毫米波大规模MIMO系统波束选择方案的设计

针对毫米波大规模MIMO系统采用全数字预编码时,所需射频链路数量过多而导致能量消耗高的问题,提出了一种基于透镜的波束选择方案。该方案首先通过分析用户受干扰的可能性,将所有的用户分为干扰用户组和非干扰用户组,然后对于非干扰用户,直接利用最大功率准则进行波束选取,而对于干扰用户,则通过低复杂度增量算法选择合适的波束使系统和速率最大化。仿真结果表明,在有效减少系统所需射频链路数量和降低计算复杂度的基础上,该方案的系统和速率能够达到接近全数字预编码方案的水平,并且能够获得更高的能量效率。     

Improved Hybrid Beamforming for mmWave Multi-User Massive MIMO

Massive multiple input multiple output (MIMO) has become essential for the increase of capacity as the millimeter-wave (mmWave) communication is considered. Also, hybrid beamforming systems have been studied since full-digital beamforming is impractical due to high cost and power consumption of the radio frequency (RF) chains. This paper proposes a hybrid beamforming scheme to improve the spectral efficiency for multi-user MIMO (MU-MIMO) systems. In a frequency selective fading environment, hybrid beamforming schemes suffer from performance degradation since the analog precoder performs the same precoding for all subcarriers. To mitigate performance degradation, this paper uses the average channel covariance matrix for all subcarriers and considers an iterative algorithm to design analog precoder using approximation techniques. The analog precoder is iteratively updated for each column until it converges. The proposed scheme can reduce errors in the approximating process of the overall spectral efficiency. This scheme can be applied to fully-connected and partially-connected structures. The simulation results show that spectral efficiency performance for the proposed scheme is better than the conventional schemes. The proposed scheme can achieve similar performance with full-digital beamforming by using a sufficiently large number of RF chains. Also, this paper shows that the proposed scheme outperforms other schemes in the frequency selective fading environment. This performance improvement can be achieved in both structures.     

Fairness and throughput enhancement based resource allocation scheme for underlay cognitive radio networks

Acquiring good throughput and diminishing interference to primary users (PU) are the main objectives for secondary users in a cognitive radio (CR) network. This paper proposes a centralized subcarrier and power allocation scheme for underlay multi-user orthogonal frequency division multiplexing considering the rate loss and the interference those the PU can tolerate. The main purpose of the proposed scheme is to efficiently distribute the available subcarriers among cognitive users to enhance both the fairness and the throughput performance of the cognitive network while maintaining the QoS of primary users. Simulation results show that the proposed scheme achieves a significantly higher CR network throughput than that of the conventional interference power constraint (IPC) based schemes and provides a significantly enhanced fairness performance. Also, contrary to the conventional IPC based schemes, the proposed scheme is able to significantly increase the achieved throughput as the number of CR users increases.     

Efficient multi-user detection scheme for overloaded group-orthogonal MC-CDMA systems

An efficient multi-user detection scheme for overloaded MC-CDMA systems is presented. The proposed detection scheme for overloaded systems achieves the optimal performance for constant-modulus modulation schemes, for example MPSK, and provides near-optimal performance for non-constant-modulus modulation, for example M-QAM. Moreover, it has overall lower complexity than the other optimal detection algorithms, especially suitable for group-orthogonal MC-CDMA systems, where group-based technique keeps multi-user receiver size relatively small.     

Multi-user adaptive orthogonal frequency-division multiplexing system for indoor wireless optical communications

An adaptive orthogonal frequency-division multiplexing (OFDM) system is proposed for multi-user communications over indoor wireless optical channels. The designed system uses multi-user least-squares detection techniques applied to space-division multiple access and OFDM schemes, in conjunction with angle-diversity reception. The system, which does not present an excessive increase in complexity with respect to the previous schemes, can support high bit rates for multiple users, beyond 100 Mbits/s. It also mitigates the channel fluctuations induced when either the space distribution or the number of emitters and receivers varies. The performance of the new proposed scheme is compared with that of a non-adaptive multi-user system and an adaptive single-user system, both described in the previous works, when they face similar environmental situations. The obtained results show a significant enhancement with respect to both the previous multi-user system and the adaptive single-user one, since the new scheme allows adaptively managing the system throughput on a multi-user environment     

