RZF预编码与MMSE-SIC检测联合的大规模MIMO系统预编码设计算法

研究了大规模多输入多输出(MIMO)系统的预编码设计算法。针对大规模MIMO系统通常利用增加用户天线数来提高系统频谱效率的方法会导致用户间干扰增大,从而对系统性能产生负面影响的问题,提出了一种将正则化迫零(RZF)预编码与最小均方误差-串行干扰消除(MMSE-SIC)检测相结合的改进算法。该算法通过在基站端采用RZF预编码对信号进行预处理以平衡用户间干扰和噪声干扰的影响,继而在接收端运用检测性能优异的MMSE-SIC算法来进一步减轻信号中的干扰,从而达到提升系统容量的目的。实验结果表明,这种将RZF预编码与MMSE-SIC检测相结合的改进算法,在用户间干扰较大时具有较好的适用性,且在完全已知和未完全已知信道状态信息情况下的频谱效率均优于传统RZF算法。     

大规模MIMO系统的全导频RZF预编码方法

研究了大规模多输入多输出(MIMO)系统的预编码。针对小区间干扰和导频污染会对预编码的有效性产生较大影响的问题,提出了一种改进的全导频正则化迫零(RZF)预编码方法。该方法通过将有限的正交导频信号分配给小区用户来对预编码矩阵中的信道向量进行优化,得到优化后的全导频正则化预编码矩阵,并依此推导出新的包含导频污染函数和用户干扰函数的和速率表达式。另外,综合考虑基站天线数、用户数以及导频重用因子,优化其配置关系,从而用较少的用户信息和更高的导频重用因子来抑制更多的小区间干扰,有效地提升系统性能。实验结果表明,这种改进的RZF预编码算法能够较好地提高系统容量,在完全已知信道状态信息(CSI)和未完全已知CSI两种情况下的频谱效率及和速率均优于传统的RZF方法。     

有限反馈SDMA系统中信道矩阵的逐列量化算法

针对多天线广播信道(MIMO BC)块对角化(BD)预编码空分多址接入(SDMA)系统对角化预编码时,直接量化信道矩阵的有限反馈方法复杂度过高的问题,利用系统中用户配置多个天线的特点,提出了基于天线合并逐列量化(PCQ)信道矩阵的有限反馈方法.该方法对接收信号做多次天线合并,将传统算法中直接量化信道矩阵转变为多次量化等效信道矢量,仿真结果表明,在总的反馈比特数相同的情况下,该方法以较少的和容量损失换来了复杂度的大幅降低.     

Optimisation of cooperative spectrum sensing in cognitive radio network

Spectrum sensing is a key problem in cognitive radio (CR). Because of a low SNR, fading and sensing time constraints, a single CR may not be able to reliably sense the presence of primary radios, which motivates the study of sensing by multiple cognitive users. Here, the authors consider cooperative spectrum sensing (CSS) using a counting rule where several cognitive users sense whether primary users exist or not and send their decisions to the centre where the final decision is made. Optimal strategies under both the Neyman-Pearson criterion and the Bayesian criterion for CSS are derived using a counting rule. In addition, the authors present simple methods to calculate the optimal settings. Another contribution here is the analysis of a randomised rule at the centre, which is a long-existing problem in the field of distributed detection systems.     

Compact ultrahigh-frequency antenna designs for low-cost passive radio frequency identification transponders

Compact planar antennas for low-cost radio frequency identification (RFID) passive transponders are disclosed. The proposed ultrahigh-frequency antenna takes advantage of its unique topology to assure conjugate matching with essentially complex impedance of the electronic chip directly embedded into the radiator. Rectenna design issues are also emphasised. An original method to characterise IC chips and antennas as taken in its entirety of transponders is presented. The characterisation of the chip takes into account the impact of connecting antennas to the rectifier by flip-chip bonding process. The proposed experimental method allows finding chip impedance exactly as it seen by antennas. Refined rectifier circuitry effectively overcomes dependence of transponder performances on the type deviation of the connected antennas. Very good antenna performance is predicted theoretically and validated experimentally over an operating bandwidth of actual RFID systems.     

