Symbol Period Research Articles

On the Robustness to Doppler Rate of the Modified LoRa using two Spreading Factors

In [1], we proposed a modified LoRa using two spreading factors (SF’s) in order to independently set the frequency difference of adjacent LoRa symbols and the LoRa symbol period, and demonstrated that the use of two spreading factors could make it less sensitive to sampling frequency error while enabling low power transmission. In this paper, as an extension of [1], we will show that our scheme has also robustness to the Doppler rate through computer simulations.

Blind Polarization Demultiplexing of Shaped QAM Signals Assisted by Temporal Correlations.

While probabilistic constellation shaping (PCS) enables rate and reach adaption with finer granularity [1], it imposes signal processing challenges at the receiver. Since the distribution of PCS-quadrature amplitude modulation (QAM) signals tends to be Gaussian, conventional blind polarization demultiplexing algorithms are not suitable for them [2]. It is known that independently and identically distributed (iid) Gaussian signals, when mixed, cannot be recovered/separated from their mixture. For PCS-QAM signals, there are algorithms such as [3], [4] which are designed by extending conventional blind algorithms used for uniform QAM signals. In these algorithms, an initialization point is obtained by processing only a part of the mixed signal, which have non-Gaussian statistics. In this paper, we propose an alternative method wherein we add temporal correlations at the transmitter, which are subsequently exploited at the receiver in order to separate the polarizations. We will refer to the proposed method as frequency domain (FD) joint diagonalization (JD) probability aware-multi modulus algorithm (pr-MMA), and it is suited to channels with moderate polarization mode dispersion (PMD) effects. Furthermore, we extend our previously proposed JD-MMA [5] by replacing the standard MMA with a pr-MMA, improving its performance. Both FDJD-pr-MMA and JD-pr-MMA are evaluated for a diverse range of PCS (entropy ) over a first-order PMD channel that is simulated in a proof-of-concept setup. A MMA initialized with a memoryless constant modulus algorithm (CMA) is used as a benchmark. We show that at a differential group delay (DGD) of 10% of symbol period and 18 dB SNR/pol., JD-pr-MMA successfully demultiplexes the PCS signals, while CMA-MMA fails drastically. Furthermore, we demonstrate that the newly proposed FDJD-pr-MMA is robust against moderate PMD effects by evaluating it over a DGD of up to 40% of . Our results show that the proposed FDJD-pr-MMA successfully equalizes PMD channels with a DGD up to 20% of .

Enabling Low Sidelobe Secret Multicast Transmission for mmWave Communication: An Integrated Oblique Projection Approach

The protection of multicast transmission with optimized secrecy in millimeter-wave (mmWave) communication is still an open problem. In this paper, we propose a low sidelobe secret multicast transmission scheme in mmWave communication based on physical layer security techniques. By utilizing oblique projection, we jointly adopt the directional modulation (DM) and the artificial noise (AN) to achieve secret multicast transmission at low computational costs, without jeopardizing the low sidelobe transmitting pattern. Specifically, considering the constraint of multibeam with the channel knowledge of all target users, a primary transmitting weight vector of the base station (BS) is designed to achieve a low sidelobe transmitting pattern. Then, in each symbol period, the transmitting weight vector of the BS is updated by performing a linear transformation on the primary weight vector with a transformation matrix, which is obtained from the oblique projection matrices of all the target users’ channel vectors. In this way, without deteriorating the primary weight vector’s low sidelobe transmitting pattern, the obtained transmitting weight vector synthesizes the expected symbols at the target users and adds randomness to the eavesdroppers at undesired directions. Finally, the simulations demonstrate that our proposed scheme achieves outstanding communication performance for the target users at low computational costs, while keeping the high symbol error rates at the undesired directions.

Intelligent joint multi-parameter optical performance monitoring scheme based on HT images and MT-ResNet for elastic optical network

