Symbol Period Research Articles

MRBNS: a new energy-efficient communication scheme in low power wireless networks

A new energy-efficient communication scheme has been proposed based on a novel source coding technique along with the idea of silent communication, so that the frequencies of occurrences of different symbols in the encoded message become very asymmetric. Keeping the symbol period with the highest frequency of occurrence as silent during transmission, we achieve substantial savings of transmitter and receiver energies by using a hybrid FSK-ASK modulation/demodulation technique. We also design the corresponding protocols for transmission and reception of messages and evaluate their performances to compare with other existing techniques. Our results demonstrate that for additive white Gaussian noise in channels, on an average, the transmitter side energy is reduced by about 53%, while at the receiver side there is about 17.2% savings. Due to the savings of both transmitter and receiver energies, our proposed scheme is particularly suitable for multi-hop communication in low power wireless networks.

Covert Communication Gains From Adversary’s Ignorance of Transmission Time

The recent square root law (SRL) for covert communication demonstrates that Alice can reliably transmit $\mathcal {O}(\sqrt {n})$ bits to Bob in $n$ uses of an additive white Gaussian noise (AWGN) channel while keeping ineffective any detector employed by the adversary; conversely, exceeding this limit either results in detection by the adversary with high probability or non-zero decoding error probability at Bob. This SRL is under the assumption that the adversary knows when Alice transmits (if she transmits); however, in many operational scenarios, he does not know this. Hence, here, we study the impact of the adversary’s ignorance of the time of the communication attempt. We employ a slotted AWGN channel model with $T(n)$ slots each containing $n$ symbol periods, where Alice may use a single slot out of $T(n)$ . Provided that Alice’s slot selection is secret, the adversary needs to monitor all $T(n)$ slots for possible transmission. We show that this allows Alice to reliably transmit $\mathcal {O}(\min \{({n\log T(n)})^{1/2},n\})$ bits to Bob (but no more) while keeping the adversary’s detector ineffective. To achieve this gain over SRL, Bob does not have to know the time of transmission provided $T(n) , $c_{\mathrm{ T}}=\mathcal {O}(1)$ .

Performance Analysis of 32 QAPM System with SC Diversity in Rician Fading Channel

Objectives: Due to demand QoS Service according to advancing the IOT technique, it is necessary to study a new modulation technique to improve the data throughput while maintaining the property of IEEE 802.15.4 radio. Methods/Statistical Analysis: To improve the data throughput of low-power radio, a proposed method adopts QAPM modulation and SC diversity. It makes the radio possible to enhance BER by reducing the influence of white noise and deep fading without additional power consumption. Findings: A core of proposed method is securing the hamming distance by degrading modulation level, reducing the influence of fading by selecting the superior signal and saving the power by having a silenceperiod for a half period of symbol. As a result, the proposed method makes it possible to achieve BER enhancement and power gain. Especially, the proposed method has the advantage that a BER performance can be further improved with increasing fading depth. Improvements/Applications: By introducing proposed method, it is expected to improve the utilization of QoS service in near field communication like WBAN.

Enabling simultaneous cooling and data transmission in the terahertz band for board-to-board communications

A system enabling simultaneous cooling and board-to-board communications is proposed and analyzed. It is shown that hollow pipes used in computer cooling systems can be applied for communications with extreme data rates at distances up to tens of centimeters. This is done by using wireless communications in the terahertz frequency band, 0.1–10THz. The experiments were performed in order to observe how straight and curved pipes of different diameters and lengths affect THz signals propagating inside the pipes. The measured pulses were recorded and used in numerical evaluation of bit error rate and throughput taking into account the effect of all possible combinations of N previous symbols. The numerical results show the dependency of the intersymbol interference on the delay profile of the channel and on the symbol period. The results demonstrate that even with simple on–off keying modulation the throughput reaches few terabits per second with qualitatively low bit error rates. This enables communications between rate-hungry electronics inside computers such as central and graphical processing units while simultaneously providing the cooling functionality.

Joint CD and PMD monitoring based on a pair of low-bandwidth coherent receivers.

