多用户准正交空时分组码MIMO系统的下行链路预编码

该文针对采用准正交空时分组码的多用户多输入多输出(QSTBC-MU-MIMO)系统,给出一种基于信漏噪声比(SLNR)准则的下行链路干扰抑制预编码方法。通过迭代优化,该文方法可以改善原始SLNR方法中由干扰用户增加所引起的系统性能下降问题,增强了算法对系统用户数的鲁棒性。由于在优化目标中考虑了系统噪声,该方法可通过恰当选取复比例因子来实现优化问题的简化求解。仿真结果验证了该文方法的有效性。     

基于最大化信干噪比的多用户MIMO下行预编码

研究多用户MIMO系统下行链路的容量，以及如何达到该容量是最近几年研究的热点．基于各用户之间干扰为零的BD（Block Diagona Jjzation）算法，由于各用户信道空间的交叠，会造成多用户MIMO系统容量较大的损失，同时BD算法要求接入点的发射天线数不能小于空间复用用户的接收天线数之和．本文提出了基于最大化信干噪比准则下的线性预编码，和减少容量损失的次优线性预编码两种方案，避免了上述两个缺点，推导出基于最大化邬恹准则的线性预编码就是各用户采用单数据流传输的方案，同时通过容量分析和误码率仿真证明，这两种算法都优于传统的BD算法。     

一种多用户MIMO下行链路的TxNZF算法

文中主要介绍一种非线性传榆预处理算法（TxNZF）。首先，给出非线性多用户MIMO下行链路传输模型：其次，分析其非线性处理产生的发射信号、接收端的检测算法以及多连接量化方案；最后，在相同的仿真环境下，对它进行了线性TxZF和非线性TxNZF性能分析，结果表明TxNZF比TxZF更能有效降低发射功率，从而提高能量效率和传榆性能。     

基于SLNR准则的MU-MIMO下行链路的预编码与用户调度

在多用户MIMO（MU-MIMO）系统的下行链路中,为了降低用户端的处理复杂度,发射端预编码的设计对多用户MIMO系统的性能非常重要,基于信漏噪比（SLNR）准则的预编码技术由于同时考虑了共信道干扰（CCI）和噪声,提高了系统的性能,但基站同时服务的用户有限,基于信漏噪比最大的用户调度能够合理地选择用户,提高了多用户分级增益,使系统获得更高的系统容量和系统性能。仿真结果表明,基于SLNR准则的多用户预编码在系统容量和误码率方面要优于单一考虑CCI的迫零预编码（ZF）和单一考虑噪声的最大化每个用户接收到信号的信噪比预编码（MRT）。在采用SLNR预编码的条件下,信漏噪比最大的用户调度系统性比轮询调度和最大信道增益调度好,并且随着待选用户数的增多,不会给系统的调度策略带来很大的影响。     

有限反馈MIMO下行系统中基于黄金码的传输方案与解码方法

针对有限反馈多输入多输出下行系统,结合黄金码与预编码技术,提出一种新的预编码设计准则、码字选择方案及新的传输方案和相应的低复杂度解码方法。事实上,在充分利用黄金码能够克服信道深度衰落这一特性的基础上,对所选预编码码字进行重新构造,得到一个二重预编码矩阵,将其作为发送信号,从而能够实现线性解码。与此同时,针对传统的MIMO下行系统传输方案提出了ML和MMSE的联合解码方法,使其能通过一个门限值动态地调节解码复杂度。数值仿真结果证明了本文所提方案性能的优越性。     

多用户MIMO系统在有限反馈下结合预编码与调度算法的研究

捅要：研究了多用户多输入多输出（MIMO）系统在有限反馈下的一种结合单位预编码与用户调度算法的方案。在该系统中每一用户都具有多个接收天线,该方案具有较大的多用户分集增益和较小的计算复杂度,从而能够减少系统中的用户间干扰。每个用户独立地决定自己的天线合并矢量,并将最优波束矢量以及对应的估计信干噪比通过有限反馈信道反馈给基站,此时基站获取了相应的用户信道信息和用户间干扰信息。基于接收到的反馈信息,基站从预定义的码本中选取和速率最大的最优子集进行系统预编码,然后依照预编码矩阵调度欧氏距离最小的用户且用户个数不超过发送天线的数目。仿真结果显示该方案有效地改善了系统速率,特别是在用户数目较多或者信道环境较好的情况下。     

上下行信道不对称性对TDD-MIMO系统的影响

时分双工和多输入多输出技术均是超三代移动通信中的关键技术。在传统的关于时分双工的文献中,发送端信道状态信息均通过上下行信道的对称性获得。然而实际中由于受温度、湿度等影响,射频电路增益会缓慢变化,于是关于上下行信道对称的假设不再成立,这必定会对性能产生影响。本文详细分析了该影响并提出通过采用射频电路参数反馈法来解决这一问题。仿真结果表明,相对于传统的上行信道重用法,采用射频参数反馈法提高了系统信道容量。     

SINR约束下的MIMO多用户下行链路预编码

基于SINR约束下的MIMO多用户下行链路的预编码设计准则,给出了一虚拟上行链路的构造方法,同时利用该虚拟上行链路和下行链路之间的对偶性,提出了对发射端和接收端的线性处理进行优化的迭代算法。该算法可以交替优化各路数据分配的功率、发射权向量和接收权向量,直至算法收敛。     

MIMO下行链路中的多用户调度算法

针对采用随机波束成形的MIMO下行链路,提出了一种多用户调度算法。在接收端利用每个用户在各个波束方向上的比例公平性参数来得到容量门限。仿真结果显示,这种调度算法相比其他门限调度算法,在系统性能无明显损失的情况下,有效地减小了反馈量。     

基于分布式部分连接结构的多用户大规模MIMO混合预编码

在多用户大规模多输入多输出(MIMO)系统中,针对传统方案受限于集中式部分连接结构和固定匹配相控算法而未能充分利用空间资源的问题,提出一种基于分布式部分连接结构的低复杂度相控迫零混合预编码方案.所提方案设计了多于射频链路数的逻辑天线子阵列,以使每个射频链路能连接多个分布子阵列,从而提供更高的空间分集增益.进一步通过分析...     