In elastic optical network (EON), joint multi-parameter optical performance monitoring (OPM) can effectively manage, diagnose, and reduce operational costs for transmission optical links. In this paper, we propose a novel joint monitoring scheme utilizing Hough transform (HT) images combined with multi-task residual neural network (MT-ResNet) for EON. The scheme can realize baud rate identification (BRI), modulation format identification (MFI), residual chromatic dispersion identification (CDI), optical signal-to-noise ratio (OSNR) and residual differential group delay (DGD) estimation at the same time. The HT image is obtained by preprocessing original constellation diagram, which is a key feature of parameter monitoring for EON signals and presents obvious differentiation in parameter space. By optimizing the skip connections in MT-ResNet, we effectively resolve the issue of details information loss or incompleteness caused by the transmission of impaired optical signals in the neural network. The simulation results demonstrate that the identification success rate can reach 100 % for two common BRs, five mainstream MFs, and seven residual CD values with different impairment degrees. The mean absolute errors (MAEs) of OSNR and residual DGD estimates are 0.42 dB and 0.014 times symbol period respectively. The scheme has excellent tolerance for fiber nonlinear effects. In experimental verification, the accuracies of BRI and MFI are 100 %, and the MAEs of corresponding OSNR estimation for PDM-QPSK/16QAM/32QAM are 0.25 dB, 0.36 dB, and 0.40 dB, respectively. Compared with the existing typical schemes, our scheme significantly improves performance and reduces complexity while simultaneously monitoring a large number of parameters.

Joint timing recovery and adaptive equalization based on training sequences for PM-16QAM faster-than-Nyquist WDM systems.

Since the timing error detectors sensitivity (TEDS) of the timing recovery algorithm is close to zero under the singularity condition of azimuth θ about ±π/4 and differential group delay (DGD) about n × 1/2T (n is an odd number, T is the symbol period), it makes the squared Gardner phase detector (SGPD) timing recovery algorithm fail to achieve timing synchronization. What's worse, in the faster-than-Nyquist wavelength division multiplexing (FTN-WDM) systems, the tight filtering introduces inter-symbol-interference (ISI) so severe that the convergence cost of the SGPD timing recovery algorithm is extremely large even under the non-singularity condition. This paper proposes a joint timing recovery and adaptive equalization scheme for FTN coherent systems based on training sequences that could calculate channel matrix and indicate polarization characteristics, thereby avoiding the influence of azimuth on adaptive equalization and polarization demultiplexing (AEPD) embedded in the timing recovery feedback loop. Since embedded AEPD could compensate for most of DGD, the TEDS could be restored and timing synchronization could be achieved under the above adverse conditions. Thanks to the innovative scheme, which equalizes ISI and DGD during the feedback process of the loop, the convergence cost of timing recovery could be reduced with similar computational complexity compared with the conventional one. The simulation results of 128 GBaud polarization multiplexing (PM) 16-quadrature amplitude modulation (QAM) FTN-WDM transmission systems demonstrate that the proposed scheme could stably achieve timing synchronization under the singularity condition. And compared with the conventional scheme, the convergence cost is reduced by at least 42% @ 0.9 acceleration factor. In addition, 40 GBaud PM-16QAM FTN experiment results show that the proposed scheme could not only achieve timing synchronization stably but also exhibit an optical signal-to-noise ratio tolerance gain of 0.8 dB compared with the conventional scheme under 800 km transmission.

The hybrid pulse amplitude width modulation scheme: high efficiency technique for dimmable VLC systems

Abstract Visible-light communications (VLC) is an environmentally friendly optical wireless communication (OWC) technology that operates in the 400–800 THz frequency band. It is currently a critical technology for 5G and 6G wireless indoor applications due to its high data rates, low latency, and superior reliability. Intensity modulated direct detection (IM/DD) is widely used in VLC systems. A channel modulation scheme is designed using L-level pulse modulation techniques such as on–off keying (OOK), amplitude modulation (PAM), position modulation (PPM), and the width modulation (PWM). We introduce a novel hybrid modulation scheme n-M-PAWM based on both PAM and PWM schemes to improve throughput and significantly increase power and spectrum efficiency in VLC communication systems. The performance of our proposed hybrid n-M-PAWM scheme is studied in several aspects, including the number of transmitted bits per symbol, average BER, information rate ratio (IRR), PAPR, bandwidth, and power requirement. In an extremely noisy VLC system, the proposed 2-M-PAWM modulation outperforms both PPWM and PAPM modulation schemes due to its better BER performances. Additionally, we examine the performance of the VLC system in terms of spectral efficiency (SE) using our proposed PAWM-based dimming control system by varying the number of pulses transmitted during one symbol period. We demonstrate through simulation results that our PAWM-based dimming control system performs significantly better compared to the other pulse modulation schemes. All results of this research show that our proposed hybrid PAWM modulation scheme has high potential for VLC technology in indoor and noisy environments.

Co-Efficient Vector Based Differential Distributed Quasi-Orthogonal Space Time Frequency Coding.

