基于新一代Wi-Fi的MIMO-OFDM技术研究

无线局域网(WLAN)是计算机网络技术和通信技术完美结合的产物,近年来新一代Wi-Fi标准IEEE802.11ac的出现,使得无线局域网的吞吐量和用户体验获得大幅度提升,而新一代Wi-Fi引入的多用户MIMO(Multiple Input and Multiple Output)技术和带宽扩展技术在提升网络容量的同时也带来了较多问题,本文针对新一代Wi-Fi的物理层关键技术MIMO-OFDM技术进行了研究,通过仿真实验分析了MIMO-OFDM技术在新一代Wi-Fi中所获得的增益。     

基于干扰对齐技术的无线通信系统设计

干扰是制约多用户无线通信系统容量的首要因素,传统正交化的干扰管理方式采用分割的方法分配无线资源,每个用户分到的资源随着用户数量的增加而减少,当用户数量较多时会严重降低用户的通信速率。干扰对齐是一种新型的信号处理技术,为提高多用户无线通信系统的容量提供了有效的解决方法。介绍了干扰对齐的基本原理,给出了完整的干扰对齐系统实现方案,包含通信流程、算法设计、信道状态的估计量化及反馈方案。最后,通过仿真验证了干扰对齐的性能。     

三小区多用户MIMO系统中干扰对齐优化算法

针对三小区多用户MIMO干扰信道系统,通过一个启发性例子,联合设计发射预编码矩阵和接收赋形矩阵,给出基于特征向量闭式解的干扰对齐优化算法,相比已有干扰对齐算法,用户端可使用更少的天线资源获得相同的自由度性能,且只需本小区内用户协作共享信道信息;并归纳出普适场景下系统配置与可达自由度之间的关系：设定每个小区中的基站配置M根天线和K个用户,用户配置N根天线,各个基站对本小区中每个用户都发送d个数据流,当M=N≥2 Kd时,所提算法总共可获得3 Kd个自由度。所提算法可以完全消除小区间干扰和用户间干扰,相比传统的正交化干扰抑制算法,系统容量得到了明显地提升。     

干扰距离最远的多用户多天线干扰对齐算法

针对多用户多天线中小区边缘用户同频干扰问题,提出了一种基于干扰距离最远准则的多用户MIMO干扰对齐优化算法,通过对等效干扰信道进行SVD分解,选择与等效干扰信道矩阵距离最大的特征子信道作为传输预编码矩阵,并分析了算法复杂度以及空间相关性对性能的影响,仿真结果显示系统频谱效率较原始算法在8天线下有31.57％的提高.     

多小区多用户MIMO系统干扰对齐的优化

多小区多用户MIMO系统中存在小区间以及小区内的干扰,传统方法提出的干扰对齐只针对2个小区或者小区内的干扰进行对齐,缺乏对小区间的干扰进行对齐处理.针对这一问题,提出了一种多小区多用户的干扰对齐优化方案,采用基于机会调制算法进行干扰对齐模式优化,不仅能够简化计算、提高量效率,而且能够消除多小区间和小区内的干扰,获得最佳的容量和多用户分集增益.     

无线ATM局域网中一种面向QoS的动态信道分配方案

提出了在无线ATM(异步传送模式)局域网中面向QoS(服务质量)的一种集中式DCA(动态信道分配)方案。此方案主要是在无线ATM局域网中,考虑了基站的相互干扰限制、目前信道资源利用以及有效连接的QoS保证等因素。仿真结果表明这种方案的系统性能获得了提高。     

IEEE 802.11ac标准的多用户MIMO信道容量研究

IEEE 802.11ac是第五代无线局域网(WLAN)通信标准,多用户MIMO技术的应用使其通信速率和信道容量得到巨大提升,从而使IEEE 802.11ac标准日趋成为无线局域网的主流标准。本文在IEEE 802.11ac标准的随机多用户MIMO无线信道容量的计算理论的基础上,对CSI未知与已知时的随机多用户MIMO无线信道容量进行仿真,并对比分析了CSI未知与已知时不同天线配置下的随机多用户MIMO无线信道的容量。     

