认知无线电网络中基于主系统有限反馈的频谱共享方案

摘 要：提出一种频谱共享方案,该方案适用于同时存在多个主用户和一对次用户的场景。各主用户依据接收机反馈的有限信道质量信息（CQI, channel quality information）分配发送功率及传输速率。次用户根据偷听到的主系统CQI有限反馈,以适当的功率及速率接入信道。次用户接入信道的行为对各主用户造成一定干扰,以致主系统传输速率遭受一定损失。本文在主系统速率损失约束条件下,研究得出了使次系统吞吐量最大化的次用户发送功率及传输速率最佳分配方案。数值结果表明,对于每个主用户仅需反馈3-4个量化比特,次系统的有效吞吐量就可堪比于主次发射端均拥有主系统链路完整CQI的情况。仿真结果显示,所提出的频谱共享方案能够满足主系统速率损失约束。     

自适应比特分配算法在高速遥测系统中的应用

提出了一种简单、快速的正交频分复用(OFDM)系统的自适应调制算法。该算法在子信道分配已经完成的前提下,通过信道参数的估计,动态地分配子信道上的比特和功率,使得发送的每个符号的总比特数最大,从而提高信道的利用率及数据传输速率,满足了高速遥测系统所要求的传输速率及误码率。仿真结果表明,与等比特分配算法相比,本自适应比特分配算法相对简单,降低了系统的传输功率,其误码率性能明显好于等比特分配算法。     

Wyner-Ziv视频编码中无反馈速率控制算法研究

为了避免在分布式视频编码系统中使用反馈信道,提出了一种基于Wyner-Ziv编码的无反馈速率控制算法。首先,利用目标码率和目标帧率进行GOP层码率分配;然后,根据原始图像的帧间相关性动态选择量化因子和量化矩阵来分配每个GOP内关键帧和Wyner-Ziv帧的比特数;接下来,利用系数带级的相关性计算相关噪声模型参数,并选择对应的LDPC校验矩阵,提出Wyner-Ziv帧的无反馈比特面速率控制算法。实验结果表明,在给定目标码率下,所提算法的编码码率误差小于0.57%,且与现有无反馈速率控制算法相比,解码恢复图像的PSNR(峰值信噪比)可以提高1dB。另外,该算法基本没有增加编码端复杂度,可用于实际分布式视频通信系统。     

一种基于OFDM的多用户认知无线电系统联合资源分配算法

针对频谱共享环境,研究了采用OFDM调制方式的多用户认知无线电系统中,综合考虑自身发射功率约束与主用户干扰功率约束的资源分配问题.基于最大化认知用户和速率的优化目标,给出了连续比特条件下最优的多水位注水功率分配表达式;针对更实际的整数比特要求情况,通过基于相对增益因子RG的子信道选择机制与每个认知用户内多约束的贪婪比特与功率分配策略,来最大限度地提高频谱利用率.仿真结果表明:联合的子信道、功率与比特分配算法在不同的参数设置下均达到了良好的性能,在不影响主用户通信的前提下有效地提高了认知系统的频谱利用率.     

存在信道反馈延迟时Turbo-BLAST系统的自适应功率分配算法

该文针对信道反馈有延迟的Turbo-BLAST系统,以误比特率(Bit Error Rate, BER)为优化目标,提出次优和最优两种自适应功率分配算法。通过系统建模和性能分析,推导出系统瞬时信噪比(Signal Noise Ratio, SNR)的条件概率密度函数,利用数学变换得到信道反馈有延迟时系统BER的表达式。发送端在总功率约束条件下,分别采用拉格朗日极值法和牛顿迭代法求解功率分配矩阵的次优解与最优解。接收端采用基于迫零(Zero Forcing, ZF)准则的软干扰抵消算法进行迭代检测。仿真结果表明,和等功率分配相比,采用该文所提两种算法均可改善系统的BER性能。最优功率分配算法以增加计算复杂度为代价更好地改善了系统的BER性能,而接收端的迭代检测可进一步改善系统性能。     

