Showing papers on "Bit error rate published in 2016"

Ambient Backscatter Communication Systems: Detection and Performance Analysis

Abstract: Ambient backscatter technology that utilizes the ambient radio frequency signals to enable the communications of battery-free devices has attracted much attention recently. In this paper, we study the problem of signal detection for an ambient backscatter communication system that adopts the differential encoding to eliminate the necessity of channel estimation. Specifically, we formulate a new transmission model, design the data detection algorithm, and derive two closed-form detection thresholds. One threshold is used to approximately achieve the minimum sum bit error rate (BER), while the other yields balanced error probabilities for “0” bit and “1” bit. The corresponding BER expressions are derived to fully characterize the detection performance. In addition, the lower and the upper bounds of BER at high signal-to-noise ratio regions are also examined to simplify a performance analysis. Simulation results are then provided to corroborate the theoretical studies.

Range and coexistence analysis of long range unlicensed communication

Abstract: A broad range of emerging applications require very low power, very long range yet low throughput communication. Different standards are being proposed to meet these novel requirements. In this paper, the technical differences between a wideband spread spectrum (LoRa-like) and an ultra narrowband (Sigfox-like) network will be explained and evaluated. On the physical layer, simulation results show that an ultra narrowband network has a larger coverage, while wideband spread spectrum networks are less sensitive to interference. When considering the contention between nodes and interference between different networks, simulations show that adaptation of frequency and modulation is imperative for efficiently dealing with varying contention and interference in long range unlicensed networks. Depending on network load, size and distance, a device in a wideband network can send 6 times more packets to the base station when there is active rate and frequency management and an intra-technology control plane.

Chirp spread spectrum as a modulation technique for long range communication

Abstract: Long range low power is a family of technologies promising to connect thousands of sensors to the future internet of things. Within this family of possible technology choices, two different branches have emerged: the standards based on spreaded wideband communication and the standards based on narrowband communication, both promising to reach long range connectivity at very low power. More specifically, this paper focuses on chirp spread spectrum (CSS). This paper presents a detailed model of CSS, showing that the symbols are not perfectly orthogonal. The results show the potential communication ranges are close to narrowband networks and the robustness against interfering signals is 22 dB better for spreading factor 10 than BPSK. Although wideband communication is robust to interference, in long range communication, this robustness is insufficient due to the long range and the larger footprint. The large propagation losses due to the long range and the larger footprint make CSS prone to collisions with other noise sources, possibly larger than the coding gain.

Performance Analysis of Gamma–Gamma Fading FSO MIMO Links With Pointing Errors

Abstract: The bit error rate (BER) performance of the free space optical (FSO) link suffers from the atmospheric turbulence. By employing additional transmit and receive apertures at the transmitter and receiver, respectively, the error rate of the FSO communication system can be significantly improved. However, the pointing errors (PEs), generated because of the building sway, have the potential to eradicate the benefits of the multiple transmit and/or receive apertures-based FSO communication system. Therefore, for a general and realistic study of the FSO multiple-input multiple-output (MIMO) system, the effect of PEs in the Gamma–Gamma (GG) fading atmospheric fluctuations is considered in this paper. We study two schemes for the FSO MIMO systems: 1) equal gain combining (EGC), and 2) maximal ratio combining (MRC). A new power series-based representation is proposed for the probability density function of the GG fading FSO links with PEs. This new series representation contains only the terms with exponent of the random variable (RV) as compared to the closed-form representation, which contains the Meijer-G function of the RV. Then, we derive the average BER for both combining schemes over the GG fading FSO links with PEs. By using the derived BER expressions, we derive the asymptotic BER for both schemes. The analytical diversity order and combining gains for both systems are also obtained. The effect of PEs over the performance of the schemes is analyzed under different scenarios and it is observed that the PEs significantly degrade the diversity of the FSO MIMO system. It is deduced by simulation and analysis that though the EGC scheme is simpler to implement in practice but the MRC scheme is more rugged to the large PEs.

