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For the mmWave MIMO system using a partially-connected structure,in order to improve the spectral efficiency,the antenna composition of each subarray will be dynamically adjusted according to the channel conditions.However,the optimal grouping of antennas requires exhaustive searching for all possible antenna combinations according to certain criteri,which leads to unacceptable complexity.In response to the problem,a low-complexity sub-array dynamic allocation method was proposed.The core was to introduce certain rules when grouping array elements,thereby significantly reducing the number of combinations and reducing the search range.Specifically,two low-complexity antenna combination algorithms were proposed.Firstly,considering the strong correlation between mmWave antennas,multiple adjacent antennas were virtualized as an array element,thereby reducing the search space.Secondly,by dividing all antennas into upper and lower half areas,the antenna combination based on partition was realized,and the search space was also reduced.Simulation results show that the proposed method can achieve a good trade-off between performance and complexity. more...

For the mmWave MIMO system using a partially-connected structure,in order to improve the spectral efficiency,the antenna composition of each subarray will be dynamically adjusted according to the channel conditions.However,the optimal grouping of antennas requires exhaustive searching for all possible antenna combinations according to certain criteri,which leads to unacceptable complexity.In response to the problem,a low-complexity sub-array dynamic allocation method was proposed.The core was to introduce certain rules when grouping array elements,thereby significantly reducing the number of combinations and reducing the search range.Specifically,two low-complexity antenna combination algorithms were proposed.Firstly,considering the strong correlation between mmWave antennas,multiple adjacent antennas were virtualized as an array element,thereby reducing the search space.Secondly,by dividing all antennas into upper and lower half areas,the antenna combination based on partition was realized,and the search space was also reduced.Simulation results show that the proposed method can achieve a good trade-off between performance and complexity. more...

The high accuracy and low overhead of elephant flows identification have a great meaning on solving the controller's single point of failure problem in SDN traffic management.Aiming at the problem of high overhead of the existing elephant flows identification method,a two-level method for elephant flows identification was proposed which included a suspicious elephant detection algorithm based on TCP write-queue in the first stage and areal elephant detection algorithm based on flow duration in the second stage.During the first stage,the suspicious elephant flows were identified in the end systems to reduce the amount of flows monitored by the SDN controller at the second stage.Analysis and simulation prove that, under the premise of ensuring the accuracy of elephant flow identification, the two-level method for elephant flows identification reduces about 85% overhead of identification compared with sampling identification method. more...

The high accuracy and low overhead of elephant flows identification have a great meaning on solving the controller's single point of failure problem in SDN traffic management.Aiming at the problem of high overhead of the existing elephant flows identification method,a two-level method for elephant flows identification was proposed which included a suspicious elephant detection algorithm based on TCP write-queue in the first stage and areal elephant detection algorithm based on flow duration in the second stage.During the first stage,the suspicious elephant flows were identified in the end systems to reduce the amount of flows monitored by the SDN controller at the second stage.Analysis and simulation prove that, under the premise of ensuring the accuracy of elephant flow identification, the two-level method for elephant flows identification reduces about 85% overhead of identification compared with sampling identification method. more...

Congestion control algorithms of TCP protocol previously used in space communications are mostly based on TCP Vegas algorithm.They always require accurately measurement of RTT,but it's very difficult to achieve in deep space communication networks which have very long and variable delay channel characteristics.An errors tolerated congestion control algorithm is proposed based on packet loss rate measurement.The algorithm sends data in the form of data blocks and gives an errors tolerated degree based on the history data.It measures the congestion state based on the current packet loss rate measurement,so it can achieve a smaller overhead and higher transmission efficiency.In addition,the usage of mathematical modeling methods simplifies the networks and simulates the real network traffic.The mentioned algorithm is compared with the classical congestion control algorithm.Analysis and simulation prove that thethroughput of improved algorithm is 34 percent better than Tahoe and 22 percent better than Reno,so it gets a better performance. more...

Congestion control algorithms of TCP protocol previously used in space communications are mostly based on TCP Vegas algorithm.They always require accurately measurement of RTT,but it's very difficult to achieve in deep space communication networks which have very long and variable delay channel characteristics.An errors tolerated congestion control algorithm is proposed based on packet loss rate measurement.The algorithm sends data in the form of data blocks and gives an errors tolerated degree based on the history data.It measures the congestion state based on the current packet loss rate measurement,so it can achieve a smaller overhead and higher transmission efficiency.In addition,the usage of mathematical modeling methods simplifies the networks and simulates the real network traffic.The mentioned algorithm is compared with the classical congestion control algorithm.Analysis and simulation prove that thethroughput of improved algorithm is 34 percent better than Tahoe and 22 percent better than Reno,so it gets a better performance. more...