Symbol Synchronization Research Articles

Synchronization Analysis for Wireless TWRC Operated with Physical-layer Network Coding

Physical-layer network coding (PNC) makes use of the additive nature of the electromagnetic waves to apply network coding arithmetic at the physical layer. With PNC, the destructive effect of interference in wireless networks is eliminated and the capacity of networks can be boosted significantly. This paper addresses a key outstanding issue in PNC: synchronization among transmitting nodes. We first investigate the impact of imperfect synchronization in a 3-node network with a straightforward detection scheme. It is shown that with QPSK modulation, PNC on average still yields significantly higher capacity than straightforward network coding when there are synchronization errors. Significantly, this remains to be so even in the extreme case when synchronization is not performed at all. Moving beyond a 3-node network, we propose and investigate a synchronization scheme for PNC in a general chain network. And we argue that if the synchronization errors can be bounded in the 3-node case, they can also be bounded in the general N-node case. Lastly, we present simulation results showing that PNC is robust to synchronization errors. In particular, for the mutual information performance, there is about 2 dB loss without phase or symbol synchronization.

An Improved Data-Aided Symbol Timing Algorithm for OFDM Systems

Synchronization is very important to orthogonal frequency division multiplexing (OFDM) systems. Taking aim at the problem that the timing inaccuracy of the S&C method and the indistinct peak of the timing metric produced by Park method under the low signal-to-noise ratio (SNR) and fading channel, a new symbol synchronization algorithm based on the training symbol is proposed in this paper. The new algorithm exploits the training symbol proposed by S&C to correlate the received signal with the known training symbol again at the receiving end to identify the start point of the OFDM symbol. The result of the simulation shows that the proposed method’s timing metric is of the impulse-shaped peak under the condition of the lower SNR and multipath fading channel, and has smaller timing errors compared with the conventional method in terms of mean-square error (MSE) of the timing estimator.

Channel length assisted symbol synchronization for OFDM systems in multipath fading channels

Despite the promising role of orthogonal frequency-division multiplexing (OFDM) technology in communication systems, its synchronization in multipath fading channels remains an important and challenging issue. This work describes a novel synchronization algorithm that exploits channel length information for use in OFDM systems. A timing function that can identify the ISI-free region and subsequently the channel length is also developed based on both the redundancy of the cyclic prefix (CP), and the drastic increase in intersymbol interference (ISI) that rises with symbol timing error in multipath fading channels. Knowledge of the channel length information allows the symbol timing to be safely set in the middle of the ISI-free region, without any ISI. Simulation results indicate that the maximum value of the timing function occurs at the correct timing offset when the signal-to-noise ratio (SNR) is high. From low- to medium SNRs, the correct timing offset is guaranteed when the signal power induced by the channel tap is more significant than the noise power. Furthermore, an efficient search algorithm is derived to reduce the search complexity (search time and computation complexity).

A multi-band OFDM ultra-wideband SoC in 90 nm CMOS technology

We present a multi-band orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) system on chip (SoC) for high speed wireless communications. The UWB SoC has a power management scheme to minimize the average power consumption and adopts hardware-efficient parallel processing architecture to reduce the logic gate count of the modem. Specifically, symbol synchronization block is implemented with the signed algorithm; automatic gain control (AGC), carrier frequency offset (CFO) estimation, and preamble delimitation check block share the eight complex multipliers during preamble transmission; and AGC, fast Fourier transform (FFT), symbol synchronization, CFO estimation, and preamble delimitation check blocks share the buffer which contains received symbols. This SoC adopts a 32-bit reduced instruction set computer (RISC) processor for high speed data transaction and supports universal serial bus (USB) 2.0 and secure digital input/output (SDIO) for host interface. The designed SoC is implemented with 90 nm CMOS technology with a core voltage of 1.2 V. The implemented chip size is about 5 mm x 5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> .