Generalized Performance Analysis of Mixed RF/FSO Cooperative Systems

Abstract: Free space optical (FSO) links provide an efficient point-to-point wireless transmission solution. They are particularly useful for filling the connectivity gap between the radio frequency (RF) access network and the fiber optic-based backbone network. To address this combined use, there has been a growing interest in so-called mixed RF/FSO systems where RF transmission is used at one hop and FSO transmission at the other in a dual-hop configuration. In this paper, we investigate the performance of mixed RF/FSO systems along with a direct RF link where the FSO link and RF links, respectively, experience double generalized gamma turbulence with pointing error and Nakagami- $m$ fading. Moreover, the effect of cochannel interference is considered at both relay and destination. Under the assumption of amplify-and-forward relaying and selection combining at the destination, we derive closed form expressions for outage probability and bit error probability in terms of Meijer’s-G and two-variate Fox-H functions. Our analysis provides a generalized framework for several existing results, since our adopted turbulence and fading statistical models are the most general ones. Based on the high signal-to-noise-ratio analysis, we further provide a diversity gain analysis and discuss the bottlenecks in the mixed RF/FSO systems.

Multi-gigabit/s underwater optical communication link using orbital angular momentum multiplexing

Abstract: In this work we experimentally demonstrated an underwater wireless optical communications (UWOC) link over a 2.96 m distance with two 445-nm fiber-pigtailed laser diodes employing Orbital Angular Momentum (OAM) to allow for spatial multiplexing. Using an on-off keying, non-return-to-zero (OOK-NRZ) modulation scheme, a data rate of 3 Gbit/s was achieved in water with an attenuation coefficient of 0.4128 m−1 at an average bit error rate (BER) of 2.073 × 10−4, well beneath the forward error correction (FEC) threshold.

A New Automotive VLC System Using Optical Communication Image Sensor

Abstract: As a new technology for next-generation vehicle-to-everything (V2X) communication, visible-light communication (VLC) using light-emitting diode (LED) transmitters and camera receivers has been energetically studied. Toward the future in which vehicles are connected anytime and anywhere by optical signals, the cutting-edge camera receiver employing a special CMOS image sensor, i.e., the optical communication image sensor (OCI), has been prototyped, and an optical V2V communication system applying this OCI-based camera receiver has already demonstrated 10-Mb/s optical signal transmission between real vehicles during outside driving. In this paper, to reach a transmission performance of 54 Mb/s, which is standardized as the maximum data rate in IEEE 802.11p for V2X communication, a more advanced OCI-based automotive VLC system is described. By introducing optical orthogonal frequency-division multiplexing (optical-OFDM), the new system achieves a more than fivefold higher data rate. Additionally, the frequency response characteristics and circuit noise of the OCI are closely analyzed and taken into account in the signal design. Furthermore, the forward-current limitation of an actual LED is also considered for long operational reliability, i.e., the LED is not operated in overdrive. Bit-error-rate experiments verify a system performance of 45 Mb/s without bit errors and 55 Mb/s with $\text{BER}\ .

Outdoor FSO Communications Under Fog: Attenuation Modeling and Performance Evaluation

Abstract: Fog is considered to be a primary challenge for free space optics (FSO) systems. It may cause attenuation that is up to hundreds of decibels per kilometer. Hence, accurate modeling of fog attenuation will help telecommunication operators to engineer and appropriately manage their networks. In this paper, we examine fog measurement data coming from several locations in Europe and the United States and derive a unified channel attenuation model. Compared with existing attenuation models, our proposed model achieves a minimum of 9 dB, which is lower than the average root-mean-square error (RMSE). Moreover, we have investigated the statistical behavior of the channel and developed a probabilistic model under stochastic fog conditions. Furthermore, we studied the performance of the FSO system addressing various performance metrics, including signal-to-noise ratio (SNR), bit-error rate (BER), and channel capacity. Our results show that in communication environments with frequent fog, FSO is typically a short-range data transmission technology. Therefore, FSO will have its preferred market segment in future wireless fifth-generation/sixth-generation (5G/6G) networks having cell sizes that are lower than a 1-km diameter. Moreover, the results of our modeling and analysis can be applied in determining the switching/thresholding conditions in highly reliable hybrid FSO/radio-frequency (RF) networks.

