基于跳频的认知无线电网络中的时隙优化策略

Time Slot Optimization for Channel Hopping in CRN

随着近几年无线通信技术的快速发展,无线电频谱资源越来越匮乏。认知无线电网络(CRN)由于可提高现有频谱资源的利用率,受到了广泛关注。针对传统的认知无线电网络中随机跳频交汇策略没有考虑信道碰撞和切换延迟的问题,提出了一种基于时隙ALOHA协议,融入了切换延迟的最优随机跳频交汇策略。首先,将整个交汇过程以时隙微分化,定义信道时长和切换时长时隙模型,并将跳频过程与ALOHA协议融合,给出策略交汇时长(TTR)的计算方法;然后,分步骤详细分析交汇策略的流程,根据联合概率推导出时隙期望关于信道数目、切换时延的公式;最后,根据求导和函数趋势图计算最低点,进而提出一种基于整数规化的时隙最优数目计算算法,以取得整体交汇策略的最优化。通过模拟实验考查了可用时隙数目和切换时延这两个重要参数,实验结果表明切换时延比可用信道数目对交汇效率的影响更大。此外,实验结果还表明:该策略在充分考虑时延的同时,总能以最优方式交汇,相比传统方式可大幅度地缩短平均交汇时间(ATTR),当时延的时隙数目不大于5时,ATTR整体上缩短了15%左右,这可促进节点快速交汇,进而加速节点信息交互,进一步提高现有频谱的利用率。

With the rapid development of wireless communication technology in recent years,radio spectrum resources are becoming scarcer.Cognitive radio networks(CRNs)attracts widespread attention because they can improve the utilization of existing spectrum resources.For the issue that the traditional random channel hopping rendezvous strategy of cognitive radio network do not considere the channel collision and switching delay,this paper proposed an optimal random channel hopping rendezvous strategy based on time slot ALOHA protocol with calculation of switching delay.Firstly,the proposed strategy differentiates the whole process in time slot,defines the model about time slot of channel staying and switching delay,integrates the channel hopping process with ALOHA protocol,and gives the calculation formula of time-to-rendezvous(TTR).Then,by analyzing the process of rendezvous strategy step by step,it derives the formula of time slot expectation for available channel number and switching delay based on joint probability.Finally,it calculates the lowest point according to the derivative and the trend graph of the function.And then according to the idea of integer programming,this paper proposed an algorithm for calculating the optimal number of slots to optimize the overall rendezvous strategy.The experiment was carried out under the control of the number of available slots and switching delay.The experimental results show that the effect of switching delay on the rendezvous efficiency is greater than that of channel number.Also,the proposed scheme can achieve rendezvous in an optimal way with full account of the switching delay.It also can reduce the total rendezvous time effectively than the traditional strategy.When the number of time slots of switching delay is not more than 5,the ATTR is generally reduced by about 15%,which can promote the rendezvous and accelerate the message exchange between nodes and futher improve the spectrum utilization.