基于动态反馈与功率分配的干扰对齐方法

在多用户MIMO系统中,信道状态的精确性严重影响干扰对齐技术的性能。该文针对信道状态信息(CSI)有限反馈导致的干扰泄露问题,提出一种基于动态反馈与功率分配的干扰对齐方法。首先从理论上分析了系统和速率与信道状态反馈比特分配和功率分配之间的关系,得到了在动态反馈和功率分配条件下系统和速率的解析表达式;在此基础上,以系统容量提升为目标,对反馈比特分配和功率分配优化问题进行建模;并根据信道的准静态特性利用库恩塔克条件(KKT)对该问题进行求解,得到功率和反馈比特分配方案。仿真结果表明,与单独考虑信道状态动态反馈条件下的干扰对齐技术相比,提出的方法能够有效减少干扰泄漏强度,提高系统和速率。     

基于干扰对齐的认知 MIMO 系统频谱共享与用户调度简

在认知MIMO多用户通信场景中,设计基于干扰对齐的信号处理算法,将认知信号与授权信号通过相互正交的子空间进行传输,实现认知用户对授权系统空闲空间信道的无冲突利用,并根据不同信道矩阵的空间传输性能的差异,实现合理的用户调度。仿真结果表明,所提方法能够有效利用空闲空间信道资源,获得多用户分集增益,在不影响授权业务的前提下提高认知用户的传输速率。     

新一代高速无线局域网中用户调度及波束成形算法

针对新一代高速无线局域网IEEE 802.11ac协议的多用户多输入多输出正交频分复用(MU-MIMO OFDM)技术,本文主要研究了该高速无线局域网协议反馈机制下的用户调度及波束成形算法。首先描述了新一代高速无线局域网协议的反馈机制,并给出了基于部分信道状态信息的预编码方法。然后利用新一代高速无线局域网的频率选择性信道环境和用户独占所有带宽的特性,提出了一种综合考虑整个带宽信道状况的基于有限反馈的半正交化用户调度算法。为了降低所提算法的计算复杂度,进而提出了一种基于最大特征值的用户调度算法。分析结果表明所提算法可有效实现多载波情况下的用户调度。数值仿真表明,所提算法相比随机调度算法有一定性能增益。      

Efficient MAC protocol design and performance analysis for dense WLANs

In this paper, we analytically study the dense basic service set network transmission problems in very high throughput (VHT, namely IEEE 802.11ac) wireless local area networks (WLANs) due to nervous bandwidth resources. Our contributions are threefold as follows. Firstly, we derive the closed-form expressions of throughput gains for primary channel establishment from multi-band selection using the optimal skipping rule, which balances the throughput gain from finding a good quality band with the overhead of measuring multiple bands. Secondly, in order to satisfy the quality of service of overlapping BSS users, we design a space interference avoidance mechanism, which can improve the system throughput for the whole dense WLANs. Thirdly, in order to further improve the transmission performance of dense BSS networks, we propose an unequal bandwidth transmission mechanism based on the VHT WLANs, which can not only clear the redundant network allocation vector duration timely but also use the limited bandwidth efficiently. The proposed protocols and mechanisms exploit both time and frequency diversity sufficiently, and are shown to result in typical throughput gains compared with the traditional IEEE 802.11 MAC protocol.     

Saturation throughput analysis of a carrier sensing based MU-MIMO MAC protocol in a WLAN under fading and shadowing

In wireless local area networks (WLANs), the traditional carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol cannot use the full benefits from multiuser multiple-input multiple-output (MU-MIMO) technique due to random medium access of the users. In this paper, we propose a carrier sensing based MAC protocol for a MU-MIMO based WLAN with full utilization of MU-MIMO technique. By modeling the WLAN system under the proposed MAC protocol as a discrete time Markov chain, we develop an analytical model for computing the saturation throughput in presence of path loss, Rayleigh fading and log-normal shadowing. The analytical model is then validated via simulation. By means of numerical and simulation results, we demonstrate that the proposed MAC protocol significantly improves throughput performance than the traditional CSMA/CA MAC protocol. Further, we compare the performance of the proposed MAC protocol with a MU-MIMO MAC protocol called Uni-MUMAC protocol and find that the proposed MAC protocol performs better than the Uni-MUMAC protocol. We also explore the effect of some of the network and wireless channel parameters on the performance of the proposed MAC protocol.