Robust Synthesis Method for Secure Directional Modulation With Imperfect Direction Angle

Abstract: Directional modulation (DM) is a secure transmission technology that is able to retain the original constellation of transmitted signals along the desired direction, while distort the constellation in the undesired directions at the same time. In this letter, we develop novel and robust DM synthesis methods for enhancing the transmission performance. Specifically, we first propose a low-complexity dynamic DM synthesis method. In this method, we derive a closed-form expression for the null space of conjugate transpose of the steering vector in the desired direction. Based on the expression derived, we construct a projection matrix in order to form artificial noises to those undesired directions. Then, we focus our attention on more practical scenarios, where there is uncertainty in the estimated direction angle. This uncertainty will cause estimation errors and seriously jeopardize the receiving performance in the desired direction. To mitigate the uncertainty effect, we further propose a robust DM synthesis method based on conditional minimum mean square error. The proposed method aims to minimize the distortion of the constellation points along the desired direction. Simulation results show that our proposed robust DM method is capable of substantially improving the bit error rate performance compared with the state-of-the-art methods.

A Survey on FEC Codes for 100 G and Beyond Optical Networks

Abstract: Due to the rapid increase in network traffic in the last few years, many telecommunication operators have started transitions to 100-Gb/s optical networks and beyond. However, high-speed optical networks need more efficient forward error correction (FEC) codes to deal with optical impairments, such as uncompensated chromatic dispersion, polarization mode dispersion, and nonlinear effects, and keep the bit error rate (BER) at long distances sufficiently low. To address these issues, new FEC codes, called third-generation codes, have been proposed. A majority of these codes are based on soft-decision decoders and can provide higher coding gain as compared with their predecessors. This paper presents a thorough survey of third-generation FEC codes, suitable for 100 G and beyond optical networks. Furthermore, this paper discusses the main advantages and drawbacks of each scheme and provides a qualitative categorization and comparison of the proposed schemes based on their main features, such as net coding gain and BER. Information about the complexity of each scheme is given as well.

Generalized Space-and-Frequency Index Modulation

Abstract: Unlike in conventional modulation where information bits are conveyed only through symbols from modulation alphabets defined in the complex plane [e.g., quadrature amplitude modulation (QAM) and phase shift keying (PSK)], in index modulation (IM), additional information bits are conveyed through indexes of certain transmit entities that get involved in the transmission. Transmit antennas in multiantenna systems and subcarriers in multicarrier systems are examples of such transmit entities that can be used to convey additional information bits through indexing. In this paper, we introduce generalized space and frequency IM , where the indexes of active transmit antennas and subcarriers convey information bits. We first introduce IM in the spatial domain, which is referred to as generalized spatial IM (GSIM). For GSIM, where bits are indexed only in the spatial domain, we derive the expression for achievable rate and easy-to-compute upper and lower bounds on this rate. We show that the achievable rate in GSIM can be more than that in spatial multiplexing and analytically establish the condition under which this can happen. It is noted that GSIM achieves this higher rate using fewer transmit radio-frequency (RF) chains compared with spatial multiplexing. We also propose a Gibbs-sampling-based detection algorithm for GSIM and show that GSIM can achieve better bit error rate (BER) performance than spatial multiplexing. For generalized space–frequency IM (GSFIM), where bits are encoded through indexing in both active antennas and subcarriers, we derive the achievable rate expression. Numerical results show that GSFIM can achieve higher rates compared with conventional multiple-input-multiple-output orthogonal frequency division multiplexing (MIMO-OFDM). Moreover, BER results show the potential for GSFIM performing better than MIMO-OFDM.

