Time-Domain Analysis of Modified Vivaldi Antennas

In the ultra-wideband (UWB) application frequency domain parameters such as gain, group delay isn’t sufficient to demonstrate the performance of the antenna. Besides frequency domain analysis, a time-domain analysis is required to characterize the transient behavior of UWB antennas for pulsed operations since pulse distortion of the UWB antenna reduces the system performance and decreases the signal to noise ratio (SNR) of the UWB communication system. Vivaldi antenna is a widely used UWB antenna, especially in microwave imaging applications. Performance of Vivaldi antennas is enhanced by adding corrugation on the edge of exponential flaring and/or grating elements on the slot area. From the measured scattering parameters of modified Vivaldi antennas, pulse preserving capabilities are observed. Pulse width extension and fidelity factor parameters are used to define the similarity between the transmitted and received pulse. The analysis is performed with angular dependence with respect to the signal transmitted at the main beam direction

Performance analysis of MIMO techniques for a pyramid receiver in an indoor MIMO-VLC system

In an indoor multiple-input multiple-output (MIMO) visible light communication (VLC) system, line of sight (LoS) channel links are present between a light-emitting diode (LED) based transmitter and a photodetector (PD) based receiver. The PDs in the receiver are closely packed resulting in a high channel correlation. To overcome channel correlation and improve the performance of the MIMO-VLC system, angle diversity receivers (ADRs) are commonly employed. The channel matrix entries depend on the normal vectors of the PDs, which in turn depend on the elevation angle (EA) of the PDs. Thus, by having normal vectors pointing in different directions, the channel correlation can be considerably reduced. This paper considers a special type of ADR called pyramid receiver (PR) and employs a 4x4 MIMO-VLC system. In this paper, different MIMO algorithms such as repetition coding (RC) and spatial multiplexing (SMP) are considered to exhibit and compare the bit-error-rate (BER) performance of the fixed and variable EA MIMO-VLC systems. The results show that an SMP-employed MIMO-VLC system outperforms the RC-employed MIMO-VLC system. SMP results in an spatial multiplexing gain that varies linearly with the number of LEDs whereas RC does not yield any spatial multiplexing gain. To attain the same spectral efficiency i.e. 4 bit/s/Hz, a larger signal constellation size is required for RC employed MIMO-VLC system to achieve the same BER as of an SMP employed MIMO-VLC system. Similarly, the BER performance of variable EA MIMO-VLC systems is better as compared to fixed EA MIMO-VLC systems

Generalized quadrature spatial modulation techniques for VLC

Çelik, Yasin ( Aksaray, Yazar)In this paper, generalized quadrature spatial modulation (QSM) techniques are proposed for multiple-input single-output (MISO) visible light communication (VLC) systems using quadrature spatial modulation subcarrier intensity modulation (QSM-SIM). Additionally, realistic channel condition including both line-of-sight (LOS) and non-LOS (NLOS) components up to the third reflection is also considered and channel coherence bandwidths are calculated for varying number of LEDs. Since the indoor MISO VLC channel has strong correlation between coefficients, particle swarm optimization (PSO) and approximated maximum minimum Euclidean distance (AMMD) based precoding on the transmitter side are studied to reduce the channel correlation under illumination constraints. As a performance metric, bit error rate (BER) performance of considered modulation techniques is analyzed for different MISO schemes. The upper bound BER performances are also derived analytically in order to validate the simulation results. According to the results, we reached three important conclusions. First one is that variable length generalized QSM (VGQSM) by having few LED arrays on the transmitter side performs the best BER results compared to other schemes that provide the same spectral efficiency (SE) and the second is that precoding is essential for indoor MISO VLC systems to reduce the channel correlation. Finally, an increase in the number of LED arrays results in a decrease in channel coherence bandwidth

Donanim duyarlı dik uzamsal modülasyon

Spatial modulation (SM) is a simple multi-input multi-output (MIMO) communication technique in which a single transmit antenna is active for each symbol period. Quadrature spatial modulation (QSM), on the other hand, is a form of SM in which independent transmit antenna selection is made for the real and imaginary parts of the symbols. In these techniques, the spectral efficiency (SE) can be increased logarithmically by increasing the number of antennas used on the transmitter-side. Besides, in classical SM and QSM schemes, the number of antennas must be the power of two. In this paper, a flexible QSM scheme is proposed, which eliminates the necessity of antenna number and increases SE value linearly with the number of antennas for RF systems. This scheme, called hardware-aware quadrature spatial modulation (HAQSM), uses optimized constellations for the desired SE value. Optimal constellations are obtained using convex optimization under a constraint aimed at keeping the distance between neighboring symbols above the desired value. The bit error rate (BER) performances of the HAQSM scheme were obtained by Monte Carlo simulations and compared with the existing schemes in the literature

Quadrature spatial modulation sub-carrier intensity modulation (QSM-SIM) for VLC

Çelik, Yasin ( Aksaray, Yazar )In this paper, a new spectrally efficient modulation scheme called quadrature spatial modulation sub-carrier intensity modulation (QSM-SIM) is proposed for multiple-input multiple-output (MIMO) visible light communication (VLC) systems. In QSM-SIM, in addition to the digital modulation symbols, two LED indices are used simultaneously for transmission of data bits with the help of a sinusoidal signal pair. Then, spatial modulation quad-LED complex modulation (SM-QCM), which is based on quad-LED complex modulation (QCM), is enhanced such that the number of LEDs is greater than four. Bit error rate (BER) performances of the considered modulation schemes are analyzed for different MIMO plans. The upper bound on BER performances of the QSM-SIM and SM-QCM schemes are derived analytically in order to validate the simulation results. In this work, pulse amplitude modulation (PAM), QCM, and SIM are used as benchmarks. In addition, for the purpose of reducing channel correlation, the power imbalance (PI) method is applied to the VLC-MIMO system. Best power imbalance factors are obtained for the considered modulation schemes and benchmarks under fixed signal to noise ratio (SNR) values. The results show that the proposed schemes outperform the benchmarks with PI communication scenarios