存在反馈延迟时V-BLAST系统的功率分配算法

针对信道反馈有延迟条件下的垂直贝尔实验室分层空时(Vertical Bell Laboratories Layered Space Time,V-BLAST)系统,提出基于最小均方误差检测(Minimize Mean Square Error,MMSE)的自适应功率分配算法.通过系统建模和性能分析,推导出系统瞬时信干噪比的条件概率密度函数,并得到V-BLAST系统的平均BER表达式.发 送端在总功率约束条件下,以瞬时BER为优化目标,利用拉格朗日极值法求解自适应功率分配矩阵.仿真结果表明,在信道反馈有延迟时,与等功率分配相比,采用所提算法可显著改善系统的BER性能.     

一种低反馈开销多用户MIMO-OFDM系统功率最小化方案

该文利用凸规划理论中的库恩-塔克条件,为基于TCM编码的多用户MIMO-OFDM系统中实时业务资源优化问题提出了一种低反馈开销的功率最小化方案。该方案首先设计速率、功率和等效信道量化门限的码本,然后根据当前的信道状态信息分配子载波并对等效信道增益量化,最后基站给用户广播资源分配结果。仿真结果表明:相比其它方案,该文提出的方案有效降低系统能耗并且具有反馈开销低的特点。     

一种基于错误传播补偿的V—BLAST自适应比特和功率分配算法

本文探讨了V-BLAST系统在总发射功率受限和一定目标误码率要求的前提下,基于自适应调制时间块的比特、功率分配问题,分析和比较了系统在采用不同串行干扰抵消顺序时的抗信道时变性能和抗错误传播性能,找出了在BER和速率两方面性能最优的串行干扰抵消顺序。针对错误传播对系统BER性能的冲击,提出了一种新的基于错误传播补偿的V-BLAST自适应比特、功率分配方案。仿真结果表明,该方案能显著提高系统在时变信道下的BER性能,有效增大自适应调制块长度,减小反馈开销。     

多用户OFDM系统中子载波比特分配算法

针对多用户OFDM系统中的功率优化问题,提出了一种新的子载波、比特分配算法。利用匈牙利算法对子载波进行初始分配,然后根据信道的状态信息为每个子载波动态地分配比特,最后对分配的结果作进一步调整,直到发射总功率不再减小为止。仿真结果表明,调整后的结果比原有方法有所改善,在满足传输速率和误码率要求的条件下,有效地降低了系统发射总功率。     

基于几何均值分解的可见光MIMO预编码优化设计

在可见光通信(VLC,Visible Light Communication)系统中，受发送信号非负约束和信道相关性较强影响，预编码后的等效子信道增益差异较大，现有的预编码需要迭代搜索等复杂的功率和比特分配算法来适配不同子信道。针对此问题，利用非线性判决反馈均衡检测器，提出基于几何平均分解的线性预编码，将信道分解成多个增益相同的子信道来提高误码率性能，避免了传统预编码中复杂的功率和比特分配问题，又基于最小均方误差准则进行功率分配，进一步提高了系统性能。最后仿真实验分析结果表明，所提两种方案均明显优于传统预编码，误码率性能获得了约8 dB～12 dB增益。     

Interference alignment based on optimizing bit allocation with limited feedback in interfering MIMO-MAC networks

A novel limited feedback for interference alignment algorithm was proposed based on the disadvantages of traditional limited feedback interference alignment schemes for MIMO uplink.Unlike the traditional linear interference alignment,an iterative scheme was presented.The pre-coder was designed through maximizing the target signal to the interference leakage and noise ratio,and interference suppression matrix was designed by maximizing the signal to interference plus noise ratio for each data stream,which can come over rate loss in low SNR.In addition,the bit allocation of traditional limited feedback schemes were based on the mean of interference leakage,which were not perfect and make the total number of the effective bits less than the bits provided by system.Thus,a novel bit allocation scheme was provided that improving bit utilize and decreasing quantization error.Theoretical analysis and simulation experiments show that compare to the existed classical algorithms,the algorithm was a stepwise enhancement of signal quality for iterative search in perfect CSI which was better than linear algorithm and has a larger space with no need for strictly align interference in limited feedback CSI which reduces the influence of quantization error more.The effective bit distribution and bit utilization are improved by bit allocation,resulting in improved performance in limited feedback.     