Distributed space time frequency coding (DSTFC) schemes address problems of performance degradation encountered by cooperative broadband networks operating in highly mobile environments. Channel state information (CSI) acquisition is, however, impractical in such highly mobile environments. Therefore, to address this problem, designers focus on incorporating differential designs with DSTFC for signal recovery in environments where neither the relay nodes nor destination have CSI. Traditionally, unitary matrix-based differential designs have been used to generate the differentially encoded symbols and codeword matrices. Unitary based designs are suitable for cooperative networks that utilize the amplify-and-forward protocol where the relay nodes are typically required to forego differential decoding. In considering other scenarios where relay nodes are compelled to differentially decode and re-transmit information signals, we propose a novel co-efficient vector differential distributed quasi-orthogonal space time frequency coding (DQSTFC) scheme for decode-and-forward cooperative networks. Our proposed space time frequency coding scheme relaxes the need for constant channel gain in the temporal and frequency dimensions over long symbol periods; thus, performance degradation is reduced in frequency-selective and time-selective fading environments. Simulation results illustrate the performance of our proposed co-efficient vector differential DQSTFC scheme under different channel conditions. Through pair-wise error probability analysis, we derive the full diversity design criteria for our code.

A novel symbol period estimation method of typical digital communication signal based on the characteristics of periodic modulation and mono-frequency

A novel symbol period estimation method of typical digital communication signal based on the characteristics of periodic modulation and mono-frequency

81 Gb/s Dual-Polarization Discrete Eigenvalue Transmission Based on Nonlinear Fourier Transform

We investigated dual-polarization (DP) discrete eigenvalue transmissions and propose to shift the solitons in one polarization by half a symbol period with respect to the soliton train in the other polarization. Simulation results are conducted to illustrate its advantages over conventional schemes. Experiments of a net 81 Gb/s dual-polarization discrete eigenvalue transmissions over 650 km are also demonstrated with the help of DP multi-symbol linear minimum mean-squared error (DP-MS-LMMSE) filters for eigenvalues and b-coefficients.

A Novel Parameter Estimation Method of FHSS Signal with Low SNR

A novel parameter estimation method of frequency hopping spread spectrum (FHSS) signal is proposed. The observed signal is divided into multiple segments and forms an observed matrix, performing FFT on the observed matrix with different segment lengths to obtain the corresponding spectrum matrix. By analyzing the convergence characteristics of the spectrum matrix, the estimation of the symbol period is realized, on this basis, the symbol‐frequency distribution is obtained and its projected spectrum in Frequency‐Amplitude plane is further obtained to select the candidate frequencies. The matrix composed of multiple single frequency signals is constructed according to the candidate frequencies and multiplied with the observed matrix under the segment length of symbol period, then the number of symbols per hopping duration is estimated according to the matrix multiplication result, so as to realize the estimation of the hopping duration, and finally the real hopping frequencies and hopping sequence can be found out from the candidate frequencies. Simulation results are presented to indicate that the proposed method has good estimation performance especially under the condition of low SNR. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Improving the Resistance of AO-OFDM Signal to Fiber Four-Wave Mixing Effect Based on Insertion Guard Interval

In this paper, a method to suppress the impact of the nonlinear effects on an all optical orthogonal frequency division multiplexing (AO-OFDM) system is proposed. By inserting a guard interval (GI), the duty cycle of the optical signal in each symbol period of each subcarrier is decreased, thus generating a ‘zeroed’ temporal. By giving different time delays to the sub-carriers, these ‘zeroed’ temporals and optical signals of the adjacent sub-carriers are interleaved, which reduces the coincidence of the optical signals between the sub-carriers and eliminates the products of the four-wave mixing (FWM) effect to suppress the influence of the nonlinear effect on the system. The simulation results show that for an AO-OFDM system with 32 subcarriers, inserting GI and introducing different delays for each subcarrier can improve the transmission distance by 30 km or enhance the spectral efficiency by 16.7%, considering the 7% hard decision forward error correction (HD-FEC) threshold. Moreover, even when the number of subcarriers is up to 256 and the power of each subcarrier is as high as 0 dBm, our proposed signal optimization scheme can still guarantee that the BER can satisfy the 7% HD-FEC threshold.

