Design and analysis of a double carrier modulation/differential detection technique for optical fiber communications /
Fiber optic long haul transmissions have been globally deployed at a staggering rate. All of the installed networks are using Intensity Modulation/Direct Detection (IM/DD). Although the IM/DD systems are proven and used widely, these networks are still subjected to many problems. The main problems a...
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| Định dạng: | Luận văn Sách |
| Ngôn ngữ: | English |
| Được phát hành: |
2003.
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| Những chủ đề: | |
| Truy cập trực tuyến: | http://ethesis.upm.edu.my/2801/ |
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| Tóm tắt: | Fiber optic long haul transmissions have been globally deployed at a staggering rate. All of the installed networks are using Intensity Modulation/Direct Detection (IM/DD). Although the IM/DD systems are proven and used widely, these networks are still subjected to many problems. The main problems associated with long haul transmission are; high dispersion and losses incurred by the fiber, and the inability of the receiver circuit to regenerate the transmitted bits. This is because of low signal power and inter-symbol interference, in addition to the masking noises. The recovery technique in the conventional receivers based on the IM/DD scheme uses an injected voltage level as a threshold into a decision circuit, which decides whether the incoming bit is a 0 or a 1. This scheme has two inherent problems; the instability of the injected threshold voltage, and the complexity of a dynamic threshold processing. As the threshold voltage has its own noise and fluctuation, it adds to the deterioration of the signal, thus limits the systems performance. Meanwhile, due to the random nature of the incoming bits, coupled with the masking noises and jitters, the threshold voltage level cannot be set at a fixed value, and therefore a dynamic voltage threshold adjustment is required. The demand of high data rate and long transmission distance impose much difficulty, therefore new approaches and techniques have to be applied to improve the system and solve these problems. This led to the development of new techniques for the system performance improvement. This thesis introduces a new transmission technique to improve the optical communication system performances. The new technique namely Double Carrier Modulation / Differential Detection (DCM/Diff.D) is presented. The system uses two carri,ers to send the data. One carrier carries the data, while the other carries the data inversion. A differential detection scheme based on the amplitude subtraction is used at the receiver end. The original signal Al and its inversion A2 are detected by two photo detectors and produce two voltage signals V I and V2. The voltage signal that is produced by the inversion data signal is subtracted from that of the original data signal. Note that no external DC voltage supply is required to be the reference threshold voltage as in conventional systems. V2 itself automatically serves as the threshold whose value is always reversal to that of the data, V I (between mark and space levels). Thus the first problem associated with threshold fluctuation and noise is minimized. At the same time, the automatic decision making is provided because both VI and V2 themselves change together dynamically depending on the received optical power levels at receivers 1 and 2 respectively. Therefore there is no need for complicated automatic threshold control schemes such as the eye-pattern scanning method. This suggests doubling the eye magnitude of the conventional system. Therefore, the new system suggests doubling the conventional distance. The new technique is presented by two models; one-fiber model and two-fiber model. A bit error rate (BER) of as good as 10'13 is achieved over 150 km distance for 2.5 Gbps data rate with OdBm transmit power, while conventional systems perform good only for 70 km distance for the same system parameters. The study carried out through a computer simulation. The relationship in design parameters namely; distance, bit rate, bit format, filters bandwidth, photodiode type, and wavelength spacing, are well studied in view of their effects on the performance parameters namely; BER and eye-opening. It is shown here that DCM/Diff.D improves the system performance significantly. |
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| Mô tả vật lý: | 93 leaves : ill. ; 30cm. |