基于干扰消除的异构蜂窝网络中断分析

在异构网络中,小小区可以为宏基站用户提供接入服务,并能够根据自身条件调节传输参数。该文研究在宏基站端干扰消除技术,来消除宏基站到小小区用户的干扰。该文分析了采用此种方案后异构网络下行链路的整体性能,推导了宏基站和小小区用户接收端信噪比的概率密度函数和分布函数。在此基础上,得到了系统整体中断概率的闭合表达式。理论推导和仿真结果表明,干扰消除方案能够有效提升异构蜂窝网络的整体性能。     

一种基于时频结合的干扰协调方案研究

LTE_A系统是对LTE系统的进一步优化和过渡,其中新添了许多新技术,其中有小区覆盖扩展CRE(Cell Range Extension)技术。CRE技术能有效均衡宏基站和微微基站的负载,但是单独采用CRE方案,处于微微基站扩展区域的微微基站用户会受到来自宏基站的强烈干扰。为了抑制来自宏基站的强烈干扰,提出了一种时频域相结合的干扰协调方案,在控制信道、数据信道中传输的信息通过功率控制与正交频率分配相结合从而达到抑制干扰的目的。通过Matlab仿真,结果表明该方案不仅能够很好地改善由CRE技术带来的干扰问题,而且很好地改善了小区吞吐量及边缘用户速率。     

一种基于自适应资源分配的干扰协调方案

在宏基站和微微基站(Macro-Pico)的异构网络中,资源分配可以有效地抑制基站间的干扰。基于降低用户的干扰和提高系统的吞吐量,提出一种自适应的频率资源分配方案。考虑分配给宏基站的每个资源块,如果距离宏基站较近的微微基站用户所受到的干扰高于最高限,采用不给宏基站分配这个资源块的方法,从而降低其对邻近微微基站用户的干扰,保证微微基站用户一定Qo S(Quality-of-Service)。系统仿真结果表明,与正交频率资源分配方案和共信道频率资源分配方案相比较,所提出的自适应频率资源分配方案降低了干扰和提高了系统的吞吐量。     

基于Q学习异构网络干扰协调算法

在LTE-A中采用异构网络能提高用户的性能,但是由于小区间使用相同的频谱资源,产生了小区间干扰,影响了用户性能,从而需要采用小区间干扰协调技术来控制小区间干扰(ICI)。虽然现有的小区间干扰协调技术可以降低小区间干扰,但是存在Macro用户性能影响较大的问题。为此,提出了基于Q学习的ETPS算法,在不影响Macro用户性能的前提下,降低小区间干扰。仿真结果表明,QL-ETPS算法较传统固定ABS/RP-ABS子帧配置方案性能更优,可以在尽量不影响Macro基站用户的前提下,提高Pico基站边缘用户的吞吐量。     

LTE-A中继网络中干扰协调算法分析

在LTE-Advanced网络中,引入中继(Relay)技术解决小区边缘用户的通信质量较差问题,但在这种中继节点与基站的同频组网的情况下,存在严重的小区内干扰,仅增大频率复用数量,会使信道质量降低,同时增加了小区内的干扰,所以设计一种好的中继网络中干扰协调算法十分重要。文章拟研究基于部分频率复用的小区内干扰协调技术,从部分频率复用的角度,针对下行链路,通过基于MATLAB的LTE系统及仿真平台测试不同的频率复用系数,从仿真显示结果找出一个合适的频率系数,使得干扰最小,频谱利用率最高。     

异构网中宏、微基站间存在频偏时的干扰协调方法

该文考虑骨干网只能进行少量信息交换的多载波异构蜂窝网络,研究微系统进行下行传输时对宏系统的干扰协调问题。针对多载波宏基站和微基站之间存在频偏的场景,在保证对宏用户的干扰小于预定干扰门限的前提下,以最大化微系统数据率为目标,在已知瞬时干扰信道和统计干扰信道信息的条件下分别设计最优和次优发射预编码。分析和仿真的结果表明,次优算法只需迭代一次就能达到接近最优算法的性能,因此具有较低的计算复杂度。所提出的方法只需要在宏基站和微基站之间通过骨干网交换少量信息,具有较低的信息共享资源开销。所提出的方法适用于微基站附近存在多个宏用户的场景。     