Iterative LDPC-LDPC product code for bit patterned media

Abstract: Bit patterned media aims at high density recording of more than 10 Tb per square inch, but a burst error mostly occurred by media defects, and data write failure can be a serious problem. However, if the burst errors are compensated by erasure decoding, the performance of low-density parity check (LDPC) code, which is a strong candidate for the error correcting code for storage systems, can be improved. In this paper, we propose an iterative LDPC–LDPC product code and show that it performs better than a simple LDPC–LDPC product code when there are only random errors and both random and burst errors.

Multi-Wideband Waveform Design for Distance-Adaptive Wireless Communications in the Terahertz Band

Abstract: Terahertz band communication is envisioned as a key technology to satisfy the increasing demand for ultra-high-speed wireless links. In this paper, a multi-wideband waveform design for the THz band is proposed, by exploiting the channel peculiarities including the distance-varying spectral windows, the delay spread and the temporal broadening effects. This scheme allows the dynamical variation of the rate and the transmit power on each sub-window and improves the distance. Moreover, the closed-form expressions of the signal-to-interference-plus-the-noise and bit-error-rate for the multi-wideband waveform are derived, by considering the inter-symbol and inter-band interferences. Then, an optimization framework is formulated to solve for the multi-wideband waveform design parameters of the transmit power and the number of frames, with the aim to maximize the communication distance while satisfying the rate and the transmit power constraints. Four sub-optimal solutions are proposed and compared. The results show that the SINR increases with the transmit power and the number of frames, at the cost of the power consumption and the rate decrease. With the transmit power of 10 dBm, the largest distance to support 10 Gbps for the multi-path propagation is 4 m, which is realized via the power allocation scheme to minimize the power/bit on each sub-window and is 10% improvement over the fixed scheme. However, for the directional transmission, this scheme under-exploits the transmit power severely. Instead, the allocation scheme that minimizes the number of frames outperforms the other three schemes. In terms of the maximum distance that achieves 30 Gbps, this scheme reaches 22.5 m.

Mixed-ADC Massive MIMO Detectors: Performance Analysis and Design Optimization

Abstract: The hardware cost and power consumption of a massive multiple-input multiple-output (MIMO) system can be remarkably reduced by using a very low-resolution analog-to-digital converter (ADC) unit in each antenna. However, such a pure low-resolution ADC architecture complicates parameter estimation problems. These issues can be resolved and the potential of a pure low-resolution ADC architecture can be achieved by applying a mixed ADC architecture, whose antennas are equipped with low-precision ADCs, while few antennas are composed of high-precision ADCs. In this paper, a unified framework is presented to develop a family of detectors on a massive MIMO uplink system through probabilistic Bayesian inference. Our basic setup comprises an optimal detector, which is developed to provide a minimum mean-squared-error estimate on data symbols. Considering that highly nonlinear steps are involved in quantization, we also investigate the potential for complexity reduction on an optimal detector by postulating a common pseudo-quantization noise model. We provide asymptotic performance expressions, including mean squared error and bit error rate for optimal and suboptimal MIMO detectors. These expressions can be evaluated rapidly and efficiently. Thus, they can be used for system design optimization.

Design and Performance Analysis of a Multiuser OFDM Based Differential Chaos Shift Keying Communication System

Abstract: In this paper, a multiuser OFDM-based chaos shift keying (MU OFDM-DCSK) modulation is presented. In this system, the spreading operation is performed in time domain over the multicarrier frequencies. To allow the multiple access scenario without using excessive bandwidth, each user has $N_P$ predefined private frequencies from the $N$ available frequencies to transmit its reference signal and share with the other users the remaining frequencies to transmit its $M$ spread bits. In this new design, $N_P$ duplicated chaotic reference signals are used to transmit $M$ bits instead of using $M$ different chaotic reference signals as done in DCSK systems. Moreover, given that $N_P , the MU OFDM-DCSK scheme increases spectral efficiency, uses less energy and allows multiple-access scenario. Therefore, the use of OFDM technique reduces the integration complexity of the system where the parallel low pass filters are no longer needed to recover the transmitted data as in multicarrier DCSK scheme. Finally, the bit error rate performance is investigated under multipath Rayleigh fading channels, in the presence of multiuser and additive white Gaussian noise interferences. Simulation results confirm the accuracy of our analysis and show the advantages of this new hybrid design.

