Due to frequency-selective and time-variant property of wireless channel together with additive noise and mismatch of oscillators between transmitter and receiver, there are always time and frequency synchronization e...Due to frequency-selective and time-variant property of wireless channel together with additive noise and mismatch of oscillators between transmitter and receiver, there are always time and frequency synchronization errors in a practical OFDM system. To investigate the effect of the two kinds of errors on system performance, the average normalized interference power (NIP) is defined. A simple supper bound for NIP caused by time synchronization error (TSE) and the tighter upper bound for NIP resulting from frequency synchronization error (FSE) are derived independently. Simulations in typical short wave (SW) and medium wave (MW) channels further verify the correctness and tightness of these upper bounds. They actually provide good approximations to NIPs. Moreover, the upper bound for NIP resulting from FSE is tighter than traditional upper bound. Additionally, a new solution is proposed to relax the precision requirement for time synchronization algorithm, which can achieve a better tradeoff between time synchronization precision and bandwidth efficiency. These upper bounds will be useful in developing and choosing time and frequency synchronization algorithms in OFDM system to achieve a specific NIP value for a given channel condition.展开更多
为提高含电缆-架空混合线路配电网故障定位精度,提出一种基于改进象群优化算法的配电网混合线路故障定位方法。首先,根据故障行波的传播特性以及配电网的结构特点,分析了多端行波信息差异矩阵的“唯一性”,并以此为基础构建了故障定位模...为提高含电缆-架空混合线路配电网故障定位精度,提出一种基于改进象群优化算法的配电网混合线路故障定位方法。首先,根据故障行波的传播特性以及配电网的结构特点,分析了多端行波信息差异矩阵的“唯一性”,并以此为基础构建了故障定位模型,将定位问题转化为寻优求解问题。然后,利用改进象群优化算法和OPTICS(ordering points to identify the clustering structure)聚类算法对第1次寻优结果中多端行波信息差异矩阵的各元素进行聚类分析,找出存在时间同步误差的坏数据。最后,在考虑正常数据的情况下进行第2次寻优,实现故障的精确定位。仿真结果表明,该方法在不需预设行波波速的情况下,能够实现较准确的故障定位,且具有较强时间误差鲁棒性。展开更多
基金supported by the National Natural Science Foundation of China(Grant No.60496311).
文摘Due to frequency-selective and time-variant property of wireless channel together with additive noise and mismatch of oscillators between transmitter and receiver, there are always time and frequency synchronization errors in a practical OFDM system. To investigate the effect of the two kinds of errors on system performance, the average normalized interference power (NIP) is defined. A simple supper bound for NIP caused by time synchronization error (TSE) and the tighter upper bound for NIP resulting from frequency synchronization error (FSE) are derived independently. Simulations in typical short wave (SW) and medium wave (MW) channels further verify the correctness and tightness of these upper bounds. They actually provide good approximations to NIPs. Moreover, the upper bound for NIP resulting from FSE is tighter than traditional upper bound. Additionally, a new solution is proposed to relax the precision requirement for time synchronization algorithm, which can achieve a better tradeoff between time synchronization precision and bandwidth efficiency. These upper bounds will be useful in developing and choosing time and frequency synchronization algorithms in OFDM system to achieve a specific NIP value for a given channel condition.
文摘为提高含电缆-架空混合线路配电网故障定位精度,提出一种基于改进象群优化算法的配电网混合线路故障定位方法。首先,根据故障行波的传播特性以及配电网的结构特点,分析了多端行波信息差异矩阵的“唯一性”,并以此为基础构建了故障定位模型,将定位问题转化为寻优求解问题。然后,利用改进象群优化算法和OPTICS(ordering points to identify the clustering structure)聚类算法对第1次寻优结果中多端行波信息差异矩阵的各元素进行聚类分析,找出存在时间同步误差的坏数据。最后,在考虑正常数据的情况下进行第2次寻优,实现故障的精确定位。仿真结果表明,该方法在不需预设行波波速的情况下,能够实现较准确的故障定位,且具有较强时间误差鲁棒性。
