何怡玲 姚毅 謝湘?zhèn)?/p>

摘要：隨著Internet商用化所帶動(dòng)的視頻、音頻及數(shù)字通信的發(fā)展，人們對(duì)光纖通信寄予了更高的希望，渴望能發(fā)現(xiàn)一種無論是在速率方面還是在容量方面都優(yōu)于傳統(tǒng)無線網(wǎng)絡(luò)的技術(shù)，OFDM技術(shù)所具備的各項(xiàng)優(yōu)點(diǎn)讓其在光通信領(lǐng)域中脫穎而出，被視作光通信領(lǐng)域的未來之光。但OFDM技術(shù)并不局限于此，而是一直向新領(lǐng)域擴(kuò)展并嘗試與各個(gè)領(lǐng)域結(jié)合。光正交頻分復(fù)用技術(shù)（Optical orthogonal Frequency Division Multiplexing Technology，O-OFDM）便是OFDM技術(shù)向其他領(lǐng)域擴(kuò)展的成果之一，OFDM技術(shù)與光通信的結(jié)合可謂是天作之合，不足的是光正交頻分復(fù)用技術(shù)具有較高的峰均功率比。不僅如此，頻率偏移和相位噪聲對(duì)系統(tǒng)的影響也較大。該文分析了光正交頻分復(fù)用技術(shù)的原理、優(yōu)缺點(diǎn)、高峰均比對(duì)光正交頻分復(fù)用系統(tǒng)的影響和措施以及頻譜偏移對(duì)系統(tǒng)的影響和抑制措施。

關(guān)鍵詞：正交頻分復(fù)用;光正交頻分復(fù)用;峰均功率比;頻率偏移

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(jì)初，科研人員發(fā)現(xiàn)OFDM技術(shù)與光通信兩者相輔相成，在光通信中OFDM技術(shù)的優(yōu)點(diǎn)被發(fā)揮得淋漓盡致，當(dāng)時(shí)“OFDM技術(shù)與光通信的融合”的研究與開發(fā)熱潮席卷全世界。OFDM技術(shù)在光通信中的運(yùn)用，不僅讓OFDM技術(shù)得到了新的發(fā)展，也讓“信息地球村”項(xiàng)目變得越來越清晰。正交頻分復(fù)用技術(shù)由于它自身所具有的優(yōu)點(diǎn)被廣泛應(yīng)用于各個(gè)領(lǐng)域，使它在移動(dòng)通信中的地位變得非常重要，成為不可缺少的一部分，以至于在未來移動(dòng)通信的標(biāo)準(zhǔn)中它依然是首選傳輸技術(shù)。不足的是，O-OFDM系統(tǒng)傳輸存在兩個(gè)主要的問題等待著后人的解決，即對(duì)頻譜偏移的敏感性和峰均比（Peak-to-Average Power Ratio，PAPR）很高。

2 O-OFDM系統(tǒng)原理

O-OFDM系統(tǒng)基本結(jié)構(gòu)如圖1所示。通過星座映射將信號(hào)反射到信號(hào)相對(duì)應(yīng)的復(fù)數(shù)形式，之后對(duì)映射的信號(hào)進(jìn)行IFFT，這就是O-OFDM的調(diào)制部分，之后這些并行的子載波經(jīng)過PS以及數(shù)模轉(zhuǎn)換即為O-OFDM信號(hào)，該信號(hào)通過光電轉(zhuǎn)換之后變成電信號(hào)，又利用模數(shù)轉(zhuǎn)換以及串并轉(zhuǎn)換之后再通過傅里葉變換就完成了解調(diào)，解調(diào)之后每一個(gè)子載波的調(diào)制信號(hào)即可恢復(fù)，最后通過串并轉(zhuǎn)換恢復(fù)到最開始的數(shù)據(jù)流，并且恢復(fù)到二進(jìn)制的數(shù)據(jù)。解調(diào)是調(diào)制的逆過程，它利用FFT將一個(gè)O-OFDM信號(hào)分解成許多個(gè)子載波信號(hào)，調(diào)制則是利用IFFT將許多個(gè)子載波信號(hào)合并為一個(gè)O-OFDM信號(hào)。O-OFDM和OFDM有著相同的基本思想內(nèi)容，都是將實(shí)驗(yàn)中要傳輸?shù)臄?shù)據(jù)流通過若干個(gè)載波信號(hào)分解為多個(gè)比特流。這些被子載波分解后的子數(shù)據(jù)被用于調(diào)節(jié)很多個(gè)載波，但是被分解后的子數(shù)據(jù)都有著很低的傳輸比特速率。若要完成多載波調(diào)制，可以通過多載波調(diào)制技術(shù)概念的基礎(chǔ)上完成OFDM技術(shù)的實(shí)現(xiàn)，這種技術(shù)讓各個(gè)不同的子載波相互正交，從而克服多載波通信技術(shù)中頻譜利用率較低的缺陷。