The medium access control (MAC) issue was discussed in mobile Ad Hoc networks (MANETs). Based on the IEEE 802.11 MAC protocol, this paper proposed two schemes, the forward-packet-first (FPF) scheme based on the adaptive backoff contention window and multihop forward chain transmission by invitation (MFCTI) scheme. In the FPF scheme, the contention window was adjusted adaptively according to the traffic priority. Route information and the broadcast characteristic of radio were utilized in MFCTI scheme. The performance of these schemes was studied in multihop environments by simulations. The results showed that the proposed schemes could improve the network throughput, reduce the end-to-end average delay, and mitigate local congestion effectively. Another attractive feature was that the schemes could be implemented with minor modifications to the IEEE 802.11 MAC.
频谱感知技术是认知无线电的核心技术之一,由于未来无线通信技术的发展对高速数据通信的需求,使得宽带频谱感知技术成为目前研究的重点方向。由于宽频带带宽较宽不能直接将整个频段划分为占用或者空闲,需要对宽频带进行细分。将信号划分为多个子频带,通过预处理将多元分类问题转化成二元分类问题。为了降低频谱感知的算法复杂度,提出了基于噪声估计(estimation of noise,EN)和支持向量机(support vector machine,SVM)的频谱感知算法,该算法利用检测性能较好的慢速感知算法作为噪声估计,再使用算法复杂度低的快速感知算法结合噪声估计的信息进行频谱感知。实验结果表明,在低信噪比下,该算法较传统的方法其检测性能有着明显的提高,在信噪比为-10dB的无线环境中能够完全识别各个子信道的使用情况。