Delay Optimization of Conventional Non-Coherent Differential CPM Detection

The conventional non-coherent differential detection of continuous phase modulations (CPM) is quite robust to channel impairments such as phase and Doppler shifts. Its implementation is on top of that simple. It consists in multiplying the received baseband signal by its conjugate version delayed by one symbol period. However it suffers from a signal-to-noise ratio gap compared to the optimum coherent detection. In this letter, we improve the error rate performance of the conventional differential detection by using a delay higher than one symbol period. We derive the trellis description as well as the branch and cumulative metrics that take into account a delay of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> symbol periods. We then determine an optimized delay <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K_{\mathrm {opt}}$ </tex-math></inline-formula> based on the minimum Euclidean distance between two differential signals for some popular CPM formats. The optimized values are confirmed by error rate simulations.

Introduction to Mediumband Wireless Communication

The multipath is unavoidable in radio frequency (RF) wireless communication, and affects almost every element of the communication systems. The impact of multipath on the received signal depends on whether the delay spread (i.e., spread of time delays associated with different multipath components) is large or small relative to the symbol period of the wireless communication system. In narrowband channels, the symbol period is set such that the delay spread is about one tenth (or less) of it. In broadband channels, it is set such that the delay spread is many times greater than the symbol period. In between these two extremes, there appears to exist an important, yet overlooked, class of channels whose delay spread is neither small nor large enough for them to fall into these two basic channel classes. In this paper, we study the effect of multipath on channels that fall in the transitional region between narrowband and broadband referred henceforth as “ <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>mediumband</i></b> ”. This paper shows that mediumband channels possess a distinct channel model, and pose both challenges and opportunities for reliable wireless communication. For instance, mediumband channels enable signalling at a significantly higher rate than that of narrowband channels, but on the flip side, as the degree of mediumband-ness increases, the quality of the channel deteriorates rapidly due to the excessive inter-symbol-interference (ISI). However, mediumband channels have an inherent ability to avoid deep fading, and if designed properly, mediumband wireless communication, which refers to wireless communication through mediumband channels, could be made to be significantly more reliable too.

Transmit Beamforming for Ambient Backscatter Communication Enabled Wireless Body Area Network in Multiuser MISO System

Wireless Body Sensor Network (WBAN) is a promising technology which can provide pervasive E-health services. However, the power consumption of wireless communications in WBAN greatly restricts its applications. Recently Ambient Backscatter Communication (AmBC) technology has been introduced to realize ultra-low power passive wireless communication, thus it is highly desirable for WBAN. In this paper we consider that AmBC, powered by a multi-antenna Base Station (BS), is incorporated in WBAN to achieve ultra-low power intra-WABN communication. To fully exploit the potential of the AmBC in WBAN, the transmit beamforming at BS, the AmBC information symbol period as well as the transmission time allocation are jointly designed, taking into account Quality of Service (QoS) requirement of WBAN and cellular users, and BS power budget. The formulated optimization problem is highly nonconvex and very challenging to solve. To tackle this issue, we employ Inner Approximate (IA) framework to reformulate the original problem and solve it in an iterative manner. Finally, numerical results are provided to show the effectiveness of the proposed algorithm under various of system parameters settings.

A Software and Hardware Cooperation Method for Full Nyquist Rate Transmission Symbol Synchronization at E-Band Wireless Communication.

Compared with the conventional pulse-shaping transmission system, the full Nyquist rate transmission system with large bandwidth is sensitive to the sampling phase. It has only one sample available in one symbol period and is easily interfered by the channel, which does not allow the traditional symbol synchronization methods to be used directly. Another challenge is that the resource utilization for sampling data processing needs to be minimized due to the excessive consumption of the high data throughput in hardware resources. To solve these issues, we propose a symbol synchronization method based on the combination of software and hardware, which mainly includes two processes: Obtaining the initial phase by using Chirp signal and MOE criterion before communication; tracking the real-time phase using an on-line gradient table and frequency domain analysis of known data during communication. Both processes are proceeded with a phase adjustable clock. Through hardware verification, the sampling phase can be kept close to the optimal phase, thus ensuring the accuracy of the sampling data, and improving the system BER performance.