一种TD-LTE系统上行干扰三维分析方法

TD-LTE上行干扰水平是评估网络质量的重要指标,当网络受到上行干扰时,上行吞吐量、尤其是小区边缘用户的上行吞吐量将受到影响,干扰严重时甚至会影响用户的接入性能。本文对TD-LTE系统上行干扰问题进行研究,提出干扰频域、时域及地理分布特征三维联合分析方法,实现了TD-LTE系统上行干扰的全方位分析,可大大提高TD-LTE干扰优化与排查工作的效率及准确性。     

一种基于预编码的异构网下行干扰协调方法

在通用移动通信系统（Universal Mobile Telecommunications System,UMTS）异构网络中,理论分析了宏基站对微微（Pico）小区边缘用户的下行干扰问题。在传统空白帧（ABS）方法的基础上,提出了一种干扰避免策略,其主要思想是通过联合时域ABS策略和空域基于码本限制的策略提高传统ABS策略的系统性能,即在ABS子帧上,宏基站并不是完全不发送数据,而是采用码本受限的预编码进行传输。限制的码本可以根据宏小区自身的负载动态进行更改,并通过广播传递给低功率节点（Low Power Node,LPN）,LPN根据得到的信息进行边缘用户的调度。仿真结果表明,提出的方法在最差5%用户吞吐率比ABS方法略有下降的情况下,使用户平均吞吐量得到了提升。     

5G近端上行时域干扰分析及解决方案研究

5G有TDD和FDD 2种模式，在TDD系统中，普遍存在远端基站下行信号对近端基站上行信号的干扰的情况。通过近端上行时域干扰的判断方法，分析得出现网受干扰的小区占比及其对5G网络性能的影响。根据近端上行时域干扰产生的主要原因，提出调整S时隙（Self-contained slot）符号比的解决方案。方案实施后有效提升站点的上行抗干扰能力，同时上行速率、UE上下文掉线率及SA接入成功率等网络性能得到明显提升。     

基于用户中断概率的D2D通信干扰协调与资源分配

在LTE系统中引入设备直传(D2D)通信技术,会因为D2D用户复用蜂窝用户资源进行通信而产生同频干扰.在现有的干扰协调与资源分配研究中,都需要基站获取各个通信链路的信道状态信息(CSI),但这样无疑会增加基站的信令负担.为减小干扰与基站的信令负担,提出了一种基于用户中断概率的干扰协调与资源分配算法,首先在保证蜂窝用户正常通信的情况下,通过限制D2D用户到基站间的距离来降低干扰;其次通过遍历所有蜂窝用户的频谱资源,选择能使D2D用户的总中断概率最低的频谱资源进行复用.仿真结果表明,所提算法能够在保证蜂窝用户正常通信的情况下,明显降低D2D用户的平均中断概率,同时还能够降低基站信令负担.     

Comparison of beamforming techniques for W-CDMA communication systems

Different beamforming techniques are employed in a wideband code-division multiple-access base station, and their uplink and downlink signal-to-interference-plus-noise ratio (SINR) performances are compared. It is found that the direction of arrival (DOA) method and the complex conjugate method have almost the same uplink SINR performance, but the complex conjugate method shifts the downlink main beam direction slightly due to the difference between the uplink and downlink carrier frequency. However, the degradation in the downlink mean SINR performance is less than 1 dB compared with that obtained by the DOA method. In the downlink, the SINR performances obtained by the single-beam method and multiple-beam beamforming technique are compared. It is found that the single-beam method has a poorer SINR performance in the low SINR region because it is more likely to suffer from deep fading. In the moderate or high SINR regions, the single-beam method has a much better SINR performance because it has a higher gain in the main path direction and a smaller angular coverage of the mainlobe, which results in a stronger signal level and smaller multiple-access interference at the mobile receiver.     

