B3G上下行链路接入方案比较

TD-SCDMA作为具有中国自主知识产权的第三代移动通信标准之一,已逐步进入全面商用化的阶段。随着移动数据服务需求的不断增大,TD-SCDMA 2Mbit/s的最大数据传输速度将不能完全满足用户的需要了。TD-SCDMA的演进越来受到业界的关注,TD-SCDMA的未来演进之路上在物理层接入技术与B3G接入技术是殊途同归的。为此,本文对主流的B3G系统的上下行链路接入技术进行简要介绍,并对各自特点进行阐述和比较。     

Design of PR NMDFB based up and down converters for transmit downlink and receive uplink of combined 3GPP LTE and UMTS radios

In this paper we present a novel application of perfect reconstruction (PR), non-maximally decimated (NMD) filter banks whose assembly gives life to compact digital up converter and digital down converter for combined Third Generation Partnership Protocol, Long Term Evolution radios and Universal Mobile Telecommunications System radios, which are Wideband Code Division Multiple Access based. The design of the PR NMD analysis–synthesis chains in both transmit downlink and receive uplink has been optimized to maximize the performance according to the specific application scenario. In the receive uplink an 80-path, 40-to-1, PR NMD polyphase down converter channelizer accomplishes the pre-processing task of decomposing the whole input frequency range and of aliasing all the spectral fragments to base-band while reducing the signal sample rate. A selector block is in charge of connecting the ports, which contain the fragments belonging to the same band, to a proper PR 2-to-N up converter channelizer, which synthesizes them in base-band. The dual architecture, composed of small N-to-2 polyphase down converters followed by an 80-path, 2-to-40, up converter, has been designed for the transmit downlink. The down converters accomplish the pre-processing task of decomposing the input spectra and of simultaneously aliasing their fragments to base-band while reducing the input sample rate to 7.68 Msps. The 80-path, 1-to-40 up converter, accomplishes the task of recombining the spectral fragments at the desired center frequencies while increasing the signal sample rate to 307.2 Msps.     

Novel techniques to improve downlink multiple access capacity for Beyond 3G

In future public mobile access with high data rates, one of the main challenges we face is spectral efficiency. In this article we will focus on the following new spectrally efficient downlink multiple access techniques that may be essential parts of China's Beyond 3G system development: dynamic code-division multiplexing, an adaptive multi-input multi-output technique in distributed wireless communications systems, and interleaver pattern division multi-access.     

Improved MLWDF scheduler for LTE downlink transmission

In long-term evolution (LTE) downlink transmission, modified least weighted delay first (MLWDF) scheduler is a quality of service (QoS) aware scheduling scheme for real-time (RT) services. Nevertheless, MLWDF performs below optimal among the trade-off between strict delay and loss restraints of RT and non-RT traffic flows, respectively. This is further worsened with the implementation of hybrid automatic retransmission request (HARQ). As these restraints grow unabated with increasing number of user demands, the performance of MLWDF further reduces. In order to ameliorate this situation, there is a need to directly incorporate the variations in user demands and HARQ implementation as parameters to the MLWDF scheduler. In this work, an improvement to the MLWDF scheduler is proposed. The improvement entails adding two novel parameters that characterise user demand and HARQ implementation. The scheduler was tested using varying three classes of service in QoS class identifiers (QCIs) table standardised by Third Generation Partnership Project for LTE network to characterise different services. It was also tested on the basis of packet prioritisation. The proposed scheduler was simulated with LTE-SIM simulator and compared with the MLWDF and proportional fairness schedulers. In terms of delay, throughput and packet loss ratio; the proposed scheduler increased overall system performance.     