     

Selective interference alignment and neutralization in coordinated multipoint using multiuser MIMO

In wireless communication, the concept of coordinated multipoint (CoMP) transmission is more attractive, and it transpired the notion based on interference management techniques. Interference alignment (IA) and interference neutralization (IN) methods can substantially align and neutralize the interference signals. The existing work in the CoMP transmission using multiuser multi-input and multi-output (MU-MIMO) had long-held problems such as specific limit of intercell (ICI) and cochannel interference (CCI) cancelation that contain low performance in cell-edge users. The proposed framework of the transmission signal in selective interference alignment and neutralization (SIAN) CoMP MU-MIMO system transmits multiple data streams in multipath by using downlink coordination between base stations and receiver side. This work contributes the individual perspectives to implement the IA and IN to align and cancel the interfered signals at the receiver side. Once the perspectives mentioned above are executed, zero-forcing (ZF) and rechanneling filter are applied on the receiver side to eliminate residual ICI. In addition, spectral efficiency significantly improves the achievable data rate and enhances the performance of cell-edge users and reduces the CCI at the receiver side. Furthermore, the antenna configuration signals are decoded to get the exact version of interference-free signals with null path loss of signal transmission. The effectiveness of the proposed framework analyzes and verifies the numerical evaluation of the achievable degree of freedom. Finally, the simulation demonstrates the comparison of the proposed CoMP scheme with MIMO ZF and non-CoMP schemes, which significantly improve the performance of spectral efficiency for cell-edge users.     

Design of Large Scale MU-MIMO System with Joint Precoding and Detection Schemes for Beyond 5G Wireless Networks

The large scale multiuser multiple input multiple output (MU-MIMO) is one of the promising communication technology for 5G wireless networks as it offers reliability, high spectral efficiency and high throughput. The lattice reduction (LR) precoding based user level local likelihood ascent search (ULAS) detection scheme is proposed in this paper for efficient signal detection in large scale MU-MIMO system. The initial solution of ULAS algorithm is obtained from the LR precoding assisted zero forcing detector. The LR precoding transforms the non-orthogonal channel matrix into nearly orthogonal channel, which helps to mitigate inter antenna interference (IAI) exists at each user. The remaining multiuser interference (MUI) imposed to each user from undesired users is cancelled by the proposed ULAS multiuser detection scheme. Thus, the proposed LR precoding assisted ULAS mitigates both IAI and MUI unlike the classical detector, those try to moderate either IAI or MUI. By contrast, the proposed ULAS detector provides performance close to optimal maximum likelihood detector with just a fraction of its complexity.

     

5G系统中基于小区分群的干扰管理

为了降低5G系统中超密度小区网络的小区间干扰（ICI）,提出了一种基于小区分群的干扰管理方案,其核心思想是将宏小区覆盖下的小小区分群,对群内干扰和群间干扰分别采用基于多小区协作和频域或时域的干扰避免。针对小区分群的关键即干扰权值的计算,提出了一种基于用户的信干噪比（SINR）和干扰泄露（SOIR）计算连续干扰权值的方案,该权值不仅反映用户间的干扰关系,而且自适应地调整干扰用户之间对资源的争夺策略;同时,把距离调和平均数作为小区分群的附加准则。仿真结果表明,与传统的小区分群方案相比,新方案的吞吐量增加20%~30%,小区性能和系统整体性能都有提升。     