An Optimized Algorithm for CR-MIMO Wireless Networks

With the rapid development of wireless communication technology, the spectrum resources are increasingly strained which needs optimal solutions. Cognitive radio (CR) is one of the key technologies to solve this problem. Spectrum sensing not only includes the precise detection of the communication signal of the primary user (PU), but also the precise identification of its modulation type, which can then determine the a priori information such as the PU’ service category, so as to use this information to make the cognitive user (CU) aware to discover and use the idle spectrum more effectively, and improve the spectrum utilization. Spectrum sensing is the primary feature and core part of CR. Classical sensing algorithms includes energy detection, cyclostationary feature detection, matched filter detection, and so on. The energy detection algorithm has a simple structure and does not require prior knowledge of the PU transmitter signal, but it is easily affected by noise and the threshold is not easy to determine. The combination of multiple-input multiple-output (MIMO) with CR improves the spectral efficiency and multi-path fading utilization. To best utilize the PU spectrum while minimizing the overall transmit power, an iterative technique based on semidefinite programming (SDP) and minimum mean squared error (MMSE) is proposed. Also, this article proposed a new method for max-min fairness beamforming. When compared to existing algorithms, the simulation results show that the proposed algorithms perform better in terms of total transmitted power and signal-to-interference plus noise ratio (SINR). Furthermore, the proposed algorithm effectively improved the system performance in terms of number of iterations, interference temperature threshold and balance SINR level which makes it superior over the conventional schemes.     

单用户毫米波大规模MIMO系统的混合预编码方案设计

对MIMO通信系统的数字预编码方法进行了深入分析,指出单用户毫米波大规模MIMO系统和传统全数字预编码方案所用射频(RF)链路数量过大致使系统实现成本大和能量消耗较高,并针对这种情况,提出了一种在系统收发两端分别采用混合预编码器和混合合成器的混合预编码方案。该方案首先通过迭代算法设计模拟预编码矩阵,并且根据信道矩阵与模拟预编码矩阵作用生成的等效信道矩阵设计数字预编码矩阵,然后根据混合预编码器设计混合合成器,从而使系统频谱效率最大化。该方案与传统全数字预编码及现有混合预编码方案的仿真比较结果表明,该方案有效降低了系统实现成本和能量消耗,且性能优于现有的混合预编码方案,与传统全数字预编码方案相比,性能非常接近。     

由交织技术构建新的最优跳频序列族

跳频技术具有抗干扰、抗截获、频带共享和码分多址等优点,在民用移动通信、军事无线电通信、现代雷达和声纳等电子系统中具有广泛的应用.寻找和设计最优跳频序列族是研究跳频通信技术的重要议题,因为跳频序列是跳频系统中不可或缺的重要组成部分.本文基于交织技术和中国剩余定理,构造了两类新的跳频序列族,导出了新序列族的各类汉明相关性质.研究结果表明,通过选择恰当的参数和已知跳频序列族,本文所提方法可递归得到大量的最优跳频序列族.     