Beyond 100-Gb/s Transmission Over 80-km SMF Using Direct-Detection SSB-DMT at C-Band

Abstract: For short-reach links, direct detection offers the advantages of low cost and low complexity. Discrete multitone (DMT) is a promising format due to its high spectral efficiency, flexibility and tolerance to chromatic dispersion (CD). In this study, we experimentally demonstrate a beyond 100-Gb/s DMT transmission over 80-km single mode fiber (SMF) without CD compensation. Using dual-drive Mach–Zehnder modulator-assisted single-sideband modulation, CD-induced power fading is eliminated after direct detection. Trellis coder modulation (TCM) is used to increase the Euclidean distance of the constellation points and nonlinearity equalization (NLE) is employed to mitigate system nonlinearities. Both TCM and NLE algorithms have contributions to improve the system performance. The experimental results show that high capacities up to 122, 110 and 105 Gb/s are achieved with bit error rate at 4.5 × 10−3 for back to back, 40- and 80-km SMF transmissions, respectively. The required OSNR after 80-km SMF transmission is 34.2 dB. To the best of our knowledge, this study reports the lowest required OSNR and highest capacity for C-band direct-detection transmission over 80-km SMF.

Robust Synthesis Scheme for Secure Multi-Beam Directional Modulation in Broadcasting Systems

Abstract: Recently, directional modulation has become an active research area in wireless communications due to its security. Unlike existing research work, we consider a multi-beam directional modulation (MBDM) scenario with imperfect desired direction knowledge. In such a setting, a robust synthesis scheme is proposed for MBDM in broadcasting systems. In order to implement the secure transmission of a confidential message, the beamforming vector of the confidential message is designed to preserve its power as possible in the desired directions by minimizing its leakage to the eavesdropper directions while the projection matrix of artificial noise (AN) is to minimize the effect on the desired directions and force AN to the eavesdropper directions by maximizing the average receive signal-to-artificial-noise ratio at desired receivers. Simulation results show that compared with conventional methods, the proposed robust scheme achieves much better bit error rate performance along desired directions for a given signal-to-noise ratio (SNR). From the secrecy-rate aspect, the proposed scheme performs better than conventional methods for almost all SNR regions. In particular, in the medium and high SNR regions, the rate improvement of the proposed scheme over conventional methods is significant.

Generalized Code Index Modulation Technique for High-Data-Rate Communication Systems

Abstract: In this paper, we propose a generalized code index modulation (CIM) technique for direct-sequence spread spectrum (DSSS) communication. In particular, at the transmitter, the bit stream is divided into blocks in which each block is divided into two subblocks: mapped and modulated subblocks. Thereafter, the bits within the mapped subblock are used to select one of the predefined spreading codes, which is then used to spread the modulated bits of the second subblock. In this design, using the spreading code index as an information-bearing unit increases the overall spectral efficiency of this system. At the receiver side, the spreading code index is first estimated, thus resulting in a direct estimation of mapped subblock bits. Consequently, the corresponding spreading code to this estimated index is used to despread the modulated symbol of the modulated subblock. Subsequently, mathematical expressions for bit error rate (BER), symbol error rate (SER), throughput, energy efficiency, and the system complexity are derived to analyze the system performance. Finally, simulation results show that the proposed modulation scheme can achieve a higher data rate than the conventional DSSS system, with lower energy consumption and complexity.

