Designand Implementation Of The Variable Rate OFDM Modulation System

With the development of telecommunications, the high real-time business with large data volume has played an important part in mobile communications nowadays. Modern wireless communications is developing to the direction of broadband, high-speeding, intelligent and comprehensive. As users'increasing demands for services provided by today's communication systems, orthogonal frequency division multiplexing (OFDM) technology is concerned by more and more people, because it has good performances in fighting against multipath fading and frequency selective fading. And it has become the key technology in B3G/4G mobile communications.For very high data rates or very long distance links, the communication channel's time-frequency characteristics often show a very poor condition, so in normal applications, according to different channel conditions, it's important to guaranteed speed and reliability of information's transmission by changing the fabric of OFDM modulation system.Firstly, this paper introduced the development of OFDM technology and research situation; explained the principle of OFDM modulation. Proposed the program to achieve variable-rate encoder, variable-rate interleaver, multi-mode digital mapping module, the pilot inserter, high efficiency and IFFT Processor on the FPGA platform by using CR and SDR technology; make sure the variable-rate OFDM modulator can change it's fabric according to different channel conditions, and it's highest data transfer rate reaches over 10Mbps.Then the author combined the theory program with the real situation of FPGA development platforms, and developed the implementations of all modules in real system.Finally, the whole system was realized by using Verilog HDL on Altera's high-performance, low power, low-cost FPGA platform: CycloneⅢ.The real system is able to change the coding rate and digital mapping style of each sub-band by using different received configuration data through the serial communication interface. So the modulator has great flexibility and adaptability.Because OFDM system supports different sub-carriers to use different digital mapping styles, so that it can adapt to the actual channel conditions more perfectly. This paper also briefly describes the forward-looking aspects of the implementation of this technology, making the design of the modulator has a strong follow-up vitality.