Digital Communications, in relation to wireless networks, have taken off in recent years due to the expanding need to communicate faster and more efficiently. A popular way to achieve this is by using wireless Multipl...Digital Communications, in relation to wireless networks, have taken off in recent years due to the expanding need to communicate faster and more efficiently. A popular way to achieve this is by using wireless Multiple Input Multiple Output (MIMO) communication systems. MIMO systems utilize Space Time Block Codes (STBC) as one of the leading ways to obtain higher data rates with limited bandwidth and power. With several STBC methods currently available, this paper analyzes simulations using Orthogonal Space Time Block Codes (OSTBC) in Rayleigh fading channels to evaluate the performance of MIMO systems. The selection to use a Rayleigh fading channel as a model for a non-line-of-sight (nLOS) environment is selected to mimic installations where a large number of signal paths and reflections are expected. All simulations are coded, generated and plotted using MATLAB resulting in graphical data representing the bit-error rate (BER) to signal-to-noise ratio (Eb/N<sub>0</sub>) or SNR. Each simulation captures how different configurations of key variables including code rate, diversity and antenna count can impact system performance. Four modulation schemes (BPSK, QPSK, 16-QAM and 64-QAM) are included in each simulation. Conclusive evidence based upon these simulations suggests higher diversity gains were achieved with a greater number of antennas. The most significant factor for increasing system performance was using a lower count of transmit antennas with a higher count of receive antennas.展开更多
已有的针对海上VHF/UHF(Very High Frequency/Vltra High Frquency)频段信道环境的研究,在电波传播特性和底噪特性方面缺少试验数据支撑.本文在VHF/UHF频段上做了一系列海上通信试验,基于试验数据,分析了传统电波传播模型对海上视距、...已有的针对海上VHF/UHF(Very High Frequency/Vltra High Frquency)频段信道环境的研究,在电波传播特性和底噪特性方面缺少试验数据支撑.本文在VHF/UHF频段上做了一系列海上通信试验,基于试验数据,分析了传统电波传播模型对海上视距、超视距、视距超视距临界等传播路径的适用性.同时本文提出了空时二维海上频率选择性信道分析方法,从空间、时间二维视角下定量描述了海上无线信道演变现象,对空时频率迁移和空时频率衰变的概念做了定义.结论可用于海上电波传播建模和异常现象分析.展开更多
IEEE1588协议定义的精确时间协议(precision time protocol,PTP)能够实现地面以太网网络节点中的时钟同步,达到亚微秒级时间同步精度;相比于稳定的地面以太网环境,深空网络环境具有长时延、时延抖动及信道不对称等特点;对PTP协议在深空...IEEE1588协议定义的精确时间协议(precision time protocol,PTP)能够实现地面以太网网络节点中的时钟同步,达到亚微秒级时间同步精度;相比于稳定的地面以太网环境,深空网络环境具有长时延、时延抖动及信道不对称等特点;对PTP协议在深空邻近空间无线信道下的时间同步性能进行了研究;首先,介绍了PTP协议的同步原理;其次,对深空邻近无线网络信道环境对于适用于地面以太网环境的PTP协议时间同步性能的影响进行了分析,并提出采用卡尔曼滤波算法和设定主从时钟钟差阈值相结合的方法,对PTP协议进行适应性改进;最后,采用损伤仪和测试仪模拟深空邻近无线网络信道环境,利用时钟分析仪对软件结合硬件实现的PTP协议进行了时间同步性能测试;测试结果表明,改进后的PTP协议提高了在深空邻近空间无线信道下时间同步的精度和稳定性。展开更多
文摘Digital Communications, in relation to wireless networks, have taken off in recent years due to the expanding need to communicate faster and more efficiently. A popular way to achieve this is by using wireless Multiple Input Multiple Output (MIMO) communication systems. MIMO systems utilize Space Time Block Codes (STBC) as one of the leading ways to obtain higher data rates with limited bandwidth and power. With several STBC methods currently available, this paper analyzes simulations using Orthogonal Space Time Block Codes (OSTBC) in Rayleigh fading channels to evaluate the performance of MIMO systems. The selection to use a Rayleigh fading channel as a model for a non-line-of-sight (nLOS) environment is selected to mimic installations where a large number of signal paths and reflections are expected. All simulations are coded, generated and plotted using MATLAB resulting in graphical data representing the bit-error rate (BER) to signal-to-noise ratio (Eb/N<sub>0</sub>) or SNR. Each simulation captures how different configurations of key variables including code rate, diversity and antenna count can impact system performance. Four modulation schemes (BPSK, QPSK, 16-QAM and 64-QAM) are included in each simulation. Conclusive evidence based upon these simulations suggests higher diversity gains were achieved with a greater number of antennas. The most significant factor for increasing system performance was using a lower count of transmit antennas with a higher count of receive antennas.
文摘已有的针对海上VHF/UHF(Very High Frequency/Vltra High Frquency)频段信道环境的研究,在电波传播特性和底噪特性方面缺少试验数据支撑.本文在VHF/UHF频段上做了一系列海上通信试验,基于试验数据,分析了传统电波传播模型对海上视距、超视距、视距超视距临界等传播路径的适用性.同时本文提出了空时二维海上频率选择性信道分析方法,从空间、时间二维视角下定量描述了海上无线信道演变现象,对空时频率迁移和空时频率衰变的概念做了定义.结论可用于海上电波传播建模和异常现象分析.
文摘IEEE1588协议定义的精确时间协议(precision time protocol,PTP)能够实现地面以太网网络节点中的时钟同步,达到亚微秒级时间同步精度;相比于稳定的地面以太网环境,深空网络环境具有长时延、时延抖动及信道不对称等特点;对PTP协议在深空邻近空间无线信道下的时间同步性能进行了研究;首先,介绍了PTP协议的同步原理;其次,对深空邻近无线网络信道环境对于适用于地面以太网环境的PTP协议时间同步性能的影响进行了分析,并提出采用卡尔曼滤波算法和设定主从时钟钟差阈值相结合的方法,对PTP协议进行适应性改进;最后,采用损伤仪和测试仪模拟深空邻近无线网络信道环境,利用时钟分析仪对软件结合硬件实现的PTP协议进行了时间同步性能测试;测试结果表明,改进后的PTP协议提高了在深空邻近空间无线信道下时间同步的精度和稳定性。
