Nash bargaining solution based multi-cell and multi-user interference alignment scheme for cellular networks

In wireless cellular networks, the interference alignment （IA） is a promising technique for interference management. A new IA scheme for downlink cellular network with multi-cell and multi-user was proposed, in the proposed scheme, the interference in the networks is divided into inter-cell interference （ICI） among cells and inter-user interference （IUI） in each cell. The ICI is aligned onto a multi-dimensional subspace by multiplying the ICI alignment precoding matrix which is designed by the singular value decomposition （SVD） scheme at the base station （BS） side. The aligned ICI is eliminated by timing the interference suppression matrix which is designed by zero-forcing （ZF） scheme at the user equipment （UE） side. Meanwhile, the IUI is aligned by multiplying the IUI alignment precoding matrix which is designed based on Nash bargaining solution （NBS） in game theory. The NBS is solved by the particle swarm optimization （PSO） method. Simulations show that, compared with the traditional ZF IA scheme, the proposed scheme can obtain higher data rate and guarantee the data rate fairness of UEs with little additional complexity.     

Hybrid scheme for three-cell multi-user MIMO cellular networks

Orthogonal schemes are usually adopted for cell-edge users in a cellular network, where the spectrum is poorly utilized. A new interference alignment （IA） based space-division hybrid （IA-SDH） scheme is proposed by joint design transmit precoding matrices and beamforming matrices for a three-cell constant cellular network, where users at cell-center work with a conventional scheme while users at cell-edge utilize an IA scheme. Therefore, the cell-edge users suffer no interference and cell-center users are only affected by negligible inter-cell interference. Analysis simulation shows that more users can be served simultaneously than that of a conventional scheme in certain user distributions.     

Multi-beam cooperative frequency reuse for coordinated multi-point transmission

Coordinated multi-point (CoMP) joint transmission is considered in the 3rd generation partnership project (3GPP) long term evolution (LTE)-advanced as a key technique to mitigate inter-cell interference and improve the cell-edge performance. To effectively apply CoMP joint transmission, efficient frequency reuse schemes need to be designed to support resource management cooperation among coordinated cells. However, most of the existing frequency reuse schemes are not suitable for CoMP systems due to not considering multi-point joint transmission scenarios in their frequency reuse rules. In addition, the restrictions of frequency resources in those schemes result in a high blocking probability. To solve the above two problems, a multi-beam cooperative frequency reuse (MBCFR) scheme is proposed in this paper, which reuses all the available frequency resources in each sector and supports multi-beam joint transmission for cell-edge users. Besides, the blocking probability is proved to be efficiently reduced. Moreover, a frequency-segment-sequence based MBCFR scheme is introduced to further reduce the inter-cell interference. System level simulations demonstrate that the proposed scheme results in higher cell-edge average throughput and cell-average throughput with lower blocking probability.     

非理想信道环境下的多小区干扰对齐技术研究

由于普遍采用频率复用因子为1的方式组网,多小区干扰已成为限制无线通信系统容量的主要因素。为了有效抑制小区间干扰提高小区边缘吞吐量,近年提出了干扰对齐技术,其优势在于可以获得干扰信道的最高自由度。一般的干扰对齐研究仅限于理想信道,研究通过非理想信道环境下的多小区干扰对齐技术,分析了时延信道信息对干扰系统容量的影响。结果表明,信道状态信息的时延大大降低了系统容量,特别是在高信噪比条件下对系统性能的影响更大。     

Joint Processing Precoding for Coordinated Multi-Point Transmission in LTE-A

Coordinated Multi-Point (CoMP) transmission is a technology targeted for Long Term Evolution Advanced (LTE-A).It is designed to reduce cell-edge interference,improve cell-edge spectrum efficiency and enlarge effective cell-edge coverage by means of multi-point coordination including coordination between Remote Radio Units (RRUs) within an eNodeB,coordination between an eNodeB and its relays,and coordination between eNodeBs.The Joint Processing (JP) technique for CoMP can maximize system performance,which is...     

