frames for IEEE 802.11a and 802.11g standards. The configuration parameters can be adjusted on-the-fly via configuration registers, such as: frame size, cyclic prefix (CP) size, data modulation type, and pilot values. Additionally, it is possible to operate in the five bandwidths required for LTE, allowing its inclusion in multi-standard design and software design radio platforms. Results have shown a moderate FPGA (Field Programmable Gate Array) consumption and good SQNR (signal-to-quantization-noise ratio) performance of 50 dB average.

The Spatial Modulation (SM) transmission scheme boosts the spectral efficiency and achieves the multiplexing gain by activating a single transmit antenna in each time slot. Radio wave propagation characteristics determined by the environment is a decisive factor for the SM system. In this paper, we investigate the performance of the SM scheme over real-world 4×4 Multi-Input Multi-Output (MIMO) channels measured in typical indoor scenarios. Firstly, a MIMO channel sounder is established. Based on the sounder, 15150 complex 4×4 MIMO channel matrices are measured inside a typical teaching building under both Line of Sight (LOS) and None Line of Sight (NLOS) scenarios. Secondly, by comparing the SM system over the measured channel and commonly-used channel models, we prove that both the Independently and Identically Distribute (i.i.d.) Rayleigh and the Spatial Correlation (SC) channel model are oversimplified, and that only practical experiences can yield definitive answers to the achievable real-world system performance. Thirdly, the Average Bit Error Probability (ABEP) performance of the SM system is studied based on the measured data under a variety of system configurations. The study of different receive antenna array settings (4×4, 4×2 and 4×1 MIMO setups) approves the significance of combining scheme at the receiver. SM systems employing different signal constellations (Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and 16 Quadrature Amplitude Modulation (16QAM)) are also investigated and some interesting results are revealed. Lastly, performance assessment of SM against State-Of-The-Art (SOTA) MIMO schemes (Space-Time Block Code (STBC) and Vertical Bell Labs Layered Space-Time (V-BLAST) code) is conducted. Results show that for a 4×4 MIMO, the low-complexity SM scheme outperforms both STBC and V-BLAST.

SummaryThis paper introduces the concept of spatial and media‐based modulated (SMBM) orthogonal frequency division multiplexing (OFDM) as a potential candidate for highly mobile next generation beyond 5G (B5G) wireless communications. The proposed SMBM‐OFDM technique utilizes not only the transmit antenna and channel state indices but also OFDM subcarriers to improve the system performance under high mobility. In addition, this study sheds light on challenging fast time‐varying channel estimation problem of MBM‐based systems by using the linear minimum mean square error (LMMSE) approach due to its optimality to investigate the achievable system performance with the aid of basis expansion modeling. The minimum lower bound on the channel estimation error (Bayesian Cramer–Rao bound) is derived theoretically and shown to be attainable by the considered LMMSE estimator. Moreover, symbol detection performance is provided for different modulation types and higher mobile velocities. Simulation results demonstrate that SMBM‐OFDM system under high mobility is able to provide around 12‐dB performance gains in terms of both channel estimation and symbol detection error compared to conventional spatial modulation (SM)‐OFDM systems without MBM. The presented framework is important due to addressing the high mobility support of SMBM‐OFDM systems for B5G wireless communications in terms of achievable channel estimation and data detection performance.

In this study, the authors presented discrete Fourier transform (DFT)-based channel estimation algorithms for a coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission system. Influence of the proposed algorithms to the performance and computational complexity of the CO-OFDM system was analysed and compared with other published algorithms. Their simulation results demonstrated that the improved DFT-based channel estimation algorithms are significantly efficient in our experimental conditions. Those algorithms can be considered as efficiently compromised systems in balance out the outcome of performance and the requirement on computational complexity. Such relatively economic and practical approaches have provided an optimistic prospect in studies of transmission systems for future optical communications.