LTE下行链路EVM测量算法的研究

EVM（误差矢量幅度）是移动通信系统终端测试指标的重要内容,它与其它常规指标（如眼图或BER测量）相比能更直观快速地反映信号的质量,已成为目前终端测试的研究热点。在传输过程中,由于信号受到噪声等因素的影响,会造成EVM测量值不准的问题。因此,基于3GPP标准,设计并实现了一种LTE下行链路EVM测量算法。本算法利用插值、查找最优测量位置和频偏补偿等处理,使最终的EVM测量值更接近真实值。算法测试结果表明,本算法的测量结果较为准确,测量时间较短,具有实际应用意义。     

3GPP LTE上行链路的仿真研究

在LTE系统中上行链路采用SC-FDMA方案,下行链路采用OFDMA方案。文中对LTE上行链路的物理层进行仿真研究,并深入探讨了频域均衡（FDE）技术在高速率无线通信系统中的作用。从仿真结果可以看出频域均衡技术在多径环境中显著提高了SC-FDMA链路的抗干扰性能。     

Joint downlink and uplink resource allocation for multi-carrier SWIPT system

A multi-carrier simultaneous wireless information and power transfer (SWIPT) communication system including one base station (BS) and one user was investigated,where both uplink and downlink adopt orthogonal frequency division multiplexing (OFDM).In the downlink,the BS transmited information and power to the user simultaneously.In the uplink,the user transmited information to the BS by using the power harvested from the BS in the downlink.The weighted sum of the downlink and uplink achievable rates by jointly optimizing subcarrier allocation and power allocation of the uplink and downlink were aimed to maximized.An optimal algorithm to solve the joint resource allocation problem was proposed,which was based on the Lagrange duality method and the ellipsoid method.Finally,the result shows the performances of the proposed algorithm by computer simulations.     

一种改进的LTE系统下行同步算法

LTE(Long Term Evolution)系统中,作为小区搜索的第一步,符号定时算法需要具备很强的鲁棒性。为了进一步增强现有符号同步算法的抗频偏性能,提出了一种优化的符号同步算法。该算法一方面保持已有分段相关同步算法的优点,同时考虑结合预频偏处理来进行符号定时与粗频偏的联合估计,再将多个相关运算集做叠加处理。理论分析和仿真实验结果表明,在多径信道下,所提算法在完成符号定时和粗频偏估计的同时,大大提高了系统抗频偏性能。     

LTE上行块状导频的信道估计研究

继第三代（3G）移动通信之后,长期演进（LTE）作为3G的演进,将是未来通信领域的主流技术。信道估计性能一定程度上决定了通信系统的可靠性,LTE系统上行采用基于块状导频的信道估计。通过MATLAB仿真分析了不同信道估计方法、不同插值方法及不同导频间隔对估计性能的影响,仿真结果可用于指导实际工程应用中信道估计参数的选择。     

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.     

Joint-directional properties of uplink and downlink channel inmobile communications

The directional properties of the uplink (UL) and downlink (DL) channel are compared experimentally for a duplex distance of 68 MHz. It is found that the first- and second-order moments of the power azimuth spectrum, for all practical purposes, can be assumed to be identical for the UL and DL bands     

LTE上行信道的八天线干扰抑制合并技术

基于最小均方误差估计准则推导了LTE多天线上行信道的干扰 抑制合并和最大比合并的均衡公式。通过仿真比较,验证了八天线干扰抑制合并接收算法在 有同频干扰情况下的优越性：随着信噪比的增大,干扰抑制合并算法的误码率大幅降低,而 最大比合并算法则形成误码平台;八天线干扰抑制合并性能明显优于两天线性能。LTE在同 频组网时,基站可以采用八天线接收的干扰抑制合并技术以提高上行链路的抗干扰性能。     

LTE多用户下行吞吐量性能建模分析

针对LTE系统中多用户下行吞吐量难以预测的问题,从LTE 系统的时域和频域资源出发,结合用户位置、终端类型以及下行MIMO模式等内容,分析了多用户条件下时域和频域调度算法的特点、影响因素和作用过程。并在此基础上建立了多用户下行吞吐量分析和估算模型,进而应用此模型对具体实例进行了预测和分析,从而对多用户性能分析工作起到一定的指导作用。     

Performance of uplink random-access and downlink TDMA techniques for packet satellite networks

In this paper the integration of ALOHA random-access schemes and TDMA techniques in a multibeam packet satellite network are analyzed. The uplink channels operate according to a slotted-ALOHA protocol, while the downlink channels use a TDMA strategy. Two different models are described. In the first model, each transponder on-board the satellite is permanently connected to a preassigned spot beam. The second model uses a number of transponders lower than the number of spot beams. Some different strategies of transmission are proposed in the latter model, able to provide full interconnection among earth stations by channel-hopping capability of the transponders. The performance of the models is evaluated through queueing theory analysis and extensive computer simulations. The obtained results suggest the second model as an efficient candidate for the implementation of a multibeam packet satellite network. In that case, the system parameters must be carefully chosen in order to avoid possible instability conditions.     