Research on uplink coordinated transmission schemes in LTE-advanced systems

The investigation of inter-cell interference mitigation techniques is a key area in wireless communications.Coordinated multiple points(CoMP) transmission/reception is a candidate technique for interference cancellation in 3GPP LTE-Advanced system.However,the coordination scheme in CoMP remains a key research problem to be solved,which will have a strong influence on the performance of CoMP.In this paper,a novel coordinated transmission scheme is proposed for the uplink LTE-Advanced system.In our scheme,several base transceiver stations(BTS) and users are selected as coordination partners which form a CoMP cluster.Joint processing is used at the receiver to mitigate interference.From the perspective of coordinated partner selection,our scheme can be divided into static and dynamic coordination which are both considered to fully exploit the throughput gain of CoMP.The proposed schemes are evaluated by system level simulation and compared with the conventional LTE system based upon single cell processing.Our simulation results demonstrate that the proposed schemes attain superior performance as opposed to the conventional system in terms of cell average and cell edge throughput.     

Cell Clustering and Resource Allocation Scheme for CoMP SU-MIMO

In view of the problem of high implementation complexity and system performance degradation in existing schemes, a novel downlink coordination scheme consisting of two steps was proposed for CoMP single-user multi-input multi-output (CoMP SU-MIMO). Firstly, through a combination of the conventional network-defined method and UE-specific method, we proposed a CoMP Cooperation Set (CCS) selection method which could provide most of the achievable throughput gain with lower complexity. Secondly, a resource allocation scheme was provided for the coordination among overlapping CCSs, by inheriting the idea of fair treatment for cell-center users and cell-edge users and conquering the limitation of the conventional schemes which could be only used for non-overlapping CCS method. Simulation results show that the proposed scheme could increase the cell average throughput significantly as well as improve the fairness between cell-center users and cell-edge users compared with the existing schemes.     

基于用户协作的小区间干扰抑制方案

以长期演进（LTE）上行链路单载波频分多址（SC-FDMA）传输方案为基础,提出了一种基于用户协作的小区间干扰抑制传输方案。该方案采用译码转发中继工作方式,位于相邻小区边缘的两用户互为中继相互协作,在3个时隙内完成用户终端到基站的信息传输。仿真研究表明：该方案能够有效抑制小区间用户共信道干扰,同时充分利用用户协作所提供的空间分集增益提高小区边缘用户链路传输可靠性。此外,该方案所采用的块空时分组编码（B-STBC）能够很好地保持用户终端发射信号的低峰均比特性。     

LTE-A系统多点协作传输技术研究

多点协作传输技术作为LTE-A中的关键技术,可显著提升小区边缘用户的速率和吞吐量。介绍了多点协作的原理,给出了相关系统模型,分析了多点协作的首要问题——协作节点的选择。针对多度协作会造成的系统性能下降,提出了适合的最大协作节点数。同时考虑到传统的PF调度算法会造成小区吞吐量下降,提出了适用于多点协作的归一化PF调度算法。最后,仿真两种调度算法在不同协作节点选择下的性能,通过比较平均小区吞吐量和边缘用户吞吐量说明归一化PF调度算法的优势。     

Progressive intercarrier and co‐channel interference mitigation for underwater acoustic multi‐input multi‐output orthogonal frequency‐division multiplexing