A joint chromatic dispersion (CD) and 1st order polarization mode dispersion (PMD) monitoring technique for both a coherent and a non-coherent single carrier system based on a pair of cost effective low-bandwidth coherent receivers is proposed and experimentally demonstrated. By jointly detecting the narrow band around ± 1/2 baud rate, the CD and PMD can be estimated simultaneously by time domain correlation and Stokes space rotational angle recovery, respectively. The CD estimation range is theoretically infinite and the PMD estimation range is limited to the maximum of 1/2 symbol period. Simulation results show that for a 28 G baud dual-polarization (DP)-16QAM transmission system, with dual 1 GHz coherent receivers, the monitoring error for CD and differential group delay (DGD) is 30 ps/nm and 0.5 ps, respectively. We also experimentally verified it for a 12 GBit/s NRZ-OOK transmission system with a full-bandwidth coherent receiver and two 1 GHz digital filters to simulate dual 1 GHz coherent receivers. The monitoring error for CD and DGD is 60 ps/nm and 1.5 ps, respectively.

Joint tracking and equalization scheme for multi-polarization effects in coherent optical communication systems.

We propose a joint multi-polarization-effect tracking and equalization method based on two extended Kalman filters, which can cope with state of polarization (SOP) tracing, polarization demultiplexing, equalization for polarization dependent loss (PDL) and polarization mode dispersion (PMD) in PDM-M-QAM coherent optical communication system. The mathematical model of the proposed method is given and analyzed in detail. Through simulation, the proposed method is proved to be very effective in a 28 Gbaud/s PDM-16QAM system. With the proposed method, SOP tracing speed is up to 110 Mrad/s for azimuth angle and 1200 krad/s for phase angle, respectively, and PDL and PMD can be equalized simultaneously in the values of 10 dB and more than half of the symbol period.

Efficient estimation and compensation of Doppler shift for multicarrier signals in underwater acoustic communications

Orthogonal frequency division multiplexed (OFDM) carriers are well studied in literature for their ability to tolerate multipath effects in the presence of ambient noise in an underwater acoustic (UWA) channel. However UWA Doppler destroys the orthogonality of subcarriers, resulting in severely degraded Signal to Noise ratio (SNR). To mitigate this effect, we present a novel method for Doppler estimation and compensation over this channel. This method involves transmitting a training preamble of up to three OFDM symbols. Doppler estimation is carried out based on a sliding window correlation over an OFDM symbol period between the received and local copy of time samples. After rejecting spurious peaks, the correlation values are normalized and existence of Doppler detected when the correlation value exceeds a set threshold. The Doppler shift is then estimated post FFT. Specifically the phase angle of received pilot samples is averaged over three OFDM symbols. This estimated shift is used to compensate the ...

Feasibility of multi‐carrier modulation signals as new illuminators of opportunity for passive radar: orthogonal frequency division multiplexing versus filter‐bank multi‐carrier

In this study, the feasibility of multi-carrier modulation signals for passive radar is investigated. The illuminators of opportunity involve orthogonal frequency division multiplexing (OFDM) and filter-bank multi-carrier (FBMC). Average ambiguity functions (AAFs) of OFDM and FBMC are derived in the similar expressions, while the discrepancies differ at the prototype filters and symbol periods. Simulation results validate the derivation of AAF and demonstrate that (i) both OFDM and FBMC are nearly perfect illuminators of opportunity in passive coherent location systems owing to their thumbtack-shaped ambiguity function; (ii) the time delay resolutions of OFDM, CP–OFDM (cyclic prefix-OFDM) and FBMC are all extraordinary because of the broadband property, despite the existence of two sidelobes as a consequence of CP insertion for CP–OFDM; (iii) the Doppler shift resolution is affected by the CP length and prototype filter designs, thus FBMC's Doppler bandwidth is larger than OFDM and CP–OFDM's Doppler bandwidth, but FBMC guarantees no existence of sidelobes due to the use of specially designed prototype filter. Therefore, multi-carrier modulation signals are attractive new candidates for passive radar surveillance.

