A Practical HFC Uplink Multiple Access System Based On Embedded System Architecture

As the national standard of digital TV is being drawn recently, the technology of digital TV is promoted rapidly and a variety of digital TV network based added-value services have arisen. The expansion of new services leads to the inter-operation of digital TV network. In order to provide interactive channels for users, it is necessary to reconstruct the original unidirectional HFC network to be dual directional. This thesis introduced the implementation of the digital TV network application of a HFC based uplink access system, which provides the uplink channel for inter-active operation.The key techniques of access system include both access control and signal transmission. In the application of inter-operation TV system, the number of subscribers are great, while the data of each one is little. Therefor, P-ALOHA and S-ALOHA algorithm can meet the uplink access control requirement in HFC network, and they both benefit the complexity of the system. In HFC network, the frequency band of uplink access channel is 5-40MHz, thus signals have to be modulated before transmission. Besides, the existence of a lot of amplifiers resulted in serious nonlinearity in HFC channels, so constant envelope modulation such as CPFSK has to be adopted for its insensitivity to nonlinearity, as that used in the presented system.In the uplink access system discussed in this thesis, access control in the receiver is performed by an embedded system constructed with VxWorks and MPC860 as its software and hardware platform respectively. MPC860 is widely used in communication with its PowerPC + CPM dual-processor architecture, plenty of interfaces, and great ability in communication processing, while VxWorks is commonly chosen as the embedded operation system in complex communication systems for its reliability and real-time performance.Firstly, the basic principles and the key techniques of access system is introduced, which includes modulation, error control, multi-address access, and embedded-system techniques.Secondly, a systematic study focused on CPFSK modulation technology, multi-address access technology, and embedded operation system VxWorks is given, and the VxWorks based software system architecture is especially analyzed, including its core mechanism, I/O system, BSP system and network system.Finally, the design of transmitter and receiver is discussed in detail, with a HFC network based uplink access system as an example. The transmitter is mainly composed of software basedaccess control module and FPGA based modulator, which carries out the modulation and transmission of base band signals under the control of MCU, while the receiver is based on embedded system, using ASIC to demodulate signals, which are transferred to control server through Ethernet after processed by MPC860. Detailed system software and hardware design is presented.