Multi‐input multi‐output orthogonal frequency‐division multiplexing (MIMO‐OFDM) has been actively studied for high data rate communications over the bandwidth‐limited underwater acoustic (UWA) channels. Unlike existing receivers that treat the intercarrier interference (ICI) as additive noise, in this paper, the proposed receiver considers ICI explicitly together with the co‐channel interference (CCI) due to parallel transmissions in MIMO‐OFDM. Using a recently developed progressive receiver framework, the proposed receiver starts with low‐complexity ICI‐ignorant processing and then progresses to ICI‐aware processing with increasing ICI levels. The key components of the proposed receiver include the following: (1) compressed sensing‐based sparse channel estimation, (2) soft‐input soft‐output minimum mean square error/Markov chain Monte Carlo detector for interference mitigation, and (3) soft nonbinary low‐density parity check decoding. In addition to simulation, we use real data from the Surface Processes and Acoustic Communications Experiment 2008 (SPACE08) and the Mobile Acoustic Communications Experiment 2010 (MACE10) to verify the system performance, where the transmitter in SPACE08 was stationary and that in MACE10 was slowly moving. Simulation and experimental results show that explicitly addressing ICI and CCI significantly improves the performance of MIMO‐OFDM in UWA systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Improved resource allocation strategy in SU-CoMP network

Coordinated multi-point transmission and reception (CoMP) for single user, named as SU-CoMP, is considered as an efficient approach to mitigate inter-cell interference in orthogonal frequency division multiple access (OFDMA) systems. Two prevalent approaches in SU-CoMP are coordinated scheduling (CS) and joint processing (JP). Although JP in SU-CoMP has been proved to achieve a great link performance improvement for the cell-edge user, efficient resource allocation (RA) on the system level is quite needed. However, so far limited work has been done considering JP, and most existing schemes achieved the improvement of cell-edge performance at cost of the cell-average performance degradation compared to the single cell RA. In this paper, a two-phase strategy is proposed for SU-CoMP networks. CS and JP are combined to improve both cell-edge and cell-average performance. Compared to the single cell RA, simulation results demonstrate that, the proposed strategy leads to both higher cell-average and cell-edge throughput.     

异构网中基于BD的协作波束赋形算法研究

波束赋形是下一代无线蜂窝网中提高频谱效率的一项重要技术,文中在多用户波束赋形技术的研究基础上,研究了CoMP中的CB技术。针对LTE系统中的小区间干扰严重,且已有的干扰协调技术无法有效解决边缘用户频谱效率低的问题,LTE-A系统引入了多点协作传输/接收技术。该技术通过相邻小区间的联合处理或协作波束赋形,可抑制小区间干扰,提高用户的接收信号质量,使系统容量和小区边缘用户的频谱效率得到有效提高。     

一种OFDMA系统半静态干扰协调算法

为了解决多小区OFDMA系统边缘用户受到严重的同频干扰问题,提出了一种基于小区边缘用户数的半静态干扰协调算法SICUN。该算法用小区边缘用户数指示小区边缘业务量的大小,结合特定的频率资源优先级规划方案以确定系统中小区中心、边缘用户的可用频率资源,在此基础上进行了补偿式功率控制。仿真结果表明:SICUN能在保证小区边缘用户性能的前提下,较大地提高系统整体性能。     

多天线两小区蜂窝系统的低开销线性干扰对齐算法

在蜂窝系统中,由于干扰的存在,用户性能受到影响,特别是对于小区边缘用户,其通信质量较差。干扰对齐作为一种能够消除干扰、提高系统容量的技术,近年来受到广泛关注。针对多天线两小区蜂窝系统的边缘用户,本文给出了一种系统开销小、需要天线数少的线性干扰对齐算法。该算法利用发送端预编码矢量消除小区内干扰,利用接收端干扰抑制矢量消除小区间干扰。采用本文算法后,在每个小区有 个用户、基站有 根发送天线、用户有 根接收天线的情况下,只需 和 就可以实现上下行的干扰对齐,整个系统可以达到 的自由度,并且在下行链路中不需要小区间反馈,而在上行链路中只需要较小的小区间反馈。仿真结果表明,本文提出的算法能够以较小的开销实现比以往的算法更好的性能。      

