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3G作业


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报告份数:

西安邮电大学
通信与信息工程学院
第三代移动通信技术与业务 课程报告





线
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专业班级: 学生姓名:

通工 1107 班 梁斓

学号(班内序号): 03111279(27)

原文:
A Survey of Radio Resource Management for Spectrum Aggregation in LTE-Advanced
Abstract — In order to satisfy the requirements of future
IMT-Advanced mobile systems, the concept of spectrum aggregation is introduced by 3GPP in its new LTE-Advanced (LTE Rel. 10) standards. While spectrum aggregation allows aggregation of carrier components (CCs) dispersed within and across different bands (intra/inter-band) as well as combination of CCs having different bandwidths, spectrum aggregation is expected to provide a powerful boost to the user throughput in LTE-Advanced (LTE-A). However, introduction of spectrum aggregation or carrier aggregation (CA) as referred to in LTE Rel. 10, has required some changes from the baseline LTE Rel. 8 although each CC in LTE-A remains backward compatible with LTE Rel. 8. This article provides a review of spectrum aggregation techniques, followed by requirements on radio resource management (RRM) functionality in support of CA. On-going research on the different RRM aspects and algorithms to support CA in LTE-Advanced are surveyed. Technical challenges for future research on aggregation in LTE-Advanced

systems are also outlined.

Index

Terms



Carrier

aggregation,

Spectrum

Aggregation,Radio Resource Management, scheduling. I. INTRODUCTION IN ORDER to meet the growing demand for high-speed and diverse wireless broadband services, the IMT-Advanced (IMT-A) requirements have established a minimum support or 1 Gbps and 500 Mbps peak rates for downlink (DL) and uplink (UL), respectively . In order to fulfil these challenging requirements, one key feature is the support for wider bandwidths (40 MHz mandatory, and up to a maximum of 100 MHz being optional) .IMT Bands, i.e. the candidate frequency bands for IMTAdvanced,identified at World Radio Conferences (WRCs) are non-continuous, and some of them are less than 100 MHz as shown in Fig. 1. Specifically, the

amount of contiguous transmission bandwidth for an operator in a certain geographical area is limited while the extent of available spectrum resources differs depending on the country, with most of the spectrum spread out over different frequency bands and with different bandwidths . In order to meet both the requirement on transmission bandwidth and the utilization of IMT bands, all IMT-Advanced candidate technologies are expected to support spectrum aggregation, within either contiguous or discontinuous

spectrum bands . Spectrum aggregation (or carrier aggregation) was introduced by 3GPP in its new LTE-Advanced standards, a candidate radio interface technology for IMT-Advanced systems. However, the concept of carrier aggregation (CA) is not totally new. It has already been deployed in HSPA based cellular systems, under the name Dual Carrier HSPA (DC-HSPA), to aggregate two adjacent carriers in the DL/UL. Both carriers must be contiguous and in the same spectrum band.Unlike DC-HSPA, however, carrier aggregation in LTE-A has extended the concept to introduce aggregation of noncontiguous spectrums in different spectrum bands . Two or more component carriers (CCs) of different bandwidths in different bands can be aggregated (up to 100 MHz with five CCs of 20 MHz) to support wider transmission bandwidth between the E-UTRAN NodeB (eNB) and the user equipment (UE) .LTE-Advanced supports the same range of CC bandwidths (1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz)that are supported in LTE Rel. 8. While LTE-A supports bandwidth extension by aggregating CCs, subject to spectrum availability and the UE’s capability [10], CC backward compatibility has been a requirement in LTE-Advanced from the outset as shown in Fig. 2. With each CC in LTE-A being LTE Rel. 8 compatible, carrier aggregation allows operators to migrate from LTE to

LTE-Advanced while continuing to provide services to any LTE users. This is made possible since the eNB and Radio Frequency (RF) specifications associated with LTE Rel. 8 remain unchanged in LTE-A [11]. By reusing the LTE design on each of the CCs, both implementation and specification efforts are minimized [12]. However, the introduction of CA for LTE-Advanced has required the introduction of new functionalities and modifications to the link layer and radio resource management (RRM) [13]. In this paper, we focus on the RRM framework to support CA functionality and present a survey of existing literature on RRM schemes for CA in LTE-A.

