Research Of Key Technologies Of CDMA In Passive Optical Network

Code Division Multiple Access is a key technology in Spread Spectrum telecommunication system. In the system there is a Spread Spectrum process before modulating module, and a despread process follow demodulating in the receiver. The spread spectrum process is using a PN code to multiply the data being transmitted. The advantage of the technology is given by the PN code. The PN code has a most important character of self-correlation. This character guarantees that the output of synchronization correlation operating will much greater than the asynchrony correlation operating. When the time difference between two transmitting paths is more than one code chip, the interference is widely decreased. The capacity of the system is increased. It also satisfies the request of secrecy.CDMA has been widely used in wireless telecommunication system. This article introduces its theory and advantages, whether it can be used in optical access network. Some difficulty exist, the most outstanding difficulty is synchronization. The optical signal only has "0"and "1", while the electronic signal has "+l" and "-1" which can be counteract in the adding process. But the probability still exists, and the problem can be resolved or steered clear of by the electronic or telecommunication methods. They are described in detail in the article.Using the spreading spectrum CMOS chip Z87200, a circuit has been designed to implement the base band spreading spectrum function. Research of the whole system has been done. Z87200 is controlled by AT89S52, which is an inexpensive chip. Using the emulator, we can control it by PC.Software researching and the performance analyzing of the system have been described in the article.