Pseudo-noise preamble based joint frame and frequency synchronization algorithm in OFDM communication systems

Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.

Two-Way Digital Video Transmission over Medium-Voltage Power-Lines Using Time-Domain Synchronous Orthogonal Frequency Division Multiplexing Technology

This paper describes field trials of two-way digital video transmissions over a 700-m long medium-voltage power cable using a frequency division duplex scheme. The purpose is to check the feasibility of using time-domain synchronous orthogonal frequency division multiplexing （TDS-OFDM） technology in powerline communication （PLC）. TDS-OFDM is the core technology in digital multimedia broadcasting-terrestrial （DMB-T）, developed by Tsinghua University for digital television terrestrial multimedia broadcast applications and successfully adopted in the Chinese Digital Terrestrial Television Broadcasting Standard. PLC systems are widely believed to be bandwidth or data throughput limited. However, the use of known pseudo random sequences as guard intervals for synchronization and channel estimation in TDS-OFDM greatly reduces the system overhead and increases the spectrum efficiency. These experiments show that TDS-OFDM is appropriate not only for broadcasting but also for PLC applications with appropriate modifications.

A New Approach to Implement Synchronous Demultiplexers in High-Speed ISDN Switching Network

This paper proves that a synchronous demultiplexer has the same logic function as a synchronous multiplexer. A new approach is proposed to implement synchronous demultiplexers in high-speed ISDN switching networks. A synchronous demultiplexer is designed utilizing the same structure as a synchronous shuffle multiplexer. Both the theoretical analysis and experimental results show that for the same capacity, the new method is more tolerant of signal delay variation, so a very high-speed synchronous demultiplexer can be designed with the larger capacity required in large capacity synchronous switching networks.

2x40 Gbit/s Polarization Division Multiplexing With Bit Slot Synchronization

Polarization division multiplexing (PDM) can double the spectral efficiency of an optical transmission system. By means of simulation, the 2x40Gbit/s NRZ PDM system performance under polarization mode dispersion (PMD) and chromatic dispersion has been investigated. To realize the best performance, the bit slots of the two channels should be synchronized.

Impact of polarization mode dispersion and nonlinearities on 2-channel DWDM chaotic communication systems

This paper has designed 2-channel dense wavelength division multiplexing （DWDM） chaotic sys- tem at the frequencies of 193.1 and 193,2THz, respec- tively. The optical chaotic signals were produced by using the semiconductor laser that is numerically modeled by employing laser rate equations. These two channels were multiplexed and then propagated through single mode optical fiber （SMF） of 80kin length with dispersion compensating fiber of 16 km length. Erbium doped fiber amplifier （EDFA） was used to compensate the power losses in the SMF. In lhis paper, we investigated the effects of polarization mode dispersion （PMD） and nonlinearities especially stimulated Raman scattering （SRS） on 2 channel DWDM chaotic communication system by varying the length of the SMF and value of differential group delay （DGD）.

Enzyme-free and multiplexed micro RNA detection using micro RNA-initiated DNA molecular motor

In this work,we have developed a sensitive,simple,and enzyme-free assay for detection of micro RNAs(mi RNAs)by means of a DNA molecular motor consisting of two stem-loop DNAs with identical stems and complementary loop domains.In the presence of mi RNA target,it can hybridize with one of the stem-loop DNA to open the stem and to produce a mi RNA/DNA hybrid and a single strand(ss)DNA,the ss DNA will in turn hybridize with another stem-loop DNA and finally form a double strand(ds)DNA to release the mi RNA.One of the stem-loop DNA is double-labeled by a fluorophore/quencher pair with efficiently quenched fluorescence.The formation of ds DNA can produced specific fluorescence signal for mi RNA detection.The released mi RNA will continuously initiate the next hybridization of the two stem-loop DNAs to form a cycle-running DNA molecular motor,which results in great fluorescence amplification.With the efficient signal amplification,as low as 1 pmol/L mi RNA target can be detected and a wide dynamic range from 1 pmol/L to 2 nmol/L is also obtained.Moreover,by designing different stem-loop DNAs specific to different mi RNA targets and labeling them with different fluorophores,multiplexed mi RNAs can be simultaneously detected in one-tube reaction with the synchronous fluorescence spectrum(SFS)technique.