دانلود رایگان مقاله گروه بندی دوباره الگوریتم برای کاهش مشکل گره های مخفی در شبکه های 802.11ah

Abstract

An IEEE 802.11ah network has been designed to service a wide range of sensor network applications where a single access point (AP) covers a transmission range of up to 1 km and needs to support more than 8000 nodes. As a result, it has much more hidden node pairs compared to conventional 802.11a/b/g/n/ac networks. In addition, since nodes in power saving mode wake up simultaneously to send frames after receiving a beacon frame from the AP, the hidden node problem can become worse, resulting in frequent packet collisions and performance degradation. The 802.11ah standard proposes a group-based contention scheme to resolve the performance degradation problem, but it cannot resolve it appropriately. In this paper, we analyze the harmful impact of the hidden node problem on network performance and propose a new grouping algorithm to alleviate the performance degradation. Our proposed hidden matrix based regrouping (HMR) algorithm first finds hidden node pairs, and generates a hidden node matrix accordingly. Then it regroups hidden nodes to alleviate the hidden node problem using the hidden node matrix. Through extensive simulations, we show that our HMR algorithm eliminates most of hidden node pairs, thereby improving the performance of the 802.11ah network significantly in terms of the number of hidden node pairs and power-save poll (PS-Poll) transmission end time.

7. Conclusion

The IEEE 802.11ah standard has been proposed to have a much longer transmission range and an enhanced power save mode to service a wide area for sensor networks applications. However, the hidden node problem can be exacerbated especially when many nodes in sleep mode are activated simultaneously. As a solution, the 802.11ah standard proposed a group-based contention algorithm, but it is not a satisfactory solution to the problem. To evaluate the performance degradation, this paper has analyzed the PS-Poll transmission end time with and without hidden node pairs. Then we have proposed a hidden node matrix based regrouping (HMR) algorithm that consists of time difference-based hidden node detection, hidden matrix generation, and hidden node regrouping. Through extensive simulations, we have con- firmed that our proposed HMR algorithm significantly outperforms the 802.11ah standard grouping algorithm. Compared to the standard algorithm, the HMR algorithm reduces the number of hidden node pairs by 98.3% and the PS-Poll transmission end time by 68.5% when the AP covers 120 nodes. The HMR algorithm also performs well with OBSS hidden nodes and hot spot topology.