| Since 90', with the continuous development of telecommunication transmission technology, synchronous digital series has been gradually becomes the new digital transmission system. Now, SDH has gradually taken place of the quasi-synchronous digital series (PDH) used in old days in digital microwave transmission network. SDH is characteristic with large transmission capacity, network agility, long-haul transmission and high quality. Therefore, it is widely used. The wide application put forward the new demands of handling style, error-correcting codes used in digital microwave system and high-efficiency modulation technique in digital microwave system.In modulation and demodulation area, with the fast development of medium and large capacity digital microwave communication system, the requirement of data transmission rate in a system is higher and higher, also, the intense degree of spectrum resources is much stronger. The three traditional digital modulation and demodulation types, amplitude-shift keying (ASK), frequency-shift keying (PSK) and phase-shift keying (FSK), became hardly satisfied the needs any more, for its low spectrum efficiency. M-ary quadrature amplitude modulation and demodulation (MQAM) became the study focus internationally, as well as nationally.In baseband processing area,base-band signal of MQAM modulation need scrambling code, serial-parallel conversion, differential encoding and constellation mapping processing, etc.In error-correcting encoding and decoding area, MQAM modulation requires error-correcting has the characteristic of phase transparency. LEE error-correcting is both of phase transparency and lower redundancy, used in MQAM modulation system a lot.This article contains a whole design of 64QAM,including the part of baseband processing, error control and quadrature modulation, and passed the simulation test. The data rate of base-band is 75Mbps. error correcting code adopts a LEE error-correcting, which is capable of correcting one of the single LEE error that is 8-ary code (84, 81) SLEC code. The handling of base-band signal and error-correcting encoding has been implicated by FPGA. At the same time, this system is fully compatible of QPSK modulation form and MQAM (M=8,16,32,…,1024) modulation form.This article mentioned an easy realization structure of MQAM modulation system; a new realization method of asynchronous FIFO which is capable of overcoming metastable stateto occur; also a new realization method of LEE error-correcting encoding adapting to FPGA.Below is the arrangement of this paper:Chapter One: Introduction. Introducing the development situation and trend of wireless communication and clarifying the significance of the research subject, as well as the main idea of the paper.Chapter Two: Research of wireless modulation transmission mode. Studying the most used digital modulation types in wireless communication, including PSK modulation, QPSK modulation, MSK modulation, FSK modulation and QAM modulation, etc.Chapter Three: Research of base-band signal processing. Introducing the content and method of base-band signal processing required by QAM modulation; including of the theory and realization method of scrambling code, differential encoding and LEE error-correcting encoding.Chapter Four: Design of 64QAM modulator plan. That is writing specifically the realization plan of the 64QAM modulator. Divides the whole system into a few modules; introduced each realization method, and give the simulation data.Chapter Five: The circuit application and test result of 64QAMmodulator.Chapter Six: Summarize. That is summarizing the whole work and significance in this paper. |
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