抑制运动强干扰的稳健波束域目标方位估计方法

为了减小来自旁瓣区快速运动的强干扰对波束域高分辨方位估计方法的影响,提出一种稳健的波束域高分辨方位估计方法。该方法在形成多波束时,将稳健自适应波束形成与零陷扩宽技术相结合,有效地抑制了运动强干扰所造成的快拍失效和扫描方向误差引起的自适应波束图畸变,从而保证波束域方法能准确地估计目标方位。仿真结果验证了该方法的有效性。     

Iterative bit and power allocation for multi-cell orthogonal frequency division multiplexing with minimum variance distortionless response beamforming

This paper develops bit and power allocation schemes with beamforming for multi-cell orthogonal frequency division multiplexing (OFDM) systems on uplink. The model of the multi-cell channel with frequency reuse is considered. The transmit signal from each mobile causes interference to the received signals of other base stations. The schemes aim to minimise the total mobile transmit power while satisfying the required data rate and the bit error rate (BER) of each mobile. The proposed schemes offer better performance than that of the fixed bit allocation method. The proposed distributed allocation scheme reduces computational complexity compared to the proposed centralised multi-user greedy method with insignificant performance degradation. The simulation results are presented to demonstrate the efficacy of the proposed schemes.     

Improved Hybrid Precoding Technique with Low-Resolution for MIMO-OFDM System

This paper proposes an improved hybrid beamforming system based on multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. The proposed beamforming system improves energy efficiency compared to the conventional hybrid beamforming system. Both sub-connected and full-connected structure are considered to apply the proposed algorithm. In the conventional hybrid beamforming, the usage of radio frequency (RF) chains and phase shifter (PS) gives high power and hardware complexity. In this paper, the phase over sampling (POS) with switches (SW) is used in hybrid beamforming system to improve the energy efficiency. The POS-SW structure samples the value of analog beamformer to make lower resolution than conventional system. The number of output data in POS is decided by the resolution of POS system. The limited number of POS decides the resolution of antenna array and the values of POSs are designed from maximum and minimum phase angle antenna array. Energy efficiency without the phase shifter is high although channel capacity is nearly similar with conventional system. Also, the amplifier with POS-SW system is proposed to improve the BER performance. According to the data bits, the output signals of POS are decided. The system with 2, 3 and 4 bits is simulated to prove the proposed algorithm. In order to overcome the loss of low-resolution system, the amplifier with POS-SW system using channel information is proposed. The average sum-rate of 4 bits system shows the similar performance with the conventional hybrid beamforming system. This structure can play an important role by increasing the energy efficiency of the wireless communication system that many antennas are used. It is shown that the BER, average sum rate and energy efficiency of the proposed scheme are more improved than the conventional hybrid beamforming system.     

Comparison of direct-sequence impulse radio and direct-sequence ultra-wide bandwidth in multi-user interference

A new ultra-wide bandwidth communication system using both a time-hopping (TH) sequence and a direct spreading sequence, called direct-sequence impulse radio (DS-IR), has recently been proposed. An exact analysis to evaluate the bit error rate (BER) performance of this new scheme in multi-user interference (MUI) is provided. On the basis of this new analysis, ultra-wideband communication systems employing TH, direct-sequence and the newly proposed DS-IR schemes operating in MUI are accurately compared in terms of the BER. Our results indicate that DS-IR outperforms the TH binary phase-shift keying (BPSK) system. However, its performance is poorer than the performance of the conventional full-duty direct sequence BPSK system. Compared with the low-duty direct sequence BPSK system, DS-IR achieves a better error rate performance for medium and large signal-to-noise power-ratio values.     