Iterative multiuser uplink and downlink beamforming under SINR constraints

We study the problem of power efficient multiuser beamforming transmission for both uplink and downlink. The base station is equipped with multiple antennas, whereas the mobile units have single antennas. In the uplink, interference is canceled by successive decoding. In the downlink, ideal "dirty paper" precoding is assumed. The design goal is to minimize the total transmit power while maintaining individual SINR constraints. In the uplink, the optimization problem is solved by a recursive formula with low computational complexity. The downlink problem is solved by exploiting the duality between uplink and downlink; thus, the uplink solution carries over to the downlink. In the second part of the paper, we show how the solution can be applied to the problem of rate balancing in Gaussian multiuser channels. We propose a strategy for throughput-wise optimal transmission for broadcast and multiple access channels under a sum power constraint. Finally, we show that single-user transmission achieves the sum capacity in the low-SNR regime. We completely characterize the SNR-range where single-user transmission is optimal.     

基于对偶理论的多点协同联合发送波束成形算法

该文针对单基站功率约束的多点协同联合发送多输入单输出干扰下行链路系统,利用拉格朗日对偶理论研究了下行链路最大化最小信干噪优化问题与虚拟上行链路最小化最大信干噪比优化问题间的对偶关系。基于对偶关系和次梯度理论,提出了一种求解虚拟上行链路最小化最大信干噪比优化问题的内外层交替迭代优化波束成形算法;同时,给出了所提算法的收敛性证明;利用实数浮点运算理论分析了所提算法的复杂度;数值仿真验证了所提算法的有效性。     

SINR Enhancement Techniques for an IS-95 Downlink SIC Receiver

Due to near-far effects and multiple-access interference, several types of multiuser detectors have been developed in recent years to reliably demodulate user signals in a code-division multiple-access (CDMA) system. The downlink of Interim Standard 95 (IS-95) is particularly well suited to one such detector known as the successive interference canceler (SIC). In order to keep the receiver complexity low, entire base station signals are typically canceled in the receiver in a sequential manner. However, for the SIC to operate effectively, a base station signal that is being canceled must be reconstructed with enough accuracy such that sufficient interference power is removed for the subsequent base station to be reliably detected. If this is not possible, it may be necessary to employ techniques, specific to the signal format specified in the IS-95 downlink, which enhance the received signal-to-interference-plus-noise ratio (SINR). In this paper, we explore the performance gains achieved with several SINR enhancement techniques, and present computer simulations to demonstrate this improvement for example cochannel signal scenarios.     

码分双工系统中的干扰抑制技术

码分双工(CDD)是近年来新提出的一种双工方式,它支持上、下行信道同时使用同一频段。但是,由于上、下行信号可能存在较大的功率差异因而会导致较严重的相互干扰。该文针对这一问题提出了一套有效的干扰抑制和消除方案。首先,文中分析了CDD系统存在的几种干扰,在此基础上提出了基站端采用分布式天线和干扰消除器处理干扰的策略,移动台间的干扰则依靠定位技术和调度算法进行抑制。最后,计算及仿真结果证明了码分双工系统的可行性。     

Interference alignment scheme for massive MIMO system

The performance of massive multiple-input multiple-output （MIMO） system is limited by pilot contamination. To reduce the pilot contamination, uplink and downlink precoding algorithms are put forward based on interference alignment criterion. In the uplink receiving processing, the target function aligns the pilot contamination and the interference signals to the same null space and acquires the maximal space degree of the desired signals. The uplink receiving precoding matrix is solved on maximal signal to interference plus noise ratio （SINR） criterion considering the impact of the pilot contamination on channel estimations. The uplink receiving precoding matrix is used as the downlink transmitting precoding matrix. Exploiting the channel reciprocity, it is proved that, if the uplink receiving precoding matrix achieves maximal S1NR, the identical precoding matrix can be used in the downlink transmission and acquires maximal signal to leakage plus noise ratio （SLNR）. Simulations show that the spectrum efficiency of the proposed algorithm can reach about 1.5 times higher than that of popular matched filtering （MF） precoding algorithm, and about 1.1 times higher than multi-cell minimum mean square error （MMSE） precoding algorithm. The performance of the proposed algorithm can be improved approximately linearly with the increasing of the number of antennas.     