Extended fully improved quadrature spatial shift keying modulation

In this paper, extended fully improved quadrature space shift keying (EFIQSSK) modulation, which is a combination of extended quadrature spatial modulation (EQSM) scheme and fully improved quadrature space shift keying (FIQSSK), is proposed. EFIQSSK uses only antenna indices to modulate data bits, achieving a bit rate of four times the number of antennas per channel usage. The proposed scheme can be implemented with any number of antennas. It has a low complexity since it does not need any radio frequency (RF) chain on the transmitter side. In our study, the bit error rate performance of this technique is compared with the schemes in the literature with the same spectral efficiency. In addition, the transmission scheme used in the method has been optimized to provide low bit error. In the Monte Carlo simulations, it has been observed that the proposed scheme outperforms other schemes in the literature with the same spectral efficiency when using 3 or more transmit antennas

Flexible quadrature spatial pulse amplitude modulation for VLC systems

Quadrature-spatial modulation (QSM) offers high spectral efficiency (SE) without interchannel interference for both radio frequency and visible light communication (VLC) systems. In this article, a new QSM scheme called flexible quadrature spatial pulse amplitude modulation (FQSPAM) is proposed for VLC systems. In space modulation techniques (SMTs), the data bit stream is divided into two groups as the index bits and the signal bits. These grouped bits are mapped independently to modulation symbols and indices of light-emitting diodes (LEDs). However, this mapping strategy puts a constraint on the number of LEDs and the size of the signal constellation. FQSPAM jointly designs the signal and spatial components of the constellation to overcome these limitations. This approach removes the constraint on the number of LEDs and the size of the signal constellation. The constellation design problem is formulated as a convex optimization problem to identify power-efficient constellations with different $M$ values. A dimming-controlled optimization algorithm has also been proposed to take into account both illumination and communication at the same time. Analytical and numerical results show the improved bit error rate performance of the proposed FQSPAM compared to spatial pulse amplitude modulation and channel adaptive bit mapping

Effect of Pulse Shaping on the Performance of Spatial Modulation

In this paper, the effect of pulse shaping in the spatial modulation (SM) method is investigated. In the SM, extra bit transmission is transmitted by selecting the active antenna in each symbol transmission, thus increasing the spectral efficiency. However, active antenna switching in each symbol transmission causes clipping in the signal if the transmitted pulse is span outside its time duration. The effects of the filter span and the roll-off factor on the SM bit error rate were investigated by Monte Carlo simulation. In the simulations, it has been observed that the low roll-off factor value and low filter span increase the bit error

Minimizing the number of effective channel taps by energy optimization in communications systems

27th Signal Processing and Communications Applications Conference, SIU 2019 April 2019, Article number 8806378 27th Signal Processing and Communications Applications Conference, SIU 2019; Sivas; Turkey; 24 April 2019 through 26 April 2019; Category numberCFP19559-ART; Code 151073Kanal gecikmeleri ve hareketlilik, iletilen sinyalin hem zaman hem de frekans bölgelerinde yayılmasına neden olarak sırasıyla semboller arası ve taşıyıcılar arası girişime neden olmaktadır. Verici ve alıcı yapılarında kullanılan filtre yapıları, söz konusu semboller ve taşıyıcılar arası girişimin büyüklüğünü etkilemektedir. Bu çalışmada, kablosuz ortamın ve kullanılan filtrelerin oluşturduğu bileşke etkiler, çok taşıyıcılı sistemlerde denkleştirici perspektifinden incelenmiş ve düşük denkleştirişi karmaşıklığı için uygun filtre yapısının belirlenmesi üzerine çalıştırılmıştır. Bileşke kanal etkisine ait etkin katsayı adedi, kanalın, verici/alıcı filtrelerin ve işaret gürültü oranının (İGO) bir fonksiyonu olarak elde edilmiştir. Bu amaçla bileşke kanal, sembol aralıklı bir sonlu dürtü yanıtlı (finite impulse response, FIR) filtre olarak modellenmiş, daha sonra katsayı adedini belirlemek için Akaike Bilgi Kriterinden (Akaike Information Criterion, AIC) yararlanılmıştır. Sonrasında, denkleştirme işleminde bileşke kanal modeline ait etkin katsayıları enerji optimizasyonu ile en aza indirgeyen verici/alıcı filtre tipleri belirlenmiştir.Channel delays and mobility cause the transmitted signal to propagate in both time and frequency regions, resulting in inter-symbol and inter-carrier interference, respectively. The filter structures used in the transmitter and receiver structures for impact shaping affect the size of the interference between these symbols and carriers. In this study, the composite effects of the wireless environment and the filters used were examined on the equalization of multi-carrier systems and the determination of the appropriate filter structure was studied. The number of effective taps of the composite channel effect was obtained as a function of the channel, the transmitter/receiver filters and the signal to noise ratio (SNR). For this purpose, the composite channel was modeled as an symbol-spaced finite impulse response (FIR) filter, then the AIC (Akaike Information Criterion) method was used to determine the number of taps. Subsequently, the transmitter/receiver filter types were determined which minimized the effective taps of the composite channel model by energy optimization in the equalization process