Multi-user interference cancellation technology in the presence of multiple frequency offsets

The performance of multi-user detectors in the presence of multiple frequency offsets under a Rayleigh fading channel environment is analysed, and techniques to estimate and remove multiple frequency offsets (FOs) for successive interference cancellation (SIC) and parallel interference cancellation (PIC) receivers are also proposed. The closed form expressions derived for bit error rate (BER) of SIC and PIC schemes in the presence of multiple FOs have been verified using extensive simulation results. The PIC is shown to be less sensitive to frequency offsets as compared to SIC. It is demonstrated through analytical and simulation results that the proposed frequency offset estimation and correction techniques provide approximately 8 dB gain in the BER performance over conventional SIC and PIC schemes in the presence of multiple frequency offsets     

一种基于跳波束天线的通信方式及其性能分析

提出了一种新的基于跳波束天线(Beam Hopping为Antennas，BHA)的通信方式，并对其在存在强方向性干扰的情况下的平均信干噪声比(SINR)性能进行了初步的分析。结果表明，相对于传统单波束天线(Single Beam．Antennas，SBA)的通信方式，这种新的BHA通信方式能够有效地改善存在强方向性干扰时的通信质量，从而提高系统的性能。     

基于ZF-DPC机制的多天线下行系统的自适应调制

以系统总速率最大化为目标,基于迫零污纸编码（ZF-DPC）机制提出了MIMO多用户下行系统的一种保障用户QoS的自适应调制方案。根据这一方案,基站应用空分多址接入（SDMA）同时支持多个用户;针对污纸编码（DPC）的极高复杂度,利用次优的ZF-DPC消除用户间的干扰;在理想信道信息情形下实现可变速率可变功率自适应调制。考虑到最优算法的高复杂度,提出了两种可应用到实际系统的低复杂度次优算法。仿真结果表明,次优算法在极大降低系统复杂度的同时,总速率比较接近最优算法的性能。     

Reactive scheduling in a dynamic and stochastic FMS environment

In this paper, we study the reactive scheduling problems in a dynamic and stochastic manufacturing environment. Specifically, we develop a simulation-based scheduling system for flexible manufacturing systems. We also propose several reactive scheduling policies (i.e. when-to-schedule and how-to-schedule policies) and test their performances under various experimental conditions, processing time variations, and machine breakdowns. Moreover, we compare offline and online scheduling schemes in a dynamic manufacturing environment. The results of extensive simulation experiments indicate that the variable-time-response is better than the fixed-time-response. The full scheduling scheme generally performs better than the partial scheduling. Finally, the online scheduling is more robust to uncertainty and variations in processing times than the optimum-seeking offline scheduling. A comprehensive bibliography is also provided in the paper.     

Beamspace adaptive beamforming for ultrasound imaging

Applying the Capon adaptive beamformer in medical ultrasound imaging results in enhanced resolution by improving the interference-suppressing capabilities of the array. This improvement comes at the expense of an increased computational complexity. We have investigated the application of a beamspace adaptive beamformer for medical ultrasound imaging, which can be used to achieve reduced computational complexity with performance comparable to that of the Capon beamformer. The idea behind beamspace beamforming is that, instead of using the spatial statistics of the elements in the array to differentiate between signals and interference, we use the spatial statistics of a set of orthogonal beams, which are formed in different directions. This represents a shift from element space to beamspace. Because the majority of interference in medical ultrasound imaging is constrained to a limited spatial interval due to the focused transmit beam, this latter space can be reduced to a dimension that is lower than that of element space. We show, using simulations and experimental data, that this dimension can be selected as low as 3 while still achieving performance comparable to its element space counterpart.     

Switched diversity approach for multireceiving optical wireless systems

A number of existing spatial diversity schemes have been shown to improve the performance of optical wireless communication systems in diversity-rich environments. Among all, switched diversity has low complexity and is simple to implement. In this paper, an innovative spatial diversity scheme based on switched diversity is proposed. The scheme, namely switch-to-dominant combining, contributes to a higher bit error rate (BER) performance when compared to conventional switched diversity schemes, including switch-and-stay and switch-and-examine diversity. The optical multireceiver wireless system operates in a spatially correlated and lognormally distributed fading channel. Analytical analyses are conducted to demonstrate BER and processing load performance offered by the new scheme and compare them to available schemes, i.e., conventional switched combining and selection combining.     

