Toward the Energy Efficiency of Resource Allocation Algorithms for OFDMA Downlink MIMO Systems

The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access (OFDMA) based systems has recently attracted significant interest. However, most studies focus on maximizing the system throughput and spectral efficiency. As the green radio is essential in 5G and future networks, the energy efficiency becomes the major concern. In this paper, we develop four resource allocation schemes in the downlink OFDMA network and the main focus is on analyzing the energy efficiency of these schemes. Specifically, we employ the advanced multi-antenna technology in a multiple input-multiple output (MIMO) system. The first scheme is based on transmit spatial diversity (TSD), in which the vector channel with the highest gain between the base station (BTS) and specific antenna at the remote terminal (RT) is chosen for transmission. The second scheme further employs spatial multiplexing on the MIMO system to enhance the throughput. The space-division multiple-access (SDMA) scheme assigns single subcarrier simultaneously to RTs with pairwise “nearly orthogonal” spatial signatures. In the fourth scheme, we propose to design the transmit beamformers based on the zero-forcing (ZF) criterion such that the multi-user interference (MUI) is completely removed. We analyze the tradeoff between the throughput and power consumption and compare the performance of these schemes in terms of the energy efficiency.     

蜂窝通信的空分多址:概念、算法和性能

蜂窝通信采用空分多址正在移动通信领域引起广泛关注。本文对空分多址的基本概念、空间信道模型及其知识利用、上下行链路的实现方法和算法、以及对系统性能的改善等诸方面,进行了比较全面的论述。对目前空分多址研究中值得关注的问题,表达了作者的观点。     

一种适用于教学实验的SDMA系统设计与实现

本文简要介绍了空分多址(SDMA)的基本原理,设计并实现了一种适用于教学实验的∞MA软件仿真系统.本软件系统可工作在两种模式下,为多个移动用户提供不同的互不干扰的空分信道,以第四维的多址方式接人基站.实验者可设置通信过程中的各种参数并观察其对整个系统性能的影响.该实验系统有助于实验者更好地理解和掌握SDMA技术,同时具有良好的可扩展性,并可与其他多址仿真系统有效地结合.     

一种基于码分多址的改进性空分多址性能分析

为解决SDMA中下行波束交叠引入的不同波束覆盖下用户群间相互干扰,研究一种结合CDMA的改进性SDMA多址技术。基站对下行链路的赋形波束进行实时的相关性检测,为高相关性的SDMA波束动态分配正交的PN码,以CDMA方式来识别不同波束,实现码分和空分的有效结合。仿真结果表明改进的SDMA多址技术在波束高度相关,也即是用户群之间干扰较强的情况下仍能获得较好性能。     

Low complexity resource allocation and scheduling algorithms for downlink SDMA systems

The downlink zero-forcing beamforming strategy in the case of random packet arrivals is investigated. Under this setting, the relevant fairness criterion is the stabilization of all buffer queues which guarantees a bounded average delay for all users. It has been shown that allocating resources to maximize a queue-length-weighted sum of the rates is a stabilizing policy. However, the high complexity of user selection and the feasible rates determination for optimal scheme may prevent the real-time scheduling operation. Two low complexity algorithms are provided taking the channel state, queue state and orthogonality into account. In particular, the authors pick the first user with the largest product between channel gain and queuing length, and select the remaining users to construct candidate user set based on the greedy user selection method or channel orthogonal user selection method. Then, the power and rate allocation for the selected users are implemented based on the modified water-filling method. The complexity of the proposed algorithms is analyzed. The average delay and average throughput are studied in homogeneous scenarios and heterogeneous scenarios, respectively. Simulation results show that the proposed algorithms can take full advantage of the multi-user diversity gain and provide average delay (or throughput) and fairness improvement compared with channel-aware-only schemes.     

The performance evaluation of spatial–temporal algorithms in W‐CDMA systems

Differing from FDMA, TDMA, and CDMA, space division multiple access (SDMA) uses space resources to improve communication system performance. Utilizing the smart antenna system is an approach to realize the SDMA technique. Smart antenna systems using the beamforming technique can reduce the co‐channel interference and multipath fading to increase the channel capacity and communication quality. In this study the smart antenna system and rake receiver are integrated. The performance of spatial–temporal structure applied to the W‐CDMA system is evaluated. From the cumulative distribution function simulation results, W‐CDMA system with spatial–temporal algorithm can exactly provide SINR gain to improve the system performance and capacity. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison between the Spectral Efficiency of SDMA Systems and Sectorized Systems

In this paper we present a comparison of the spectral efficiency of Spatial Division Multiple Access systems with conventional omni-directional and sectorized systems. Our analysis attempts to incorporate the effect of co-channel interference (CCI) for users sharing the same channel within a cell (intra-cell interference) as well as the CCI from other cells (inter-cell interference). To determine the outage probability we utilize exact results for combined Rayleigh and Log-normal shadowing in conjunction with a generic antenna pattern. The study is limited to the forward link only and the switched-beam approach. Results are provided for the outage probability and spectral efficiency for various reuse distances and blocking probabilities. These demonstrate that under most conditions, SDMA systems have higher spectral efficiency than conventional omni-directional or sectored systems. Nevertheless under certain conditions such as high blocking probabilities or large reuse distances, the spectral efficiency of SDMA systems is lower than conventional systems.     

Blind Source Separation,ISI Cancellation and Carrier Phase Recovery in SDMA Systems for Mobile Communications

Current rates of demand for radio cellular services will soon reach the saturation point of the actual cellular infrastructures. Thus, spectral bandwidth-saving multiple access schemes are necessary to expand the actual networks' capacity. In the Spatial Division Multiple Access (SDMA) approach, users within the same cell share the same time/frequency channel and the base station receiver exploits the spatial dimension of the radio resource to remove crosstalk. In this paper, we present a blind multi-user equalization technique for SDMA architectures which performs the separation of digital sources, in the presence of intersymbol interference (ISI) and phase carrier drifts. We take advantage of the sources' joint finite alphabet and statistical properties, and use only second-order statistics in order to produce valid channel estimates based on short data packets. Computer simulations using the TU-GSM multipath channel model for radio communications in urban environments demonstrate the potential of our technique.     

多用户环境下阵列响应的闭式盲估计方法

本文通过剖析多径多用户环境下阵列输出信号二阶统计量的数据结构,提出了一种基于特征分解的闭式阵列响应盲估计方法,该方法适用于任何几何形状的阵列和未校准的阵列,且对信号特性和传播参数（散射源分布和入射角散布范围）的约束极少。理论分析与仿真结果是在近程该方法能够有效地进行阵列响应估计和信号分离,在空分多址（ＳＤＭＡ）的实现方面具有较强的实用性。     

移动通信中的空分多址技术

在信息时代，人们对通信业务的需求不断增加，这对通信技术提出了更高的要求，空分多址（SDMA）技术由于其在提高系统容量和频谱利用率方面的独特优势而引起了人们的广泛关注。本文从基本概念、信道模型、系统实现和对通信系统的性能改善等几个方面对空分多址技术进行了较为全面的论述。