| Currently, the business communication network rapid development,however, the traditional communication lines no longer meet the demand of our time. Operators of backbone network communication system has been completed from 10 Gbit/s, 40 Gbit/s to the 100 Gbit/s optical fiber communication system upgrade, but we also need high speed large capacity optical communication system to meet the increase of the amount of information. On the one hand, we can use the higher-order modulation to improve spectrum efficiency, for example QPSK, 16-QAM has been widely used , can increase the spectrum efficiency of two and four times respectively. On the other hand the super-channel are also ways to improve spectrum efficiency, such as the Nyquist-WDM system and Faster-than-Nyquist (FTN) system, can accelerate in the time domain or frequency domain signals respectively. Such as Nyquist signaling make the signals with the symbol rate of 50 Gbaud hold in a 5 0GHz WDM channel without the inter-channel interference (ICI). The rate of Faster than Nyquist signaling can compress the occupation bandwidth to be a fraction of bandwidth that is half the Nyquist signaling' occupies, so it has highter spectral efficiency than Nyquist signaling. But the inter-symbol interference (ISI) is introduced in the same time. This paper focus on the study of Faster than Nyquist system related theory.Signal is damaged during transmission because of device technology and the influence of the external environment, then the receiver signal bit error rate will be high. In the ideal of the coherent optical communication system, we assume that the optical signals of the transmitter laser and local oscillator laser at the receiving end are single frequency, that is the time domain signal change cycle is constant and frequency. But in practice, the production process and the influence of the external environment makes the light signal is no longer a single frequency, causing the receiver signal phase having the phenomenon of the rotation, affect the signal's decision.So it's very important to recover various kinds of damage signals at the receiving end. In the FTN system, because of the presence of ISI, the traditional signal carrier phase recovery algorithm is no longer good effect.This paper focuses on the related theory of Faster than Nyquist system and Faster than Nyquist system of carrier phase recovery algorithm, the main work is as follows:(1) Studied the carrier phase recovery algorithm is commonly used in the traditional system and comparing the performance between them. Including the Viterbi-Viterbi phase algorithm (VVPE),QPSK-partition algorithm, blind search algorithm (BPS) and constelation transformation (CT) algorithm.(2) Studied the forming method of the Faster than Nyquist signal in the system, and simulation to implement the FTN signal, the algorithm of receiver is analyzed in order to eliminate the intersymbol interference (ISI), which includes the Viterbi algorithm, BCJR algorithm and frequency domain equalization algorithm, finally realized the reception of FTN signal.(3) Studied the phase noise model caused by the laser line width in the FTN system, and analyses the difference of the model between the FTN system and the traditional system. In order to recover the carrier phase better in the FTN system, we modified the fourth power of traditional phase recovery algorithm. The algorithm can overcome FTN system phase cycle slips problem well, and get good performance. |
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