Probabilistic 16-QAM Shaping in WDM Systems

Abstract: This work proposes a probabilistic shaping scheme for optical WDM systems, where nonlinear interference noise depends on the input optical signal power distribution. With $16$ -QAM, a white Gaussian channel analysis shows that the shaped constellation is able to achieve a reach improvement of up to $7\%$ , while split-step Fourier method simulations suggest that even higher gains are possible in practice. An example system is developed for a transmission distance around $3280$ km. A constellation mapping and a low-density parity-check code are developed for this regime to show a reach improvement of $7.1\%$ . These shaping schemes can also be extended to $64$ -QAM, where a reach improvement of over $10\%$ is expected.

Performance Characterization of Relay-Assisted Wireless Optical CDMA Networks in Turbulent Underwater Channel

Abstract: In this paper, we characterize the performance of relay-assisted underwater wireless optical code division multiple access (OCDMA) networks over turbulent channels. In addition to scattering and absorption effects of underwater channels, we also consider optical turbulence as a log-normal fading coefficient in our analysis. To simultaneously and asynchronously share medium among many users, we assign a unique optical orthogonal code (OOC) to each user in order to actualize OCDMA-based underwater network. The most significant challenge in underwater optical communication is in the ability to extend the short range of its coverage. In order to expand the viable communication range, we consider multi-hop transmission to the destination. Moreover, we evaluate the performance of a relay-assisted point-to-point UWOC system as a special case of the proposed relay-assisted OCDMA network. Our numerical results indicate significant performance improvement by employing intermediate relays, e.g., one can achieve 32 dB improvement in the bit error rate (BER) of $\text{10}^\text{-6}$ using only a dual-hop transmission in a 90 m point-to-point clear ocean link.

Underwater wireless transmission of high-speed QAM-OFDM signals using a compact red-light laser.

Abstract: We first study the transmission property of red light in water in terms of extinction coefficient and channel bandwidth via Monte Carlo simulation, with an interesting finding that red light outperforms blue-green light in highly turbid water. We further propose and experimentally demonstrate a broadband underwater wireless optical communication system based on a simple and cost-effective TO56 red-light laser diode. We demonstrate a 1.324-Gb/s transmission at a bit error rate (BER) of 2.02 × 10-3 over a 6-m underwater channel, by using 128-QAM OFDM signals and a low-cost 150-MHz positive-intrinsic-negative photodetector, with a record spectral efficiency higher than 7.32 bits/Hz. By using an avalanche photodetector and 32-QAM OFDM signals, we have achieved a record bit rate of 4.883 Gb/s at a BER of 3.20 × 10-3 over a 6-m underwater channel.

NR-DCSK: A Noise Reduction Differential Chaos Shift Keying System

Abstract: One of the major drawbacks of the conventional differential chaos shift keying (DCSK) system is the addition of channel noise to both the reference signal and the data-bearing signal, which deteriorates its performance. In this brief, we propose a noise reduction DCSK system as a solution to reduce the noise variance present in the received signal in order to improve performance. For each transmitted bit, instead of generating $\beta$ different chaotic samples to be used as a reference sequence, $\beta/P$ chaotic samples are generated and then duplicated $P$ times in the signal. At the receiver, $P$ identical samples are averaged, and the resultant filtered signal is correlated to its time-delayed replica to recover the transmitted bit. This averaging operation of size $P$ reduces the noise variance and enhances the performance of the system. Theoretical bit error rate expressions for additive white Gaussian noise and multipath fading channels are analytically studied and derived. Computer simulation results are compared to relevant theoretical findings to validate the accuracy of the proposed system and to demonstrate the performance improvement compared to the conventional DCSK, the improved DCSK, and the differential-phase-shift-keying systems.

MMSE precoder for massive MIMO using 1-bit quantization

Abstract: We propose a novel linear minimum-mean-squared-error (MMSE) precoder design for a downlink (DL) massive multiple-input-multiple-output (MIMO) scenario. For economical and computational efficiency reasons low resolution 1-bit digital-to-analog (DAC) and analog-to-digital (ADC) converters are used. This comes at the cost of performance gain that can be recovered by the large number of antennas deployed at the base station (BS) and an appropiate pre-coder design to mitigate the distortions due to the coarse quantization. The proposed precoder takes the quantization non-linearities into account and is split into a digital precoder and an analog precoder. We formulate the two-stage precoding problem such that the MSE of the users is minimized under the 1-bit constraint. In the simulations, we compare the new optimized precoding scheme with previously proposed linear precoders in terms of uncoded bit error ratio (BER).

