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为提高智能交通系统(ITS)有效传输各类信息服务流的能力,将自适应调制编码(AMC)和正交频分多址接入(OFDMA)技术引入车辆通信接入子系统,提出了一种自适应传输模式选择策略。当车辆行驶在非特殊地理区域或行驶速度低于60km·h-1时,车辆通信接入系统将启动自适应传输模式选择进程。与典型策略采用固定不变的AMC传输模式信噪比切换阈值相比,建议策略的切换阈值可变,且由ITS信息服务流目标分组差错率来决定,从而使系统在传输不同类型的ITS信息服务流时,有可能在相同的接入信道状况下采用不同的调制编码模式等级,进而获得更高的数据有效传输速率。通过数学分析对选择策略的各类服务流目标分组差错率和系统平均有效数据传输速率进行性能评估。分析结果表明:建议策略能够在传输可靠性和高效性之间做出更好的权衡;当第1、2、3类ITS信息服务流的目标分组差错率分别为10-6、10-5、10-2时,建议策略能够在满足传输可靠性要求的同时,将典型策略的系统平均有效数据传输速率提升8%。
In order to improve the ability of Intelligent Transportation System (ITS) to effectively transmit all kinds of information service flows, Adaptive Modulation and Coding (AMC) and Orthogonal Frequency Division Multiple Access (OFDMA) technologies are introduced into the Vehicle Communication Access Subsystem Adaptive Transmission Mode Selection Strategy. When the vehicle is driving in a non-special geographical area or the traveling speed is lower than 60km · h-1, the vehicle communication access system will start the adaptive transmission mode selection process. Compared with the threshold of signal to noise ratio (SNR) switching of typical AMC transmission mode using a typical strategy, the switching threshold of the proposed strategy is variable and is determined by the target packet error rate of ITS information service flow, so that the system is transmitting different types of ITS information In the service flow, it is possible to adopt different modulation and coding scheme levels under the same access channel conditions to obtain a higher data efficient transmission rate. Through mathematical analysis, the performance of each service flow target packet error rate and system average effective data transmission rate of selection strategy is evaluated. The analysis results show that the proposed strategy can make a better trade-off between transmission reliability and efficiency. When the target packet error rates of the first, second and third class ITS information service flows are 10-6, 10-5, 10-2, the proposed strategy improves the system’s average effective data transmission rate of typical strategies by 8% while meeting the transmission reliability requirements.