Long Term Evolution (LTE) has many desirable features such as high data rate, better signal, and low latency which are required for modern communication systems. The LTE technology is based on an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme. For these benefits, LTE uses for the majority of communication systems that are used on civilian and military applications. Electronic Warfare (EW) researchers are interested in measuring the performance of the LTE communication systems in presence of intentional optimized jamming techniques. In this paper, the standard 3GPP (TS 36.104 v8.7.0) LTE Downlink Frequency Division Duplexer Single Input Single Output (DL FDD SISO) communication system designed on the SystemVue 2015.01 software program libraries has been used. The performance of the LTE communication system has been studied in the Additive White Gaussian Noise (AWGN) Channel without jamming for the three available modulation types for the Physical Downlink Shared Channel (PDSCH) [QPSK – 16QAM – 64QAM] by swept the Signal to Noise Ratio (SNR) versus Bit Error Rate (BER). The effectiveness of jamming has been studied by fixed the SNR and swept the Jamming to Signal Ratio (JSR) versus BER in two different cases. Firstly, the AWGN jamming signal has been added to the AWGN channel. Secondly, the optimized jamming signal has been added to the AWGN channel. Finally, the results of the jamming signal modulation type, bandwidth, and its location in the frequency and time have been optimized.

A novel encryption scheme using chaotic Zadoff-Chu matrix transform (ZCMT) precoding is proposed to improve both of the data security and performances in orthogonal frequency-division multiplexing (OFDM) transmission, where the security is significantly enhanced with a huge key space of ∼10400 provided by hyper digital chaos. The chaotic ZCMT matrix is generated with the reconfigurable parameters and row permutation of ZCMT matrix, both of which are predetermined by a hyper digital chaos. The OFDM data encryption using the chaotic ZCMT precoding effectively reduces the peak-to-average power ratio (PAPR) and consequently improves the OFDM transmission performance, if compared with the traditional OFDM transmission. The significant PAPR reduction is numerically analysed via the autocorrelation and the complementary cumulative distribution function (CCDF).

In various areas, wireless systems are used. In order to allocate the available time and frequency resources, these wireless systems require flexible mechanisms. With 5G, transmission rates will be higher, latency will be lower and quality of service and channel capacity will be higher. The physical layer must be able to generate flexible waveforms to meet the above requirements. Currently, Orthogonal Frequency Division Multiplexing (OFDM) transmission does not support 5G communication. In the case of 4G/OFDM, there are many problems in terms of out of band emission, spectral efficiency, and peak to average power ratio (PAPR). An alternative transmission scheme Universal Filtered Multicarrier (UFMC) is introduced to address this problem. The paper compares OFDM with UFMC. The purpose of this paper is to discuss Spectral Density, Spectral Efficiency, Signal to Noise Ratio (SNR) and Bit Error Rate (BER). In comparison to OFDM, UFMC provides better performance.

Orthogonal frequency division multiplexing (OFDM) has been adopted in various wireless communication standards to exploit its high spectral efficiency and robustness against multipath fading channels. Along with the potential benefits of OFDM transmissions, a stringent requirement on orthogonality among subcarriers makes OFDM highly susceptible to synchronization errors, i.e., time and frequency offsets. Addressing the carrier frequency offset (CFO) estimation problem, the paper proposes a pilot-aided CFO estimation scheme for both coarse and fine carrier frequency synchronization in single-input single-output (SISO) OFDM receivers. By exploiting the maximum likelihood (ML) principle, the proposed ML-based CFO estimation algorithm functions properly over a wide range of CFO values and outperforms existing correlation-based schemes.

In this paper, we propose a novel Artificial-Noise-Aided PHYsical layer Phase Challenge-Response Authentication Scheme (ANA-PHY-PCRAS) for practical orthogonal frequency division multiplexing (OFDM) transmission. In this new scheme, Tikhonov-distributed artificial noise is introduced to interfere with the phase-modulated key for resisting potential key-recovery attacks. Then, we address various practical issues for ANA-PHY-PCRAS with OFDM transmission, including correlation among subchannels, imperfect carrier, and timing recoveries. Among them, we show that the effect of sampling offset is significant and a search procedure in the frequency domain should be incorporated for verification. With practical OFDM transmission, the number of uncorrelated subchannels is often insufficient. Hence, we employ a time-separated approach for allocating enough subchannels, and a modified ANA-PHY-PCRAS is proposed to alleviate the discontinuity of channel phase at far-separated time slots. Finally, the key equivocation is derived for the worst case scenario. We conclude that the enhanced security of ANA-PHY-PCRAS comes from the uncertainties of both the wireless channel and introduced artificial noise, compared with the traditional challenge-response authentication scheme implemented at the upper layer.