BER performance analysis of asynchronous NOMA with arbitrary phase offset

An asynchronous transmission scenario for non-orthogonal multiple access (NOMA) user signals with arbitrary phase offset is investigated in this paper. To improve the system performance in the user power-balanced conditions, we adopt a synthetic detection method at the receiver, i.e., the jointly optimal maximal likelihood detection aided triangular successive interference cancellation (JO ML-TSIC) method. Analytical bit error rate (BER) solutions are obtained for a two-user case with the optimal, intentional one-half symbol period time delay implemented between the user signals. Furthermore, closed-form BER solutions for the case using the triangular successive interference cancellation (TSIC) detection method are also derived for comparisons. Numerical results show that the JO ML-TSIC receiver for the asynchronous system outperforms the TSIC receiver as well as the synchronous successive interference cancellation (SIC) receiver in all the conditions concerned. The results also show that the superiority of the JO ML-TSIC receiver is strengthened when the signals experience flat Rayleigh fading channels compared to the TSIC and the synchronous SIC receivers.

Mutualistic Mechanism in Symbiotic Radios: When Can the Primary and Secondary Transmissions Be Mutually Beneficial?

In symbiotic radio (SR), a secondary transmitter (STx) transmits messages by modulating its information over the radio frequency (RF) signals received from a primary transmitter (PTx), and in return, the secondary transmission provides multipath gain to the primary transmission. In this paper, we are interested in the fundamental mutualistic mechanism between the primary and secondary transmissions, which describes the condition through which the two systems can benefit each other. Since the symbol period ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> between secondary and primary transmissions is an important system parameter that affects the mutualistic symbiosis, we first derive the theoretical performance in terms of bit error rate (BER) for both primary and secondary transmissions for arbitrary <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> by using QPSK modulation scheme at the PTx and BPSK modulation scheme at the STx as an example setup. Then we the obtain closed-form expressions for the condition on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> to enable mutualistic symbiosis in SR, which is not related to the specific channel realizations but determined by the average strengths of the direct and backscatter links when the number of receiving antennas is large. Meanwhile, we analyze the average BER performance and the diversity orders for both transmissions in the high signal-to-noise-ratio (SNR) regime. Extensive simulations and numerical results are provided to verify the accuracy of our theoretical analysis and demonstrate the interrelationship between the primary and secondary transmissions.

Optimization for faster‐than‐Nyquist signaling based combining under multi‐path channel

SummaryWe propose a faster‐than‐Nyquist (FTN) signaling based combining scheme to increase the achievable rate for the single‐input‐single‐output (SISO) system and the single‐carrier system under the multi‐path channel, where the combining scheme aims to combine the signals received at all symbol periods during the channel length for each transmitted symbol. An important feature of the FTN signaling based combining scheme is that the transmitter ceases the transmission for b symbol periods after transmitting each symbol. By proposing the optimization algorithm for finding the optimum b that maximizes the achievable (information) rate, we propose in this paper the optimal FTN signaling based combining scheme. We first establish the optimization problem and then present a theorem for proving the existence of the optimum b that maximizes the lower bound of the average achievable (information) rate. On the basis of this theorem, we present the steps of the proposed optimization algorithm. Numerical results are provided, and they confirm that the proposed optimization algorithm can find the optimum b.

Dual-Mode Chirp Spread Spectrum Modulation

In this letter, we propose dual-mode chirp spread spectrum (DM-CSS) modulation for low-power wide-area networks. DM-CSS is capable of achieving a higher spectral efficiency (SE) relative to its counterparts, such as Long Range (LoRa) modulation. Considering the same symbol period, the SE in DM-CSS are augmented by: (i) simultaneously multiplexing even and odd chirp signals; (ii) using phase shifts of 0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> radians for both even and odd chirp signals; and (iii) using either up-chirp or down-chirp signal. The SE increases by up to 116.66% for the same bandwidth and spreading factor relative to LoRa. We present a complete transceiver architecture along with non-coherent detection process. Simulation results reveal that DM-CSS is not only more spectral efficient but also more energy efficient than most classical counterparts. It is also demonstrated that DM-CSS is robust to phase and frequency offsets.

Azimuth Estimation for the Backscatter Device in Ambient Backscatter Communication System

In this letter, we study the azimuth estimation for the backscatter device (BD) in ambient backscatter communication system, where the receiver is equipped with the uniform linear array (ULA). By utilizing the covariance matrices in two symbol periods with different BD symbols, we apply the conventional multiple signal classification (MUSIC) algorithm to estimate the azimuths of both the BD and the ambient radio frequency (RF) source. Then, we propose a novel eigenvector-based algorithm to identify the azimuth of the BD from the two estimated azimuths. Moreover, we qualitatively analyze the impacts of the reflection coefficients on the performance of the proposed azimuth estimation approach. Finally, the simulation results are provided to validate the effectiveness of the proposed method and to justify the qualitative analytical conclusions.