A Highly Efficient Algorithm for Phased-Array mmWave Massive MIMO Beamforming

With the rapid development of the mobile internet and the internet of things (IoT), the fifth generation (5G) mobile communication system is seeing explosive growth in data traffic. In addition, low-frequency spectrum resources are becoming increasingly scarce and there is now an urgent need to switch to higher frequency bands. Millimeter wave (mmWave) technology has several outstanding features—it is one of the most well-known 5G technologies and has the capacity to fulfil many of the requirements of future wireless networks. Importantly, it has an abundant resource spectrum, which can significantly increase the communication rate of a mobile communication system. As such, it is now considered a key technology for future mobile communications. MmWave communication technology also has a more open network architecture; it can deliver varied services and be applied in many scenarios. By contrast, traditional, all-digital precoding systems have the drawbacks of high computational complexity and higher power consumption. This paper examines the implementation of a new hybrid precoding system that significantly reduces both calculational complexity and energy consumption. The primary idea is to generate several sub-channels with equal gain by dividing the channel by the geometric mean decomposition (GMD). In this process, the objective function of the spectral efficiency is derived, then the basic tracking principle and least square (LS) techniques are deployed to design the proposed hybrid precoding. Simulation results show that the proposed algorithm significantly improves system performance and reduces computational complexity by more than 45% compared to traditional algorithms.     

Efficient Gauss-Seidel Precoding with Parallel Calculation in Massive MIMO Systems

A number of requirements for 5G mobile communication are satisfied by adopting multiple input multiple output (MIMO) systems. The inter user interference (IUI) which is an inevitable problem in MIMO systems becomes controllable when the precoding scheme is used. In this paper, the horizontal Gauss-Seidel (HGS) method is proposed as precoding scheme in massive MIMO systems. In massive MIMO systems, the exact inversion of channel matrix is impractical due to the severe computational complexity. Therefore, the conventional Gauss-Seidel (GS) method is used to approximate the inversion of channel matrix. The GS has good performance by using previous calculation results as feedback. However, the required time for obtaining the precoding symbols is too long due to the sequential process of GS. Therefore, the HGS with parallel calculation is proposed in this paper to reduce the required time. The rows of channel matrix are eliminated for parallel calculation in HGS method. In addition, HGS uses the ordered channel matrix to prevent performance degradation which is occurred by parallel calculation. The HGS with proper number of parallelly computed symbols has better performance and reduced required time compared to the traditional GS.     

Frequency domain interpretation of power ratio metric for cognitive radio systems

Software radio (SWR) is an enabling technology for cognitive radio (CR) systems which promises to (de) modulate any signal, at any frequency. SWR signal therefore is composed of different standard's signals, and each standard's signal is either multicarrier or multiplex of single carriers. This combination leads to high temporal fluctuations and thus SWR signal inherits high peak to average power ratio (PAPR) or simply high power ratio (PR). Nonlinear analogue components (amplifiers, converters etc.) cause distortions (in and out of band distortion) for high PR signals which result in system performance degradation. Usually PR problem is addressed in time domain, and here frequency domain interpretation of PR which is more appropriate in SWR context is presented. Gaussian equivalence between SWR signal and orthogonal frequency division multiplexing (OFDM) signal is proved first to accentuate high PR issue in SWR as OFDM suffers the same problem. Then frequency domain interpretation of PR metric is discussed which results in a PR upper bound. This PR upper bound depends only upon spectral values of the signal thus associates spectrum with PR. As a result this bound assists in spectrum access for CR systems by providing PR metric information related to any available bandwidth. Thus bandwidth allocation in a spectrum access scenario under PR constraint is simplified.     

An Enhanced Jacobi Precoder for Downlink Massive MIMO Systems

Linear precoding methods such as zero-forcing (ZF) are near optimal for downlink massive multi-user multiple input multiple output (MIMO) systems due to their asymptotic channel property. However, as the number of users increases, the computational complexity of obtaining the inverse matrix of the gram matrix increases. For solving the computational complexity problem, this paper proposes an improved Jacobi (JC)-based precoder to improve error performance of the conventional JC in the downlink massive MIMO systems. The conventional JC was studied for solving the high computational complexity of the ZF algorithm and was able to achieve parallel implementation. However, the conventional JC has poor error performance when the number of users increases, which means that the diagonal dominance component of the gram matrix is reduced. In this paper, the preconditioning method is proposed to improve the error performance. Before executing the JC, the condition number of the linear equation and spectrum radius of the iteration matrix are reduced by multiplying the preconditioning matrix of the linear equation. To further reduce the condition number of the linear equation, this paper proposes a polynomial expansion precondition matrix that supplements diagonal components. The results show that the proposed method provides better performance than other iterative methods and has similar performance to the ZF.     