Adaptive bit allocation scheme in multi-cell cooperative block diagonalization systems with delayed and limited feedback

In multi-cell cooperative multi-input multi-output(MIMO) systems,base station(BS) can exchange and utilize channel state information(CSI) of adjacent cell users to manage co-channel interference.Users quantize the CSIs of desired channel and interference channels using finite-rate feedback links,then BS can generate cooperative block diagonalization(BD) precoding matrices using the obtained quantized CSI at transmitter to supress co-channel interference.In this paper,a novel adaptive bit allocation scheme is proposed to minimize the rate loss due to imperfect CSI.We derive the closed-form expression of rate loss caused by both channel delay and limited feedback.Based on the derived rate loss expression,the proposed scheme can adaptively allocate more bits to quantize the better channels with smaller delays and fewer bits to worse channels with larger delays.Simulation results show that the proposed scheme yields higher performance than other allocation schemes.     

协作多基站多用户MIMO系统中有限反馈比特分配方案

For the cooperative multi-cell systems with multi-user MIMO, a new limited feedback bit allocation scheme is proposed to minimize the rate loss caused by quantization error. In the proposed scheme, the Channel State Information (CSI) feedback of cell-edge user for the local service cell and the adjacent interference cell are separately quantized. Based on the upper bound of the rate loss of cell-edge user due to the limited feedback, the number of feedback bits for quantized CSI of the local service cell and the adjacent cell are optimized with the fixed total bits of the limited feedback. The simulation shows that our proposed scheme of feedback bits allocation efficiently decreases the interference and increases the rate of systems compared with that of equal bits allocation and those of other allocations .     

宏微协同组网下基于小区分簇的联合传输与无线资源分配

针对宏微协同组网下小区间无线资源管理问题,文章提出一种大规模多入多出系统下基于微小区分簇的联合传输和动态频谱分配策略,该策略分两步执行以优化网络加权和速率.首先,所提算法根据各用户当前的信道状态执行微小区分簇,以尽可能地降低小区间干扰,提升系统容量.接着,宏基站和各微小区簇根据所服务用户当前的业务请求信息分别为其动态分配子载波,以最大化网络加权和速率,并提升资源利用率.仿真结果显示,该文提出的微小区分簇和动态频谱分配策略能在尽可能降低宏微协同组网中用户间干扰的同时,有效地提升系统吞吐量.     

Optimum Power Allocation for Single-User MIMO and Multi-User MIMO-MAC with Partial CSI

We consider both the single-user and the multi-user power allocation problems in MIMO systems, where the receiver side has the perfect channel state information (CSI), and the transmitter side has partial CSI, which is in the form of covariance feedback. In a single-user MIMO system, we consider an iterative algorithm that solves for the eigenvalues of the optimum transmit covariance matrix that maximizes the rate. The algorithm is based on enforcing the Karush-Kuhn-Tucker (KKT) optimality conditions of the optimization problem at each iteration. We prove that this algorithm converges to the unique global optimum power allocation when initiated at an arbitrary point. We, then, consider the multi-user generalization of the problem, which is to find the eigenvalues of the optimum transmit covariance matrices of all users that maximize the sum rate of the MIMO multiple access channel (MIMO-MAC). For this problem, we propose an algorithm that finds the unique optimum power allocation policies of all users. At a given iteration, the multi-user algorithm updates the power allocation of one user, given the power allocations of the rest of the users, and iterates over all users in a round-robin fashion. Finally, we make several suggestions that significantly improve the convergence rate of the proposed algorithms.     

