APP下载

光正交频分复用技术的研究

2021-09-14何怡玲姚毅谢湘伟

电脑知识与技术 2021年22期

何怡玲 姚毅 谢湘伟

摘要:随着Internet商用化所带动的视频、音频及数字通信的发展,人们对光纤通信寄予了更高的希望,渴望能发现一种无论是在速率方面还是在容量方面都优于传统无线网络的技术,OFDM技术所具备的各项优点让其在光通信领域中脱颖而出,被视作光通信领域的未来之光。但OFDM技术并不局限于此,而是一直向新领域扩展并尝试与各个领域结合。光正交频分复用技术(Optical orthogonal Frequency Division Multiplexing Technology,O-OFDM)便是OFDM技术向其他领域扩展的成果之一,OFDM技术与光通信的结合可谓是天作之合,不足的是光正交频分复用技术具有较高的峰均功率比。不仅如此,频率偏移和相位噪声对系统的影响也较大。该文分析了光正交频分复用技术的原理、优缺点、高峰均比对光正交频分复用系统的影响和措施以及频谱偏移对系统的影响和抑制措施。

关键词:正交频分复用;光正交频分复用;峰均功率比;频率偏移

Abstract: As Internet commercially by the development of video, audio, and digital communication, people had higher hopes for optical fiber communication, eager to find a kind of both in terms of speed and in capacity is superior to the traditional wireless network technology, OFDM technology has the advantages of let it stand out in the field of optical communication, is seen as the light of the future in the field of optical communication. However, OFDM technology is not limited to this, but has been expanding into new fields and trying to combine with various fields. Optical orthogonal Frequency Division Multiplexing Technology (Optical Orthogonal Frequency Division Multiplexing Technology, O - OFDM) is extended to other fields of one OFDM Technology, the combination of OFDM Technology and Optical communication is a match made in heaven, high speed and large capacity of OFDM Technology in the field of Optical communication is play incisively and vividly, is the lack of Optical orthogonal Frequency Division Multiplexing Technology has high peak power ratio. Not only that, frequency offset and phase noise have great influence on the system. In this paper, the principle, advantages and disadvantages of OFDM technology are analyzed, and the method to solve the high peak-to-average ratio of the system and the measures to suppress the influence of spectrum offset on the system are studied.

Key words: orthogonal frequency division multiplexing; optical orthogonal frequency division multiplexing; peak to average power ratio; frequency deviation

1引言

在20世紀初,科研人员发现OFDM技术与光通信两者相辅相成,在光通信中OFDM技术的优点被发挥得淋漓尽致,当时“OFDM技术与光通信的融合”的研究与开发热潮席卷全世界。OFDM技术在光通信中的运用,不仅让OFDM技术得到了新的发展,也让“信息地球村”项目变得越来越清晰。正交频分复用技术由于它自身所具有的优点被广泛应用于各个领域,使它在移动通信中的地位变得非常重要,成为不可缺少的一部分,以至于在未来移动通信的标准中它依然是首选传输技术。不足的是,O-OFDM系统传输存在两个主要的问题等待着后人的解决,即对频谱偏移的敏感性和峰均比(Peak-to-Average Power Ratio,PAPR)很高。

2 O-OFDM系统原理

O-OFDM系统基本结构如图1所示。通过星座映射将信号反射到信号相对应的复数形式,之后对映射的信号进行IFFT,这就是O-OFDM的调制部分,之后这些并行的子载波经过PS以及数模转换即为O-OFDM信号,该信号通过光电转换之后变成电信号,又利用模数转换以及串并转换之后再通过傅里叶变换就完成了解调,解调之后每一个子载波的调制信号即可恢复,最后通过串并转换恢复到最开始的数据流,并且恢复到二进制的数据。解调是调制的逆过程,它利用FFT将一个O-OFDM信号分解成许多个子载波信号,调制则是利用IFFT将许多个子载波信号合并为一个O-OFDM信号。O-OFDM和OFDM有着相同的基本思想内容,都是将实验中要传输的数据流通过若干个载波信号分解为多个比特流。这些被子载波分解后的子数据被用于调节很多个载波,但是被分解后的子数据都有着很低的传输比特速率。若要完成多载波调制,可以通过多载波调制技术概念的基础上完成OFDM技术的实现,这种技术让各个不同的子载波相互正交,从而克服多载波通信技术中频谱利用率较低的缺陷。