Pulse position modulated space?time trellis coding for ultra-wideband impulse radio multiple-input multiple-output communication systems

The design of pulse position modulated (PPM) space-time trellis codes (STTC) for ultra-wideband impulse radio (UWB-IR) multiple-input multiple-output (MIMO) communication systems over slow and fast fading multipath channels is considered. First, A probability of error analysis is carried out to derive upper bounds on pairwise symbol error probability at high and low signal-to-noise ratios (SNRs). From the upper bounds, A new distance notion is introduced and novel design criteria for optimal (in error rate performance) M-ary PPM STTC are deduced for UWB. An optimal binary-PPM STTC is designed for two transmit antennas. Finally, simulation results of the UWB-IR MIMO system, using the optimal STTC, confirm significant improvement in bit-error-rate performance over the uncoded UWB-IR single-input single-output system and also over previously proposed space-time coding scheme for UWB, at higher SNR.     

Blind adaptive and iterative interference cancellation receiver structures based on the constant modulus criterion in multipath channels

Blind adaptive and iterative interference cancellation (IC) receiver structures for direct sequence code division multiple access systems in multipath channels are proposed. A code-constrained constant modulus design criterion based on constrained optimisation techniques and adaptive algorithms for receiver and channel parameter estimation are described for successive IC (SIC) and parallel IC (PIC) detectors and a new hybrid IC (HIC) scheme in scenarios subject to multipath fading. The proposed HIC structure combines the strengths of linear, SIC and PIC receivers and is shown to outperform the conventional linear, SIC and PIC structures. A novel iterative detection approach that generates different cancellation orders and selects the most likely symbol estimate on the basis of the instantaneous minimum constant modulus criterion is also proposed and combined with the new HIC structure to further enhance performance. Simulation results for an uplink scenario assess the algorithms, the proposed blind adaptive IC detectors against existing receivers and evaluate the effects of error propagation of the new cancellation techniques.     

Antenna subset selection in measured indoor channels

Antenna subset selection can greatly reduce the implementation complexity of multiple input multiple output (MIMO) systems while retaining most of their benefits. This paper investigates the diversity gain and capacity of such systems in wireless personal area networks. Considered scenarios include both the communication between access point to a laptop, and between two handheld devices. We analyse the performance of different antenna selection algorithms and signal combining methods in measured dual-polarised narrowband and wideband propagation channels. We find that line-of-sight and non-line-of-sight situations have fairly similar behaviour. Different polarisations result in similar signal-to-noise ratio gains when the multiple antennas are used for diversity, but result in noticeably different capacities in spatial-multiplexing systems. We also find that radiofrequency (RF) preprocessing of the signals is less effective for handheld handsets with non-uniform antenna arrangements than for uniform linear arrays. For communications between handheld devices, simple selection (of one out of four antennas) shows extremely high performance gains compared to no-selection. Finally, we compare bulk selection (same antenna subset is used for all frequency sub-channels) to per-tone selection (different antenna subsets can be used for each frequency sub-channel) for wideband channels. Bulk selection together with RF preprocessing performs almost as well as per-tone selection for some scenarios.     

基于二进制树的RFID系统自适应多分支防碰撞算法

为提高射频识别(RFID)系统的识别效率,研究了系统的标签防碰撞问题。考虑到对标签进行多分支处理能够有效地提高RFID系统标签识别效率,而传统的多分支防碰撞算法都是在标签估计的基础上对标签进行最优分组,标签估计产生的时延和误差都会影响整体的识别效率,提出了一种基于二进制树的自适应多分支(AMB)防碰撞算法。该算法根据二进制树结构特点,利用识别的标签数目对树结构中右节点标签进行估计并进行分组识别,经过多次调整的自适应多分支防碰撞算法,可以规避一次标签估计所引入的估计误差,从而提高系统的识别效率。仿真结果表明自适应多分支算法可以大大提高标签识别效率,在标签数量较大时系统效率可达43%左右。同时该算法实现简单,只需在阅读器中增加若干计数器,不需要改变任何空中接口,很容易与现有协议兼容。     