一种基于最大化Rayleigh熵的稳健干扰对齐算法

干扰对齐在消除干扰方面具有独到的优势,但需要完美的信道状态信息(CSI),这在实际中很难实现。该文分析了传统稳健干扰对齐方案的优缺点,在此基础上,提出一种最大化Rayleigh熵的稳健干扰对齐算法,并对收敛性,自由度和频谱效率等进行了分析。不同于MAX-SINR算法,该文通过最大化信号的Rayleigh熵,求得干扰抑制矩阵。在正向通信中,考虑到数据流之间的相关性取干扰抑制矩阵为原始干扰抑制矩阵的酉矩阵形式,并采用注水功率分配实现用户数据流间的最佳功率分配;基于信道的互惠性,在反向通信时,做类似的处理。通过迭代计算,逐渐将干扰压缩。最后,在完美CSI和误差CSI时,仿真表明该算法显著地提高了系统的性能。     

Degrees of freedom of MIMO interference channel with distributed space-time interference alignment

In the context of K-user MIMO interference channel (IC),achievable degrees of freedom (DoF) were investigated with distributed space-time interference alignment (DSTIA).By precoding with distributed current and outdated channel state information at the transmitters (CSIT),new tradeoff regions between achievable DoF and CSI feedback delay/frequency were achieved for MISO system.The impact of the number of transmit antennas on achievable DoF in the MISO system was analyzed,revealing that DoF results approach to the outer bound as the number of transmit antennas increases.Further,the impact of the number of receive antennas on achievable DoF was characterized,deriving the range of CSI feedback delay that preserves achievable DoF in the MIMO system.Theoretical and numerical analyses show that,the proposed DSTIA scheme can achieve better sum-DoFs by eliminating inter-user interference perfectly,tighten the gap between achievable DoF and outer bound,as well as improve the achievable rate of the system.     

Interference Alignment Algorithm Based on Feedback Concentration in D2D Communications

This paper proposed an effective interference alignment algorithm based on channel state feedback concentration (FCIA) for device-to-device (D2D) communications. The algorithm iteratively calculates the precoding matrix by using the global channel state information. Furthermore, as D2D discovery is the premise of the D2D communications, an effective interference alignment algorithm based on D2D discovery is also proposed. Simulation results show that, the proposed FCIA algorithm reduces the feedback overhead for transmission coordination compared with the existing full feedback based algorithm. The proposed interference alignment scheme based on D2D discovery feedback is compared with the existing D2D discovery scheme: it is found that although the discovery time slots has increased by about 6.2%, the sum rate achieved by interference alignment is improved by almost 50%.

     

Optimal Power Allocation with Limited Feedback of Channel State Information in Multi-User MIMO Systems

In this paper,an expression for the user’s achievable data rate in the multi-user multiple-input multiple-output(MU-MIMO)system with limited feedback(LF)of channel state information(CSI)is derived.The energy efficiency(EE)is optimized through power allocation under quality of service(QoS)constraints.Based on mathematical equivalence and Lagrange multiplier approach,an energy-efficient unequal power allocation(EEUPA)with LF of CSI scheme is proposed.The simulation results show that as the number of transmitting antennas increases,the EE also increases which is promising for the next generation wireless communication networks.Moreover,it can be seen that the QoS requirement has an effect on the EE of the system.Ultimately,the proposed EEUPA with LF of CSI algorithm performs better than the existing energy-efficient equal power allocation(EEEPA)with LF of CSI schemes.     

基于部分信道信息的自适应资源分配

在保证一定吞吐量前提下,为了降低传输功率,文中提出了一种基于部分信道反馈信息的多用户OFDM系统子载波分配方案。该方案利用少量已反馈子载波的状态信息来线性推导未反馈子载波的信道增益。仿真结果表明,在平坦瑞利信道衰落中,相比传统方式该方案在不增加反馈开销的前提下该方案能够大幅度地改善系统的性能,提高资源利用率。