Delay analysis for sleep-based power saving mechanisms with downlink and uplink traffic

In wireless networks, sleep-based power saving mechanisms can reduce the energy consumption at the expense of additional packet delay. This paper proposes a queueing model to analyze the packet queueing delay. Compared with the existing models which consider downlink traffic only, both downlink and uplink traffic are considered in the analysis.     

Coalition-based downlink resource allocation for LTE system with divide-and-conquer approach

To take advantage of the multiuser diversity resulted from the variation in channel conditions among the users,it has become an interesting and challenging problem to efficiently allocate the resources such as subcarriers,bits,and power.Most of current research concentrates on solving the resource-allocation problem for all users together in a centralized way,which brings about high computational complexity and makes it impractical for real system.Therefore,a coalitional game framework for downlink multi-user resource allocation in long term evolution(LTE) system is proposed,based on the divide-and-conquer idea.The goal is to maximize the overall system data rate under the constraints of each user’s minimal rate requirement and maximal transmit power of base station while considering the fairness among users.In this framework,a coalitional formation algorithm is proposed to achieve optimal coalition formation and a two-user bargaining algorithm is designed to bargain channel assignment between two users.The total computational complexity is greatly reduced in comparison with conventional methods.The simulation results show that the proposed algorithms acquire a good tradeoff between the overall system throughout and fairness,compared to maximal rate and max-min schemes.     

LTE上行多用户SC-FDMA系统中时变信道估计方法

针对高速移动时分双工长期演进(TDD-LTE,time division duplex-long term evolution)上行单载波频分多址(SC-FDMA,single carrier-frequency division multiple access)系统,提出了一种新型的变换域时变信道估计方法.在所定义的变换域中,基于两块导频符号的信道参数估计,提出利用基于判决导向的非线性内插方法来估计数据符号的信道参数.为了便于SC-FDMA系统均衡,推导给出了变换域信道与频域信道的转换表达式,利用该式可以直接将变换域信道参数估计转化为频域信道响应.计算机仿真结果表明,新方法的性能远远优于传统方法的估计性能,且具有低的计算复杂度.     

LTE系统中上行协同技术及其实践

LTE系统中的上行协同主要基于软合并技术,且适用于具备理想传输条件的小区间,因而在实际网络中部署受限。根据TD-SCDMA系统中的多小区联合检测原理提出了基于干扰抑制合并的上行协同技术,并应用于不具备理想传输条件的小区间。试验表明,基于软合并的上行协同技术可以提升主测小区边缘用户的平均吞吐量达89.9%,而基于干扰抑制合并的上行协同技术则可提升29.3%,两者的有机结合可有效提升全网用户感知。     

Call admission control for mobile multimedia communications withtraffic asymmetry between uplink and downlink

The call admission control (CAC) for mobile communications is one of the most important engineering issues since it belongs to the category of resource management and the radio spectrum is a very scarce resource. In future mobile cellular systems, the CAC scheme should be efficient for multimedia services as well as for voice services. This paper proposes an advanced CAC scheme for mobile multimedia communications. A characteristic of the proposed scheme is that it takes account of the traffic (load) asymmetry between uplink and downlink in mobile multimedia environments, we evaluate the performance of the proposed scheme using Markov analysis. The performance measures on which we focus are the utilization of resources and the blocking probabilities of handoff calls and new calls. We present some numerical examples with practically meaningful parameter values. As a result, we show that the proposed CAC scheme can be a good choice for mobile multimedia systems such as the International Mobile Telecommunications-2000 systems     

一种基于协同侦收的卫星上/下行信号关联方法

针对移动卫星L频段上行信号侦收覆盖范围小导致难以监测广大区域用户上行通信行为的问题,提出了一种基于协同侦收的卫星上/下行信号关联方法.通过构建协同侦收方案,实现卫星通信过程中返向链路的L频段上行信号、C频段下行信号与前向链路的L频段下行信号的协同接收,之后综合利用卫星随机接入信道(Satellite Random Ac...