Djordjevic Ivan, Arabaci Murat, Xu Lei, Wang Ting
University of Arizona, Department of Electrical & Computer Engineering, Tucson, Arizona 85721, USA.
Opt Express. 2011 Mar 28;19(7):6969-79. doi: 10.1364/OE.19.006969.
We propose a coded N-dimensional modulation scheme suitable for ultra-high-speed serial optical transport. The proposed scheme can be considered as a generalization of OFDM, and hence, we call it as generalized OFDM (GOFDM). In this scheme, the orthogonal subcarriers are used as basis functions and the signal constellation points are defined over this N-dimensional linear space. To facilitate implementation, we propose using N-dimensional pulse-amplitude modulation (ND-PAM) as the signal constellation diagram, which is obtained as the N-ary Cartesian product of one-dimensional PAM. In conventional OFDM, QAM/PSK signal constellation points are transmitted over orthogonal subcarriers and then they are multiplexed together in an OFDM stream. Individual subcarriers, therefore, carry N parallel QAM/PSK streams. In the proposed GOFDM scheme instead, an N-dimensional signal constellation point is transmitted over all N subcarriers simultaneously. When some of the subcarriers are severely affected by channel impairments, the constellation points carried by those subcarriers may be lost in the conventional OFDM. In comparison, under such conditions, the overall signal constellation point will face only small distortion in GOFDM and it can be recovered successfully using the information on the other high fidelity subcarriers. Furthermore, because the channel capacity is a logarithmic function of signal-to-noise ratio but a linear function of the number of dimensions, the spectral efficiency of optical transmission systems can be improved with GOFDM.
我们提出了一种适用于超高速串行光传输的编码N维调制方案。所提出的方案可被视为正交频分复用（OFDM）的推广，因此，我们将其称为广义OFDM（GOFDM）。在该方案中，正交子载波用作基函数，信号星座点在这个N维线性空间上定义。为便于实现，我们建议使用N维脉冲幅度调制（ND-PAM）作为信号星座图，它是通过一维PAM的N元笛卡尔积得到的。在传统的OFDM中，QAM/PSK信号星座点在正交子载波上传输，然后在一个OFDM流中复用在一起。因此，各个子载波承载N个并行的QAM/PSK流。而在所提出的GOFDM方案中，一个N维信号星座点同时在所有N个子载波上传输。当一些子载波受到严重的信道损伤影响时，在传统OFDM中，那些子载波所承载的星座点可能会丢失。相比之下，在这种情况下，GOFDM中的整体信号星座点只会面临较小的失真，并且可以利用其他高保真子载波上的信息成功恢复。此外，由于信道容量是信噪比的对数函数，但却是维度数的线性函数，因此GOFDM可以提高光传输系统的频谱效率。