다중 반송파 통신 시스템에서 효과적인 CFO와 STO추정 및 보상방법

Orthogonal frequency division multiplexing (OFDM) 환경에서 sample timing offset(STO)과 carrier frequency offset(CFO)은 inter-symbol interference (ISI), inter-carrier interference (ICI) and phase error를 발생 시키는 원인으로 작용하고 있다. OFDM의 특성상 STO와 CFO에 민감하고, 특히 ICI 가 발생될 경우 보상이 어렵다. 또한 보상을 위해 많은 복잡도를 가진 equalizer가 요구된다. 이 논문에서는 블록 파일럿과 동기화 신호를 가지고, feedback방법을 이용해 STO와 CFO의 효과적인 정정 방법을 제시한다. 주파수 축에서 동기화 신호와 pilot을 이용해 추정한 값들을 시간 축으로 피드백 시킨 후, 시간 영역에서 sample & holder의 시간 타이밍과 oscillator의 주파수의 교정을 통해 정정한다. 시뮬레이션 결과 보상기 없이 피드백 구조만으로 STO와 CFO를 보상하여 성능을 개선 시켰다. Sample timing offset (STO) and carrier frequency offset (CFO) are caused by inter-symbol interference (ISI), inter-carrier interference (ICI) and phase error in orthogonal frequency division multiplexing (OFDM) system. OFDM characteristic is sensitive about STO and CFO. So when ICI occurs, compensation is hard and complex equalizer is needed. In this paper, we propose an effective correction method using feedback process with pilot and synchronization symbol. After feedback with estimated value in frequency domain, STO and CFO are corrected by control sample & and holder and oscillator. As a result of simulation, we confirm that STO and CFO can be corrected without equalizer through feedback.

Ultra-dense WDM-PON delivering carrier-centralized Nyquist-WDM uplink with digital coherent detection

We introduce an "ultra-dense" concept into next-generation WDM-PON systems, which transmits a Nyquist-WDM uplink with centralized uplink optical carriers and digital coherent detection for the future access network requiring both high capacity and high spectral efficiency. 80-km standard single mode fiber (SSMF) transmission of Nyquist-WDM signal with 13 coherent 25-GHz spaced wavelength shaped optical carriers individually carrying 100-Gbit/s polarization-multiplexing quadrature phase-shift keying (PM-QPSK) upstream data has been experimentally demonstrated with negligible transmission penalty. The 13 frequency-locked wavelengths with a uniform optical power level of -10 dBm and OSNR of more than 50 dB are generated from a single lightwave via a multi-carrier generator consists of an optical phase modulator (PM), a Mach-Zehnder modulator (MZM), and a WSS. Following spacing the carriers at the baud rate, sub-carriers are individually spectral shaped to form Nyquist-WDM. The Nyquist-WDM channels have less than 1-dB crosstalk penalty of optical signal-to-noise ratio (OSNR) at 2 × 10(-3) bit-error rate (BER). Performance of a traditional coherent optical OFDM scheme and its restrictions on symbol synchronization and power difference are also experimentally compared and studied.

An Adaptive Symbol Synchronization for OFDM Systems Based on PN Sequence-weighted Preamble

An Adaptive Symbol Synchronization for OFDM Systems Based on PN Sequence-weighted Preamble

Symbol Synchronization Exploiting the Symmetric Property in Optical Fast OFDM

We propose a new simple method to achieve precise symbol synchronization using one start-of-frame (SOF) symbol in optical fast orthogonal frequency-division multiplexing (FOFDM) with subchannel spacing equal to half of the symbol rate per subcarrier. The proposed method first identifies the SOF symbol, then exploits the evenly symmetric property of the discrete cosine transform in FOFDM, which is also valid in the presence of chromatic dispersion, to achieve precise symbol synchronization. We demonstrate its use in a 16.88-Gb/s phase-shifted-keying-based FOFDM system over a 124-km field-installed single-mode fiber link and show that this technique operates well in automatic precise symbol synchronization at an optical signal-to-noise ratio as low as 3 dB and after transmission.

