Study On QAM Sequence With Low Peak-to-mean Average Power Ratio Based On OFDM

The modern wireless communication technology developed by leaps and bounds, as the core of the wireless communication technology, The orthogonal frequency division multiplexing（OFDM） technology have the influence to be reckoned with. The high spectrum efficiency, low cost and can effectively eliminate the ISI phenomenon in the process of signal multipath transmission have made OFDM a system that widely used in various kinds of digital communication transmission. Early adoption of mobile wireless FM channel, for example, high bit rate digital subscriber line（HDSL）, asymmetric digital subscriber line（ADSL）, digital audio broadcasting（DAB） systems, digital video broadcasting（DVB） and HDTV ground transmission system; broadband wireless access systems and the third generation（3G） and the fourth generation（4G） mobile communications system（which has downlink OFDM, uplink DFT- S- OFDM as modified technology）. Also can easily combining with space-time coding and diversity, interference suppression and smart antenna technology, greatly improve the transmission reliability of information in the physical, too. Combining with the adaptive technology and dynamic allocation technology, further enhance the performance of OFDM system, is another reason that OFDM being more and more popular. But the high PAPR and easily affected by the frequency deviation obviously lowed the practical process of the system, so it’s urgent to low the comparison of the system and reduce the PAPR.Signal distortion in advance technology, signal scrambling technology and coding technology is the existing three technologies to lower PAPR. Signal distortion in advance technology is a nonlinear process which is more direct and effective, by directly reduced the signal amplitude of signals whose power is higher than the given threshold, but it will bring the signal distortion. Signal scrambling technology is by reducing the probability of peak power signals appear to achieve the purpose of reducing PAPR.Coding technology is a linear process, only the codes word satisfy the limited conditions can be transmitted, which can avoid signal peak, does not cause the signal distortion, but results in redundant and the decline of system transmission rate. This article focuses on the discuss of PMEPR on the QAM constellation diagram, Golay sequence is a good subsequence to construct higher-order sequences, because it has the PMEPR less than 2, combined with certain technologies it can expand the codes subsets under the condition of PMEPR change little, and improve transmission efficiency. The specific content of this article is:1. Introduce the basic knowledge of OFDM system. This paper introduce the advantages and disadvantages and the development of OFDM system, which is the core technology of communications; then introduced the basic principle of OFDM and its system structure, as the theoretical foundation for later research on OFDM and its PAPR.2. The introduction of the PAPR problems on OFDM system. First, introduces the definition of peak to average power ratio, because the high PAPR on the system requires much to the system hardware; then give the influence caused by nonlinear amplifier, and gives three ways to lower PAPR, namely the signal pre-distortion technology, signal scrambling technology, as well as the method of coding. Also introduces limiting filtering technology, window and offset in peak technology, extension and compression transformation technology that belongs to signal pre distortion method, Selective mapping and part of the transmission method that belong to signal scrambling technology, also gives the concrete implementation process of the various methods and their respective advantages and disadvantages.3. Introduces the method of lower PAPR by coding technology. Relatively common encoding methods including Block Coding, Golay Complementary Sequence, GCS and Reed Muller code, etc., this paper simply introduces the idea of Block Coding, mainly introduces the application of Golay Complementary Sequence, this paper also introduces peak-to-mean envelope power ratio, namely the PMEPR,which is more convenient to calculate, give the QAM constellation diagram based on the Golay sequences, respectively give the method to construct 2²ⁿ-QAM and 2²ⁿ⁺¹ QAM（10）- Sequence, at the end of the article,gives the respective upper bound of the system.