带内全双工多用户MIMO系统中的用户选择

考虑一种多用户MIMO的传输设计,配置发射天线阵列和接收天线阵列的蜂窝基站可以工作在带内全双工传输模式。在该全双工通信方案中,基站的下行发射信号对基站的上行接收产生显著的干扰,即自干扰。这里,下行预编码处理和上行发射协方差矩阵处理将被依次进行,以简化全双工的设计。其次,为了进一步改善上、下行信道的和速率性能,我们提出一种尝试性的下行用户选择方案,其基本思想是:当某一个下行用户的信道矩阵的范数较小时,关闭该下行用户的数据流。计算机仿真结果表明,在基站下行总发射功率受限时,在低的和中等的下行信噪比区域,用户选择有助于提高下行和速率;在高的上行信噪比区域,简化的用户选择使得上行和速率明显提高。      

QoS‐based space‐frequency prefiltering for TDD MC‐CDMA systems in slowly time‐varying channels

This work presents a space‐frequency prefiltering scheme for slowly time‐varying TDD MC‐CDMA downlink communications with multiple antennas at the base station (BS). Unlike the conventional spatially uncorrelated block fading channel model, both channel variation in each packet and spatial correlation are considered in the design. In the TDD mode, the mobile terminals (MTs) transmit training signals at the end of each uplink packet. In the following downlink packet, the BS computes the signal weights on different antennas and subcarriers for each MT in each symbol period based on the channel state predicted from the received training signals. The goal is to minimize the total required transmit power while keeping the received signal‐to‐interference‐plus‐noise ratio (SINR) as the target for each MT. Moreover, the maximum packet length for satisfying the SINR requirements has been determined. The results indicate that the total required transmit power can be reduced by a lower mobile speed or more BS antennas. As a result, the maximum packet length can be extended in virtue of the power reduction. Copyright © 2008 John Wiley & Sons, Ltd.     

MIMO异构网络中一种基于人工噪声的抗主动窃听者的鲁棒安全传输方案

为保证MIMO异构网络面临多天线主动窃听时的安全性,该文提出一种基于人工噪声的抗主动窃听者的鲁棒安全传输方案。首先,考虑窃听者发送上行导频干扰的情形,研究了其发送的上行导频干扰对合法用户信道估计的影响。随后,基于信道估计结果对宏基站、微基站的下行数据与噪声信号的预编码矩阵进行设计,并推导了此种情形下系统安全速率的表达式。然后,以系统安全速率最大化为目标对基站的下行数据与噪声信号的发送功率进行优化设计,并提出一种基于1维线性搜索的求解方法。进一步地,考虑窃听者在发送上行导频干扰后,继而发送噪声干扰用户下行通信的情形,提出一种基于离散零和博弈方法来获取最优的发送功率设计。仿真结果验证了所提方案的安全性和鲁棒性。     

Capacity of Multirate Multicell CDMA Wireless Local Loop System with Narrowbeam Antenna and SINR Based Power Control

In this paper, we evaluate the capacity performance of multirate multicell DS-CDMA wireless local loop system with narrowbeam antenna and SINR based power control. Multiple access interference from the surrounding cells in the multicell environment is firstly studied for both uplink and downlink. It can be seen from the results that the capacity can be improved effectively by directional antenna equipped at the subscriber side. More significant improvement can be achieved if multielement antenna array is employed at the base station. In addition, the analysis is also extended to the situation of multimedia multirate transmission. The results show that, regardless of the voice to data user population ratio, the bit rate traffic supported by the system is roughly constant for a set of predetermined parameter values.