高效灵活的正交频分复用无源光网络技术的研究
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摘要
正交频分复用（OFDM）技术具有频谱效率高、兼容各种基带调制格式和便于利用数字信号处理算法等优点，因此被研究者公认为是下一代光接入网——无源光网络（PON）中最具竞争力的方案之一。但是当前OFDM-PON系统中，OFDM技术更多的是作为一种传输手段。因此如何充分利用OFDM技术的优点，针对PON系统的特点设计合理的方案以提高OFDM-PON系统的效率和灵活性成为OFDM-PON系统研究亟待解决的问题。
针对系统的传输效率问题，论文主要从提高系统频谱利用率以及减小传输冗余两个方面着手。在提高频谱效率方面，论文提出了一种基于离散傅立叶变换的快速OFDM信号的产生和解调方法，使快速OFDM具有了和普通OFDM一样的单边带信号的特性和几乎一样的产生和解调方法，使其能方便的用于OFDM-PON系统。在减小传输冗余方面，论文充分考虑OFDM-PON作为接入网系统传输距离较短，链路切换迅速，信道特性相对固定等特点，提出了一种新的链路色散补偿方法。在只添加一个训练码的条件下，利用每个子载波上星座图本身的特点来进行链路色散补偿，不仅大大减小了因为频繁添加训练码导致的传输冗余，还提高了系统对于链路切换的响应速度。
论文主要从光网络单元（ONU）无色化和基于选择性接收的OFDM-PON系统速率分配两个方面着手提高系统灵活性。论文利用OFDM信号频谱与其基带数据之间的特殊对应关系，构造出一种信号边带与载波相分离的特殊的OFDM信号，因此下行信号的载波很容易被滤出并复用做上行传输。基于此论文提出了一种利用周期性光滤波器的无色ONU方案，并实现了系统上行、下行的对称速率传输。在带宽分配方面，论文将关注点转移到实际的传输速率上，提出综合利用Bitloading和Power loading在固定用户带宽的情况下进行传输速率灵活分配的方案；在信号接收方面，论文打破当前以OFDM边带为最小接收单位的思路，提出一种利用相干混频以及带限接收机的选择性接收方案，使得ONU可以直接接收其感兴趣的任意子载波。论文提出的基于选择性接收的系统速率分配方案极大的降低了OFDM-PON系统对ONU接收机的带宽要求，从而大大降低了系统成本。
Orthogonal frequency division multiplxing (OFDM) technology is now widelyconsidered to be one of the most promising candidate of the next generation opticalaccess networks——passive optical network (PON) for its advantages of high spectraefficiency, compatibility with all kinds of baseband modulation formats, and convenientapplication of digital signal processing. While in the current OFDM-PON systems,OFDM is just used as a transmission method, how to improve the transmissionefficiency and flexibility based on the characteristics of OFDM technology and PONsystem becomes the key issues.
To improve the transmission efficiency of OFDM-PON systems, proposals aregiven on further increasing the spectra efficiency and reducing the redundancy of thesystem. In order to further increase the spectra efficiency of OFDM-PON system, a newsignal generation and demodulation method based on fast Fourier transformation (FFT)for fast-OFDM is proposed. As a result, fast-OFDM realizes signal-sideband signalgeneration and shares the same system signal modulation and demodulation processwith the ordinary OFDM system， making it possible to utilize the new fast-OFDM tofurther increase the spectra efficiency of OFDM-PON system. To reduce thetransmission redundancy of the system, considering the characteristics of the shorttransmission distance, fast transmission link switch and relative stable channelcharacteristic of the access network, a new transmission chromatic dispersioncompensation method is proposed. The consteallation of every single subcarrier is usedto compensate the chromatic dispersion originated from transmission on the conditionthat only one training symbol is added before the data stream. Not only the transmissionredundancy because of frequent training symbol addition is greatly reduced, and theresponse of channel switch is improved as well.
To increase the flexibility of OFDM-PON system, efforts are devoted to therealization of colorless optical network unit (ONU) and transmission capacity allocationbased on subcarrier selectively receiving. The fantastic correspondence between thespectrum and the baseband data of OFDM signal is utilized and a special OFDM signalis intentionally generated, where there is a freuquency gap between the optical carrier and the OFDM signal band. As a result, the optical carrier of the downstream OFDMsignal can be easily filtered out and reused for upstream transmission. Based on this, acolorless ONU scheme with periodical optical narrow band pass filter is proposed, andsymmetric transmission of both downstream and upstream transmission is also realized.For flexible system capacity allocation, the focus is shifted from the bandwidth to thereal transmission capacity of the ONUs. A flexible transmission capacity allocationstrategy is proposed by bit loading and power loading method under the premise ofkeeping the bandwidth of every ONU fixed. To receive signal more efficiently, thelimitation of the OFDM band is broken and a new selectively receiving scheme withcoherent detection and bandwidth-limited receiver as well as the corresponding signalprocessing algorithm is proposed, making it possible for the ONUs to only receive anyof their interested subcarriers instead of the whole OFDM band. With the proposedselectively receiving based transmission capacity allocation scheme, the bandwidthrequirement of the receiver in the ONUs is greatly relaxed, but the expense of thesystem is also tremendously reduced.