Tomlinson-Harashima precoding with imperfect channel state information

Nonlinear Tomlinson-Harashima precoding (THP) is an attractive solution for a scenario where the transmission system employs multiple antennas at transmitter and multiple users with a single antenna at the receiver, so that the cooperation among the receive antennas are impossible (downlink scenario). THP solution based on zero forcing (ZF) and minimum mean square error (MMSE) criteria is one of the important techniques to achieve near multiple input multiple output channels capacity with reasonable complexity. In this paper, the effect of channel imperfection on THP is considered. At first, the achievable rate of THP with respect to ZF criterion in an imperfect channel state information (CSI) scenario is calculated. Moreover, based on MMSE criterion, a new robust solution is derived which provides a significant improvement with respect to the conventional optimisation method. Then, the effect of channel estimation error on THP is considered as an improved optimisation where THP filters are optimised together with a channel estimator. Spatial power loading is found to be important to the THP performance. This loading for robust/joint optimisation of MMSE THP is developed by minimum average symbol error rate sense. Simulation results show the capacity loss, the performance advantage attained by the robust/joint optimisation and the power loading in an imperfect CSI scenario.     

基于卡方检验的多天线认知无线网络协作频谱感知算法

研究了基于分集的多天线认知无线网络的频谱感知技术。针对天线独立性会导致已有的基于协方差矩阵的协作频谱感知算法性能急剧下降甚至失效的问题,提出了一种基于卡方拟合优度检验的多天线协作频谱感知算法。该算法将频谱感知问题转化为一个多项分布检验的问题,然后利用卡方拟合优度检验判决频谱是否空闲,从而实现频谱感知。理论分析和仿真表明,该算法的性能不受天线相关性以及噪声不确定度的影响。     

Spectrum etiquettes for terrestrial and high-altitude platform-based cognitive radio systems

Two spectrum etiquettes are developed for the use on the downlink of coexisting high-altitude platform (HAP) and terrestrial fixed broadband systems that are intended for future application with cognitive radio-based user terminals with directional antennas. The spectrum etiquettes are based on the interference to noise ratio and carrier to interference plus noise ratio levels at the receiver of an incumbent user. Antenna beamwidths and multiple modulation scheme levels determine the parameter settings for coexistence performance. It is shown that coexistence performance can be improved by exploiting the surplus transmitter power of the terrestrial system, thereby enabling the incumbent terrestrial system to accommodate additional interference arising from a newly activated HAP system.     

Enhanced two-antenna structures for universal mobile telecommunications system diversity terminals

The design of several universal mobile telecommunications system multi-antenna systems with radiators having a high isolation, a high total efficiency and a low envelope correlation is presented. First, two planar inverted-F antennas (PIFAs), closely positioned at the top edge of a small ground plane whose size is representative of the printed circuit board of a mobile phone, are described. A technical solution is then proposed to increase the isolation between the antennas and enhance their total efficiency when still keeping them closely spaced. The technical solution is based on an optimal neutralisation technique, applied between the antennas of the structure. Several optimal systems, based on different parameters, are fabricated and measured. The simulated and measured S-parameters are presented in addition to the gain radiation patterns, the surface currents on the structure and the theoretical and experimental total efficiencies. The envelope correlation coefficients are also computed using two different equations. It is then demonstrated that, with the help of the neutralisation technique, a system composed of two closely spaced PIFAs located at the top edge of a small ground plane can lead to a high total efficiency and a low envelope correlation coefficient. In conclusion, this technique can be easily implemented at the terminal side of a wireless link and may enhance its diversity gain and multiple input multiple output performance.