聚合干扰下小小区网络的协作传输方案及性能分析

该文针对聚合干扰下小小区网络协作传输的场景,分析了宏小区基站的物理位置服从泊松分布,且多用户预编码采用线性预编码时用户端的性能。通过基于概率密度函数的性能分析法,推导出小小区网络协作传输的中断概率、容量以及误符号率的闭合表达式,结果表明由于聚合干扰的存在,仅仅依靠小小区网络基站天线数的增加并不能持续提高用户端的性能。进一步,针对小小区网络中用户的接入问题,提出了一种基于能效最大化的用户接入方案,并对所提方案进行了性能分析和仿真验证,从结果可以看到所提小小区网络用户接入方案在提高系统能效方面要优于其他接入方案,仿真结果验证了基于能效最大化的接入方案的优越性,并验证了本文理论分析的正确性。      

一种改进的信号泄露噪声比多用户预编码算法

时分复用(TDD)系统通过信道互异性可以在发送端得到下行信道矩阵。由于上下行信道存在着处理延时,时变信道下,延时带来的信道误差会降低多用户MIMO预编码的系统性能。信道预测在某些情况下能够较好地改善信道误差,但预测误差又会给系统性能带来损失。该文针对预测误差带来的性能损失,提出了一种基于预测误差改进的预编码算法。改进算法根据预测误差的方差对预编码向量进行修正,能够进一步提高系统误码率性能。仿真结果表明,在高车速情况下,该算法比传统的预测预编码算法能带来更大的性能增益。     

Effectiveness of Explicit Stations Grouping in Crowded Wireless LANs

In this letter, we evaluate the effectiveness of a multi-stage contention scheme for wireless local area networks (WLANs) medium access control (MAC). Multi-stage contention schemes basically divide the stations into smaller groups to resolve the contention more efficiently. Previous researchers have proposed virtual grouping schemes for WLANs MAC. Here we quantitatively analyze what can be achieved with a simple grouping scheme, i.e. through multi-stage contention. Our analysis shows that the multi-stage scheme is efficient in resolving contention, making it a good alternative to the commonly used exponential backoff mechanism.     

A MIMO-Based Collision Mitigation Scheme in Uplink WLANs

Although there exist random backoff schemes in WLANs, a collision problem among stations (STAs) is one of the critical factors that degrade the performance of WLAN systems. To mitigate this collision problem, a MIMO-based uplink collision mitigation scheme is proposed by utilizing additional degrees of freedom through multiple antennas, and, consequently, enhances the system performance. Analysis and simulation results show that there is at least 30% throughput enhancement in a basic service set (BSS) with more than 10 STAs, compared to the performance of conventional WLANs in case of saturation traffic.     

QoS Guaranteed Resource Allocation Scheme for Cognitive Femtocells in LTE Heterogeneous Networks with Universal Frequency Reuse

In this paper, we propose a novel resource allocation scheme for co-channel interference avoidance in LTE heterogeneous networks with universal spectrum reuse where both macro users (MUs) and cognitive femto base stations (FBSs) within the same macrocell coverage can dynamically reuse whole spectrum. Specifically, resource blocks (RBs) are shared between cognitive FBSs in underlay mode while the resource sharing among FBSs and MUs is in overlay mode. The macrocell is divided into inner and outer regions with the inner region further divided into three sectors. The proposed scheme addresses co-channel interference (CCI) by employing fractional frequency reuse (FFR) for RB allocation in the outer region of the macrocell and increase the distance of users that reuse the same RB within the macrocell. Part of RBs are allocated to the outer region of the macrocell with a FFR factor of 1/3, while the remaining RBs are dynamically allocated to each sector in the inner region of macrocell based on MUs demand to efficiently utilize the available spectrum. A basic macro base station (MBS) assistance is required by the FBS in selection of suitable RB to avoid interference with MU in each sector. With the proposed solution, both macro and femto users can dynamically access the whole spectrum while having minimum bandwidth guarantee even under fully congested scenarios. Moreover, the proposed scheme practically eliminates the cross-tier interference and the CCI problem in heterogeneous network reduces to inter-femtocell interference. The throughput and outage performances of the proposed scheme are validated through extensive simulations under LTE network parameters. Simulation results show that the proposed scheme achieves a performance gain of more than 1.5 dB in terms of SINRs of both macro user and femto user compared to traditional cognitive and non-cognitive schemes without bandwidth guarantee for femtocells.