Chaotic direct-sequence spread-spectrum with variable symbol period: A technique for enhancing physical layer security

In chaotic direct-sequence spread-spectrum (DSSS) technique, chaotic sequences with typical properties such as aperiodic variation, wideband spectrum, good correlation, and initial condition sensitivity have been used as spreading codes in order to improve the security at physical layer. However, a number of recent studies have proved that an intruder can recover chaotic sequences by blind estimation methods and use the sequences to detect symbol period, which will result in the original data being exposed. To overcome this security weakness, this paper proposes a novel chaotic DSSS technique, where the symbol period is varied according to behavior of the chaotic spreading sequence in the communication process. The data with variable symbol period is multiplied with the chaotic sequence to perform the spread-spectrum process. Discrete-time models for the spreading scheme with variable symbol period and the despreading scheme with sequence synchronization are presented and analyzed. Multiple-access performance of the proposed technique in the presence of the additional white Gaussian noise (AWGN) is calculated by means of both theoretical derivation and numerical computation. Computer simulations are carried out and simulated performances are shown to verify the estimated ones. Obtained results point out that our proposed technique can protect the DSSS systems against the detection of symbol period from the intruder, even if he has full information on the used chaotic sequence.

Rate‐varying space‐time coding scheme for multiple‐input multiple‐output fading channel with zero‐forcing receiver

In this study, a rate-varying space-time pre-coding scheme for a multiple-input multiple-output system in a fast-fading channel is proposed. In particular, unlike the traditional fixed rate space-time coding scheme, the transmitter which has no channel state information keeps choosing a pre-coding matrix randomly at each space-time symbol period to deliver the information until it is successfully decoded by the receiver. Since the number of received symbol vectors needed to successfully decode the information is determined by the channel realisation, the coding rate of the proposed scheme can adapt to the fast-fading channel. The exact expression of the equivalent signal-to-noise ratio gain after the post-combining and zero-forcing equalisation at the receiver side is derived, and a design criteria to achieve optimal performance in terms of average error probability and ergodic capacity under the mean power constraint is provided. Based on this, a minimal variance pre-coding (MVP) scheme is designed, which is compared with an intuitive Gaussian pre-coding scheme. It is shown that the MVP scheme has better performance and could adapt to different channel conditions.

A Wavelet Multiplexing to Reduce Phase Noise Effects in OFDM based DVB-t

Orthogonal Frequency Division Multiplexing (OFDM) is a highly recommended multiplexing/modulation scheme for high data rate communications due to its high spectrum efficiency and robustness against Inter Symbol Interference (ISI). The OFDM is based on dividing the available spectrum into narrow band orthogonal subcarriers and modulating data on each subcarrier. Due to long symbol period, OFDM system is more sensitive to phase noise of the oscillator compared to single carrier systems. The Phase noise of oscillators used in the transmitters & receivers results in two effects, Common Phase Error (CPE) & Inter Carrier Interference (ICI). These effects results in increasing SNR requirement at the receiver to achieve certain BER. The design & simulation of OFDM based DVB-t system with wavelet multiplexing & demultiplexing and analysis of phase noise effects on BER is presented in this paper. The performance of simulated DVB-t system is analysed by considering SNR requirement to achieve certain BER in the presence of oscillator instabilities on AWGN & mobile radio channels. The modelled Wiener phase noise is generated for different 3dB bandwidths of noise spectrum. The simulation results shows that, the SNR required to achieve a bit rate of 10-2 in wavelet multiplexing is around 6dB lower as compared to FFT counterpart. The result also reveal that PAPR is also less, however wavelet multiplexing computational intensive.

Spectral Efficiency of Random Time-Hopping CDMA

Traditionally paired with impulsive communications, time-hopping code-division multiple access (TH-CDMA) is a multiple access technique that separates users in time by coding their transmissions into pulses occupying a subset of $N_ \mathsf {s}$ chips out of the total $N$ included in a symbol period, in contrast with the traditional direct-sequence CDMA (DS-CDMA), where $N_ \mathsf {s}=N$ . This paper analyzes the TH-CDMA with random spreading, by determining whether peculiar theoretical limits are identifiable, with both optimal and suboptimal receiver structures, in particular in the archetypal case of sparse spreading, that is, $N_ \mathsf {s}=1$ . Results indicate that the TH-CDMA has a fundamentally different behavior than DS-CDMA, where the crucial role played by energy concentration, typical of TH, directly relates with its intrinsic uneven use of degrees of freedom.