A0模态兰姆波触控屏声指纹库质量评价方法

影响A₀模态兰姆波触控屏性能的核心要素是声指纹库质量,基于曼哈顿距离统计和分析方法研究了声指纹库的质量评价及优化问题。首先,采用有限元方法仿真建立了900种激励-接收节点布局方案对应的触控介质声指纹库;其次,提出了曼哈顿距离图谱及其频次分布图谱的构建方法,利用图谱特征(最小非零频次和峰值分布区间的左临界点)和频次直方图的加权量化指标,对声指纹库质量进行评价,并对激励-接收节点布局方案进行了优选;最后,分析了激励信号对声指纹库质量的影响,相比窄带猝发(Tone burst)信号激励形式,宽频带的线性调频(Chirp)信号激励条件下获得的声指纹库质量明显更优。该研究为超声兰姆波触控屏声指纹库质量的优化提供了基础方法借鉴。     

服务机器人目标同时识别与位姿判定研究

目前机器人尚难以自主建立起目标姿态的概念,通过人机交互方式辅助机器人对目标建模则不失为一种可行方案。提出了一种基于新型目标模型的离线/在线两步目标识别与位姿判定系统。离线阶段采用人机交互方式构建目标模型,在线阶段通过场景图像与目标模型的特征点对应即可自动发现目标,并计算其相对于机器人的位姿。实验证明,该系统能够有效完成对纹理目标的同时识别与位姿判定。     

基于波束空间的改进TOPS宽带DOA估计

提出了一种基于波束空间的改进投影子空间正交性测试算法,以克服投影子空间正交测试(Test of Orthogonality of Projected Subspace,TOPS)算法在低信噪比时容易出现伪峰的缺点。通过对TOPS算法中的正交性测试矩阵添加对角修正矩阵,并利用波束空间方法对阵元接收数据进行预处理,从而实现对宽带信号的波达方向估计。仿真结果表明,文中所提出算法与TOPS算法相比,能够抑制波束指向范围内的伪峰,并能提高分辨概率和减少运算量,是一种具有应用前景的新算法。     

Feature selection and fault‐severity classification–based machine health assessment methodology for point machine sliding‐chair degradation

In this paper, we propose an offline and online machine health assessment (MHA) methodology composed of feature extraction and selection, segmentation‐based fault severity evaluation, and classification steps. In the offline phase, the best representative feature of degradation is selected by a new filter‐based feature selection approach. The selected feature is further segmented by utilizing the bottom‐up time series segmentation to discriminate machine health states, ie, degradation levels. Then, the health state fault severity is extracted by a proposed segment evaluation approach based on within segment rate‐of‐change (RoC) and coefficient of variation (CV) statistics. To train supervised classifiers, a priori knowledge about the availability of the labeled data set is needed. To overcome this limitation, the health state fault‐severity information is used to label (eg, healthy, minor, medium, and severe) unlabeled raw condition monitoring (CM) data. In the online phase, the fault‐severity classification is carried out by kernel‐based support vector machine (SVM) classifier. Next to SVM, the k‐nearest neighbor (KNN) is also used in comparative analysis on the fault severity classification problem. Supervised classifiers are trained in the offline phase and tested in the online phase. Unlike to traditional supervised approaches, this proposed method does not require any a priori knowledge about the availability of the labeled data set. The proposed methodology is validated on infield point machine sliding‐chair degradation data to illustrate its effectiveness and applicability. The results show that the time series segmentation‐based failure severity detection and SVM‐based classification are promising.     

Spatial frequency scheduling for long term evolution single carrier frequency division multiple access-based uplink multiple-input multiple-output systems

Mathematical expressions are derived for the received signal to interference plus noise ratio of uplink single carrier (SC) frequency division multiple access (FDMA) multi-user multiple-input multiple-output (MIMO) systems with spatial frequency domain packet scheduling. The scheduler is able to exploit the available multi-user diversity in time, frequency and spatial domains. Our analysis model is confined to 3GPP uplink SC-FDMA transmission in which we specifically investigate multi-user spatial division multiplexing MIMO schemes.