Iterative Detection and Decoding Algorithms for MIMO Systems in Block-Fading Channels Using LDPC Codes

Abstract: We propose iterative detection and decoding (IDD) algorithms with low-density parity-check (LDPC) codes for multiple-input multiple-output (MIMO) systems operating in block-fading and fast Rayleigh fading channels. Soft-input–soft-output minimum-mean-square-error (MMSE) receivers with successive interference cancelation are considered. In particular, we devise a novel strategy to improve the bit error rate (BER) performance of IDD schemes, which takes into account the soft a posteriori output of the decoder in a block-fading channel when root-check LDPC codes are used. A MIMO IDD receiver with soft information processing that exploits the code structure and the behavior of the log-likelihood ratios is also developed. Moreover, we present a scheduling algorithm for decoding LDPC codes in block-fading channels. Simulations show that the proposed techniques result in significant gains in terms of BER for both block-fading and fast-fading channels.

Nonlinear Digital Pre-distortion of Transmitter Components

Abstract: We present a linear and nonlinear digital pre-distortion (DPD) tailored to the components of an optical transmitter. The DPD concept uses nonlinear models of the transmitter devices, which are obtained from direct component measurements. While the digital-to-analog converter and driver amplifier are modeled jointly by a Volterra series, the modulator is modeled independently as a Wiener system. This allows for a block-wise compensation of the modulator by a Hammerstein system and a pre-distortion of the electrical components by a second Volterra series. In simulations and extensive experiments, the performance of our approach for nonlinear DPD is compared to an equivalent linear solution as well as to a configuration without any DPD. The experiments were performed using M -ary quadrature-amplitude modulation ( M -QAM) formats ranging from 16- to 128-QAM at a symbol rate of 32 GBd. It is shown that the DPD improves the required optical signal-to-noise ratio at a bit error ratio of 2·10 −2 by at least 1.2 dB. Nonlinear DPD outperforms linear DPD by an additional 0.9 and 2.7 dB for higher-order modulation formats such as 64-QAM and 128-QAM, respectively.

Constellation Shaping for WDM Systems Using 256QAM/1024QAM With Probabilistic Optimization

Abstract: In this paper, probabilistic shaping is numerically and experimentally investigated for increasing the transmission reach of wavelength division multiplexed (WDM) optical communication systems employing quadrature amplitude modulation (QAM). An optimized probability mass function (PMF) of the QAM symbols is first found from a modified Blahut–Arimoto algorithm for the optical channel. A turbo coded bit interleaved coded modulation system is then applied, which relies on many-to-one labeling to achieve the desired PMF, thereby achieving shaping gains. Pilot symbols at rate at most 2% are used for synchronization and equalization, making it possible to receive input constellations as large as 1024QAM. The system is evaluated experimentally on a 10 GBd, 5 channels WDM setup. The maximum system reach is increased w.r.t. standard 1024QAM by 20% at input data rate of 4.65 bits/symbol and up to 75% at 5.46 bits/symbol. It is shown that rate adaptation does not require changing of the modulation format. The performance of the proposed 1024QAM shaped system is validated on all 5 channels of the WDM signal for selected distances and rates. Finally, it is shown via EXIT charts and BER analysis that iterative demapping, while generally beneficial to the system, is not a requirement for achieving the shaping gain.