In the development o f wireless communications, to provide high-speed data services and wide bandwidth become a challenge. One technique to make it happen is by using Multicarrier Orthogonal Frequency Division Multiplexing (OFDM) modulation, where in OFDM, frequency selective fading channel effect will be perceived flat fading by each subcarrier. One communication system that supports OFDM technology is Long Term Evolution (LTE) with various types of bandwidth configurations provided. To improve LTE performance in capacity building, coverage area and data rate, it can use multi antenna technique both in receiver and sender, and integrate with High altitude platform station (HAPs) system. In this study the estimation used is Linear Minimum Mean Square (LMMSE). The relationship o f the elevation angle and the K factor is directly proportional, but the elevation angle value is inversely proportional to the diameter o f the HAPs coverage area. In addition, the more the number o f used antennas, the greater the capacity served. Based on the simulation results, the system with estimation can be used to expand the coverage area to 215.77 km which is from 0.032 km in QPSK modulation, speed 60 kmpj with 2x2 antennas.

A full digital linearization technique based on a predistorter scheme with a look-up table (LUT) is applied to the orthogonal frequency-division multiplexing (OFDM) transmission scheme, such as a WiMAX system. The OFDM transmission is an efficient way to deal with multipath, being its implementation less complex than traditional equalizers. This together with an efficient implementation, using the Fast Fourier Transform algorithm, has made it ideal for using in new technologies. However, it is also very sensitive to nonlinear distortions due to its greatly variable envelope and high peak to mean envelope power ratio values. The proposed method includes also a peak cancellation stage in order to reduce this problem and to improve the efficiency of the power amplifier. The method functionality has been verified by means of simulation, obtaining a reduction in the adjacent channel interference level and also an improvement in the error vector magnitude (EVM) measurement.

In this paper, we propose a multi-user orthogonal frequency-division multiplexing (OFDM) transmission scheme with partial channel reusing between users, suitable for multiple-input multiple-output (MIMO) systems with not-so-large antenna arrays. The spectrum efficiency is improved at the price of adding multiuser interference (MUI) which can be overcome by the multiplexing gain of MIMO. In addition, we propose to employ the spread spectrum OFDM (SS-OFDM) modulation with the Walsh-Hadamard (WH) codebook for such a multi-user system to further mitigate the MUI. The bit error rate (BER) performance of the proposed scheme in the additive white Gaussian noise (AWGN) channels is derived analytically and then verified through Monte-Carlo simulations. Moreover, the proposed SS-OFDM system with partial bandwidth reuse is compared with the OFDM-based solution in a moderate-scale MIMO system with equal gain combining (EGC) precoding. It is shown that the proposed SS-OFDM MIMO system outperforms the classical OFDM approach in frequency-selective fading channels when the number of transmit antennas remains moderate.

This paper compares Single Carrier Frequency Division Multiplex (SC-FDM) with Orthogonal Frequency Division Multiplex (OFDM) for underwater acoustic communication. One of the drawbacks of OFDM transmission is the large variations in the instantaneous transmit power. This implies a reduced efficiency in power amplifiers and results in lower average power of the transmission signal. SC-FDM is utilized for 4G radio access technology such as Uplink communication of Long Term Evolution (LTE) in order to mitigate the above drawback of OFDM. Among the modulations in this communication system are QPSK, 16QAM and 64QAM. Zadoff-Chu sequence is used as Pilots for SC-FDM both for Channel Estimation and Phase Compensation of Doppler shift. Both Field Experiment at sea port in Okinawa, Japan and computer simulation show the quantitative merits of SC-FDM than OFDM. Peak-to-average Power Ratio (PAPR) of the transmitted signal has been successfully reduced by 1.5–2.0 dB for various modulations and roughly 50% of communication distance can be extended.