Research and Implementation of High-Speed Data Streams Symbol Synchronization Algorithm Using Training Sequence in IMDD-OOFDM System

We propose a symbol synchronization algorithm for high-speed data streams in IMDD-OOFDM system using a training sequence. Sampling point phase offset approximately sustains within ±π/32 and symbol synchronization deviation stabilizes within ±0.5 sampling point in a real-time system of 1.5Gsa/s.

Optimized Doppler Estimation and Symbol Synchronization for Mobile M-ary Spread Spectrum Underwater Acoustic Communication

In mobile underwater acoustic (UWA) communications, the Doppler effect causes severe signal distortion, which leads to carrier frequency shift and compresses/broadens the signal length. This situation has a more severe impact on communication performance in the case of low signal-to-noise ratio and variable-speed movement. This paper proposes a non-data-aided Doppler estimation method for M-ary spread spectrum UWA communication systems in mobile scenarios. The receiver uses the spread spectrum codes dedicated to transmitting signals with different frequency offsets as local reference signals. Correlation operations are performed symbol by symbol with the received signal. The decoding and Doppler estimation of the present symbol are achieved by searching the correlation maximum in the code domain and frequency domain. The length of the current symbol is corrected for the next symbol synchronization using the estimated Doppler coefficient. To optimize the process of Doppler estimation and symbol synchronization, a heuristic search method is used. By adjusting the Doppler factor search step size, setting the threshold value, and using the Doppler factor estimation of the previous symbol, the search range can be significantly reduced and the computational complexity decreased. The Fisher-Yates shuffle algorithm is used to traverse the search range to ensure reliability of the results. Simulation results show that enlarging the frequency-domain search step size in some degree does not affect the decoding accuracy. On 15 May 2021, a shallow-water mobile UWA spread spectrum communication experiment was conducted in Weihai, China. The horizontal distance between the transmitter and the receiver is 3.7–4.0 km, and the communication rate is 41.96 bits per second. The transmitting ship moves at a speed of 0–3 m/s, and the bit error rate (BER) is lower than 1e−3, which is better than that of the sliding correlation despreading method with average Doppler compensation.

SMPPM a Modified Optical Wireless Multi-pulse PPM

Synchronized multi-pulse PPM “SMPPM” is a new proposed modulation scheme based on MPPM proposed for wireless optical systems. The proposed scheme resolves the symbol synchronization problem which may simplify the encoding and the decoding operations. It shows an important improvement in terms of data speed and bandwidth efficiency compared with conventional MPPM. On the other hand, SMPPM modulation shows a moderate power efficiency. In this article, we present the coding algorithm, expressions of spectral efficiency, normalized power requirements, and the data rate normalized to PPM, and we also present comparison of results with conventional MPPM.