Symbol Synchronization Algorithm Research Articles

Robust Symbol and Frequency Synchronization Method for Burst OFDM Systems in UAV Communication

This paper introduces a robust synchronization method for orthogonal frequency division multiplexing (OFDM) in multi-unmanned aerial vehicle (UAV) communication systems, focusing on minimizing overhead while achieving reliable synchronization. The proposed synchronization scheme enhances both frame efficiency and implementation simplicity. Initially, a high-efficiency frame structure is designed without a guard time interval, utilizing a preamble sequence to simultaneously achieve both symbol synchronization and automatic gain control (AGC) before demodulation. Subsequently, a novel 2-bit non-uniform quantization method for the Zadoff–Chu sequences is developed, enabling the correlation operations in the traditional symbol synchronization algorithm to be implemented via bitwise exclusive OR (XOR) and addition operations. The complexity of hardware implementation and the energy consumption for symbol synchronization can be reduced significantly. Furthermore, the impact of AGC on frequency synchronization performance is examined, and an improved frequency synchronization method based on AGC gain compensation is proposed. Finally, the performance of the proposed method is rigorously analyzed and compared with that of the traditional method through computer simulations, demonstrating the effectiveness and superiority of the proposed approach.

An MPSK Millimeter-Wave Point-to-Point Link With Radio Over Fiber Synchronous Baseband Receiver

This paper demonstrates a millimeter-wave point-to-point radio link of MPSK (QPSK, 8-PSK, and 16-PSK) modulation without using any analog to digital converter (ADC). The proposed point-to-point radio link, not only use the radio over fiber (RoF) concept to extend the transmit distance of the central unit and the remote radio unit, but also use the clock and data recovery (CDR) applied in the optical-electrical converter (OEC) to recover the MPSK intermediate frequency (IF) signals frequency offset. Compared with the traditional RoF link, the proposed point-to-point synchronous radio link eliminated the high-speed ADC requirement for the digital-intermediate-frequency-over-fiber (DIFoF) link, which can significantly reduce the complexity and the cost of the remote radio unit. Simultaneously, we have designed a simple symbol synchronization algorithm to realize the real-time point-to-point radio link on an Field Programmable Gate Array (FPGA). The proposed millimeter-wave radio link has successfully demonstrated 6 Gbps QPSK transmission and can tolerate a frequency offset up to 100 MHz.

Symbol synchronization algorithm using complex envelop samples without PLL

Symbol synchronization algorithm using complexes envelop samples without PLL was proposed. Two different symbol synchronization algorithms were compared. A dependency of the bit error rate on white gaussian noise is given.

Research and Implementation of Cross-correlation Symbol Synchronization Algorithm for Long Training Sequence Based on OFDM System

Through the analysis of the classic protocol IEEE 802.11a in OFDM system. An OFDM symbol synchronization algorithm based on Long Training Sequence (LTS) is studied. The symbol synchronization estimation using the LTS sequence symbol cross-correlation method can improve the two parameters of the correlation delay D and the synchronization point decision threshold. It reduces the interference of noise on the decision threshold under the Gaussian White Noise (AGWN) channel and the difficulty of FPGA implementation; improves the accuracy of symbol synchronization and the probability of detecting symbol synchronization under a low signal-to-noise ratio. Simulation experiments and FPGA hardware implementation show that compared with conventional algorithms, the system performance is improved.

High-Precision and Low-Complexity Symbol Synchronization Algorithm Based on Dual-Threshold Amplitude Decision for Real-Time IMDD OFDM-PON

We propose a low-complexity and high-precision symbol synchronization algorithm based on dual-threshold amplitude decision for field programmable gate array-based real-time intensity modulation direct detection orthogonal frequency division multiplexing-passive optical network (OFDM-PON) system. In addition, a new criterion to judge symbol synchronization accuracy is proposed first based on bipolar non-return-to-zero codes in time domain. Experimental results show that 95% synchronization precision rate can be achieved after 25 km standard single-mode fiber transmission with the received optical power as low as –21 dBm. Compared with the previously proposed one threshold symbol synchronization algorithm, the synchronization performance has been greatly improved, which brings a maximum signal bit rate gain of 35% when the received optical power is lower than –16 dBm. Furthermore, it is verified that the proposed algorithm is robust. It has wide transmission range which is applicable for OFDM-PON optical access networks within 100 km and has good sampling frequency offset (SFO) tolerance, which can cover the SFO up to 500 ppm without any discard on synchronization precision rate. Finally, complexity analysis shows that our algorithm has the lowest computational complexity and hardware resource consumption, which account for only 0.9% of system resources without any multipliers.