功率约束条件不同时下行相干CoMP传输异构网的性能

本文研究在异构网中进行相干协作多点传输时低复杂度迫零（ZF）预编码的性能。我们考虑在同构网中常用的低复杂度ZF预编码结构,即先进行ZF波束形成再进行功率分配,分析在采用和功率约束及单基站功率约束下使和数据率最大的功率分配时协作传输的性能,并与实际系统中常用的等功率分配的性能进行比较。分析结果表明,在异构网多载波系统中进行下行相干协作传输时,与在同构网中的结果不同,协作传输后单基站功率约束的性能远优于其他功率约束下的性能。但是,当协作的宏基站与微基站最大功率差别较大时,宏用户的性能在协作后甚至不如不进行协作传输,而微用户的性能会有所提高。这意味着在异构网中设计协作预编码时必须考虑单基站功率约束,而且不能只对功率分配进行优化设计。      

On the detection of a class of fast frequency-hopped multipleaccess signals

The capacity of a fast frequency-hopped multiple access (FHMA) system is dictated by two major related design concerns: the hopping pattern and the receiver structure. This paper studies the impact of these two factors. We present a maximum likelihood (ML) diversity combiner for detecting asynchronous FHMA multilevel PSK (MPSK) signals in Rician fading channels and analyze the performance of a close approximation of the ML receiver. We compare systems using random hopping patterns and those using optimal hopping patterns of Einarsson (1980). Performance comparisons between chip-synchronous and chip-asynchronous systems are made as well. We propose and examine the effectiveness of a two-stage multiuser detector, in which the first stage makes an initial decision while the second stage tries to reduce multiple access interference (MAI) and resolve the ambiguity left by the first stage detector. The MAI caused by undesired users is constituted by a cochannel interference (CCI) contribution and an interchannel interference (ICI) contribution. This detector is of modest complexity and is capable of removing most of the CCI and part of the ICI. Two methods for mitigating MAI are also examined     

Fair and efficient opportunistic interference alignment algorithm based on round-robin scheduling

Opportunistic interference alignment (OIA) algorithm was proposed for the practical implementation of interference alignment (IA).A fair and efficient OIA algorithm was presented for the unfairness in resource allocation and high dependence of tremendous users in the existing OIA algorithms.Firstly,the users with the best channel was selected in the primary cell based on round-robin scheduling after the coordinate cluster was determined.Then,the interference from the primary users was eliminated by skillfully designing the useful signal spaces in the subordinate cells.Furthermore,the users with the minimum interference leakage was selected in the subordinate cells.Finally,the fairness performance was theoretically analyzed.Simulation results show that both the sum-rate and fairness of the proposed algorithm are significantly higher than that of the conventional algorithm with less interference leakage.Besides,the users can achieve a quick access.     

LTE—AdvancedCoMP中自适应动态小区选择方案

为了提高小区边缘用户的性能,满足小区边缘频谱效率的要求,LTE—Advanced系统中引入了协作多点传输技术（ CoMP, Coordinated Multi- Point transmission）。提出一种新的下行协作方案,该算法首先判定网络中的用户类型,其次为小区边缘用户选择协作集合。此方案利用信干噪比（SINR, Signal- to- Interference plus Noise Ratio）阈值自适应的确定协作小区的数量,能有效避免不必要的协作,能降低系统的信息传输负担。仿真结果表明,提出的算法相比已经存在的算法能够明显改善协作效率同时能够降低基站间的信息传输负担。     

Low-complexity SAGE-based MMSE channel estimation for CoMP multi-user systems

Coordinated multiple point(CoMP) transmission/reception has been investigated recently as a promising technology to increase the cell-edge user performance of long term evolution-advanced(LTE-A),and channel estimation is a crucial technology for CoMP systems.In this paper,we consider a reduced-complexity minimum mean square error(MMSE) channel estimator for CoMP systems.The estimator uses space alternating generalized expectation maximization(EM)(SAGE) algorithm to avoid the inverse operation of the joint MMSE estimator.In the proposed scheme,the base stations(BSs) in the CoMP system estimate the channels of all the coordinated users serially and iteratively.We derive the SAGE-based estimators and analyze complexity.Simulation results verify that the performance of the proposed algorithm is close to the joint MMSE estimation algorithm while reducing the complexity greatly.     

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。