科研之友
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摘要
In a wireless network, where propagation delay is high but known, slotted Aloha (S-Aloha) is synchronized with respect to the receiver%26apos;s time slots. Since the transmitter knows the propagation delay to its receiver, after a frame is generated, the transmitter introduces a suitable delay before its transmission, such that the frame arrives exactly in a slot at the receiver. However, in an underwater wireless network, due to significantly less signal propagation speed, the channel dynamics has a significant effect on the time dispersion of propagation speed. Due to this uncertainty in propagation speed, even if the transmitter receiver distance is exactly known, it is likely that a perfect synchronization at the receiver is not possible. %26lt;br%26gt;In this paper, we first show that, even a little-less-than-perfect synchronization at the receiver reduces the throughput of receiver synchronized S-Aloha (RSS-Aloha) to that of pure Aloha. We modify the RSS-Aloha for underwater by accommodating the error in delay estimate while deciding the receiver-end slot size. Via probabilistic analysis, supported by simulations, we show that our proposed modified protocol offers a gradual increase in throughput as the propagation delay uncertainty decreases. We also show that the throughput of our proposed modified protocol is consistently higher compared to the transmitter synchronized S-Aloha when operating under the same propagation delay uncertainty. However, when the uncertainty is high, delay performance of the modified RSS-Aloha remains poorer than that of the transmitter synchronized S-Aloha in a system with smaller nodal communication range.
- 出版日期2013-6
