基于部分中继选择的能量收集双跳网络信息年龄优化

针对传统中继协作网络传感器节点能量受限导致信息传输延迟较高的问题，将短包通信（SPC）和能量收集技术相结合，构建了一种双跳中继无线传感器网络模型。网络中源节点和中继均需从专用能量基站收集射频信号能量以保证信息的持续传输，中继采用半双工解码转发协议将源节点发送的状态更新信息以短包形式传递到目的节点，利用中继选择策略与最大比合并技术提出了基于时效性的最早部分中继选择方案。考虑该网络信息的新鲜度，首先，分析了SPC传输性能，推导了中继和目的节点处的平均包错误率。其次，利用顺序统计量描述了源节点到中继端数据包的重传次数，基于更新过程理论推导了网络的平均信息年龄（AoI）表达式，并采用梯度下降方法优化了影响网络平均AoI的部分参数。最后，仿真分析结果表明，优化中继数量和数据包长度可以有效提高网络信息新鲜度，同时，通过对比优化部分参数得到的最优值与贪婪方法得到的最小化平均AoI理论值，可以验证部分中继协作方案在双跳状态更新网络中的可行性。 

Optimization of Age of Information for Energy Harvesting Two-hop Networks Based on Partial Relay Selection

? ?To solve the problem of high information transmission delay caused by energy limitation of sensor nodes in traditional relaying cooperative networks， a two-hop relaying wireless sensor network model is constructed by combining short packet communication （SPC） and energy harvesting. In this network， both the source and the relay need to collect RF signal energy from the dedicated energy base station to ensure the continuous transmission of information. The relay uses half duplex decoding and forwarding protocol to transmit the status update information sent by the source node to the destination in the form of short packets. Using relay selection strategy and maximum ratio combining technology， the earliest partial relay selection scheme based on timeliness is proposed. Considering the freshness of the network information， firstly， the SPC transmission performance is analyzed， and the average packet error probability at the relay and destination is derived. Secondly， the order statistics are utilized to describe the number of packet retransmission attempts of the packets from the source to the relay， the expression of the average age of information （AoI） of the network is derived based on the update process theory， and the gradient descent method is used to optimize some parameters affecting the average AoI of the network. Finally， the simulation results show that optimizing the number of relays and the length of packets can effectively improve the freshness of network information. Meanwhile， comparing the optimal value obtained by optimizing some parameters with the theoretical value of minimum average AoI obtained by greedy method， which can verify the feasibility of partial relay cooperation scheme in two-hop state update network.