Downlink scheduling of multiuser MIMO systems with transmit beamforming

This article deals with downlink scheduling for multiuser multiple-input multiple-output （MIMO） systems, where the base station communicates with multiple users simultaneously through transmit beamforming. Most of the existing transmission schemes for multiuser MIMO systems focus on optimizing sum rate performance of the system. The individual quality of service （QoS） requirements （such as packet delay and minimum transmission rate for the data traffic） are rarely considered. In this article, a novel scheduling strategy is proposed, where we try to optimize the global system performance under individual QoS constraints. By performing scheduling into two steps, namely successive user selection and power allocation, the scheduler can achieve efficient resource utilization while maintaining the QoS requirements of all users. Extensive simulations and analysis are given to show the effectiveness of the proposed scheduler.     

A distributed transmit beamforming synchronization strategy for multi-element radar systems

The distributed transmit beamforming has recently been discussed as an energy-effective technique in wireless communication systems. A common ground of various techniques is that the destination node transmits a beacon signal or feedback to assist source nodes to synchronize signals. However, this approach is not appropriate for a radar system since the destination is a non-cooperative target of an unknown location. In our paper, we propose a novel synchronization strategy for a distributed multiple-element beamfoming radar system. Source nodes estimate parameters of beacon signals transmitted from others to get their local synchronization information. The channel information of the phase propagation delay is transmitted to nodes via the reflected beacon signals as well. Next, each node generates appropriate parameters to form a beamforming signal at the target. Transmit beamforming signals of all nodes will combine coherently at the target compensating for different propagation delay. We analyse the influence of the local oscillation accuracy and the parameter estimation errors on the performance of the proposed synchronization scheme. The results of numerical simulations illustrate that this synchronization scheme is effective to enable the transmit beamforming in a distributed multi-element radar system.     

Power control and beamforming for systems with multiple transmit and receive antennas

This paper investigates the performance of narrowband, slowly fading, and delay-limited multiple-antenna systems where channel state information (CSI) is available at the transmission end. This situation can arise in time-division duplex (TDD) based two-way systems where channel state estimation can be performed using the signal received from the opposite link. Power control methods which attempt to keep the transmission rate constant at the expense of randomizing the transmit power are considered. It is shown that significant savings in average transmit power (sometimes on the order of tens of decibels) can be expected compared to systems which keep the total transmit power constant. Several practical channel coding examples using are illustrated and their bit and frame error rate performance are discussed.     

Effect of angle-of-arrival on transmit diversity and beamforming systems under correlated fading

A comparative analysis of transmit diversity and beamforming systems, using outage capacity as performance measure, is presented. The objective is to examine the effect of angle-of-arrival (AOA) distributions on two systems with angle spread. This is done by comparing the performance of transmit diversity with a system that uses beamforming to point a relatively narrow beam at the mobile station. Results show that the transmit diversity system, using uniform linear arrays with truncated Laplacian AOA, always performs better, even at smaller angle spreads, as compared to other energy distributions.     

Performance analysis of scheduled transmit beamforming systems under non-identically delayed feedback channels

Wireless Networks - In this paper, we investigate the performance analysis of a scheduled transmit beamforming system under non-identically delayed feedback channels. This paper derives the exact...     

TD-LTE下行链路波束赋形技术研究

在波束赋形系统模型和算法准则的基础之上,给出一种相对传统特征值分解方法有一定简化的算法。该方法能够有效克服波束赋形过程中复杂度较大且会引起系统延迟的问题。根据TD-LTE系统物理层协议规定生成信号源并进行建模,通过搭建完整的赋形链路来获得波束赋形的加权系数。在多径衰落信道下,对传统的基于QR分解的特征值分解算法和简化算法进行仿真分析。结果表明：在相同的仿真条件下,简化后算法能够在保持一定精度的基础上,复杂度降低为原来的1/60。     

Downlink beamforming for DS-CDMA mobile radio with multimediaservices

Downlink beamforming is a promising technique for direct-sequence code-division multiple-access (DS-CDMA) systems with multimedia services to effectively reduce strong interference induced by high data rate users. A new downlink beamforming technique is proposed that converts the downlink beamforming problem into a virtual uplink one and takes into account the data rate information of all users. Since the main complexity of this method is due to the existence of multidelay paths, two simplified algorithms are suggested using an equivalent one-path channel vector to replace multipath channel vectors. Computer simulation results are given to evaluate the downlink capacity of DS-CDMA systems using a base station antenna array and the new algorithms proposed     

Distributed transmit beamforming: challenges and recent progress

Distributed transmit beamforming is a form of cooperative communication in which two or more information sources simultaneously transmit a common message and control the phase of their transmissions so that the signals constructively combine at an intended destination. Depending on the design objectives and constraints, the power gains of distributed beamforming can be translated into dramatic increases in range, rate, or energy efficiency. Distributed beamforming may also provide benefits in terms of security and interference reduction since less transmit power is scattered in unintended directions. Key challenges in realizing these benefits, however, include coordinating the sources for information sharing and timing synchronization and, most crucially, distributed carrier synchronization so that the transmissions combine constructively at the destination. This article reviews promising recent results in architectures, algorithms, and working prototypes which indicate that these challenges can be surmounted. Directions for future research needed to translate the potential of distributed beamforming into practice are also discussed.