The Research Of Pseudo-code Synchronization Tracking Technology Of DSSS Receiver Based On FPGA

Spread spectrum communications, fiber-optic communications and satellite communications are called the three major high-tech communications transmission mode while access to the information age. With the development of personal communication services and the application of global positioning system, the users of spread spectrum technology has more than 100 million so far.80's at the end of the 20th century, Europe's GSM digital technology diffused rapidly ,occuping the undisputed market leader when communication technology changed from analog to digital cellular globally. CDMA (Code Division Multiple Access)technology came into being at the same time with GSM technology. CDMA is a new and mature wireless communications technology developed on the basis of spread spectrum communication technology. It can use spectrum resources fully and solute the problem of shortage of spectrum effectively. So CDMA is considered to be the preferred realization of the 3rd generation mobile communication. It has several advantages such as good anti-jamming, anti-multipath fading capability, system capacity increases, good communication quality,etc.The PN code sequence spread spectrum system synchronization is unique technology of spread spectrum and technical difficulties. CDMA system requires that the local receiver pseudo-random code keep the same with the received PN code in the structure, frequency and phase. Otherwise the system can not be able to receive the information but noise. Thus, PN code synchronization is the key technology of CDMA spread spectrum communication.Synchronization process is divided into PN Code Acquisition (coarse synchronization) and the PN code tracking (fine synchronization). Capture, also known as the initial synchronization, complete the coarse synchronization, making the phase difference between the local spreading codes and received spreading codes less than one symbol interval. Tracking known as the fine synchronization, is based on the capture, reducing the phase error between send-side and receive-side ulteriorly. It must ensure that send-side pseudo-random code phase will follow the received pseudo-random code phase in a permitted change range.With the rapid development of software radio technology, receiving equipments based on traditional hardware have been gradually replaced by digitial IC products. To be programmable logic device designed according to ASIC, FPGA becomes an important means of pre-research and development due to its rich logic resources and re-configured advantage,.This paper starts from the overall design of direct sequence spread spectrum receiver, proposing FPGA realization solution and the software radio system based on Altera Cyclone II EP2C20Q240C8N FPGA with a certain significance in engineering practice. Cyclone II series FPGA chip fundamentally designed for low-cost and supply customization features for high-volume cost-sensitive applications, achieving the high performance and low power less than the cost of ASIC. It has wide distribution of density, rich in memories and embedded multipliers, providing a wide range of package options. Cyclone II devices also support low-cost applications in a variety of common external memory interfaces and I / O protocol. Parameterized IP core simplifies the application interface and protocol.This paper makes a detailed analysis of characteristics of three pseudo-code synchronous tracking method, using matlab and verilog HDL to simulate. Completion of the work are as follows:(1) Expound the principles of spread spectrum receiver and generation method of pseudo-random code. It also use verilog HDL and matlab to generate pseudo-random code in detail.(2) Expound the design process of spread spectrum receiver from the system perspective and the main function of the various parts.(3) The development of software radio based on FPGA platform, verifing the function of the system from software prespective.(4) Focus on three different pseudo-code synchronous tracking methods, making a systematic co-simulation with the delay locked loop.