Semi-coherent Detection and Performance Analysis for Ambient Backscatter System

Abstract: We study a novel communication mechanism, ambient backscatter, that utilizes radio frequency (RF) signals transmitted from an ambient source as both energy supply and information carrier to enable communications between low-power devices. Different from existing non-coherent schemes, we here design the semi-coherent detection, where channel parameters can be obtained from unknown data symbols and a few pilot symbols. We first derive the optimal detector for the complex Gaussian ambient RF signal from likelihood ratio test and compute the corresponding closed-form bit error rate (BER). To release the requirement for prior knowledge of the ambient RF signal, we next design a suboptimal energy detector with ambient RF signals being either the complex Gaussian or the phase shift keying (PSK). The corresponding detection thresholds, the analytical BER, and the outage probability are also obtained in closed-form. Interestingly, the complex Gaussian source would cause an error floor while the PSK source does not, which brings nontrivial indication of constellation design as opposed to the popular Gaussian-embedded literatures. Simulations are provided to corroborate the theoretical studies.

On the Performance of Adaptive MIMO-OFDM Indoor Visible Light Communications

Abstract: In this letter, we propose an adaptive indoor multiple input and multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) system using a receiver module with angular diversity. In order to improve the capacity of indoor MIMO-OFDM VLC systems, tilted receivers are utilized to increase channel diversity, thus reducing channel correlation. With the help of singular value decomposition-based technique, which decomposes the MIMO VLC channels into independent parallel sub-channels, adaptive resource allocation, namely, bit and power loading, is used for these sub-channels to further improve the proposed system’s capacity. Based on a $4\times 4$ indoor MIMO-OFDM VLC system, we investigate bit error rate (BER) performance of the proposed adaptive system with different polar angles in two typical indoor scenarios. Numerical simulation results show that with 50-MHz modulation bandwidth, average BER can be improved from $4.97\times 10^{\mathrm {-3}}$ to $1.66\times 10^{\mathrm {-5}}$ and from $1.90\times 10^{\mathrm {-3}}$ to $1.59\times 10^{\mathrm {-6}}$ for the two scenarios, respectively.

Shuffled Multiuser Detection Schemes for Uplink Sparse Code Multiple Access Systems

Abstract: The existing multiuser detection schemes for uplink (UP) sparse code multiple access (SCMA) systems are based on a parallel message update for message passing algorithm (MPA). In this letter, a shuffled MPA (S-MPA) scheme for UP SCMA systems is proposed, based on a serial message update strategy. Since the updated messages can join the message propagation immediately in current iteration, the convergence rate is accelerated, so that the complexity of the proposed S-MPA scheme can be substantially reduced with negligible bit error rate (BER) degradation. Simulations show that the proposed S-MPA scheme with two iterations provides similar BER performance to the original MPA scheme with six iterations. Furthermore, a parallel form of the proposed S-MPA scheme, termed group S-MPA, is developed to decrease the detection delay of the proposed S-MPA scheme, which offers a good BER-latency tradeoff.

System Design and Performance Analysis of Orthogonal Multi-Level Differential Chaos Shift Keying Modulation Scheme

Abstract: A novel non-coherent multi-level differential chaos shift keying (DCSK) modulation scheme is proposed in this paper. This new scheme is based on both the transmitted-reference technique and $M$ -ary orthogonal modulation, where each data-bearing signal is chosen from a set of orthogonal chaotic wavelets constructed by a reference signal. Thanks to this signaling design, the new scheme can achieve a higher attainable data rate, lower energy loss in reference transmission, increased bandwidth efficiency, better data security and better bit error rate (BER) performance as compared to the conventional DCSK. Unlike other DCSK-based systems that separate the reference and data-bearing signals using the TDMA scheme, this new system employs I/Q channels to send these two signals in a parallel and simultaneous manner, making the system easily extendable to multi-carriers. This transmission mechanism not only can further increase data rate but also can remove all radio frequency delay lines from detectors. Analytical BER expressions of the proposed system are derived for both additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. Relevant simulation results are given and compared to non-coherent binary/ $M$ -ary DCSK systems. In addition, the impacts of various system parameters on noise performance are discussed. Both theoretical analysis and simulation results confirm the promising benefits of the new design.