A Data-Aided Symbol Synchronization Algorithm for OFDM Systems

A Data-Aided Symbol Synchronization Algorithm for OFDM Systems

Blind Minimum Interference Symbol Synchronization for OFDM Systems in Long ISI Channels

This letter introduces a blind minimum interference symbol synchronization for orthogonal frequency-division multiplexing (OFDM) systems based on the cyclic prefix (CP). The basic idea of our contribution is to obtain an estimate of the channel-tap powers from the correlation characteristics of the CP. Based on the estimate of the channel-tap powers, a minimum interference metric is proposed. The proposed algorithm has low complexity and can be used to cope with long inter-symbol-interference (ISI) channels with length up to twice the CP length.

Re-configurable digital receiver for optically envelope detected half cycle BPSK and MSK radio-on-fiber signals

We present the first known integration of a digital receiver into optically envelope detection radio-on-fiber systems. We also present a re-configurable scheme for two different types of optically envelope detected wireless signals while keeping the complexity of used optical components low. Our novel digital receiver consists of a digital signal processing unit integrating functions such as filtering, peak-powers detection, symbol synchronization and signal demodulation for optically envelope detected half-cycle binary phase-shift-keying and minimum-shift-keying signals. Furthermore, radio-frequency signal down-conversion is not required in our proposed approach; simplifying evens more the optical receiver front-end. We experimentally demonstrate error-free optical transmission (bit-error rate corresponding to 10 −3 related to FEC-compatible levels) for both 416.6 Mbit/s half-cycle binary phase-shift-keying and 104.17 Mbit/s minimum-shift-keying radio-frequency modulated signals after 30 km of fiber transmission.

Symbolic dynamics and synchronization of coupled map networks with multiple delays

We use symbolic dynamics to study discrete-time dynamical systems with multiple time delays. We exploit the concept of avoiding sets, which arise from specific non-generating partitions of the phase space and restrict the occurrence of certain symbol sequences related to the characteristics of the dynamics. In particular, we show that the resulting forbidden sequences are closely related to the time delays in the system. We present two applications to coupled map lattices, namely (1) detecting synchronization and (2) determining unknown values of the transmission delays in networks with possibly directed and weighted connections and measurement noise. The method is applicable to multi-dimensional as well as set-valued maps, and to networks with time-varying delays and connection structure.

Basic Simulation Models of Phase Tracking Devices Using MATLAB

The Phase-Locked Loop (PLL), and many of the devices used for frequency and phase tracking, carrier and symbol synchronization, demodulation, and frequency synthesis, are fundamental building blocks in today's complex communications systems. It is therefore essential for both students and practicing communications engineers interested in the design and implementation of modern communication systems to understand and have insight into the behavior of these important and ubiquitous devices. Since the PLL behaves as a nonlinear device (at least during acquisition), computer simulation can be used to great advantage in gaining insight into the behavior of the PLL and the devices derived from the PLL. The purpose of this Synthesis Lecture is to provide basic theoretical analyses of the PLL and devices derived from the PLL and simulation models suitable for supplementing undergraduate and graduate courses in communications. The Synthesis Lecture is also suitable for self study by practicing engineers. A significant component of this book is a set of basic MATLAB-based simulations that illustrate the operating characteristics of PLL-based devices and enable the reader to investigate the impact of varying system parameters. Rather than providing a comprehensive treatment of the underlying theory of phase-locked loops, theoretical analyses are provided in sufficient detail in order to explain how simulations are developed. The references point to sources currently available that treat this subject in considerable technical depth and are suitable for additional study.

