Research And Verification Of Key Technology Of DSL Code Division Multiple Access In Integrated Transmission Of Fiber And Copper

DSL(Digital Subscriber Line)access is a key part of the telecom service and user interconnection,occupying an important position in the access network,from the birth to the present has been more than 20 years.From the beginning of the simple DSL access technology to the recent years of hybrid fiber coaxial technology,DSL access technology continues to innovate.With the addition of fiber and the promotion of DSL transmission rate,hybrid fiber coaxial has become an indispensable part of the telecommunication service.In the original scheme for the integration of fiber and copper,for the problem the central office equipment close to clients,the thesis proposed to pull away the central office,and increase the near and far access equipment,thereby increasing the number of users of the coverage of the central office,and reduce the cost of maintenance of central office equipment.The integration of fiber and copper includes DSL and fiber,and the main body of the thesis is the transfer of DSL and fiber.When transmitting,the multi-channel DSL signal is aggregated by code division multiple access,and transmitted to the optical fiber for transmission.When receiving,the signal transmitted from the optical fiber is mainly separated by code division multiple access,and the multiplexed DSL signal is provided to multi-users.The key work of the thesis is as follows:Firstly,design the spread code.When transmitting,multi-channel DSL signal will be spread,spread code design is critical.The thesis chooses Walsh code with length 64 from several commonly used spreading codes.As the thesis requires 48 sets of spread code,and 64-length Walsh code has 64 groups.At this point,we need to design the optimal algorithm,from the 64 groups of Walsh code selected the best performance of 48 groups,as the final available spread code.The optimal use of the algorithm reduces the additional interference caused by random combinations.Secondly,design the synchronization code.After spreading,multi DSL signal need to go through aggregation and sending.Before sending,multi DSL signal need to superpose synchronization code,synchronization code design is also critical.Taking into account the scene requirements,in order to reduce the additional interference,still use Walsh code as a synchronization code.And then through the computer simulation,select Walsh code of the best autocorrelation from the same length Walsh code,and in the application of the scene,through the simulation to obtain the required length of the synchronization code.Thirdly,design the time synchronization program.When receiving,the received signal and the local signal will be biased,resulting in producing serious multiple access interference in dispreading.For the generated multiple access interference,the thesis analyzes the influence of synchronization bias on multiuser detection performance,and obtains the suppression precision multiple access interference,the required synchronization precision is 1/128 chip.Then the thesis designs the time synchronization scheme according to the required synchronization precision.Finally,in the multi-scene,according to the design of the synchronization algorithm,the computer simulations are carried out.The synchronization precision of this synchronization scheme has achieved 1/128 chip.This scheme suppresses multiple access interference,and multiuser detection SNR has achieved 40 dB.