II. OVERVIEW OF CARRIER AGGREGATION Three different types of carrier aggregation are identified according to the way in which CCs are arranged .This is illustrated in Fig. 4.Intra-band contiguous CA: In this case, a contiguous bandwidth wider than 20MHz is used for LTE-Advanced.The spacing between centre frequencies of contiguously aggregated CCs is forced to be a multiple of 300 kHz.This may be a less likely scenario given frequency allocation today, but it can be applied for example, to broadband allocation in the 3.5 GHz band.Intra-band non-contiguous CA: When the contiguous spectrum blocks

are not available for aggregation, multiple non-contiguous CCs belonging to the same band can be used .Inter-band non-contiguous CA: In this case, communications are performed using different frequency bands, such as the 2 GHz band and the 800 MHz band. With this type of aggregation, robustness to mobility can potentially be improved by exploiting different radio propagation

characteristics of different bands. The support for both contiguous and non-contiguous CA of CCs with different bandwidths offers significant flexibility for efficient spectrum utilization, and gradual reframing of frequencies previously used by other radio access systems.However, from the physical layer

perspective, it is easier to implement contiguous CA without making many changes to the physical layer structure of LTE system . In order to achieve contiguous CA for an LTE-Advanced UE unit,it is possible to use a single fast Fourier transform (FFT)module and a single RF unit while providing backward compatibility to the LTE systems. For the non-contiguous CA, in most cases, multiple RF chains and FFT modules will be required. From the perspective of resource allocation and

management, contiguous CA is also easier to implement. Different CCs will exhibit different propagation path loss and Doppler shift which will affect the system performance. For example, Doppler shift influences the gains from frequency domain packet scheduling within a CC [13]. In LTE-Advanced, for the UL, the focus is currently on intra-band non-contiguous CA, due to difficulties in defining RF requirements for simultaneous transmission on multiple CCs with large frequency separation, considering realistic device linearity constraints. For the DL, however, both intra- and inter-band cases are considered in Rel. 10, while specific RF requirements are being developed .

译文:
LTE-Adanced 中多频谱整合对无线资源 的管理概述
摘要: 为了满足未来IMT(国际移动电话系统)中对移动通信的要求,3GPP在它最新提出的 版本--LTE-Advanced标准(Rel.10)中,提出了多频谱整合的概念。尽管,多频谱整合允许载 波分量分散在不同的频带上,并且允许组合不同在载波分量。但是,多频谱整合被希望在 LTE-Advanced中可以有力的推动用户的数量。不管怎样,在LTE--A中的载波分量都是向后 兼容的。 这篇文章在功能上支持载波聚合的情况下, 提供了对多频谱整合技术在无线资源管 理功能上的看法。持续调查了为了支持LTE--A中载波聚合这个技术,无线资源管理所做的 改变以及算法。在LTE-A系统中,对整合这个方面的研究,所带来的技术挑战也在这篇文章 中也做了大概说明。 概述: 为了满足对高速和多样的无线宽带服务的日益增长的需求。IMT--A要求下行链路(DL) 各上行链路(UL)的峰值速率最小达到1Gbps和500Mbps。为了达到这些具有挑战性的要求, 关键在于提供更宽的带宽。 (必须在40MHZ以上,最高值可为100MHZ) 。 IMT频带,也就是IMT的候补频带,世界无线会议(WRCs)中被提出,并且他只非连 续的,其中一些频带宽度小于100MHZ。特别的是,在一个确定的地理区域,对于操作领近 带宽间的传输的次数是被限制的。在 不同的国家中,许多频谱扩散到不同频谱带中,并且 有着不同的带宽,所以可用频谱资源的延长也是不同的。为了同时满足传输带宽的要求和 IMT频带的使用,所有LTE-A的候补技术都要求支持多频谱整合,无论是在连续的频谱带之

