Singh Jaswinder
Department of Electronics and Communication Engineering, Beant College of Engineering and Technology, Gurdaspur, Punjab, India.
Appl Opt. 2010 Mar 10;49(8):1355-63. doi: 10.1364/AO.49.001355.
A novel family of three-dimensional (3-D) wavelength/time/space codes for asynchronous optical code-division-multiple-access (CDMA) systems with "zero" off-peak autocorrelation and "unity" cross correlation is reported. Antipodal signaling and differential detection is employed in the system. A maximum of [(W x T+1) x W] codes are generated for unity cross correlation, where W and T are the number of wavelengths and time chips used in the code and are prime. The conditions for violation of the cross-correlation constraint are discussed. The expressions for number of generated codes are determined for various code dimensions. It is found that the maximum number of codes are generated for S < or = min(W,T), where W and T are prime and S is the number of space channels. The performance of these codes is compared to the earlier reported two-dimensional (2-D)/3-D codes for asynchronous systems. The codes have a code-set-size to code-size ratio greater than W/S. For instance, with a code size of 2065 (59 x 7 x 5), a total of 12,213 users can be supported, and 130 simultaneous users at a bit-error rate (BER) of 10(-9). An arrayed-waveguide-grating-based reconfigurable encoder/decoder design for 2-D implementation for the 3-D codes is presented so that the need for multiple star couplers and fiber ribbons is eliminated. The hardware requirements of the coders used for various modulation/detection schemes are given. The effect of insertion loss in the coders is shown to be significantly reduced with loss compensation by using an amplifier after encoding. An optical CDMA system for four users is simulated and the results presented show the improvement in performance with the use of loss compensation.
报道了一种用于异步光码分多址（CDMA）系统的新型三维（3-D）波长/时间/空间码族，其具有“零”非峰值自相关和“单位”互相关。该系统采用了对映信号和差分检测。为实现单位互相关，最多可生成[(W×T + 1)×W]个码，其中W和T分别是码中使用的波长数和时间码片数，且均为质数。讨论了违反互相关约束的条件。确定了各种码维下生成码数量的表达式。发现当S≤min(W,T)时生成的码数量最多，其中W和T为质数，S为空间信道数。将这些码的性能与早期报道的异步系统二维（2-D）/三维（3-D）码进行了比较。这些码的码集大小与码大小之比大于W/S。例如，对于码大小为2065（59×7×5）的情况，总共可支持12213个用户，在误码率（BER）为10^(-9)时可支持130个同时用户。提出了一种基于阵列波导光栅的可重构编码器/解码器设计，用于三维码的二维实现，从而消除了对多个星形耦合器和光纤带的需求。给出了用于各种调制/检测方案的编码器的硬件要求。通过在编码后使用放大器进行损耗补偿，结果表明编码器中插入损耗的影响显著降低。对一个四用户的光CDMA系统进行了仿真，结果表明使用损耗补偿后性能有所提高。
