This paper investigates the timing synchronization problem of a space optical orthogonal frequency division multiplexing (OOFDM) communication system. First, based on the good autocorrelation property of generalized chirp-like sequence, a training sequence is constructed to fit the non-negative light intensity signal requirement of the OOFDM system, of which the front and rear portions are cyclical and the whole is mirror-symmetric. No longer a periodic-repetition structure, the mirror-symmetric structure can effectively avoid the side lobe of objective function and reduce the complexity of correlation calculation, and thereby can improve the synchronization performance. Then, the constructed training sequence is superimposed on a complete data symbol for transmission to efficiently utilize transmitting power and spectrum resources of the communication system. At the receiver, the position of timing synchronization is estimated using maximum-likelihood algorithm and the correlation between the local sequence and the received signal. Simulation results show that, compared with several existing methods, the proposed timing synchronization method achieves better synchronization performances under both strong and weak atmospheric turbulence channels.
The channel estimation problem for asymmetrically clipped optical orthogonal frequency division multiplexing wireless communication systems is investigated. In order to resolve the noise-sensitive problem of traditional least squares-based channel estimation method, a new channel estimation method which is based on superimposed training sequence and guarantees the linear minimum mean square error estimate is proposed. Cycle training sequence is added at variable power ratio to the information sequence at the transmitter prior to transmission. Then, statistical average method is employed to separate training and information sequences at the receiver. Simulation results show that the power ratio of training sequence needs to balance between the mean square error (MSE) of estimation and the error bit rate. Moreover, compared with the traditional least squares-based method, the proposed method has significantly improved the estimation performance under the condition of low signal-to-noise ratio, especially, when the MSE of the estimation reduces 1 to 2 orders.
Optical burst switching (OBS) is regarded as a promising optical switching paradigm for next generation optical Internet.
More and more real-time traffic is transported by IP and it is important for OBS to support real-time traffic. Based on the
delay analysis of OBS networks, a pipeline scheme is proposed to reduce the delay and efficiently support real-time
traffic for OBS networks in the paper. When real-time traffic is transported in the core nodes of the established pipeline
and its burst head packet can not need to be processed. So the pipeline scheme reduces the offset time and delay of realtime
traffic. The simulation result shows that the pipeline scheme effectively reduces the end-to-end delay of real-time
traffic in the OBS networks.
An efficient fault detection method, employing cycle cover theory, is proposed. Three classic cycle finding algorithms
are compared in terms of cost-saving and feasibility. We through computation and statistic find that our proposed
method is economical and practical.
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