Transparent Amplify-and-Forward Relaying in MIMO Relay Channels

In this paper, we investigate the performance of a single-relay assisted cooperative link, where the source, relay, and destination terminals are equipped with multiple transmit and receive antennas. We focus on the so-called transparent amplify-and-forward (T-AaF) for MIMO relay channels, in which the relay requires neither channel state information (CSI) nor synchronization of symbols or carrier. Specifically, we propose and analyze new selection schemes, where the relay, based on the received signal energies, selects the "best" received signal on the S → R hop and forwards it to the destination terminal with either repetitive or selective transmission. Through the derivation of pairwise error probability (PEP) expressions and asymptotic order of diversity (AOD) analysis, we demonstrate that the proposed selection schemes preserve full diversity order, while maintaining low complexity implementation, which makes them attractive from a practical point of view. Furthermore, we show that adopting selective transmission on the R → D hop provides better performance, better throughput, and significantly better energy efficiency than repetitive transmission. A Monte Carlo simulation study is also presented to corroborate the analytical results and to provide detailed performance comparisons between the two schemes under consideration.

Real-time experimental demonstration of optical OFDM symbol synchronization in directly modulated DFB laser-based 25km SMF IMDD systems

A simple optical OFDM (OOFDM) synchronization technique utilizing subtraction and Gaussian windowing at the symbol rate is proposed and implemented in FPGA-based OOFDM receivers. End-to-end real-time symbol synchronization of 128-QAM-encoded OOFDM signals at raw bit rates of 6.56Gb/s is experimentally demonstrated, for the first time, over directly modulated DFB laser-based 25km SMF intensity modulation and direct detection (IMDD) systems. Experimental investigations show that the proposed synchronisation technique offers a number of salient advantages including low complexity, fast tracking speed, high accuracy and suitability for high-capacity optical transmission systems.

Synchronization and correction of channel parameters for an OFDM-based communication system

A review and description of synchronization problems that occur in communication systems based on OFDM (orthogonal frequency division multiplexing) are presented. Solutions for symbol, frame, and frequency synchronization are covered. An account is given and results are presented of the simulation of devices for the estimation of the channel parameters. Results on the simulation of communication systems employing different methods for synchronization and estimation of the channel parameters are presented. A review of the influence of additive noise, multipath propagation, and Rayleigh fading on the synchronization is given.

Real-Time 2.5 GS/s Coherent Optical Receiver for 53.3-Gb/s Sub-Banded OFDM

A real-time receiver for the coherent optical orthogonal frequency-division multiplexing (CO-OFDM) detection is realized in a field-programmable gate array (FPGA). Each building block of the CO-OFDM receiver, such as symbol synchronization, channel estimation, and phase estimation is described and discussed in respect of special technical requirements of real-time implementation. The real-time receiver is successfully demonstrated with a receiver sampling rate of 2.5-Gsamples/s to receive a subband of 53.3-Gb/s multiband CO-OFDM signal. The measured bit error rate (BER) is as low as 3.7 × 10-8 which is a record in real-time or offline CO-OFDM demonstration.

On a ZCZ Code Including a Sequence Used for a Synchronization Symbol

This paper presents a ZCZ code which are combinedly used for spreading sequences and a synchronization symbol in quasi-synchronous CDMA systems using PSK, ASK or BFSK. Furthermore a simple matched filter is presented, which simultaneously calculates correlations with any sequences in the ZCZ code.

A survey of error-correcting codes for channels with symbol synchronization errors

We present a comprehensive survey of error-correcting codes for channels corrupted by synchronization errors. We discuss potential applications as well as the obstacles that need to be overcome before such codes can be used in practical systems.

Glenn Research Center quantum communicator receiver design and development

We investigate, design, and develop a prototype real-time synchronous receiver for the second-generation quantum communicator recently developed at the National Aeronautics and Space Administration (NASA) Glenn Research Center. This communication system exploits the temporal coincidences between simultaneously fired low-power laser sources to communicate at power levels several orders of magnitude less than what is currently achievable through classical means, with the ultimate goal of creating ultra-low-power microsize optical communications and sensing devices. The proposed receiver uses a unique adaptation of the early-late gate method for symbol synchronization and a newly identified 31-bit synchronization word for frame synchronization. This receiver, implemented in a field-programmable gate array (FPGA), also provides a number of significant additional features over the existing non-real-time experimental receiver, such as real-time bit error rate (BER) statistics collection and display, and recovery and display of embedded textual information. It also exhibits an indefinite run time and statistics collection.