Optimization of Spread-Spectrum ALOHA Communication Systems Using Generic Algorithm

近年来，遗传算法作为一种优化技术，不仅从统计学的角度，而且从工程的各个领域的角度都引起了人们的注意。在这项研究中，我们研究了遗传算法的适用性，设计方法的扩频时隙ALOHA通信系统在给定的各种条件下，如分组丢弃概率和平均分组传输延迟。在扩频时隙ALOHA通信系统中，存在许多需要优化设计的参数，例如，分组重传算法、允许的重传尝试次数（重传截止）、前向纠错的编码率等。利用突变理论研究了指数退避和重传截止对有限种群跳频时隙ALOHA系统稳定性的影响。在系统中，分组重传问题 ...更多信息 相对于所经历的不成功传输的数目几何地分布能力，并且分组将在一定数目的不成功传输之后被丢弃。首先推导出在平衡点应满足的表达式。然后，对尖点和分歧集进行了数值计算。最后，我们可视化的指数退避方案和重传截止的影响上的可调区域。数值结果表明，指数退避方案可以有效地抑制有限种群系统的混沌行为。然而，它也表明，有渐近的指数退避计划对系统的稳定性没有影响的无限人口。此外，我们已经发现，遗传算法可以适用于时隙ALOHA通信系统的设计。进一步的研究包括; 1）结合扩频技术的时隙ALOHA通信系统的优化，2）在更现实的条件下的优化，例如95%的分组传输延迟，和3）导出更精确的分组丢弃概率的表达式。少

Recently, genetic algorithms attract one's attention as an optimization technique from the view point not only of statistics but also various fields of engineering. In this research, we examine the applicability of genetic algorithm to design methods of spread-spectrum slotted ALOHA communication systems under given various conditions such as the packet dropping probability and the average packet transmission delay. In spread-spectrum slotted ALOHA communication systems, there exist a number of parameters to be optimally designed, for example, the packet retransmission algorithm, the number of retransmission trials (retransmission cutoff) to be allowed, coding rate for forward error correction, and so forth. Particularly, the combinatorial effect of an exponential backoff scheme and retransmission cutoff on the stability of frequency-hopping slotted ALOHA systems with finite population was investigated in terms of the catastrophe theory. In the systems, the packet retransmission probab … More ilities are geometrically distributed with respect to the number of experienced unsuccessful transmissions and a packet will be discarded after a certain number of unsuccessful transmissions. Expressions which should be satisfied at equilibrium points are first derived. Then, the cusp point and the bifurcation sets are numerically evaluated. Finally, we visualize how the exponential backoff scheme and retransmission cutoff effect on the bistable region. Numerical results show that the exponential backoff scheme can mitigate bistable behavior of the system with finite population. However, it is also revealed that there is asymptotically no effect of the exponential backoff scheme on the stability of the system with infinite population. Furthermore, we have found that genetic algorithms can be applicable in designing slotted ALOHA communication systems. Further studies include ; 1) optimization of slotted ALOHA communication systems in conjunction with spread-spectrum techniques, 2) optimization under more realistic conditions such as the 95% packet transmission delay, and 3) derivation of more precise expressions for the packet dropping probability. Less