针对系统的传输效率问题，论文主要从提高系统频谱利用率以及减小传输冗余两个方面着手。在提高频谱效率方面，论文提出了一种基于离散傅立叶变换的快速OFDM信号的产生和解调方法，使快速OFDM具有了和普通OFDM一样的单边带信号的特性和几乎一样的产生和解调方法，使其能方便的用于OFDM-PON系统。在减小传输冗余方面，论文充分考虑OFDM-PON作为接入网系统传输距离较短，链路切换迅速，信道特性相对固定等特点，提出了一种新的链路色散补偿方法。在只添加一个训练码的条件下，利用每个子载波上星座图本身的特点来进行链路色散补偿，不仅大大减小了因为频繁添加训练码导致的传输冗余，还提高了系统对于链路切换的响应速度。
论文主要从光网络单元（ONU）无色化和基于选择性接收的OFDM-PON系统速率分配两个方面着手提高系统灵活性。论文利用OFDM信号频谱与其基带数据之间的特殊对应关系，构造出一种信号边带与载波相分离的特殊的OFDM信号，因此下行信号的载波很容易被滤出并复用做上行传输。基于此论文提出了一种利用周期性光滤波器的无色ONU方案，并实现了系统上行、下行的对称速率传输。在带宽分配方面，论文将关注点转移到实际的传输速率上，提出综合利用Bitloading和Power loading在固定用户带宽的情况下进行传输速率灵活分配的方案；在信号接收方面，论文打破当前以OFDM边带为最小接收单位的思路，提出一种利用相干混频以及带限接收机的选择性接收方案，使得ONU可以直接接收其感兴趣的任意子载波。论文提出的基于选择性接收的系统速率分配方案极大的降低了OFDM-PON系统对ONU接收机的带宽要求，从而大大降低了系统成本。
Orthogonal frequency division multiplxing (OFDM) technology is now widelyconsidered to be one of the most promising candidate of the next generation opticalaccess networks——passive optical network (PON) for its advantages of high spectraefficiency, compatibility with all kinds of baseband modulation formats, and convenientapplication of digital signal processing. While in the current OFDM-PON systems,OFDM is just used as a transmission method, how to improve the transmissionefficiency and flexibility based on the characteristics of OFDM technology and PONsystem becomes the key issues.
To improve the transmission efficiency of OFDM-PON systems, proposals aregiven on further increasing the spectra efficiency and reducing the redundancy of thesystem. In order to further increase the spectra efficiency of OFDM-PON system, a newsignal generation and demodulation method based on fast Fourier transformation (FFT)for fast-OFDM is proposed. As a result, fast-OFDM realizes signal-sideband signalgeneration and shares the same system signal modulation and demodulation processwith the ordinary OFDM system， making it possible to utilize the new fast-OFDM tofurther increase the spectra efficiency of OFDM-PON system. To reduce thetransmission redundancy of the system, considering the characteristics of the shorttransmission distance, fast transmission link switch and relative stable channelcharacteristic of the access network, a new transmission chromatic dispersioncompensation method is proposed. The consteallation of every single subcarrier is usedto compensate the chromatic dispersion originated from transmission on the conditionthat only one training symbol is added before the data stream. Not only the transmissionredundancy because of frequent training symbol addition is greatly reduced, and theresponse of channel switch is improved as well.
To increase the flexibility of OFDM-PON system, efforts are devoted to therealization of colorless optical network unit (ONU) and transmission capacity allocationbased on subcarrier selectively receiving. The fantastic correspondence between thespectrum and the baseband data of OFDM signal is utilized and a special OFDM signalis intentionally generated, where there is a freuquency gap between the optical carrier and the OFDM signal band. As a result, the optical carrier of the downstream OFDMsignal can be easily filtered out and reused for upstream transmission. Based on this, acolorless ONU scheme with periodical optical narrow band pass filter is proposed, andsymmetric transmission of both downstream and upstream transmission is also realized.For flexible system capacity allocation, the focus is shifted from the bandwidth to thereal transmission capacity of the ONUs. A flexible transmission capacity allocationstrategy is proposed by bit loading and power loading method under the premise ofkeeping the bandwidth of every ONU fixed. To receive signal more efficiently, thelimitation of the OFDM band is broken and a new selectively receiving scheme withcoherent detection and bandwidth-limited receiver as well as the corresponding signalprocessing algorithm is proposed, making it possible for the ONUs to only receive anyof their interested subcarriers instead of the whole OFDM band. With the proposedselectively receiving based transmission capacity allocation scheme, the bandwidthrequirement of the receiver in the ONUs is greatly relaxed, but the expense of thesystem is also tremendously reduced.
引文
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