基于时域统计特征的天然气管道泄漏检测方法

根据管道动态压力信号在时域的幅值统计特性,提出一种基于时域统计特征的信号提取方法,实现对天然气管道的泄漏检测。通过每帧信号归一化的频率分布直方图(k-P图),提取动态压力信号时域幅值在均值上、下特定范围内波动的概率特征,使得时域的特征提取与信号幅值及波形无关,并且不受信号频率成分偏移的影响,具有较好的工况适应性。以PCA降维后的正常工况下动态压力信号时域统计特征向量为目标类样本,建立PCA-SVDD诊断模型,实现了对管道泄漏的可靠检测。历史数据的离线检验以及连续、实时的现场检验结果表明该方法可实现天然气管道的泄漏检测。

非理想信道估计下OFDM系统按比例自适应的子载波分配算法

在满足用户带宽接入需求约束下,针对时分双工OFDM下行链路系统最大化系统加权和速率问题,提出按比例自适应子载波分配算法。在最大信噪比(SNR)子载波分配策略基础上,引入用户权重,提出按比例自适应子载波分配策略,据此给出用户带宽接入概率表达式,通过求解具有约束条件的非线性最优化问题,得到满足用户带宽接入需求的用户权重。仿真结果表明:所提算法可自适应地根据用户带宽需求因子和平均SNR给出对应用户权重,并据此按比例地为用户分配所需带宽;随着用户平均SNR的增大,信道估计误差方差减小,当平均SNR达到17.5 d B时,几乎可以达到与理想信道估计下子载波分配算法相同的性能。

Frame length optimization for multi-antenna downlink systems based on delay-bound violation probability constraints

A flame length optimization scheme is proposed for multi-antenna downlink systems to guarantee diverse delay- bound violation probability constraints. Due to the difficulties of extracting the quality of service （QoS） metrics from the conventional physical-layer channel models, the link-layer models named effective bandwidth and effective capacity are applied to statistically characterize the source traffic patterns and the queuing service dynamics. With these link-layer models, the source traffic process and the channel service process are mapped to certain QoS parameters. The packet delay-bound violation probability constraints are converted into minimum data rate constraints and the optimization problem is thus formulated into simultaneous inequalities. With the assumption of ergodic block-fading channels, the optimal frame lengths of single-user and multiuser systems are calculated respectively by numerical iterative methods. Theoretical analyses and simulation results show that the given delay-bound violation probability constraints are well satisfied with the optimal frame length.

A NEW METHOD OF FREQUENCY-HOPPING(FH) SIGNAL DETECTION

A new Frequency-Hopping(FH) signal detection method is proposed.Different from pre-vious methods which need to monitor the total band,it can monitor part of the band and decrease the range of the bandwidth.According to this method,a new detection model is set and the computation formulas of the detection probability and false-alarm probability are given.The parameters of a VHF radio are used to prove the validity of the method.Simulation results show that this method can de-crease the range of the bandwidth and detect the FH signal with some penalty on the SNR and signal loss.

Spectrum Allocation for Cognitive Radio Networks with Non-Deterministic Bandwidth of Spectrum Hole

The spectrum allocation for cognitive radio networks(CRNs) has received considerable studies under the assumption that the bandwidth of spectrum holes is static. However, in practice, the bandwidth of spectrum holes is time-varied due to primary user/secondary user(PU/SU) activity and mobility, which result in non-determinacy. This paper studies the spectrum allocation for CRNs with non-deterministic bandwidth of spectrum holes. We present a novel probability density function(PDF) through order statistics as well as its simplified form to describe the statistical properties of spectrum holes, with which a statistical spectrum allocation model based on stochastic multiple knapsack problem(MKP) is formulated for spectrum allocation with non-deterministic bandwidth of spectrum holes. To reduce the computational complexity, we transform this stochastic programming problem into a constant MKP through exploiting the properties of cumulative distribution function(CDF), which can be solved via MTHG algorithm by using auxiliary variables. Simulation results illustrate that the proposed statistical spectrum allocation algorithm can achieve better performance compared with the existing algorithms when the bandwidth of spectrum holes is time-varied.