Costas Loop Homodyne Detection for 20-Gb/s QPSK Signal on the Optical Frequency Synchronous Network

This paper demonstrates a decision-directed, stable and high-sensitivity Costas loop homodyne receiver for 20-Gb/s QPSK signals based on our concept of the “optical frequency synchronous network.” The receiver sensitivity is shown to approach the theoretical shot-noise limit (as degraded by spontaneous emission) and the symbol-error rate is stably measured to be around 10−3 even though the optical signal was chirped by fiber chromatic dispersion and was delayed by 50% of the symbol period. This high-performance phase-locked loop can be realized by utilizing optical frequency stabilized (synchronized) several kilohertz spectral line-width external cavity laser diodes (E-LD's), compensating the frequency modulation (FM) response of the E-LDs, and consisting of only differential mode logical circuits. The compensation of the E-LD's FM response by the loop filter improves the receiver sensitivity by 3 dB.

UHDTV 방송을 위한 공간 변조 다중 안테나 시스템 수신 성능 분석

In this paper, the reception performance of spatial modulation multiple-output multiple-input (MIMO) is analyzed for high speed terrestrial broadcasting. The MIMO scheme is required to reduce the inter symbol interference (ISI) and spatial correlation. The spatial modulation scheme solves the problem of ISI, but the spatial correlation degrades the reception performance of SM scheme. The space-time block coded spatial modulation (STBC-SM) is combined the SM system with space-time block code (STBC) for reducing the effects of the spatial correlation. However, the STBC-SM scheme degrades the spectral efficiency by transmitting same data in the two symbol period. The double space-time transmit diversity with spatial modulation (DSTTD-SM) scheme transmits the data with full antenna combination. To adapt these SM MIMO systems into the terrestrial broadcasting system, the reception performance is analyzed using computer simulation in SUI channel environments.

Jitter floor elimination for blind feedforward/feedback symbol‐timing recovery exploiting the extended zero‐crossing property

SummaryCarrier‐blind and non‐data‐aided recovery of the symbol timing is of paramount importance in digital receivers, that is, detailed knowledge about carrier frequency and phase or any pilot sequence is not necessary for proper operation. In this context, feedforward algorithms are particularly helpful in packet‐oriented systems, where rapid and stable acquisition of the major transmission parameters is essential for subsequent processing stages. On the other hand, feedback algorithms are typically used to track small deviations from the stable equilibrium point. In the current paper, we propose a new approach for blind feedforward and feedback recovery of the symbol timing, which needs just one or two samples per symbol. The method is characterized by a second filter operated in parallel to the receiver‐matched filter. Under Nyquist conditions, exemplified by baseband pulses having a square‐root raised cosine spectrum, this filter exhibits an impulse response satisfying the extended zero‐crossing property, that is, it vanishes for all integer multiples of the symbol period including the origin. Using this idea for symbol‐timing recovery, it is shown that the annoying jitter floor – typical for most timing recovery schemes and caused by inter‐symbol interference – can be avoided irrespective of the selected modulation scheme. Copyright © 2015 John Wiley & Sons, Ltd.

Hybrid Analog-Digital Channel Estimation and Beamforming: Training-Throughput Tradeoff

This paper designs hybrid analog-digital channel estimation and beamforming techniques for multiuser massive multiple input multiple output (MIMO) systems with limited number of radio frequency (RF) chains. For these systems, first we design novel minimum mean square error (MMSE) hybrid analog-digital channel estimator by considering both perfect and imperfect channel covariance matrix knowledge cases. Then, we utilize the estimated channels to enable beamforming for data transmission. When the channel covariance matrices of all user equipments (UEs) are known perfectly, we show that there is a tradeoff between the training duration and throughput. Specifically, we exploit that the optimal training duration that maximizes the throughput depends on the covariance matrices of all UEs, number of RF chains and channel coherence time ($T_c$). We also show that the training time optimization problem can be formulated as a concave maximization problem {for some system parameter settings} where its global optimal solution is obtained efficiently using existing tools. In particular, when the base station equipped with $64$ antennas and $1$ RF chain is serving one single antenna UE, $T_c=128$ symbol periods ($T_s$) and signal to noise ratio of $10$dB, we have found that the optimal training durations are $4T_s$ and $20T_s$ for highly correlated and uncorrelated Rayleigh fading channel coefficients, respectively. The analytical expressions are validated by performing numerical and extensive Monte Carlo simulations.