Enhanced Efficiency BPSK Demodulator Based on One-Dimensional Convolutional Neural Network

In this paper, a novel binary phase shift keying demodulator based on 1-D convolutional neural network (1-D CNN) is proposed. The utilization of neural networks to detect the locations of phase shifts in the modulated data distinguishes the proposed scheme from other neural network demodulators, which decide the symbols corresponding to the sampled data in a symbol period. Meanwhile, coordinating with the symbol synchronization algorithm, the proposed structure is able to deal with the carrier frequency offsets and sampling frequency errors. Compared to the conventional demodulators, the proposed 1-D CNN demodulator presents better bit error rates performance.

A High-Efficiency Multiplierless Symbol Synchronization Algorithm for IEEE802.11x WLANs

This work presents a novel high-efficiency multiplierless symbol synchronization algorithm for IEEE 802.11x wireless local area networks (WLANs). In our proposed scheme, according to IEEE 802.11x specifications, the element of the local known training sequence in the frame header is approximated and represented by its nearest value of integer power of 2. The multiplication in the cross-correlation for OFDM symbol synchronization can be directly reduced to a shift operation. Therefore, the correlator in the OFDM symbol synchronization for IEEE 802.11x WLANs can be economically implemented by merely utilizing the logic resources in hardware without notable performance loss. Since the multiplers and adders are replaced by the simple shifters, the implementation complexity of the correlator is significantly reduced. Experimental results demonstrate that our proposed method can achieve almost the same performance as the original correlation algorithms with multipliers, and has higher correct detection probability than the existing multiplierless technique at given low SNR.

Research on Symbol Synchronization Algorithm of LTE System

This paper designs and realizes algorithm of symbol synchronization for LTE system. In order to validate the feasibility of symbol timing synchronization algorithm, a series of simulations are performed with LTE channel models and the simulation results are analyzed carefully. Simulation shows that this algorithm has a great advantage of system implementation. It can be found the symbol start position within the shortest time.

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.

A Data-Aided Symbol Synchronization Algorithm for OFDM Systems

A Data-Aided Symbol Synchronization Algorithm for OFDM Systems

Burst mode synchronization of QPSK on AWGN channels using kurtosis

This paper explores the use of kurtosis in synchronizing with a QPSK burst transmission. The start and end of the burst are a priori unknown and are detected without the use of pilot signals. After frame level synchronization, signal level synchronization is performed. The symbol timing, carrier frequency and carrier phase are recovered without the assistance of known symbols or synchronization words in the data stream, i.e. totally blind synchronization. The performance of frame, symbol and carrier synchronization algorithms is evaluated through computer simulations.

OFDM symbol synchronization using frequency domain pilots in time domain

In this paper, we describe and evaluate a novel symbol synchronization algorithm for orthogonal frequency division multiplexing (OFDM) systems especially suited for channels with very long echoes. Most of the OFDM based standards provide known pilots in the frequency domain for channel estimation purposes. The basic idea of our contribution consists of interpreting the frequency domain pilots in the time domain to obtain a rough channel estimate before performing the discrete Fourier transform (DFT) and use it to properly position the DFT window. The proposed method aims to maximize the signal-to-inter-block-interference ratio after the DFT windowing. In short channels, where the channel length is shorter than the cyclic prefix length, the proposed method looks for an interblock-interference free windowing of the OFDM symbol. In long channels, where the channel length is longer than the cyclic prefix of the OFDM symbol, the proposed method search for the minimum inter-block-interference power windowing of the OFDM symbol.

Blind Symbol Synchronization Based on Cyclic Prefix for OFDM Systems

In this paper, a blind symbol synchronization algorithm is presented for orthogonal frequency-division multiplexing (OFDM) systems, and a new timing function based on the redundancy of the cyclic prefix (CP) is introduced. It proves that the maximum of this function necessarily points to the correct timing offset, irrespective of channel conditions when the signal-to-noise ratio is high. Using the timing function, the timing offset is estimated through a searching algorithm. Channel power profile and channel length information are unnecessary. Simulation results show that the proposed algorithm is robust and outperforms the existing CP-based algorithms, particularly in frequency-selective fading channels.

A new low-cost demodulator for 2.4 GHz ZigBee receivers

A new low-cost demodulator for ZigBee receivers satisfying requirements of IEEE802.15.4 standard is presented, which is designed for ISM 2.4 GHz band and based on Zero-IF receivers. This demodulator extracts symbols directly from baseband signal rather than recovering PN code chips, so its structure is simple. Two main techniques are used to improve the performance of demodulator. One is Phase-Axis Crossing Detector (PACD) which detects the phase correlation of baseband signal. The other is symbol synchronization and sampling clock correction algorithm. The result shows that this demodulator performance, Symbol Error Rate (SER) and Packet Error Rate (PER) meet IEEE 802.15.4TM standard requirements and the demodulator can handle frequency offset in excess of 200 kHz, involving a Zero-IF receiver with a Noise Figure (NF) lower than 17 dB, which is easily implemented in standard CMOS technology.