内,还是在不连续的频谱带之内。 多频谱整合(载波聚合)是由3GPP在它最新的LTE-A标准中提出,是LTE-A系统的候 补无线接口技术。事实上,载波聚合这个概念并不是完全是一个全新的概念。在蜂窝小区系 统中的高速分组接入(HSPA)技术中,已经应用了载波聚合这个概念。它在系统中整合两 个邻近的载波到上行链路或下行链路。 所有载波必须是邻近的且在同一频带内。不像DC--HSPA,LTE-A的载波聚合中,载波 可以是不同频谱带并且可以是不连续的。 两个或两个以上组合的载波可以被整合 (最高可整 合5个20MHZ的载波分量,达到100MHZ)去支持在E--UTRAN NodeB(eUB)和用户设备 (UE)中更宽的传播带宽。 LTE-A 支 持 LTE Rel 8 中 的 相 同 幅 度 的 载 波 载 波 分 量 带 宽

(1.4MHZ,3MHZ,5MHZ,10MHZ,15MHZ20MHZ) , 尽管LTE-A支持载波聚合后的延长带宽, 但仍受制于频谱的可用性和用户设备的容量。LTE-A中,发端的载波分量向后兼容性成为必 要条件。由于LTE-A与Rel 8中的LTE的载波分量都是兼容的。载波整合允许操作者从LTE中 转移到LTE-A,同时对所有LTE使用者提供服务,这使得LTE-A中的eNB和射频(RF)的规 格与Rel 8保持不变成为可能。 通过再次使用LTE中的每个载频分量, 实现LTE-A与其规格所 付出的代价最小化。但是,LTE-A中载波聚合的提出同时也对链路层与无线资源管理提出了 新的功能和改变的要求, 在这篇文章中, 我们关注的是支持载波聚合功能的无线资源管理的 框架,展示了现有文献中对LTE-A中支持载波聚合的无线资源管理方案的调查。

载波聚合的综述: 由载波不同的组合方式,载波聚合可分为三种情况。 1)带内连续的载波聚合: 在这种情况下, LTE--A使用一个连续的大于200MHZ的带宽,

并且连续聚合的载波分量中心频率间的空隙被要求在300KHZ左右。虽然这个频率分配的方 案在今天看来是不可能的,但是,它可以被应用在带宽为3.5GHZ的宽带分配的方案中。 2)带内不连续的载波聚合:当连续的频谱区不能用来聚合时,在一个频带内的许多不 连续载波可以用来去载波聚合。 3)带间不连续的载波聚合:在这种情况下,将使用不同频带来通信。比如,2GHZ和 800MHZ的频带。在这种聚合方式中,通过开发不同带宽间的不同无线传播特性,可以潜在 地提高移动通信的稳定。 支持不同带宽间的载波分量的载波聚合,不管是连续的还是不连续的,提供了重要和 灵活的频谱有效的利用。 逐渐改变以前其它无线系统使用的频率。 不管怎样, 就物理层来说, 在原有的LTE系统结构之上,不作过多的改变,实现连续的载波聚合更容易些。为了实现 LTE--A中的UE的连续载波聚合, 可以使用简单的快速傅里叶变换模式和一个简单的射频RF 单元,同时与LTE--A向后兼容。对于不连续的载波聚合,在大多数情况下,都要求多样的 射频链和FFT模型。从资源分配和管理的角度来讲,连续的载波聚合是更容易实现的。不同 的载波分量会有不同的传播路径损耗和多普勒频移, 并且这种效应会影响系统性能。 比如说, 多普勒频移会影响由载波成分组成的频率域数据包的增益。在 LTE--A中,对于上行链路, 主要应用的是带间不连续的载波聚合。 这是因为实际设备线性的限制, 在一个大的频率分离 情况下,要达到多载频分量的同时传输的要求,RF的设计是有困难的。但是对于下行链路, 不管是带内还是带间,都可以在Rel .10中应用当然对于RF的要求也随之提高。


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