On Detection in MIMO-OFDM Systems Over Highly Mobile Wireless Channels

High mobility support of multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) systems plays a major role in wireless communication systems. Conventional detection approaches for MIMO-OFDM systems assume the channel is constant for at least one OFDM symbol duration. However, the time variation of the channel on account of mobility over an OFDM symbol period causes a loss of subchannel orthogonality which results in inter-carrier interference. In this paper, we propose the space alternating generalized expectation maximization (SAGE) based signal detection for MIMO-OFDM systems and compared by the zero forcing (ZF), minimum mean square error (MMSE), vertical Bell laboratories layered space-time (VBLAST) detection methods by considering complexity and performance tradeoffs. Simulation results show that the SAGE based detection has comparable performance with the VBLAST while needs lower computational complexity. It is also shown that both SAGE and VBLAST have a clear BER performance advantage over the MMSE and ZF detections. We also investigate the sensitivity of detection MIMO-OFDM signals to channel estimation errors by the application of a simple frequency domain based pilot based channel estimation. It is shown that the superiority of the SAGE scheme is also valid in the case of channel imperfections.

Blind Cyclostationarity-Based Symbol Period Estimation for FSK Signals

In this letter, we propose an algorithm for blind estimation of the symbol period of frequency-shift-keying (FSK) signals affected by fading channels. The algorithm exploits the property of the second-order cyclic moment magnitude to exhibit a change in the peak pattern at a delay equal to the symbol period, which we prove analytically. It has the advantage that it requires neither channel estimation nor carrier recovery, while providing a good performance.

Mitigation of phase noise in all-optical OFDM systems based on minimizing interaction time between subcarriers

A new approach to mitigate the phase noise in all-optical OFDM systems is analytically modeled and numerically demonstrated. The interaction time between subcarriers is minimized by shaping the envelopes of QAM subcarriers and making a delay time between even and odd subcarriers. Return-to-zero (RZ) coding is adopted for shaping the envelopes of subcarriers. In addition, the subcarriers are alternately delayed (AD) by optical time delayers. The performance of an all-optical OFDM system, that implements the proposed technique, is analyzed and simulated. This system has 29 subcarriers with symbol rate of 25Gsymbol/s and is composed of coupler-based inverse fast Fourier transform (IFFT)/fast Fourier transform (FFT) schemes. Each subcarrier is modulated with QAM format before shaping with RZ coding. Due to RZ being more affected by dispersion; a full periodic dispersion map is adopted to keep the total accumulated dispersion low. The results reveal that the nonlinear phase noise (NPN) due to fiber nonlinearity is significantly mitigated when the time delay between the odd and even subcarriers is equal to half the symbol period. The total phase noise variance is reduced from 9.3×10−3 to 6.1×10−3rad2 when employing AD RZ-QAM for a transmission distance of 550km. Furthermore, both the transmission distance and optical signal to noise ratio (OSNR) are improved when compared to all-optical OFDM systems that adopt traditional QAM modulation formats.

Improved symbol rate identification method for on–off keying and advanced modulation format signals based on asynchronous delayed sampling

Symbol rate identification (SRI) based on asynchronous delayed sampling is accurate, cost-effective and robust to impairments. For on–off keying (OOK) signals the symbol rate can be derived from the periodicity of the second-order autocorrelation function (ACF2) of the delay tap samples. But it is found that when applied this method to advanced modulation format signals with auxiliary amplitude modulation (AAM), incorrect results may be produced because AAM has significant impact on ACF2 periodicity, which makes the symbol period harder or even unable to be correctly identified. In this paper it is demonstrated that for these signals the first order autocorrelation function (ACF1) has stronger periodicity and can be used to replace ACF2 to produce more accurate and robust results. Utilizing the characteristics of the ACFs, an improved SRI method is proposed to accommodate both OOK and advanced modulation formant signals in a transparent manner. Furthermore it is proposed that by minimizing the peak to average ratio (PAPR) of the delay tap samples with an additional tunable dispersion compensator (TDC) the limited dispersion tolerance can be expanded to desired values.