Maximum-likelihood symbol synchronization for IEEE 802.11a WLANs in unknown frequency-selective fading channels

Based on the maximum-likelihood principle and the preamble structure of IEEE 802.11a wireless local area network (WLAN) standard, this paper proposes a new symbol synchronization algorithm for IEEE 802.11a WLANs over frequency-selective fading channels. In addition to the physical channel, the effects of filtering and unknown sampling phase offset are also considered. Loss in system performance due to synchronization error is used as a performance criterion. Computer simulations show that the proposed algorithm exhibits better performances than the simple correlation-based algorithms. When compared to the algorithm based on the generalized Akaike information criterion, the proposed algorithm presents comparable performance and exhibits reduced complexity.

Coarse symbol synchronization algorithms for OFDM systems in multipath channels

A maximum-likelihood (ML) coarse symbol synchronization algorithm for OFDM systems in multipath channels is derived. Several simplifying assumptions reduce the rather impractical ML algorithm to more practical forms of minimum mean-squared-error and maximum correlation algorithms. All of the derived algorithms exploit the cyclic prefix and thus do not require a known training sequence. Estimating the position of the first arriving path, the algorithms allow maximum utilization of the guard interval thus minimizing intersymbol interference.

The effect of non‐ideal interpolation on symbol synchronizer performance

AbstractThis contribution deals with the symbol synchronizer performance of a fully digitally implemented receiver, operating on a narrowband M‐PSK signal (one‐sided bandwidth not exceeding the symbol rate). The considered digital receiver operates on samples of the complex envelope r(t) of the received signal, taken by a fixed clock which is not synchronized to the transmitter clock. The synchronized samples required for the symbol synchronization algorithm are computed by interpolating between the available non‐synchronized samples. Because of finite memory, interpolation is non‐ideal; hence, some amount of distortion is introduced, which affects the performance of the symbol synchronizer. By means of theoretical analysis, we investigate the tracking performance of a specific decision‐directed feedback synchronizer, assuming interpolation of orders zero, one and two. We show that non‐ideal interpolation gives rise to a loop noise spectrum containing spectral lines, that mainly occur near/= 0 when the number of samples per symbol is close to an integer. Unless a sufficiently small loop bandwidth is chosen, the contribution of these spectral lines could dominate the timing error variance, which then becomes much larger than for synchronized sampling.

PSK symbol synchronization performance of ML-oriented data-aided algorithms for nonselective fading channels

Two maximum-likelihood (ML)-oriented data-aided (DA) symbol synchronization algorithms are investigated in this paper. They operate on a noisy M-PSK signal (M>2) transmitted over a slowly time-varying nonselective Rician fading channel. The first algorithm is channel-aided (CA): it makes use of an estimate or the instantaneous channel gain. The second algorithm is nonchannel-aided (NCA): timing is acquired independently of the channel gain estimation. Both algorithms operate either with a known training sequence or in a decision-directed mode, and are suitable for fully digital implementation. We find that the CA algorithm yields a smaller tracking error variance than the NCA algorithm, but the difference in performance decreases with increasing carrier-to-multipath (C/M) ratio. >

Tracking performance of ML-oriented NDA symbol synchronizers for nonselective fading channels

In this paper we investigate the tracking performance or two maximum-likelihood (ML)-oriented nondecision-aided (NDA) symbol synchronization algorithms, operating on a noisy M-PSK signal (M>2) transmitted over a time-varying nonselective Rician fading channel. The first algorithm is nonchannel-aided (CA): timing is acquired independently of the channel gain estimation. The second algorithm is channel-aided (CA): it makes use of (an estimate of) the instantaneous channel gain. As the channel gain estimator requires timing information, use of the CA algorithm implies that the timing and the channel gain must be acquired jointly. Both algorithms are suitable for fully digital implementation, and have a similar complexity. For E/sub 3//N/sub 0/ values of practical interest, we show that the NCA algorithm is to he preferred over the CA algorithm. >

On the synchronizability and detectability of random PPM sequences

The problem of synchronization and detection of random pulse-position modulation (PPM) sequences is investigated under the assumption of perfect slot synchronization. Maximum-likelihood PPM symbol synchronization and receiver algorithms are derived that make decisions based on both soft and hard data; these algorithms are seen to be easily implementable. The author derives bounds on the symbol error probability and the probability of false synchronization that indicate the existence of a severe performance floor, which can be the limiting factor in the overall system performance. The performance floor is inherent in the PPM format and random data and becomes more serious as the PPM alphabet size Q is increased. A way to eliminate the performance floor is suggested by inserting 'special' PPM symbols in the random data stream. >